Boyle, Robert, New experiments physico-mechanicall, touching the spring of the air and its effects, 1660

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Author: Boyle, Robert
Title: New experiments physico-mechanicall, touching the spring of the air and its effects
Date: 1660

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Document ID: MPIWG:SUV5ZB7D
Permanent URL: http://echo.mpiwg-berlin.mpg.de/MPIWG:SUV5ZB7D

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Copyright: Max Planck Institute for the History of Science (unless stated otherwise)
License: CC-BY-SA (unless stated otherwise)
1
NEW
EXPERIMENTS
Phyſico-Mechanicall
Touching the Air.
1
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1
NEW
EXPERIMENTS
Phyſico-Mechanicall,
Touching
The SPRING of the AIR,
and its EFFECTS,
(Made, for the moſt part, in a New
PNEuMATICAL ENGINE)
Written by way of LETTER
To the Right Honorable Charles
Lord Vicount of Dungarvan,
Eldeſt Son to the EARL of CORKE.
By the Honorable Robert Boyle Eſque
1[Figure 1]
OXFORD:
Printed by H: Hall, Printer to the Univerſity,
for The: Robinſon. 1660.
1
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12[Figure 2]
To the Reader.
ALthough the following Trea­
tiſe being far more prolix
then becomes a Letter, and
then I at firſt intended it; I
am very unwilling to en­
creaſe the already exceſsive bulk of the
Book by a Preface, yet there are ſome par­
ticulars that I think my ſelf oblig'd to take
notice of to the Reader, as things, that will
either concern him to know, or me to have
known.
In the firſt place then: If it be demand­
ed why I publiſh to the World a Letter, which
by its Stile and diverſe Paſſages, appears
to have been written as well For, as To a
particular Perſon; I have chiefly theſe two
things to anſwer: The one, That the Ex­
periments therein related, having been ma­
ny of them try'd in the preſence of Ingeni­
ous Men; and by that means having made
1ſome noiſe among the Virtuoſi (inſomuch
that ſome of them have been ſent into Fo­
reign Countries, where they have had the
luck not to be deſpiſ'd) I could not without
quite tyring more then one Amanuenſis, give
out half as many Copies of them as were ſo
earneſtly deſired, that I could not civilly
refuſe them. The other, That intelligent
Perſons in matters of this kinde perſwaded
me, that the publication of what I had ob­
ſerv'd touching the Nature of the Air,
would not be uſeleſs to the World; and that
in an Age ſo taken with Novelties as is ours,
theſe new Experiments would be grateful to
the Lovers of free and real Learning: So
that I might at once comply with my grand
Deſign of promoting Experimental and
Uſeful Philoſophy, and obtain the great ſa­
tisfaction of giving ſome to ingenious Men;
the hope of which, is, I confeſs, a tempta­
tion that I cannot caſily reſiſt.
Of my being ſomewhat prolix in many
of my Experiments, I have theſe Reaſons
to render, That ſome of them being altoge­
ther new, ſeem'd to need the being circum­
ſtantially related, to keep the Reader from
diſtruſting them: That divers Circum­
ſtances I did here and there ſet down for fear
of forgetting them, when I may hereafter
1have occaſion to make uſe of them in my o­
ther Writings: That in divers caſes I
thought it neceſſary to deliver things cir­
cumſtantially, that the Perſon I addreſſed
them to, might without miſtake, and with
as little trouble as is poſsible, be able to re­
peat ſuch unuſual Experiments: and that
after I conſented to let my Obſervations be
made publick, the moſt ordinary Reaſon of
my prolixity was, That foreſeeing that ſuch
a trouble as I met with in making thoſe try­
als carefully, and the great expence of time
that they neceſſarily require, (not to mention
the charges of making the Engine, and im­
ploying a man to manage it) will probably
keep moſt men from trying again theſe Ex­
periments; I thought I might doe the gene­
rality of my Readers no unacceptable pece
of ſervice, by ſo punctually relating what
I carefully obſerv'd, that they may look up­
on theſe Narratives as ſtanding Records in
our new Pneumaticks, and need not reite­
rate themſelves an Experiment to have as
diſtinct an Idea of it, as may ſuffice them
to ground their Reflections and Speculations
upon.
And becauſe ſometimes 'tis the Diſcourſe
made upon the Experiment that makes it
appear prolix, I have commonly left a con-
1ſpicuous interval betwixt ſuch Diſcourſes,
and the Experiments whereunto they belong,
or are annexed; that they who deſire onely
the Hiſtorical part of the account we give
of our Engine, may read the Narra­
tives, without being put to the trouble
of reading the Reflections too: Which I
here take notice of, for the ſake of thoſe
that are well verſ'd in the New Philoſophy,
and in the Mathematicks; that ſuch
may skip what was deſign'd, but for ſuch
Perſons as may be leſs acquainted even then
I, with matters of this nature (ſcarce ſo
much as mention'd by any Writer in our
Language) and not for them from whom
I ſhall be much more forward to learn, then
to pretend to teach them. Of my being
wont to ſpeak rather doubtfully, or heſitant­
ly, then reſolvedly, concerning matters
wherein I apprehend ſome difficulty, I have
in another Treatiſe (which may, through
Gods Aſsiſtance, come abroad ere long)
given a particular, and I hope a ſatisfacto­
ry account: Wherefore I ſhall now defend
my Practice but by the Obſervation of Ari­
ſtotle, who ſomewhere notes, That to ſeem
to know all things certainly, and to ſpeak
poſitively of them, is a trick of bold and
yong Fellows: Whereas thoſe that are in-
1deed intelligent and conſiderate, are wont to
imploy more wary and diffident Expreſsi­
ons, or (as he ſpeaks) σιφέαδ ἀεὶ τὸ ς,
τὸ τὰχα.
There are divers Reflections, and other
Paſſages in the following Epiſtle, and even
ſome Experiments (occaſionally mention'd)
which may ſeem either impertinent or ſu­
perfluous, but are not ſo: Being purpoſely
written, either to evince ſome truth oppoſ'd,
or diſprove ſome erroneous conceit main­
tain'd, by ſome eminent New Philoſopher,
or by ſome other Ingenious Men, who, I
preſum'd, would eaſily forgive me the ha­
ving on ſuch occaſions purpoſely omitted
their Names; though an inquiſitive Perſon
will probably diſcover divers of them, by
the mention of the Opinions diſprov'd in
the Experiments I am excuſing.
Ever ſince I diſcern'd the uſefulneſs
of ſpeculative Geometry to Natural Phi­
loſophy, the unhappy Diſtempers of my Eyes,
have ſo far kept me from being much con­
verſant in it, that I fear I ſhall need the par­
doz of my Mathematical Readers, for ſome
Paſſages, which if I had been deeply skill'd
in Geometry, I ſhould have treated more ac­
curately.
1
And indeed, having, for Reaſons elſe­
where deduc'd, purpoſely kept my ſelf a
ſtranger to moſt of the new Hypotheſes in
Philoſophy, I am ſenſible enough that the
Engine I treat of has prevail'd with me to
write of ſome ſubjects which are ſufficient­
ly remote from thoſe I have been moſt con­
verſant in. And having been reduc'd to
write the greateſt part of the enſuing Letter
at a diſtance, not onely from my Library,
but from my own Manuſcripts, I cannot
but fear that my Diſcourſes do not onely
want many choice things wherewith the
Learned Writings of others might have en­
riched or imbelliſhed them: But that partly
for this Reaſon, and partly for that touch'd
upon a little before, It is poſsible I may
have mention'd ſome Notions already pub­
liſh'd by others, without taking notice of the
Authors, not out of any deſign to defraud
deſerving Men, but for want of knowing
ſuch particulars to have been already pub­
liſh'd by them: Eſpecially the Experiments
of our Engine being themſelves ſufficient
to hint ſuch Notions as we build upon
them.
The order of the Experiments every
Reader may alter, as ſuits beſt with his own
Deſign in peruſing them; For not onely all
1thoſe betwixt whom there is an Affinity in
Nature (by belonging to one ſubject) are not
always plac'd one by another, but they are
not ſtill ſet down ſo much as in the order
wherein they were made; but moſt common­
ly in that caſual one wherein my occaſions in­
duc'd me to diſpatch them to the Preſs. And,
which is worſe, I did uſually ſend quite a­
way the former Experiments, before the
later were written, or perhaps ſo much as
made: Whereby I loſt the advantage of cor­
recting and ſupplying the Imperfections of
what I had formerly written, by the light of
my ſubſequent Tryals and Diſcoveries.
Beſides all this, the diſtemper in my eyes
forbidding me not onely to write my ſelf ſo
much as one Experiment, but even to read
over my ſelf what I dictated to others. I can­
not but fear, that beſides the Authors miſtakes,
this Edition may be blemiſh'd by many, that
may be properly imputed to a very unskil­
ful Writer (whom I was often times by haſte
reduc'd againſt my cuſtom to imploy) and
may have eſcaped the Diligence of that
Learned Friend, that does me the favor to
over-ſee the Preſs; eſpecially there being
the diſtance of two days Fourney betwixt it
and me.
I need not perhaps repreſent to the equi-
1table Reader, how much the ſtrange Confu­
ſions of this unhappy Nation, in the midſt
of which I have made and written theſe
Experiments, are apt to diſturb that calm­
neſs of Minde, and undiſtractedncſs of
Thoughts, that are wont to be requiſite to
Happy Speculations. But I preſume,
that by all theſe things put together, he
will readily perceive, That I have been
ſo far from following the Poets prudent
Counſel touching the ſlow Publication of
Books deſign'd to purchaſe credit by,
—— Nonumque prematur in Annum
that I ſuffer this Treatiſe to come abroad
into the World with a multitude of Diſad­
vantages.
But if it be demanded, why then I did
not make it fitter for the Preſs before I ſent
it thither? my Anſwer muſt be, That not
at firſt imagining that this ſort of Experi­
ments would prove any thing near ſo trouble­
ſome, either to make, or to Record, as I
afterwards found them, I did, to engage
the Printer to diſpatch, promiſe him to ſend
him the whole Epiſtle in a very ſhort time:
So that although now and then the occaſional
vacations of the Preſs, by reaſon of Feſti-
1vals, or the abſence of the Corrector, gave
me the leiſure to exſpaciate upon ſome ſub­
ject; yet being oftentimes call'd upon to diſ­
patch the Papers to the Preſs, my promiſe,
and many unexpected Avocations, obliged
me to a haſte, which, though it have detract­
ed nothing from the Faithfulneſs of the
Hiſtorical part of our Book, has (I fear)
been diſadvantageous enough to all the reſt.
And I made the leſs ſcruple to let the fol­
lowing Papers paſs out of my hands, with
all their Imperfections; becauſe, as the
publick Affairs, and my own, were then
circumſtanc'd, I knew not when (if at all)
I ſhould be again in a condition to proſecute
Experiments of this kinde; eſpecially,
ſince (to omit my being almoſt weary of be­
ing, as it were, confin'd to one ſort of Ex­
periments) I am pre-ingag'd (if it pleaſe
God to vouchſafe me Life and Health) to
imploy my firſt leiſure in the publication of
ſome other Phyſiological Papers, which I
thought 'twould make me much the ſitter to
take in hand, if I firſt diſpatch'd all that
I had at this time to write touching our
Engine.
I have this further to adde, by way
of Excuſe, That as it has been my deſign
in publiſhing theſe Experiments to gratifie
1Ingenious men; ſo, if I have not been
much flattered, I may hope that the vari­
ous hints to be met with in the following
Letter, will (at leaſt) ſomewhat awaken
mens thoughts, & excite them to new ſpecula­
tions (ſuch as perhaps even inquiſitive men
would ſcarce elſe light upon) and I need not
deſpair, that even the examination of ſuch
new Suſpicions and Enquiries will hence al­
ſo, at leaſt Occaſionally be facilitated: I
ſaid Occaſionally, becauſe it being, as 'tis
proverbially ſaid, Facile Inventis addere.
It ſeems not irrational to expect, that our
Engine it ſelf, and divers of our Experi­
ments, will be much promoted by the Indu­
ſtry of Inventive and Mathematical Wits,
whoſe contrivances may eaſily either correct
or ſupply, and conſequently ſurpaſs many of
thoſe we have made uſe of. And, particu­
larly, if Men by skill and patience can ar­
rive both to evacuate ſuch Receivers as
ours, till there be no more Air left in them,
then there ſeems to have remain'd in the
Glaſſes made uſe of about the Magdebur­
gick Experiment (hereafter to be mention­
ed) and to keep out the Air for a competent
while, the Uſefulneſs and Diſcoveries of our
Engine, will not be a little advanc'd. And
perhaps that may belong to it, which I re-
1member Seneca ſpeaks of Nature, Initia­
tos (ſays be) nos credimus, in Veſtibulo
ejus hæremus: For being now in a place
where we are not quite deſtitute of moderate­
ly skilful Artificers, we have, ſince the
Concluſion of the following Letter, made
ſome Additions to our Engine, by whoſe help
we finde (upon ſome new tryals) that we
may be able, without much of new trouble,
to keep the ambient Air out of the exhau­
ſted Receiver for a whole day; and perhaps
we ſhould be able to keep it out much longer,
if before we ſhall have diſpatch'd ſome ur­
gent Affairs, and publiſh'd ſome Papers for
which a kinde of Promiſe is thought to make
us Debtors to the Preſs, we could be at lei­
ſure to proſecute ſuch Experiments, as may
poſsibly afford a Supplement to the follow­
ing Treatiſe, from which I ſhall now no lon­
ger detain the Reader.
I know
1
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13[Figure 3]
Friendly Reader,
I Know all Perſons
that have a publick
Spirit for the Ad­
vancement of Lear­
ning, will think much that this
piece came not out in a Lan­
guage of more general Uſe,
then this you ſee it now attir'd
in; eſpecially ſince the Excel­
lent Noble Perſon, who is the
Author, is known to be well a­
ble himſelf (being almoſt uni­
verſally a Linguiſt) to have gi­
ven it either the Old Latin, or
1the newer French Dreſs.
But if it be an Honor to a
Language to be preferr'd, and
this Honor breeds ſometimes an
Emulation, as anciently it did
between the Greeks and Ro­
mans, it cannot be thought
unhandſome for an Engliſh
Nobleman to have preferr'd
his own: And it may be a ſuf­
ficient Reaſon for the Gentry
of Forein Parts to learn our
Speech, or keep Interpreters,
that they are ſure to have for
their requital, from many of
our Engliſh Writers (as here
from this piece) much curiouſly
ingenious, and profitable Lear­
ning.
1
But as to this particular (give
me leave to uſe Words from a
Story) Since the Mountain
cannot come to Mahomet,
Mahomet will go to the
Mountain: I mean thus;
Becauſe many witty Men, Per­
ſons of Honor and Eſtate eſpe­
cially, may be ſuppoſ'd to be a­
ble to make a better account, by
employing their Studies and
Time on Matter then Words,
and ſo are juſtly impeded from
learning Languages; And be­
cauſe (as I may judge) the no­
ble Author is willing to oblige all
Men, He has already provi­
ded, that this piece ſhall ſhort­
ly be done into Latine, that ſo
1it may come home to divers wor­
thy Perſons in its Stream, who
cannot travel to finde it out in
its firſt Origine.
Having therefore leave ſo
to do, I cannot forbear to give
the World the Advertiſement
of this Latine Edition, leſt
ſome skilful Artiſt ſhould take
needleſs pains about a Work,
which will, ere long (by Gods
furtherance) be done to his
Hands; For ſuch unprofitable
expences of Study have too fre­
quently happened, and too much
to the diſadvantage of Learn­
ing, for want of a ſufficient
Correſpondence and Intercourſe
between ſuch as are exerciſed
1in the Mines of Wiſdome.
This is all the trouble I ſhall
at preſent give you: Nor ſhall I
need minde thee, if you have a
true guſt for the Book you read,
to have an honor and thankful
regard to the Perſon that has
favor'd us with the Communi­
cation of theſe his Tryals, & is
manifeſtly ſo great a Patron
and Friend to Experimental
Learning, and all true Wiſdom;
for ſhould you fail in this, you
might deſervedly be depriv'd of
ſome other Obſervations on the
ſame ſubject, which the Au­
thor, I heare, has made ſince the
finiſhing of this Treatiſe.
I deſire to be excuſed that I
1not make Excuſes for the ſlow­
neſs of the Publication, hoping
that the long expectation you
have had of it, will enhance, and
not diminiſh your delight in the
enjoyment of a piece like to be,
amongſt the ſtudents in accurate
Philoſophy, of ſo generall accep­
tance. Farewel.
R: Sh.
4[Figure 4]
15[Figure 5]
A Summary of the chief Matters treated
of in this Epiſtolical Diſcourſe.
THe Proæmium, wherein is ſet down the
occaſion of this Diſcourſe, 1. The mo­
tives that induc'd the Author thereunto, 2 &c.
The hints he received, 5. The things where­
in this Engine excels any that have yet been
made uſe of, 6 &c. The deſcription of the
Engine and its parts, 8 &c. The way of pre­
paring and uſing it, 15 &c. The diviſion of
the Experiments tryable thereby into two
ſorts, and the difficulty of excluding the
Air. 18 &c.
The firſt Experiment, touching the man­
ner of pumping out the Air, and by what de­
grees the Receiver is emptyed, 20, &c. A di­
greſsion touching the Spring or Elaſtical
power of the Air, with an attempt for a Me­
chanical Explication thereof, neceſſary to be
premiſ'd for the explanation of the Phæno­
mena, exhibited in this and the ſubſequent
Experiments. 22 &c.
The ſecond Experiment, touching the preſ­
ſure of the Air againſt the ſides of the Bodies
it invirons, 37 &c. with a digreſsive Ex­
plication of the preſſure of the Air included
within an ambient Body. 39 &c.
1
The third Experiment, touching the
force requiſite to draw down the Sucker, 42
&c. The Opinion of an eminent Modern
Naturaliſt examin'd. 44 &c.
The fourth Experiment, touching the
ſwelling of a Bladder; with the degrees by
which it increaſes, 45 &c. Another Opini­
on of a Learned Author examin'd. 48 &c.
The fifth Experiment, touching the break­
ing of a Bladder in the Receiver, 49 &c.
And of another by heat. 52
The ſixth Experiment, of divers ways by
which the elaſtical expanſion of the Air
was meaſur'd. 52 &c
The ſeventh Experiment, touching what
Figure does beſt reſiſt the preſſure of the Air. 62 &c.
The eighth Experiment, tending to a fur­
ther Demonſtration of the former, from the
breaking of glaſs a Helmet inward. 64 &c.
The ninth Experiment, contains a fur­
ther confirmation from the breaking of a
Glaſs outward, 66 &c. with an Experiment to
prove, that theſe Phænomena proceed not
from an invincible Fuga vacui 69. A de­
ſcription of other ſmall Receivers, and their
Conveniencies, 70 &c. A Receipt for the
making of a Compoſition to Cement crackt
Glaſſes. 73
1
The tenth Experiment, touching the fla­
ming of Candles incloſed in the Receiver. 74 &c.
The eleventh Expertment, touching the
burning of Coals, 78. And the laſting of
the excandeſcence of an included piece of I­
ron. 80.
The twelfth Experiment concerning the
burning of Match. 82
The thirteenth Experiment, concerning
the further proſecution of the preceding,
tending to prove the extinction of the Fire
in the former Experiments, not to have
proceeded from the preſſure of the Fire by the
Fumes, 84. Some remarkable Circumſtan­
ces of it, 86. The Experiment of Match
try'd in a ſmall Receiver. 87
The fourteenth Experiment, touching the
ſtriking Fire, and kindling of Powder with
the Lock of a Piſtol in the evacuated Recei­
ver. 88 &c.
The fifteenth Experiment, touching the
unſucceſsfulneſs of kindling included Bo­
dies with a burning Glaſs, and the Au­
thors intention to proſecute it further. 102
The ſixteenth Experiment, concerning the
operation of the Loadſtone. 105, &c.
1
The ſeventeenth Experiment, touching the
gradual deſcent of the Quick-ſilver in the
Torricellian Experiment, 106 &c. Some
obſervable Circumſtances concerning it,
112 &c. The ſame Experiment try'd in
one of the ſmall Receivers, 115. How
this Experiment may be made uſe of to know
the ſtrength of the preſſure of the Air for
every degree of Rarefaction, 116 &c. The
tryal of the ſame Experiment in a Tube not
two foot long, 118. The raiſing of the Mer­
curial Cylinder, by the forcing of more Air
into the Receiver, 119. Some Allegations
for and againſt a Vacuum conſider'd, 120
&c. Some Advertiſements concerning the
inconveniencies that may ariſe from the di­
verſity of meaſures made uſe of for the defi­
ning the Altitute of the Mercurial Cylinder;
and from the neglect of little parcels of Air
apt to remain between the Mercury and the
concave ſurface of the Tube, 123 &c. Some
Expedients for the more exact filling the
Tube, 127. The height the Author once found
of the Mercurial Cylinder, according to En­
gliſh meaſure. 128.
The eighteenth Experiment, containing
a new Obſervation touching the variation
of the height of the Mercurial Cylinder in
the ſame Tube, with an oſſer at the reaſon
1thereof. 129 &c.
The 19th Experiment, touching the ſub­
ſiding of a Cylinder of Water, 140 &c. The
ſame try'd in a ſmall Receiver. 143
The 20th Experiment, touching the Ela­
ter of Water, with a digreſsive Experiment
to the ſame purpoſe 144 &c.
The 21 Experiment, being a proſecution
of the former Enquiry, by Experimenting
the Generation of Bubbles under Water, a
recital of ſome notable Circumſtances, with
ſome obſervable Corollary's deduc'd there­
from. 147 &c.
The 22d Experiment, tending to a deter­
mination of the Enquiry propoſ'd in the for­
mer Experiment, by proving the matter of
theſe Bubbles from their permanency to be
Air: The Experiments try'd in the great
and ſmall Receivers, evincing the ſame
thing, 155 &c. An Experiment wherein
there appear'd Bubbles in Quick-ſilver,
160. The Authors Inference, 162. A di­
greſsive Enquiry, whether or no Air may be
generated anew; with ſeveral Hiſtories and
Experiments, tending to the reſolving and
clearing thereof. 162 &c The Authors ex­
cuſe for ſo long a Digreſsion. 181
The 23d Experiment, containing a fur­
ther Enquiry touching Bubbles mad with
1common and diſtill'd Water. 182
The 24th Experiment, wherein the inqui­
ry is proſecuted with other Liquors, as with
Sallet Oyl, Oyl of Turpentine, a Solution of
Tartar, Spirit of Vinegar, Red-wine, Milk,
Hen's Eggs, Spirit of Urine, Spirit of
Wine and Water, Spirit of Wine. 187 &c.
The wonderful expanſion of the Spirit of
Wine. 194
The 25th Experiment, touching the ex­
panſion and gravity of the Air under wa­
ter. 195 &c.
The 26th Experiment, touching the Vi­
brations of a Pendulum. 202 &c.
The 27th Experiment, touching the pro­
pagation of ſound: And the Authors inten­
tion of trying ſome other Experiments, for
the further elucidation thereof. 210 &c.
The 28 Experiment, touching the ſudden
cruption of Bubbles from the water, when
the airs preſſure was ſpeedily remov'd. 214
The 29 Experiment, touching the cauſe
of the aſcent of Fumes and Vapors, wherein
'tis prov'd (from the ſeveral motions, which
the Fumes of a ſtrange ſmoaking Liquor, of
the Authors, were obſerv'd to have in the Re­
ceiver, upon the exſuction of the Air) that
the reaſon of their aſcent proceeds from the
gravity of the ambient air, and not from any
poſitive levity of their own. 217 &c.
1
The 30 Experiment, concerning the na­
ture of a fluid Body, illuſtrated by the exam­
ple of ſmoak which in ſeveral circumſtances
ſeems very much to reſemble the property of a
fluid Body, 224 &c. A conjecture of the
cauſe of the Suns undulation. 228
The 31 Experiment, concerning the Phæ­
nomena of two flat Marbles exactly plain'd
and wrought together, and the true reaſon
thereof, 229. The Authors intention for the
further proſecution thereof, & what hindred
him; the reaſon why the under Marble did
not fal from the upper (being onely conjoynd
with Spirit of Wine) when the Receiver was
evacuated. And a notable relation concern­
ing the coheſion of flat Bodies. 231 &c.
The 32 Experiment, touching the forcible
preſſure of the Air againſt the outward ſu­
perficies of a Valve, faſten'd upon the ſtop­
cock of the Receiver. The Diameter of it,
and the weight it ſuſtain'd. 233 &c.
The 33 experiment, touching the great preſ­
ſure of the Air againſt the under ſuperficies
of the Sucker, 236 &c. what weight was re­
quiſite to depreſs it, & what weight it would
lift and carry up with it, 239 &c. what im­
provement & uſe there may be made of this
experiment, 242. A Diſcourſe touching the
nature of Suction, proving that fuga vacui
is not the adequate cauſe thereof. 243 &c.
1
The 34th Experiment, containing ſeveral
attempts for the weighing of light Bodies in
the exhauſted Receiver. 258 &c.
The 35th Experiment, touching the cauſe
of Filtration, and the riſing of Water in
Siphons, 262 &c. A relation of a new
kinde of Siphon, of the Authors, upon
the occaſion of trying the Experiment
lately obſerv'd by ſome French-men, and fur­
ther improv'd by himſelf; and ſome conje­
ctures touching the cauſe of the exhibited
Phænomena. 267 &c.
The 36th Experiment, touching the weigh­
ing of a parcel of Air in the exhauſted Veſ­
ſel; and ſome other Obſervations for the ex­
plication thereof, 272 &c. An accidental
Experiment, tending to the further confir­
mation of the Authors Reflections upon the
firſt Experiment; with a digreſsive Obſer­
vation, noting the ſubtil penetrancy of ſome
Spirits, to exceed by far that of the Air, 275
&c. And ſome other Experiments to ſhew the
difficulty of the ingreſs of the Air into the
pores or holes of ſome bodies into which Wa­
ter will readily inſinuate it ſelf, 279 &c. with
a conjecture at the cauſe thereof, 282. The
Author returns to the proſecution if the in­
quiry after the gravity of the Air: But firſt,
(upon the occaſion of the tenacity of a thin
1Bubble of Glaſs) ſets down his thoughts con­
cerning the ſtrange exuperancy of ſtrength
in Air, agitated by heat, above what the
ſame has unagitated, 283 &c. And then pro­
ceeds to the examination of the weight of the
Air by an Æolipile, and compares the reſult
thereof, with that of Merſennus, 286. The
Opinions and Experiments of divers Au­
thors, and ſome of his own, touching the
proportion of weight betwixt Water and Air,
are compar'd and examin'd by the Author,
288. The reſult thereof, 290. Merſennus
his obſervation reconcil'd, with that of the
Author; and the proportion between the gra­
vity of Water and Air about London, 291
&c. After the recital of the Opinions of ſe­
veral Writers, touching the proportion of
gravity between Water and Quick-ſilver,
the Author ſets down his own tryals, made
ſeveral ways, together with his concluſion
therefrom, 293 &c. The uſe he makes of this
inquiry for the gheſsing at the height of the
Atmoſphere, 297. What other Experiments
are requiſite to the determination thereof.
299 &c.
The 37th Experiment, touching the ſtrange
and odde Phænomenon, of the ſudden flaſh­
es of light in the cavity of the Receiver; the
ſeveral circumſtances and difficulties of it,
1with ſome attempts towards the rendering at reaſon
thereof, 301, &c. The Difficulty of ſo doing fnr­
ther ſhewn from the conſideration of the various
changes of Air which doe not immediatly fall un­
der our ſenſes, 315. this laſt propoſition prou'd
by ſeverall obſervations. 316.
The 38. Experiment, touching the freezing of
water, 319. &c. Aproblem, (concerning the great
force wherewith a freezing Liquor extends its ſelfe,)
propoſ'd upon the Conſideration of divers admirable
effects wrought thereby. 320 &c.
The 39. Experiment, containing an inquiſition
after the temperature of the ſubſtance that remain'd
in the cavity of the Receiver, after the Air was well
exhauſted. The relation of a Phænomenon, ſeeming
to proceed from the ſwelling of the Glaſs. With an
advertiſement concerning the pliableneſs of Glaſs in
ſmall peices. 322. &c.
The 40. Experiment, touching the difficulty that
occur'd in making tryall whether rarified Air
were able to ſuſtaine flying inſects. 326. &c
The 41. Experiment, Exhibiting ſeverall try­
alls touching the reſpiration of divers ſorts of ani­
malls included in the Receiver, 328, &c. With a
digreſſion containing ſome doubts touching reſpira­
tion wherein are delivered ſeverall Experiments re­
lating thereunto. 335 &c.
The 42. Experiment, touching the differing o­
peration of corroſive Liquors in the emptied Receiver
and in the open Air. 384
The 43. Experiment, touching the ſpontaneous E­
bullition of warm Liquors in the exhauſted Receiver. 388
The Concluſion. 394
1
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110[Figure 10]
TO THE
LORD
OF
DUNGARVAN,
My Honoured and Dear
NEPHEW.
My Dear Lord,
REceiving in your laſt from
Paris, a deſire that I would
adde ſome more Experi­
ments to thoſe I formerly
ſent You over: I could not
be ſo much your Servant as I am, without
looking upon that Deſire as a Com­
mand; and conſequently, without think­
ing my ſelf obliged to conſider by what
ſort of Experiments it might the moſt ac­
ceptably be obey'd. And at the ſame
1time, perceiving by Letters from ſome
other Ingenious Perſons at Paris, that ſe­
veral of the Virtuoſi there, were very
intent upon the examination of the Inte­
reſt of the Ayr, in hindring the deſcent
of the Quick-ſilver, in the famous Expe­
riment touching a Vacuum: I thought I
could not comply with your Deſires in a
more fit and ſeaſonable manner, then by
proſecuting and endeavoring to promote
that noble Experiment of Torricellius:
and by preſenting your Lordſhip an ac­
count of my attempts to illuſtrate a ſub­
ject, about which, it's being ſo much diſ­
courſ'd of where you are, together with
your inbred Curioſity, and love of Ex­
perimental Learning, made me ſuppoſe
you ſufficiently inquiſitive.
And though I pretend not to acquaint
you, on this occaſion, with any ſtore of
new Diſcoveries yet poſſibly I ſhall be ſo
happy, as to aſſiſt you to know ſomethings
which you did formerly but ſuppoſe; and
ſhall preſent you, if not with new Theo­
ries, at leaſt with new Proofs of ſuch as
are not yet become unqueſtionable. And
if what I ſhall deliver, have the good for­
tune to encourage and aſſiſt you to proſe­
cute the Hints it will afford, I ſhall ac-
1count my ſelf, in paying of a duty to
you, to have done a piece of Service to
the Commonwealth of Learning. Since
it may highly conduce to the advance­
ment of that Experimental Philoſophy,
the effectual purſuit of which, requires
as well a Purſe as a Brain, to endeere it
to hopeful Perſons of your Quality: who
may accompliſh many things which o­
thers can but wiſh or, at moſt, but deſign,
by being able to imploy the Preſents of
Fortune in the ſearch of the Myſteries of
Nature.
And I am not faintly induc'd to make
choice of this Subject, rather then any
of the expected Chymical ones, to enter­
tain your Lordſhip upon, by theſe two
Conſiderations: The one, That the Ayr
being ſo neceſſary to humane Life, that
not onely the generality of Men, but
moſt other Creatures that breath, can­
not live many minutes without it; any
conſiderable diſcovery of its Nature,
ſeems likely to prove of moment to
Man-kinde. And the other is, That the
Ambient Ayr, being that whereto both
our own Bodies, and moſt of the others
we deal with here below, are almoſt per­
petually contiguous; not onely its alte-
1rations have a notable and manifeſt ſhare
in thoſe obvious effects, that men have
already been invited to aſcribe thereunto
ſuch as are the various diſtempers inci­
dent to humane Bodies, eſpecially if cra­
zy, in the Spring, the Autumn, and alſo
on moſt of the great and ſudden changes
of Weather) but likewiſe, that the fur­
ther diſcovery of the nature of the Ayr,
will probably diſcover to us, that it con­
curs more or leſs to the exhibiting of ma­
ny Phænomena, in which it hath hither­
to ſcarce been ſuſpected to have any inte­
reſt. So that a True Account of any
Experiment that is New concerning a
thing, wherewith we have ſuch conſtant
and neceſſary intercourſe, may not one­
ly prove of ſome advantage to humane
Life, but gratifie Philoſophers, by pro­
moting their Speculations on a Subject
which hath ſo much opportunity to ſolli­
cite their Curioſity.
And I ſhould immediately proceed to
the mention of my Experiments, but that
I like too well that worthy ſaying of the
Naturaliſt Pliny, Benignum eſt

& plenum ingenui pudor is, fateri
per quos profeceris, not to con­
form to it, by acquainting your Lord-
1ſhip, in the firſt place, with the Hint I
had of the Engine I am to entertain you
of. You may be pleaſ'd to remember,
that a while before our ſeparation in Eng­
land, I told you of a Book that I had
heard of, but not peruſ'd, publiſh'd by
the induſtrious Jeſuit Schottus, wherein
'twas ſaid, He related how that ingenious
Gentleman Otto Gericke, Conſul of Mag­
deburg, had lately practiced in Germany a
way of emptying Glaſs Veſſels, by ſuck­
ing out the Ayr at the mouth of the Veſ­
ſel, plung'd under water: And you may
alſo perhaps remember, that I expreſſ'd
my ſelf much delighted with this Expe­
riment, ſince thereby the great force of
the external Air (either ruſhing in at the
open'd Orifice of the empty'd Veſſel, or
violently forcing up the Water into it)
was rendred more obvious and conſpicu­
ous, than in any Experiment that I had
formerly ſeen. And though it may appear
by ſome of thoſe Writings I ſometimes
fhew'd your Lordſhip, that I had been ſol­
licitous to try things upon the ſame
ground; yet in regard this Gentleman
was before-hand with me in producing
ſuch conſiderable effects, by means of the
exſuction of Air, I think my ſelf oblig'd
1to acknowledge the Aſſiſtance, and En­
couragement the Report of his perfor­
mances hath afforded me.
In .
lib. 1.
But as few inventions happen to be at
firſt ſo compleat, as not to be either ble­
miſhd with ſome deficiencies needful to be
remedy'd, or otherwiſe capable of im­
provement: ſo when the Engine we
have been ſpeaking of, comes to be more
attentively conſider'd, there will appear
two very conſiderable things to be de­
ſir'd in it. For firſt, the Wind-Pump (as
ſome body not improperly calls it) is ſo
contriv'd, that to evacuate the Veſſel
there is requir'd the continual labor of
two ſtrong men for divers hours. And
next (which is an imperfection of much
greater moment) the Receiver, or Glaſs
to be empty'd, conſiſting of one entire
and uninterrupted Globe and Neck of
Glaſs; the whole Engine is ſo made, that
things cannot be convey'd into it, where­
on to try Experiments: So that there
ſeems but little (if any thing) more to be
expected from it, then thoſe very few
Phænomena that have been already ob­
ſerv'd by the Author, and Recorded by
Schottus. Wherefore to remedy theſe
Inconveniences, I put both Mr. G.
1and R. Hook (who hath alſo the Honor to
be known to your Lordſhip, and was with
me when I had theſe things under conſi­
deration) to contrive ſome Air Pump,
that might not, like the other, need to
be kept under water (which on divers oc­
caſions is inconvenient) & might be more
eaſily manag'd: And after an unſucceſsful
try all or two of ways propoſ'd by o­
thers, the laſt nam'd Perſon fitted me
with a Pump, anon to be deſcrib'd. And
thus the firſt Imperfection of the German
Engine, was in good meaſure, though
not perfectly, remedy'd: And to ſupply
the ſecond deſect, it was conſidered that
it would not perhaps prove impoſſible to
leave in the Glaſs to be empty'd, a hole
large enough to put in a Mans Arm
cloath'd; and conſequently other Bodies,
not bigger then it, or longer then the in­
ſide of the Veſſel. And this Deſign
ſeem'd the more hopefull, becauſe I re­
membred, that having ſeveral years be­
fore often made the Experiment De Va­
cuo with my own hands; I had, to exa­
mine ſome conjectures that occurr'd to
me about it, cauſed Glaſſes to be made
with a hole at that end, which uſes to be
ſeal'd up, and had nevertheleſs been able
1as occaſion requir'd, to make uſe of ſuch
Tubes, as if no ſuch holes had been left
in them; by deviſing ſtopples for them,
made of the common Plaiſter call'd Dia­
chylon: which I rightly enough gheſſ'd,
would, by reaſon of the exquiſite com­
mixtion of its ſmall parts, and cloſeneſs
of its texture, deny all acceſs to the ex­
ternal Air. Wherefore, ſuppoſing that
by the help of ſuch Plaiſters, carefully
laid upon the commiſſures of the ſtopple
and hole to be made in the Receiver, the
external Air might be hindred from inſi­
nuating it ſelf between them into the Veſ­
ſel, we cauſ'd ſeveral ſuch Glaſſes, as
you will finde deſcrib'd a little lower, to
be blown at the Glaſs-houſe; and though
we could not get the Work-men to blow
any of them ſo large, or of ſo conveni­
ent a ſhape as we would fain have had; yet
finding one to be tolerably fit, and leſs
unfit then any of the reſt, we were con­
tent to make uſe of it in that En­
gine: Of which, I ſuppoſe, you by this
time expect the Deſcription, in order to
the Recital of the Phænomena exhibited
by it.
To give your Lordſhip then, in the
firſt place, ſome account of the Engine it
1ſelf: It conſiſts of two principal parts; a
glaſs Veſſel, and a Pump to draw the Air
out of it.
The former of theſe (which we, with
the Glaſs men, ſhall often call a Receiver,
for its affinity to the large Veſſels of that
name, uſed by Chymiſts) conſiſts of a
Glaſs with a wide hole at the top, of a
cover to that hole, and of a ſtop-cock
faſtned to the end of the neck, at the
bottom.
The ſhape of the Glaſs, you will find
expreſſ'd in the firſt Figure of the annex­
ed Scheme. And for the ſize of it, it
contain'd about 30 Wine Quarts, each of
them containing near two pound (of 16
Ounces to the pound) of water: We
ſhould have been better pleaſ'd with a
more capacious Veſſel, but the Glaſs-men
profeſſed themſelves unable to blow a
larger, of ſuch a thickneſs and ſhape as
was requiſite to our purpoſe.
At the very top of the Veſſel, (A) you
may obſerve a round hole, whoſe Dia­
meter (B C) is of about four inches; and
whereof, the Orifice is incircled with a
lip of Glaſs, almoſt an inch high: For
the making of which lip, it was requiſite
(to mention that upon the by, in caſe
1your Lordſhip ſhould have ſuch another
Engine made for you) to have a hollow
and tapering Pipe of Glaſs drawn out,
whereof the Orifice above mentioned
was the Baſis, and then to have the cone
cut off with a hot Iron, within about an
Inch of the Points (B C.)
The uſe of the lip, is to ſuſtain the
cover delineated in the ſecond Figure;
where (D E) points out a braſs Ring, ſo
caſt, as that it doth within and without
cover the lip (B C) of the firſt Figure,
and is cemented on upon it with a ſtrong
and cloſe Cement. To the inward taper­
ing Orifice of this Ring (which is about
three Inches over) are exquiſitely ground
the ſides of the Braſs ſtopple (F G;) ſo
that the concave ſuperficies of the one,
and the convex of the other, may touch
one another in ſo many places, as may
leave as little acceſs, as poſſible, to the ex­
ternal Air: And in the midſt of this cover
is left a hole (H I) of about half an inch
over, invironed alſo with a ring or ſocket
of the ſame mettal, and fitted likewiſe
with a braſs ſtopple (K) made in the form
of the Key of a ſtop-cock, and exactly
ground into the hole (H I) it is to fill; ſo
as that though it be turn'd round in the
1cavity it poſſeſſes, it will not let in the
Air, and yet may be put in or taken out
at pleaſure, for uſes to be hereafter men­
tioned. In order to ſome of which, it is
perforated with a little hole, (8) traverſing
the whole thickneſs of it at the lower
end; through which, and a little braſs
Ring (L) faſtned to one ſide, (no matter
which) of the bottom of the ſtopple
(FG) a ſtring (8, 9, 10) might paſs, to
be imploy'd to move ſome things in the
capacity of the empty'd Veſſel; without
any where unſtopping it.
The laſt thing belonging to our Recei­
ver, is the ſtop-cock deſigned in the firſt
Figure by (N.) for the better faſtening
of which to the neck, and exacter excluſi­
on of the Air, there was ſoder'd on to
the ſhank of the Cock (X) a Plate of
Tin, (MTUW) long enough to cover
the neck of the Receiver. But becauſe
the cementing of this was a matter of
ſome difficulty, it will not be amiſs to
mention here the manner of it, which
was, That the cavity of the tin Plate was
fill'd with a melted Cement, made of
Pitch, Roſin, and Wood-aſhes, well in­
corporated; and to hinder this liquid
Mixture from getting into the Orifice (Z)
1of the ſhank, (X) that hole was ſtopt
with a Cork, to which was faſtned a ſtring,
whereby it might be pull'd out of the up­
per Orifice of the Receiver; and then,
the glaſs neck of the Receiver being well
warm'd, was thruſt into this Cement, and
over the ſhank whereby it was effected,
that all the ſpace betwixt the tin Plate and
the Receiver, and betwixt the internal
ſuperficies of the Receiver, and the
ſhanck of the Cock, was filld with the
Cement; and ſo we have diſpach'd the
firſt and upper part of the Engine.
The undermoſt remaining part conſiſts
of a Frame, and of a ſucking Pump, or
as we formerly call'd it, an Air Pump, ſup­
ported by it: The Frame is of Wood,
ſmall, but very ſtrong, conſiſting of three
legs, (111) ſo plac'd, that one ſide of
it may ſtand perpendicular, that the free
motion of the hand may not be hindered.
In the midſt of which frame, is tranſverſly
nail'd a board, (222) which may not im­
properly be call'd a Midriff, upon which
reſts, and to which is ſtrongly faſtned, the
main part of the Pump it ſelf, which is
the onely thing remaining to be deſcri­
bed.
The Pump conſiſts of four parts, a
1hollow Cylindre, a Sucker, a handle to
move that Sucker, and a Valve.
The Cylindre was (by a pattern) caſt
of braſs; it is in length about 14 inches,
thick enough to be very ſtrong, notwith­
ſtanding the Cylindrical cavity left with­
in it; this cavity is about three inches
Diameter, and makes as exact a Cylin­
dre as the Artificer was able to bore.
This hollow Cylindre is fitted with a ſuck­
er, (4455) conſiſting of two parts, the
one (44) ſomewhat leſs in Diameter then
the cavity of the Cylindre, upon which
is nail'd a good thick piece of tan'd ſhoe
Leather, which will go ſo cloſe to the
Cylindre, that it will need to be very
forcibly knock'd and ram'd in, if at any
time it be taken out, which is therefore
done, that it may the more exactly hin­
der the Air from inſinuating it ſelf be­
twixt it and the ſides of the Cylindre
whereon it is to move.
To the midſt of this former part of the
Sucker is ſtrongly faſtned the other,
namely a thick and narrow plate of Iron,
(55) ſomewhat longer then the Cylindre,
one of whoſe edges is ſmooth, but at the
other edge it is indented (as I may ſo
ſpeak) with a row of teeth delineated in
1the Scheme, into whoſe intervals are to
be fitted, the teeth of a ſmall Iron nut;
() (as Tradeſ-men call it) which is faſt­
ned by two ſtaples (22) to the under ſide
of the formerly mention'd tranſverſe
board (222) on which the Cylindre reſts,
and is turn'd to and fro by the third piece
of this Pump, namely, the handle or
manubrium, (7) of which the Figure gives
a ſufficient deſcription.
The fourth and laſt part of this Cylin­
dre, is the Valve, (R) conſiſting of a
hole bored through at the top of the Cy­
lindre, a little tapering towards the cavi­
ty; into which hole is ground a tapering
Peg of braſs, to be thruſt in, and taken
out at pleaſure.
The Engine being thus deſcrib'd, it
will be requiſite to adde, that ſomething
is wont to be done before it be ſet on
work, for the more eaſie moving of the
Sucker, and for the better excluſion of
the outward Air: which when the Veſſel
begins to be exhauſted, is much more dif­
ficult to be kept out then one would eaſi­
ly imagine.
There muſt then be firſt powr'd in at
the top of the Receiver a little ſallad oyl,
partly to fill up any ſmall intervalls that
1may happen to be betwixt the contigu­
ous ſurfaces of the internal parts of the
Stop-cock: And partly that it may be
the more eaſie to turn the Key (S) back­
wards and forwards. Pretty ſtore of oyl
muſt alſo be pour'd into the Cylindre,
both that the Sucker may ſlip up and
down in it the more ſmoothly and freely,
and that the Air might be the better
hindred from getting in between them:
And for the like reaſons, a little oyl is to
be uſed alſo about the Valve. Upon
which occaſion, it would not be omitted
(for it is ſtrange) that oftentimes, when
neither the pouring in of water, nor even
of oyl alone, prov'd capable to make the
Sucker move eaſily enough in the Cylin­
der; a mixture of both thoſe Liquors
would readily (ſometimes even to admi­
ration) perform the deſired effect. And
laſtly, the braſs cover of the Receiver,
being put into the braſs ring formerly de­
ſcrib'd, that no Air may get between
them, it will be very requiſite to plaiſter
over very carefully the upper edges of
both, with the plaiſter formerly mention­
ed, or ſome other as cloſe, which is to be
ſpread upon the edges with a hot Iron;
that being melted, it may run into and
1fill up all the crannies, or other little ca­
vities, at which the Air might otherwiſe
get entrance.
All things being thus fitted, and the
lower ſhank (O) of the ſtop-cock being
put into the upper Orifice of the Cylin­
der (&), into which it was exactly ground;
the Experimenter is firſt, by turning the
handle, to force the Sucker to the top of
the Cylinder, that there may be no Air
left in the upper part of it: Then ſhut­
ting the Valve with the Plug, and turning
the other way, he is to draw down the
Sucker to the bottom of the Cylinder;
by which motion of the Sucker, the Air
that was formerly in the Cylinder being
thruſt out, and none being permitted to
ſucceed in its room, 'tis manifeſt that the
cavity of the Cylinder muſt be empty,
in reference to the Air: So that if there­
upon the Key of the Stop-cock be ſo
turn'd, as that through the perforation of
it, a free paſſage be opened betwixt the
Cylinder and the Receiver, part of the
Air formerly contain'd in the Receiver,
will nimbly deſcend into the Cylinder.
And this Air, being by the turning back
of the Key hinder'd from the returning
into the Receiver, may, by the opening
1of the Valve, and forcing up of the Suck­
er to the top of the Cylinder again, be
driven out into the open Air. And thus
by the repetition of the motion of the
Sucker upward and downward, and by op­
portunely turning the Key, and ſtopping
the Valve, as occaſion requires, more or
leſs Air may be ſuck'd out of the Recei­
ver, according to the exigency of the Ex­
periment, and the intention of him that
makes it.
Your Lordſhip will, perhaps, think that
I have been unneceſſarily prolix in this
firſt part of my Diſcourſe: But if you
had ſeen how many unexpected difficul­
ties we found to keep out the externall
Air, even for a little while, when ſome
conſiderable part of the internal had been
ſuckt out; You would peradventure al­
low, that I might have ſet down more
circumſtances then I have, without ſet­
ting down any, whoſe knowledge, he that
ſhall try the Experiment may not have
need of. Which is ſo true, that, before we
proceed any further, I cannot think it un­
ſeaſonable to advertiſe Your Lordſhip,
that there are two chief ſorts of Experi­
ments, which we deſign'd in our Engine
to make tryal of: The one, ſuch as may
1be quickly diſpatcht, and therefore may
be try'd in our Engine, though it leak a
little; becauſe the Air may be faſter drawn
out, by nimbly plying the Pump, then
it can get in at undiſcern'd leaks; I ſay at
undiſcern'd leaks, becauſe ſuch as are big
enough to be diſcover'd can ſcarce be un­
eaſie to be ſtopt. The other ſort of Ex­
periments conſiſts of thoſe that require
not onely that the internal Air be drawn
out of the Receiver, but that it be like­
wiſe for a long time kept out of it. Such
are the preſervation of Animal and o­
ther Bodies therein, the germination and
growth of Vegetables, and other tryals
of ſeveral ſorts, which it is apparent can­
not be well made unleſs the external Air
can, for a competent while, be excluded:
Since even at a very ſmall leak there may
enough get in, to make the Vacuum ſoon
looſe that name; by which I here declare
once for all, that I underſtand not a ſpace
wherein there is no body at all, but ſuch
as is either altogether, or almoſt totally
void of Air.
Now this diſtinction of Experiments
I thought fit to premiſe to the enſuing
Narratives, becauſe upon tryal, we found
it ſo exceeding (and ſcarce imaginable) dif-
1ficult a matter, to keep out the Air from
getting at all in at any imperceptible hole
or flaw whatſoever, in a Veſſel immedi­
ately ſurrounded with the compreſſed At­
moſphere, that in ſpight of all our care
and diligence, we never were able totally
to exhauſt the Receiver, or keep it when
it was almoſt empty, any conſiderable
time, from leaking more or leſs: although
(as we have lately intimated) by unwearyed
quickneſs in plying the Pump, the inter­
nall Air can be much faſter drawn out
then the external can get in, till the Re­
ceiver come to be almoſt quite empty.
And that's enough to enable men to diſ­
cover hitherto unobſerved Phænomena of
Nature.
The Experiments therefore of the firſt
ſort, will, I fear, prove the onely ones
wherewith my Avocations will allow me
to entertain Your Lordſhip in this Letter.
For till your further Commands ſhall en­
gage me to undertake, by Gods permiſ­
ſion, ſuch an Employment, and more lea­
ſure ſhall better fit me for it, I know not
whether I ſhall be in a condition to try
what may be done, to enable me to give
you ſome account of the other ſort of
Experiments alſo.
1
TO proceed now to the Phænomena,

exhibited to us by the Engine above
deſcribed; I hold it not unfit to begin
with what does conſtantly and regularly
offer it ſelf to our obſervation, as depend­
ing upon the Fabrick of the Engine it ſelf,
and not upon the nature of this or that
particular Experiment which 'tis employ­
ed to try.
Experi­
ment 1.
Firſt, Then upon the drawing down
of the Sucker, (the Valve being ſhut) the
Cylindrical ſpace, deſerted by the Sucker,
is left de void of Air; and therefore, up­
on the turning of the Key, the Air con­
tained in the Receiver ruſhes into the em­
ptyed Cylinder, till the Air in both thoſe
Veſſels be brought to about an equal
meaſure of dilatation. And therefore,
upon ſhutting the Receiver by returning
the Key, if you open the Valve, and force
up the Sucker again, you will finde, that
after this firſt exſuction you will drive
out almoſt a whole Cylinder full of Air:
But at the following exſuctions, you will
draw leſs and leſs of Air out of the Recei­
ver into the Cylinder, becauſe that there
will ſtill remain leſs and leſs Air in the
1Receiver it ſelf; and conſequently, the
Particles of the remaining Air, having
more room to extend themſelves in, will
leſs preſs out one another. This you will
eaſily perceive, by finding, that you ſtill
force leſs and leſs Air out of the Cylin­
der; ſo that when the Receiver is almoſt
exhauſted, you may force up the Sucker
almoſt to the top of the Cylinder, be­
fore you will need to unſtop the Valve to
let out any Air: And if at ſuch time, the
Valve being ſhut, you let go the handle of
the Pump, you will finde the Sucker for­
cibly carryed up to the top of the Cylin­
der, by the protruſion of the external Air;
which, being much leſs rarified then that
within the Cylinder, muſt have a more
forcible preſſure upon the Sucker, then
the internal is able to reſiſt: And by this
means you may know how far you have
emptyed the Receiver. And to this we
may adde, on this occaſion, that conſtant­
ly upon the turning of the Key to let out
the Air from the Receiver, into the em­
ptied Cylinder, there is immediately pro­
duced a conſiderably brisk noiſe, eſpeci­
ally whil'ſt there is any plenty of Air in
the Receiver.
1
For the more eaſie underſtanding of the
Experiments tryable by our Engine, I
thought it not ſuperfluous, nor unſeaſon­
able in the recital of this firſt of them, to
inſinuate that notion by which it ſeems
likely that moſt, if not all, of them will
prove explicable. Your Lordſhip will
eaſily ſuppoſe, that the Notion I ſpeak
of is, That there is a Spring, or Elaſti­
cal power in the Air we live in. By which
ἐλατγ̀ρ or Spring of the Air, that which
I mean is this: That our Air either con­
ſiſts of, or at leaſt abounds with, parts of
ſuch a nature, that in caſe they be bent or
compreſſ'd by the weight of the incum­
bent part of the Atmoſphere, or by any o­
ther Body, they do endeavor, as much as
in them lies, to free themſelves from that
preſſure, by bearing againſt the contigu­
ous Bodies that keep them bent; and,
aſſoon as thoſe Bodies are remov'd or
reduced to give them way, by preſently
unbending and ſtretching out themſelves,
either quite, or ſo far forth as the con­
tiguous Bodies that reſiſt them will per­
mit, and thereby expanding the whole
parcel of Air, theſe elaſtical Bodies com­
poſe.
1
This Notion may perhaps be ſome­
what further explain'd, by conceiving the
Air near the Earth to be ſuch a heap of
little Bodies, lying one upon another, as
may be reſembled to a Fleece of Wooll.
For this (to omit other likeneſſes betwixt
them) conſiſts of many ſlender and flexi­
ble Hairs; each of which, may indeed,
like a little Spring, be eaſily bent or roul­
ed up; but will alſo, like a Spring, be
ſtill endeavouring to ſtretch it ſelf out
again. For though both theſe Haires,
and the Aerial Corpuſcles to which we
liken them, do eaſily yield to externall
preſſures; yet each of them (by vertue of
its ſtructure) is endow'd with a Power or
Principle of ſelf-Dilatation; by vertue
whereof, though the hairs may by a Mans
hand be bent and crouded cloſer together,
and into a narrower room then ſuits beſt
with the nature of the Body: Yet whil'ſt
the compreſſion laſts, there is in the fleece
they compoſe an endeavour outwards,
whereby it continually thruſts againſt the
hand that oppoſes its Expanſion. And
upon the removall of the external preſ­
ſure, by opening the hand more or leſs, the
compreſſed Wooll does, as it were, ſpon­
taneouſly expand or diſplay it ſelf towards
1the recovery of its former more looſe and
free condition, till the Fleece have ei­
ther regain'd its former Dimenſions, or
at leaſt, approach'd them as near as the
compreſſing hand (perchance not quite
open'd) will permit. This Power of
ſelf-Dilatation, is ſomewhat more conſpi­
cuous in a dry Spunge compreſſ'd, then
in a Fleece of Wooll. But yet we ra­
ther choſe to imploy the latter, on this
occaſion, becauſe it is not like a Spunge,
an entire Body, but a number of ſlen­
der and flexible Bodies, looſely com­
plicated, as the Air it ſelf ſeems to
be.
There is yet another way to explicate
the Spring of the Air, namely, by ſuppo­
ſing with that moſt ingenious Gentleman,
Monſieur Des Cartes, That the Air is no­
thing but a Congeries or heap of ſmall
and (for the moſt part) of flexible Parti­
cles; of ſeveral ſizes, and of all kinde of Fi­
gures which are raiſ'd by heat (eſpecially
that of the Sun) into that fluid and
ſubtle Etheriall Body that ſurrounds
the Earth; and by the reſtleſſe agi­
tation of that Celeſtial Matter where­
in thoſe Particles ſwim, are ſo whirl'd
1round, that each Corpuſcle endeavours
to beat off all others from coming within
the little Sphear requiſite to its motion
about its own Center; and (in caſe any,
by intruding into that Sphear ſhall op­
poſe its free Rotation) to expell or drive
it away: So that according to this Do­
ctrine, it imports very little, whether the
particles of the Air have the ſtructure re­
quiſite to Springs, or be of any other
form (how irregular ſoever) ſince their
Elaſtical power is not made to depend
upon their ſhape or ſtructure, but upon
the vehement agitation, and (as it were)
brandiſhing motion, which they receive
from the fluid Ether that ſwiftly flows
between them, and whirling about each
of them (independently from the reſt)
not onely keeps thoſe ſlender Aërial
Bodies ſeparated and ſtretcht out (at leaſt,
as far as the Neighbouring ones will per­
mit) which otherwiſe, by reaſon of
their flexibleneſs and weight, would
flag or curl; but alſo makes them hit
againſt, and knock away each other, and
conſequently require more room, then
that which if they were compreſſ'd, they
would take up.
1
By theſe two differing ways, my Lord,
may the Spring of the Air be explicated.
But though the former of them be that,
which by reaſon of its ſeeming ſomewhat
more eaſie, I ſhall for the moſt part make
uſe of in the following Diſcourſe: yet
am I not willing to declare peremptorily
for either of them, againſt the other. And
indeed, though I have in another Treatiſe
endeavoured to make it probable, that the
returning of Elaſtical Bodies (if I may ſo
call them) forcibly bent, to their former
poſition, may be Mechanically explica­
ted: Yet I muſt confeſs, that to deter­
mine whether the motion of Reſtitution
in Bodies, proceed from this, That the
parts of a Body of a peculiar Structure
are put into motion by the bending of the
ſpring, or from the endeavor of ſome ſub­
tle ambient Body, whoſe paſſage may be
oppoſ'd or obſtructed, or elſe it's preſſure
unequally reſiſted by reaſon of the new
ſhape or magnitude, which the bending of
a Spring may give the Pores of it: To
determine this, I ſay, ſeems to me a mat­
ter of more difficulty, then at firſt ſight
one would eaſily imagine it. Wherefore
I ſhall decline medling with a ſubject,
which is much more hard to be explica-
1ted, then neceſſary to be ſo, by him,
whoſe buſineſs it is not, in this Letter, to
aſſign the adequate cauſe of the Spring of
the Air, but onely to manifeſt, That the
Air has a Spring, and to relate ſome of
its effects.
I know not whether I need annex that,
though either of the above-mention'd
Hypotheſes, and perhaps ſome others,
may afford us an account plauſible enough
of the Air-ſpring; yet I doubt, whether
any of them gives us a ſufficient account
of its Nature. And of this doubt, I
might here mention ſome Reaſons, but
that, peradventure, I may (God permit­
ting) have a fitter occaſion to ſay ſome­
thing of it elſewhere. And therefore I
ſhould now proceed to the next Experi­
ment, but that I think it requiſite, firſt,
to ſuggeſt to your Lordſhip what comes
into my thoughts, by way of Anſwer to
a plauſible Objection, which I foreſee you
may make againſt our propoſ'd Doctrine,
touching the Spring of the Air. For it
may be alleadged, that though the Air
were granted to conſiſt of Springy Par­
ticles (if I may ſo ſpeak) yet thereby
we could onely give an account of the
Dilatation of the Air in Wine-Guns and
1other pneumatical Engines wherein the
Air has been compreſſ'd, and its Springs
violently bent by an apparent externall
force; upon the removall of which, 'tis
no wonder that the Air ſhould, by the
motion of reſtitution, expand it ſelf till
it have recovered its more natural dimen­
ſions: whereas in our above-mentioned
firſt Experiment, and in almoſt all others
tryable in our Engine, it appears not
that any compreſſion of the Air prece­
ded its ſpontaneous Dilatation or Expan­
ſion of it ſelf. To remove this difficul­
ty, I muſt deſire Your Lordſhip to take
notice, that of whatever nature the Air,
very remote from the Earth, may be, and
whatever the Schools may confidently
teach to the contrary, yet we have divers
Experiments to evince, that the Atmoſ­
phere we live in is not (otherwiſe then
comparatively to more ponderous Bodies)
light, but heavy: And did not their
gravity hinder them, it appears not why
the ſteams of the Terraqueous Globe, of
which our Air in great part conſiſts,
ſhould not riſe much higher then the Re­
fraction of the Sun, and other Stars
give men ground to think, that the At­
moſphere, even in the judgement of thoſe
1Recent Aſtronomers, who ſeem willing
to enlarge its bounds as much as they dare,
does reach.
But leſt you ſhould expect my ſeconding
this Reaſon by Experience; and leſt you
ſhould object, That moſt of the Experi­
ments that have been propoſ'd to prove the
gravity of the Air, have been either barely
propoſ'd, or perhaps not accuratly try'd; I
am content, before I paſs further, to menti­
on here, That I found a dry lambs-bladder
containing near about two thirds of a pint,
and compreſſ'd by a packthred tyed about
it, to looſe a grain and the eighth part of
a grain of its former weight, by the receſs
of the Air upon my having prickt it: And
this with a pair of Scales, which when the
full Bladder and the correſpondent weight
were in it, would manifeſtly turn either
way with the 32 part of a grain. And if
it be further objected, That the Air in
the Bladder was violently compreſſ'd by
the Pack-thred and the ſides of the
Bladder, we might probably (to wave
prolix anſwers) be furniſh'd with a Re­
ply, by ſetting down the differing weight
of our Receiver, when empty'd and when
full of uncompreſſ'd Air, if we could here
procure ſcales fit for ſo nice an experiment;
1ſince we are informed, that in the German
Experiment, commended at the begin­
ning of this Letter, the Ingenious Tryers
of it found, That their Glaſs Veſſel, of
the capacity of 32 meaſures, was lighter
when the Air had been drawn out of it,
then before, by no leſs then one ounce
and (3/10) that is, an ounce and very near a
third: But of the gravity of the Air, we
may elſewhere have occaſion to make fur­
ther mention.
Taking it then for granted that the Air
is not deyoid of weight, it will not be
uneaſie to conceive, that that part of the
Atmoſphere wherein we live, being the
lower part of it, the Corpuſcles that com­
poſe it, are very much compreſſ'd by the
weight of all thoſe of the like nature that
are directly over them, that is, of all the
Particles of Air, that being pil'd up up­
on them, reach to the top of the Atmoſ­
phere. And though the height of this
Atmoſphere, according to the famous
Kepler, and ſome others, ſcarce exceeds
eight common miles; yet other eminent
and later Aſtronomers, would promote
the confines of the Atmoſphere, to ex­
ceed ſix or ſeven times that number of
miles. And the diligent and learned
1Riviolo makes it probable, that the At­
moſphere may, at leaſt in divers places, be
at leaſt 50 miles high. So that according to
a moderate eſtimate of the thickneſs of
the Atmoſphere, we may well ſuppoſe,
that a Column of Air, of many miles in
height, leaning upon ſome ſpringy Cor­
puſcles of Air here below, may have
weight enough to bend their little ſprings,
and keep them bent: As, to reſume our
former compariſon, if there were fleeces of
Wooll pil'd up to a mountainous height
upon one another, the Hairs that com­
poſe the lowermoſt locks which ſupport
the reſt, would, by the weight of all the
Wool above them, be as well ſtrongly
compreſſed, as if a man ſhould ſqueeze
them together in his hands, or imploy any
ſuch other moderate force to compreſs
them. So that we need not wonder, that
upon the taking off the incumbent Air
from any parcel of the Atmoſphere here
below, the Corpuſcles, whereof that un­
dermoſt Air conſiſts, ſhould diſplay them­
ſelves, and take up more room then be­
fore.
And if it be objected, That in Water,
the weight of the upper and of the lower
part is the ſame: I anſwer, That beſides
1that it may be well doubted whether the
obſervation, by reaſon of the great diffi­
culty have been exactly made, there is a
manifeſt diſparity betwixt the Air and
Water: For I have not found, that upon
an Experiment purpoſely made, (and in
another Treatiſe Recorded) that Water
will ſuffer any conſiderable compreſſion;
whereas we may obſerve in Wind-Guns
(to mention now no other Engines) that
the Air will ſuffer it ſelf to be crouded in­
to a comparatively very little room; in
ſo much, that a very diligent Examiner
of the Phænomena of Wind-Guns would
have us believe, that in one of them, by
condenſation, he reduc'd the Air into a
ſpace at leaſt eight times narrower then it
before poſſeſt. And to this, if we adde
a noble Phænomenon of the Experiment
De Vacuo; theſe things put together, may
for the preſent ſuffice to countenance our
Doctrine. For that noble Experimenter,
Monſieur Paſcal (the Son) had the com­
mendable Curioſity to cauſe the Torri­
cellian Experiment to be try'd at the foot,
about the middle, and at the top of that
high Mountain (in Auvergne, if I miſtake
not) commonly call'd Le Puy de Domme;
whereby it was found, That the Mercury
1in the Tube fell down lower, about three
inches, at the top of the Mountain then
at the bottom. And a Learned Man a
while ſince inform'd me, That a great
Virtuoſo, friend to us both, has, with not
unlike ſucceſs, tryed the ſame Experi­
ment in the lower and upper parts of a
Mountain in the Weſt of England: Of
which, the reaſon ſeems manifeſtly enough
to be this, That upon the tops of high
Mountains, the Air which bears againſt
the reſtagnant Quick-ſilver, is leſs preſſ'd
by the leſs ponderous incumbent Air; and
conſequently is not able totally to hinder
the deſcent of ſo tall and heavy a Cylin­
der of Quick-ſilver, as at the bottom of
ſuch Mountains did but maintain an Æqui­
librium with the incumbent Atmoſphere.
And if it be yet further Objected a­
gainſt what hath been propoſ'd touching
the compactneſs and preſſure of the Infe­
rior Air; That we finde this very Air to
yield readily to the motion of little Flies,
and even to that of Feathers, and ſuch o­
ther light and weak Bodies; which ſeems
to argue, that the particles of our Air are
not ſo compreſſ'd as we have repreſented
them, eſpecially, ſince by our former
Experiment it appears, that the Air rea-
1dily dilated it ſelf downward, from the
Receiver into the Pump, when 'tis plain,
that it is not the incumbent Atmoſphere,
but onely the ſubjacent Air in the braſs
Cylinder that has been remov'd: If this,
I ſay, be objected, we may reply, That
when a man ſqueezes a Fleece of Wool in
his hand, he may feel that the Wool in­
ceſſantly bears againſt his hand, as that
which hinders the hairs it conſiſts of, to
recover their former and more natural ex­
tent. So each parcel of the Air about the
Earth, does conſtantly endeavour to thruſt
away all thoſe contiguous Bodies, whe­
ther Aërial or more groſs, that keep
them bent, and hinder the expanſion of
its parts, which will dilate themſelves or
flie abroad towards that part, whether up­
wards or downwards, where they finde
their attempted Dilatation of themſelves
leſs reſiſted by the neihgboring Bodies.
Thus the Corpuſcles of that Air we have
been all this while ſpeaking of, being un­
able, by reaſon of their weight, to aſcend
above the Convexity of the Atmoſphere,
and by reaſon of the reſiſtance of the ſur­
face of the Earth and Water, to fall down
lower, they are forced, by their own gra­
vity and this reſiſtance, to expand and
1diffuſe themſelves about the Terreſtial
Globe; whereby it comes to paſs, that
they muſt as well preſs the contiguous
Corpuſcles of Air that on either ſide op­
poſe their Dilatation, as they muſt preſs
upon the ſurface of the Earth, and, as it
were recoyling thence, endeavor to thruſt
away thoſe upper particles of Air that
lean upon them.
And as for the eaſie yielding of the Air
to the Bodies that move in it, if we con­
ſider that the Corpuſcles whereof it con­
ſiſts, though of a ſpringy nature, are yet
ſo very ſmall, as to make up (which 'tis
manifeſt they doe) a fluid Body, it will
not be difficult to conceive, that in the
Air, as in other Bodies that are fluid, the
little Bodies it conſiſts of are in an almoſt
reſtleſs motion, whereby they become
(as we have more fully diſcourſed in ano­

ther Treatiſe) very much diſpoſed to
yield to other Bodies, or eaſie to be diſ­
plac'd by them, and that the ſame Cor­
puſcles are likewiſe ſo variouſly mov'd, as
they are intire Corpuſcles, that if ſome
ſtrive to puſh a Body plac'd among them
towards the right hand (for inſtance)
others, whoſe motion has an oppoſite de­
termination, as ſtrongly thruſt the ſame
1Body towards the left; whereby neither
of them proves able to move it out of
its place, the preſſure on all hands being
reduced as it were to an Æquilibrium: ſo
that the Corpuſcles of the Air muſt be as
well ſometimes conſidered under the no­
tion of little Springs, which remaining
bent, are in their entire bulk tranſported
from place to place; as under the notion
of Springs diſplaying themſelves, whoſe
parts flie abroad whilſt as to their entire
bulk they ſcarce change place: As the
two ends of a Bow, ſhot off, fly from one
another, whereas the Bow it ſelf may be
held faſt in the Archers hand; and that it
is the equal preſſure of the Air on all ſides
upon the Bodies that are in it, which cau­
ſes the eaſie Ceſſion of its parts, may be
argu'd from hence: That if by the help
of our Engine the Air be but in great
part, though not totally drawn away
from one ſide of a Body without being
drawn away from the other; he that ſhall
think to move that Body too and fro, as
eaſily as before, will finde himſelf much
miſtaken.
In a Diſ­
courſe
touching
ſluidity
and firm­
neſs.
In verification of which we will, to di­
vert your Lordſhip a little, mention here
a Phænomenon of our Engine, which even
1to divers ingenious perſons has at firſt
ſight ſeem'd very wonderful.
THe thing that is wont to be admired,

and which may paſs for our ſecond
Experiment is this, That if, when the
Receiver is almoſt empty, a By-ſtander
be deſired to lift up the braſs Key (former­
ly deſcribed as a ſtopple in the braſs Co­
ver) he will finde it a very difficult thing
to do ſo, if the Veſſel be well exhauſted;
and even when but a moderate quantity of
Air has been drawn out, he will, when he
has lifted it up a little, ſo that it is ſome­
what looſe from the ſides of the lip or
ſocket, which (with the help of a little
oyl) it exactly filled before, he will (I ſay)
finde it ſo difficult to be lifted up, that
he will imagine there is ſome great weight
faſtned to the bottom of it. And if (as
ſometimes has been done for merriment)
onely a Bladder be tyed to it, it is plea­
ſant to ſee how men will marvail that ſo
light a Body, filled at moſt but with Air,
ſhould ſo forcibly draw down their hand
as if it were fill'd with ſome very ponder­
ous thing: whereas the cauſe of this pret­
ty Phænomenon ſeems plainly enough to
1be onely this, That the Air in the Recei­
ver, being very much dilated, its Spring
muſt be very much weakn'd, and conſe­
quently it can but faintly preſs up the
lower end of the ſtopple, whereas the
Spring of the external Air being no way
debilitated, he that a little lifts up the
ſtopple muſt with his hand ſupport a preſ­
ſure equal to the diſproportion betwixt
the force of the internal expanded Air, and
that of the Atmoſphere incumbent upon
the upper part of the ſame key or ſtopple:
And ſo men being unuſ'd to finde any re­
ſiſtance, in lifting things up, from the
free Air above them, they are forward to
conclude that that which depreſſes their
hands muſt needs be ſome weight, though
they know not where plac'd, drawing be­
neath it.
Experi­
ment 2.
And that we have not miſ-aſſign'd the
cauſe of this Phænomenon ſeems evident
enough by this; That as Air is ſuffer­
ed by little and little to get into the Re­
ceiver, the weight that a man fancies his
hand ſupports is manifeſtly felt to decreaſe
more and more, the internal Air by this
recruit approaching more to an Æquili­
brium with the external, till at length the
Receiver growing again full of Air, the
1ſtopple may be lifted up without any dif­
ficulty at all.
By ſeveral other of the Experiments
afforded us by our Engine, the ſame no­
tion of the great and equal preſſure of the
free Air upon the Bodies it environs,
might be here manifeſted, but that we
think it not ſo fit to anticipate ſuch Ex­
periments: And therefore ſhall rather
employ a few lines to clear up a difficulty
touching this matter, which we have ob­
ſerv'd to have troubled ſome even of the
Philoſophical and Mathematical Specta­
tors of our Engine, who have wonder'd
that we ſhould talk of the Air exquiſitely
ſhut up in our Receiver, as if it were all
one with the preſſure of the Atmoſphere;
whereas the thick and cloſe body of the
Glaſs, wholly impervious to the Air, does
manifeſtly keep the incumbent Pillar of
the Atmoſphere from preſſing in the leaſt
upon the Air within the Glaſs, which it
can no where come to touch. To eluci­
date a little this matter, let us conſider,
That if a man ſhould take a fleece of
Wool, and having firſt by compreſſing it
in his hand reduc'd it into a narrower com­
paſs, ſhould nimbly convey and ſhut it
cloſe up into a Box juſt fit for it, though
1the force of his hand would then no lon­
ger bend thoſe numerous ſpringy Body's
that compoſe the Fleece, yet they would
continue as ſtrongly bent as before, be­
cauſe the Box they are incloſ'd in would
as much reſiſt their re-expanding of
themſelves, as did the hand that put them
in. For thus we may conceive, that the
Air being ſhut up, when its parts are bent
by the whole weight of the incumbent
Atmoſphere, though that weight can no
longer lean upon it, by reaſon it is kept
off by the Glaſs, yet the Corpuſcles of
the Air within that Glaſs continue as
forcibly bent as they were before their in­
cluſion, becauſe the ſides of the Glaſs
hinder them from diſplaying or ſtretch­
ing out themſelves. And if it be ob­
jected that this is unlikely, becauſe ev'n
Glaſs bubles, ſuch as are wont to be
blown at the flame of a Lamp, exceeding
thin and Hermetically ſeal'd will not
break; whereas it cannot be imagin'd
that ſo thin a Priſon of Glaſs could re­
ſiſt the Elaſtical force of all the included
Air, if that Air were ſo compreſſ'd as we
ſuppoſe. It may be eaſily reply'd, That
the preſſure of the inward Air againſt the
Glaſs, is countervail'd by the equal preſ-
1ſure of the outward againſt the ſame Glaſs.
And we ſee in bubles, that by reaſon of
this an exceeding thin film of Water is
often able, for a good while, to hinder the
eruption of a pretty quantity of Air. And
this may be alſo more conſpicuous in
thoſe great Spherical bubles that boyes
ſometimes blow with Water, to which
Sope has given a Tenacity. But that, if the
preſſure of the ambient Air were remov'd,
the internal Air may be able to break
thicker Glaſſes then thoſe lately men­
tion'd, will appear by ſome of the follow­
ing Experiments; to which we ſhall there­
fore now haſten, having, I fear, been but
too prolix in this Excurſion, though we
thought it not amiſs to annex to our firſt
Experiments ſome general Conſiderati­
ons touching the Spring of the Air, be­
cauſe (this Doctrine being yet a ſtranger
to the Schools) not onely we finde not
the thing it ſelf to be much taken notice
of; but of thoſe few that have heard of it,
the greater part have been forward to re­
ject it, upon a miſtaken Perſwaſion, that
thoſe Phænomena are the effects of natures
abhorrency of a Vacuum, which ſeem to
be more fitly aſcribeable to the weight
and Spring of the Air.
1
WE will now proceed to obſerve that

though, by the help of the handle,
the Sucker be eaſily drawn down to the
bottom of the Cylinder; yet, without
the help of that Leaver, there would be
required to the ſame effect, a force or
weight great enough to ſurmount the
preſſure of the whole Atmoſphere: Since
otherwiſe the Air would not be driven out
of its place, when none is permitted to
ſucceed into the place deſerted by the
Sucker. This ſeems evident, from the
known Torricellian Experiment, in which,
if the inverted Tube of Mercury be but
25 Digits high, or ſomewhat more, the
Quick-ſilver will not fall but remain ſuſ­
pended in the Tube; becauſe it cannot
preſs the ſubjacent Mercury with ſo great
a force, as does the incumbent Cylinder
of the Air reaching thence to the top of
the Atmoſphere: Whereas, if the Cy­
linder of Mercury were three or four digits
longer, it would over-power that of the
external Air, and run out into the Veſſel'd
Mercury, till the two Cylinders came to
an Æquilibrium, and no further. Hence
we need not wonder, that though the
1Sucker move eaſily enough up and down
in the Cylinder by the help of the Manu­
brium; yet if the Manubrium be taken off,
it will require & conſiderable ſtrength to
move it either way. Nor will it ſeem
ſtrange, that if, when the Valve and
Stop-cock are well ſhut, you draw down
the Sucker, and then let go the Manubri­
um; the Sucker will, as it were of it ſelf,
re-aſcend to the top of the Cylinder, ſince
the ſpring of the external Air findes no­
thing to reſiſt its preſſing up the Sucker.
And for the ſame reaſon, when the Re­
ceiver is almoſt evacuated, though, ha­
ving drawn down the Sucker, you open
the way from the Receiver to the Cylin­
der, and then intercept that way again by
returning the Key; the Sucker will, up­
on the letting go the Manubrium, be
forcibly carried up almoſt to the top of
the Cylinder: Becauſe the Air within the
Cylinder, being equally dilated and weak­
ned with that of the Glaſs, is unable to
withſtand the preſſure of the external Air,
till it be driven into ſo little ſpace, that
there is an Æquilibrium betwixt its force
and that of the Air without. And con­
gruouſly hereunto we finde, that in this
caſe, the Sucker is drawn down with little
1leſs difficulty, then if the Cylinder, be­
ing devoid of Air, the Stop-cock were
exactly ſhut: We might take notice of
ſome other things, that depend upon the
Fabrick of our Engine it ſelf; but to ſhun
prolixity, we will, in this place, content
our ſelves to mention one of them, which
ſeems to be of greater moment then the
reſt, and it is this; that when the Sucker
has been impell'd to the top of the Cylin­
der, and the Valve is ſo carefully ſtopp'd,
that there is no Air left in the Cylinder a­
bove the Sucker: If then the Sucker be
drawn to the lower part of the Cylinder,
he that manages the Pump findes not any
ſenſibly greater difficulty to depreſs the
Sucker, when it is nearer the bottom of the
Cylinder, then when it is much further off.
Which circumſtance we therefore think fit
to take notice of, becauſe an eminent Mo­
dern Naturaliſt hath taught, that, when the
Air is ſucked out of a Body, the violence
wherewith it is wont to ruſh into it again,
as ſoon as it is allow'd to re-enter, pro­
ceeds mainly from this; That the preſſure
of the ambient Air is ſtrengthned upon
the acceſſion of the Air ſuck'd out; which,
to make it ſelf room, forces the neighbor­
ing Air to a violent-ſubingreſſion oſ its
parts: which, iſ it were true, he that draws
1down the Sucker, would finde the reſiſt­
ance of the external Air increaſ'd as he
draws it lower, more of the diſplaced Air
being thruſt into it to compreſs it. But, by
what has been diſcourſ'd upon the firſt
Experiment, it ſeems more probable, that
without any ſuch ſtrengthning of the preſ­
ſure of the outward Air, the taking quite
away or the debilitating of the reſiſtance
from within, may ſuffice to produce the
effects under conſideration. But this will
perhaps be illuſtrated by ſome or other of
our future Experiments, and therefore
ſhall be no longer inſiſted on here.
Experi­
ment 3.
HAving thus taken notice of ſome of

the conſtant Phænomena of our En­
gine it ſelf, let us now proceed to the Ex­
periments tryable in it.
Experi­
ment 4.
We took then a Lambs Bladder large,
well dry'd, and very limber, and leaving in
it about half as much Air as it could con­
tain, we cauſ'd the neck of it to be ſtrong­
ly ty'd, ſo that none of the included Air,
though by preſſure, could get out. This
Bladder being convey'd into the Receiver,
and the Cover luted on, the Pump
was ſet awork, and after two or three
exſuctions of the ambient Air (where­
by the Spring of that which remain'd in
1the Glaſs was weaken'd) the Impriſon'd
Air began to ſwell in the Bladder, and as
more and more of the Air in the Recei­
ver was, from time to time, drawn out; ſo
did that in the Bladder