present and former weight is the weight of
the air that was contained in the flask.
What princi- . 584 ' THE SUCKER. A
pie does " the cL-cular piece of wet leather, with a string
Sucker "illus- attached to the centre, being pressed upon a
smooth surface, will adhere with considerable
tenacity, when drawn upwards by the string. The string in
this case must be attached to the leather, so that no air can pass
under the leather.
What is the **^* -^ HE MERCURIAL OR WATER TUBE. :
object of the Exhaust the air from a glass tube three feet
long fitted With a st P- cock at one end ' and then
immerse it in a vessel containing mercury or
water. On turning the stop-cock, the mercury will rise to the
height of nearly thirty inches ; or, if immersed in water, the
water will rise and fill the tube, and would fill it were it thirty
feet long. This experiment shows the manner in which water
is raised to the boxes or valves in common water-pumps.
How is the elas- *^6. EXPERIMENTS SHOWING THE ELASTICITY
ticity of the air OF THE AIR. Place an india-rubber bag, or a
illustrated? bladder, partly inflated, and tightly closed, un-
der the receiver, and, on exhausting the air, the air within the
bag or bladder, expanding, will fill the bag. On readmitting
the air, the bag will collapse. The experiment may also be
made with some kinds of shrivelled fruit, if the skin be sound.
The internal air, expanding, will give the fruit a fresh and plump
appearance, which will disappear on the readmission of the air
587. The same principle may be illustrated by the india-
ruober and bladder glasses, if they have stop-cocks tc confine
588. A small bladder partly filled with air may be sunk in a
vessel of water by means of a weight, and placed under the
receiver. On exhausting the air from the receiver, the air in
the bladder will expand, and, its specific gravity being thua
diminished, the bladder with the weight will rise. On read-
mitting the air, the bladder will sink again.
TT 589. AlR CONTAINED IN WATER AND IN WOOD.
now can trie
presence of air Place a vessel of water under the receiver, and,
in wood be de- on exhausting the air from the receiver, ihe air
tected? . .,...,, . ,
in the water, previously invisible, will make its
appearance in the form of bubbles, presenting the semblance
590. A piece of light porous wood being immersed in the
water below the surface, the air will be seen issuing in bubble*
from tho pores of the wood.
Explain che prin- 59L THE PNEUMATIC BALLOON. "*
ciple of the Pneu- Fig. 96 represents a small glass bal-
matic Balloon. loonj witt itg car i mmerse d in a jar
of water, and placed under a receiver. On exhaust-
ing the air, the air within the balloon, expanding, gives
it buoyancy, and it will rise in the jar. On readmit-
ting the air, the balloon will sink.
692. The experiment may be performed without the
air-pump by covering the jar with some elastic sub-
stance, as india-rubber. By pressing on the elastic Jm,
covering with the finger, the air will be condensed, the
water will rise in the balloon, and it will sink. On removing
the pressure, the air in the balloon, expanding, will expel part
of the water, and the balloon will rise. This is the more conve-
nient mode of performing the experiment, as it can be repeated
at pleasure without resort to the pump.
593. The following is a full explanation : The pressure on
the top of the vessel first condenses the air between the covei
162 NATURAL PHILOSOPHY.
and the surface of the water; this condensation presses upo&
the water below, and, as this pressure affects every portion of
the water throughout its whole extent, the water, by its upward
pressure, compresses the air within the balloon, and makes room
for the ascent of more water into the balloon, so as to alter the
specific gravity of the balloon, and cause it to sink. As soon
as the pressure ceases, the elasticity of the air in the balloon
drives out the lately-entered water, and, restoring the former
lightness to the balloon, causes it to rise. If, in the commence-
ment of this experiment, the balloon be made to nave a specific
gravity too near that of water, it will not rise of itself,
after once reaching the bottom, because the pressure of the
water then above it will perpetuate the condensation of the air
which caused it to descend. It may even then, however, be
made to rise, if the perpendicular height of the water above it
be diminished by inclining the vessel to one side.
594. This experiment proves many things ; namely :
First. The materiality of air, by the pressure of the hand! on the
top being communicated to the water below through the air in the
upper part of the vessel.
Secondly. The compressibility of air, by what happens in the
globe before it descends.
Thirdly. The elasticity, or elastic force of air, when the water is
expelled from the globe, on removing the pressure.
Fourthly. The lightness of air, in the buoyancy of the globe.
Fifthly. It shows that the pressure of a liquid is exerted in all direC'
tions, because the effects happen in whatever position the jar be
Sixthly. It shows that pressure z> as the depth, because less press-
ure of the hand is required the further the globe has descended in
Seventhly. It exemplifies many circumstances of fluid support
A person, therefore, who is familiar with this experiment, and can
explain it, has learned the principal truths of Hydrostatics and
595. The Pneumatic Balloon also exhibits the principle on which
the well-known glass toy, called the Cartesian Devil, is constructed ;
and it may be thus explained: Several images of glass, hollow
within, and each having a small opening at the heel by which water
may pass in and out, may be made to manoeuvre in a vessel of
water. Place them in a vessel in the same manner with the bal-
loon. Out, by allowing different quantities of water to enter thf
Apertures in the. images, cause them to differ a little from one
another in specific gravity. Then, when a pressure is exerted on
the cover, the heaviest will descend first, and the others follow in
the order of their specific gravity ; and they will stop or return to
the surface in reverse order, when the pressure ceases. A person
exhibiting these figures to spectators who do not understand them,
while appearing carelessly to rest his hand on the cover of the ves-
sel, seems to have the power of ordering their movements by his
will. If the vessel containing the figures be inverted, and the cover
be placed over a hole in the table, through which, unobserved, press-
ure can be made by a rod rising through the hole, and obeying the
foot of the exhibitor, the most surprising evolutions may be pro-
duced among the figures, in perfect obedience to the word of com-
596. EXPERIMENTS WITH CONDENSED AIR.
What ts the m ^ T-.
use of the Con- -"- HE CONDENSING AND EXHAUSTING SYRINGE.
densing and The Condensing Syringe is the air-pump reversed.
The* Exhausting Syringe is the simple air-pump
without its plate or stand. These implements
are used respectively with such parts pig. 97.
of the apparatus as cannot conveniently
be attached to the a ; .r-puinp, and as
an addition to such pumps as do not
perform the double office of exhaustion
and condensation. In some sets of
apparatus the condensing and exhaust-
ing syringes are united, and are made
io perform each office respectively, by
merely reversing the part which con-
tains the valve.
For what purpose 597 - THE AlR '
is the Air-cham- CHAMBER. The air-
krused? chamber, Fig. 97, is
a hollow brass globe prepared for the reception of a stop-cock,
and is designed for the reception of condensed air. It is made
in different forms in different sets, and is used by screwing it to
a condensing pump or a condensing syringe.
What prin- **98. STRAIGHT AND REVOLVING JETS FROM
tiple <*f Pneu- CONDENSED AIR. Fill the air-chamber (Fig.
164 NATURAL PHILOSOPHY.
. . 97) partly with water, and then eondense the
mattes is illus- ' " J
trated by the air. Then confine the air by turning the cock ;
straight and a ft er which, unscrew it from the air-pump, and
revolving jets? ^ QW ^ ^ Btra ; ght Qr ^ revolving j et Then
open the stop-cock, and the water will be thrown from the
chamber in the one case in
a straight continued stream,
in the other in the form of
a wheel. Figs. 98 and 99
represent a view of the
straight and the revolving jets. In the revolving jet
the water is thrown from two small apertures made at
each end on opposite sides, to assist the revolution. The
circular motion is caused by the reaction of the water on the
opposite sides of the arms of the jets ; for, as the water is forced
into the tubes, it exerts an equal pressure on all sides of the
tubes, and, as the pressure is relieved on one side by the jet-
hole, the arm is caused to revolve in a contrary direction. This
experiment, performed with the straight jet, illustrates the
principle on which "Hero's ball" and "Hero's fountain" are
Explain the ^9. THE PRINCIPLE OF THE AIR-GUN. With
principle of the air-chamber, as in the last experiments, a
the Air-gun. gmall bragg cylinder or gim . barr ei 5 Fig. 100, may
be substituted for the jets, and loaded with a small shot f ig . 10 o
or paper ball. On turning the cock quickly, the* con-
densed air, rushing out, will throw the shot to a consider-
able distance. In this way the air-gun operates, an
apparatus resembling the lock of a gun being substituted
for the stop-cock, by which a small portion only of the
condensed air is admitted to escape at a time ; so that
the chamber, being once tilled, will afford two or three dozer*
discharges. The force of the air-gun has never been eqial to
more than a fifteenth of the force of a common charge of powder,
and. the loudness of the report made in its discharge is always
as great in proportion to its force as that of the comuou gun
600. Condensed air may be weighed in the
iir 'tv/tat must air-chamber, but, in estimating its weight, the
\lways he temperature of the room must always be taken
into consideration, as the density of air is ma-
terially affected by heat and cold.
What doc th ^^' ^ XPERIMENTS SHOWING THE INERTIA OF
Guinea and AIR. THE GUINEA AND FEATHER DROP. The
Feather Drop inertia of air is shown by the guinea and feather
illustrate? ,.,. A . J . . ,. , ,,
drop, exhibiting the resistance which the air
opposes to falling bodies. This apparatus is made in different
forms, some having shelves on which the Kg. 102.
guinea and feather rest, and, when ihe air is
exhausted, they are made to fall by the turn-
ing of a Jiandle. A better form is that repre-
sented in Fig. 101, in which the guinea and
feather (or a piece of brass substituted for the
guinea) are enclosed, and the apparatus being
screwed to the plate of the pump, the air is
exhausted, a stop-cock turned to prevent the
readmission of the air, and the apparatus being
then unscrewed, the experiment may be repeatedly
shown by one exhaustion of the air. It will then
appear that every time the apparatus is inverted the
guinea and the feather will fall simultaneously. The
two forms of the guinea and feather drop are ex-
hibited in Figs. 101 and 102, one of which, Fig. 101, is fur-
nished with a stop-cock,^ the other, Fig. 102, with shelves.
What prin- 602. EXPERIMENTS SHOWING THE FLUIDITY OP
ciple is explain- AIR. THE WEIGHT-LIFTER. The upward press-
erf by means of ^ . ,, ^, A . *'..
the weight- ure * Q air ' one * tne P r P ertie s of its fluidity,
liftsr? may be exhibited by an apparatus called the
* Most sets of philosophical apparatus are furnished with stop-cocks
and elastic tubes, for the purpose of connecting the several parts with the
pump, or with one another. In selecting the apparatus, it is important
to have the screws of the stop-cocks and of all the apparatus of similar
thread, in order that every article may subserve as many purposes as pos-
sible This precaution is suggested by economy, as well as by co iveuieuc*
166 NATURAL PHILC SOPHY.
weight-lifter, made in different forms, but all
on the same principle. The one represented
in Fig. 103 consists of a glass tube, of large
bore, set in a strong case or stand, sup-
ported by three legs. A piston is accu-
rately fitted to the bore of the tube, and a
hook is attached to the bottom of the piston,
from which weights are to be suspended.
One end of the elastic tube is to be screwed
to the plate of the pump, and the other
end attached to the top of this instrument.
The air being then exhausted from the tube, the weights will ba
raised the whole length of the glass. The number of pounds'
weight that can be raised by this instrument may be estimated
by multiplying the number of square inches in the bottom of
the piston by fifteen.
Explain the 603. THE PNEUMATIC SHOWER-BATH. On the
Pneumatic principle of the upward pressure of the air the
pneumatic shower-bath is constructed. It con-
sists of a tin vessel perforated with holes in the bottom for the
shower, and having an aperture at the top, which is opened or
closed at pleasure by means of a spring-valve. [Instead of the
spring-valve, a bent tube may be brought round from the top
down the side of the vessel, with an aperture in the tube below
the bottom of the vessel, which may be covered with the thumb.]
On immersing the vessel thus constructed in a pail of water,
with the valve open, and the tube (if it have one) on the outside
of the pail, the water will fill the vessel. The aperture then
being closed with the spring or with the thumb, and the vessel
being lifted out of the water, the upward pressure of the an
will confine the water in the vessel. On removing the thumb
or opening the valve, the water will descend in a shower, untiJ
the vessel is emptied.
What tw ^^' -M- ISCELLANEOU8 EXPERIMENTS DEPENDING
properties ON TWO on MOKE OF THE PROPERTIES OF AIR.
of air are THE BOLT-HEAD AND JAR. Fig. 104, a glasb
illustrated ly globe with a long neck, called a bolt-head (or
means of the ,, ,, , .,,
Bolt-head and an J long-necked bottle), partly tilled with water,
is inverted in a jar of water (colored with a few
drops of red ink or any coloring matter, in order Fig 104
that the effects may be more distinctly visible), and
placed under the receiver. On exhausting the air in
the receiver, the air in the upper part of the bolt-
head, expanding, expels the water, showing the elas-
ticity of the air. On readmitting the air to the
receiver, as it cannot return into the bolt-head, the
pressure on the surface of the water in -the jar forces
the water into the bolt-head, showing the pressure
of the air caused by its weight. The experiment
may be repeated with the bolt-head without any
water, and, on the readmission of the air, the water will nearly
fill the bolt-head, affording an accurate test of the degree of
What two 605. ^ HE TRANSFER OF _ FLUIDS FROM ONH
principles are VESSEL TO ANOTHER. The experiment may bo
concerned in made with two bottleg tightly closed. Let one
the transfer of 6 J
fluids from De partly tilled with water, and the two con-
one vessel to nected by a bent tube, connecting the interior of
the empty bottle with the water of the other, and
extending nearly to the bottom of the water. On exhausting
the air from the empty bottle, the water will pass to the other,
and, on readmitting the air, the water will return to its original
position, so long as the lower end of the bent tube is below the
What ex eri- m EXPERIMENTS WITH THE SIPHON. Close
msnts are per- the shorter end of the siphon with the finger or
formed with w ith a stop-cock, and pour mercury or water into
the longer side. The air contained in the shorter
side will prevent the liquid from rising in the shorter side.
But, if the shorter end be opened, so as to afford free passage
lt>& NATURAL PHILOSOPHY.
outwards for the air, the fluid will rise to an equilibrium m
both arms of the siphon.
607. Pour any liquid into the longer arm of the siphon until
*ne shorter arm is filled. Then close the shorter end, tc pre-
vent the admission of the air ; the siphon may then be turned
in any direction arid the fluid will not run out, on account of
the pressure of the atmosphere against it. But, if the shorter
end be unstopped, the fluid will run out freely.
What effect is 608> AlR ESSENTIAL T0 ANIMAL LIFE. If
produced on an .
animal placed an animal be placed under the receiver, and the
under an ex- air exhausted, it will immediately droop, and, if
cewer? ~ the air be not s P eei % readmitted, it will die.
609. AIR ESSENTIAL TO COMBUSTION. Place
How is it
shown that air & lighted taper, cigar; or any other substance that
is essential to w iu produce smoke, under the receiver, and ex*-
haust the air ; the light will be extinguished, and
the smoke will fall, instead of rising. If the air be readmitted,
the smoke will ascend.
What effect is 610. THE PRESSURE OP THE AIR RETARDS
^herundlran EBULLITION.* Ether, alcohol, and other distilled
exhausted re- liquors, or warm water, placed under the receiver,
caver ? w j}} appear to boil when the air is exhausted.
a. , 611. The existence of many bodies in a liquid
the pressure of f rm depends on the weight or pressure of the
the air on the atmosphere upon them. The same force, like-
lodies * wise, prevents the gases which exist in fluid and
solid bodies from disengaging themselves. If, by
rarefying the air, the pressure on these bodies be diminished,
they either assume the form of vapors, or else the gas detaches
itself altogether from the other body. The following experi-
ment proves this : Place a quantity of lukewarm water, milk
or alcohol, under a receiver, and exhaust the air, and the liquid
* EBULLITION. The operation of boiling. The agitation of liquor bj
teat, which throws it up iuto bubbles.
will either pass off in vapor, or will have the appearance of
612. An experiment to prove that the pressure
What expert- r .
ment shows of the atmosphere preserves some bodies in the
that the liquid liquid form may thus be performed. Fill a long
form of some . -. , v , , T .,,
bodies is de- v ' or a closed at one end, with water, and
pendent on invert it in a vessel of water. The atmospheric
atmospheric pressure w m re tain the water in the vial. Then,
pressure *. 5 i "" i
by means or a bent tube, introduce a lew drops
of sulphuric ether, which, by reason of their small specific
gravity, will ascend to the top of the vial, expelling an equal
bulk of water. Place the whole under the receiver, and ex-
naust the air, and the ether will be seen to assume the gaseous
form, expanding in proportion to the rarefaction of the air
under the receiver, so that it gradually expels the water from
the vial, and fills lip the entire space itself. On readmitting
the ar, the ether becomes condensed, and the water will re-
ascend into the vial.
a 613. A simple and interesting experiment con
water be frozen nected with the science of chemistry may thus b^
under a rt- performed by means of the air-pump. A watch-
glass, containing water, is placed over a small
vessel containing sulphuric acid, and put under the bulbed
receiver. When the air is exhausted, vapor will freely rise
from the water, and be quickly absorbed by the acid. An
intense degree of cold is thus produced, and the water will
614. In the above experiment, if ether be used instead of the
acid, the ether will evaporate instead of the water, and, in the
process of evaporation, depriving the water of its heat, the
water will freeze. These two experiments, apparently similar
ha effects, namely, the freezing of the water, depend upon two
different principles which pertain to the science of chemistry.
What is the 615> THE PNEUMATIC PARADOX. An inter-
Pneumatic . ..-* *\i
Paradox? esting experiment, illustrative or the pueaiuatic
170 NATURAL PHILOSOPHY.
paradox, may be thus performed : Pass a small open tube (yjs
a piece of quill) through the centre of a circular card two or
three inches in diameter, and cement it, the lower end passing
down, and the upper just even with the card. Then pass a pin
through the centre of another similar card, and place it on
the former, with tne pin projecting into the tube to prevent
the upper card from sliding off. It will then be impossible
to displace the upper card by blowing through the quill,
on account of the adhesion produced by the current passing
between the discs. On this principle smoky chimneys have
ur^en remedied, and the office of ventilation mpre effectually
61G ' WlND ' Wind i 8 ^ P ut in motion.
617. There are two ways .in which the motion
In what two . . .
ways may the * tne air mav anse - ma j be considered as
motion of the an absolute motion of the air, rarefied by heat
a / r 5T an< ^ condensed by cold ; or it may be only an
apparent motion, caused by the superior velocity
of the earth in its daily revolution.
618. When any portion of the atmosphere is heated it becomes
rarefied, its specific gravity is diminished, and it consequently
rises. The adjacent portions immediately rush into its place, to
restore the equilibrium. This motion produces a current which
pushes into the rarefied spot from all directions. This is what
we call wind.
619. The portions north of the rarefied spot
v^ndlav^ed? P ro ^ uce a north wind, those to the south produce
a south wind, while those to the east and west
in like manner, form currents moving in opposite directions
At the rarefied spot, agitated as it is by winds from all direc-
tions, turbulent and boisterous weather, whirlwinds, hurricanes,
rain, thunder and lightning, prevail. This kind of weather
occurs most frequently in the torrid zone, where the heat is
greatest. The air, being more rarefied there than in any other
part jf the globe, is lighter, and, consequently, ascends ; that
about the polar regions is continually flowing from the poles to
the equator, to restore the equilibrium; while the air rising
from the equator flows in an upper current towards the poles,
so that the polar regions may not be exhausted.
620. A regular east wind prevails about the
prevails in the equator, caused in part by the rarefaction of the
equatorial air produced by the sun in his daily course from
' east to west. This wind, combining with that
xrom the poles, causes a constant north-east wind for about thirty
degrees north of the equator, and a south-east wind at the
same distance south of the equator.
621. From what has now been said, it- appears that there is a
circulation of air in the atmosphere ; the air in the lower strata
flowing from the poles to the equator, and in the upper strata
flowing back from the equator to the poles. It may here be re-
marked, that the periodical winds are more regular at sea than on
the land ; and the reason of this is, that the land reflects into the
atmosphere a much greater quantity of the sun's rays than the
water, therefore that part of the atmosphere which is over the land
is more heated and rarefied than that which is over the sea. This
occasions the wind to set in upon the land, as we find it regularly
does on the coast of Guinea and other countries in the torrid zone.
There are certain winds, called trade-winds, the theory of which
raav be easily explained on the principle of rarefaction, affected, as
it is, by the relative position of the different parts of the earth with
the sun at different seasons of the year, and at various parts of the
day. A knowledge of the laws by which these winds are controlled
is of importance to the mariner. When the place of the sun with
respect to the different positions of the earth at the different seasons
of the year is understood, it will be seen that they all depend upon
the same principle. The reason that the wind generally subsides
at the going down of the sun is, that the rarefaction of the air, in
the particular spot which produces the wind, diminishes as the sun
declines, and, consequently, the force of the wind abates. The
great variety of winds in the temperate zone is thus explained.
The air is an exceedingly elastic fluid, yielding to the slightest
pressure ; the agitations in it, therefore, caused by the regular
winds, whose causes have been explained, must extend every way
to a great distance, and the air, therefore, in all climates will suffer,