tiplying the number opposite to any substance in the above table by on-
thousand, we obtain the weight of a cubic foot of that substance in ounce.
Thus, a cubic foot of platinum is 23,000 ounces in weight.
In the above table it appears that the specific gravity of living men is
about one-ninth less than that of common water. So long, therefore, as
the lungs can be kept free from water, a person, although unacquainted
with the art of swimming, will not completely sink, provided the hands and
arms be kept under water.
The specific gravity of sea-water is greater than that of the water of
fakes and rivers, on account of the salt contained in it. On this account,
the water of lakes and rivers has less buoyancy, and it is more difficult to
swim in it.
* The gold will weigh less in the water than out of it, on account of the
upward pressure of the particles of water, which in some measure supports
it, and, by so doing, diminishes its weight. Now, as the upward pressure
of these particles is exactly sufficient to balance the downward pressure of
a quantity of water of exactly the same dimensions with the gold, it follows
that the gold will lose exactly as much of its weight in water as a quantity
of water of the same dimensions with the gold will weigh. And this rule
applies to all bodies, heavier than water, that are immersed in it. They
will lost, as much of their weight in water as a quantity of water of their own
dimensions weighs. All bodies, therefore, of the same size, lose the same
quantity of their weight in water. Hence, th<t specific gravity of a body is the
weight of it compared with that of water. As a body loses a quantity of its
weight when immersed in water, it follows that when the body is lifted
from the ivater that portion of its weight which it had lost will be restored.
This is the reason that a bucket of water, drawn from a well, is heavier
when it rises above the surface of the water in the well than it is while it
remains below the surface. For the same reason our limbs feel heavy is
fttviug a bith
m water, the loss in water is one ounce. The weight out of water,
nineteen ounces, being divided by one (the loss in water), gives
nineteen. The specific gravity of gold, then, would be nineteen ;
or in other words, gold is nineteen times heavier than water.
462. The specific gravity of a body that will
specific gravity not s ^ n ^ * n water ^ ascertained by dividing its
of a body weight by the sum of its weight added to the
loss of wei ' ht which ii; occasions in a
previously balanced in water.* 1 (See par. 1436.)
463. If a body lighter than water weighs six ounces, and, on being
attached to a heavy body, balanced in water, is found to occasion it
to lose twelve ounces of its weight, its specific gravity is determined
by dividing its weight (six ounces) by the sum of its weight added
to the loss of weight it occasions in the heavy body ; namely, 6
added to 12, which, in other words, is 6 divided by 18, or ^,
which is J.
464. Questions for Solution.
(1.) A body lighter than water caused the loss of 10 Ibs. to a heavier
body immersed in water. In air the same body weighed 30 Ibs. What
was its specific gravity 1
Solution. 30 Ibs., its weight, divided by (30+10=) 40 (the sum of its
weight added to the loss of weight which it caused in another body pre-
vtously balanced in the water). Ans. .75.
(2.) A body that weighed 15 Ibs. in air weighed but 12 in water. What
^as its specific gravity 1 Ans. 5.
(3.) If a cubic foot of water weigh 1000 ounces, what is the weight of an
e tual bulk of gold 1 Ans. 1210 Id.
(4.) The weight of an equal bulk of lead 1 Ans. 708 II. 2 oz.
(5.) The weignt of an equal bulk of cork 1 Ans. 15 Ib.
* The method of ascertaining the specific gravities of bodies was dis-
covered accidentally by Archimedes. He had been employed by the King
of Syracuse to investigate the metals of a golden crown, which he suspected
had been adulterated by the workmen. The philosopher labored at the
problem in vain, till, going one day into the bath, he perceived that the
water rose in the bath in proportion to the bulk of his body. He instantly
perceived that any other substance of equal size would raise the water just
as much, though one of equal weight and less bulk could not produ'ce the
same effect. He then obtained two masses, one of gold and one of silver,
each equal in weight to the crown, and having filled a vessel very accu-
rately with water, he first plunged the silver mass into it, and observed the
quantity of water that flowed over ; he then did the same with the gold,
and found that a less quantity had passed over than before. Hence he
inferred that, though of ef\ual weight, the bulk of the silver was greater
than that of the gold, and that the quantity of water displaced was, in encb
experiment, equal to the bulk of the metal. He next made trial with the
crown, and found that it displaced more water than the gold, and less than
the silver, which led him to conclude that it was neither pure gold no/
(6.) The weight of an equal bulk of iron 1 A",e. 486 'ft. 12 o*
(7.) What is the weight of a cubic foot of mahogany 1 Ans. 62 Ib. 11 era.
(8.) The weight of a cubic foot of marble \ Ana. iTQlb. 2 OK.
(9.) Wtat is the weight of an iceberg 6 miles long, . mile wide, *n<i
400 feet thick 1 A ns. 904,304.600 tons.
(10.) What is the weight of a marble statue, supposing it to be exactly
a yard and half of cubic measure 1 Ans. 7214,06 #>. -f-
(11.) If a cubical body of cork*exactly 9 inches on each side be placed
in water, how deep will it sink 1 Ans. 2.16 in.
(12.) Suppose that 4 boats were made each out of one of the following
kinds of wood, namely, ash, beech, elm and fir, which would carry tfhe
greatest weight without sinking 1 Ans. That ojfir.
What is an 465. An Hydrometer is an instrument to ascer-
Hydrometer? tain the specific gravity of liquids. (See par.
and on what -[Aof\\
principle is it
constructed? 466> T^ hydrometer is constructed on the
principle that the greater the weight of a liquid, the greater will
be its buoyancy.
How is an hy- ^67. The hydrometer is made in a variety of
drometer con- foras, but it generally consists of a hollow ball
of silver, glass, or other material, with a gradu-
ated scale rising from the upper part. A weight is attached
Otslow the ball. When the instrument thus constructed is im-
mersed in a fluid, the specific gravity of the fluid is estimated by
the portion of the scale that remains above the surface of the
fluid. The greater the specific gravity of the fluid, the less will
the scale sink.
Of what use ^68. The hydrometer is a very useful instru-
1*5 the hydrom- ment for ascertaining the purity of many articles
in common use. It sinks to a certain determinate
depth in various fluids, and if the fluids be adulterated the hy-
drometer will expose the cheat. Thus, for instance, the specific
gravity of sperm oil is less than that of whale oil, and of course
has less buoyancy. If. therefore the hydrometer does not sink
to the proper mark of sperm oil, it will at once be seen that the
Article is not pure.
Of what does Hy- 469. HTDEAULICS. Hydraulics treats of
draulics treat? liquids in motion, and the instruments by
whicli their motion is guided 01 controlled. (See par. 1437.)
470 This branch of Hydrodynamics describes tLj ejects ot
liquids issuing from pipes and tubes, orifices or apertuies, the
motion of rivers and canals, and the forces developed in the
action of fluids with solids.
471. The quantity of a liquid discharged in a
& iven time tlm >ugh a P^P 6 or orifice is equal to a
be discharged column of the liquid having for its base the orifice
from an orifice or the area of the bore of the pip6j and a helght
given size ? equal to the space through which the liquid would
pass in the given time.
472. Hence, when a fluid issues from an orifice in a vessel, it ia
discharged with the greatest rapidity when the vessel from which it
flows is kept constantly full.* This is a necessary consequence of
the law that pressure is proportioned to the height of the column
From what orifice ^73. When a fluid spouts from several orifices
will a fluid snout * n * ne 8 ^ e ^ a vesse l> it is thrown with the
to the greatest greatest random from the orifice nearest to the
distance ? centre the random being measured horizon-
tally from the bottom of the vessel.
474. A vessel filled with any liquid will discharge a greater quan-
tity of the liquid through an orifice to which a short pipe of pecu-
liar shape is fitted, than through an orifice of the same size without
a pipe. _ (See par. 1457.)
This is caused by the cross-currents made by the rushing of the
water from different directions towards the sharp-edged orifice.
The pipe smooths the passage of the liquid. But, if the pipe pro-
ject into the vessel, the quantity discharged will be diminished,
instead of increased, by the pipe.
475. The quantity of a fluid discharged through a pipe or an
orifice is increased by heating the liquid ; because heat diminishes
the cohesion of the particles, which exists, to a certain degree, in
476. Water, in its motion, is retarded by the
a current of ^^ion f tne bottom and sides of the channel
water flows through which it passes. For this reason, the
most rapidly, ve i oc i ty O f tne surface of a running stream is
and why ? J
always greater than that of any other part.
* The velocity with which a liquid issues from an infinitely small orifice
in ihe bottom or sides of a vessel that is kept full is equal to that which a
Heavy body would acquire by falling from the level o? khe surface to thf
of the orifice. Brndt.
180 NATUKAL PHILOSOPHY.
477 In consequence of the friction of the banks and beds of
rivers, and the numerous obstacles they meet in their circuitous
course, their progress is slow. If it were not for these impediments,
the velocity which the waters would acquire would produce very dis-
astrous consequences.* An inclination of three inches in a mile, in
the bed of a river, will give the current a velocity of about three
uiiles an hour.
478. To measure the velocity of a stream at its surface, hollow
floating bodies are used ; as, for example, a glass bottle filled with
a sufficient quantity of water to make it sink just below the level of
the current, and having a small flag projecting from the cork. A
wheel may also be caused to revolve by the current striking against
boards projecting from the circumference of the wheel, and the
rapidity of the current may be estimated by the number of the rev-
olutions in a given time.
How may the 479. The velocity of a current of water at any
portion of its depth may be
depth be ascer- ascertained by immersing in
iained? ft a ^nt tube, shaped like a
tunnel at the end which is immersed.
480. Fig. 70 is a tube shaped like a
tunnel, with the larger end immersed in an
opposite direction to the current. The
rapidity of the current is estimated by the _jj
height to which the water is forced into the
tube, above the surface of the current. By
such an instrument the comparative velocity
of different streams, or the same stream at different times, may
How are waves 481. Waves are caused, first, by the friction
caused? between air and water, and secondly, and on a
much grander scale, by the attraction of the sun and moon
exerted on the surface of the ocean, producing the phenomena
of the tides.
482. The hand of a wise and benevolent Creator is seen in nothing
more clearly than in the laws and operations of the material world.
Were it not for the almost ceaseless motion of the water, the ocea?
* See what is stated with regard to fr ction in Nos. 373 and 374.
What are the
ments or ma-
itself would become unbearable. Decayed and decaying matter
would be constantly emitting pestilential vapors, poisoning the at-
mosphere, and spreading contagion and death far beyond the borders
of the ocean. The " ceaseless motion " distributes the poisonous in-
gredients, and aids tliat change which renders them harmless.
483. The equilibrium of a fluid, according to recent discoveries,
cannot be disturbed by waves to a greater depth than about three
hundred and fifty times the altitude of the wave.
484. When oil is poured on the windward side of a pond, the
whole surface will become smooth. The oil protects the water from
the friction of the wind or air. It is said that boats have been pre-
served in a raging surf, iu consequence of the sailors having emptied
a barrel of , oil on the water.
485. The instruments or machines for
raising or drawing water arethe common
pump, the forcing-pump, the chain-pump, the
siphon, the hydraulic ram, and the screw of,
[The common pump and the forcing-pump will be Fig. 71.
aoticed in connexion with Pneumatics, as their opera-
tion is dependent upon principles explained in that
department of Philosophy. The fire-engine is nothing
more than a double forcing-pump, and will be noticed in
*ne same connexion.]
486. The Chain-pump is
a machine by which the water
is lifted through a box or
channel, by boards fitted to the channel
and attached to a chain. It has been used
principally on board of ships.
487. Fig. 71 represents a Chain-
pump. It consists of a square box
through which a number of square
ooards or buckets, connected by a chain, is
ir^de to pass. The chain passes over the wheel
C and under the wheel D, which is under
crater. The buckets are made to fit the box,
* The undulations of large bodies of water have also produced material
jhanges on the face of the globe, purposely designed by Creative T ~~
working by secondary causes, the uses of which are described in the
Wliat is the
132 NATUEAL PHILOSOPHY.
so as to move with little friction. The upper wheel C is turned
by a crank (not represented in the Fig.), which causes the chain
with the buckets attached to pass through the box. Each
bucket, aj5 it enters the box, lifts up the^vater above it, and
discharges it at the top.
488. The screw of Archimedes is a ma-
What is the c hj ne ggj^ have been invented by the plr-
chimldes ? losopher Archimedes, for raising water and
draining the lands of Egypt, about two hun-
dred years before the Christian era.
Fig. 72 repre-
Ezplain gents tne screw O f
single tube, or two tubes,
are wound in the form of
a screw around a shaft or
cylinder, supported by the gs
prop and the pivot A, and
turned by the handle n.
As the end of the tube dips into the water, it is filled with the
fluid, which is forced up the tube by every successive revolution,
until it is discharged at the upper end.
What is the 489. The Siphon is a tube bent in the form
Siphon f O f fo Q i e ^ er "TJ, one side being a little longer
than the other, to contain a longer column of the fluid.
Explain 490. Fig. 73 represents a Siphon. A siphon Kg. 73.
Fig. 73. i s use d by fining it with water or some other
fluid, then stopping both ends, and in this state immers-
ing the shorter leg or side into a vessel containing a
liquid. The ends being then unstopped, the liquid will
run through the siphon until the vessel is emptied. In
performing this experiment, the end, of the siphon which
is out of the water must always be below the surface of the
water in the vessel.
On what prin- 491 The principle on which the siphon acts
ciple does the j s tnat tne i on g er co lumn having the greater
siphon act? ' &
hydrostatic pressure, the fluid will run down in
the dhection of that column. The upward pressure in the
smaller column will supply a continued stream so long as that
column rests below the surface of the water.
[N. B. This principle will be better understood after the principle is ex-
plained on which the operation of the common pump depends ; for the
upward and downward pressure both depend on the pressure of the atmos
492. The siphon may be used in exemplifying the equilibrium ol
fluids ; for, if the tube be inverted and .two liquids of different
density poured into the legs, they will stand at a height in an in-
verse proportion to their specific gravity. Thus, as the specific
gravity of mercury is thirteen times greater than that of water, a
column of mercury in one leg will balance a column of water in the
other thirteen times higher than itself. But, if but one fluid be
poured into both legs, that fluid will stand at equal height in both
Explain the toy ^93. The toy called Tantalus' * Cup consists
called Tantalus' of a goblet containing a wooden figure, with a
^ U P' siphon concealed within. The water being
poured into the cup until it is above the bend of the siphon,
rises in the shorter leg, which opens into the cup, and runs out
at the longer end, which pierces the bottom.
494. Fig. 74 represents the cup with the siphon,
the figure of the man being omitted, in order that the
position of the siphon may be seen.
495. THE HYDRAULIC RAM + is an i
What is the Hy- . ,. L , f '
draulic Ram ? nious machine, constructed for the purpose
of raising water by means of its own im-
pulse or momentum.
* Tantalus, in Heathen mythology, is represented as the victim of per-
petual thirst, although placed up to the chin in a pool of water ; for, as soon
as he attempts to stoop to drink, the water flows away from his grasp ;
hence our English word tantalize takes its origin. In the toy described
above, the siphon carries the water away before it reaches the mouth of the
f The Hydraulic Ram, sometimes called by its French name, Better Hy-
134 NATURAL PHILOSOPHY.
496 In the construction of an hydraulic ram, there musst no,
in the first place, a spring or reservoir elevated at least four 01
five feet above the horizontal level of the machine/*
Secondly, a pipe must conduct the water from the reservoir
to the machine with a descent at least as great as one inch for
every six feet of its length.
Thirdly a channel must be provided by which the superflu-
ous water may run off.
497. The ram itself consists of a pipe having two apertures,
both guarded by valves of sufficient gravity to fall by their own
weight, one of which opens downwards, the other opening up-
wards into an air-tight chamber. An air-vessel is generally
attached to the chamber, for the purpose of causing a steady
stream to flow from the chamber, through another pipe, to the
desired point where the water is to be discharged.
Explain the con- 498 ' Fi g' 75 re P resent s the hydraulic ram.
struction of the A B represents the tube, or body of the ram,
havin g two apertures, C and D, both guarded by
valves ; C opening downwards, D opening up-
draulique, in its present form, was invented by Montgolfier, of Montpelier
An instrument or machine of a similar construction had been previously
constructed by Mr. Whitehurst, at Chester, but much less perfect in ita
mode of action, as it required to be opened and shut by the hand by
means of a stop-cock. Montgolfier's machine, on the contrary, is set in
motion by the action of the water itself.
* Such an elevation may easily be obtained in any brook or stream of
running water by a dam at the upper part of the stream, to form a reser-
voir. It has been calculated that for every foot of fall in the pipe running
from the reservoir to the ram sufficient power wjll be obtained to raise
about a sixth part of the water to the height of ten feet. With a fall of only
four feet and a half, sixty-three hundred gallons of water have been raised
to the height of one hundred and thirty-four feet. But, the higher the res-
ervoir, the greater the force with which the hydraulic ram will act. The ope
ration of the principle by which the hydraulic ram acts is familiar to those
who obtain water for domestic purposes by means of pipes from an elevated
reservoir, as is the case in many of our large cities. A sudden stoppage of
the flow, by turning the cock too quickly, causes a jarring of the pipes, which
is distinctly perceived, and often loudly heard all over the building. This
is due to the sudden change from a state of rapid motion to a state of rest.
The ineitia of the fluid, or its resistance to a change from a state of rapid mo-
tion to a state of rest, a property which it possesses in common with all other
kinds of matter, explains the cause of the violent jarring of the pipes, the
stopping of which arrests the motion of the fluid ; and the violence, which
is in exact proportion to the momentum of the fluid, is sometimes po jjreal
as to burst the pipes
vrards, and both falling by their own weight. .Let us now suppose
the valve C to be open and D shut. The water, descending through
the tube A. B with a force proportionate to the height of the
reservoir, forces up the valve C and closes the aperture, thus
suddenly arresting the current, and causing, by its reaction, a
pressure throughout the whole length of the pipe ; this pressure
forces up the valve D, and causes a portion of the water to enter
the chamber above D. The current having thus spent its force,
the valve immediately falls by its own weight, by which
means the current is again permitted to flow towards the aper-
ture C. The pressure at D thereby being removed, that valve
immediately falls, and closes the aperture. When this takes
place, everything is in the same state in which it was at first.
The water again begins to flow through the aperture at C, again
closing that valve, and again opening D ; and the same effects are
repeated at intervals of time, which, for the same ram, undergo
but little variation.
The water being thus forced into the chamber E, as it cannot
return through the. valve D, it must proceed upwards through
the pipe G, aad is thus carried to any desired point of dis-
charge. An air-vessel is frequently attached to the chamber
of the ram, which performs the same office as it does in the
forcing-pump, namely, to cause a steady stream to flow from
the pipe Gr. The action, both of the ram and the forcing-pump,
without the air-vessel, would be spasmodic.^
How are Springs 499 ' SPRINGS AND RIVULETS. Springs and
and Rivulets Rivulets are formed by the water from rain,
foi-med? snow, &c., which penetrates the earth, and
descends until it meets a substance which it cannot penetrate,
A reservoir is then formed by the union of small streams under
ground, and the water continues to accumulate until it finds an
Fig. 76 represents a vertical section of the crust of the eart*
", c, and e are strata, -either porous, or full of cracks, which per
niit the water to flow through, while b, d and /, are impervious
to the water. Now, according to the laws of hydrostatics, the
water at b will descend and form a natural spring at g : at i it
will run with considerable force, forming a natural jet ; and at
I, p and g, artesian wells may be dug, in which the water will
rise to the respective heights g h, p k, and I m, the water not
* The simplicity and economy of this mode of raising water have caused
it to be quite extensively adopted in the Northern States. When well con-
structed, an hydraulic ram will last for years, involving no additional
trouble and expense, more than occasionally leathering the valves when
they have been too much worn by friction. The origin of the name will be
readily perceived from the mode of its action.
*' Et potum pastas age, Tityre et inter agendum,
Ocoursare capro, curnuferit ille, caveto " Virg. Bucolic 3, r. 2i
faYDft AH LICS.
b?ing allowed to come in contact with the porous soil through
which the bore is made, but being brought in pipes to the sur-
face ; at n the water will ascend to about o. and there will be
no fountain. This explains, also the manner in which water i
obtained by digging wells.
How high will 50 - A s P rin 8 wil1 rise nearl 7 as hi 8 h ' but
the water of a cannot rise higher than the reservoir from
spring rise? whence it issues.
Friction prevents the water from rising quite as high as the reser-
Co what height 501. Water maybe conveyed over hills and val-
may water be leys in bent pipes and tubes, or through natural
conveyed in passages, to any height which is not greater than
tubes ? the level of the reservoir from whence it flows.
502. The ancient Romans, ignorant of this property of fluids,