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Richard Green Parker.

A school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of online

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Online LibraryRichard Green ParkerA school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of → online text (page 10 of 38)
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feet in a second, could penetrate a wall, with what velocity inudt a can-
non-ball weighing 24 Ibs. move to do the same execution 1

57GO X ll = 63360 -:- 24 2640 feet, or one half of a mile in a second

(2.) If a battering ram have a momentum of 58,000 and a velocity of 8.
what is its weight '1 Ans. 7250

(3.) If a ram have a weight of 90,000 and a momentum 81,000, what is
its velocity 1 Ana. .9

(4.) What is the weight of % ram with a velocity of 12 and a momentum
60,000? Ans. 5000.

(5.) Will a cannon-ball of 9 Ibs. and a velocity of 3,000, or a ram with a weight of
15,000 and a velocity of 2, move with the greater force? . Ans. The ram,

What is the 398. THIS GOVERNOR. The Governor is an

Governor? ...,, A ,

ingenious piecfc of mechanism, constructed on

the principle of the centrifugal force, by means of which
the supply of power in machinery is regulated.*

Explain 399. Fig. 59 represents a governor. A B and
rig.m. ^ Q are ^ WQ i everSj or arm s, loaded with heavy

one hundred and six feet long. At the siege of Jerusalem Vespasian em-
ployed a ram fifty feet long, armed with an iron butt, with twenty-five pro-
jecting points, two feet apart, each as thick as the body of a man. The
counter weight at the hindmost end amounted to 1075 cwt., and 1500 men
were required to work the machine.

* This very useful appendage to machinery, though long used in mills
and other mechanical arrangements, owes its happy adaptation to the steam
engine to the ingenuity of Mr. James Watt.

In manufactures, there is one certain and determinate velocity with
tfhich the machinery should be moved, and which, if increased or dimin-
ished, would render the machine unfit to perform the work it is designed to
execute. Now, it frequently happens that the resistance is increased or
diminished by some of the machines which are worked being stopped, or
others put on. The moving power, having this alteration in the resistance,
would impart a greater or less velocity to the machinery, were it not for
the regulating power of the governor, which increases or diminishes the
supply of water or of steam, which is the moving power.

13ut, besides the alteration in the resistance just noticed, there is, also,
frequently, greater changes in the power. The heat by which steam is
generated cannot always be perfectly regulated. At times it may afford an
excess, and at other times too little expansive power to the steam. Water,
also, is subject to change of level, and to consequent alteration as a moving
power. The wind, too, which impels the sails of a wind-mill, is subject to
great increase and diminution To remedy all these inconveniences is th<
duty assigned to the governor.



itEGULATO-RS (F MOTION.



107




balls at their extremities B and C, and
suspended by a joint at A upon the ex-
tremity of a revolving shaft AD. A
a is a collar, or sliding box, connected
with the levers by the rods It a and c a :
with joints at their extremities. When
the shaft A D revolves rapidly, the cen-
trifugal force of the balls B and will
cause them to diverge in their attempt to
fly off, and thus raise the collars, by means
of the rods b a and c a. On +he con-
trary, when the shaft A D revolves slowly, the weights B and
C will fall by their own weight, and the rods b a and c a will
cause-the collar a to descend. The steam-valve in a steam-
engine, or the sluice-gate of a water-wheel, being connected
with the collar a, the supply of steam or water, which puts the
works in motion, is thus regulated.

What is the ^' ^ ne Main-spring of a watch consists of a

Main-spring long ribbon of steel, closely coiled, and contained
*f a watch? in a round box> j t ig em pi y e( i i ns tead of a

weight, to keep up the motion.

401. As the spring, when closely coiled, exerts a stronger force
than when it is partly loosened, in order to correct this inequality
the chain through which it acts is wound upon an axis surrounded
by a spiral groove (called a fusee] , gradually increasing in diameter
from the top to the bottom ; so that, in proportion as the strength
9f the spring is diminished, it may act on a larger lever, or a larger
wheel and axle.

Explain 402. Fig. 60 represents a spring coiled in a round box
Fig. 60. A B is the fusee,
surrounded by a spiral groove,
on which the chain C is wound.
When the watch is recently
wound, the spring is in the
greatest state of tension, ana
will, therefore, turn the fusee
5



Fig. 60.




108 NATUKAL PHILOSOPHY.

by the smallest groove, on tlie principle of the wheel and
axle. As the spring loses its force by being partly un-
wound, it acts upon the larger circles of the fusee ; and
the want of strength in the spring is compensated by the
mechanical aid of a larger wheel and axle in the larger
grooves. By this means the spring is made at all times to
exert an equal power upon the fusee. The motion is com-
municated from the fusee by a cogged wheel, which turns
with the fusee.

Of what does 403. HTDEOSTATICS.* Hydrostatics treats
Hydrostatics ., ., n . ,

treat ? f the nature, gravity and pressure of fluids.

What is tTie dif- 404. Hydrostatics is generally confined to
&%% the consideration of fluids at rest, and Hy-



Hydrostatics f draulics to fluids in motion.

What is a 405. A Fluid is a substance which yields

Fluid f fa the slightest pressure, and the particles of

which, having but a slight degree of cohesion, move easily
among themselves.!

* The suijects of Hydraulics and Hydrostatics are sometimes descrioea
under the general name of Hydrodynamics. The three terms are from the
Greek language, compounded of nJop (hudor), signifying water, and Svrums
(dunamis) , force or power ; oraTtxog (staticos), standing, and uuXog (aulos), a
tube or pipe. Hence Hydrodynamics would imply, the science which treats
of the properties and relations of water and other fluids, whether in a state
of motion or rest ; while the term Hydrostatics would be confined to the
consideration of fluids in a state of rest, and Hydraulics to fluids in motion
through tubes or channels, natural or artificial.

t There is this remarkable difference between bodies in a fluid and
bodies in a solid form, namely, that every particle of a fluid is perfectly
independent of every other particle. They do, not cohere in masses, like
the particles of a solid, nor do they repel one another, as is the case with the
particles composing a gas. They can move among one another with tho
least degree of friction, and, when they press down upon one another ir
virtue of their own weight, the downward pressure is communicated in aU
directions, causing a pressure upwards, sideways, and in every possible
manner Herein the particles of a fluid differ from the particles of a solid,
even when reduced to the most impalpable powder ; and this it is which con,
ttitutes fluidity, namely, the power of transmitting pressure in every direction.
and that, too, with the least degree of friction. The particles whioh compos*
a fluid must be very much smaller than the finest gnan of OD iiuyal t >.i')le
pow ier.



HYDROSTATICS. . 109

Sow does a 406. A liquid differs from a gas in its de-

l froma^or ^ Qe of compressibility and elasticity. Gases
\japor ? are highly compressible and elastic. Liquids,

on the contrary, have but a slight degree either of com-
pressibility or of elasticity.*

407. Another difference between a liquid and a gas arises from
the propensity which gases have to expand whenever all external
pressure is removed. Thus, whenever a portion of air or gas is
removed from a closed vessel, the remaining portion will expand,
and, in a rarer state, will fill the whole vessel. Liquids, on the
contrary, will not expand without a change of temperature. Liquids
also have a slight degree of cohesion, in virtue of which the particles
will form themselves into drops ; but the particles of gases seem to
possess the opposite quality of repulsion, which causes them to ex-
pand without limit, unless confined within the bounds of some ves-
sel, or restricted within a certain bulk by external pressure.

408. The fluid form of bodies seems to be in great, measure, if
not wholly, attributed to heat. This subtle agent insinuates itfeelf
between the particles of bodies, and forces them asunder. Thus,
for instance, water divested of its heat becomes ice, which is a
solid. In the form of water it is a liquid, having but in a very
slight degree the properties either of compressibility or elasticity.
An additional supply of heat converts it into steam, endowed with
a very great degree both of elasticity and compressibility. But, so
soon as steam loses its heat, it is again converted into water.
Again, the metals become liquid when raised to certain tempera-
tures, and it is known that many, and supposed that all, of them
would be volatilized if the required supply of heat were applied.



* The celebrated experiment made at Florence, many years ago, to test
the compressibility of water, led to the conclusion that water is wholly
incompressible. Later experiments have proved that it may be com
pressed, and that it also has a slight degree of elasticity. In a voyage to
the West Indies, in the year 1839, an experiment was made, at Vne sugges-
tion of the author, with a bottle filled with fresh water from the tanks on
the deck of the Sea Eagle. It was hermetically sealed, and let down to the
depth of about seven hundred feet. On drawing it up, the bottle was still
full, but the water was brackish, proving that the pressure at that great
depth had forced a portion of the deep salt water into the bottle, previously
compressing the water in the bottle to make room for it. As it rose to the
surface, its elasticity restored it to its normal state of density.

At great depths in the sea the pressure of the superincumbent mass
increases the density by compression, and it has been calculated that, at H
depth of about ninety miles, water would be compressed into one-half of ite-
volume, and at a depth of 360 miles its density would be nearly equal t<
that of mercury. Under a pressure of 15,000 Ibs. to a square inch, .Mr.
Perkins, of Newburyport, subsequently of London, has sh:wn that witer ia
reduced in bulk one part iu twenty-four.



110 NATUKAL PHILOSOPHY.

The science of Geology furnishes sufficient reasons for believing
that all known substances were once not only in the liquid form,
but also previously existed in the form of gag.*

How do fluids 409. GRAVITATION OF FLUIDS. Fluids gravi-
gramtatef ^ a ^ e j n a more perfect manner than solids, oc
account of their want of cohesiv e attraction. The particles of a
solid body cohere so strongly that, when the centre of gravity
is supported, the whole mass vill be supported. But every
particle of a fluid gravitates independently of every other par-
ticle.

yy, 410. On account of the independent gravita-

fluids be tion and want of cohesion of the particles of a

moulded into fl u i ( j > they cannot be formed into figures, nor pre-
served in heaps. Every particle makes an effort
to descend, and to preserve what is called the level or equi-
librium.



What is the ^11. The level or equilibrium of fluids ia
equilibrium of the tendency of the particles so to arrange
themselves that every part of the surfao
shall be equally distant from the centre of the earth ; that
is. from the point towards which gravity tends.

What is the 412. Hence the surface of all fluids, when in a

Surface* of all state of rest) ' P artakes tlie spherical form of the
fluids ? earth.

413. For the same reason, a fluid immediately conforms itself tc>
the shape of the vessel in which it is contained. The particles of a
solid body being united by cohesive attraction, if any one of them
be supported it will uphold those also with which it is united.
But, when any particle of a fluid is unsupported, it is attracted
down to the level of the surface of the fluid ; and the readiness with
which fluids yield to the slightest pressure will enable the particle,

>y its own weight, to penetrate the surface of the fluid, and mis

jrith it.



* The science of Chemistry unfolds the fact that all the great changes in the
constitution of bodies are accompanied by the exhibition of heat either in a free
or latent condition.



* HYDROSTATICS. 11 J

mat is Ca- 414. OAPILLAKY ATTRACTION. Capillary
pMaryAttrac- Attraction is that attraction which causes
What are Ca- fluids to ascend above their level in capillary
pillary Tubes ? tubes. Capillary * tubes are tubes with very
fine bore.

415. This kind of attraction exhibits itself not only in tubes, but
also between surfaces which are very near together. This may be
beautifully illustrated by the following experiment. Take two
pieces of flat glass, and, having previously wet them, separate their
edges on one side by a thin strip of wood, card or other material ;
tie them together, and partly immerse them perpendicularly in
colored water. The water will then rise the highest on that side
vhere the edges of the glass meet, forming -a beautiful curve down-
wards towards the edges which are separated by the card.

416. Immeree a number of tubes with fine bores in a glass of
colored water, and the water will rise above its equilibrium in all,
but highest in the tube with the finest bore.

417. The cause of this seems to be nothing more than the ordi-
nary attraction of the particles of matter for each other. The sides
of a small oiifice are so near to each other as to attract the particles
of the fluid on their opposite sides, and, as all attraction is strongest
in the direction of the greatest quantity of matter, the water is
raised upwards, or in the direction of the length of the tube. On
the outside of the tube, the opposite surfaces cannot act on the
same column of water, and, therefore, the influence of attraction is
here imperceptible in raising the fluid.

418. All porous substances, such as sponge, bread, linen, sugar,
&c., may be considered as collections of capillary tubes; and, for
this reason, water and other liquids will rise in them when they are
partly immersed.

419. It is on the same principle that the wick of a lamp will
carry up the oil to supply the flame, although the flame is several
inches above the level of the oil.f If the end of a towel happen to

* The ^ord capillary is derived from the Latin word capilla (hair), and it
Is applied to this kind of attraction because it is exhibited most prominently
In tubes the borex of which are as fine as a hair, and hence called capillary
kabes.

t The reason why well-filled lamps will sometimes fail to give light is,
lhat the wick is too large for its tube, and, being thus compressed, the
japillary attraction is impeded by the compression. The remedy is to
reduce the size of the wick. Another cause, also, that prevents a clear
light, is that the flame is too far from the surface of the oil. As capillary
ittraction acts only at short distances, the surface of the oil should always
fc within a short distance of the flame. But another reason, which requires
particular attention, is, that all kinds of oil usually employed for lamps
contain a glutinous matter, of which no treatment can wholly divest them.
This matter fills the pores or capillary tubes of the wick, arid prevents the



1- NATURAL PHILOSOPHY.

be left in a basin of water, it will empty the basin of its contents
On the same principle, when a dry wedge of wood is diiven. into
the crevice of a rock, as the rain falls upon it, it will absorb the
water, swell, and sometimes split the rock. In this manner mill-
stone quarries are worked in Germany.

420. ENDOSMOSE AND EXOSMOSE. In addition to the capillary
attraction just noticed as peculiar to fluids, another may be men-
tioned, as yet but imperfectly understood, which seems to be due
partly to capillary and partly to chemical attraction, known under
the names endosmose and exosmose.* These phenomena are mani-
fested in the transmission of thin fluids, vapor and gaseous matter,
through membranes and porous substances. The ascent of the sap
in vegetable, and the absorption of nutritive matter by the organs
of animal life, are to be ascribed to these causes.

421. When two liquids of different densities are separated by a
membranous substance or by porcelain unglazed, endosmose will
carry a current inwards, and exosmose will force one outwards, thup
causing a partial mixture of the fluids.

. 422. Eocperimsxt. Take a glass tube, and, tying a piece of bladder 01
clean leather over one end for a bottom, put some sugar into it, and having
poured a little water on the sugar, let it stand a few hours in a tumbler, of
water. It will then be found that the water has risen in the tube through
the membranous substance. This is due to endosmose. If allowed to stand
several days, the liquid will rise several feet.

If the experiment be reversed, and pure water be put into the tube, and
the moistened sugar into the tumbler, the tube will be emptied by exosmose.

423. The liquid that has the less density will generally pass to the
denser liquid and dilute it.

What peculi- 424. GRAVITATION OF FLUIDS or DIFFERENT
arity is there DENSITIES. When solid bodies are placed one
l tation of'fluids a ^ ove an other, they will remain in the position in
of different which they are placed so long as their respective
densities? centres of gravity are supported, without regard
to their specific gravity. With fluids the case is different.



ascent of the oil to feed the flame. For this reason, the wicks of lamps
should be often renewed. A wick that has been long standing in a lamp
will rarely afford a clear and bright light. Another thing to be noticed by
those who wish the lamp to perform its duty in the best possible manner
is, that the wick be not of such size as, by its length, as well as its thickness,
to fill the cup, and thereby leave no room for the oil. It must also be
remembered that, although the wick when first adjusted may be of the
proper size, the glutinous matter of the oil, filling its capillary tubes, causes
the wick to swell, and thereby become too large for the tube, producing the
Fame difficulty as has already been noticed in cases where the wick is too
large to allow the free operation of capillary attraction,

* Endosmose, from evdov, within, and ua^og, impulsion Exosmose, from
i,'?, uulwai d, aud ujjuo{, impulsion



HYDKOSTATICS.

Fluids of different specific gravity will arrange themselves in
the order of their density, each preserving its own equilibrium.

425. Thus, if a quantity of mercury, water, oil and air, be put
into the same vessel, they will arrange themselves in the order of
their specific gravity. The mercury will sink to the bottom, the
water will stand above the mercury, the oil above the water, and
the air above the oil ; and the surface of each fluid will partake of
the sphericaJ form of the earth, to which they all respectively
gravitate.

What is a Spirit 426. A Water or Spirit Level is an in-
Level, or Water strument constructed on the principle of the
equilibrium of fluids.. It consists of a glass
tube, partly filled with water, and closed at both ends.
When the tube is not perfectly horizontal, that is, if one
end of the tube be lower than the other, the water will
run to the lower end. By this means the level of any line
to which the instrument is applied may be ascertained.

427. Fig. 61 represents a Water Level. A B is a
Fig 61* S^ ass * u ^ e partly filled *ith water.
C is a bubble of air occupying the
space not filled by the water. When both
ends of the tube are on a level, the air-bubble
will remain in the centre of the tube ; but, if either end of the
tube be depressed, the water will descend and the air-bubble
will rise. The glass tube, when used, is generally set in a woode^
or a brass box. It is an instrument much used by carpenten
masons, surveyors, &c.

.[N. B. The tube is generally filled with spirit, instead of water, o
account of the danger that the water will freeze and burst the gliss. Henct
the instrument is called indifferently the Spirit Level or the Water Level.]

428. EFFECT OF THE PECULIAR GRAVITATION
Why do falling _. .

fluids do less OF -FLUIDS. bond bodies gravitate in masses,

damage than their parts being so connected as to form a

whole, and their weight may be regarded as

concentrated in a point, called the centre of gravity; while each




114 NATUKAL PHILOSOPHY. -

particle of a fluid may be considered as a separate mass, gravi-
tating independently.

It is for this reason that a body of water, in falling, does less
injury than a solid body of the same weight. But if the water be
converted into ice, the particles losing their fluid form, and being
united by cohesive attraction, gravitate unitedly in one mass.

In what direc- 4-29. PEESSUEE OF FLUIDS. Fluids not
^SL* onl y P ress downwards like solids, but also
of their weight f upwards, sidewise,* and in every direction.
(See Appendix, par. 1418.)

430. So long as the equality of pressure is undisturbed, every
particle will remain at rosv. If the fluid be disturbed by agitating
it, the equality of pressuie will be disturbed, and the fluid will not
rest until the equilibrium io restored.

TT ffo 431. The downward pressure of fluids is

downward, lat- shown by making an aperture in the bottom of

eral and up- a yesse i O f wa t cr . Every particle of the fluid

ward pressure . . . , 1,1

qf fluids shown ? above the aperture will run downwards through

the opening.

432. The lateral pressure is shown by making the aperture
at the side of the vessel. The fluid will then escape through
the aperture at the side.

433. The upward pressure is shown by taking a glass tube,
open at both ends, inserting a cork in one end (or stopping it
with the finger), and immersing the other in the water. The
water will not rise in the tube. But the moment the cork is
taken out (or the finger removed), the fluid will rise in the tube
to a level with the surrounding water.

Pig. 62. * If the particles of fluids were arranged in

Fig. 63. regular columns, as in Fig. 62, there would be
no lateral pressure ; for when one particle is per-
pendicularly above the other, it can press only
downwards. But, if the particles be arranged as
in Fig. 63, where a particle presses between tw
particles beneath, these last must suffer a lateral pressure. In whatever
manner the particles are arranged, if they be globular, as is supposed, there
muht be spaces between them \See Fig. I, page 22.]




HYDROSTATICS.



115



What is the ' P ressure a u s in P r OP r "

law of fluid tion to the perpendicular distance from the
surface; that is, the deeper the fluid, the
greater will be the pressure. This pressure is exerted in
every direction, so that all the parts at the same depth
press each other with equal force. (See par. 1423.)

435. A bladder, filled with air, being immersed in water, will
te contracted in size, on account of the pressure of the water in all
Hrectiong ; and the doeper it is immersed, the more will it be con-
tacted.*

436. An empty bottle, being corked, and, by means of a weight,
iet down to a certain depth in the sea, will either be broken by the
pressure, or t>tO cork will be driven into it, and the bottle be filled
with wetrr. This will take place even if the cork be secured with
wire and peeled. But a bottle filled with water, or any other liquid,
may be iet down to any depth without damage, because, in this
case, the internal pressure is equal to the external. f



* T'ae weight of a cubic inch of water at the temperature of 62o of Fah-
lonheit's thermometer is 36066 millionths of a pound avoirdupois. The
pr&asure of a column of water of the height of one foot will therefore be
twelve times this quantity, or .4328 (making allowance for the repeating
decimal), and the pressure upon a square foot by a column one foot high
will be found by multiplying this last quantity by 144, the number of
square inches in a square foot, and is therefore 62.3332

Hence, at the depth of

Ibs. Ibs.



1 foot

2 feet

3 "

4 "

5 "

6 "

7 "

8 "

9 "

10 "
100"



the pressure on a square in-ih is



.4328, on a square foot, 62.3232

.8656, 124.6464

1.2984, 186.9696

1.7312, 249.2928

2.1640, 311.6160

2.5968, 373.9392

3.0296, 436.2624

3.4624, 498.5856

3.8952, ' 560.9088

4.3280, 623.2320

43.2800, " " 6232.3200



Fiom this table, the pressure on aty ..-u^face at any depth may easily be
found.

It will thus be seen that there is a certain limit beyond which divers
cannot plunge with impunity, nor fishes of any kind live. Wood that has



Online LibraryRichard Green ParkerA school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of → online text (page 10 of 38)