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Dr. Frank E, Fleisdell
a
kas Ath, te)
ina 23— Sb ZF,
hick? Fell
REVISED EDITION.
INTRODUCTORY COURSE
or
NATURAL PHILOSOPHY
rom Tue use OF
HIGH SCHOOLS AND AUADEMIES.
EDITED ¥KOM
GANOTS POPULAR PHYSIOS.
WEIS
MECCA Lx TUK ACIDOL OF MANE.
anvinn ny
LEVI S, BURBANK, AM.
HATE PEISCIPAG Yr TAKMEY ACADRMY, WOOLEN, NAM,
axe
JAMES 1. HANSON, A.M.
FREEGEAL OF ‘Tie fiolt scoot, WouURS, Mase,
NEW YORK © CINCINNATI» CHICAGO
AMERICAN BOOK COMPANY
A. S. BARNES & CO
Entered according to Act of Congress, i
Br WILLIAM G. PECK,
District Court for the Southern Distret of
New York,
Copyright, 1981, by A. 8. Barnes & Co,
your 1868, 1875,
Copyright renewed, 188, by Wittiax G. Pack.
PREFACE TO THE REVISED EDITION.
‘Tur revision of “ Peck’s Ganot” was begun by Mr.
Burbank in the spring of 1880, and completed by him
as far as the subject of “ Ballooning,” on page 164,
when the progress of the work was interrupted by his
death. The revision of the remaining portions is my
own work.
‘The essential characteristics and general plan of the
book have, so far as possible, been retained, but at
the same time many parts have been entirely rewritten,
mach new matter added, a large number of new cuts
introduced, and the whole treatise thoroughly revised
and brought into harmony with the present advanced
stage of scientific discovery.
Among the new foatures designed to aid in teaching
the subject-matter, are the summaries of topics, which,
it is thought, will be found very convenient in short
reviews.
“As many teachers prefer to prepare their own ques-
Hions on the text, and many do not have time to spend
in thie solution of problems, it has beon deemed exye
BB9R28
iv PREFACE.
dient to insert both the review questions and problems
at the end of the volume, to be used or not at the dis-
cretion of the instructor.
I desire to acknowledge my obligations to all who
have in any way given me aid and advice in the prep-
aration of this revision, and especially to Professor
PeckHam, of Adelphi Academy, Brooklyn, N. Y., who
has kindly looked over many of the proof-sheets, and
furnished me with valuable suggestions.
J. I. HANSON,
Wosvan, July, 1681,
EDITOR'S PREFACE.
Tae rapid spread of scientific knowledge, and tho
continually widening field of its application to the
useful arts, have created an increased demand for new
and improved text-books on the various branches of
Narernan Parosorny.
Of the elementary works that have appeared within
& few years, those of M. Gaxor stand pre-eminent, not
only as popular treatises, but as thoroughly scientific
expositions of the principles of Paystcs. His “ Traité
de Physique” bas not only met with unprecedented
success in France, but has been extensively used in
the preparation of the best works on Physies that
have been issued from the American pre
Tn addition to the * Tmité de Physique,” which is
Intended for the use of Colleges and higher institut’
08
of learning, M. GANoT has recently published a more
elementary work, adapted to the use of schools and
academies, in which he has faithfully preserved the
racy of
ey features and all the scientific
the Tanger work. Tt is charwcterized by a well-b
vi PREFACE,
distribution of subjects, a logical development of seien-
tifle principles, and u remarkable clearness of definition
and explanation. In addition, it is profusely illusteated
with beautifully executed engravings, admirably ealeu-
Jated to convey to the mind of the student # clear
conception of the principles unfolded. Their complete-
ness and accuracy are such as to enable the teacher to
dispense with much of the apparatus usually employed
in teaching the elements of Physical Science,
Iu preparing an American edition of this work on
Porviar Puysies, it has not been the aim of the
editor to produce a strict translation. No effort, how-
has been spared to preserve throughout, the spirit
and method of the original work. No changes have
eve:
been made, except such as have seemed caleulated to
harmonize it with the system of instruction pursued in
the achools of our country.
By a special arrangement with M. Gaxor, the Amer
ican publishers are enabled to present facsimile copies
of all the original engravings.
New Yous, June 1, 1800.
CONTENTS.
CHAPTER
PROPERTIES OF MATTER
Sreriox
1. Desryrrioxe axn Grverir PRorerrres or Marten
11. Sprouie Paorurries op Siren rey
OHAPTER UL
MECHANICAL PRINCIPLES.
1. Motiox axp Force . . .
UL Provcienes verespext ox re Array:
TATION = tay far
TIL Worx axp Exescy . . — - Sa
CHAPTER M1
APPLICATION OF PHYSICAL PRINC
PLES TO MACHINES
1 Garena Perscuries . a + .
TL Eresevrary Macuxes
UL Ressrasces ro Moriox eT a aro ar
CHAPTER IV.
™
MECHANICS OF LIQUIDS.
PANT 1. —itYPROSTATICS
Gexunan Prancirits
Rotstrnares ov Ligvres
Arrircarions o tux Princtets or Eqestassiee
Parsstne Ox Scramscrp Booixs
Sracrvs Geaviry ov Booiss .
sSBr-
2
viii CONTENTS.
PART 11. — HYDRODTKAMICS.
I. Frow or Liqums . . . ss.
I. Water as a Motive Power...
UL Macuinus ro naisixo WATER. 2 ee ee
CHAPTER V.
PNEUMATICS.
A Tne Armospoers © 2. 2 1 ee
IL Measure or tur Ezastic Force oF Gases
TIL Pours ayp oTmen Macuixes. . . . .
IV. Appuication to Batuoosixo.. . s+ +
CHAPTER VL
ACOUSTICS.
I. Propuction axp Proracation or Souxp . . . . .
IL Musican Sousps - 2 1 ee ee ee
LL. Orticat Stopr oF Socxps.— Musicat Inernowests. —
Tne Humax Voice axp Ear. — Tur Puoxocrara
CHAPTER VIL.
MEAT.
I. Grserat Properties or Heat... . .
IL. ‘Tesreraturs.— Tue THErwometer . 4
TIT. Laws or Exraxsioy or Sotips, Liquips, axp Gast
IV. Dirrvstoy or Heat... eat fue
V. Cuasox or State oF Boots ay Fosiox axp Coxe
VI. Vaporizatioy.— Etastic Force or Varors. . .
GELATION
VII. Coxpexaatioy or Gases axp Vavors.—Srrciric Hear.
—Sorrces or Heat axp Corp. ss eee
VIL. THermo-pyxamica ... batts
IX. Hyoxosetny.— Ratx.—Dew —Winps—Sionat Senvicg
CHAPTER VIL
oprics.
TL. Gewerat Prixcirues .
II. Reruecrioy or Licut.—Minnons. |. |
TIL. Rerractiox or Liont. — Le: wat
IV. Decourositiox oF Liowr.—Couoxs or Bones...
V. Taxorr axp Coxsrructioy or Orrican InstRumExts
110
9
121
125
140
142
162
169
182
197
sig
B21
387
359
381
CONTENTS ix
CHAPTER 1X.
ELECTRICITY,
FART 4. —a\0snTIAx
1 Narene or Execrmonry.—Genenan Peorearies oF Mag-
<a : - 8 5
TL ‘Tenmesreiat, Maoverias, — Compasses et
Ut Me De OF EMPARTIXG Macwht ese - 46
FAME 11. — rwterioNaL x
1. Buccrmtoat Provunrtis c + 490
LU. Purxorene oF Ixvcrios.— Kuxctaican Macurxns 432
I. Exremomesrs wire run Exnornc Ma . 442
IV. Arxosrmmnic Buecrewire 463
FART 111, — DYNAMICAL exaCTMECITT,
1. Fexpaxnwran Parscrrees . td . 400
IL Arriscatiows ov Ganyaxtc Excermterr - 4%
IT. Fuxpamasran Pervcirizs ov Etscrro-xaone tian 478
IV. Besermosowerte Teceonarns.—'fe Kexctnomorom 486
¥. Ixpoctiow. — Maonnroennermsoire
cur . ee e miaaire at
ELEMENTARY PHYSICS.
————
CHAPTER I,
PROPERTIES OF MATTER,
SKOTION 1, — DEFINITIONS AND GENERAL PROPERTIES OF MATTER.
Physics — Physical Agents. — NArcRAL Puttos-
, o& Pirysics, treats of the general properties of
bodies, and of the causes that modify these properties
without altering their constitution.
‘The principal causes that modify the properties of
bodies are: Gravitation, Heat, Light, and Electricity.
These causes are called Physical Agents or Forces,
2. A Body is 4 collection of material particles; as a
‘stone, or a block of wood. A body which is exceedingly
‘smnall is called n Material Point.
3. Molecules and Atoms. —Bodlies are made up of
‘simall particles, called Molecules, and these again are com-
pores of still smaller clements, called Atoms.
A molecale is the smallest particle of snatter that can exist by
‘An atom in tho smallest particle of matter that can exist in
combiuatiou,
A Wnoleoale may consist of two or more utows of the mame kind
‘of shatter, or it may be composed of several utoms of different kinds ;
Thus, anplecule uf sulphur is « combination of two atous of sulphur,
=
‘sodium combined with an atom of ehlorine,
Atoms are joined and held together by a kind of
chemical affinity.
Molecules are kept in place by the action of two,
snolociulas, attrition apd molecular repuleion.
4. Mass and Density.— The Mass ote
quantity of matter which it contains.
‘The Dewsrry of a body is the degree of cl
particles.
Different bodies, having the sane volumo, contain vers
quantities of matter; for example, a cuble Inch of lend ¢
neatly cleven times as much matter ns a cubic inch of
anasses of bodies are proportional to their weights.
‘Those bodies in which the particles ary closo together are
bo dense ; thus, platinum and mereury are dense bodies. _
‘which tho particles aro not close together are said to be rare 1
steam and alr are rare bodies. The densities of bodies having |
saine hull are proportional to thole weights. a
5. Three States of Bodies.—Boilles may exist in
three different states, solid, liquid, and aeriform,
Sotep bodies tend to retain a permanent form,
their molecules are held together by forces of attraction wl
are greater than the repellent forces that would tond to sepa-
rate them.
Tn Ligurps the attractive and repellent forces are nearly
balanced, and their molecules move freely among one another.
* Liquids have no tendency to retain a permanent form, bat
‘issume at once the form of the containing vessel.
In Axnivort bodies the repellent are more powerful than
the attractive forces, and their molecules constantly tend to
separate and occupy & greater space. Air and all gases and
vapors ave examples of aeriform bodies.
‘The term Fit is applied to both tiquid and acriform bodies.
Many butlies muy exist iin every ove of the three states in succession.
‘Thus, if ico be heated until tho repellent forces balance thuee of at~
THE METRIC SYSTEM. 5
tracthoa, It passes into the liquid state and becomes water; if still
more heat be applied, the repellent forees prevail over those of at
traction, and it passes into the etate of rapor aud becomes steam.
GENERAL YROPERTIES OF BODIES.
6. The most important properties which all bodies possess
are: Extension, Weight, Impenctrability, Inertia, Porosity,
Divisibility, Compressibility, Expansibility, and Elasticity.
7. Extension.is the property by virtue of which a body
occupies space.
Macsrrupe and Fons depenit upon Extension.
‘To coenpy space a bedy must have the three dimensions, length,
Sreadth, aud thickness. ‘The space vecupiod by body is called its
volume,
8. English Measures.—For the purpose of measuring
the dimensions of bodies a standard unit of length is needed.
To England gui the United States the yard lus been adopted as
the stasdan! wait, and with its divisions aud multiples is im eounnon
ise,
9. The Metric System. — This system is in gencral use
in Frauee and in most of the counties of Europe.
‘It is adopted by scientific writers everywhere, and will
$00n come into general use throughout the civilized
World, Its use in the United States has been legalized by
act of Congress.
“Whe Unit of this system is the meter, whieh is the ten-inillionth
‘part of a quadraut of that meridian of the earth which passes through
‘Paria, It ix equal to 30.37 inches, nearly.
Tis dixisivas sus maltiples vary in a tenfold ratio, and frown
; j measures of surfico, volume, and weight aro derived.
anevelature Is derived from the Greek and Latin numerals,
k prefixes deka (10), hekto (100), kilo (1000), and myria
tised for the multipler, am tho Latin prefixes dhoci (7s),
, HNL Cygne Use fur the divisions of the unit,
Measures of Length.—In the following
I dchominations of linear measure dre given
6 GENERAL PROPERTIES OF MATTER
in their order, with the English equivalents, and the abbreyi-
ations used.
1 Millimeter Qn.) = 0.001 in, = 0.08037 inch:
Centimeter (ow.) = 0.0 mn 0.3037
Docimover (dim.)
1
‘
1 Meter (w.)
1 Dokameter (Dm.)
i
1
1
Hoktometer (iw,)
Kilometor (Km.) =
fanoter (Mw.) = 10000. == G.2197 alles
In the figure in the mangin ene deeiunster i
compared with a seale of inches, Tt will tee
won that the decinoter ie a little lees then 4
inches,
With the equaco meter and the euble snoter
as units, tables are constructed for the meastines
of surface and roluime, in the same way as with
tho English measuses; the amtlo 100, (10%)
being used for surfaco measures, und LOK
(10%, for volumes.
Thos, 100 equare millimeters
centimeter, ete. 1000 cubic
1 eubie centimeter, ete.
tr. Measures of Capacity.— For
measuring articles which by the Englial
system are sold by dey or liquid measure,
| the unit adopted is the fiter, which is equal
to one cubic decimeter,
The denominations ar as follows.
Ratio 10.
Milliliver (tol) = J eubie contimeter
Comtiliter (cl. = 10 © “
t
1
s—4 1 Deciliter Gl.) = Ino “
: 1 Litr Q) =100% “
4B 1 Dekaliter (DL) 10“ deciineters
LES} «| t Hektoliter (HI) = 100“ “
1
Kiloliter (KL) = 1 moter
THE METRIC SYSTEM. L/
‘The liter is equal 10 1.0567 Liquid quarts, or 0.908 of «dry quart.
Tt mng thervfore be use conveniently in place ef both,
42. Weight. —A body falls, when not supported, because
it is altrneted toward the centre of the earth. When it rests
upon another hody or upon the surface of the earth, ite ten~
dency to fall is not destroyed, and it presses downward with
& foree proportioned to the degree in which it is attracted.
Hence weight is the measure of the earth's attraction. The
torm weight. fs commonly used in this Timited sense, but, since
the attraction of gravitation is aniversal, a bocly would have
weight if placed on or near the surface of any of the planets
‘or other heavenly bodies.
‘The anit of weight in the English syste is the aveirdupoie pool
of 7000 Tn the Metrie System the unit adoptest is the gram,
which Is the weight of one cubic centimetor of distilled water at ite
groatest density, that ix, at the temperatare of 39.2° Bahmnheit or
# Contignule.
13. Metric Table of Weight.— Ratio 10.
Ove Milligran (ue) = 00154 grain
* Coutigram (eg) ons
* Decigram (dg) = IonRm
“Gram (g.)) = 14m «
“ Dekagrun (De) = 0.8887 ounce ay.
© Hektogram (Hz.) R5a74
“ Kilogram (Kg.) 22046 por
“ Myriagran (Mg.) 2018
“ Quintal — (Q) Ee
“ Tonnean (1) OL woe
14. Impenetrability is tint property by virtue of which
80 two bodies can occupy the same place at the same time.
‘Thig property ie eclf-evident, although phenomenn are ob-
fart would seem to conflict with it. Thus, when a
Of alcohol is mixed with a pint of water, the volume of
the resulting mixture is leas than a quart, This diminution
fee from the particles of one of tle fluids inain-
ital Detwoon those of the other; but it (5 cloar
Me
RAL PROPERTIES OF MATTER.
8 6.
that where a particle of alcohol is, there a particle of water
cannot be.
It nay bo shown by several simple experiinents that air and water
cannot oecapy the mune epace. Tuvert a glass tumbler and preees it
dlownward into a vessel of wate seater will net enter and fill
the tumbler. Close ove end of # glass tube
with the thumb and thrust the other end fate
the water, ‘The water cannot fill the tube
while the air is retained. Remove the thumb:
eo that the air ean escape, and the water will
immediately rise and fill the tube, Passa fun=
nel through a cork fitted air-tight to a Bottle,
Leta bent tube pass through another hale fa
the cork, ani ut the other end dip into ® tumn=
bier of water, as shown in Fig, 2 If then
exuter is poured into the fonnel, as fivst as ft
centers the bottle air will eecape iv bubbles from the end of the tube
is the tumbler,
Fig. 2
15. Inertia is the tendency which a body has to maintain
its state of rest or motion. If a body is at rest it has no
power to sot itself in motion, or if it is in motion it has no
power to change either its rate of motion or the direction in
which it is moving. Hence, if a body is at rest, it will re
main at rest, or if in motion, it will move om uniformly in a
straight line until acted upon by some force.
‘The reason why we do not see herlies coating’ to wore om amie
formly in straight lines, when sot is wotloo, is that they are contina-
ally acted upon by forces which change their stare of motion. ‘Thus,
a ball thrown from the band, besikes meeting with the resatanon of
the alr, is contlieslly drawn deqwawanls by the attmetion of the
carth, tll wt laet It is browght to rest.
Many y the principle of ine
ertia, For example, when av le suddenly arrested,
loose articles is it arv thrown to the fruwt, became they ted to keop
the motions which they had acquired,
If a person Jumps froin # car in mphl motion, be is Wkely to be
thrown violently to the ground } thr Wie body rtaine its onward tee
Hoo, while bis feet are stuppedl by striking the rowel,
reiliar pve
+
POROSITY. — DIVISIBILITY. 9
‘Let & card with a coin placed wpon it be balanced on ono of the
fingers of the Ieft hand ; then snap it suddenty with the middle fiagee
of the right hand, ns represented v
leaving
finger,
ettin of the coin is net overcome
by the
and 3
where it was firet plocod on the Fig. 3.
(6. Porosity is that property of a body by whieh spaces
exist between its molecules.
All bowties aro more or less porous.
Actual cavities or cells that are visible are valled Seasble
Pores. The invisible spaces that separate all the molecules
of w body are called Physical Pores.
The metals, in whieh no pores can be secu even by the wid of the
tolerseope, are shown to be porns by the fnet that hy
pressure Hiquida and gies may be made to pase through then,
17. Divisibility.—All bodies are capable of being di-
vuled and subdivided; and in many cases the parts that may:
‘be obtained are of almost. inconcelvable minutencss.
‘The following examples serve to show the extreme sinaliness ul
ea of matter. A single grain of enmnine imparts a sensi-
color to & gallon of water; this gallon of water may be separated
’ ‘of drops, and if we suppose each drop to contain ten
‘of carmine, which is a low estiroate, wo shall have divided
‘earmine into ten millions of wolveales, each of which ix
tho naked vyo.
reveuls to va, in certain vegetable infusions, awi-
severnl hundreds of them ean swim in a drop of
Faitheres to the point of w needle, “These little animale
Eof motion, and even of preying upon ech other; they
Organs of notion, digestion, aml the ke. How
Ve the molecules which go to make up these
10 GENERAL PROPERTIES OF MATTER
A gain of snusk is capable of diffusing its odor througls an apart-
went for years, with sexrcely au appreciable dissinetion of ite weight.
‘This hows that the anolecules of musk continually given off te ro-
plouish the odor are of inconceivable smallness.
‘The blood of aninals consists of minate red globules swimming
in a serous fluid; chose globules are so sinall that a drop of harman
blood no larger than tho head of a small pin coutaine at beast
50,000 of them. Tu many animals these globules are still senaller ;
in the musk deer, for cxunple, a single drop of blood of the size of a
pin’s led contains at least « million of then
18. Compressibility is the property of being reduced to
a sinaller space hy pressure. ‘This property is a consequence
of porosity, and the change of bulk comes from the particles
being brought nearer together by the pressure. Sponge,
india-ubber, cork, and clder-pith are examples of compres-
sible bodies ; they may be sensibly diminished in volume by
the pressure of the fingers. Gases are, however, the best
examples of compressible bodies.
Somo of the gases nay be reduced to liquids by pressure aloue ;
and rocent experiments have proved that all the gascs known ean
Lo liquefied by great pressury and intense eobl combined.
Liquids are but slightly eoiprossible; but careful experiments
have shown that they yield somewhat to great pressure,
Metale are compressib!
culms, medals, and the like.
shown in the process of statnping
19. Expansibility is the property which a body possesses
of increasing in bulk or yoluine under certain circumstances,
All bodies
Gases expand most, liquids next, and solids least, when
subjected to the same degree of heat. The molecules of air
and the gases constantly repel each other, so Uhat these sabe
stances have a continual tendeney to increase in volume, even
without the fnfluence of leat.
and on being heated.
Tho following experiment illustrates thie property uf air. A sinall
rubber bag, nearly empty and fasteved at the neck with a stop-cock,
is placed under the receiver of au air-pomp. ‘Then let the air bo
ELASTICITY. i
Pounped out from the reeciver, ee that it no longer exerts pressure:
‘cu the outside of the bag, aod the nir within will expand and folly
inilate the bag.
‘Other exanples of expansibility will be
given horeafter lu Mostrating the effects of
beat.
20, Elasticity is the property which
Deelies possess of recovering their ori
nal shape and size after having been
either compressed or extended.
Bodies differ in their degree of clas-
tieity, yet all are more or less cinatic, Fig.
fodia-rubber, ivory, and whalebone are examples of bighly
elastic bodies. Putty and clay are examples of those wiich
are only slightly elastic.
[air be compressed, ite clusticity tends tw restore it to its original
balk; this property has been vtilized in waking air-beds, alr-cush-
foes, and even iu forming car-sprinzs. If a spring of steel be beut,
ite clastioity tends to unbond it; this principle is employed in giving
metiog wo watches, clocks, and the like. Ifa body be twisted, ite
‘elasticity tovde to untwist it, as ie observed in the tendouoy uf yur
‘aud thread to untwist; thie priuciple, ander the name of torsion, is
tuted to measure the dotlective force of magnotian. If a body be
stretched, its elasticity tends to reduce it to it inal Loagth, ws is
shows by stretching a piece of india-rnbber, aud then allowing to
wag it may
jceular displacement, "Thus,
Whew air ix cwinprosses!, the repulsions between the welerates teud to
expand it. Again, whew a spring is bent, the particles on the vut-
‘sido ure drawn asunder, whilst these inside aro pressed to-
(gether § the uttructious of the former and the repalsions uf the latter
tend to restore the spring to its original shupe,
The most elastic bodies arw aso; after thoin cone tempered stech,
earliness
—
ry; laws, ote.
twethod of showing that ivory it elastic,
12 GENERAL PROPERTIES OF
and at the same timo that the cause of ite
Lar displacement. It represents w polished plate of
: wt rund
° fog « cireular impression om
plate, which fs the larger oie
Dall falla from a grater belgtit.
‘This experiment shows that the
Dall is flntteued each thie by the
fall, that the Hatteuing Tuereases
asthe height inereases, and that
the repelleut action of the cou
prrased iolognles causes 1 to Me
bound.
‘The property of elasticity Is
uti iu the arts in a great
variety of ways. When a eork is foreed into the iouth of a bottle,
Hts clasticity causes it to expand und Gill the neck so ws to render
Doth water and air tight. Tt is the elasticity of air that eausos tndiat~
rubber balls, filled with alr, W rebound when thrown open Bank
subistances. ots (tof use In springs
for inorlng: uuschin the wotion of carriages
lasticity of cords that renders them
ver rough rons. It is th
suitable for iwusical instrusnents. It ie the elasticity oF air SAP reni=
ders it a fit wohiele for transuaitting sound,
Fig. 6
Summary. —
Physical Agents or Forces
A Bolly
Molecules and Atoms
Mase and Density:
Three States of Bodies.
Gextean Peorrnries or Bopies.
Eixtension. — Maguits Fou.
Englieh Moastirns.
The Merrie System.
The Metric Table of Length,
Mesures of Capacity, — Mutrle Table,
COHESION AND ADITESION. 13
Weight. Unite of Weiglt.
Merrie Table of Weight.
Impencteobility. Experiments,
Inertia, Mlustrations.
Porosity. Sensible Pores.
Physical Pores.
Dicisibitity. Wostrations,
Compressibitity.
Exxpansibitity of Gases.
«Liquid,
4 4 Solids,
Bluaticity of rossure.
“ Tension,
4 4 Perion.
4 4 Phexure,
SECTION 1. —SPECIFIC PROPERTIES OF MATTER
ax. The specific or characteristic properties of matter
depend upon certain forces, which are continually acting
between the molecules of bodies. Those which cause
the molecules to altract one another are called Molecular
Porees. They are Cohesion, Adhesion. and Chemical
Affinity, These act only at insensible distances.
‘Phe altimate particles, even of sofid bodies, do not touch one
another, but are kept in plice by the combined action ef forces
of attmetion abil repulsion. Heat is tho repellent fore that toads
fo peparate the molecules; althongh not usually classed asa molec
ular foreo, it here dete ax one, and, like those metitioned, at Insensi-
Me “Chemical attinity bolonge t Chemistry. and will oot
be considered here.
a2. Cohesion and Adhesion. —Couestox is the force
that holds molecules of the same kind together.
Antiesiox holds nnlike molecules together.
‘The jermanont form of solid bodies copends upon cohesion
whieh binds the particles together and keeps them In plac
Tea alitd bedly be Broken vr divided in any way, the parts cannot,
Te Beseral, be mide to evhore by simply Uringiug thew teaether.
4 SPECIFIC PROPERTIES OF
‘Tho season is that the molecules are not brought
each other for cohesion to act. In the brasil so
ever, the parts may bo brought within the 1
attraction, by pressure, by partial oe eae ts
‘Two picces of lead with mnooth, fcahly ent surfices will eobero
strongly if presed finnly together. Several pieces of iron may’
forned into ono cohcront mass by the process of welding, in
the parts are softened by intense heat, and then hammered
Ia pleco of pure india-rubber be ent in two, and the parts pean
together again, they will anite and cohere strongly.
The force of adhesion gives value to mortar, glue, and
kinds of cements. a
Souwriow is due to adhesion. "Thus, when sugar dissolves:
in water, it is because the adhesion between the molecules of
sugar and water is stronger than the cohesion between the
molecules of sugar. When a liquid tends to spread over the
surface of a solid it is sald to wet it, as water upon glass. If
it gathers in globules it docs not wet it, as quicksilver upon
glass.
Tu the firet caso tho force of adhesion between the water and the
gluss overcomes the free of cohesion which would tend to eollect
the water iu globules. fa the secomd ense tho formation of the
globules shows that the foree of cohesion in the inereury is greater
than that of adhesion between the glass and the yoroury.
Fig. 6. Fig 7. Figh *
ag. Capillarity. — When a bexly is plunged into a
Uquid which is capable of wetting it, a3 when a glass rod ia
CAPILLARITY. uw
planged into water, it is observed that the liquid is slightly
elevated about the body, taking a concave form, a3 shown in
Fig. 6.
If a hollow tube is used instead of a rod, the liquid will
also rise in the tube, as shown in Fig. 7. The smaller the
Hore of the tube, the bighor will the liquid rise, and the more
concave will be {ts upper surface. A tbe one hundredth
of an inch fa diametor will support a column of water four
inches high.
Instead of a tobo two plates of glass bronght vory near together
tuay be placed in water, and the water will rise in the space between
tern, ‘Tho nearer the plates, wie higher the liquid will ries. Two
plates one headredth of aa inch apart
will support a column of water two
inches fn height. If the plates are iu
ecoutaet nt the elges ou «mo side, and
lightly separated at the other, as shown
fy Fig. 9, the water takes the shape of
‘curve called the hyperbola.
When a tube is plunged into a liquid
whieh is aot capable of wetting it, ae
when glass is planged inte quick. ———————
wilver, the Liquid is depressed both ou Fig. 0.
the ontside and on tho inside, tuking a convex surfuco, as shown in
Pig.8. The smallor the tube, the greater will be the depression,
sand the more conver wilt bo the upper surfs.
24. Applications of Capillarity.— tt is in consequence of
fuipillary action that oil is raised through the wicks of lamps, to
supply the farne with combustible wnattor. ‘The fibres of the wieks
eave between them * species of capillary tabes, through which the
Of sugar have its lower end dipped in water, the water
the capillury interstices of the sugar aud fill then,
‘out the air and renders the sugar thore soluble than when
FY into water, in which case the contained air resists the
end retants solution,
uf he boat inte the form of « siphon, amd the sliwoet
16 SPECIFIC PROPERTIES OF MATTER.
arm be dipped into a yersel of mercury, the meroury will rise inte
the lead by capillary action, and flowing over the edge of the vessel
will descend along the lower braoch and ¢seape from the lower
extremity. Tn this way the vessel may be slowly emptied of the
quicksilver.
Many fluids may be drawn over the edges of the containing vessels
hy a siphon of candle-wieking or other eapillary sobstanes.
25. Absorption is the penetration inte a porous body, of
any foreign body, whether solid, liquid, or gaseous.
Carbon, in the form of charcoal, has a great capacity for
absorbing gases. Ifa burning coal be introduced into a bell-
glass filled with earbonie neid collected over mereti
volume of the gas is diminished by being absorbed hy the
coal. It is found that the charcoal absorbs in this way thirty-
five times its own volume of the gas. Charcoal also absorbs
other gases in even still greater quantities.
Spongy platinum absorbs hydrogen so rapidly as to heat
the platinum red-hot.
blow and animals we have many examples of absorption,
‘The roots of plants absorb fram the earth the material necessary ts
the growth of the stew and Wranehea.
In tho animal world, absorption plays an Important part in the
process of nutrition and growth. Animal tissues alsa absorb solid
substances. Por example, workmen engaged in handling Toad abe
sorb through the skin and Jouge more or Lees of this eubstance, whieh
often gives rise
When ve
erally aug
To vege
ery merions dive
and animal eu
nces abeorh water, they gea-
This fret explains snany omens ef
% in vO
mn
daily observation.
Wa
again cont
sheet of paper he moistened, it inerewses in size, and
is when dried. This property is ernployed by draughts-
wen to stretch paper ou boants. ‘The paper & moistened, aud after
Lcing allowed to capoud, ite edges ure glued tou draveing-beard 5
wou drying it fs stretched, forming a smooth surfuce for drawing pen.
The same property eauscs the paper to peel fiom the walls of rwont
when ixposed to moisture
When a workin would Wend pice uf wood, le dries eae ship
aind anuisteus the other. ‘The side which is dried evmtewets, anual the
OSMOSE. li
opposite side expands, so that the pleco is curred. It is the absorp.
tion of moisture that eanses the wood-work of houses, fieniture, ete.
to awell and shrink with atincepheric changes, and which necessi-
tates their being painted and varnished. Paints and varnishes, by
filling the pores, prevent absorption.
26. Osmose. — If two liquids of different kinds are sepa.
mited by a porous or membranous partition, ench liquid will
begin to pass through the wembrane and mix with the other,
and after a time there will be a mixture of both liquids on
each side of ihe partition, This movement of the liquids is
called csmose, The currents are generally unequal, sv that
there is an actual gain of substance on one side, and a cor-
responding loss on the other.
‘The current that acts to produce an increase on one side
is called endosmose, and the opposite current is called ex»
der filled with strong syrup be ted to
the figare. The syrup xoon becomes «i-
Inted by the flowing in of water, ari tho
mixture rites in the tobe; at the same
Hime a portion of the eyrop flows oot
avd mixes with the water. ‘The flowing
fn of the water Se endosmose, and the
Sowing out of the syrsp is erosmose.
Siauilar results aro cbtained by using
other
in aniinal and vegetable
> ‘The circulation of fluids ©
‘the tissues and vessels of the
| bedy, the abeorption of water
‘roots of plants, the circulation Fig. We
way wither vital pheuoieun depend upou this
ul
—_
18 SPECIFIC PROPERTIES OP MATTER,
27. Dialysis. —The practical application of the principle
‘of osmose in separating the constituents of a liquid is called
dialysis,
Substances which ane capable of forming erystals will, when in
solntion, readily pass through membranes or porous partitions Pure
sugar and various kinds of salts are substances of this kind.
On the other hand, substances which do not erystallize, like geln-
tine, gum arabic, ete., do not eo readily pass Hirongh septa. Hence
pare orystallizable sugar may, by this procoss, bo separated from the
syrup of sorghum, or that of the beet-reot, which ‘eontaiae gadmny
substances that would otherwise prevent crystallization,
28. Tenacity is the resistance which 2 body offers to
rupture when subjected to n force of tmetion, that is, a
which tencls to tear the particles asunder.
ho tenacity of a body inay be determived ia pounds. For this
purposo it is wrought into a cylindieal form, having a given eroas-
section ; {ts upper end is thou made fast, and a seale-pan Is attached
to tho lower end; weights are then placod in the pam until rapture
takes place. ‘These weights measure the tenneity of the body.
Mewils arc the inort tenacious of bodies, but thoy diffe greatly
from each other in this respect. The following table exhibits the
weights required to break wires of sf} of an inch in diameter, farmed
of the motals indicated :—
Tron
Copper
Platioum
Silver
Gold
Leait
Teh
uf wee
beeu shown by the
'y and confirmed by experiment, that
nders of equal Iongth and containing the same amnount of
waterial, oue being solid and the other hollow, the latter Is the
hls latter prinelple ix also true of cylinders resquired to support
weights; the hollow eylinder is better adapted to resist a erasliiug:
force than the solid one of the same weight, aud hence it ix that
columns aud pillars for the support of Uuildings are wade hollow.
This principle also tudiewtes that the Loues and quills of binds, the
HARDNESS. 19
stoma of grasses and other plaints, being hollow, are best adapted to
sccure a combination of Bgbtiees and strength.
‘Tho tenawity of motals is yreaily increased by drawing them into
wire, Hence eablos formed of fine iron wire twisted together aro much
stronger than chalus or soll rods of the same weight. Such cables
‘are extensively used for suspension bridges and for many other
purpowen.
ag. Hardness is the resistance which a boy offers to
being scratched or worn by another. Thus, the diamond
seratehes all other bodies. and is therefore harder than any
of them,
Por the purposo of determnining the relutive hardness of minerals,
the following senle has been adopted, in which any substance is
scratched by those above it in nurnerieal order: —
Scace or Hanosxess or Moxenas.
1. Tale, 6. Feldspar.
2 Gypsum. 7. Quartz.
K Caleespar. 8. Topaz.
4, Pluor-spar. 9. Sapphire,
5. Ayntite. 10 Diamer
A body which neither seratches nor ix semtehed by any given
smincral of the tale ia aid to bo of the degree of huniness ropre-
ented by that mineral
AT it scratches one of thom, bat is itself soratehod by tho next
ene above it in the scale, the degree of hantness is between the
two with which it ls comparcd. ‘Thus, a pico of tho mineral
ext be seravched hy feldspar, bar will seratch a piece of
‘apatite; hence ita hardooms in betwoon & and 6 of tho vale.
‘Hardness wust vot be confounded with resistance to shocks or
Glass, dismond, and rock-ersstal ure much harder
‘Wan iron, brass, and the like, and yet they are less capable of re-
and forces of compression ; they are more brittle,
Ad alloy or mixture of metals is generally harder than the sepa-
mite motala of whieh it ix compord. ‘Thus, gold and silver ure eof
soetals, anil, in ondor to snake thern hard enough for coins, and joweley,
they are wlloyod with small portion of copper. In order w render
for the manufacture of domestic urensils, it bs
‘quantity of load
i
Hiph
20 SPECIFIC PROPERTIES OF MATTER.
‘Tho property of hardnoss is utilized in the arts. ‘Lo polish bodics,
powders of emery, tripoll, and other hard minerals are used. Dia
mond boing the hardest of all bodies, it ean be polished only by
means of its own powder, Dismond-dust is the most efficieut of
the polishing substances.
30. Ductility is the property of being drawn out into
wires hy forces of extension,
Was, clay, and the like, are s tenacious that they ean ensily bo
flattened by forces of compression, mud readily wrought between the
fingers. Such bodies are plastic, Glass, resins, and the like be-
come tenacious only when heated, Glass at high temperatures is
so highly ductile that it may be «pan into fine threads aud woven
jute fabrics. Many of the swotals, as iron, geld, stlver, and copper,
uso duetile at onlinary temperatures, and are eapable of being drawa
out into fine wires by means of wire-drawing machines.
‘The following metats wre arranged in the order of their ductility =
platinum, silver, iron, copper, gold, zinc, tin, lead,
3t. Malleability is the property of being flattened or
rolled out into sheets, by forces of compression.
This property uften angoents with the temperatures every one
knows that iron is wore esuily furged when hot than when cold.
Gold Is highly malleable at ordinary temperatures Gold is reduce
to thin chects by being rolled ont into plates by a machine; these
plates are cut up in small squares, and again extended ‘by ham
tnoring unti} thoy become extremely thin. ‘They are thea eut up
again [nto squares, aud hammered between membranes, called gokl-
bea By this process gold uiay be weought into loaves so
thin that it would take 282,000, placed vue upou another, to make
an ine in thickness. ‘These leaves are einployed in gilding metals,
woods, paper, aud the like, Silver and eopper are wrought im the
os
amanner as gol
‘Tho tnost malleable of the metals are not necessarily the invest
ductile, Lead and tin, for example, have very little ductility, bat ure
inalleable to a veey high degree. Zino is only slightly malleable
when cold, bat i easily rolled out into sheets nt a temperature ef
300° or 400? F
‘The matleability of the metals is not the same when hammered wa
when rolled, The following is the order of walleability under the
SUMMARY zi
hammer: Zewi, tim, golf, rine, steer, copper, platinum, iron.
Uuiler the mlling-mill the order is as follows: Gold, silver, copper
tin, lead, zine, platinuse, irom,
Summary. —
Specie PRorerres of MATTER
Molecular Forces.
Cohesion, Experiments.
Aherion. Guo und Cements,
Solution.
Copittarity in Tabes.
© between Plates
Applications of,
Absorption
Osnose.
Dialy
Tenocity, Measure of.
“Table of.
of Motals : how
Hardueas
Seale of Hardness
Hardness of Alloys
Votishing Powders
¥
Metals inost ductile
Malleaditity.
Effect of Heat
Goli-beating.
Malleability under the Hanuner
¢ * @ Bolling-mill
Ductil
CHAPTER II.
MECHANICAL PRINCIPLES.
SRCTION |. MOTION 4¥D FORCE,
32. Mrcnantes is that branch of Physics which treats
of the laws of vest and motion. It also treats of the
action of forces upon bodies.
93. Rest and Motion.—A body is at nesr when it re-
tains its position in space. It is in morrow when it continu-
ally changes its position in space
A body is at rest with respect to surrounding bodies, when
it retains the same relative position with respect to them, and
itis in motion with respect to surrounding objects when it
continually changes its relative position with respect to them,
‘Those states of rest and motion are called Relative Rest and
Relative Motion, to distinguish them from Absolute Rest ane
Absolute Motion.
Whew borly reais fixed on the deck of moving vessel or boat,
it in at reat with reepeet to the parts of the vessel, although it par-
takes with them Iu the common motion of the vessel. When a muah
walks abont the deck of a -vesscl, he is in motion with respect to the
t with
yarts of the vessel, but he may be at n spect to objects an
fast nw tho wetsel
sails, but fa an opposite direction, In consequence of the earth's
# and about the
solar system throagls sy
shore; this will be the caeo when ho trivels a
anotion
of the whe
of our systeun is in a state of «
pund its a on, together with the motie
it is wot Jihely Chat any yaar
lute rest at any tne.
34. Uniform Motion is that m which a body passes over
equal spaces in equal times. Thus, every point on the sure
LAWS OF MOTION. 23
face of the earth Is, by {ts revolution, carried around the axis
with a uniform motion.
Ta this kind of motion the space passed over in one second
‘of time is called the reforvty, Thus, if a train of cars travel
uniformly at the rate of 20 miles per hour, its velocity is
29.3 feet. Instead of taking a second as the unit of time, we
might adopt a minute or am hour, In the same case a8 before
wo might say that the velocity of the train is one thin of a
mile per minute, or twenty miles per hour.
35 Varied Motion — Accelerated and Retarded
Motion. — Vamp Mortox is that in which n body passes
‘over unequal spaces in equal times. If the spaces passed over
in equal times goon increasing, the motion is accoleroted ; such is
the motion of a train of cars when starting, or that of a body
falling towards the surface of the earth. If the spaces passed
over go on decreasing, the motion is refarded; such is the
motion of a train of cars when coming to rest, or thatof a
body thrown vertically upwanis.
When the spaces passed over in equal times are continually
Ineressedl or decreased by the same quantity, the motion is
natformly accelerated, o¢ uniformly retarded, ‘The motion of
a body falling in a vactwum is witfornly accelerated ; that of a
hody shot vertically upwards in a vacuum is uniformly re-
teareked.
36. Laws of Motion.— The principles of Mechanics
are all based upon three propositions, known as New-
ton's Laws of Motion. ‘The following is—
First Law. — Zeery body continues in «
‘of wuiform motion in a straight Line unless it te
aieted upon by some external force. This is called the Law of
paeryed because ft depends upon that property of matte
“What we beady ennuot ser itself iu motion, and that hodios set in
‘Wotlon teil to wove ii straight lines, are facts that are verified by
0 that stnte of motion is ws natural to 0 body
uu MOTION AND FORCE.
as a stato of rest, but a little consideration of certain facts will show
that this is also true.
In the firet place, it may be observed that whenever a moving
body is brought to rest it is iu consequence of resistance of some
kind; und in proportion as the resistance is removed the mation is
Jonger continued, ‘Thus, a ball rolled along the ground will seu
be stopped ; if rolled with the saine force upon a smoot: Boor it will
go much farther, and still farther if rolled along m smooth shect of
jee. We cannot prove that it would continue to move on Gniformly
forever if thers were wo resistance, but we amay infer that it would
from tho fact that the Joes tho resistanoe the moro walform t¢ the ate
of motion, and the longer it continues to move.
38. Newton's Second Law. —Tho following is New-
ton’s Second Law of Motion : —
Motion, or a change of motion, is proportional to the force ine
pressed, and ts in the direction of the line in which that force wets,
ndlerstand the action ofa force, three things mirst
t3 point of application, its direction, and Its intensity.
The point of application is the point where the force exerts
its action.
The direction of a force is the line along which it acts,
The tuteasiy of a force is the energy with which it note.
In ord
be known :
‘The intensity of » force ix weasured ko waits vf weights ths, a
foree of fifty pounds is the force required to snetuin a weight Of fifty
pounds. Tho intensity of a force may be ropresented by a distance
nid off on its ne of direction. Assuming some unit of length, say
‘ono tenth ofan inch, to represent one pound, this is set off as snany
nes aus the force contains pounds.
c, The diagram here sven represents twe forces applicd
voint A, and acting ut right angles to each other
Baud C respectively. Let the force which acts
from A townrds I
equal twenty pounds,
awd that whieh ans
from A to @ equal teu
A+ ——_——_-»_ pom.
Fig. 11 Adopting the seule
LAWS OF MOTION, 25
of ope tenth of ax inch to the pound, the line A B must be two inches,
aud the line 4 Cone inch in length, to represent correctly the relative
intensity of the two forces.
39. Simple and Compound Motion. —Simple motion
is produced by the action of a single force. Compound
motion is produced by the simultancous action of two or more
forces. When a body is acted upon by a single force it will
‘more in a straight line in the direction of that force.
If a body fs acted upon by two or more forces in the *ame
direction, it will move with an intensity represented by the
eum of the forces. If acted upon by two forces in opposite
directions, it will move with an intensity represented by the
difference of the forces, and in the direction of the greater
force.
Tf two or more forces uct upon a body, neither in the same
Hor in opposite directions, but in lines forming some angle
with exch other, it will not, in general, move in the direction
‘of any one of them, but will move in some intermediate di-
rection as if impelled by a single forec.
In any of those cases the single force which resulte from the
combination of two or several foreen ix called their Resultant.
The separate forces are called Components of the resultant.
40. Parallelogram of Forces.—In the disgram let
ABand AD represent wo forees acting at A, their resul-
tant will be represeatod by
AC. Thatis,ifteo forces a
are represented in direction ~ \
n\
ed tn direction and in- wig. 42
ze Hat diagonal which passes through their point of
is called the Paratlelogram of Forces.
of finding tho resultant when Ove comyo-
26 MOTION AND FORCE.
nents are given is called Composition of Forces; the revere
operation is called Resolution of Forces,
ny “When two forces:
off distances
ant AC is known,
Fig 1% and the directions
of its
are given, we draw through C the lines @D and @B paraltel
to their directions; then will the intercepted Imes A D and
A B be components of the force A C
41. Example of Composition of Forces.—A bind, in
flying, strikes the air with both wings, and the latter offers a
LAWS OF MOTTON. aT
resistance which propels him forward. Let A Kand AH, in
Fig. 14, repreacot these resistances. Draw A B and AD equal
to each other, and complete the parallelogram 4 C; draw also
the iagonal AC. ‘Then will AC represent tho resultant of
the two forces, and the bird will move exactly as though im-
pelled by the single force C4.
42. Example of Resolution of Forces, — When a sail-
boat is propelled by a breeze acting on the quarter in the
direction va (Vig. 15) we may, by the mule in Art. 40,
resolye the intensity of the wind imto two components,
one, éa, in the direction of the keel, and the other, a6,
Fig 1
‘at right angles to it. Tho first component alone is effective
fn giving © forward motion to the boat, whilst the second
is partly destroyed by the resistance which the water offers
to the keel, and partly employed im giving a lateral motion
to the boat. ‘This lateral motion is called leeway.
43. Resultant of Paralle] Forces, — When two forces
act in the same direction, as when two horses pull at the ends
of a whiftietroo
to draw a wagon, their resultant te equal to the
When they act in » contrary direction, as
of a steamboat ascending a river, where the force
nets to propel the boat forward while the cur-
ita progress, their resultant is equal to the
28 MOTION AND FOROR.
44. Composition of more than Two Forces. —If
more than two forces net upon the same point, the resultant
of any two may be combined with a third, this resultant with
a fourth, and so on. ‘The Inst resultant will represent the
combined action of all the given forees.
Summary.
Mnciaxacan Prixcrniics,
Best and Motion.
Absolute.
Relative
Uniform Motion.
Velocity.
ated Motion.
Retarded Motion.
Laws of Motion,
ewtou's First Law
‘The Law of Inertia.
Mlustrations
Newton's Second Law
Point of Applica
Intontity of For
Direotion of F
Meaauro of Intensity.
Simple and Compound Motion
tions of Force.
Components
ultant
sgrain of Poree
Composition of Pore
Resolution of Ferees. — Example
— Example
Resultant of Parallel Forces.
Composition of more than Two Forces
45: Momentum. —7%e Momentum of a body is ite querntity
of motion
Tt may
which a body moves.
If the same amount of force is employed in putting in
motion bodies of different weight, it is evident that the
Iso be defined as the measure of the force with
MOMENTUM, 29
greater the weight of the body the less will be the velocity
imparted. A force that will move a body of one pound
weight through ® space of ten feet in a second, will move a
body weighing two pounds through only: half the space in the
samo time.
Tt is evident, howover, that the quantity of motion will be
the same in each case; for if we suppose the larger body to
be divided into two equal parts which move side by side,
the sum of the distances described will be equal to the dis-
tance through which the body weighing one pound will move
in the sane time.
Of two equal masses that which moves with the greater
velocity has tho greater momentum ; of two unequal masses
having the samo velocity, tho heavier mass has the greater
momentum.
Momentum depends, therefore, upon weight and velocity,
and may be estimated by the following rule >—
Multiply the weight of the body by its velocity.
Example What is the moinentam of » ten-pound ball moving wt
the rate of 500 feet per seoond
10 x 900 = 6000, “Ans.
Tt will bo acon that nesarding to this rule bodies of immense
weight may mave with great foree, though the rateof motion may
de very slow. For example, an icoberg, whose motion is hardly
tuay exert o tremendous crushing foree upon any object
with which it comes in contact.
A Marge veese) moving slowly up to a wharf hos so great ino
tentum that wuleas some proeaution be uscd thero is dangor of
damage both to the vessel and the wharf. To prevent this it is
¢eatomary W place a coil of rope or some other elastic nnd yielding
Ietween the sides of the ressel and the wharf.
(Ot the other hand, a body of very small weight may move with
Veloeity eo great as to exert a creater force than a lange body wor-
ing Hlowly. Thus, « bullet fired from a gun hes a greater momen-
tam than a stoue many times heavier thrown from the hand,
"48. Collision of Bodies. —The term momentum, as now
“generally used. refers only to the force expended \o Yee
—
80 MOTION AND FORCE.
motion of the moving body itself, and to its power of com-
munieating motion to other bodies, ‘This does not represent
the whole effect which a moving body prodaces upon another
body upon which it strikes.
Tf bullet ts fied into a wooden block, which ix suspended by a
cord so that it is free to move, the momentum of tho bullet ia trans
ferred to the block, and the momentum of the block afer impact Es
equal to that of the ballet before it strikes. But the foreo of the
bullet is not all expended in setting the block in motion; it pene
trates the block to a groator or leas extont according to ite volocity-
If the whole of the force with which a body moves is
upon an immovable obstacle, it is found that the effect produced is
proportional to the square of the velocity.
‘Thus, suppose a bullet to be fired into an immovable Wook, with
1 force that causes it to penetrate to the depth of one Sich 5 if ik stile
the block with tioice that colocity it will sink into it four Inches; or
with three times the velocity, to the depth of uine inches.
47- Striking Force. — The power of a moving body to
overcome resistance 1s called its striking or living force (vis
viea), and is proportional to the «quare of Ue velocity.
Tt appears, then, that two bodies may have the same momentum
and at the eame time differ greatly in their striking foree.
For example, an iron ball weighing 40 pounds and moving 300
feet per eocond, and a # xl hall weighing 5 pounds and moving:
1,000 feet per second, will lave the 5,000). The
striking foree of the first will equal 50 x 100* 500,000, "That of
the second will be equal to 5 x 10008 = 5,000,000, Hence, if both
bank of oarth, the second would penetrate ten
‘This subject will be further treated of «m=
aine 1nementam
re thrown against
dor tho heal of Energy
48. Action and Reaction — Newton's Third Law.—
We use tho torm Aetion to denote the power which 2 moving
body has to impart inotion or foree to another body, and the
term Reavtion, to express the power whieh the body acted upon
has to deprive the acting body of ite motion or force, or to
impart motion in an opposite direction.
ACTION AND REACTION. a1
‘The following is Newton’s Third Law, which expresses the
relation of these two forms of force.
Action aud reaction ore always equal, and are in opposite die
rections.
49. Reaction in Non-Elastic Bodics.— Let two bulls
of elay or spine Other uoo-clustic sabstance bo senei hy cords
of equal Iengtl, so as to bang side by side =
in front of m graduated are, ae shown in
Pig. 16, If one be drawn aslo and let fall
80 as to strike the other, beth will move
foeward, but not so far as tho first would
have moved alone. If the tuills are of equal
sass, the two will move tezether through
half the distance that the first alone would
have traversed, The first ball loses belf its
meomentom by the reaction of tho sceand,
wed the scoond gains precisely the samo
antecut of momentain by the action of the
first. The momentum of the coinbination therefore remains the same
after impact as beforo.
50 Reaction in Elastic Bodies. —If two equal balls
of some elastic substance, a ivory, be similarly placed, and
the same experiment repeated, the first ball will give the
whole of Its motion to the second and remain motionless,
while the second ball will swing as far as the first would
have gone had it met no resistance. In this case, aloo,
action and:reaction are equal; = —
for the same amonnt of force
required to stop the first ball
enifices to give an equal mo-
How to the second.
enw princpto may te CS
I tins
Reeeietety on
io Pg 17 Fig. 7
Eat the tall A be drawn out a certain distanee and let fall
‘pon G, the next in onder; it will thea comummicate ‘ha ween
32 MOTION AND FORCE.
to Gand recive a resection fromm it whieh will destroy ite own
tnotion.
But the ball G cannes wove without
it reecived from H to F, and reviving from Fa reaction srtich will
atop ite motion. In like mainner the motion and mesction mre re-
ceived by every one of the balls J, D, C, 2, A, amit the Yast tell, A
is reached ; hat there being ov hall beyond A to act upou ity AC wilt
fy off as far from A as 27 wos denwn spurt from G,
These results would be strietly as stated if the balls were perfoesly
elastic. In practice it wilt be found that the Tast teill will sot trove
quite #0 faraa the theory requires, while the whole syetom will be
slightly throws forwani by the force of the first ball,
A few Gmiliar and interating Ulustrations of this Liw may corre
to call the attention of the stadent te the large sumber of examples
he meots with iu his every-day life.
The flight of birds, tl motion of the steamboat, the
rebound of the baruiner from the anvil, the meeodl of « gum, the
ascent of a rocket, are common examples of the law. When we
strike the table with the hand, it is the reaction of the table thar
hurts the hand; so, when we spring from the ground, the earth i
really pushed away from ux The motioa i not seen, however,
beewuse it is diffused through so large a mass
Fig 18
5t. Reflected Motion. — When an elastic body is thrown
against a hard, smooth surfu
If it be thrown In a direction perpendicular to the surface, it
will rebound in the same directi if thrown obliquely, it
will rebound obliquely in an opposite direction. ‘The dire
tion in which the body approaches the reflecting surfuce is
its Line of dneidence, and that in whieh it rebounds the Lime
CENTRIFUGAL AND CENTRIPETAL FORCES. %3
of Reflection. "The angle included between the line of inei-
dence and a perpendicular to the surface is called the Angle
of Incidence. “The angle Included between the line of reflec-
tion and the perpendicular is called the Angle of Reflecti
The Angle of Reficetion is equal to the Angle of Incidence.
‘This is the Low of Reflected Motion.
Tr the Mastration given in Fig. 18, 4 ball shot from A will be
rotleetod at B back to C, making the angle CB D equal to A BD.
The law hore given applics not only to the motion of solid bodies,
but to all forees which uct in straight Lines and are expable of mite:
fioa. It is especially inoportant in ite application 1 the lawe of
Heat and Light.
§2- Centrifugal and Centripetal Forces. — The Cen-
trifagal Force, 60 called, is not properly-a forve, but is simply
& manifestation of inertia. It is the resistance which a moving
body offers toa force which ‘tends to tam it from its course.
‘Th consequence of its inertia, a body always tends to move
in a straight fine, and if we see it move in a curved line it ix
heeause some force is acting to turn it from its path. This
deflecting force has been called the Centripetal Force, because
ih cireuiar motion it tenils to clraw the moving body towards
the centre of the circle
If a ball ts whirled about the hand, being retained by a
string, it lias a continual tendency to fly off, which tendency
is resisted by the strength of the string ; the tendency to fly
off Es due to the centrifigul force, and Laat which resists this
tendency {s the centripetal force.
‘The curved path it which a body movea may
be reganied as nado up of short straight lines ;
and if at any instant the centripetal foree is de-
stroyed, the bely will continne to move along
‘that Tine on which it was sitnated, that is, ite new
‘be tangent to fis old one.
Th the example given abore, if the string is Fig. 16.
broken fn whirling, the eentripetal foro no longer obs 3
‘nets, and the ball in consequence of its inertia woves on in a straight
Mine which is tangent to the circle, ax shown in Pig. 19.
—
‘The existence of the centrifugal force may be shor
ally by the apparatus represented in Fig. 20. Tn
AB, having its ends bent up so as to held a wiro |
‘between them. On this wire two ivory bulls are st
alide along it, and the whole bar is inade to turn al
right angles to it by means of « cranie and two
‘When the bar is made to revolve about the axis, the lal
y the contrifugal force, are thrown against the end af
‘an energy which becomes greater as the wotiun of revo
more rapid.
Fig 2.
53. Some Effects of the Centrifugal Force. —When
‘a train of ears turns round a curvo in the road, the centrifugal Saree
tenis to throw the train off the track, a tendency which is resisted by
rising the outer rail and by making the wheels conical,
It ia in consequence of the centrifugal foreo, that tho mud adhering
1 the tire of a earriago-whoel is thrown off in all dirmetions.
Ta the elreus, where horses are made to travel rapidly around in a
a =
CENTRIFUGAL AND CENTRIPETAL FORCES. 85
curved path, the centrifugal foree tends to overturn them outerunts,
which tendency & partly overcome by making tho outside of the
track higher than tho inside, and partly by both hore and rider
inclining inwards, so as to make the resultant of their weight and
the centrifugal foree perpendicular to the path,
When a sponge filled with water and held by a string is whirled
rapidly around, the eentrifiygal force throws wf the water and leaves
the spongo dry.. This priveiple has been used for drying clothes in
tho laundry.
A very remarkable effet of the centrifugal force is the fattening
of our earth at the poles. ‘The earth tarne on its axis every twenty~
four hours, which rotation gives riew toa centrifagal furce at every
point of its mefaee. At the oyuator tho eontrifagal force ix groatest,
because the velocity fe there the greatest, and from the equator it
grows fecblor towards cach pole, where it is ero. The centrifugal
foree ut every point Is perpendicular to the axis, aud may be resolved
into two components, one directed outwards from the centre, and the
wther perpendicular to this. The former component lessens the
weight of bodies, and the lattor acts to heap the particles up towards
the equator, It has been found that the earth is a sphervid, fattened
‘at the poles, The polar diaunotor is about twenty-rix iniles ehorter
than the equatorial diameter. Observations
upon the heavenly bodies show that other
planets are in like manner flattened at their
‘The manoer in which the centrifugal
free acts to Hatten & ephere is shown ox-
Perimentally by an apparatus represented
in Fig. 21, This apparatus consists of a
‘vertical rod to whieh « motion of rontion
tay be iinpartel, as shown in Fig. 20.
At the lower part of this red four strips
of brass are firnly fastened and bent into
‘ciccles, a8 shown by the duttad lines; thelr
fonds aro fastened to a ring whieh is Fig. 21.
@ alide up anil down the rod. When theaxls is made to revolvo
the centrifugal force cause tho ring to slide down the rod,
become more curvel, as shown in the figure, wnd the whole
wetinnes the Appeurance of a flattoued sphere.
a
86 MOTION AND FORCE.
‘Thore Is a tendency in all bodies to revolve about thelr shortest
axis, and from this fret wo infer that the earth will always roainiain
{ts present rotation about its shortest or polar diametor.
is principle can be verified in various ways. If a-eylinder bo
suspended by « string whieh is attached # litle 10 one side of tho
‘longer axis, and thea be made to revolve rapidly by twiating the
string, the cylinder will change its position aud revolve uboet as
axis perpendicular to its length; that is, it rotates about ite shorter
axis.
This raw
one, chia
tendency is observed if, instead of a wylinder, we use a
rite.
54. The Gyroscope (Fig. 22) is an instrument to illustrate
the composition of rotary motions, It consists of a disk, 7)
revolving in a ring, ©.
‘The disk is wade to rotate by winding #
cord about the
ing it of | W
of the axis is placed upon the pivot,
instead of falling, the whole begins to re-
in a horizontal plane about
the vertical support, Pg. If the ring, @,
be dopressed while the disk is in mation |e
will rise again and rovolve Tu the same
Fig. plane as before.
‘This motion Is the resultant between the foree of gravity and the
rotary motion of the wheel.
volve rap
Summary. —
Momentum
Quantity of Motion,
Relation to Yolocity and Weight.
Rale for fiadiag Momentuin.
Exauiples.
Coltision of Borties
Seri
Rule for Stri
Exauipl
GRAVITATION, 87
Action and Reaction,
Newton's Thint Law.
Reaction in Non-Elastic Bodies.
«© Elastic Bodies.
Faxiitiar Ulustrations.
Reflected’ Motion.
Lines of Tncidence and Reflection,
Angles of Incidence and Retleetion,
Law of Reflected Motion.
Mlustration.
Centrifugal and Centripetal Forces.
Centrifugal Fores or Manifestation of Inertia.
Curved Path of a Moving Body made up of straight Hines,
Mlustration,
Effoets of Centrifagal Fores.
Spheroldal Shape of the Barth.
Experiments.
The Gyroscope,
SECTION I, —TRINCIFLES DEPENDENT ON THE ATTRACTION OF
GRAVITATION.
55 Universal Gravitation. —The earth exerts a force
of attraction upon all bodies near it, tending to draw them
towards its centre. This force, called the Force of Growity,
when tnresisted, imparts motion, and the body ts sald to
fall; when resisted, it gives rise to pressure, which is called
Weight.
Newton showed that the force of gravity, ms exhibited at
the cartl’s surthee, is only » particular case of a general
‘sitraction extending throughout the universe, and continually
toning to draw bodies together. ‘This goneral attraction he
called Unirersal Gravitasion, Ut is mutually exerted between
any two bodies whatever, und it is hy virtue of it that the
Treayenly bowlies are retained in their orbits
—
38 MOTION AND FORCE.
‘Tho law of Grsvitation discovered by Newrox, may bo ox-
prussed as follows: Any tio bodies exert mpan each other « muta
attraction, which varies directly as their masses, and inversely as
the equare of their distance apart.
‘The first pert of tho law can te best explainal by lemurs
When a stone falls to the earth there is a suutual attraction betwee
the earth and the stone, hat the ninet of the former iso mueb greater
than that of the latter that no perceptible effect & prodoed epom i
by the stove. ‘The attractive influence of the earth is not confined to
objects in its immediate vicinity, but is felt alo by the sun, moon, and
planets, and these in tur attract the earth. By the superior attrac
tion of the earth the moon is compelled to be dts constant attendant
in it comwles journey Uhrvogh space, The sum by yirtae of ite
greator mass keops the planots in their orbite and preserves the ir
mony of the solar system. If a leaden Lol be suspended near the
precipitous side of a mountain, there will he notiond a leaning of the
ball from the vertical towans the mountain,
When we say that any two bodies exert upon each other a
mutual attraction that varies directly as their masses, wo
mean simply that if one contains twice as much mass as the
other its power of attraction is twice as great as the other;
if its maas is one half as great as that of the other, its power
of attraction will also be
one half as great,
The sveoud. purt of the
lave, that the attraction of
the bodies varies inversely ms
the equate of their distance
apart, may be farther fils
tuatod by Pig. 23. Let She
the centre of attraction, and
the diverging Ives the lines
of the attractive furee, At
the distance frown the peat
Pig, 23. S the four lines of attraction
evelows the tingle squary A, and hence it receives the fall farce of
the attraction, The squire J ix four times as largo ax Ay but
receives only tho maine amount of attraction; that ts, the attrnetion
GRAVITATION. 39
‘sproul over four times ws mach space, so that a portion of B equal
size to A would only be attracted one fourth as much.
At is plain, then, that as the distance from S increases tho attrac-
tion decreases, and a» the distavoe decreases the attraction increases,
showing an darerss ratio. We also see that while the attraction of
one of B's squares ie four tires low thon A's, it is only teice ae fur
from 8; hence, to ascertain the ditainution of attraction at B we
maust equare ite distance from S comparyd with A's distance. C in
nine times as large as A und three timesas far from 8; the altraction
‘of one of its aquares will be one ninth of A's,
Sinow all bodies attract one another we should naturally suppose
thet any two bodies on the earth's surface wonld come together, as
two books placed upon a table; but the superior attraction of
earth binds them to the table, and this neutralizes their mutual
itrwetion.
55. Effect of Gravitation on the Planets. —It is by
the influence of gravitation that the planets are retained in
their orbits. Their motion is the same as if they had been
projected into space with an impulse, and then continually
drawn from the right lines along which inertia tends to carry
them by the attraction of the sun. The planets also attract
the sum, but their masses being exceedingly small in com-
parigon with that of the sun, their effects in disturbing its
position are very small, The orbits of the planets are ellipses,
differing Nut little from circles.
57. The Force of Gravity is that force of attraction
‘wiiieh the earth exerts upon all bodies, tending to draw them
towards its contre.
As bas born stated, it ix only a particular cuse of Univer-
sal Gravitation. It is, therefore, subject to the same law,
hat iS, it varies directly as the mass of the body acted upon,
twee” of its distance from the centre of the
Rete darth has been shown by carefill mensuirement to
De that of a eplidroid, that is, of a ephero slightly flattened ut the
——_
40 GRAVITATION,
poles. The mean rudius is» little less than 4,000 :mikes. Ons nerotint
of the fatiening of the earth at the poles, dilierent points are at
slightly ditferwnt distances from the contre, and consequently the fers
of gravity varies slightly at differrnt places on the surfice For
ordinary purposes, however, we may regard the earth as a perfect
sphere, aud the foree of gravity ax coustunt all over its surface.
58. Vertical and Horizontal Lines. — A Vitertoat.
Linx is a Tine along which a body falls freely. All vertices!
lines are directed towards the centre of the earth, but for
places near together they may be reganted as parallel.
In Fig, 24, the lines «0 avd bo are vertical, but if they are wot fir
apart, their convergence is so sinall that they mny be siken ws pur
allel, 1, howewer, their divtan is considerable, they eanmot
be regarded ns parallel. A man standing erect has his bedy in a ver=
tical, and it may hoppen that two poreons on oppoeite sides of the
globe, ax nt and 2%, may both stand erect, and yet thelr heads
Je tured in exactly opposite directions, thoir fect being fumed
wants each other, Points whero this may happen are sald t be
emntipodes.
A Honzoxran Luxe, or Puane, at any place is one which
is perpendicular to a vertical line at that place. ‘The surface
of still water is horizontal, or level. For small arcas this sur=
fhoe may be reganted as a plane, but when a large surface i
considered, as the occan, it must be regarded as curved, eon-
forming to the general ontline of the earth's surface.
CENTRE OF GRAVITY. 4
Upon the principle of verticals and horizontals all of our
instruments for levolling and making astronomical observa-
tlons are constructed.
5$9- Weight.—Tho Wesarr of a body is due to the force
of gravity, aeting upon all ite particles, but it mast not be
confounded with the force of gravity. Weight is only the
effect of gravity when resisted; when gravity is unresisted
it prodaces quite anothor effect, that is, motion,
At th same place the weights of bodies are proportional to their
fuastes, of the quantities of maxtor which they contain, We shall
see hereafter that the weight of bodies may be dotermined by means
ef the Valance; the fore of gravity is determined by tho velocity
which it can impart to a body in a certain time, as will be shown
rnore fully berenfter
60. Centre of Gravity. —The Cextnr or Grayrry of a
body fs that point through which the direction of its weight
always passes,
We have seen that the weight of a body is the resultant of
the actlon of gravity upon all of its particles. Now, whatever
ray be the form of a body, or whatever Its position, the dirce-
tion of its welght always passca through a single point. ‘This
point is the centre of gravity. Hence, in calculations, the
weight of m body may be considered ax concentrated in the
centre of gravity,
‘The vortical lin= hich passes throngh the centro of gravity
fs called the line of direction.
Th the ense of solide of rogular figure and uniforin density, the
contre of gravity ta at the eentre of the figure ‘Thos the centro of
gravity fm aphere, a cube, or a regular octahedron, is in cach eae
at the contre. In a eylinder ic is at the centre of the axis; in a
pa at tho intersection of itn diagonals; in n pyramid,
om its axis at one fourth of ite length from the base
In plates or shoots of wniform thickness and density, the centre of
gravity Isat the contre of she surface, or rather at the middle of the
‘short line which joins the centres of the opposite eurfaces,
2 GRAVITATION.
‘Who the surface is of irregular outline the position of the centre
of gravity may be found in the followlng way: —
Suspend tho body by avy part of its edge eo that it ean move
freely, and, by moans of plumb-tine, mark on it a vertical Line from
tho point of suspension ; again euapend it froin some otbier point of
the edge and mark the vertical line; the pout where these lines in-
torset will show the contro of gravity.
By «similar method the position of the centre of gravity in any
solid body inay be dotormined; for it will always be found at the in-
terseetion of any two lines of direotia
In gotne cases the centre of gravity it not within the substance of
the body itself, us, for example, ina ring, a bow, or a cask; yet its
recively the same way.
y bo determined
Fig. 26. Pig. 26.
61. Equilibrium of Heavy Bodies.—Tho centre of
gravity being the point at which the weight is applied, it
follows that, if this point ia held fast by any support what-
ever, the effect of the weight is completely counteracted, anid
the body will be in a state of equilibriam,
Tf a body has but « single point of support, it ean be in
equillbrinn only when its centre of gravity lies somewhere on
a vertical throngh that point
EQUILIBRIUM. cd
If a bosly has bub two points of support, it can be in
equilibrium only when its contre of gravity lies in a vertical
drawn through some point of the line joining these two points,
An example is shown in Fig. 25, which represents a man
standing on stilts. ‘To be in equilibrium, his centre of
gravity must be exactly over the line joining the feet of his
stilts.
if a body has three supports not in a straight line, it will
be is equilibrium wlien the centre of gravity lies on a vertical
drawn through any point of the triangle formed by joining
these points. An example is shown in Fig. 26, which repre-
sents a three-legged table. ‘The centre of gravity being at
gs the table will be in equilibriam 60 long a8 the yertical
through that point pierces the triangle formed by uniting the
feet of the tuble.
Pye 27. Fig. 28.
62, Different Kinds of Equilibrium. — When bodies
are acted upon by the force of gravity alone, and have one
OF moro points of support, three kinds of equilibrium may
exist Stable, Unstable. and Newtrat Equilibrium,
1. Selle Ryuilibrium.— A voy ix in stable equilibrium
When, om being slightly disturbed trom its state of rest, it
tends to return to that state.
Be the case when the contre of gravity is lower
SAR L
in its position of rest than it is in any of the veighiboriug yo-
ES
Hh GRAVITATION,
sitions, for in this case the weight of the body acting at the
slightly disturbed from the lowest position, the weight will act
to draw it back, and so establish the equilibrium.
We have an exanple of stable equilibetum represented fa Figs. 27
and 98 which represent iinages often wet with in the toy-xbops If
the image We inelined to one side, as shown in Pig. 23, it will ly its
own weight right itself, and tke tho position shown in Fig. 27.
‘Thess figures aro hollow and light, and aro ballasted with Med at
their Lower part su a9 to throw the centro of gravity very low. “The
result Ix, that when the figure is inclined, the centre of gravity i
raised, and the weight acte to restore it. ‘The figure settles im its
pritnit te of rest uly aftor several sel
lations, are duo to the inertia of the
body, ‘The explanation. of this oscillation is
that given for the peeillation of the
the saine
dulum.
When tho contre of gravity is considerably
below the polut of support, a body may be in
stable oqnilitriun even when the base is very
narrow, ‘Thus a cork with two pocket-knives
sticking uf muy rest upou the point of « necille and De in stable
oquilibrimn, as shown in the figure. In this ease the heavy ban
of tho knives bring the contre of gravity below the point of suppor.
Tn the case of the toy shown
in Fig. 30, tho hoxey Dall ut-
tuched to the figure brings the
contro of gravity of the whole
below the points of support. Tt
is therefure another exatple of
stable equilibrium,
2. Unstable Bquilibrinne.
—A body is in umalable
equilibrium when, on being
slightly disturbed from its
state of rest, 1t does mot
Fig. 20 tend to retum to that state,
hut continues to depart from it more and more.
Vig. 2
STABILITY OF BODIES. 45
‘This will be the case when the centre of gravity is higher in its
position of rest than tn any of the neighboring positions. When the
edly fs slightly disturbed, the weight sets not only to prevent its
retarn, bint also to canse ft to descend still lower.
8. Neutral Equilibrium. — A body is in neutral equilibriem
when, on being slightly clisturbed, it has no tendency either
to return to its former position or to depart farther from it.
‘This will be the case when the ceutre of gravity is at the xune
height whoo at rest as in nny other position ; for example, in a ball
resting upon a horizoutal table,
Examples of the three kinls of equilibrium are given in Fig. 81.
‘Tho cove A is tn stable equilibrium, because its contre of gravity is
ut its lowest possible position. The couo 2 is in unstuble equilibrium,
for thongh it may possibly be balanced on its apex, the slightest mave-
koout will throw the Hine of dircetim beyond the bave and the cone
will fall. The cone € is in neutral equilibrium, bocanse, if it is rolled
nround, the contre of gravity will not be raised or lowered.
B e
Fig. 3
63. Stability of Bodies. —From what, has heen said in
the preceding articles, It follows that bodies will in general be
most stable wlien their bases are largest, For in such casos.
“even afer a considerable inclination, the line of direction
of the weight will pass within tho original base, and the
‘weight will act to return the body to its original state of rest.
Hence chairs, lamps, candlesticks, and many other familiar
tensile, are constructed with brond bases, to rnder them
more stable,
The leaning tower of Pisa in sy much inclined that it appears
Abest to all; yor it stands, becwuse the vertical through the centre
OF gravity posses within the base of the tower. - BZ represen,
———
46 GRAVITATION.
‘a tower at Bologna, which is even more inclined thaw that at Pisa.
‘This towor was bnilt in the year 1112, and revolved its inellaation
from unoqual settling of the ground on which it was built. Tt docs
not fall, beeanso the vertical through the contro of gravity, @, passes
within its base.
Fig. 82
In tho cases considered, tho position ef the contre of gravity re
tains the same for the same body. With men ond animals the
Position of the centre of gravity changes with every change Of mttie
tude, which requires a proper adjustinent of the feet, to maletain a
position of stability.
When a man carries « burden, as shown in Fig. 33, be leans for-
wand, that the dircetion of his own weight with that of Ns Banden
fas naes between his feet. Wheo a man carries a weight in ono
=
SUMMARY. 47
hand, ms shown in Fig. 34, he throws hix body toward the opposite
tide for the same neaain.
In tho art of ropo-danclng, the great difficulty consists iu keeping
the centre of gravity exactly over the rope. To attain this rewult
the more easily, a rope-danicer earries x long pole, called a balaneing
polo, and when he fecls hitneelf inclining towards one side, he ad-
ennices his pols towahls the other side, so as to bring the common
eontre of gravity over the rope, thus proserving his equilibriam. The
rupe-dancer Ia in « couthiual state of unstable eqeilibeinm,
‘Law of Tniversal Gravituion.
Motiqn of Planets to their Orbits.
Tervestrial Gravity.
Law of Terrestrial Gravity.
Gravity at Different Places on the Earth's Surface.
Vertical and Horizontal Lincs.
Weighe an Bifieot of Gravity.
Centre of Gravity.
Line of Diretkn.
Position of Centre of Gravity in Bodies of various Forms
“Cente of Gravity fn Stable Equilils
ons
GRAVITATION.
Eqquitibrium (continued).
Unstable Equilibriun.
Position of Centre wf Gravity,
Noutndl Equilibrium.
Position of Centre of Gravity.
Examples,
Stability of Bodies. r
L
\ning ‘Towers.
Equilibrinn of Men and Aaiinals.
Rope-daneing.
64 Laws of Falling Bodies. — When bodies starting
from a state of rest fall freely in a vacuum, that is,
without experiencing any resistance, they conform to
the following laws: —
1, All bockies full equally fast,
2. The velocities acquired daring the
fallore proportioned to the times cceupied
tn falling.
3. The spaces passed over are pro-
portional to the squeres of the times
ocenpied in falling,
‘The first law is verified by the following:
experiment, A glass tube, six feet Tong
(Big. 35), ts closed at one end, and at the
other it has a stop-cuck, by which it eum
bo closed or opened at plousure. A small
lemon ball and a feather are jutroduced
within the tube, So long as the tabe ix
full of air, if it be suddenly inverted, it
will be observed that tho ball reaches the
Dotiom sooner than the feather, If mow
the air be exhausted by moaus of am aire
pomp, and the tubo suddenly inverted,
Doth the ball and the feather will be sent
to fall through tho length of the tube in
the sane tine. ‘This experiment, beshles
verifyiug the law, shows also that the ait
LAWS OF FALLING BODIES. 49
vifers & resistance, which is greater for light than for heavy bodies,
‘Thin resistance ix proportional to the surface offered to the direation
wf thee fall,
2. The second law is a consequence of Inertia combined
with the continued action of gravity.
Let a borly fall from a state of rest, and nt the end of the first sce
‘wud it will hawe acquired # certain velocity, If gravity should then
cease to act, the body would, in consequence of ita inertia, continue to.
fall ac the xine nuiforn rate. But the eontinaed action of gravity
dusing the next second generates the anne velocity as in the firet,
and this added w the velocity aequired during the first secand gives
the velecity at the end of two scconds, whieh ix twice that which is
attained at the end of the first second.
Se aleo the velocity at the end of two seconds added to that ae
‘quired during the third second will make the velocity at the en of
the think second threo tines aa great as at tho oud of the first second,
Tn tho samo way it inay bw shown that the velocity at the end of the
fourth second will be four times ae gront as at the end of tho first,
and so on.
‘The space Uough which a body will fall, under the ine
fluence of gravity olone, during the first second is found by
‘experiment to be about 167, fect. Its oxeraye velocity dur-
ing tho first second ix therefore 16;', feet por second.
Now, as the body begins to fall from « state of rest, or at the ve~
locity of zero, it follows that ita velocity at the end of the tirst second
Will be just twrico its avorge velocity during that seoond, or 2h feet
per scoond.
Whis is the tnerement of velocity, 1. 0. the amount by which the
¥elocity is Increased during exch secoul of the boly’s descent. Tak-
the avomige velocity of the descout during the first sceund ss
unity, the velocities at the end of each successive second will be rep
sented by the serios of even numbers 2, 4, 6, 8, eto,
“H Toestinats the space through which the body passes during exch
‘pemond OF its éseent, Jot 1 rupresont the space described during the
Brak eesti “Then, im cemsequence of its acquired velocity alone, the
Mn the uext second pars through two such spaces, while
wontiuued nctlou of gravity will carry It through one space, teaak-
‘nig the total slescont 3, that is, thrve thes that of the Bee seem.
=
60 GRAVITATION.
Then at the beginning of the third second, the body having acquired a
velocity of 4, its inertia alone will carry it through four spaces, and
the action of gravity during this second will add one apaos, makings
the whole space traversed ia the thint second equal 5,
Tn the same way it can be shown that the spaces traversed during
the succeeding seconds will be indicated by the series of odd numbers
7,9, U1, ete.
It will Lo seen that the nummbery of this nerica may be obtained by
ailding one to each of the even nuinbers representing the velocities,
whking zero to represent the initial velocity.
4. The total space passed through at the end of any given
time may be found by adding the numbers which denote the
apace passed througl during each successive accond; thas, at
the end of the fourth second, we find, by adding the numbers
1, 8, 5, 7, that the total space ix represented by the number 16_
It will bo soon that this eum is always equal to the squary of the
ing which the body is falling.
‘Thia agreca with the third law of falliug bodies, aa previously stated.
These results are shown in the following table: 16/)f, =
the unit of space.
number of seconds du
Number Volooltics wt the Spaces traversed Total Number of
of Secunda txt of eagh Second, daring each Secoud, Spaces Kravernat
1 1 L
4 a 4
% 6 5 2
‘ 8 7 i
4 10 o 25
6 12 " mi
ete ete. ete. ote.
From the principles here developed we
rive the following:
rules : —
1 find the velocity acquired by a falling body at the
end of any given time,
Multiply 32} ft. by che number of arconds in the given tinte,
Exasre. Find the velocity of a falling body wt the ond of the
fifth second.
wh. x 5 = 160pfL, Ava
LAWS OF PALLING BODIES. 51
2. To find the space passed over during any given second
of the descent,
Multiply \6y'y ft. by that one én the series of odd numbers which
corresponds to the number of the second.
Exaurre. Find the space traversed by a falling body during the
Fourth seound of its descont.
WG yy fhe 6 7 = Nyy fe, Ane
3. To find the whole distance traversed hy a falling body
during a given time,
Multiply U6, ft. by the squere of the given number of seconds.
Examrut. Pind tho whole distance traversed by a falling body iu
ee asal 16, 1. x 36 = GTO NL, Ans.
65. Apparatus for verifying the Laws of Falling
Bodies. —When bodies are allowed to full freely from a
height, it is not ensy to compare, or measure accurately, the
spaces deseribed dnring each second of their descent.
Methods have therefore been devised which diminish the
velocity withont otherwise changing the character of the
motion. The simplest of these methods ia that adopted by
Galileo. He used an inclined pline, having « groove, down
which a heavy ball was made to roll. By making the incli-
nation small. the rte of motion was so redaced that it could
Ta Fig, 36, Itt the line A B roprosent on inclined plane, and sop.
‘pase the inclination to by such that a ball placed at ¢ will move over
the apace ed in one ercond, In the nest second it will traverse a
space, te, three times as great, and Jn the third sevemd a space five
Mines SAME, ae in The first second; and so on in the ratio of the
series of add nuinbers, a8 given in the table
By measuring the space described during any given number ot
seconds, fe will be found 10 be equal to that deseribed during the Giver
——
62 GRAVITATION,
second, multiplied by the equare of the number of secondas thus, if
the ball moves one foot in the first second, in three seconds it will
move over a space of nine foot. ‘These experiments verify the laure
already stated.
66. Bodies thrown perpendicularly upward.—It
has been shown that a body falling freely gains in velocity
2} fect during each second of its descent, The force of
gravity diminishes an upward motion in the same degree that
it increnses a downward motion; hence a body thrown por
pendicularly upwand will Jose in velocity 82) feet during exch:
second ite ascent.
‘Lhe number of seconds during which it will continue to rise
may therefore be found by dividing its initial velocity, or
that with which it was projected upward, by 32}.
For example, a body thrown upwant with a velocity of 1289 feet
pee second, will continue to rise during four seconds.
Having &
ily ascertained
vund the thne, the whole distance to which the body wit
rise fn for it is the «ame ox the distance through
whieh the body would fall in the given tine,
EXAMPLE. Suppose a body thrown upward with a velocity of
193 feet per second, to what distance will it rise
193 + 3} 16 jy X 36 = S79 Me. Ave.
67. Projectiles. — A body thrown into the air wt any angle
ball is fired from 4 in the
horizontal direction AR If
— | the foree of gravity did not
. |
is called a projectile. Suppose 1
act, the ball would mowe unk
formly in the direction 4 Fy
passing over equal spaces im
| equal times. Tf the ball moved
from A to B in one second,
it would reach @ in two sec
onde, D in three seconds, and
oon. But ifthe ball were let fall from 4 without any other
force than gravity to act upon it, it would move in a vertical
direction, and the spaces 4 4, LM, MN, etc,, described in
p —_______
Pig. 8,
TIME OF A PROJECTILE. 53
suecessive seconds, would be as the numbers 1, 3, 5, 7, ete.
Tf, pow, the hall be acted upon by both these forces, it will
be found at the close of each second at the extremity of the
dingonal of » parallelogram whove sides represent these aepa-
rate motions; that is, at the end of the first second it will he
found at 1, at the end of the next second at 2, at the end
of the third at 3, and so on,
‘The curve thus described is called a parabola,
Ifa ball be fred obliquely upwand it will movo in a eurve of the
amie kind, but vurying according to the anglo of clevation, as shown
in Fig. 38. The greatest range ot hori- =
zontal distance will be attained with an ery
elevation of 45°, and the range will be
the same for clevations equally above
or below 45°, ax at 20° and 70°.
‘These results are correct only for
hodies moring in a vacuum. In the
cace of bodics moving very owiftly
through the air, a8 a cannon-batl or 2b
ride-Dallet, tho naturo of the curve is Wig. 88.
modified by tho roststance of tho alr. ‘Tho angle of olevation neces:
sary for the greatest rango is also changed to about 40° instead of 45°
68. Time of a Projectile. —A ball flrod horizontally
will reach the level ground at the same time as if it were
dropped; if fired obliquely upwand, it will reach the groand
in twice the time required to fall from ite highest point of
elevation. These results are, however, modified by the ree
sistance of the alr.
ook
‘
Laws of Falting Bodies.
Statoment of the Laws.
Verification of First Law.
Dexonateasion of Second Law,
Deworstration of Third Law,
Tatler Statement.
Roles and Exmnples.
- Galileo's Method.
5A GRAVITATION.
Burlies thrown upward.
Law snd Examples,
Projectiles.
Path of a Projectile.
Time of a Projectile,
Range of a Projectile.
69. The Pendulum.—A Pespcrem is a heavy body
suspended from a horizontal axis about which it is free to
Thus, the ball m, suspended from @ by a string
and 40), is a pendulum.
When the centre of the ball, a,
7 i. cxnctly below the point of sas.
\ pension, C (Pig. 39), it is im equi
librium, for in that position the
action of gravity is renieted by the
tension of the string. 1f, howener,
the ball be drawn aside to # (Pig.
10), it fa no longer in equilibrinn,
for in that position the force of
y, wnwvity acta to draw it back to wy,
at which polut it will arrive sith
the samo velocity as thongh it had
height om. In conseqaence of its Inertia
the ball doos not stop at mi, bat angves 6a
towanls p. Iu descendivg fran m to m, the foree of gravity acts
lorating force, but in ascending from m to p, itacts ak a
force, hence the ball moves slower and slower wntil it
The distanco mp woukl bo rigorously equal to at
fillen through the vertie
nit aequired voloe
reneh
p
were it not for the resistanee of the alr.
ane state 8
The ball, having reached p, is in the
wis at RB;
siw acts to driw it buck to m, whence, hy virtue of ita
Inertia aud velocity, it ugain rises tom, anil so ob fudefinitely,
‘This backward aud forward motion is called Oscillatory Motion.
A slugle excursion from mw p or feom ton, is called
Oscillation, or Vibration. Aw excursion fren # to p, wid bac
& Double Oscillation. ‘Tho unglo p Cn is ealled 4
Amplitude of the oscillation.
ice of the alr, the amplitude iy
the weight 4
tom, is
angle of the
Tu evusequence of tho resis
THE PENDULUM, 55
tinnally diminiehing, and the ball eventually comes to reet, though
often uot Hill after the lapse uf some hours,
70. Simple and Compound Pendulums. —A Sire
Pexposm is such a pendulum as would be formed by ans-
pending « single material point hy a string destitute of
weight,
Such a pondotain may exist in theory, and ix thus usefal in
arriving at the Inws of oscilintion, but in practice it can only be
approximated to by making the Wall very small and the string very
fine.
A Conroox Prsvcion is any heavy body which is free
to oscillate about « horizontal uxis.
Ts may be of any form, but in general it courista of a stem, 7
(Fig. 41), which Is cithor of wood or metal. ‘The stern terminates
aboro ina thin und flexible plate, a, usually of stecl; it terminates
below In a disk of metal, L, enlled the ball, wl is of a lentienine
shape, that the resistance of the nie to its motion inay be as Little ws
7. Laws of Oscillation of the Pendulum.—The
‘oscillations of the pendulum take place in accordance with
the following Jaws: —
1. For pendulums of wiequat lengths, the times of oscillation
tare proportional to the square roots of their lengths.
2 For the same pendulum, the time of oscillation ts independent
of the amplitude, provicled the amplitude be small
B. For pendutians of the sane length, the time of oscillation és
independent of the nature of the material.
‘Peadolume of wood, iroo, copper, ghia, all being uf the mane
Tevgib, will all oscillate tm the saine tine.
4. For the same pendulum ut different places, the times of oscit-
fation are inversely as the square roots of the force of gravity at
those places.
Those tawe are deduced from a course of matheuution! rewsonine
bh thin theoretical sirople peodulus, bar they may Le verified expti-
imeutully by employing x very suall bull of platixuw, vr other heavy
inetal, ated sutpeuallug It with w very five alll heel.
i
66 GRAVITATION.
To verify the first law with sneha peadatum, we begin by making
it vibrate, and then counting the number of vibrathons in ane tinete,
Suppose, for exainple, that it makes seventy-two per arnute. Now
mnke the string four times ax Jong as before, and it will bo foewd
that the pendulum makes only thirty-six cecillations per minute. If
the atring i¢ made ning t as lore ak in the first instinee, it will
be found that the peadalum makes only twenty-four escillations: per
minate, and soon. In the second ease the time ef oseillarion i twire
as great, aud in the third ease it is three times as great as in the first
ease. Now, because two, three, ete, aro the square roots of four,
it follows that the law is verified.
‘To verify the second law, let the same pendalum oscillate, at first
through an are, pw (Pig. 40), aud then through auy otherare, ngs St
will be found that the number of oscillations per minute is the same im
ach case. Hence the law is verified. It is to be observed that the
does not hold trne unless the ares pm and rg are very small, that
is, not more than three or four degrecs.
The property of penduluins, that their tines of oseillation are
Independent of the amplitude of vibra desiguoted by the name
isochronixm, from two Greek words, signifying equal times: oscilia-
d isochronal.
ovored the that stall cseillations af @
J towards tho end of the slstecnth eentary.
It is stated that ho was led to the diseovery by noticing the osedl-
Intioua of a chandelicr suspended from the eciling of the Cathedral
of Psa
72. Centres of Suspension and Oscillation. —In the
compound peudulnn the weight of the suspending-rod-and of
the hall Since a short pendulum vie
brates more rapidly than a long one, it is plain that the parts
nearest the polut of suspension will tend to vibrate In the
shortest time, and those farthest from that point in the longest
time. But the whole must move together. and consequently
the rapid vibrations of the upper part of the pendulum are
retarded by the slower vibrations of the lower part. ‘Phere
is a point, however, where the watural rte of viluation is
noither avocleratod nor retarted, the accelerating effect of
the part above being exactly balanced by the retarding
nine,
tione performed in equal times are ¢
Gatareo first db
pendula were isc
hrc
w to be considered
THE PENDULUM. it
effect of the part below, This point is enfled the centre of
coseiMeation.
‘The dsstance between the point of suspension and the
centre of oscillation is to be taken as the
effective length of the pendulum,
73- Applications of the Pendulum.
—On account of the lsochronism of its
vibrationa, the pendulom has been ap-
plied to regitlate the motion of clocks.
Tt-was first used for this purpose in 1657.
by Horeness, a Dutch philosopher. The
motive power of a clock is sometimes a
weight acting by a cond wound sround a
drum, and sometimes a colled spring
munilar to a watch-spring. ‘These motors
act Co set a train of wheel-work in motion,
‘which in tarn imparts motion to the hands
that move round the dial to point ont the
hour, Tis to impart uniformity of ino-
tion to this train of whoel-work that the
pendolum ts used.
Fig. 42 shows the mechanisin by sivas of
whieh the pondalum acts ne a mgulator, A
toothed wheel, H, called a seape-wheel, is ern
nected with the train driven by the inotor, and
this amapewheel isehecked by an anchor, mn,
which i* nttachod to the ponduluin avd vibrates
with it Thoarichor hax two projecting paints,
m sad w, called pallets, whieh engage alter-
ately with the toeth of the seape-wheel in
sack & manner that only one tooth can pass
at each swing of the pendulim. ‘The motor
‘turas the teape-whoel in the dirrstion of the
SANE Hintil One OF the teeth comes In contact Fig. al,
With) the pallet w, whiok stops the motion of the whoel-work ull
ewig Of the pendulum fifts tho pallet m from between the two teeth,
Whed W kinigle tooth panser, aud the wheel-work moves on Until
—
58 GRAVITATION.
again arrested by the pallet , falling between two teeth on the
other side, A second swing of the pendalum lifts out the pallet s,
soffers another tooth to pass, when the wheel-work is again arrested
by the pallet m, and so on indefinitely. ‘The beata of the peodalam
boing ideehrooons, the interval of timo botween the eonsecdtive Oseape
Gf two teeth is always constant, and thus the motion of the wheel
work is Kept uniform. "The loss of foree which the pendulum eon-
tinually experiences is supplied by the wotor through the seape-wheet
audtheanchor, ‘Thisis eallod the sustaining power of the pendulan.
‘Owing to expansion and contraction from variations of tempera~
ture, the length of the pendulum varies, and nenording to the first
law, its time of vibration changes In nico clocks this change is
compensated by 4 combination of metals. In common slog it ix
rectitiod by longthening er shortening the pendulum by a wat and
serow, shown at v, by weans of whieh the leutiealar bob may be
moved up and down, In summer the peodulum elongates and the
clock loses tine, or runs too slow; this is rectified by screwing ap
the nat and shortening the pendulum, In winter the pendatins
contmers and the clock gains time; this is reetified by unserewing:
the nut nd longthening the pendulum,
74 Compensation Pendulums are made
by sing two metals in such a way that the
ansion of one part downward may be exactly
materacted by the upward expansion of the
part, thus making the etfective length of
4 the pendulum always the same.
4
. x One of tho. most. common forme is shown ini Figs
42 Iv is conatrnctod as follows: The pendolamensl,
AB, supports a glass jar partly filled with anenouryy
work, CDE. When
the weather ie warm, the rod and fruaework expand
and thus inervase the lougth of the pendalam. Bat at
the same time the mereury io the glass jar expands aud
ris jjustiment the centr of
artied xe far upward by the expansion
ary ue downwanl by the expansion of the
rod and framework, ‘The distinos between the cewtrss
of suspension and oscillation remaining the sane, the vibrations of
the pendulum continue unaltered.
enclosed in the steel fren
wo that by a proper
oscillation
c >
Fig. 42
of tho i
THE PENDULUM fa)
Tn another form of the ccinpensating pendulum, the ball is sup-
ported by a framework composed of rods of different metals, so
‘adjusted that the downward expansion of oe part is exactly com-
pensated by the upwand expansion of tho other part.
Tu the form shown iu Fig. 48, called the gridiron pendulum, there
are five steel lars expanding downward and four
‘brass bare expanding upward, As the relative
expansibility of brass compared with stoel is us
100 to G1, the leagth of the stecl bars is 4y\2 that
ed the brass.
75. Length of the Seconds Pendu-
lum. — The length of the pendulum vibrat-
ing seconds has been very accurately deter-
mined. At the same place it is invariable,
but it varies with the latitade. At the
equator it fs 89.0217 inches: at Now York,
$9.10237 inches ; at Spitzbergen, 59.21614
inches, "The cause of this variation is the
difference in the force of gravity in different
plsees, due to the spheroidal shape of the
earth.
‘The pular diameter of the carth bring twen
six intles shorter than the equatorial diame
‘any poist on the eurface of the carth near either
pole is nearer the centre, and the force of terres-
trial gravity is stronger than at points on or near
the equator, Consequently, a pendalum which vibrates seconds at
the equator, om being carried to a latitude of 40° to 50°, ia more
strongly acted upon by gravity, anil vibrates more rai Tn onder,
thereforn, that it may continue to make exactly one vibration ia each
the mpidity of vibration sonst be diminished by increasing
secon,
the length of the pendulum.
Fig 48,
‘Summary.—
The Penubalur.
Vilrration or Oscillation.
Tiustration.
Simple Pendulum,
- Compound Pendulum.
60 WORK AND ENERGY.
Lanes of Oseitlation of the Pendulum.
Statement of the Laws
Verifleation of Pirst La
ee Second Law.
Coatres of Suspension and Oscillation.
Application to Clock Werk.
TMustracion.
Compensation Pendulums.
The Mercurial Peudolum.
‘The Gridiron Pondatum.
Lenyth of the Seconds Pendutum,
1. At the Equator.
2. In High Latitudes.
Causo of the Variation,
SECTION 1], — WORK AND ENKMOY,
76. Work. —'The term srork as used in mechanies means
the produrtion of motion against resistance,
It is obvious that this definition will apply not only to the
labor of men and animals, but to the action of forces of other
kinds—ax those of wind, woter, and steam —when om-
ployed in overcoming resistance.
Tn this sense, drawing loads, raising weights, pumping
water, forging fron, pressing cotton, etc., are all examples
of work, whatever may be the forces employed In the various
operations.
urement of Work. — Tho work done in mais:
ly taken as a stands
77. Mi
ing a we
ight to a viven height is gene:
an for the measurement of work
In this country and in England the anit of work commonly
adopted ts the foot-pound,
This {s the amount of work required to raise one pound
e of gravity.
jie Systor is the work required to
one foot againat the for
The unit of the Me
HORSE-POWER. 61
ralae one kilogram to a belght of one meter, It is called a
Ulogram-meter,
‘Torfind » namerical expression for the work in a given example,
wo saultiply tho mamber of weight units raised by the number of
Minewe unite in the vertical height vo which the body is mised. A
weight of 20 Ibe. raised 4 foot, o a weight of 4 Ibs. rnised 20 feot
represents £0 foot-pounds. A weight of 25 kilograms mised 5 weters
represents 125 Lilogram-meters.
78. Horse-Power. — It has been estimated that the
strength of a horse is on the avernge, suflicient to mise
$3,000 pounds vertically throngh one foot {n'a minute: hence
& horse-power is a power which can perform 33,000 units of
work ina minute.
‘The capacity of steam-engines and ether powerfal machines is
genorally muted by horse-powurs ; thus, an engine is suid to be of ten
horse-peer if it is capable of doing work equivalent to mixing 93,000 _
Shs. 10 foot in one minute, or 330,000 Tbs. one foot inn minute,
"The time required for the work is an eseential part of tho ealeula~
tiem. Tf an enyine ein do 39,000 units of work in half a minute, it
is Of theo horae-power; if it can do the same work in one second, ft is
of skxty horae-power.
99- Energy is the power of doing work, that is, of over.
fotming resistance. Any moving body can overcome ronist-
‘ance, and therefore possesses a certain amount of energy.
The amount of onergy in a moving body depends upon its
weight and velocity. The dirvetion in which it moves makes
no difference in the energy with which it acts. If its energy
fs expended in lifting itself against the foree of gravity, we
ban, If ite weight and velocity are known, determine the
‘amount of this enengy: in foot-pounds, or kilogram-moters.
‘EP ilo this we havo simply to find the vertiesl beight to whbeh
the given velocity woold lift the body, and wultiply the weight by
the height, Let m =the maxs of a body, and w tho velocity with
whieh it is moving, and its enenzy will be oxpressed by the formula
that 46, ite ouenzy ie equal tw one Avlf ite mass multiplied
: beloettyy.
42 WORK AND ENERGY
80. Kinetic and Potential Energies. —To understand
these two types of energy. let as consider the case of a heavy
body thrown directly upward into the air, As it begins to
rise, it has a certain amount of energy depending upon the
velocity with which It moves, This is Its energy of motion.
As it continues to rise, its velocity, and consequently its
energy of motion, decreases, until at the highest point whiteh
{t reaches it has no longer any energy of motion. Bat in
consequence of its elevated position, it has the power of
doing work in its fall to the earth again; that is, it has
energy of position
Energy of motion is called dinetic energy.
Euergy of position Is called poteatial energy,
In the case just given, the sum of the two types of energy resualns
the samo for ovory position of the body} for, ms it rises, Kkinetie en-
ergy decreases, and potential cnergy increases Iu exactly the same
le in its descent potential energy decreases amd
es Ull the body eotes to rest in its original
proportion, w
kine
pinition,
A body may have eaurgy of position from other causes than being
raised to a height
energy &
of a watch that is wound ap, or
+ stored up has potential enemy
A. bow that is bent, the toninsp
any body in which reserved fa
Summary.
Work
Dofinition of Work.
Exanpl
Measurement of Work.
Unit of Work
Tho Foot-Pound
The Kilogram-Meter,
Horse-Power.
Energy.
Menaurnment of Energy.
Kin
Potential Energy
Mlustration,
araples of Poteatial Eergy-
CHAPTER II.
APPLICATION OF PHYSICAL PRINCIPLES TO MACHINES.
‘SECTION L — GENERAL PRINCIPLES,
81. A Machine is a contrivance by means of which
a force applied at one point is made to produce an
effect at some other point.
The force applied is called the power, and tha foree to be overcome
ts called the weight, or load.
82. Motors. — Tho working of a machine requires a con-
tinged applleation of power. ‘The source of thls power ix
called the Moron.
Some of the mest important motors are muscular effort, ax exerted
by man of beast, in various kinds of work; the weight and impulse
of water, ax in water-willls; the impulse of air, as in wind-mills;
the elastic force of springs, as in watches; the expansive force of
vapors and gases, as in stun xnd hot-air engines. The last Is,
perhaps, the most uxeful of the motors mentioned
83. Object and Utility of Machines. —The object of a
machine i to tranamit the power furnished by the motor, and
to modify its action in auch a manner as to cause it to pro-
duce a isefhl effect.
Th no ewan does a muchine add anything to the power applied to
it} 00 the contrary, it akeorbs more or less of this power, seconting
to the fatima of the work to be done and the connection existing be
one
? eiroomstances which eave uti nteorption of power
cil
Of GENERAL PRINCIPLES.
are the rubbing of one part ypon another, the stiffiess of Ihamds amd
belts, the resistance of the air, the adhesion of one part to anther,
and the want of handuess aud elasticity in yhe materials of which the
machine is constructed. ‘Tho rosistancoe arising frow these eating are
called hurtful resistances. "Thoy not only absorb much af the power
applied, but they also contribute to wear ont the machine, ‘The
existence of these resistances in every machine requires a eontinned
supply of power to overeome then in addition to that necessary to
perform the useful work. Hence the absurdity of attempting te ob-
tain perpetual motion.
84. General Laws of Machines. — The idea of Worx,
in mechanics, implies that a force is continually exerted, and
that the point at which it is applied moves through a cortain
space, Thus, in raising « weight, the work performed do-
pends first upon the weight raised, and secondly upon the
height throngh which it is raised. The quantity of work of =
force in tiny given time is measured by the intensity of the force,
multiplied by the distance through which it ie exerted. This
distance is culled de path described.
The work of the power is always equal to the work of the toad,
Honee, if by the use of a machine, a power of one pound can
be made to raise a weight of ten pounds, the power must move
through ten times the distance traversed by the weight; and
as the spaces are traversed in the same time the power must
move ten times as fast ws the weight
‘The power is not necessarily less than the weight; fora
machine may be so constructed thata power of ten pounds will
be required to lift a weight of one pound; but in this ease
the weight will move through ten times the space, and with
ten times the velocity of the power. Machines, therefore,
may be used in two ways, — by making the power move with
great velocity to move heavy weights very slowly, or by the
pidly
In either case the following general laws will apply to
machines of all kinds,
use of grent power to move small weights very
1. What is gained in intensity of force is lost in time, velocity.
, CORDS —THE LEVER. 65
or distance ; and what ix gained in time, eetoeity, ar distance ix
fost in intensity of force.
2. The power multiplied by the distance through which it
mower ix equal to the weight multiplied by the distance through
wliiok it moves,
B. The power multiplied by its velocity equats the weight mul-
tiplied by ite velocity.
SMETION 11. -RGRMENTARY MACHINES
85. Mechanical Powers. — The elementary machines
are seven in number, viz., the cord, the lever, the inclined
plane, the pulley, the wheel and axle, the screw, and the
wedge. These seven are called mechanical powers. The
first three are simple elements ; the remaining ones are
combinations of these three.
86. Cords, ard Baxns or Bers, are used for transmitting
motion from one point to another, as in the pulley. Chains
are often employed for the sume purpose, as in the watch.
Conds, Iwiis, and ehnins should be as tlexible ax is consistent with
sufficicut strength.
87. The Lever.—A Lxven is un inflexible bar free to
turn about a fixed point, called the Pulerwn, and acted upon
by two forees which tend to turn it in opposite directions,
‘The force which acts a8 a motor is enlled the Power; the
other one is called the Weight, or Load.
Levers may be cithor straight or curved. The distances
from the fulcrum {o the lines of direction of the power and
weight are called fever aris.
Tu the lover MN (Ply. 44), F in the
filerom, MP and NR ure the lines of
dizection of the power ant weight, FA is
‘The lover atm of the power, and 2° ix
the Tever arm of the wight.
“Levers aro divided ints three classes :
—_
66 ELEMENTARY MACHINES,
Tn the first class (Fig. 45), tho falerwn bs between the power and
the weight
In the second class (Pig. 46), the weight ie between the power and
the fuloram,
Tu the third class (Pig. 47), the power is between the woight amd
the fuleram,
ae
Fig. 46. Fig 46 Fig. 47.
88, Law of the Lever. — The product of the power mule
tiplied by its distance from the fulerum ts equal to the product of
the load multiplied by ite distance from the fulerum.
Examrces. In a lover of the firet kind & feet long with the
weight 2 feet from the fulcrum a power of 10 pounds will bakauee
a weight of 30 pounds.
Tn a lever of the second kind, § feet Jong, with the weight 2
foct from the fulerum, a power of 10 pounds will balance « weight
of 40 pounds.
In a lover of the third kind 8 fect long, sith the power 2
foot from the fuleruin, a power of 10 pounds will balance a welght
of 2} pound,
are of continual tee
arly every machine.
89. Examples of Levers. — Le
in the arts, forming component parts o!
Pig. 48
A pair of scissors affords an example of the first class of
levers. Tho fulcrum is at © (Fig. 48), the hand furnishes the
power, and the substance to be eut the resistance,
THE LEVER. 67
The cowmon balance, yet to be described, is a lever of this class,
ne is leo the hanille of a puwnp.
‘The ordinary nut-cracker is an example of levers of the
second class. The fulcrum is at © (Fig. 49); the power is
the hand, and the resistance is the nut to be cracked,
e
Fig. 44
‘The common crow-bar is used as a lever of the first kind
when ft Is pressed dowuward over the fuleram to mise a
weight (Fig, 50). When one end rests on the ground as
@ fulerum, and the other is lifted upward to raise the weight,
it becomes a lever of the second kind (Fig. 51).
i 2 |
Fig. OL
‘The oars of a boat ure lovers of the second elas. The end of the
‘oar in the water is the fulorain, the band is the power, aud the boat,
or rather the resistance of the water which it has to overoome, is the
resistames, The shoars enrploye! for cutting metals belong to this
lass of lovers.
‘The limbs of animals are examples of levers of the third
class. The figure shows a
asa lever.
sucket, isthe power; and the
weight ef the Tianb art what-
‘ever resistances te may oppose Fig. 62,
—
68 ELEMENTARY MACHINES.
to motion Is the welght. ‘The fore-arm and hand aro enised Uhrwexte
‘a mpace of one foot by the coutmetion of a muscle applied aear the
elbow, moving through less than gy that space. ‘The wnselo, ther-
furo, exerts 12 times the fores with which the hand moves.
90. Weight between two Supports. — Ifa weight ix
attached to a beam or pole which rests upon two supports,
the beam nets as a lever of the second class, and the part
carried by cither support may be found by considering it as
the power and the other support as the fulcrum. If the
weight rests on the middle of the beam, it is obvious that each
support will bear half the burden. If, as shown in Fig, 53
the loud is one-third the length of the beam from A, the sup-
port 4 will bear two-thirds of the weight.
Fig. 63.
9t- Compound Levers.— When o small force is re
quired to sustain a considerable weight, and it fs not eon~
venient to use a very long lever, « combination of levers, or
a compound lever, is employed. When such a system is in
equilibrium, the power, multiplied by the continued product of
the alternate arms of the levers, commencing from the peaver, i
equal to the weight multiplied by the continued product of the
alternate arms, commencing from the we
Fig. of
For example, the system represented ia Pig. G4, coustating of
three lovers of the firet class, will bo in equilibrium when
PXAFXBPXOF’=W"WXDE XCF XBE
If the long arms are 6, 4, and 5 feet, and ench of the short anna
J foot, then 1 pound at A will sustain 12% pounds at 2,
THE BALANCE. 69
92. The Balance. —A Batance is « machine for welgn-
ing bodies.
Balances are of continual use in commerce and the arts,
in the laboratory, and in physical researches: they are con-
sequently extremely various in their forms and modes of
Fig. &
‘constriction. We shall only describe ome of the forms which
4s in common tase in the shops.
TE Gonsixts of a metallic bar, A # (Fig. 55), called the
Which ts simply a lover of the first onder. At its
Point i a knifeedged axis n. called the Fulerum.
70 ELEMENTARY MACHINES.
‘Lhe fuleram projects from the sides of the beam, and rests
on two supports at the top of firm and inflexible standard,
‘The knife-edged axis, and the supports on which St rests, are
both of hardened steel, and nicely polished, In order to make
the friction as small as possible, At the extremities of the
beam are suspended two plates or basing, called Soale- Ptaws,
in one of which is placed the bedy to be weighed, and in
the other the weights of iron or brass to counterpoise it.
Finally, a needle projecting from the beam, and playing in
front of a graduated scale a, serves to show when the beam
iy exuctly horizontal.
To weigh a body, we place it in one of the scale-pans, and
then put weights into the other pan until the beam becomes
horizontal, The weights put in the second pan indicate the
weight of the body. A
93: Requisites for a good Balance. —A good balance
ought to satisfy the following conditions: —
1. The lever arms, 4n and Bn, should be exactly equal.
We have soon, in discussing the lever, that its arms must be equal,
in order that there may be an equilibricm between the power «nd
resistance when these are equal. Tf the arms are not equal, the
weights placed in one seale-pan will not indicate the exact weight
‘of the body placed in the other
2. The balance should be sensitive > that ia, it should turn
on a very small difference of weights In the two scale-pans,
‘This requires the filernm and its supports to he very hard and
tnooth, a0 as to produce Little friction. By making the needle Tong,
a alight variation from the horizontal will be more readily per
ceived,
. The centre of gravity of the beam and seale-pans should
ho lightly below the edge of the fulcrum.
If it were in the edge of the faleram, the beam would not come
to a Borizontal position when the scales wore equally loaded, tut
would remain in any position where it might chance to be placede
If it were above the edge of the fuleram, the beam would romain,
THE BALANCE. 7
Horizontal if placed 205 but if slightly deflected, it would tend to
overturn by the action of the woijght of tho bean.
The nearer the contre of gravity comes to the rlge of the faleram,
the more accurate it will be; but ut the sume time it would tura
more slowly, avd might finally come to turn too slowly to be of use
for
Tt ls to bo observed that when the sewle-paus are heavily loaded,
‘an nereased weight is thrown of the fulcrum, which cans an in~
crease of friction, and coureducatly « diminution of sensitivencss.
94. Methods of testing a Balance. —To see whether
the arma are of equal length, let » body be placed in one seale-
pan, and counterbalanced by weights put in the other; then
change places with the body and the weights. If the beam
remains horizontal after this change, the arms are of equal
length ; otherwise the balunce is false.
‘To test the sensitiveness, load the balance and bring the
beam to a horizontal position, then deflect it slightly by a
small force and see whether it returns slowly to its former
position, Tt ought to come to a state of rest by a succession
of oscillations.
95- To weigh correctly with a false Balance. —'To
weigh a body with a false balance, place it in one scale-pan
and counterbalance it by any heavy matter, as shot or sand,
placed in the other pan. ‘Chen take ont the body and replace
it by weights which will exactly restore the equilibrium of the
balance. The weights will be exactly equal to the weight of
the body. The reason for this method is apparent.
96. The Steel-Yard.—‘The common steel-yard used in
weighing f& a lever of the first class, which differs from the
‘talance in having unequal arms. Tig. 56 represents a form
in common tse.
‘Ihe pivot @ is the filorum; tho weight HW’ is suspended from
the hook A, and the power P ts movablo on the long arm of the
fever, which is graduated to indicate pounds and ounces. It is evi-
Hout that pound woight at D will balance us many pounds at
—
72 BLEMENTARY MACHINES.
W as tho distanco 4 C is contained times in DO, Tho sme
counterpoise P may bo used for a greater weight by tuming the
bar over and suspending it
from another pivot E nearer
the hook A, fn this que
8 pound weight at 2D will
halanco ne many pounds at
W as the distanee AE is
contained times in DE.
‘The scales used for wellghe
ing coal, bay, ¢to., are gea~
erally compound levers, and
their operation depend:
pon principles already ex-
Fig @ plained.
Summary.—
Principles of Machines.
Definition of a Machine.
Power and Weight.
M
Ttility of Machinos
Lous of Power.
General Laws of Machines
Quantity of Work, how estimated.
General Law of Work
Three Laws relating to Intensity of Force, Velocity, and
Distance or Space.
Mechanicat Powers.
Elementary Machines,
The Corel
The Lever
Power, Weight, Folorum.
Three Classes of
Law of the Lover.
Tilustrations — The Scissors, Nat-crackers, the
Crow-bar, Ours, Limbs of Animaje
Weight between two Supports,
Compound Lever.
WHEEL AND AXLE. 73
The Balance.
Description.
Requisites for good Balance.
Methods of Testing.
Weighing with a fulso Balinese.
‘Tho Steel- Yard.
Seales for Great Weights.
97. The Wheel and Axle consists of a wheel, or drum.
A, mounted upon an axle, #2 The
power is appliod at one extremity of a on :
cond wrapped aronnd the wheel, and
the resistance at one extremity of a
second cord wrapped around the axle
in & contrary direction. The whole is 2
stipported on a suitable frame, by means
of pivots projecting from the ends of Fig. 67.
the axte.
‘The wheel and asle acts as a perpetual lever of the first
kind, the filerom being at the common centre, and the radii
of the wheel and axle being respectively the ars of the
lever.
In Fig. 58 Fis the fulcrum, A Fis tho power arm, and FB the
wevight arm of the lever. Hence, aeconling tw the
Wx EB. i ,
on of the [pf b\,
wheel and axle the power mores through a space aS)
‘equal 16 the eitenmferonce of the wheel, and tho —
wredglit thenigt w'epace equal to the circuinference
‘of the axle, “Hence, ansorliny to tho second general
law of machines, the power maltiplied by the cir Ae
eeniference of the wheel ix equal te the weight wal- © )
Aiplied by the circumforence of the axle. Big. 58.
Since the radii of circles are proportional to thelr circum-
ferences, the law of the wheel and #Xle may be stated in two
ways, viz. :—
The poieer multiplie? by the radius of the wheel equate the
——
*
74 ELEMENTARY MACHINES.
weight multiplied by the radiue of the axle; or the power multi-
plied by the circumference of the wheel equale the weight multiplied
by the circumference of the axle,
98 The Windlass. — The Wixnhass consists of nn axle, or
arbor, 4B, und w crunk, BOD,
by means of which it is torned
‘The crank consists of an arm, BO,
perpendicnlar to the axle, ealled
B the crank arm, and second army,
DC, porpendicalar to the first, called
the crank handle ‘The power is
applied to the erm handle, and
Fig. 59. tho resistance to a repo Wrpped
around the axle, ‘The windlass {s principally used in raising weights,
99 The Capstan is a form of the windlass in which the
axis is vertical. It is used chiefly on
shipboard for raising the anchor or
drawing the vessel up to the dock.
The head of the capstan is pierced
with holes, in each of which a lever
may be placed so that a number of
men cag work at the same time.
100. The Differential Windlass. —This differs from
the common windlass in having
an axle formed by two drums,
and B, of different diameters. A
cord is nttached to the langer eyline
der, and wrapped several thnes
around it, after which it passes
under a movable pulley, ©, and is
then wrapped in = contrary diree-
tion sround the smaller cylinder.
‘The power is applied to the erank
arm, and the resistance to the
Fig. 61 block of the movable palley.
TRAINS OF WHEELS %
‘When the handio is tamed so a8 to wind up the rope on the eylin-
dor B, it is at tho samo time unwound froin the cylinder A, and at cach
revelution the rope ts shortencd only by the difference in the eireum~
ferences of the estinders. If these are nearly equal, the weight moves
very slowly and great power ix gained.
tor. Trains of Wheels. — The power furnished by the
motor of a complex machine is usually transmitted through
@ succession of pieces to the working point. ‘These connect-
ing pieces aro, in general, wheels and axles, and, taken to-
gether, they form what Ix called a train. A wheel which
imparts motion to a succeeding one is called the driver; that
to which motion is imparted is called the follower.
102. Mode of Connection. —Thero are various methods
by meana of which one wheel may be made to act upon
another, ;
First, By simple contact. The driver,
A, being slightly pressed against the fol-
lower, B, the friction between the wheels
is sufficient to impart « motion of rota-
tion from the former to the latter.
Tu {nrmase the frletion and avold sliding. the surfwes are tre
quently covered with soft leather. In all cases the motion of the
follower is in = contrary sense to thut of the driver, ws indicated by
the arrows.
Stoondly. By means of bands or belts, The band is passed
around the cireumferences of both wheels, and when tight
ened, # suificient amount of friction is produced to impart
motion from the driver to the follower.
ee) Ore
Fig. a8 Fig 4
When the band does not cross botuwen the wheels, they both ra-
volve ii the exme dirvetion, os indicated in Fig, 63 When the
Fig. 62.
——
73 ELEMENTARY MACHINES,
Jand crosses between the wheels, they revolve in opposite dinretions,
ap indicated in Fig. G4 Belts aro made of leather, gatte-pensha,,
and the like. ‘They are flat and thin, wad the drums om which they
ran should bo slightly clewuted toward the eniddlo of thelr thieknons.
Cords are made of catgut, hempen fibres, or wire, nearly eylindriest.
‘Tho druins, of pulleys, on which they run, #bould be elevated wt tbe
edges. Chains ure also used, aud in this ease the drums shoudl Le
grooved, mnd either notehed or toothed, #0 as to fit the Tinks of the
ebain,
Thirdly. By means of projections on the ciroumferences of
the wheels called teeth,
A stall wheel, C, mounted on the axle of « lange one, B, i called
a pinion, and ita projections are called
Traces. In the figure, the tooth of the
wheel A engage with the leaves of the
pinion C, and the teoth of the wheel B
engage with the leaves of tho pinion J.
Ifthe wheel A is turned in the dirretion
indicated by the arrow, the wheel B will
revolve in a contrary direction, aud. the
wheel J’ in the same dirvction, A wheel
whose teeth project from ite elmouinfors
exce, an shown in Fig. 65, 4 called a
103. Law of Wheel-work.— Whatever may be the
mode of connection in a train of wheels, the law of their
action is the same as that of the compound lever. Henee,
the coutinued product of the power and the radit of the wheels ts
equal to the continued product of the weight end the radii af the
arles. for example, in the train shown in Pig. 65, let the
B, and F, be represented by the mums
bers 12, 12, and 8; and the rudiiof exch of the three pinions,
by the sumb then, the power will be to the welght as
2x 2X 2to 12 X 12% 8, i.e. na # to 1162, or as T to 144,
Suppose a power of 20 pounds to be applied to the first wheel :
20 x 1162 = Weight x 8, hence, Weight = 20% 1152 8 =
2830,
radii of the wheels
THE PULLEY. 7
Tn-common cloeks and watehes we have familiar examplos
of wheel-work In which the velocity is inereased at the ex
pense of the power. ‘Thus, in a watch, the force of the main-
spring is applied to a wheel thay revolves once in four hours.
This force is tranamitied through the wheel-work with dimin-
ished intensity and increased velocity, to give the second-hand
a revolution ence a minute,
404. The Pulley. —A Pveuxr is a wheel free to turn
about on its axis and having a groove around it to receive a
cord. The axis turns In a frame called a dlock,
A pulley ie said to be firat or morable, soeorling
a8 its block fy fixed of movable.
105. Single Fixed Pulley. — In this pulley
the block, O, is fixed, and the wheel, AB, tums
within it. The effect of the fixed pulley is sim-
ply to change the direction of a force. Fig: 64.
106. Single Movable Pulley. — In this pulley the block,
0. is movable, and the wheel turns within it. o
Patlege are combinations of the cord and lever.
Tn the fixed pulley we may regal 4B as» lever, 7
whose lever arms are OA and OB, and whos fulcrum to
is O In tho movable palloy we may rgard 4 Basa
ever of the second eluss, whose fal- Is
rum is A, and whose lever arms are
ABand a0. 8
Although no power ix gained by
the use of fixed palleys, thore iy often
great advantage derived from their
ues, ‘Thos, a man standiag on the
ground may, by using « Axed pnllny,
mito heay articles to the loft of a
Fig. 67.
warehouse, [tis easier to pull the
mipedownwand than to lift the weight
upward; tut this fe not the waly
Fig as. advantage gained, for if, instead of
using the pailley, he shouli carry the articles up a flight of stairs, he
————_
18 ELEMENTARY MACHINES,
would incur the sdditional labor of lifting his own weight through
tho whole apace. Two fixed pulleys may also be used to change
horizontal inotion to vertical, ms shown in Fig. 68,
107, Combinations of Pulleys. — Movable pulleys are
generally used in combination with fixed pulleys. Fig. 69
shows a combination of one fixed with onc
movable pulley. It is evident that the
weight, 1, is supported equally by the two
parts a and 6 of the cord which passes
around the moyable pulley, 4, Half the
weight therefore is eupported by the hook,
H, and the other half by the cord 6, which
passes over the fixed pulley. 2; and since
a(®) to power is galaed by the fixed pulley, the
r, P, must be equal to half the weight,
pow
I, in order to maintata eqailibelum. If it
ral be required to raise the weight,
additional force must be ap-
Fig. 00, plied at P, to overcome frieti
In the combinations of pulleys in most com=
mon use, several fixed pulleys are contained fn
© block, and an equal number of mayable pal
loys in another block. Fig. 70 shows such
combination of two fixed pulleys in the upper
block, and two movable ones in the lower block.
In this case, one continuous cord passes through
the system, and the tension of the weight is
equally distributed among the four parts of the
cord which sustain the lower block. The power
applied at P ix required to valance the weight
supported by only one of the parts at a; hence
the system will be in equilibrium when the power
is equal to one fourth of the weight.
‘The following is the law of such combinations: The seerght
equals the power multiplied by the number of parts of the cord
that support the movable Wack.
—<_
Fig. 70.
THE INCLINED PLANE, 79
Polleye are often used in combination with other mechanical
power. Crapves aod ilerricks are combinations of wheel-work with
pulleys, and are osed im raising great weights, as stone in quarries,
coal from vessels at the wharves, and for similar purposes,
Summary. —
Wheel and Arle.
Explained ao a Lever.
The Windlass
The Capetan.
‘The Differontial Windlass,
Trains of Wheels.
Modes of Connection.
1, By Simple Contact,
2 By Means of Bundy,
& By Tooth.
‘Lane of Wheel-work,
Examples
The Pulley.
Binglo Fixed Polley.
Single Movable Pulley
Advantage of Fixed Pulleys
Combinations of Pulleys.
Mostestions.
Law of Coubined Pulleys.
Common Applications of Pulleys.
-
108. The Inclined Plane. —The inclined plane is a
hard plane surface which is inclined to a horizontal plane.
‘When 2 body rests on a horizontal plane, as for example
‘oo a table, the action of gravity tending to draw it down is
completely counteracted by the resistance of the plane, ant
it remains at rest. It is not 90, however, when a body is
pon an inclined plane. Th this ease the action of
gravity may be resolved into two components; one perpen
dicular to the plane, and the other parallel to lt. ‘The action
‘of the first component ts counteracted by the resistance of the
‘plane, whilst the second component causes the body to move
down the plane.
ES
80 ELEMENTARY MACHINES.
It is evident that the nearer the plane approaches to a
horizontal surface, the greater will be the portion of the
weight supported by the surface. Let the plane be elevated
toward the perpendicular, and it will support leas and leas off
the weight, till, when it reaches the perpendicalar, no part of
the weight will be supported.
Whatever may be the inclination of the plane, the action
of gravity upon a body placed upon it is resolved into two
componenta which have the same ratio to each other that the
perpendicular height of the plane has to the horizontal base.
Fig. 71.
Of these two components, that one only which depends
upon the perpendicular height must be supported by the
power applied to maintain the body in its position,
Hence, the power is to the weight as the perpendicular height
of the plane is to its length
Fig. 71 represents a movable inclined plane which inay be ade
Justed 90 a9 to form different angles with the horizontal tase, If it
bo arranged so that the plane, FS, is twico as long as tho height, $7,
‘one pound at J will balance two pounds on the plane between Ht
and & If the height, $7, were only one fourth of 7S, one pound
at P would balance four on RS
1 railroads um largely made wp of inelined
Common roa
THE WEDGE. 81
planes, and their inclination i estimated by the beight which eorre-
sponds to some stated length. Thus, a road ix sald to rise one foot
in thirty, oF one foot in fifty. Tn the case of milroads the inclination
is called the grade, and is estimated by the number of feet in weetical
height coreponding to a mile in length. ‘Thus, we speak of a
gende of fifty feot, or eighty foot to the mile.
‘When a carringe ia drawn by horacs om a level road, the power ie
expendéd!'in overvomfag frletlon. On a roud which rises one foot
in twenty, the horses must lift one twentieth of the load, besides ower-
coming the friction, which varies from one fifteenth to one fiftieth of
the loed. Oo railroads tho rude i# seldom mado higher than cghty
foet to the mile, a rise of one foot in sixty-rix.
tog. The Wedge. —The Wxner is a solid, bounded by
@ rectangle, BD, called the back; two rectangles, A FP and
DP, called faces, ani two
triangles, A D# and BOP,
called rads. The line & F,
fin which the faces meet, is
called the edge.
The form generally used
fs the double wedge, repre-
sented in Fig. 73, The ro-
Fig. 72 sistance in this case acting Fig. 74.
At right angles to the opposite fnces of the wedge, the power
is to the resistance as half the thickness of the wedge is to
its length.
‘No aceurate extinute ean be made of the force exerted by a wedge
ae ordinarily used, for the following reasons: —
4. The power is by-exerted blows, the foree of which eannot be
mace,
2. The surfaces separited ofton uct as Jovers, and greatly ussist
the netion of the wedge.
B. The fesetion is much greater than with the other mechasieat
powers, and cannot be neourately estimated.
Tit wore net for the ection whe wedge would rrooil after every
Blow, tind 06 practical nse could be made of it.
‘Wedges are uset where au intense force isto be exerted throwgh
=
82 ELEMENTARY MACHINES.
very small space, and especially for splitting masses of wood er sone,
for blocking up buildings, and for raising vessels in docks.
‘The edges of kuives, scissors, chives, axes, and all cutting instra-
ments aro wedges.
110. The Screw. —The Scnxw is essentially a combi-
nation of inclined planes. It consists of a solid cylinder,
enveloped by a spiral projection called the #hread.
The two faces of the thread are nothing more than
inclined planes wound around the cylinder of the
screw.
The screw works into a solid, fitted to receive
it, called the mu. The nut may be fixed, the
Fig. 74 screw turning within it, or the screw may be fixed,
the mut turning upon it. Motion is imparted to the one or
the other, as the ease may be, by means of a lever, at the
extremity of which the power is applied. By increasing the
length of the lever, and diminishing the distance between
the threads, the force exerted at the point of resistance may
be almost indefinitely increased.
Fig. 75 shows the use of the
coinbined lever and sctew in pro:
ducing great pressare, A iis the
screw, Bihe nut, and B the block
on which the substance to be
pressed is placed. The power it
Applied at the end of the lover,
Acconling to the general
law of machines, the foree ex=
erted at D will be ns many times
ieater than the power applied at
Y aa tho circumference. throruehs
which A’ moves is greater thar
the distance hetween the threads:
of the serew.
Suppose the distance between
the Uirends to be one fines, sind
that the ond of the lever, N, doveribes a circle of ton fect in eiroam-
base
Pig. 76
THE SCREW. 83
ference in once turning round, then the ratio of the power to the
weight will be as one inch to ten foet, or ne 1 to 120.
Now if mau exerts n force of one hundred pounds ut the end of
the levor, the screw will advanco with n foree of 12,000 pounds. If
the distance between the threads were only half an inch the force
would be doublad. Hence it is evident, that, with a moderate power,
the serew may be made t exert an enormous mechanical force, It
mast not be forgotten, however, that the work done upon the body
to be compressed ean never exceed that done at the point of applica-
thon of the power; on the contrary, it is always less In this ease
there is a loss, by friction, of nearly onc fourth of the whole effect.
ir, Law of the Screw. —Not taking into account
the effects of friction, the law of the screw may be stated as
follows :—
The power is to the weight as the distance between two adjoin-
ing turax of the thread is to the circumference described by the
power.
a12. The Endless Screw is 1 scrow secured by shoul-
ders, so that it cannot move in the
dirvetion of its length, and working
into as toothed wheel, When the
screw is turned, it imparts motion to 6
the wheel, which, in turn, may be
made to move a train of wheel-work.
Machines of this kind are axed in regi
tering the number of turaa of an axle, us,
for example, the shaftof a steambout, An |
endless serew is armnged 80 as to tum ar {
many times ax the shaft, and is connected
with a train of Hight wheel-work. Tho Fig. 70.
‘wheels bear indices, by means of which the number of turus in any
given time may be read off. This arrangomont is oxteusively used
im gas aod water meters, and also in various branches of mana~
facturn,
be RESISTANCES TO MOTION,
SECTION fl. —RBMISTANCES TO MOTION,
113. Friction is the resistance which one body experi
ences in moving upen another when the two bodies are
pressed together, ‘This resistance arises from inequalities
in the surfaces, the projections of the one sinking fate the
depressions of the other, To overcome tho resistances thas
produced, a force must be applied sufficient to break off, or
bend down, the projecting points, or else to Tift the moving
body over the inequalities.
Friction is distinguished as sliding and rolling. ‘The former aries
when one body is drawn upon another; the latter, when one body
is rolled upon another. Everything else being equal, the former ts
greater than the latter.
114. Measurement of Friction. — The comparative
friction for many different surfaces has
been determined by the ap-
paratus shown in Fig. 77.
Blocks of different ma-
terials and of different size
and shape, sometimes load-
ed with weights, were made
to move over surfices of
different kinds, by means
of weights placed in the
xperiments the following fuets bave been
amount of sliding
Wig. 71.
pan, P. By the
ascertained : —
1, Friction is nearly proportional to pressure:
2. Friction is not affected by extent of surface, except seithin
extreme limite,
The sitne foree is required to draw a brick nero w boant, whether
it reste on its broad fhee or on ite ed
8. Friction is greater between saft bodies than hard ones.
4, Friction is greater between surfaces of the sume materiale
than betwoen thote of different kinds.
FRICTION. 85
‘The friction of iron upon iron is greater than that of iron upon
copper or brass.
For this reason the axles of railway care being snado of steel, the
Tnoxes in which they revoleo are mado of brass oF como other motak
Foe the same reason, the axles In the wheel-work of the best
reatches aro mado to revolve in holes bored in tho harder precious
Stones, Such watches are said to be “jewelled."
5. Friction is diminished by polishing or lubricating the sur-
faces.
Polishing removes projecting paints that would catch against each
other sud increneo friction. The application of lubricants Like oils,
tallow, black-lead, ete,, diminishes friction by filling up minute eavi-
ties and atnoothing the surfaces.
6, Friction ts greatest ut the beginning of motion.
Whew surfaces remain long in contact, expecially under pressure,
the projections of one sink deeper into the depressions of the other,
ised render is more difficult to separate them.
445. Advantages of Friction. — Although friction occa-
sions a loss of powor in the working of machines, it has some
advantages,
‘Comanon nails and sorews would be neclees were it not that friction
holds them in place. A wedge could not bo driven if friction dit not
Hold it and provent it from rebounding after a blow. A looomotive
depends upon friction for its power to draw a heavy train af ears.
Sometimes whon great loads are to be moved tho friction of the
driving wheels upon the mils is not sufficient to prevent slipplag,
dand therefore boxes ané provided fran which sand may be sifted
upon the rails when required, thus increasing the friction and ena~
Wing the emgine to draw ite load,
416. Stiffness of Cords. — When a cord ia wound upon
& wheel or axle, acertain amount of force is required to bend
it. ‘The resistanee which the cond thus offers to bending is
elassed as a hurtful resistance. ‘This resistance should be
Obviated, as far as possible, by selecting bands and cords
Which are a6 flexible as is consistent with due strength.
_——
36 RESISTANCES TO MOTION.
117. Atmospheric Resistance.—The atmosphero ex-
erts a powerful resistance to the motion of bodies moving
through it. It has been found, both by theory anil experi-
ment, that this resistance is proportional to the greatest cross
section of the body, made by a plane perpendicular to the
direction of the motion, and also to the square of the body"s
velocity. To obviate this resistance as far as possible, the
pieces which bave a rapid motion should baye as small a
otoss section as is consistent with due strength.
Summary.
The fnelined Plane.
Resolution of the Force of Gravity in a bady resting on an
Inclined Plane.
Law of the Inclined Plane,
Mostration by Movable Inclined Plane,
Common Reads and Railroads.
The Wedge. Reasons why the For
cannot bo aceurately estimated.
Practical Applications of the Wedge.
The Serew.
Combined Lever and Serew
Law of the Sorew.
‘The Endless Screw
Revistances to Motion,
Friction. Sliding and Relliug Friction,
Measurement of Friction.
Six Facts relating to Frietiou,
Advantages of Friction.
Stiffness of Cards
Alwcopheric Resistance
CHAPTER IV.
THE MECHANICS OF LIQUIDS.
Part 1. ~ HYDROSTATICS.
SECTION | —ORXERAL PRINCHrLEs
118, Hydrostatics and Hydrodynamics. — The
Mechanies of Liquids is divided into two branches:
Hyprostaties, which treats of the laws of equilibrium
of liquids, and Hypropysamics, which treats of the
laws of motion of liquids.
419. Properties of Liquids. —The following properties
are common to all liquids:
1. The molecules of liquids are extremely movable, yield-
ing to the slightest force,
‘There ls very little cohesion betwoon tho molecules of liquids,
whence thelr rendiness to slide among ono another. It is to this
principle that they owe their fluidity.
2. Liquids are only slightly compressible.
Liquide are #0 slightly compressible, that fora long time they were
ws absolutely incompressible, In 1823, Oxrsren
strated, by an apparatus which bie contrived, that liquids are sligt
He showed that for a pressare of ono atmosp
is, of 15 pounds on each square inch of surface, wate
The yeaeesth of ite original voluine. Slight as ie
off outer, 1 Is noverthelees toe: thes ax compressible as mercury.
B. Liquids are porous, elastic, and impenctrable, like other
88 HY DEOSTATICS.
That liquids ase porns, has already been shown. "That they are
clastic, ia shown by their recovering thelr volume after the eoeny
ing forve ia removed. Tt ts also shown by the faet that they tranainit
sound. ‘Their ipenotrability is shown by plonging n solid Ledy bite
@ vessel filled with liq If there is no imbibition, a yolumne of water
will flow over the veesel just equal to that of the palid introdaced,
Upon these three properties of liquids depends their prop-
erty of transmitting pressures in all directions.
120. Transmission of Pressures. — Principle of
Pascal. —Let a bottle be filled with water and corked, as
represented in Fig. 78. If the cork be presse
inwards, the pressure will be transmitted to the
molecules in contact with it; these moleceles
will in their torn press apon the neighboring
ones, and so on until the pressore is finally
transmitted to every point of the laterior sur
face of the bottle.
It is shown by experiment that the pressure thas
transinitted is equal to that applied to the cork ; that
ia, the prresure apon each square inch of the Interior
surfice of a vessel i8 equal to that opan a square inch
of the cork. ‘The proseure is everswhere perpendica-
lur to the surface, as shown by the arrow-heads.
‘This principle io called the Principle of Pasout,
becanse it waa first demonstrated by Bua Pascan tn the seven
teenth century. Upon it depends the whole theory of Hydrostaties.
‘The une principle
may be chown by an-
other experiment. A
cylinder (Pig. 72) ura
vided with @ piston te
fitted into a hollow
sphere. Perpendicular
to the sides of the globe
are snall tubalar open
ings, Ful with water, and prees the platen
againat the water, wud it will come from all the orifices eyunily, and
not merely from that whieh is opposite the
PRESSURE OF LIQUIDS. 89
tar. Pressure due to the Weight of Liquids. — If
a cylindrical vessel ix Glled with a heavy liquid, ita weight
produces & pressure upon the walls of the vessel. If we sup:
pose the liquid divided into horizontal layers of equal thick=
ness, it ls plain that the second layer from the top supports
#& pressure equal to the weight of the first, the third layer
supports & pressure equal to the weight Of the second and
first, and 60 on to the bottom. Hence, the pressure upon any
layer ts proportional to its depth below the npper surface, and is
equal to the weight of the column of fluid above it.
Fig. 0
Th consequence of the Principle of Pasear, this pressure is
transmitted laterally, and acts against the sides of the vessel
with an equal intensity. Hence, every part of the sverfince is
prened with a force equal to the weight of a column of liquid
whose be ix the surface pressed, and whose height is equal to the
chstance from that surfisce to the upper level of the fluid.
122, The Pressure on the Bottom of a Vessel.
arising from the weight of a liquid, is entirely independent
‘Of the shape of the vessel, ax well as of the quantity of liquid
whieh it contains. It depends only on the size of the sur
———
90 HYDROSTATICS.
face pressed, and its distance below the upper surface of the
liquid.
‘This principle may be demonsaraed by mesos of 20 spparaton
shown in Fig. 80. The apparatus consists of & tube, @, firmly at-
tached to the cover of a glass vessel, P. By means of a serew joist,
different-shaped vessels, A, B, C, may be attached to the upper cud
of the tube. A disk, of ground glass ix held in contact with the
lower end of the tube by a string, which is secured at its upper ex-
tremity w an arm of a balanee.
Tho vessel A ia screwed on, and filled with water until the down-
wanl pressure exactly counterpolses a given welght in the seale-pan,
Mf, when the upper surface of the water is marked by n sliding
bead, m. The other vessels, Band C, are successively screwed om,
and filled with water up to the level, 7; if any mone water is poured
into either, the downward pressure overcomes the weight, Afy aiid
tho water eeeapes into the vessel, P.
‘This principle of pressure on the bottom of vessels Is sometimes
called the Hydrostatic Peradex. 11 is 90 called, because the same
pressure may be obtained by using very different quantities of the
aaine liquid.
123. Hydrostatic Bellows.—A good illustration of
the principle that the pressure exerted by a colamn of water
depends upon its height and not ite amount is
soon ina form of apparatus eallod the Aydro
static bellows. It consists (Fig. 81) of two
boards connected by leather, in which a tabe,
A, is inserted.
When water is poured into the tubes pressure 1
exerted upen the upper board C, which will Tw
weight as inany times greater than the weight of
the water in the be, as the area of the bound is
croater than the area of a cross-section of the tite.
By plicing another tube upou 4, we ean ineresse
Yi 5! the pressare and lifting power.
124. Lateral Pressures. — Reaction Wheel. — The
fect that liquids exert lateral pressures upon the walls of
vessels Is demonstrated by means of the reaction wheel:
PRESSURE OF LIQUIDS. on
This wheel is shown in Fig. 82; it consists of a vertical
eylindrieal tube, C, turning freely in a ring, 1, near its upper
extremity, and resting upon » pivot at Its lower extremity.
Just above the pivot the tube terminates in a cubical box,
from the faces of which
Project four tubes, having
their ends carved, as rep:
resented in the figure.
Water is supplied from a
cistern throngh the fun-
nel, D, When the water
is admitted, it flows down
the tube, C. and escaping
through the curved tabes
at the bottom, the wheel
is tarned in the direction
indicated by the arrow.
head.
‘The reason of this will be
b
Ve
ie» plan of two of the tubes.
‘The weight of the water
enuses & pressure upon 4,
es vol
being open, the presse upon *
Fig.
acts from a towunls A, producing retary motion. Tho preasures in
all of the tubes couspire to produce rotation in the same dirvetion.
425. Pressure Upwards. —That liquids exert a pres-
sure upwards fs demonstrated by moans of the apparatus
shown in Fig. 83.
Ti ckuatists of a tabe of gia, with a movable disk, a, eround po as
to fit the botiom of the mbe. ‘The disk being held closely agalest
ES
92 HYDROSTATICS,
the tube by a string, 6, tho whole is pilanged into a vessol of water.
Tn this state the dick, though heavier than the water, dues wot fall
to the bottom, showing that it is
Deld in place by an upywand pres:
sure. If water now be pouréd Ente
the tube in a gentle streme, the
disk will adhere till the latter te
filled to the level of the feild oo
the onteide, This shows that the
upward pressure fs equal te the
weight of @ culm of water whowe
ase is thatef the tube, and whowe
altiude is its distanee below the
upper surface of the fluid.
‘The upward pressure of Molds is
called their Buoyant Bifort. Te te
in consequence of thelr buoyaut effort
that floide sustain lighter bodes en
their surfaces, ‘The sume principh
of all kinds, diminishing the weigh
‘ones to float
Fig. 83.
126. Pascal's Experiment.—
‘The following experiment was made
dy Pascar, in 1617. Ho fitted ieee
the upper head of « strong ens « tube
of small dinmeter mmd about thiirty-
four fect in length, aa shown in Figs
a. he ewsk being filled with water,
de succeeded in bursting it by pourkag
a comparatively small quantity nif water
into the tube, Tn this ease the piece
je aterally was The site am
though the tube hat been direughous
of the samo diameter as the cask, oF
even greater.
sure e
Tig. &.
127. Hydraulic Press. — The principle of equal pres-
sures has been applied fi Ue construction of a press, by
HYDRAULIC PRESS. 93
means of which a single man may exert an enormous power.
‘This press is shown in perspective in Fig. 85, and in section
in Fig. 86, the letters im both figures corresponding to the
same parts.
‘The peoss consists of two eylinders, A and B, of mequal aian-
cers Too the cylinder B is a slid piston, C, which risce a the
Fig. 5.
Water ik forent into B, and thus forces up a platform, A. ‘The
eylinder A forms the bare! of a puwp, by means of whieh water is
milsed from a reservoir, P, aud forced into the cylinder Bt. This
Pump is worked by a lever, 0, attached to 0 solid piston, a. When
the piston a fy raized, « vacuum is formed behind it, which fs filled
by water from the reservoir, P, which cuters by opening the
walve When tlic piston tx dopreseed, the valvo S closes, the
———
94 H¥DROSTATIOS.
valve m i oponed, and a portion of tho water is fireod
the pipe, d, into the eylinder B. By continuing w work the
piston @ up and down, additional quantities of watee aro furced
into the large eylinder.
In cousequenes of the principles of eguat pressures, the force
applied tw the piston @ is trausuittod thmnugh the tube, @, and ix
Hinally exortod upwards aypiust the piston C, te elfect Being naukti-
plied by the uumber ef thnes that the section of tbe piston © is
wreater than that of the piston a. For exanple, if the section of
Cio 150 times as grout a8 that of a, every pound of pressure on the
Jatter will prodace 150 pouuds of pressure on theformer, This offeet
Fig, 86,
ix farther wnltipliol by weans of the lever, 0. "The pressure exerted
upon @ forces up the platform, A, with an energy that may be
utilized in comproteing any eubstance placod between it and the top
of the press, Af. ‘This upward presume may also be used fur
raising heavy weights.
By vurylug the rvlative dimensions of the parts of the machine,
tinay bé exerted. Tn the arta, presses Of this Kind
able of exerting a forve of more than a hunderd
wa ininense por
are coustructed
thonsand pounds.
‘The hydraulic pross ix used in compressing seeds to obtain oils, In
packing hay, cotton, and other goods fur shipment, in preseiag books
for the binder, and iu w great variety of other operations,
|
EQUILIBRIUM OF LIQUIDS. Li}
‘Tho bmnenso tubular bralge over the Menai Straits was raised
frotn the Jovol of tho water wo the top af the pigrs by ineans of
preases wf this déseripdow. ‘The hydrwulle preas was also weed in
Jaunehing the Great Eastern, the heaviest movable structure over
constructed by wwe.
Summary. —
Hydrostatics and Hydrodynamics,
Properties common to all Liquide,
Tranemiasion of Pressures.
Experiraens,
Principle of Pascal.
Experhuent.
Pressure due to the Weight of Liquists.
Law of Pressure.
Prossure on tho Botton uf a Vessel.
Hyurystatic Parulox.
Hydrostatio Bellows.
Lateral Pressures.
Resotion Wheel.
Proseure Upwards.
Experinent.
Puseal's Experiment.
Hyslrautio Prose.
SECTION Hh. —EQUILIBWIUN OF LIQUIDS.
128. Conditions of Equilibrium. —A solid body is in
equilibrium when its centre of gravity Is supported, beesuse
tlie particles of the body are eld together by cohesion, In
Tiquids the particles do not colierc, and unless restrained they
would flow away and sproad out indefinitely. A liquid can
be in egailibriam only when restrained by a vessel or some-
thing equivalent. Furthermore, each particle mast be equally
pressed in all directions, which requires that the free surface
should be level, that is, everywhere perpendicular to the force
of gravity.
————
6 UYDROSTATION
Tn saying that the free surface nat be level, we ‘that the
liquid is acted upse ony by te furee uf gravity, the ondi-
ary cae. Ut, howerer, it is acted apou by uther frees, the free
surface wust, ut every point, be perpeadioular to the reseltant of all
the frees acting at that priut; fur if i were mot ey, this mouliast
tight be resulved into two emnponents, vue penpenibetilar te the
surface, aud the other parallel to it, “The former would be tweasted
by the reactiva of the Liquid, mand the latter, being:
would produce motiou, whieh is contrary te the hypothesis of
equilibriain.
129. Level Surface. —The surface of a liquid is Leven
when it is everywhere perpendicular to the direction of
gravity. Small level surfaces coincide sensibly with hori=
goutal planes. Large level surfaces are curved 80 as to con-
form to the general form of the earth's surface. ‘That the
surface of the ovean is curved [s shown by the phenomena
presented by a ship viewed from the shore, as exhibited fa
Fig. 87, As the vessel recedes, we first lose sight of her bull,
then her lower sails disappear, then her higher sails, until at
last the entire vessel is lost to view.
A= wai
EQUILIBRIUM OF LIQUIDS. 7
Ta defining’ « lovol eusface, we aaidl that it is everywhere perpen=
dicular 10 the direction of gravity ; snore strictly speaking, it is per~
penilicalar to the resultant of gravity and the coutrifugal foree due
ty the earth's nutation on He axis. Were it not for the centrifugal
foroe, the earfico of tho ooean would bo perfectly splorisal, but in
couseypence of that furee, it ix ellipseddal ; thus is, the cecuns are
vlewated about the equator and depressed about the poles.
The general level of tie ocean is called the true leoel ; a horizon-
tal phine at auy point is galled the apparent level.
The carvature of the earth is about eight inches per taille, and
inereases as the square of the distanes.
Pig, 8%
130. Equilibrium of Liquids in Communicating
Vessels. — When a fiquid is contained in vessels whieh
communicate with one another, it will be in equilibrium if its
upper surface in all of the vessels is in the same horizontal
plane.
This principle ie demonstrated by means of tho apparatus rupee
Gat to Big. 88, This apparatus consicts of w system of glass
Weasels uf lifforent shapes and cipacities, all of which communicate
bya tube, mc Mf any amount uf water or other liquid be poured
ito o6e of the branches und allowed t) como to rest, it will be ween
a=
98 AYDROSTATICS.
that its upper surface in all of the vessels is in the sume horkeontal
Plane, ‘The reason of this is, obviously, a nooeseary eonseynence uf
tho principle of equal pressures,
131. Vessels containing Liquids of different Den-
sities. — When liquids of different densities are contained in
communicating vessels, they will be in equilibrium when the
heights of the columns are inversely as their densities.
Fig. 8.
This principle is demonstrated by means of an apparatus showtt fm
fg The apparatus consists of two glass uibes, A and B, open
at top, and communicating at bottom bys sinaller tube. Ia quan~
thy of mereury be poured into one of the tubes, it will come to a Towel
in both tube wding to the principle expliined in the preceding
ariel. If a quantity of water he poured inte the tube A, the Tevol
«f the wereury iu that tube will bo depressed, whilet it will be ele-
vated in the tube B, The difference uf level, dc, cat be determined
by tho gridunted scales on tho ta 1k will be found by tesaure-
meut shat the column of water, ad, is LAG times as high aa the
—.
EQUILIBRICM OF LIQUIDS. v8
column of mereary, de which it supports Tt will be shown
Dereafter, that mereury is 18.6 tlines us dense as water; Tieuce the
principle is proved, Other liquids may be employed with eimilue
results.
132. Equilibrium of Heterogencous Liquids. — If
liquids of different densities, but which do not mix, be poured
into a vessel, (hey will arrange them-
selves in the onder of their densities,
the heaviest being at the bottom, and
the upper surface of each will be
horizontal.
‘Thisis shown by x vial (Fig. 90) con-
taining liquide of different deusitios, a»
norenry, water siturated with potassiuin
carbonate, ulevhol reddened by anilino,
wud uapbita. We can float on the ditfer-
ent surfaces balls of cork, wax, wood,
wud glass If the vial be shaken, the
liquids appear to mix; but if allowed
to stand, they arninge theanselves in hor-
izontal layers, the denseet liquid at tho
11 ie it meoondanee with this principle
[
that efrain rises on willk, and oil ou Fig. 90.
water, ‘Tho principle ie often omployed to separate liquids of differ-
wut Hensity by tho process of decanting.
ESCO WE—APPLICATIONS OF THE PRINCIPLE oF
HQUILIDRIEM,
tg3- The Water Level. —A Waren Lever is an in
stfument employed for determining the «difference of level
Detween two points. It consists of a lovizontal tube of
metal 24 or 3 feet in length, Into the extromitios of which
two glass tales are inserted perpendicular to It. The whole
—_—_————
100 HYDROSTATICS.
rests upon a three-legged support, called a tripod, as shown
in Fig. 91. A quantity of water tinged with carmine or other
coloring matter is introduced into one of the glass tabes,
which, fowing through the horizontal tube, rises to the same
level in the other, by the principle of equilibrium of liquids
in communicating vessels. A visual ray directed along the
surfaces of the water in the two glass tubes will be « hori
zontal line, or a line of apparent level.
In uaing the instrament, the squate, seen at the left of the figure,
can be mised or lowered to agree with the dotted ling,
Fig. 01.
e levelling instrament and the distance of the horizontal mark
om the square from the ground.
134. The Spirit Level. — The Srmrr Lever. consists of
s nearly filled with alcohol, and closed at its
two extremit ‘The tobe is slightly curved, and when
placed horizontally, the bubhk oh it containg rises
to the middle of the upper side of the tube. If either end be
depressed, the bubble runs toward the other end. When
need it is ordinarily mounted in a wooden case.
This form af level is rnuch used by masons, carpenters, and other
_ |
a tube of
EQUILIBRIUM OF LIQUIDS. ToL
‘artisana. ‘To ascertain whether a surface is lovel, tho instrament is
Jaid upon It, avd the position of the bubble noticed. If the bubble
is in the middle of the tube, the surface is level,
In the level used by carpenters there are generally two tabes in
the same cxse situated at right angles to each ether, —one for hori-
zontal surfaces, the other for vertical.
‘The form of level shown in Fig. 92 is attached to rnany kinds of
sarveying aud astronomical fnstruments.
Figs
= ‘Springs. — Fountains. — Rivers. — Itis the prin-
lj
equal pressures that causes water to rise in springs
and fountains. The water which feeds them is contained in
natural or artificial reservoirs higher than the spring or foun-
tain. These reservoirs communicate with the springs or
fountains by natural or artifiefal channels, and the pressure
of the water in them causes that in the spring or fountain to
boil up, or sornetimes to shoot up in a jet.
‘The wnter of a jet tends to rise to the level of thit in the reser
Soir, and woald do ee wer it not for the resiatunoe of the air, the
friction of the water against the pipe, and the resistance offered by
the falling particles, all of which combine to render the jot lower
than the foanula-heal,
‘The same principle determines the flow of streams from the higher
1 the lower gronnds. The water of lakes, seas, and oceans ix
continually evaporating te form vapors and clouds These are cou-
deesed in the form of rain, and the particles of water, urged by their
own weight, scl a lower level. ‘The rivalets guther to forin brooks,
god these unite to form-rivers, by which the wuter is one inore e+
tureed tothe oceank and lakes All of the water docs not flow buck
fo the Otean along tht surface, but a portion percolates throngh the
peter Selle and accunubstes bx cavities to food our eprings and
wells,
La
102 HYDROSTATICS.
Fig. 93 roprosents a fountain. Tho reservoir ie on the bill 10
the left, and the water reaches the bottom uf the basin by a pipe
rypresentad by dotted lines,
It will be observed that the column of water does not rise a& high
‘as the position occapied hy the water in tho reservale on the hill, for
tho reasons just given.
Pig. 68.
136. Artesian Wells ure deep wolls, formed by boring
through rocks and strata of varions kinds of earth to reach
a supply of water. These wells are named from the province
of Artois, in France, where they were first used.
Pig. 94 illastrates the principle of these wells. 20 is the natural
surfuoe of the earth, A Hand © Dare curved strata of elay or rock
which do not allow of the percolation of water. KX ix au inter~
mediate strtnm of sand or gravel, which permits water fo penetmte
it, Wheu a hole, Z, is bored down to strike the water-bearing stra-
tum, KK, the pressure of the water in the stmitam furees it mpin a
o well of Grenelle, in Paris, is nearly 1800 feet deep, and
water coming from the hill of Champagne, which are
tnuel bigher than Paris. ‘The supply of water from this well i ha-
mnense.
Lug +
EQUILIBRIUM OF LIQUIDS. 108
Many Artesian wells have been sunk in our own country.
‘There are two im 81. Louis, one of which reaches the depth of
BS4R5 feet, and one in Columbus, Ohio, having a depth of 27754
feet. In California these wolls are used in providing water for
trrigation. a
‘The so-called flowing wells of tho oil regions of Pennsylvania are
exumples of Artesian wells Tn some eases, however, the cause of
the violent outhurst which often takes place, when the resertoir
containing petrolonm fs first penetrated, is tho pressure of confined
alt and gases.
Fig
The water of many Artesian wells contains great quantities
of common salt and other substances in solution.
Summary. —
Equilibrivn of Liquids.
Condisions nf Equilibrives
. Level Surface.
Apparent and True Level.
Liquids in Connected Vesela.
Tilastration.
104 HY DROSTATICS.
Applications uf Principle of Equilibrium,
‘The Water Level.
‘The Spirit Level,
Springs, Fountains, Rivers
Artesian Wells.
Flowing Wells.
SECTION IV, —PRESKURE ON SUBMERGED BODIES.
137- Principle of Archimedes. —If a boty is sab-
merged in a fuid, it will be pressed in all directions, but not
equally.
‘To Illustrate, suppose a cube Immersed in water, as shown in
Fig. 95 The lateral faces, « and will be eqaally pressed and
in opposite directions, ‘The same will
xr» bo true for the other lateral faces.
Hence the horizontal pressures wall
exnotly outealise each other The
) upper and lower fneea, e und a, sill
| bo uncqually ‘pressed, and’ ta epposiia
directions. "The face ¢ will be pressed
upwards by a foree equal to the weight
of s colum of the liquid whuse eross-
ction is that of the eube, and whoas
: Ta height is the distance of «¢ from the
wurfieo uf tho Haid. ‘The face a will
be pressed downwanls hy the wolght
of a colman of tho Hquid, having the san ss-ecetion as the
cube, and 4 height equal to the distance of d frum the surface of
tho liquid; tho resultant of these two presucee fk an apwanl
for tw the weight of a volome of the liquid equal te
that of the cube. ‘This upward pressure ie tho buoyant effort of
the Quid.
The principle Just explained is called the Prineiple of
Archimedes. It may be expressed by saying that a sub
merged boy loses a portion of its weight equal to that of the
disphiced fluid,
Fig. 9
pquiv
PRESSURE UN SUBMERGED BODIES, 105
138. A Hydrostatic Balance is a balance having a
hook attached to the lower fee of each scale-pan, and 0
constructed that the beam may be raised or lowered at
pleasure,
Fix. 96 ropresenta u hydrostatic balance. ‘The eylindor ¢ is solid,
and fitted wo slide up and down in the hollow cylinder d. ‘The
eylinder ¢ may be confined in any position by meaus of w clamp
sero,
199- Cylinder and Bucket Experiment. — The prin-
‘ciple of Ancitimznes may be iMnstrated by what is called the
Cylinder and Bucket Rrperiment, us shown in Fig. 98. A
hollow cylinder or bueket, 4, of brass, is attached to the
hook of one of the seale-pana, and from it is suspended «
solid cylinder of brass, just large enough to fill the bucket
ani the two are balanced by weights placed in the opposite
seale-pan, A glass vessel haying been placed beneath the
eylinder. water is gradually poured into it, until the cylinder
fs immersed. The opposite seale-pan will descend, showing
106 HYDROSTATICS.
that the cylinder is baoyed up by some force. If we sow fill
the backet, 4, with water, the equilibriam will be restored,
and the beain will come to a level, Beeause the water poured
Into the bucket is equal to that displaced by the cylinder, we
infer that the buoyant effort is exactly equal to the weight
of the displaced fluid.
‘The principle of Arcrinennes is 00 called beowese it was Grat
discavernd by the Elistrious philosopher of that name, He was led
to the discovery in au attempt to detect # feaad perpetrated upon
Hiro of Syracase by a goldsmith who had been eumploynd so make
a golden crown. The artisan mixed a portion of silver with the
gold thet was givea im fur making the crown: but, by means of
the principle abowe explained, Anciimenes was able to determine
the exact anount of each material employed.
140. Floating Bodies. — Principles of Flotation, —
When a body is plunged into a liquid, it ts anged downward
nd upward by the buoyant effort of
the liq’ to the relative intensities of these
two forces, throe cases may arise; —
1. If the density of the imumersed body is the sate as that of the
Tiquid, ite weight will be equal to the buoyant effort of the Bquid,
aud it will remain in eyailibriun wherever i eaay be placed. This
is practically the ease with fishes. They malntale themselves in
any position in which they may happen to be, without ert.
2 If the the body is greater than that oF thé Bquid,
its weight will be has the booyant effort, amd the body will
sink to the botiom, This is what happens whea a Moae Oe pater
om is thrown into water
If tho density of the body is less than that of the lqwily its
weight will be lew thas the booyant e@ort, und the body will rise
te the surface. The bedy will continge to rise mutil the waght
© body, when it will comme
to rest. It ls then said to float, ‘Thes, a piece of wood Seaite Spon
water, and in like mater a plseo of iron Hats upon mnercarys
When o tloating body comes to rest os Hqubd, the plane of the
apper surface of the liquid is called the Plane of Flotation.
Tt sometimes happens that a body which i more dense than a
fe ok
by its proper weight,
and, accordin
letssit
uf the disph
d Tiqubd eqyaals that of
PRESSURE ON SUBMERGED BODIES. 107
liquid floats upon it. ‘Thus, a porcelain saurer floats upon water,
‘This arises from its form being such that it displaces its own weight
of water when only partially immersed. For the sane reason iron
ships float freely on the ocean,
341. Mlustration of the Principles of Flotation, —
‘The principles of flotation may be illustrated by an instrument
shown in Fig. 97 which, under
varions forms, is sold in the shops
as a child's toy.
Ta the firm shown, it consists of «
high and narrow glass vessel, sur
mounted by brass cylinder, A, in
which is an air-tight piston that may
be raised or dopreesed by the hand.
Tho vessol is partially filled with wator,
and contains # light body, as a fish,
hollow, and of porcelain or gluse ‘The
fish is atinched to « sphere of glass, m,
filled with air, and with a small hole,
9, ot its lower side, through which
water cin How in or out, as the pres~
sure is increased or diminizhed,
Under wntinary cirumnstances the
spharn, m, with ita attached fieh, floats
at tho surfaco of the water. If the
piston & deprewel, the alr beacath {1
is compressed, and scting upon tho
water forres a portion of it into the
globe, The apparitus then becomes
thors deviat than the water, nnd sinks. By relieving the pressure,
the alr Iu the globe expands and drives the water ont, when it
again Boats om the surface. ‘The experiment may be rrpeated at
pleasure,
142, Swimming Bladder of Fishes. —In many fishes
there is = bladder filled with air, situated directly under the
backbone. This is culled the Swimming Bladder.
Whies the fish wishes to descend, it compresses this Viadder by
——
108 HYDROSTATICS.
a muscular effort, and thon, as the quantity of water dieplaced i leas
than Lefore, the weight of the fish prevails over the buoyant effort,
and the fish sinks. On relaxing the offurt, the bluddor expands, tho
buoyant effort of the water prevails over the weight of the fish, and
it rises.
143. Swimming. —Tho human body is lighter than water,
especially than the salt water of the ocean, and tends natarally to
float when immersed. ‘The only reason why inen do not swin matu~
nally is the diifleulry of keeping the bead out ef water, so ax to be
able to breathe. The hoad is the heaviest part of the body, and
tends continnally to sink into the water.
Many quudrupeds «wim uaturally, beewnse the hood is small fn
proportinn to the body, and is so placed upon the trunk that ir ie
easy to keop it above the surfiee.
‘The safest position for a person in the water, who does not keaw
how to swim, is upon the back. ‘The tondeney to naiag the arms wat
‘of the water should be resisted, as thix diminishes the buoyast effary
of the fluid without diminishing the woight.
Many kinds of binds, as ducks, geese, swans, and the Whe, sin
untunally aud without effort. ‘hey owe this faculty tum thick layer
of down and feathers which are very light, and impermeable ly
water. ‘They therefore divplace a lange volurne of water ii pro~
portion to their weight, gi ine (0 watrong buoyant effort.
Summary. —
Pressure on Submerged Bodies,
Principle of Archimedes
Mluateation.
Hyirostatic Balance.
Cylinder and Bucket Experiment.
Hiero’s Crown.
Floating Bodies.
Bodies of the same Density as the Liquid. — Bodies
of greater Donsity. — Bodiog of less Density,
Plane of Flotation.
Ulostration of Flotation.
Swimming Bladder of Fishes,
Swimming.
many Animals wim naturally,
Aquatic Binds,
SPECIFIC GRAVITY. 109
SECTION V,— SPECIFIC GRAVITY OF DoDiE.
144. The Specific Gravity of a body is its relative
weight ; that is, it is the number of times the body is
heavier than an equivalent volume of some other body
taken as a standard.
Tt is & matter of daily observation that some bodies are heavier
than others under the same volume. Thus, gold is heavier than
silver, lead than iron, stones than woud, and s0 on. In onder to
compare the relative weights of different bodies, all are referred to a
common standard,
Distilled water is generally adopted ax a standard, and because
water varies in donsity at different temperatures, it is usual to take
it at the temperature of HPS Fahrenheit, or 4° Centigrade, wator
being most dense at that temperature.
Tn onder to find the specific gravity of any body, all that
we aye to do is to find how many times heavier any given
volame of the body is than an equivalent volume of distilled
water at 39°.2 F. Ths Is the method of fixing the specific
gravity of solids and liquids; we shall sec hereafter how it is
possible to fix the specific gravity of gases and vapors.
145. Specific Gravity of Solids, —The following are
some of the methods of determining the specific gravities of
solids s =
1. By the Hydrostatic Balance. —Vluce the body in one of
the seale-pans and balance it by known weights in the other
pain. These will give the weight of the body in air. Next
suspend the bely in a vessel of distilled water by means of a
thread oF wire attached to one of the scale-puns, us shown in
Fig. 99, and balance it by welghts placed in the other pan,
‘On account of the buoyant effort of the water, the weight of
‘the body In water will be less than that in alr, Subtract the
weight of the body in water from that in air, and the differ
ence will be the weight of the dinplaced water, that is, the
weight of a volume of water equal to that of the body.
110 HYDROSTATICS,
Having found the weight of the body in air, and the weight
of an equivalent volume of water, divide the former by the
latter, and the result will be the specific gravity required.
This method is sometimes briefly stated in the following
role: Divide the weight in air by the loss in water.
EXxAMvne. A pices of marble weighs 24 gnomes In alr and
15.5 grammes in water; what ie its specific gravity #
24 — 15: 85 U+85—282-, Ane
Fig. 98
‘The specific gravity of « olld that firwts in water snay be found
by the following method. Attach to \t some body heay enough te
sink it, and weigh both ‘ther in air, and then in water; aad, by
om, find how much the combined solids lose in water. Then
tako the beary body alone and find how mnch it foses in water.
Sobtract this from the loss sustained by rhe two, and it will give the
weight of the water displaced by the Eghtor body. Now divide the
body's weight In uir by this remainder apd ft will give the speeitie
gravity
sabtrieti
SPECIFIC GRAVITY. iu
FExamrie To find the specific gravity of » piece of wood weigh
ing G ounces Attneh to it 8 ounces of load,
Weight of combined solids in air... 14 ounces.
We find their weight im water tobe. . 4.5
Loss of combined solids in waver. . 9.5 *
Weight ofloadaloneinair . , . . . 8 *
Tt weight in waterisfoand tobe . . . 7.3 “
Leadlossinwater . 2. 2... 7 “
The loss doe tu the wood alone equals 9.5 —.7 = 88. Specific
gravity of the wood = 6 + 8.4 — .b82 nearly.
Nicholoor’s Hydrometer. — Nrcworsox's Urpnowerne
‘of & hollow cylinder of metal, ax shown in Fig. 99,
the bottom by a heavy body, d, to make it float,
vet, and terminating above by @ thin stem, ¢, which sup-
1 ecale-pan, a, The instrument {s 0 constructed that
od of determining the specitic wravity by eas of this
shown in Pin 100 and 101. Suppose it were r ssid
112 HYDROSTATICS.
‘Tho bar Is placed In the pan and weights added tif] it sinks to the
noteh in the stom, as shown in Fig. 100, These weights, subtmeted
from 500 graius, give the weight of the bar in alr, Next giluoe the
har in the cup, d, as chown in Fig. 101, and add weights esough to
make the instrument sink agaiv to the notch in the stem. ‘The East
weights will denote the buoyant effort of the fluid, or the weight of
the water displaced by the bar. Divide the weight of the bar in nie
by the woight of the displaced water, and the result will be the
xpecifio gravity sought,
3. By « Flask, his method is used when a body exists
in a state of powder, or in fine particles like sand. A stall
flask, whose exact weight is known, ie first filled with the
powder and the whole carefully weighed, “The entire weight.
diminished by that of the flask, is the weight of the body.
'The flask is then filled with watcrand weighed. ‘This weight,
diminished by that of the Mask, is the weight of an equivalent
volume of water. Divide the weight of the body by tliat of
ivalent volume of water, and the result will be the
specific gravity required.
It is evident that by this method we obtais the specific gravity
of tho entire contents of the flask is one mass, Suclading the air thet
its
it inay contain,
146. Specific Gravity of Liquids. —The following are
some of the methods of determiving the specifi gravities of
liquids: —
1. By Fabrenieits Hydrometer. ~ Fanmesner’s Hrorome
Ten consists of a glass cylinder ballasted at the bottom ly
asmall globe filled with mercury, and provided at top with
& stem and seale-pan, as shown in Fig. 102. Its weight is
carefully determined.
‘To aso the bydrometer, it is Hest plunyged into distilled water, aml
weights placed in the seale-pan till it sinks te the soteh filed on the
stem. ‘These weights, Increased by thar of the Instrument, will give
the weight of the displaced water. ‘The instrament is next plengid
inte the Liquid in question, and weights are placed in the pan tl tig
jn sinks to the notch, ‘These weights, added te that
instrament W
SPECIFIC GRAVITY OF LIQUIDS. 118
of the instrament, give the weight of the displaced liquid. Now the
‘elnines displaced are the sawe in both cama, exch being that of the
subinorged Instrument ; henee, if we divide the weight of the dis-
plhcod liquid by that of the displaced water, the quotient will be the
‘specific gravity required.
Wig. 102.
2. By the Plusk, —A& flask is constructed ao as to hold a
given weight of distilled water, say 1000 grains. ‘This Mask
is first weighed when empty, and then when filled with the
Tiqnid in question. The difference of these results is the
weight of the liquid, and this, divided by 1000 grains, will be
the specific gravity required,
A Knowledge of the xpecitic gravitior of bodies ix of frequent
‘application, In mineralogy it aide in de\ermining mineral species.
"Tho jeweller detonnines by ite ald the precious stones. It enabl
tes to find the weight of a body when we kuow its volume. Thus a
cable foot of lead weighs 11.35 times as much as a enbic foot of
water; but a cubic foot of water weighs 1000 ounces, hence a cabic
foot of lend weighs 13,350 ounces, of about 709 pounds.
“The sperifie gravities of some of the most inportant substances
hy the following table: —
114 HY DROSTATICS.
Table showing the Specific Gravitien of Solid and Liquide,
Platinum (rolled)... 22.07 | Merury . 5... 18.00
Jold (stamps). | Solphurio Add. 2... 18
pad (cast) Mik" 502 etna
Iver (east) Sea Water... . 18
Trou (bur) Distilled Water... 1.00
Zino (cat) Bordeane Wines... O00
Diamond Olive Ol. + OM
White Marble Spirits of Turpentine . . O87
Glass (flint) . Absolute Alcohol . . . O79
Ivory Ordinary Ether. 2. O72
It will be seen that platinum is the heaviest sulid, and that mer
cury is the heaviest quid.
147. Beaumé's Areometer consists of a bulb of glass,
ballasted at bottom by in sccond bulb containing mercury,
and terminating at top in a cylinder of uniform diameter, as
shown in Fig. 108.
When plunged inte liquids, it sinks
till the weight of the displaced fait
equals that of the areometer, In fight
fluids {t therefore sinks deeper than fn
eavy ones,
‘The plan of graduating Beaume’s anor
inas follows. It it ballasted so that
{in distilled water it will sink to the point a,
‘on tho etem, which is marked @ A mbe-
tur of salt and pore water is then forned,
in the proportion of 15 of the former to 85
of the latter, into which the instrament is
plunged. ‘The upper eurfuce then ente the
stein at some point, ¢ which is marked 15,
The intermediate «pace between @ and ¢ is
divided into 15 equal
Fig. 108
i+ continned downmants on the stom. ‘The
arv on a slip of pusper i f the stem.
‘The uso of the instrament thus graduated ie to ascertain the
amount of salt io any sclation of salt iu water. It is plunged inte
SPECIFIC GRAVITY OF LIQUIDS. 116
tho salution iu question, and the number to which It sinks denotes
the degree of saturation of the eoluticn.
Tustruments constructed on this principle have been dovised for
dotermining the strength of othor tolutions, whothor of ncide or
sults; also for detertmining the strength of saccharine solutions andl
the Kho,
148. The Alcoholmeter is similar in its construction
to the areometer just described. It Is graduated so as to
show the porcentagn of alcohol in any mixture of alechol and
water.
‘The instrument is frst ballasted so that when
plunged In pare wniter It will tloat with noarly all
‘of its ster abore the water. ‘The line of flotation
ie marked. Mixtures are then formed, containing
one, two, three, ete, per cent of pure alcohol and
water, and the instrument is plunged into them in
succession. The lines of Hotation urv marked 1,2,
@, ete, as in the instrament provionsly. To this
cave the numbers ran upwants, It ix necessary to
gradeato it throoghout by trial, as tho divisions
are oot uniform.
‘To use the instrument, it Is plunged Into the
mixture of aleohol and water to be tested, and the
percentage is rad off on the paper scale within Mig. 7
the tube, or else the scale is scratched upon the stem with o
dineaond,
Summary,—
Spreific Gravity.
Standard of Specific Gravity.
Specific Gravity of Solids.
Method by Hydrostatic Balanca,
Rolo and Example.
Solid Lighter than Water.
Role and Example.
Method by Nicholson's Hydrometer.
Method by a Flask,
116 HYDRODYNAMICS.
Specific Gravity af Liquiits.
By tho Hydrometer,
By the Fbwk.
Applications.
‘Table of Spocitic Gravities.
Boaumé’s Arcometer,
‘The Alooholineter.
THE MECHANICS OF LIQUIDS
Part 11.—HYDRODYNAMICS,
SECTION L — FLOW OF LIQUIDS,
149. Flow of Liquids from Orifices. —It has already
ed by a fluid is propor-
in a vessel filled with water,
openings be made at different depths from the sarfkec, as
shown in F it is evident that the water will flow out
with the greatest velocity at the greatest depth from the
surface
But the velocity does not increase if) the simple ratio of
pth; it ts found to be in proportion to the square root
of the depth. ‘This result is in accordance with the laws of
falling bodies.
been shown that the pressure
tional to its depth. If thes
The water jesues from the jot nt # with a velocity which
would curry it to the same height with the surface in A, were
it not for friction and the resistance of the air.
This velocity is the same that would be acquired by a body
in falling froely through the distance from h to #,
Since the whole space described by n falling body Is proportioned
to the square of the time, while the velocity Increases in the simple
f tho timo, it follows th jnired is proportioned
to the square soot uf the whole space through which the body falls
Thus, fans vessel containing mater, 16 fy feet
he voloe
werture bo mad bo
PLOW OF LIQUIDS. it
Below the surface, the water will cseape with o velocity of 32} fect
per second ; for this ix the velocity acquired by a body falling through
that distance.
A streain thrown out in any other direction than the vertical will
have the same velocity, alnco the pressure to which the velocity is
doe remains the same.
The range of x horizontal jot will be greatest when it is half-way
between the surface and the level of the place where it strikes.
‘Thue the jet shown at m in the figure has the groatest range. Fete
issuing from orifices at equal distances above and below the middle
point, as at g and n, will have the sane nunc.
Fig. 105.
aso. Volume of Liquid Discharged. — In theory, the
volume discharged will be equal to the velocity multiplied by
the area of the orifice. For example, if water issucs with a
volocity of ten feet per second, from an orifice having an area
of two square inches, the volume discharged in one second
fs equal to (10 * 12) X 2 — 240 cubic inches.
“This rule does not give quite accurate results, for in practice
‘the amobnt disehanzed i& considerably diminixhed by friction, and
TA of what is called the cena contracta, or contracted
ial
118 HYDRODYNAMICS.
Whon water flows through a circular opening in & lange vere!
having thin sides, it rushes frou vent directions towards the
opening and forins contlicting currents that diminish the velocity.
On leaving the orifice the jet contracts, so that at a distance souse-
what los than tho diameter of the opening, the ark of ite eres
section is only aboot two-thirds of that at the urtfice,
‘This numow portion of the stream fs called the wena contract.
By attaching suitable tubes to the orifice, the formation of the
“contracted vein” way be prevented and the flow of water consider-
ably increased.
151. The Flow of Liquids through Pipes. — When
water from # reservoir Is conveyed to # distance in pipes, the
velocity of the flow is greatly diminished by friction, especially
in the case of small pipes.
A pipe 200 foot long and one inch in diameter, laid horizontally,
will discharge only one-fourth as wich water as a tube of the sane
sizo ono inch long. A pipo of the «une Iength, two inches ity dinsn=
eter, will dischange about five tines as raueh water as one of one
inch in diameter. ‘The areas of their crows sections being as the
squares of their diameters, the ratio should be ws 4-to 1, Wut the effcet
of fiction in retarding the How is much greater in proportion in
small pipes than in lange ones.
152. The Flow of Rivers.— A very slight inelination
is sufficient to flow of water. Three inches to a mile
in » smooth, straight channel is sufficient to give a velocity
of about three miles per hour,
‘Pho forvo of the earrent in rivers is greatly diminished by frietion
apon the bottom and upon the banks, and consequently the strougest
carrent is near the surface of the deepest part of the strat.
‘The parts of a river-bed, where the stenpest inclinations oeewr, are
luvost always filled with masses of roek, whieh obstruct the flow
ant greatly diminish the velocity of the stream.
WATER. WHEELS. 119
SECTION IL —WATER Ag A MOTIVE POWER.
453. Water-Wheels. — Wherever water is collected
in reservoirs or lakes above the level of the sea, it com-
prises a store of potential energy which, by its down-
ward flow, becomes kinetic cnergy—a working power.
This power is applied to usefal purposes by means of
water-wheels. Water-wheels are turned (1) by the force
of « current, (2) by the weight of the water, or (3) by
both combined,
154. The Undershot Wheel is moved by the force of
the eurrent striking against
float-boards, which are ar-
ranged 60 a4 to be more or
less sobmerged.
This is the least effective
form of thy waterwheel, atil-
izing not more than twenty-five
‘water frean & reservoir or dasn.
‘This for of wheel & represented iu Fig. 106,
15§- The Overshot Wheel. — This form of water-
wheel is called ** overshot” because the water is received at
the top and passes over the wheel, ax shown In Fig. 107,
It ia moved principally by the we of the water, whieh
flows into cols, called * buckets,” formed on the cireum-
ference of the wheel, and shaped so as to retain as much
of the water ax possible till they reach the lower part of the
wheel, where they are emptied.
120 HYDRODYNAMICS.
‘This ts a very eBcetive
form of the wheel, tiliz~
ing nearly three-foerths of
the total moving power of
the water, It is eepectally
adapted for use with a
sinall stream whieh hos
great fall. Wheels of
this kind are often soade
of fihy feet or more in
diameter.
Fig. 107,
156. The Breast Wheel. — In the breast wheel the
water is received nearly at the level of the axis. Tn some
wheels of this kind the water flows into buckets similar to
those of the overshot wheel; but generally it acts npon float-
boards placed perpendicular to the circumferences, and the
ruce-way, or passage for the water,
is made to fit closely to the eireum-
ference of the wheel, The water
being thus enclosed acts partly by
its weight and partly by its mo-
mentum.
Fig. 108, represents this form of
In “its best form the
Lieast wheel will mtilize about sixty=
five per cent of the inoving power uf
the water. It was fonnerly in goneral use, but is pow mostly super-
soded by the * turbine."
157. The Turbine Wheel ix the most effective of all
the forms of water-wheels. Many different varieties are In
use, One of these is shown in perspective and in horizontal
section in Figs, 109 and 110,
‘The wheel in this form is wholly anbmergod in water under the
prossure of a considerable head. ‘The water enters at the eireun-
water-w
Fig. 108
MACHINES FOR RAISING WATER. 121
foronces of the wheel B, through an enclosing xe, D, which ix
stationary. Tt ix directed by the openings In D so as to strike tho
eueved floats or buckets of 2 in the direction ef the greatest efficiency.
It then escapes from the central part of the wheel by a tube, which
is extended vertieally downward,
A central shat, A (Pig. 109), communicates motion to the
miaehinery abore.
"The whee! Is. protected from the vertical pressury of the water by
the top, 7, whieh is attached to the encloalag case, D.
Tn anether form of the turbine the water enters through w fixed
tube at the eentre, and, direetod by fixed curved partitions, imparts
motion to the outer easing, which revolves, and is connected with
the shaft,
‘The best forms of the turbine, when tied under w full hoad of
seuter, have wen found to utilize from cighty to eighty-five per eeut
‘of the foree of the water.
SECTION M1. —MACMINES FOR RAISING WATER
Mosr of the machines in common use for raising
water depend upon the action of the atmosphere, and
‘will be described ander the head of Pneumatics.
‘Archimedes’ Screw. —The screw of Ancnimeprs,
‘the philosopher of that name, is one of the most
128 HYDRODYNAMICS.
ancient contrivances for raising water, Tt was in ase before
the Christian era, and it is still used in Holland for draining
low grounds.
Aa shown in Fig. 113, it con-
sists of « we wound iu a spiral
form around a solid eylinder,
which is made to revolve by
turning the handle, H. If
placed at as proper incliuativn,
the water, a8 the handle is turwed,
will continue to flow int those
parts of the tubethat are broaght
successively below the shaft till
finally it will be dishanged at the
Fig. 111. top.
159. The Chain Pump consists of a tube, the lower
part of which enters the well or reservoir, and the apper part
extends to the polot where the water is to be discharged.
An endless chain passes over a wheel at the top, and also
around another wheel placed in the water at the bottom.
This chain earries at equal distances flat disks whieh fit
closely into the tube. As the wheel revolves the disks carry
the water before them into the tube, and finally discharge it
at the top.
160. The Hydraulic Ram.—When water under a con-
siderable head is flowing through a long pipe, if at any point
the flow is suddenly stopped, the momentam of the water
causes great and sudden pressure, often sufficient to burst
the pipe. ‘The hydraulic ram males use of this pressure in
raising a portion of the water fo a greater height.
The principle of its construction is shown in Hig. 122.
The pipe, A, leading from the resereoir, terminates im the small
oslinder, B, which opens apwant and is fitted with a wnbve, D,
which a heav jough to fall when the water in the pipe ie still, or
moving very slowly. When the current through A acquires saifigiont
velocity, ft mises the valve and suddenly shots off the water at 22
MACHINES FOR RAISING WATER. 123
‘The sudden pressure thus precueed opens the valve J lending to an
air-chamber, G, into which part of the water is then discharged,
‘The air in the chamber, G, ix condonsod by tho suddon influx, but,
immediately reacting by its vlasticity, it forces « portion of the water
up into the amall tabe, H.
As soon as the water in the pipe B ceases flowing, the valve 2)
opens by fis own weight; tho valve in the alr-chamber eloses, and
the water again flowing through A, soon acquires velocity enough
to shut the valve, ‘The whole operation is thus continually repeated;
weccemive portions of water are forced into the air-chamber, and
thenes, by tho elasticity of the confined air, discharged in a continn-
‘ua streain through the pipe HE.
Fig. 112.
‘The hydraulic ram furnishes a very efficient and economical
method of raising a small quantity of water to a great height, wher-
ever & sulficiont fall of water can be obtained.
Summary. —
Bow of Liquids from Orifices.
Velocity and Range.
Volume Discharged.
Flo: of Liquids through Pipes
Effects of Friction.
lose of Rivers.
Potential Ener af Reserooirs of Water.
—e
124 HYDRODYNAMICS.
Water Power — How Applied.
The Undershot Wheel.
The Overshot Wheel.
The Breast Wheel.
The Turbine Wheel.
Methods of Raising Water.
Archimedes! Screw.
‘The Chain Pump.
The Hydraulic Ram,
CHAPTER V.
PNEUMATICS,
SecrioNs 1, — THe ATMOSrIERE
161. General Properties of Gases and Vapors. —
Gases and Varors are highly compressible and elastic
fluids. is
Their particles, like those of liquids, move freely, and
transtait pressure in all directions; but they differ from
liquids in the predominance of the repellent force ex-
erted between their molecules, in consequence of which
4 mass of gas always tends to expand.
The force that elastic fluids exert in this way is
called their tension.
‘The distinction between a gas and a vapor is not very
clear, When a body in the gaseous form can be reduced to
a liquid by cooling, or by « moderate pressure, it is usually
eallod a vapor.
It ts now known that all the gases may be reduced to the
liquid form by great pressure and intense cold combined,
162. The Atmosphere. — Common air possesses all tho
mechanieal properties that. belong to gases and vapors. It is
therefore taken as the type of ceriform bodies.
Phe atmosphere that surrounds the earth is transparent,
without odor, and colorless exeept in grent masses, In
=
126
masses ft assumes a blue tint, and is the
color of the sky,
Tt is composed of oxygen, nitrogen, carbonie acid, swatery
PNEUMATICS,
vapor, and some accidental impurities,
‘The principal ingredicnts are oxygen aud sitrogen, and these are
inixed in the proportion of twenty-one parts by volume of onysren
to seventy-nine parts of nitrogen.
Carbonic acid forms but a small portion of the atmosphere, but
it is an constant and very important element. It is continually
{ Fig. 118,
supplied to the nie by the res=
piration of by the
combustion of eon! and other
foel, and by the decay of aui~
mal and vegetable substances.
‘The burning of « single toa
of cont sends Into the atinom
phere more than throe tous of
thin gas. ~
Oo the other hand, all
growing plants absorb it and.
retain the carbon, but restore
to the air the oxygen which
it contains, It i found that
the supply and Toss are very
nearly talanced, so that the:
proportion of earbonie aeld in
the atmosphere remmmaing nearly
constaut.
Tt amounts, to volume, to
about one part In twenty-five
hundred of the whole atuace-
phore.
163. Expansive Force of Air-—Alr and the gnaow
filways tend to assume a greater volume.
To show thin property, take w bhuider or rubber bag, fitted with
8 stop-cock, ns shown in Fig. 113. Prose ont noarly all the alr, then
clos the stop-cook and place the bag under the receiver of am ate
=
ATMOSPHERIC PRESSURE. 127
pomp. Thee paimp the air out of the receiver, and the clastic force
ef the alr in the bag will eanse it to expand.
To the same way ft may be shown that any gas is expansible,
164. Weight of Air. — Air, like other bodies, hax
weight,
‘To show this, take a hollow globo of glass,
fitted with a stop-cock, as shown ia Fig. 14,
Having attached it to ove sealo-pan of a delicate
balance, counterpoise it by weights placed in the
ether. Then by means of the air-pamp exhanst
the ale from the globe ; the oppesite scale-pan
will desend, and some weights will havo to bo
adiled to the first scalo-pan to restore the equilih-
rom, ‘The weights added will indiente the weight
of the exhausted air.
165. Atmospheric Pressure. — Since
the atinoephere has weight it exerts a prea~
sare on all bodies upon which it rests. This pressure de-
creases a8 we ascend into the atmosphere.
If we suppose the atmosphoro to be divided into layers parallel
to the surface of the carth, it is evident that cack layer ix ee
down pC ale all above it. Hence, tho higher layers are
Jes ‘than those below them. Being les compressed,
rarefied. ‘Che existence of atmospheria
shown by a variety of experiments, eome of which
Fig WA.
i
66. Bursting a Membrane. — A glass cylinder open at
ite upper ond covered by a plece of oiled silk or
A sirvtehied membrane, such as ix used by gold-beaters, and its
herve end ie ground go as to fit the plate of an air-pump, as shown
to Pig. 115,
PEAY wis, the membrane is pressed down by the
wweight of the atmosphere above it, and this preseure is realsted by
the tension of the air within tho cylinder. If now the air be ex
\ i the eylinder, the membrane will no longer be pressed
from anit will finally burst with a loud report.
Am
128 PNEUMATICS.
‘Tho bursting of the membrane shows the presmre of the alr.
‘The report arises from the sudden rush ot sie wo Bl yee
hansted cylinder.
Ifa piece of thin sheet rubber be used in place of the membrane,
It will bo gradually foreod inward as the air is exhausted, and will
be stretched in proportion to the degree of exhaustion,
Fig. 115.
167. The Magdeburg Hemispheres. — This
nained from the eity where it was invented, comsists of two hollow
hemispheres of brass, which are ground so as to fit each other with
an air-tight joint. The hemisphores are shown in Fig. LG. One of
them is so propared that it can be attached to an wir-pump, and is
provided with a stop-eock, by means of which a commanication
ermal air can be opened or elowd at pleasure,
‘The two bemitpheres being placed ove apon the other, the pene
sure of the exterual air js exactly counterbalanced by the tension af
i —!
ATMOSPHERIC PRESSURE. 129
that within, and no obstacle prevents them from being drawa apart.
If, however, the air be exhausted from within, tho external pressure
Is np louger counteructod by an expansive force
frven, within, and it requires a considerable effort
to elfect their separation. Wo ahall eee hereafter
that the hemispheres aro pressed together by a
force equal to fiftcen pounds, multiplied by the
number of square inches in their common exose
section.
The experiment was devised by Orro vox
GuemcKe, of Magdeburg, He constructed two
hemispheres more than two feet in diameter, and
after having exhausted the air, it la reported that
ic required several horses w draw thet asunder.
268. Upward Pressure of the Air.—
Gases, like liquids, transmit pressure in all Figs 116
directions ; hence the pressure of the alr
is exerted not only downwands, but up-
wards, and in all other directions. This
is shown by the experiment with the
hemispheres. which are held together
with the same
forve in what-
ever position
they may be
Tet, placed.
The following experiments illus-
trate the upward pressure of the
airrc—
Fill a tambler (Fig 117) with water,
and cover it with a piece of paper; then,
Tolding the paper in contact with tho
‘water, invert the tumbler, On removing
the hand, if the experiment be carefully f
‘wade, the water will remain in the tuw-—
Dler, being held there by the upward Fig. 08
Promure of the alr, Whe covering «f paper serves to prevent the
—
130
ale frora entering so as to allow the water
thine.
Fig. 118 represent a glace eylindor, Aywith w tight
B, to whieh a heavy weight is attached. Let tho:
from the eylinder by an nit-purnp connected with © by a rubl :
and the weight will be lifted by the upward prussure of the nin
169. Torricellian Tube. — Measure of the Atmos-
pheric Pressure. —'The preceding experiments show that
the atmosphere exerts a force of
pressure; the Beaty of that
force may be by other
means, Pe tal
‘TorrioeLet, a pupil of Gat
Lxo, showed, in 1648, thab this
pressure amounts to about fiftcen
pounds on each square inch of
surface, at the level of the sex.
To order to repeat Tornicmnas's
experitnent, take « glass tube about
three feet in Tength, closed at one
end and opon at the other. ‘Tarning
tha ceed a downwards, let it be
filled with merenry. ‘Then holding
the Singer over the open end, let it
be inverted fn a vessel of merenry,
as shown in Fig. 119, On removing
the finger, the meroary sinks in the
tubo until the column, AB, is about
30 inches bigh, when it comes toa
stato of equilibrium.
Tn this condition, the amereury Is
sustained by tho pressure of the air
upon the surface of the free mereury
in the vowel, transmitted
to the law explained ia Ark 129
At the level of tho sea, the height of the column, AB, ix, om am
average, not far from 30 luches, or 2f feet.
eae ill
Fig. 119.
ATMOSPHERIC PRESSURE. 131
If we suppose the cross-section of the tube to be ove square inch,
the atmospheric pressure upon that surface must bo suticient to
balance the weight of 80 cubic inches of mercury. Now the weight
Of 30 cable tiches of inervary is a Little lesa than 15 pounds; honeo,
we say the measure of the atnowpheric presyure ls 15 pounds on each
square inch.
A pressure of fiftcen pounds on each square inch is often
called aa atmosphere, und this becomes a unit for expressing
the pressures of gases and vapors. Thos, when we say, In
any given case, that the pressure of steam in a boiler is four
atmospheres, we mean that it exerts a pressure of sixty
pounds on each square inch of surface.
370. Pascal’s Experiments. — As soon as Tonmcrata's
experiment was known in France, Brain Pascat undertook
to ascertain by experiment whether the mercury was actually
retained fn the tube by the pressure of the atmosphere, or by
some other cause.
He caused a friend to repeat Tonrcetus’s experiment upon
the top of the mountain of Puy-de-Dome, correctly reasoning
that, ifthe height of the mercurial column is due to ateos-
pherie pressure alone, it ought not to be so great on the
mountain top as at the Ievel of the sea. The result of the
‘experiment showed that the height of the column was leas
‘4 the top of the mountain than at its baso.
He next reasoned, that if the tube were filled with any
liquid Joss dense than mercury, the height of the column
ought to be proportionally greater. Consequently, he made
at Rouen, in 1646, the following experiment. He wok a
tobe, similar to that of Tonnicenti, but nearly fifty feet in
Jength. and after filling it with wine. inverted it in a vessel
of the same liquid.
PASCAL observed that the column fell until it was about
thirty-five feet high, when it came to rest. In this case the
colvmn was fourteen times as high as when mercury was
‘tiéed, and as mercury Is foarteen times ax dense as wine, be
=
PNEUMATICS.
concluded that the sole cause of the phenomenon fn. question
was the pressure of the atmosphere,
171, The Barometer. — A Banoweren is an instrument
for measuring the pressure of the air, If ta
Fig. 120.
tube were fitted a scale for measuring the
exnet altitude of the mercurial column, it
would be a barometer,
Several forms have been given to the
barometer, some of which will be described
in th following articles.
172 The Cistern Barometer.— Fig.
120 represents a Cisreny Bancateren, such
as is in common use in France and in this
country.
Tt consists of & glass tube, ai, about 34 inches
Jong, closed at the top and open at the bottom.
‘This tube has a diameter of about four tenths of
an inch. It is filled with mereury and inverted
m a cistern, A, which is partially filled with the
suine liquid, as explained in Art. 165. ‘The mer
cury settles in the tube till the height of the eolarna
{s about 30 inches at the level of the sen.
‘Tho cistern, A, is 3 or 4 inches in diameter,
and It Is so adapted to the tube a, aa to
the air to penetrate to the elstera at the juint &
Only a part of the cistorn ts seen in the Bgure,
the remainder being let into the frame whieh
supports the whole instrament. At the top af
the frame is a seale, ¢, having its 0 point at the
Jovel of the mercury in the later or, om the
opposite side, is a scale on which are marked
cortuln woather indieations.
A curved piece of metal embraces the tube
aud carries au index, which, ns the plece is ralsed
or depromed to correepond to the top of the column, points ont upon
tho sale, 6, the height of the columa. Two thermometers, 066 of
twereury und one of
hal, are also attrehod to the frame, which,
el
THE BAROMETER. 133
. serve to show the temperature of the instrument and of the mercury
whieh it contains,
‘The 0 point, or bogiuning of the sealo, is at the surface of the
tnereury in the cistern, When che brent pe aegis ea
portion of the mereury in the cistern is forces! up
lute the tube, and the 0 point descends; whea
the pressure diminishes, the reverse takes place.
Hut inasnnch as the surfiwe of the mercury in
the cistern is very great in comparison with that
in the tube, this rise aud fall is, for most purposes,
qoite unimportant. When great accurney is re
quired, the bottom of the cistern ix nade of leather,
and can, by means of a kerew, be rained or de
peossed until the surface of the mercury in the
eistern Jost gmzes the point of an trory pin pro-
jecting from: the top of the cistern. ‘This Im-
ween See Forrix, is now in general
“to determine the height of tho barometer, the
0 poiat is fret adjusted, then the curved piece is
slid up of down till it coincides with the surface
“of the mercary in the tube, and the height is then
‘read off on tho sealoc. The height of the ther-
mometer should alse be noted.
Th the Instrument deseribed, the reale ¢ does
pet extend throughout the whele length of the
inetmment, because, in oninary cases, only a
small part.of the scale is neoled. When a barom-
‘eter is to he used in high altitades, the sale is con-
tinned dorrnwards as fur as necessary.
473. The Siphon Barometer. — Fig.
121 represents a Sirnowx Baromeren. It
consists of a curved tobe, a5, having two
simequal branches, the shorter one acting as Pig. 121,
‘cistern. In the longer branch, there is a vacuum above
‘meroury, bot the shorter one is supplied with air, which
iT ‘with the external atmosphere throngh a small
| There are two scales, one at the upper part of
134 PNEUMATICS,
each branch, and in front of each is a movable index, which _
may be raised or depressed antil it comes to the free surface
ot the mercury in each branch. By means of these scales
the difference of level in the two branches may be measured.
‘This difference ia the height of the barometric column.
To provent violent cecillations when the
Instrument is moved from pltea 10 place, the
two branchos comtmunieate through
a fine, almost eapillary tube. This
arrangement also prevents the pos-
sibility of a bubble of alr penetrating
from the shorter to the longer branch,
when the instrument és inclined,
174, The Wheel Barom-
eter.— This is a form of the
Sievow Baromeree in whieh the
rise snd fall of the mercury are
shown by the movements of an
index around # graduated circle,
‘The manner in which it acts is
shown in Fig. 122.
As ‘Tho index is attached to an axis
b! which bears a pulley. Passing over
7 this pulley is a five wire, at one and
of which is attached an iron weight,
@, which rises when the height of
Fig. 122, the mervury diminishes, nud falls
when this height increnses At the
manterpoine, 8, which
second extremity is
keeps the wire tense, and eanses the wheel to
turn as the weights rise and fall.
Fig, 123 shows its external appearancs with a thermometer
attached,
It will be seen that @ slight change in the level of the moreury
in the tube will produce a cousidersble movement of the Index,
Notwithstanding this advautage, this fora of barometer ia of little
value when accurate observation Is required, The iron weight, a,
Fig. 12%
THE BAROMETER. 185
it somewhat: heavier than tho counterpoise, b, and thos therm is a
slight fron in addition to the pressure of the air, which acts to sus
tain the column of mercury. Again, when the merenry in the shorter
branch teods to rise, it mast orerccine the excess of weight ina, and
consequently vory misute changes of pressure are not recorded by
this juetrument,
175. The Aneroid Barometer.— The action of this
curious instrument depends upon the effect produced by
atmospherio preesure opon & metallic box from which the air
has been partially exhausted. —Tts
appearance and construction are
shown in Fig, 124.
An increased atmospheric pres-
sure tends to force the cover in-
ward; but when the atmospheric
pressure diminishes it is pressed
outward by its own elastic force,
aided by a spring in the interior.
‘The movements of the cover, trans-
mitted by a combination of delicate
levers, came an index to move over
= gradunted scale. Fig 6
Being evry easily portable, this form of barometer has lately eumo
inte extensive use, expecially for measuring the heights of mountains,
Thatrisnents of this kind aro now made that muy be earried in the
pocket like a wateh, ind thoy aro so seusitive to alight changes of
pressure that they will indicate a change of Ievel of pot more thas
three ar four fort.
276. Causes of Barometric Fluctuations.— Since the
mereury in the barometer fs sustained by the weight of the
column of alrabove it, changes in the weight of this column
of air will produce changes tn the height of the mercurial
column, Such changes are constantly going on, and conse-
quently the barometor is continually fluctuating.*
© The atmosphere surrounds the earth Ike an irumenso ocean,
fifty tallies Ges depths. Itje never at rest, but has ite great currents and
des; and, like the ocean of water benenth, it is ugitated by storms, arch
‘The barometer, then, ata aiee
rises where there is a contraction of the
177. The Barometer as a Weath
barometer is often called a weather-glass,
the instrument is sometimes inscribed with
indicate the weathor that may be
the column stands opposite them. ‘This,
an incorrect notion, for a change in we r
by the absolute height of the mercury at any
Moreover, there are other conditions b
the atmosphere, which wre quite as wii r
prediction of the weather. The 1
of moisture in the atmosphere, and toe
of the wind, are oll to be considcns| as
problem.
It Is true, however, that changes in the heat, |
follows the crest of the waves,
USES OF THE BAROMETER. 187
or the movements of the nir, are almost always accompanted,
or immediately followed, by changes in the height of the
barometer, Hence the changes in the height of the mercurial
column may, to a certain extent, he relied on for predicting
‘the weather. The following rnles are generally reliable: —
1. The rising of the mercury indicates the approach of fhir weathers
the falling of the mercury shows the approach of foul wenther.
2. A groat and sudden fall of the inercury precedes a violent storm
‘of short duration.
3. If, during fair wenther, the mercury falls continnally fur several
days, » long succession of foul weather will probably follow 5 and,
pesscske ad fool weather whieh comtinues for a long tine, the
‘rises, fair weather may be expected to follow and
nese gal days.
4, A floctuating and unsettled state in the mercurial column indi-
-eates unsettled weather.
478. Measure of Mountain Heights. — One of the
‘most important applications of the barometer is to the meas
urement of the height of any place above the level of the sea.
As we ascend above the level of the sea, the’ pressure of the aie
‘xxi the barometer falls, Formulas have boon deduced,
‘by means of which the difference of level between any two places
‘ean be found, when wo have the heights of the mercurial columns at
‘the two places, toyether with the tomperatures of the air and mereury
Picola,
st rule for finding the height of a mountain by this method
wee wt Allnwennce musi he made for temperature and
ean each station; and other minor corrections are to be
The following rule is given by Todhunter as venrly accutate for
La ink ar 2000 feet: —
je renult is made more accurate hy widing « vhown
in the snm of the temperatures above 64° Thus,
: 1° by 419. Therefore the result obtained
i "be increased by the yhho part of iteelf,
188 PNEUMATICS,
The following table shows the height of the barometer nt
different altindes where observations have been made >—
Level of the Ocean
Summit of Vesuvius... . 2. 2 | 8087 | 2508
Sumiit of Mt. Washington, Sf. 6.288
City of Quito, South America 2 BOAT 210
Summit of Mont Blane T8748 | 16.60
On the Chimborazo - | goo | tat
Highest Ascent in a Balloon (Glaisher) | 47,000 | 7.00
179- Pressure on the Human Body, —The pressure
on eaah square inch of the
body is fifteen pounds ; bence,
con the whole body the pres-
sure is enormous, If we take
the surface of the human body
equal to 2000 square Inches,
which is not far from the
ayernge in the case of an
adult, the pressure amounts
to 30,000 pounds, or fifteen
tons.
If it be asked why the body
is not crashed by this enor
ure, the answer fs,
because it is uniformly die
tributed over the whole sur-
face, und is resizted by the
elastic force of air, and other
gascs, distributed through the
tissues of the body.
‘The following experiment will
Pig. 12 show that the tissues of theliuyran
mous pro
SUMMARY. 120
body contain air and gares, whoso clusticity resists the atmogpheric
pressure, Lat tho hand be pressed elosely upon the month of a
glass cylinder, whoee interior eoimenicates with tho nir-pump, as
shown in Figs 125, No tucoavenionee will be felt. Bau if the air
be exhausted from the eylinder, the Hosk ef the hand will be forced
Into the eplinder by the pressure from without, which is uo Iouger
resisted by the presenne ofthe air. ‘The hand swells, aud the blood
tends to flow vat throngh the pores,
‘Tho question may be asked, why, when the hand i& plical upon
a besly, it & vot svtained thore by the prossure of the atmosphere.
‘The azawer is, thore is a thin layer of air botwven the hand and the
body, which courtly countertalances the effeet of the external pros
sure. Were the ait porfvetly exeluded from between the hand and
the body, there would be a strong tendency w adhereuce between
them.
‘The operation of capping, in medicine, depends upon the prinel-
ple jast explained.
Summary. —
Properties of Gases and Vapors,
‘Teasion,
Reduction to Liquids.
The Atmosphere.
Physical Propertios.
‘Chemical Composition.
Expansive Forvo,
Experiment.
Weight
Experiment.
Almoapheric Pressure,
Experiments.
Magdeburg Hemispheres.
Uprrand Pressure.
Experimenta.
Torricellian Tube.
Paneal's Experimenta,
The Barometer.
The Cistern Barometer,
‘Tho Siphon Barcaneter.
name. Maworre's Law may be enunc
The clastic force of ay given amount ¢
ture remains the same, varies inversely aa its wa
As a consequence of this law it follows @
Af the temperature remains comstant,
as the density.
181. Mariotte’s Tube. — Maiiorre’s Li
by meana of an apparatus, shown in Pige.
Mariotte's Tube. This tube is of glass, bent
a letter J. The short branch is closed, f
‘open at the top. The tube is attached to a wook
provided with suitable scales for measuring wh
mereary and alr in the two branches.
‘The instrument having been placed vertical, a
of mercary is poured into the ling branch to eut off eon
‘between the two branches, as shown in Fig. 125.
imereury in the two branches is the same, and this k
point of the two seales, The aig in tho shor brinch
nS
MARIOITE'S LAW. ul
Jeneity, and has the same teusion, as that of the external atmos
phere.
If an additional quantity of mercury be yeurnd inte the longer
brave’ of the tube, it will press upon the alr in the shorter branch,
trical column, ax shown in
» the
rs. or 29.92 inche
air will be compressed into BC, one hinlf of its original bulk.
‘The burrel is connected by a tobe with
to which the receiver, Hy is carefully fitted
‘Tho ontennce to this tube is fitted with eonleal
Jif the valve but stightly abave the opening.
‘The following is its mode of operation : —
Suppose the piston to bo nt the bottom of the eplinder.
when It Is mised, the valve, 5’, is opeved, aad the air fr
ceiver, B, rushes into the cylinder, When the piston
a
PUMPS AND OTHER MACHINES. 48
again, the valve, 8% closes; the air which has etered the eylinier
cannot return fnte the receiver, and, on being compressed, raises the
valee, 8, in the piston and escapes into the nir outside,
Oe ralsing the piston again, another portion of aie will pass from
tho meeiver into the cylinder, and this will be removed, aa before,
when the piston is lowered ngnin,
If this wotion is continned, a portion of the alr in the receiver will
be romoved at exch siccessive stroke; and, finally, noarly all the air
may be exhansted from the receiver.
‘The vacmin produced tn this way can never be perfect, however,
for the process of exhatstion can continue only so long as the air
rermelniag tn the meciver hus olastic fore enongh to expand and
Bow through the pipe to fill the cylinder, when the piston by raised,
Pig. 129 represents one of the bost of the sitaplo forns of tbe
instrament, as made by BE. 8. Rerourn, of Bes
144 PNEUMATICS,
183. The Mercurial Gauge. — In onler to measure the
degree of rarefaction produced, a glass cylinder, 7 (Fig. 126),
is connected with the pipe leading from the receiver, In
this cylinder is a glass tube bent into the form of the letter
U, one branch being closed at the top, and the other open.
The tube has ite closed branch filled with mercury, and is
called a riphon gauge.
‘The mercury, under ordinary circumstances, is kept in the
closed branch by the atmospheric pressure, but ns the air
becomes rarefied in the receiver, the tension of the air be-
cones lexs and less, and finally the mercury falls in the closed
branch and rises in the open one. The difference of level
between the mercury in the two branches is dae to the
tension of the rarefied air, and if this difference is determined
by means of a proper scale attached to the gauge, the tension
can be found. has, if the difference of level is reduced to
one inch, the tension of the air in the receiver will be only
one-thirtieth part of the tension of the external atmosphere.
The siphon guage s nometimes counceted with the reeiver im
a different way; as seen in Fig. 113 and 125. It is only nese
sary that it should be # plac that the air will be exhausted
from it at the same time, aud to the same degree as frum the
recelver.
184. Sprengel’s Alr-Pump.—Varlous mothods bave
been employed for obtaining a more complete vacuum then
can be produced by the ordinary airpump. One of the most
effective instruments for this purpose is Sprengel’s Atr-Pamp,
represented in Fig. 180. 5
To the funnel, A, is attached a glass tube, longer than a Ibarem-
eter tube. Its Inwer end enters the glas veel. 2B, and reaches
nearly to the bottorn. ‘The upper part of the tube beanehes off at ay
sand is counected with the receiver that in to be exhausted,
Mewoury is poured into the famnel, A, and os it flows down the
tube, air from the receiver enters at x, and is carried along with it.
‘The tube below i thon seen to be filled with oylinders eff mereury
separated by eylindere of air, all moving downwards.
&
PUMPS AND OTHER MACHINES, 15
‘The mercury in the bottom of the vessel, #, prevents the
air from passing back into the tubc, and it escapes while the
mercury flows into the vessel, .~
As the process goes
on, the cylinders are
seen to be separated
by smaller and smaller
spaces of air, till it ap-
parently passes down
as a solid column, no
air spaces appearing,
‘This indicates the com-
pletion of the process.
‘The only labor re
quired is that of lifting
and pouring the mer
cury back into the fun-
nel after it flows out.
The operation is very
slow, but it produces &
vacuum so nearly perfect
that less thanone-millionth
part of the original quan-
tity of air minaine in tho
receiver,
By employing tubes of
enffichent length water can
be sed instesd yf incr
cary.
The filter-purnpr, pow Fig. 132
mach teed in chemical laboratories, are constructed on the
same principle.
185. Experiments with the Air-Pump. —Soveral ex-
Herments requiring the use of the air-pump have already been
deseribed, Most of these scrve to show the pressure of the
146 PNEUMATICS.
atmosphere, Fig, 181 shows’ the elastic force of a confined
body of air.
‘Two bottles, A and B, ary eonnectod by a tabe whieh be fitted air
tight into A, but loosely into J “Phe tube
extends nearly 40 the bottom of A, whieh &
partly filled with water. When bods ase
placed under the reeviver, and the aie ex-
hausted, the ehustic fores of the alr in
caves it to expand and drive the water over
into B
Figo 181. If a Lighted candie be placed andor a
receiver, aud the air exhausted, the candle will go out aud the sinoke
will sink, showing that it ts heavier than tho rarefied air of the
revel ver.
Tf an animal or bird be placod
under the receiver, aud the air
exhovsted, it will stroggle and
soon die. ‘This experiment is
shown in Fig, 132,
186. Practical Uses of
the Air-Pump. — The most.
important practical applica-
tion of the airpump is in
diminishing the pressure of
the atmosphere to facilitate
evaporation of liquide.
In onlor to concentrate the
syrup of sugar without employ-
ing a high degree of beat, it is
placed in closed vessels called
toowum pans, and the air and
the steatn that rise are removed
by powerful air-pumps driven by
steaso-power. By this method the watery vapor is rxpully carried
off, and the syrup brought 10 the proper degroe of eoncontration
without employlag a degree of hent that would bara or diseober
the syrup.
THE CONDENSER. WT
‘The same process ie esiployed in waking or reac s. #
ouletgeb gripe nsutestants Wat are wel in wedi.
The air-pump lias alse been employed for exbinstlag long
tabes that are used for transmitting letters, messages, and
various small packages. ‘These are called Pnenmatic Tubes.
To London, where these tubes are extousively used, they are
made of Iead enclosed in tobes of trou. They are made suiovth
oo the fuskle, and fitted with
pistons consisting of cylinters
of gutta-percha, in whieh the
articles to be traneuitted are
plaent, ‘Tho alr Is then ex-
wusted, and the pressure of the
utinosphiers drives the piston
through the whole leugth of
the tube ‘The tubes used for
this purpose wre aboot 24 Inches
in diameter; and sume of them
aro more thas two wiles in
length.
187. The Condenser. —
This machine is simply on
airpump with the valves re
versed, It is used for com-
pressing ale and forcing it
into a small space. Fig. 188
shows the construction of ono
of the common forms. At
the bottom of the pomp-bar-
rel there is a valve, 4, which
opens downward; ata, in a Fig. 188.
{esas dteston valve which opens inward. 2 ix
es = china Which is screwed upon the lower port
OF the pat
When the piston ts formed downivan! the air enters the roseiver
6, whieh prevents Hs retarm. At the upwurd
» the wre the aylinder, through a, As the movement
160 PNEUMATICS.
essentially of cylinders fitted with pistons, to which the drills
were attached, Biglit or ten of these
to a heavy iron framework rvsting om wheels, Mos it
could be moved forward and back, on rails laid for the pur-
pose (Pig. 134). nie
When in use, this framework was brought up and fry fi
near the heading" to be operated ua. The chins were
Pig. 185.
per position on the framework, and the even
sreaied air from the pipe wus conducted to the several machines
Ly menaller flexible tubes. Here it was adinitted to the eplindons,
alternately before and behind the pistons whieh eared the drills,
driving them with great force and mpidity against the noes
Fig. 135 represents the iron framework, or eerriage, with fur
drills attached. Tho Hexible tubes shown in the figure carey the
air to the macsines from the iton pipe laid along the bottom ef the
‘vannel,
then fixed in the p
APPLICATIONS OF CONDENSED AIR. il
Fig. 126 ropreeents form of the drilling-machiae which is now
extensively wed in mining eperitions. 11 is mounted upon a eclum,
on which it snay bo raisod or lowered by meane of the seryw-thread
ut upon its surface, Tt is also arranged xo that tho drill may be
driven in avy direetion require.
Fig. 198.
90. Advantages in the Use of Compressed Air. —
Pana inaeaOs deep mines, and other confined spaces,
there are several advantages in the use of compressed air: —
1. The power may be transmitted through a great distance
with vory slight lose.
Atithe Houme Tunnel, when the work was done at n distance of
neatly three miles from the compressors, the lows of power was less
then four per cent of the whole.
2. "Tho air, after doing ita work in the machines, eseapes
gpd serves us a fresh supply of pure air, and drives out the
a
me
smoke and the noxious gases which would otherwise secomn-
late from the blasting, the burning of lamps, and the breath
ing of the workmer
3. In deep mine:
expansion of the a
where the heat is often oppressive, the
es it escapes, lowers the temperatare,
191. Artificial Fountains. — Water may be forced up-
ward, in the form of a jet, by the tension of compremsed air,
Hero's Fountain, one form of which is shown fu Figedaty is
operated in this way
L
SUMMARY, 158
It consists of two globes of glass, connected by two metallic
tubes. The upper globe is surmonnted by a brass basin,
connected with the globe by tubes, ns shown in the figure.
"To use the instriinent, the tole whieh forms the jet is withdrawn,
and thragh the opening thus inade, the upper globe is nearly filled
with water, the Yuwer one containing air anly, ‘The jet tube is then
replaced, and come water is poured into tho busin.
‘The water in the basin, acting by ite weight, flows into the lower
globe, through the tube shown on the left of the figures as indicated
‘by the arronr-head. ‘This flow of water Into the lower globe forces
the air in Ht, which, ascending by the tube shown on
re, accumulates in the upper globe. ‘The pres-
Fin the upper globe, acting upon the water in that
= |, forces a part of it up through the jet tube,
giving | 8 jet of water, which may be wade to play for several
hours without refilling the instrument.
partially filled with ink iv Fig. 138, The body
thr-tight. Near the bottom is a tube for supplying
nted, and aloo for filling
d when necessary. It ix he \
-prowonte the ini
fra When the ink hus -.
heen bed till ite level fille below 0,
ebere the tube Joins the main bly uf Fig: 138
the inkstand, @ bobble of air enters, nud rising to the top, acts
its pressure to AU the tube again, and se on until the ink is
haasted.
Summary. —
“Messue of the Elastic Force of Gases
Mariotte's Law
Verification of the Law,
Seas Moats
wre employed.
Vpletign likes
WATER-PUMPS, 155
which represent sections of the pump in different states of
action. In all of the figures, a is the sleeping-valve, © the
pistoa-valve, and B the sucking-pipe.
Suppose the piston to be at the lowest point of ite play;
there will then be an equilibrium between the pressure of the
air within the pump and that without, When the piston is
ralsed to the highest point of its play, the air beneath it is
‘rarefied, and its tension diminished ; the tension of the atr fn
the sacking-pipe then forces up the slecping-valve, and a
portion of it escapes Into the barrel. The tension of the
air fit the sucking-pipe being less than that of the external
quantity of water rises in the pipe. to restore
the equilibria, ‘The water continucs to rise till its weight,
pear ied tension of the air in the pump, is jst equal
to the tension of the external air. When the equilibrium is
plog-valve closes by [ts own weight.
156 PNEUMATICS
Nowy if the piston bo dopresacd, the air in the barrel is condensed,
forves open the piston-valve, and a portion escapes luto the external
atmosphere. If the piston be mizod again, an odditional quantity uf
water will be forved into the puinp, and after one or wo strokes of
the piston, ie will begin to slow init the barrel, as shown in Big. 1),
When the water rises above the lowest lint of the play of the
piston, tho latter in its descent will wet to compross the water in the
barrel. ‘This pressure forces open the piston-valve, and a portion uf
the water passes ubovo tho piston, ax shown In Fig. 140. By ean-
tinuing to elevate nud dopress the piston, the water will be riksed
higher and higher in the purmp, vill at length it will How freon the
spout, as shown in Pig. 14].
Aa the water is raisnd in the painp hy atinospherie prvsatin, i
necessary that the lowest limit of the play of the piston ehonbh not
be more than 34 fect ubove the surfsee of the water in the reservoir,
even at the level of the sea, ‘To provide against barometric fluctua~
Yona and othor contingencies, it ia usual to make this distaneo con-
alderably leas than 3H feet.
195. The Forcing-Pump. — In the Forceso-Pume the
sucking-pipe may be dispensed with, and the barrel plunged
directly into the reservoir, as shown in Figs. 142 and 148, or
a sucking-pipe may be employed, as will be explained here-
after. We shall first consider the case in which the sueking-
pipe is omitted,
Tn this case the piston fs solid, and a lateral pipe, 4, called
the delivery-pipe, is introduced elow the leyel of the lowest
position of the piston, ‘There are two valves, both fixed, the
yvalve, 4. a8 in the sucking-pump, and a valve, ¢,
ing into the delivery-pipe.
When the piston ia raised to its highest position, as shown
in Fig. 142, the pressure of the atmosphere on the water in
the reservoir forces open the sleeping-valve, and the barrel
is Milled with water up to the bottom of the piston, when the
sleeping-valve closes by its own weight. On depressing the
piston, the valve, ¢, is forced open, and a portion of the water
in the barrl is forced into the delivery-pipe. When the
piston reuches its lowest position, the weight of the water in
feS5 =
WATER-PUMPS. Wi
the delivery pipe closes the valve, ¢, and prevents the water
iu the delivery-pipe from retornmg into the barrel.
By cousivelly raising and depressing the piston, additional quan-
tities of water amv forved into. the delivery-pipe, which finally esenpe
fru the spout at the top af the delivery-pipe, ax shawn in Fig, 143,
‘To regulate the flow of the water through the delivery-pipe, and
to fucilitate the working of the pump, au air-vessel Is generally in-
yoduced, as will be explained io Art. 196. Sometimes the working .
Pig. 142
ie rendered uniform by combining two forcing-pumps in such a
manuer at the plstow of the one ascends whilst that of the other
descends. ‘This combination is explained in Art. 197,
196. The Forcing-Pump with Air-Chamber.— This
differs from the simple forcing-pump, described in Art
in having 4 sucking-pipe and an air-vessel. It consists of a
barrel, 4, a sucking-plpe, 2, 2 sleeping-valve, @, and a solid
piston, ©, worker by a lever. #, and piston-rod, D. A pipe
Teads from the bottom of the burrel, through a sleeping.
aa
158 PNEUMATICS.
valve, #, into an air-vessel, A. The delivery-pipe, 4, enters
the air-chamber ot its top, and extends nearly to the bottom,
r ‘To explain the action of the pump, mup-
poee it empty aud the pixton at its boweet
position; when It ts ralsed to is highest
position, the uir in the barrel is ruretied,
the tension of the wir in the sucking~plpe
furces open the valve, @, and & portion of it
escapes into the burrel; the water is thea
forced up the sucking-pipe by Ube tensive
of the exterual air acting on the aurfiee of
the water in the reservoir until an equilit—
riuin is prodocod, when the walre, G, closes
by its own weight,
Wig. 14a
densed untll Sts tension exceeds that of the external air, when it
forvos open tho valve, F, and a portion escapes into the ir-remsel,
After a few double strukes of the piston the water rises through
the valve, G, and the action becomes the same as in the pam
described in Art. 195, with the exception of the alr-vessel, whick
erves to keep up a continuous streain theoagh the delivery=pipe.
" ought not to be more than O4 feet above the reservoir.
ay bo at any height abowo A.
pipe composed of leather
al. It is used, as its name implies,
for extinguishing fires.
145 shows a suction of the essential parts of a fire-
In this Ggure, 7 Q is the lever to which are attached
the piston-rods that more the pistons, m and n; 2 is an air
vessel with two valves, one admitting water from cach barrel;
Z is the wntrance to the hose or delivery pipe; Af and ¥ are
rods sus ng the framework of the machine.
Tho two barrels are plunged into n reservoir which is kept
supplied with water. ‘This water tlows into a space beneath
the barrels throagh holes represented on the right and Jeft
SS _
THE FINE-ENGINE. 159
of the igure, ait from thence fs forced into the air-vessel in
@ manner entirely similar to that explained in the the last
article, When the water is forced into the air-vessel, 2, the
aie is at Gest compressed, after which it acts by its tension to
foree a continuous current through the howe.
‘Phe lover 4 provided with Tong handles at right angles to ite
lesgth, a9 that it may bo worked by eoveral men acting together.
Fig. 146.
Wahin a fow yoars many improvements have been introduced
fete the fireengine, one of the most important being the application
cof steaxn a8 a motor,
198. The Siphon. — The Sirnos is a bent tube, by
means of which a liquid may be transferred from one reser-
Pol to another, over an Intermediate elevation, “The siphon
may be used with advantage when it is required to draw off
the tipper portion of au liquid without disturbing the lower
portion. ‘This operation is called decanting.
i =
PNEUMATICS
‘The siphon consists of two branches of unequal lengths, sus
shown in Fig. 146. The shorter one is planged into the
liquid to be decanted, and the flow takes place from the
longer one.
‘To use the siphon, it must first be filled with the liquid ‘This
wperativa may be eflveted by applying the mouth to the voter end of
the siphon, und exhausting the air by sation, or it may be inverted
wnd filled by pouring in tho liquid, and stopping both cuds, alter
whieh it is again inverted,
ssune instant. Sometimes a sueking-pipe is employed to exhavest the
sir and fill the siphon,
When the tlow enmmences, it will continue antil the liquid in the
firet reservoir falls below the level of the end of the siphon.
To understand the action of the siphon, we must consider
tho forces called into play. ‘The water is unged from a
towards 4, by the pressure of the atmosphere on the fluld fn
the reservoir, together with the weight of the water in the
outer branch of the siphon ; that is, by the weight of a column
of water whose height is a6, This motion is retarded by
am ——"
ADHESION OF LIQUIDS AND GASES. 101
the pressure of the atmosphere at }, together with the weight
of the Muid im the inner branch; that is, by the weight of a
column whose height is cd. The ditference of these forces
is the weight of « column of the liquid whose height is the
excess of ah over ed, and it is by the action of this force
that the flow Is kept ap. The greater this difference the
more rapid will be the flow, and the less this difference the
slower the liquid will escape. When this difference becomes
zero, the flow ceases altogether,
‘The siphon is used for conveying water over hills, but for this
purpose the highest point of the tube shoald not be more than thirty
feet above the level of the water in the reservoir, thie being about
the height at which the atmospheric pressure will austain a column
of water,
199. Adhesion of Liquids and Gases, — A rmpid
current or jet, either of a liquid or = gas, tends te carry
slong with it the surrounding particles of air which adhere to
it, and thus to produce a purtial vacuum. This principle is
amade use of in raising liquids through tubes. Let a powerful
jet of steam be directed horizontally over the open end of a
vertical tube, the lower end of which is plunged in water;
the air frorn the tube is awopt along by the steam, a vacuum
Is produced, the water rises, and is, in its turn, driven for-
ward by the Jet of steam.
Tn the apparatess known as Gif-
fant’s Injector, water lx supplied
to the boiler uf a stoam-engine by
fw Jet of seam, which by throws
with great foree through & «mall
Pipe inte the centre of a larger
tube connected with tho supply
eof water. A vacuum being formot
wbout the jet, water is drawn for-
want and thrown into the bwiler.
The siane peivciple ix nade use :
Of foe tirerring a fine spray of Fig 147.
BALLOONING. 168
.
‘The Bancscorr consists of a beam like that of a balance,
#4 plunged into a gas, it is tuoyed up by @ force
‘of the displaced gas.
it effort is greater than the weight of the body,
‘Fikes if it ix lems, the body will fall; if the two are
i tloat io the atinosphere without either rising
fises, bocanse it is lighter thas the air which
ities to rise until it reachos a stratum of ait
164 PNEUMATICS.
where its weight is just equal to that of the displaced air, whea it
will come to ret and rernain snxponded. A scap-bubble filed with
warm air floats for a coasidemble time In the attnespbery, being
nearly of the same weight as the displaced air.
203. The Balloon.—A Bautoon is a spherical envelope
filled with somo gas lighter than air.
‘The first balloon made was filled with heated air and
smoke, furnished by burning damp straw, paper sind the
like, under the balloon, the lower part of which was left open
to receive them, When filled, it rose to a height of more
mile; but it soon beearne cooled, and fell te the earth.
The use of hot-air balloons was, however, entirely given ap
on account of the serious accidents to which they were liable.
Swall balloons of this kind, called fire-balloons, are often made
for toys. A spherical tag of light paper is made, with = Large open-
ing at the bottom, across which are stretched wires; t theme &
sponge saturated with alcohol is fastened. ‘Tho alechol boing set
on fire, the air in the balloou becomes heated aad rarefied till the
whole is lighter than an equal bulk of the atmosphero, when If rises.
202. Balloons of the Present Day. — Balloons hy
il are, at the present day, generally filled
with hydrogen or coal gas, ‘The Intter, although heavier
than the former, yet by reason of its cheapness, and the
facility with which it can be procured, is usually preferred.
The euvelope is made of silk, rendered air-tight by caontebone
varnish on both sides of it. Sometimes two eheets of sille are used,
with n sheet of indin-fubber between them.
The basket, or car, made of wiekor-work or whalebone, ts am
pended by means of cords to a network which completely covers she
alloon or the enti upper half, ‘This network is attached
manaer as to distribute the weight of the car and its eon
only us possibile
At the top of the balloou is a valve kept closed by a springs it
can be opened by wneans ef a ste conding through thé balloon
te the car of the erronaut, When ho wishes to descend, be opens
tho valve, and allows « portion of the gas to escape. ‘To axsortain
is aseendin, ronvut ls provided with
which persons asc
whether b or descending, the
BALLOONING. 165
4 barometer; when ascending, the barometric column falls, and
whon descending, it rises. By meansof' the barometer, the height at
any time may be determined.
‘A long flag fixed to the car will indicate, by the position it tales,
either above or below, whether the balloon is rising ur falling.
‘To enable the balloon to rive, it must displace a volume of
sir greater in weight than itself and all it carries. When the
volume of alr cisplaced {s leas fn weight, the balloon will sink
when equal, \t will, after a few oscillations, come to rest in
that stratum of the atmosphere.
‘The rocasurements for n balloon of the ordinary dimensions, whieh
ean curry threo porsons, have been given ax follows: 16 yards high,
12 yanks io diameter, and, when it ts quite full, wbout 680 cubic yards
in volume, The balloon itself weighs 200 pounds; the acocesories,
such as the rope and car, 100 pounds.
Many attempts have been made to direet the course af balloons
in the air, but so far all have failed. ‘They preennt 30 extensive a
surface, that the resistance of the air is aufficiont to neutralize any
efforts to propel them in uny desired direction, with a degren of xpoed
worth attaining,
203. Method of filling a Balloon and making an
Ascent. —The balloon is filled by rising it three or four fect
abore the ground by palley+, when the gas is introduced by means
ef pipe or hose whieh connects with a gasometer. Ax the balloon
fills with gs it fe held down by ropon, and when noarly filled, the
ear Is attached. Care should be taken not to fill the balloon com-
pletely, ax tho gas expands in rising, aud unces wn allowance is
snade for this expansion the balloon might be ruptured.
To regalate the nsconsional power, the ear is ballastod by and,
coutalned fy stoall bags. Everything being ready, the ropes are
detached, and the balloon xscende with greater or loss velocity, ae-
confing 1 the arcensional force,
‘When the aeronaut finds that he does not assond fast onough, he
Thereases the aacensional fire by emptying ove or more of the sand-
twat Tu Hho manner, In descending, if the velocity ts too great, or
if the Yellnon tends 1 fall in a dangerous place, the weight of the
Dallooh & disniiished by emptying some of the eand-bage.
‘To render the deswent less difficult, the aeronaut is provided with
(el
166 PNEUMATICS,
an anchor or grapple, suspended from a rope, hy means of whict he
ean acize upon sone terrestrial oljoot when be comes neat the earth.
Whew the anchor is made fast, the aeronaet draws down. the bulloon
by pulling apon the rope.
204. The Uses of Balloons. — Balloons have been
used in war to some extent for making observations within
the lines of an enemy, and also as #@ means of communica-
tion between parties besieged and those without the lines of
use of the balloon, thas
far, has been in making
scientific observations
in the higher regions of
the atmosphere, Much
valuable meteorological
information bas Deen
gathered by the experi-
ments in aerial pavi-
gation, especially by
Gratsue, an English
acronaut. The greatest
height everattained ina
balloon was « little over
seven miles, and was
reached by GiaisHeR On
September 5, 1862.
205. The Parachute.— A Panacntin is nn sipparntus
means of which an aeronaut may abandon his balloon, and
descend slowly to the earth,
The form and construction of a parachute, when Aetached
from the balloon, are shown in Fig. 149
Tt consists of a cireular piece of clith, 15 ar 16 feet in diameter,
presenting, when spread, the form of a kage umbrella, ‘The site
mds, which, being contiuned, aro atmiched to a wicker
Fig. 140.
are maul
ean, as shown In the figure.
THE PARACHUTE. 167
A hole is made mt the top, in the centre, whieh, by allowing a
part of the compressed ait to escape, direots the dracent, aud prevents
vinlont oseillations, that might prowe dangerous by the alr eseaping
froan under the edge of the parachnte,
Mr, Wise, an American seronaut, several times exploded
his balloon, when high in the air, to show what he considered
to bo always the case, that the fragments with the network
would, ander such circumstances, form a pantchute which
would moderate the rate of descent,
and allow the aeronaut to reach the
earth in safety.
If from any cause it appoare impracti-
cable to effeet a descent from the balloon
itaolf, tho parachute may be of the greatest
service to the navigator. At preseut, how-
ever, it seems to be used to astonish the
public by the skill and courage of the
seronamt, who dares to Iaunch hiimself
into space in this frail craft when no danger
threutems his balloon.
‘All things considered, it is generally
réganied as safo to offoct a descont with
the balloon as with the parachute.
Tn Fig. 159 is shown the balloon with
parachute, attached to the network by
imeank of a cont, which passes mound a
palley, and bs fixed at the other end to the Fig. 100,
ear. When the cord Ia cut tho parnchute descends with rest
rapidity; But the air soon spreads the cloth, and then, acting by
its resistance, the velocity is diminished, and the acronunt reaches
the ground without injury.
Summary. —
Buoyant Effort of the Atmosphere.
Baroscope.
Principle of Archimedes.
The Bolloon.
Hot-air Balloon.
Toy Ballow,
168
PNEUMATICS.
The Balloon (continued),
Construction of Moder Balloons,
Mode of Navigation.
Principle that enables a Balloou to vise,
Measurements of a Balloon.
Directing tho Courso of « Balloou.
Method of fling « Balloon and propuring for tes
Ascent.
Valuable Information guined by Balloons,
The Parachute.
Use
Experinoat ol
Gow.
Ww
Exhibition of the Courage of the Aeronant.
Llustration of the Method by which the Parsehute
is detached from the Balloon,
wud Constr
CHAPTER VI.
ACOUSTICS
SROTION {. — PRODUCTION AND FROPAGATION OF SOUND.
206. Acoustics is that branch of Physics which treats
of the Jaws of generation and propagation of sound.
207. Sound is x motion of matter capable of affecting the
esr with a sensation peculiar to that organ.
Sound is eaused by the vibration of some body, and is
transmitted by successive vibrations to the car. The original
vibrating body is said to be sonorous. A body which trans-
mits sound is called a medium. ‘The principal medium of
sound is the atmosphere; but all clastic bodies transmit
sound, and are, therefore, medio.
a
Fig. 151
Let us take, for Mustration, » stretched cont which is made to
vibeato by » bow, as in a violin, for example. When tho cord iy
sexton From itk position of reat, ae b (Ig. 151), to the position, ado,
every point of the cord Is drawn from its position of equilibrium ;
sehen it Te fet go, Its elasticity causes it to spring back to its original
position. Th retorning to thi position, it docs
170 ACOUSTICS.
208. Sound-Waves in Air.— Mode:
—Sound-waves are produced in the wir by t
some sonorous body. When the body
strikes the alr in front of it, and condenses a
thickness depends on the rapidity of penile Vu heir
of this stratum impart the condensation to these of the next,
and these in turn to those of the next, aid so on; the con-
densation thus transmitted outward is called the eandenaed
pulse. When the body moves backward, the air in front of
it follows, and prodaces rarefaction in a stratum whose thick
ness depends on the rapidity of vibration ¢ this eauses a back=
ward movement and consequent rarefaction in the next
stratum, which is transmitted to the next, and 60 on; the
rarefaction thus propagated outward is called the rarefed
pulse.
Fig. 02
Fig. 152 ilustentes the formation of sound-waves sibra-
tious of a tuning-fork. The prong, a, as it Wied Ee
denzea the air in front, nnd then, receding, leaves behind it a qe
yacuum. ‘Thus cach complete vibration genemtes a eundonsed and
rarefied puleo, and those together constitute « sound-waye. ‘The
dark spaces, a, 6 ¢ dy roprsent the condensations, snd the
spaces, a’, U', ¢, dl’, tho rurefuctions ; the wave-longths aro the €is-
tances a}, bo, cd.
‘When a bell is ring, the air around it is set in motion, axa
waves are geucrated, which move vatwanl in every diceeton ba the
formn of ephorical shells, a shown in Fig, 153,
‘The rate ot which the sound-wave tavels is the wy
sound; the fistance through which it travele in the
SOUND- WAVES, MW
vibration of the soncrons body is the ware-length, Tho fur of the
sound-waye is transmitted through the air, but the individual particles
of air simply useillate to and fro in the direction of wave propaga
ium, moviug forward ov the passage of the coudensed and backward
om the passage of the rarefied pulse; the distance through which
each particle oscillates is called the amplitude of vibration of the
Ang tio particles situated on a line in the direction of propaga
‘ion, sind at a distance from each other equal to a wave-lougth, are
always moriny in the saino direction and with equal velocities; euch
particles are said to be tn the earn phase, All the partiolos of any
wave that aro ix the anine phase are on the surface of a sphere, which
is called wave-front.
Pig 169,
209- Combinations of Sound-Waves, — Many sounds
may be transmitted through the air at the same time, and in
some cases there is no perceptible interference of the sound-
waves. Th listening to a concert of instruments a practised
ear can detect the particular sound of each instrument.
Sometimes, howerer, an inten sound covers up or drowns a more
feeble ane; thus, the sound of a drum might drown that of the
bruman voloe. ‘Somnetinnes feeble sounds, which are oo faint to be
‘peparately, by their union produce 4 sort of murmur. Sucks
quie of the kaunwur of waves, the rusting sound of « breeze
j the leaves of a forest, and the indistinet buin of =
we ACOUSTICS.
210. Coincidence and Interference of Sound-
‘Waves. —‘T'wo sets of sound-waves may coincide so as
to increase the Intensity of the sound, or they may interfere
0 ux to neutralize cach other and produce silence.
Suppose we have two tuuing-forks, A and B, whieh produce
waves of exactly the sune Iength. Let them bo placed @ ware
Tength apart, as shown in Fig. 14. The two sete of eibrations
a A c
Fig. 154.
will coincide, and the intonsity of the sound will be greater than
if ove were vibrating alone. The same would evidently coeur if
the distance between it and B were any number of whole wave
Jengthes
Bot suppose A aud B to be only half a wave-longth apart, Tt i
evident Uhat the rarefaction: of ove of the systetns of waves will then
TN
BoA
RT
U
Fig. 165.
and the result
will be interference, by which both aystems cf waves willbe de-
‘This result is indicated by the wniformity of shading tn
coincide with the condensarions of the other syst
Fig. 1
Th
taning-fork, and then holding
ference of sound-waves can be shown by steiking w small
© short distance feom the eaf,
between the thumb and finger,
sound-waves neutralise one
another aed po soced ls heard, aud also several where the waves
coincide and thore is « reinforcement of wound.
rolling the stem at the same ti
Wo shall find sevoral positions whew t
PROPAGATION OF SOUND. 173
arr. Beats,— When two tuning-forks which are not quite
in unison are sounded together, thore is no continuous sound
produced, but a peculiar, palpltating effect, which is owing to
a series of alternate reinforcements and diminutions of the
sound. ‘This succession of sounds with the intervals of com-
parative silence is known to musicians by the name of brats,
and is the result of the coincidence and interference of the
sound-waves.
Soppose one of the forks vibrates 100 times ina seecnd, and the
ether 101 times, Lf the waves start at the oatno moment the con-
denmations will enincide ant also the rarefuctions, but they begin to
interfere more and more, inasnuch o9 one syutern has been gradually
falling behind the other, until at the middle of the secoud it will
have amounted to hulf u wave-length, and the two souude will destroy
each other,
At tho end of the second, when ono fork bas evnnpleted its 100th
vibration and the other its 101st, one eysten has fallen bebind the
‘other one wave-length, and there is coincidenm again of crest and
depression, and the full effect of bouk sounds reaches the ear, We
havo, thon, one beat aud dine interval in every second.
In geveral, beats are produced by two musical sounds of nearly tho
amo piteh emitted at the eame time. The manber of beats per ae
red ts equal fo the difference of the rates of vibration.
‘Beats are frequently heard in the sound of church bells, and in the
fower octaves of Tage organs. Telegraph wires, when rato to
vibeuts by a strong wind, produce beats. These ean be observed by
pressing one Gur against 9 cmuph-pest and closing the other.
If we sicko pimaltanesnaly ono of the Inwer white keys of a planw
eal tho adjncont black key, besite will be heard,
Beate ato of grout value in tuning tousical instranents, The notes
given wut Ly two musical iusteninents of slight slifference in piteh
eau be brought into unisun Vy tuning watil the beats disappear.
212. Sound is not propagated in a Vacuum. —That
some medium ie necessary for the transmission of sound
may be shown by the following experiment
“A bell is placed under the receiver of anair-pump, provided
with a striking apparatus set in motion by clock-work. Welore
————
ear at the other end, even when it might Ie inau
equal distance througl the sir.
‘The carth transmits sounds, aud by plackag the ear
with it, sounds may be distinguished at © great:
hearing approaching footsteps of men or’
uandorstucel by hunters, Te the coustruction of sub
for winlng purposes, the wiver is oRten guided, ns to
should take, by souuds traustaitted through lange
saved rock.
arq. Velocity of Sound in the Air, —T!
vecuples an appreciable time in passing from int
i
VELOCITY OF SOUND. 15
may be shown by many fumiliar examples. If we notice a
man cutting wood ata distance, we perceive that his axe
falls some time before the sound of the blow reaches the ear.
If o gun is discharged, we see the flash before we hear the
report. In like manner, the flash of lightning is seen before
we hear the thander.
In 1822 a oumber of scientific men undertook a scries of
very nice experiments to determine the velocity of sound.
‘They placed a cannon on the hill of Montlery, near Paris,
and another on a plain near VilleJuif, the distance between
them being 61,017 feet. At cach station twelve dischanges
were made at intervals of ten minutes; the discharges alters
nating between the stations at intervals of five minutes.
‘Observers placed at each station observed the intervals of
time that elapsed between seeing tie flash and hearing the
report of the cannon at the other station. The average inter-
val was 54.6 seconds, and the temperature was G1" F.; the
actual velocity was found to be 1118 feet per second, which,
after correcting for temperature, gave 1090 feet per second
for the temporature 32° F.
This shown by experiment that if tho elasticity of the air be in-
ervased, the density remaining the same, the velocity of sound is
Increased ; or, the elasticity remaining tho same, if the donsity be
eereased, the volocity is also inereased. When our atmosphere Is
heated by the sau, its density is made lows whilo its elasticity is not
changed. The velocity of sound is found to Encrease thereby about
one foot per second for each degroe Fahrenheit.
‘The velocity of sound in air depends vo the clusticlty of the alr
tn relation to ite density. The greater the clasticity, the greater the
velocity; the grearer the vousity, the less the velocity, This can be
expressed as follows: —
The celocity is directly proportionat to the squore root of the elas-
tioity 7 it te iavereely proportional to the sqware root of the density,
ats. Velocity of Sound in Liquids. — Sound is trans-
rapidly in liquids than in sir. Its velocity in
ciate caaaesse, by Cottavox and Srom, in 1826, at
—
176 ACOUSTICS.
the Luke of Geneva, in Switzerland. Two boats were moored
ata distance of nearly nine miles from each other. One of
them supported a bell of about 140 pounds weight immersed
in the lake. Its hammer was moved by a lever so arranged
that, at the instant of striking the bell,
it ignited a small quantity of gunpowder,
An observer in the other boat heard the
sound by means of a trampetshaped
ube (Fig. 157), the lower end of which
was covered with membrane, and
tarned in the direction from which the
sound came.
By observing the iuterval between seeiog
the Hash and hearing the soand, the velocity
was found to be about 4700 feet In a second, which is move than
fonr times its velocity in nin,
216, Velocity in Solids. —Solid belies transmit sound
more rapidly than gases or liquids. The velocity varies in
different, solids, and is grentest in dense and highly elastic
bodies, Through steel wire sound moves at the fate of
15,470 fect per second; through silver, at 10,900 feet per
second, —jast ten times the velocity in air.
Fig.
‘That sound travels faster io ire than in sir aay be shown by
placing the car at one extromity of a long iron bar or tubo, while it is
struck on the other ead with a hammer, ‘Two sounds will be heard,
the first transmitted through the iren and the second throngh the air,
‘The true reason that the velocity of sound in liquids and solids is
greater than in air is found in the faet that their elastiqition, when
compared with their densitics, are greater than that of ait compared
with its donsity
217, Reflection of Sound. —Echoes.— When sound-
waves in air strike upon a solid surface they are reflected, or
thrown back; and, as in the ease of clastic solid bodies, the
angle of refh to the angle of incidence. A wave
of sound falling perpendicularly on a wall or other flat sur
on Is equ
OES i
ACOUSTIC CLOUDS. V7
face returns in the same direction to the spot from which
it emanated, and produces there an echo,
A hard or perfectly smooth surfice is not necessary to
secure reflection of sound. It Is reflected from cliffs, from
wooded slopes of mountains, from the surface of water, and
even from clouds, in sach a way as to form distinct echoos.
A sharp, quick sound may be rewarned as an echo from a
distance of fifty-five feet, but, to repent spoken words or
eyHables distinetly, the reflecting surface must be so far dis
tant from the speaker a8 to yequire at least the fifth of a
second for sound to travel to tt and return.
Tei not possible to pronounce or to hear distinetly more than five
syllables fu, a-sccond, ‘Tho velocity of sound being 100 foet per
second, it follows that sound travels 218 foot in one fifth of a second.
If, then, an-obstacle be placed at the distance of 100 feet, sound will
go to itand retarn in one fifth of a second. At that distance the
last syllable only of the echo will reach the car after the sentence
is pronounced. Such an echo Is enlled monasylladie. If the echo
takes place from an obstacle at a distance of 218 feet, we bear two
syllables; that is, the echo is dissyllabio, At distunces of 327 foet,
the echo is trinyilabie ; und 90 on.
‘When sound is reflected from several surfaces situated in different
directions and at different distances, multiple echoes ure produced ;
that is, a single sound or syllable is repented several times. The
nomber of times that» single sound will be repeated depends upon
tho mumber of reflecting surfaces; tho number of syllables or words
that vill be repeated afier a speaker depends upon the distance of »
single reflecting surfaco.
Sound i wested by repented reflections. Floors and partitions
‘are deadenad by moans of mortar, sawdust, and the lke, so that the
nas by irregular reficetion of the sonorous Waves may
diminish the intensity of the sound.
218. Acoustic Clouds. — It hae generally been supposed
that fogs, rin, snow, and huil interfere with the transinis-
sion Of sound ; Dut, according to experiments made by Tya-
Wall. they seem to have no sensible power in olvatronkinyg,
Therefore the connection supposed to exist We-
ae
|
178 ACOUSTICS.
tween a cloar atmosphere and the transmission of sound i
dissolved. He also found that the air associated with fog ie
uéually highly homogeneous and favorable to the transmission
of sound.
He supposed the existence in the air, even in the clearest weather,
of clouds of vapor impervious to soand, called aoowstic clowde
‘Theeo havo vo connection with ordinary clouds, fogs, or haze. ‘The
sound-waves are thrown back frum these clouds, as Yeht from ondi-
nary clonds, and the intensity of the ound is weakened by repeated
teflections.
‘The fact that sound is thus turned buek aay explain the warke
tions in distance at which familiar sounds are oflen heard nt different
times, and eepecially why, at a given point, the bound prodwecd by »
cannon may be heard nt some places and not at others equally dis
tant from the spot. We may have days when the stinosphere ix
very transparent to the eye, but on account of the presence of aowextie
elonds very opaque to the ear.
arg. Resonance.— When sounds are reflected from a
distance too small to produce a distinct echo, the effect ts
to strengthen the original sound. ‘This effect is ealled Reso
nance.
It is the resonance from the walls of a room that aulkes It tasker
té speak in a elosed apartment than in the «pen air. "The resonance
is more clearly perceived when the walls are clastie Tn rooms
where there aro carpets, cartaing, stuffed furnitare, and the like, the
sound-waves are broken up, and the resomance is dinniniahed ; but im
houses where there i no furnitore the resonance be
Hence it is that the sound of voices, foolsteps, te, ie 60 atroaely
marked in deserted and unfurnished buildings.
220. Refraction of Sound. —Sound may be refracted,
or bent out of [ts course, when passing from one mediam to
another of different density. This is shown in Fig. 158.
B (s a collodion or rubber balloon filled with carbonic aga
gas. The envelope is so thin that the sound-waves are trams-
mitted to the gus inside.
Let a watch, ©, be bung ocar this gas-Jene, B, New place the
=
INTENSITY OF SOUND, 179
oar a Cow feet from the lens, at f; using w glass funnel, f°, to assist
the car, By moving the funnel about, « position is found where the
ticking ts Jonder than elsewhere, The sound-waves are bent from
thelr evarse, and brought to a focun at f.
‘The laws of reflectod and rvfeacted sound are the sare as those uf
light, and will be treated under that subject.
aar. Intensity of Sound.—This quality depends upon
‘the anplituds of the vibrations, that is, the space through which
the molecules move to and fro, It varies very nearly as the
square of the amplitude of vibration of the molecules of air.
‘The intensity of sound diminishes as the square of the
distance from the sonorous body increases; that is, de fa
tensity of sound varies inversely 0s the square of the distance from
the sonorous body.
‘The density of the ale nodifier sound. In rarefied air sounds are
feeble, while lu condensed alr they are londer than in the onlisary
atinosphere. The wind modifies sound. The velocity wf sound is
fucrensed or diminished by the velocity of the wind, accunling as
the direction of tho wind conspires with ot opposes the propagation,
‘The oelfect of the wind is ty move the whole mas of air, carrying
along the sound-waves unaltered.
‘Sound bs fwereased in intensity when the sonvrous body is in cons
tact with, or ereh in the neighborhood of another body capable of
vibrating in unison with it Hence the sound of a vibrating conl is
‘réinforesd or strengihened by stretching it over a thin box Elie
‘with nit, ne ta the violin. To this ouse the wir i the Woy vi Wee
(am
sive reflections of sound-waves from the beh I h
tho instrument is coiposod, hy virtoo of wi voice is tras
mitted ouly in the direetion of the uibe, eZ
But the fact iz, that the sound transmitted ie mot
in direction of its axis, but ia all directions. This
that ite effect should be attributed to a reinforcement.
the vibration of the column of air contained iu the
with 11, acconting to the principle that sound is reinfu
Mary vibrating body.
224, The Ear-Trumpet.— The Ear-Trn
ployed by persons whose henring is defective.
the speaking-trumpet reversed, although the prin
sume, Tt consists of a conical tube, tamed In an
venient direction, 40 that the smaller opening 1
car.
to colleet amt concentrate the sounds:
SUMMARY, 181
thes enabled to produce « more powerfal lavpression on the dram of
the ear, The shape of the ear in man and in animals is such as to
perform the fimetion of the trampet
Summary. —
Production of Sound.
Tihusteated by a Stretehed Cord.
Stunde Waves in Ay
Propagation illustrate by Taning-Fork and Boll.
‘Combinations of Sound- Waves.
Coincidence and Interference of Somnil- Waves.
Mastrated by a Tuning-Fark,
Sound increased by Colucideace of Sound-Waves.
Sound destroyed by Interference of Sound-Waves.
Examples.
Beats.
Definition.
Mastnated by Tuning-Fork.
Examples.
Propagation of Sound.
Tn the Air and
Tn Liquids and §
Velocity of Sundin Air.
Examples to determine ite Volocity,
Effect of the Density aod Elasticity ow its Velocity,
‘Tho Law of its Velocity.
Velocity of Sound in Liquiits
Experiment to dotennine the Velocity
Velocity of Sound in Solids.
Greater in Dense and Elastic Bodies.
‘locity in different Solids.
ity of Sound through Liquide
and Solids being greater than throagh Air,
Reflection of Sound,
Echoes, — How formed.
Examples,
Moltiple Eehoes,
Sound wasted by Heflections
Acoustle Clon
Explanations.
a Vacoum.
is
182 ACOUSTICS.
Reflection of Sound (continued).
Effect of these Clonde on Sound,
Resonance,
Eufraction of Sound.
Mastrated with Balloon and Wateh_
Intensity, of Sound
Law of Intensity.
Modified by the Wind.
Modified by Coutnet with a Sonorous Body,
Intensity of Sound in tuber.
Speaking-Tube.
Spoaking- Trumpet,
Eor-Trumpet
ae
|ON 11. — MUSICAL, SOUNDS,
225. A Musical Sound results from m succession of
vibrations at oqual intervals and of sufliciont rapidity.
226. Noise results from a single impulse, or from a xtc
cession of vibrations at irregular intervals. Thus, the crack
of a whip, the discharge of a pistol. the mttling of thunder,
of the waves of the ocean, are destitute of musical
value, and nre simply noises.
The difference between a musical sound and a noise can be
illustrated by Savanr's Wheel (Fig. 159). ‘This consists of
a he: frame supporting two wheels, 4 and B, which are
by a band, D.
he crank, Af, the toothed wheel, B, cam te mnie to
rd bo hold against the teeth,
cal tone is produced, which
il the separate taps
the nr
connec
By turn
revolve with gront rapidity. If a
i rapid motion, a ebeellD cee
shrill aw
inst. the ant are heard.
» that when the taps recur with sufficient frequency, that is,
form a continnons sound, the effet
ust the wheel lew than 16 teeth
ly will be heand, but uo musiesl tone
the speed slackena, u
the teeth
Ww
more than 16 per second, #9 xs 1
is musieal. If the card strikes
per second, the
will be receguized
arate
ay
PITCH OF SOUNDS.
We have at 27 an apparatus for indicating the number of rovoln-
tions of the toothed wheel. The card, being struck by ench tooth,
takes as many vibrations as thers are teeth, Multiply the number
‘of revolutions by the number of tecth in the wheel, and we have the
a smumber of vibrations, Divide the product by the number of
seconds, and we get the umber of vibrations per vecond.
2a7. Pitch of Sounds.— The Pitch of a musical sound
depemls apon the frequency of the vibrations. This waa
shown In Fig. 152.
—_ Fig 160,
‘The faster tho wheel tame the more rapid aro the vibrations of
the cand, aud the sbeiller is the sound, or, in other words, the higher
‘the piteh. ‘Tha slowor dho-wheel urns, tho rovorse fs the exse.
238, Music. —Those sounds which result from very rapid
L * cente, whilst those whieh arise from very
slow rations are ‘called grace.
Th ‘or Toudiwss, of musical sounds, as in the case of
‘other: ‘of the urnplitade of the vibrations,
nm. — The Siren is an instrament osed for
toues, and at the same time determining
160) of & cylindrical bos of Weas.C 5 te
184
ACOUSTICS.
a tube opening into it frown below, for the purpose of adinit-
ting air. The top of the cylinder is covered with a Dress
Fig. 160,
plate, #4; this is perfornted with four
series of holes arranged in four con-
centric circles, containing 8, 10, 12,
and 16 apertures respectively; de i
a brass disk, also perforated with four
series of holes, corresponding, in their
general arrangement and distanee from
ope another, with those In the plate,
ab, below.
Through the contre of this disk passes
a steel axis whose ends, p and pi, are
smoothly bevelled, py’ to fit into the
socket, 2, and p to receive a brass cap
when the instrament is ready for use.
‘The perforations do. not paws perpen
dicularly throngh the plates, but elope in
opposite dirretions, so that when air ie
foreod through the holes in the lower
plate, it will impinge on ene side of the
holes in the upper plate, and this blow it
round in a definite direction, As it re-
velves, tho holes in a} are alternately opened und closed. "The air
coming {nto the eylinder thevagh the tube, f thus esexpes trough
Fig. 161
the aperture in ite upper plate in a
succession of puffs ‘The pails come
throagh ‘lowly at fing aml ean be
counted, bat as the disk rotates faster
oe they unite thelr vibrations
into snusieal note, the pitel of which
is higher in proportion te. the ineromse
of velocity.
Tho revuluitions of the isk wre aagiee
tered by inoams of the apparatus shows
in Pig. 101, On tee opper part ef the
axis of the disk is an endless screw counectiag with a pair of toothed
oe
THE SIREN. 185
wheels. By pushing a, the recording apparatas f4 set in motion, and
by pushing b the motion i« etupped.
In Fig. 162 are seen the gradaated dial-plates om the front of
the Siren. Tho Indexes of each dial aro connected with the eloek-
work fust described. ‘They move over the dials with the revolu-
tioas of the wheels, and register the revolutions. ‘The stops, m,n,
©, p, are used to open ur close the different series of orifices.
230. Method of determining
the Rapidity of the Vibrations
of a Sonorous Body. — Let air
he forced into the Siren by means
of bellows. Note carefully when
the tone of the Siren blends with
that of the sounding body, the
number of whose vibrations we
wish to ascertain. Snppose the
outer series to be open, sixteen in
number, allow the disk to vibrate
one minute, then read trom thé
dials the namber of revolutions it
has made.
‘We will suppose the number to be
1440, best for every revolution of the
disk there were 16 puff of air or
sound-waves; thorefore the whole
wamber is found by multiplying be
1440 by 16, which gives a result of Fig. 12.
23,040. This wumber also rypresents the vibrations of the sound-
ing bedy. Divide this result by 60, and we get 354, the number
for eae evcand,
Musleal tones are in unieon when the number of vibrations iu a
secured ly the same.
If the inner series of holes should be opened, the tone produced
woald be an octave lower than that made by tho outer cow, the
wibeations being one half ax iwany. Heneo the octave of auy tone is
foand by multiplying the vibratio Ihe touw by 2; if we donkle
the vibetions of the netave, wo got ite octave, awd so vu.
=
Ind. ACOUSTICS.
ag1. Length of the Sound-Wave.— The distance
through which a sound-wave tnively im one vibration of the
sonorous body is the wave-length, and by knowing the velocity
of sound for any temperature the length of the sound-wave
can be easily found.
Suppose tho temperstaro is such as to give a velocity of 1120 feet
per second for the foremost wave. ‘There are 384 soncroue waves.
Dividing 1120 by 384, wo find the length of eseh wave to be about
Bfeet, If the number of wares be 512, the wavelength would be
2 feet 2 inches. ‘Therefore the higher tones ane praiiced ty the
shorter waves; the grave, or lower «mea, by the longer,
‘The ordinary pieh of a woman's volen Is considered to be as
octave above a man's io the lower sounds of conversation; in the
higher, about two octaves. ‘The sonnd-waves generated by w insists
voeal organs in ordinary conversution are from 8 to 12 feet, those of
awoman 2to 4. ‘The hurnan ear is Tirnited in ite mange of heuriag
musical eounds, Helinboltz bas fixed the lower limit at 16 vibra
tions, and the higher at 38,000, per seeand,
Summary,—
Masical Sounds.
Difforonce betwoon # Musical Sound avd a Noise.
Mastrated by Savart's Wheel,
od of finding the Number of Vibrations per Second,
Masical Sounds.
Illustrated by Sqvartte Wheel.
Intensity of Musical Sounds,
The Siren.
Constroetion.
of Operation.
Method of recording the Vibrations of a Sounding Body.
Method of finding the Noinber of Vibrations per Second.
Tulse of Musical Tones
Rule for Boding the Octave of any Tone.
Length of Sound Wares,
Limit of the Human Eav in hearing Musieat Sounde.
232. Transverse Vibrations of Cords. — We have
already seen (Art. 207) that whon a stretehed cond is dimen
from its position of equilibrium and abandoned, it returns te
— =
VIBRATIONS OF CORDS. 187
its position of rest by succession of continually decreasing
vibrations.
‘Cons sec in musical instruments are generally made of
‘catgut or of twisted wires, They are made to vibrate by
drawing a bow across them, as in the violin; by drawing
them aside, as in the harp; or by percussion with little ham-
mers, as in the piano. In all of these cases the vibrations
are tromscersal, that is, the movements take place perpen-
dicularly to the direction of the cord,
‘The number of vibrations of a stretched cord in any given time,
a fo On0 eeeond, for exainple, depends upon its length, its thickness,
fis tensing, and its density,
Fig 168
233. Investigation of the Laws of Vibrations. — For
‘studying the vibrations of cords, an Instrument called the
Sonometer (Fig. 163) is used. Tn its preseut form it consists
‘of a wooden box about four feet in length, upon which are
mounted two fixed bridges. A and #, and a movable one, D.
‘On these Iwidges, two cords. C.D and A B, fastened firmly
‘at one end and passing over pulleys at the other end, are
stretched hy means of weights, P.
The following arv the laws that goveru the wanber of Woearhoa
tite 2 —
188 ACOUSTICS.
1, Te tension being constant, the number of etbrations wares
inversely ars its length.
Ifa given cord makes 18 vibrations por seeoud, Ht will knake 36 if
its length Le reduced to vue half, 54 if ite length be redgced to ame
third, and so on, ‘This property is atilized inthe violin. By applly-
ing the Sager, we virtually reduce the length of the vibrating portion
at pleasure.
2. The tension and length being the same, the number of witsrax
tions varies inversely as its diameter.
Stnall conte vibrate more rapidly than large ones, and consequently
render more acute sounds A cord of any given shee males tyice aa
many vibrations ax one of double the size, Other things being
equal, the notes rendered differ by an vetave.
8. The length and size being the sume, the number of vibrations
varies aa the square root of the tension.
Ifa cond renders « given note, it will, if its tension be quadrapled,
rend votave higher, and so on. This property is stilizest
in stringed instruments by incans of an apparatus for increading or
diminishing the teusion at pleasure,
4. Other things being equal, the number of vibrations varies
inversely as the square root of the density.
Dense cords render graver notes than those (if less density, Sinall,
light, and short cords, etrougly stretched, yield acute notes, Lange,
ched, yield grave notes.
a nat
douse, od long conls, not strongly stre
234. Verification of the Laws.,—'These laws can be
verified as folk
Lat the cords
nsactly alike and steot
If tho bridge, D, be movnd su as to render ©) equal to one half of
AB, the notes of the two cords will differ by an oetaves that Ss,
CD will vibrate twice as fast as 4B. ICD be made equal te
une thint of 4B, by moving the bridge, J), the former will vibrate
threo times ws fut ax the latier, aud so ou, This verities Uke firat
Law.
To verify the second law, we remove the bridge, D, and use thre
cords, one of whieh is twice as lange as the other, It willbe found
Alvet the notes yielded will differ by an octave. Ifowe cued ts thee
wd by equal weights.
ae Eee zsh
FORMATION OF NODES. 189
Hones ax lafge as the other, the latter will be found to vibrate throe
times as fast as the fonner,
‘Te verify tho third law, lot the two cords be alike, and stroteh
one by « weight four timos as great as that employed to stretch the
wther. Tho notes will differ by an Getave. If the atrotohing faree in
4
Pig. 164.
one is nino times that in the other case, the former will vibrate three
times ax fast as the latter, and so on.
To verify the fourth law, wo make axe of cords equal in length,
size, and equally stretched, but of different densities, Is will be
fined that the aw is verified in overy cum.
Fig. 105
235. The Formation of Nodes. — In the Sonometer
the cord is shortened by means of a movable bridge which
holds it firmly. If, instead, we place a feather on the centre
of the cont (Pig. 164), and draw a bow across one ballot &,
wo shall get the octave of the tone given by Ue whole sting.
(mm
a screw fastened to one prong of a tu
‘end je wound about a peg some distance
Tighten the string by turning the peg,
whole, when the bow is drawn across the
expands into the form of a spindle whose ; u
& beautiful appeurnneo, Let tho atring be relaxed a
have oro vibrating segments; relax still more, and
and if we continue the process, twenty and more
‘The stationary nodes couteast finely with the ose)
237. Longitudinal Vibrations. — Strings o
algo be made to vibrate longitudinally by
the direction of their length with = bow or ploc
leather covered with rosin. ‘The soands thus obta
of much higher pitch than those produced by tra
‘SYMPATHETIC VIBRATIONS. 191
vibrations and the higher the pitch. ‘This ix independent of the
form or diameter of the sections. Rub one of the wires of the
‘sonometer with resined leather in the direction of its length,
and we have a musical sound, Move the bridge so as to
divide the wire into two equal parts, rub one of the halves,
and the octaye of the whole wire is given. This law holds
true in regard to rxde as well os wires. If we change the
tension of the wire, the longitudinal vibrations are unaltered.
A musical instrument (qo
to show the tongitadinal
‘vibrations has boon eon-
structed (Ply. 16) some~
thing like a harp in :
appearance, compesed of
wooden rods of different
Jengths fixed at one end,
60 that notes of different
piteh are emitted, “The
rods nro sor in vibration
by rubbing them with
we Ht. glass tbe by its centre
with one lsuxd, aud nib the upper half briskly
with a wet fa the other band, the tongi-
may be sufficient to shiver Fig, 167,
the end Sarthest from the hand into ring-shaped fragments, ne seen
fa. Pig. 167-
238. Sympathetic Vibrations. —If a tuning-fork is
made to vibrate, another fork of the same piteh an:
the vicinity will be thrown into vibrations also by the impact
of the sound-waves in the air; if the forks “are mounted oa
Gr tto9000 00
192 ACOUSTICS.
near 2 piano, a wire of the same piteh ag the tone will respond
to it. If the piteh be changed, another wire will respond.
Mony examples might be brought farwand to illustrate this
“Tf owo clocks, for example, with pendelams of the same period of
vidration, bo placed agaiust tho same wall, and if one of the okeks
be set going and the other not, the ticks of the moving clock, trans
mitted through the wall, will act upon its neighbor. “The quires
pendulum, moved by a single tek, swings throngh a very stall are,
but it roturns to the limit of ite «wing just in time to receive another
impulse, By continuanee of this process the inpulses ee add them-
selven togethor as Bnally to get the clock gokng. It ie by
of impulses that a properly pitched voice can cause
and that the sound of an organ can break a
Fig: 168,
239. Vibration of Plates. — Fig. 168 represents « plate
of metal seipported at its centre. Sprinkle some fine, dry
sand over it, Hold the thumb and finger on one edge of the
plate, and draw the bow lightly across the opposite edge.
‘The cand at once leaves the vibrating ports and secorndlates op
the nodal Tines, ‘These lines vary in number and position aesord-
ing w the form of the plates, their elasticity, tho mode of exel-
tation, and the number ef vibrations. By touching the vibrating
plate wt different points, the yxsition of the nodal Nues may be doter-
mined. In Pig. 160 may Lo seen some of the nodal forms obtained
Ly Cunaune
—— —
OVERTONES. — TIMBRE, 193,
Nodes may be formed in a similar way in belle, aul all other
socndiog bodies,
240. Overtones, or Harmonics. — It has boon shown,
by the experiments Just given, that a stretched string vibrates
a8 4 whole, and at the samo time in equal parts. ‘Tho same
may be said of any sounding body. ‘Tones of simple charne-
ter cannot, therefore, be given out by vibrating bodies.
When the boty vibentes ns a whole, the tone produced is ealled
the findamentel. The higher tones are made hy the vibration of
the Oqaal parte, and are ealled Aarmonica, or overtones. By piteh
vee abso knram the fundianental sound
24%. Quality. — Timbre. — ‘The mingling of the over-
tones with the fundamental determines the quality or charae-
ter of the sound, called by the French, tinbre.
Thue we can understand why it is wh
like the piand, the violin, or the tute,
mental sound, that they have such di
wnable te instantly to identify th
overtones. The waperiority of ono singer over nnothor is undoubtedly
doe, 1 ® great memsure, to 4 much Hiner ulugling of the overtones
with the fowdamental que.
o. ‘The human voice & rieh in
——
194 ACOUSTICS.
242. Musical Scale. —Gamut. — The ear not only dis»
tinguishes between given sounds, — which ie most grave, and
which is most acute, — but it also appreciates the relations
between the number of vibrations corresponding to each.
We cannot recognize whether for one sound the number of
vibrations is precisely two, three, or foar times as great ag
for another, bat when the number of vibrations correspond.
ing to two successive or simultancous sounds have to each
other a simple ratio, these sounds excite an agreeable impres-
sion, which varies with the relation between the two sounds,
From this principle there results a series of sounds charac-
terized by relations which have their origin in the nature of
our mental organization, and which constitute what is called
‘a musical scale.
The whole series of mnsical tones is divided into setave, or
groups of eight tones each, Each group constitutes what ts called
the gamut, or diatonic scale.
‘The notes are wamed do, re, ni, far, e0t, to, si, dos bot they are
designated by the laters C, D, BE, F, G, A, B,C, Ta the table
below is given the relative number of vibrations for each mote, 1
denoting the number corresponding to €: —
1 4 4 ¢ 1 COR
C D E F G A B c
‘The relative lengths of strings required to produce the eight notes
of the ale are expressed by the reciprocal of these quantities, ax
follows: —
ut ¢ 4 ? * 3
e D E r G A B ec
If we know the number of vibrations of C, we can find the
others by multiplying those of (’ by the fractions placed over
the other notes in the first table. Let 256 represent the
vibrations of C, then the following numbers will denote the
vibrations for each note : —
TE
c D & F @ A B c
ES _==all
MUSICAL SCALE. 105
‘Thore are really but #even notes in what is called the diatonic
wale, the eighth note, C, being truly the first of seven other wotes
above, having rolations to one another similar to those of the notes
below, and constituting another octave.
The resulta obtained in these tables can be verified by the Siren
and Sepormeter.
243. Intervals. — The interval between any two notes ix
called a musical interval.
‘The numerical value of any interval is found by dividing
the number of vibrations in a given tone by the number of
vibrations in that proceding it.
‘The intervals between consecutive notes, called seconds, is given
in the following table : —
CwD, Dek, EwF, FwG, GtoA, AwB, Boe.
OS a
Tf the interval comprise two, three, four, ete, eeven notes, it is called
4 Grd, a fourth, a fifth, ete, an eighth or an octave; thus, the
interval between @ and B is a third, wud is equal to $j the interval
from © to Fis a fourth, and is equal to §; the interval from any
note fo the next note of the saine name is an octave, and is always
equal to 2
Tn the following table fa « summary of the results already given,
for on6 ortave of the diatonic seale, arranged on the musical staf: —
—— SS}
Numeof interval. tm 2d 31 4th Sth 6th 7th Fh
Syllables 2. Do He Mi Fa Sol Lo Si Do
Nimedylits. © D HE F G AB OC
Relative nmnber 3 5
mamas ¢ t¢ ft gH 8
s
Abeta number! erg 288 m0 D111 B84 4201 460 512
eos + ik tk
‘am
196 ACOUSTICS.
244. Melody. — A number of tones of Like quality,
varying more or less in pitch, following one another with
regularity, is called a melody.
The air in « pigeo of snusio is an example of molody.
245. Chords. — Harmony. — Discord. — When two or
more sounds are produced at the same time, having agreeable
relations to one another, we haye a chord.
A succession of chords in melodious order constitutes
harmony.
‘The air, in music, with accompaniment, is an example of
harmon
Wh
Tho simplest aud rnomt age
tions aro equal in numbe
) theae agreeable relations do not exist, we have dieeord.
le harmony veeurs when the eibra-
hen comes the octave, in whieh the
number of vibrations corresponding to ous eound is double that
comsponding to tie other; then the fh, in which the numbers
are aa 3 to 2; then the fourth, in which the numbers are wa 4 to 35
and finally the Hird, in whieh the ratio is that of 5 to 4,
The more frequent the coincidences between the vibrations, the
greator the harmony.
Summary.—
Transverse Vibrations of Cords,
Investigation of the Laws of Vibrations.
Description of the Sonometer.
Laws of Vibrations.
Verification of the Laws.
Formation of Noder.
Tlustrated with the Sonometer,
ition of Nodes on a String.
Vibration of the String as a Whole or in Segments.
Longitudinal Vibrations of Wires and Rods.
Experiments.
Vibration of Pi
Experiment with Plate and Sand,
Chladni's
, or Harmon
al Forint.
OPTICAL STUDY OF SOUNDS. 197
Quality, of Timbre, of Sounds,
Musical Soate.
Names of Notes
Letters used in desigaating Notes.
Relative uumber of Vibrations of each Noto, in
‘Tabulated Porm.
Relative Jeogth of Strings to give euch Note, iu
‘Labuluted Eorm.
Absolute number of Yibnations for each Note, in
‘Tabalated Form,
A Mosteal Interval.
‘Tabulated results on the Musical Staif
Melody, — Harmony. — Distort.
BRCTION Hf. —OPTICAL STUDY OF HOUNDS — MUSICAL [88TRUMENTS.
THE HUMAN VOICE AND EAR —THE PHUNOORAPH.
246. Optical Study of Sounds.—It has been shown
in « previons article how the vibrations executed hy a sono-
rons body can be counted. The Siren and Savanr’s Wheel
are instruments used for this perpose.
During the last few years physicists have studied carefully
the vibratory motions of sounding bodies by means of the
eye, and have thus been independent of the aid of the ear fn
dotermining the relationship of sounds, A deaf person, by
this optical method, can become skilful in judging of the
character and pitch of sound-waves.
247. Lissajous’ Representation of Vibrations. —Ono
of the best methods of making vibrations apparent has been
devised by M. Lissisovs, a French physicist, Hoe attaches a
small metallic mirror to one prong of a tuning-fork, and to
the other a counterpoise to secure regularity of vibrations,
A my of light from a hole in o darkened chimney, a few
‘yards distant, is made to strike this mirror, and from this it
is reflected to another mirror, which sends \\ to an adhrorantn,
198 ACOUSTICS,
this lens is so placed as to project the
images on a screen.
Wheu the fork is at rest, we have on the screen a luminous pokat,
the iuage of the hole in the chitaney ; when it vibrates the mirror
vibrates with fi, and the polit moves ap and dawa with such rapidity
as to leave a linc of light on the seroon. If-wo rotate the fark while
it is vibrating, we get instead of the straight line @ bright sinuous
one. ‘The position of the parts is shown In Fig. 170, exeopt that
tho fixed mirror takes the place of the vertical tauing-forke.
248. Vibratory Motions at Right Angles. —If we
use two forks, one horizontal and the other vertieal, boul
arranged as in Pig, 170, we shall
riety of images.
provided with mirrors au
have thrown on the screen
Fig. 170,
If the vertical fork vibrates, we perceive « luninous Tine in a vere
the horizontal one vibrates, while the vertical fork
Is at rest, the lumluc mtu.
If both forks vibrate at the sume time, the two movements at
nbine aud produce # lominogs eurye, the form of
wm the umber of vibrations of the twee Gila
arrows show the direction of the cay of light
of eurwe ane repre
tieal direction ;
line Is hori:
right angles will
whieh will depend uj
inagiven time.
sereen. Some vari
sage to th
WN
¢ will of those principles, tuning-forks ean be sompared with
et precision than would be the ease with
a standard fork wi
the most susceptible ear.
i =
OPTICAL STUDY OF SOUNDS. 199
Liss.ovs! figures can also be produced by means of the vibra
tions of « peulalumn ina slower and eusier way than by means of
the tuning-furk-
249. Kaleidophone, —The optical study of vibrating
rods ean be made by meins of an apparatus called the kal
dophoue, ‘This can be constructed by a very simple process
Insert, the aid of an awl, a knitting-needle with a
bead on the end, firmly in an inch board several inches
Fig. 171
square. Place the Woard on a table, and hold it tightly with
the hand while the needle vibrates.
Allow the tight of a lamp to fall upon the bead when still
we have a sinall spot on the screen intensely iMuminated
now caiise the needle to vibrate, and the spot will be drawn
out into a brilliant line which will change into a circle; and
thas the character of the v
ations is shown.
250. Koenig's Mangmetric Flames. — Other ingenious
instruments have been constructed for illustrating the oytheal
method. The apparatus of Korxio transmits Une movements
200 ACOUSTICS.
of the sound-waves to gas-flames, and these, by their pulsa-
tions, show the nature of the sound,
We have, in Fig. 172, a metal eapsnle, A, in scetion. ‘This ix
vided into two compartments by a mombrane of gold-benter's akin
‘or thin rbber. Tmmediutely below the section, A, is seen the eap-
sule supported on a stand; on tho right ts the gas-jet, below it the
tnbe for conveying the gas jo the compartinent at the right of the
membrane; on tho left is the tube for the sound-waves to reach
the membrane. To this may be attached a rabber tube, whieh ean
terminate in a mouth-picee or be connected with am orgun-pipe.
When the sound-waves enter the mouth-picee and nibe, the thin
metnbrane is set vibrating. Tho gas, while passing through the
ut at the left, is caused to vibrate In a corresponding way,
If is ehalcen wp and down,
in the length of tho flame are scarcely jrereeptible
corved direetly. Hat to ale them distinetly vEiible
M, with four faces. ‘This is made
tore ndlo,
While the lame burus steadily there appears in the titrror, when
turned, a contin 1. But if the fundamental sete te
in the tube on the left of the capsule, the Image of the fame
whon it ie <
they may be received on & miere
by ineans of two eog-whools and ah
&
MUSICAL INSTRUMENTS. 201
tukos the form represented in Pig. 173 If the octave be sounded,
the image of the flame takes the form seen in Pig. 174.
Many varieties of forms onn be prodaced when several svands of
different intensitios enter the tube simultancously.
‘hese Hames just described are called manometric flames, The
succession of sepanite images of the flames, which we see on tumn-
ing the mirror, ie die to the fact that the image of an object
remains on the retina for a litth: time after tho object itself has
Fig. U4
251. Stringed Instruments. — All stringed instruments
of music are constructed in accordance with the preceding
laws. They are divided into instruments with fixed eounds,
and instratnents with enviable sounds.
'To the former class belong the piano, the harp, ete. They
have @ cord for each pote, or clee an arrangement is made
g0 that by placing the finger at certain points, as in the
guitar, the same cord may be made to render sev
in succession.
‘To thie latter class belong the violin, the violoncello, ete.
‘Thay are provided with cords of catgut, or sometimes of
total, pat in vilrstion by « how. Various arcangemends
ul notes
a
202 ACOUSTICS,
are made for regulating the notes, such as Increasing the
tension, placing the finger upon tho cords, and the like.
These instruments are difficult to play upon, and require
great nicety of car, but in the hands of skilful players they
possess great power. They are the soul of the orchestra,
and it is for them that the finest pieces of music have been
composed.
252. Sound from Pipes.— When the air in a pipe, of
hollow tube, és put into vibration, it yields
case it is the air which is the sonorous Lge
the sound dopending upon the form of the pipe and the
manner in which the vibrations of its contained alr are pro-
duced.
‘To produce a sound frou a pipe, the eontalied ale mest thrown
into a sneccagion of rapid eondonsations and rarefactions, which is
effected by introducing a current of air throagh « suitable mouth
piece, “Two principal forme aro given to thé mGath) a
which the parts main fixed, and in the other there
vingne, ealled a reed.
253- Pipes with fixed Mouth-pieces. — Pipes with
fixed mouth-pieces are of wood or metal, rectangular or
cylindrical, und always of considerable length compared with
their cross section. To this class belong the flute, the ongam
pipe, and the like, Some of the forms given to pipes of thik
class are shown in Figs. 175-179.
Fig. 175 represents a rectangular pipe of wood) amdiEien 126
shows the form of ite longitudinal seetion, JP represents the tube
through which air is forced inte it, ‘The alr passes through @ tar
row opening, i, called the vent. Opposite the vent is an epering in
the side of the pipe, called the month. The upper border, a, of the
mouth is bevelled, anil is called the upper tip; the lower booder te
not hevelled, and is called the lower lip.
The current of air forced through the vent strikes agaiest the
upper Lip, is compressed, aud by its cluticity, rewets apee the enter
Jog current, and for an instant arcosts it. This stoppage be naly far
—_ —
MUSICAL INSTRUMENTS. 203
nt Instant, for the compressed air fads an outlet through the mouth,
again permitting tho flow. No souer has the flow commenced
than it is « seooud time arrested as before, again to be resumed,
and s0 08.
‘This continand arreat and release of the current gives Hiso to a
suevession of vibrations, which are propagited through the tbe,
causing alternate and rapid condensations und rurefactions, which
P
Fig 176 Fig 116) Fig. 177. Fig ATK Hg. 179.
Forelt ins contluious sand, ‘The vibrations are the moro rapld 8
ube catrent introdinsed Is etronger, and ae the upper lip approaches
‘pearer the went.
This is but a odifcation
‘The letters indicate the saue
204 “ACOUSTICS.
An open organ-pipe yields a note an octave higher thas that ofa
closed pipe of the sune length. When & ‘ongati-pipe sounds
te fundamental uote, the column of air is undivided by auy node; but
the closed end will always be a node, because the air partielow at that
fart are necessarily at rest. Wheo on open pipe sounds its fenda-
mental note, the columa is divided by a node at ite centre, ‘The
open pipe really consists of two stopped pépes with « common base.
‘The existence of nodes and vibrating segments within a ome
pipe snay be shown by lowering into the pipe a
strotehed over n frame, with some fine, ary exnd
surface. The front of the pipe is of glass, 0 that
body in it. When the saad is in segment it will
when it a node it will remain at roat.
If 4 node ts connected with Koxsta’s capsule, #
violently ugitated than wheo a sogtnent ia jelned.
the continual change in the density of the alr tal
node, while at o segment the density is notmensibly
the wir fs in a state of vibration,
Fig. 179 repreacuts the form of the mouth-piece
and ft will be b
already explained. In the flute, an opening fx m
the pipe, which changes the Tength of the segments:
of air that are vibrating, and thas determines the
‘The arrest and tlow of the curmnt are effected ‘by the
of the lipe of the plager.
asq. Reed Pipes. —In Rren Press the mouth
provided with a vibrating tongue, called a reed, by me
which the air is pot in vibration, ‘To this class bel g
clarinet, the hautboy, and the like, ‘The need may be so
arranged as to beat against the sides of the opening, or it
may play freely through the opening in the tubes
Figs. 180 and 181 show the arrangement of a reed of the first kind.
A piece of enetal, a, shaped like a spoon, is fitted with an elastie
tongue, 4 which can completely close the opening, A pisee of
metal, r, which may be elevated or depressed by a tod, }, sere
to Jengthen or shorten tho vibrating part of the reed. ‘This axmitugy-
ment enables us to diminish or increase the rapidity of yilmtion at
pleasure,
——
MUSICAL INSTRUMENTS, 205
‘The mouth-piece, as deveribed, connects with the tube, 1, and is
set in a reetaagular box, AN, which is in communication with a
bellows, from whieh the rind is supplied. For the purpose of class
demonstention, the upper part of the tube, AN, has glass windows
‘ui three sides to, show the motion of tho reed.
‘When a current of air is forced inte the tube, KN, the reed ix set
in rapid vibration, causing a succession of rarcfactious and conden-
ty
‘Fig. 180. Fig. 181. Pig. 182.
sations fn the airof the pipe, 7, and eausiag it to emit a soun
air entering the tube, KN, first closes the opening by prossing se
reed Wt; the read then rocolls by virtue of its elssticlty, per-
c ‘of condensed air to enter the pipe, when the reed
is . the opening, and so ot: us long as tho current
of alt bs Te bs evident that tho rxpidity of vibration will be
pelo ichpcte ile the ténsion of the alr from the bellows, aud
the vibrating part of the reed,
206 ACOUSTICS.
Fig. 182 shows tho arrangement of the free reed: ‘The vibrating
plate, 1, ia placed so ae to pass Lackwands through an opening fu Uhe
side of the tube, ea, alternately closing ani opening a eommunieation
hetween the tube and the air from the bellows ‘The regulator, ry is
entirely similar to that shown in Figs. 190and 181) as ang the remains
ing parts of the arrangement. ‘The explanation of the wetion of thie
species of reed is entirely sisilar ta that alrwadty deseribed.
255. Wind Instruments.
—Winxp Lssrrusexts of music
consist of pipes, either straight
or curved, which dre made to
sound by & current of air prop-
erly directed,
Wig. 185,
In some, the current of air is
directed by the mouth upon an
opening made in the side, 28 in
the flute. In others, the current
of nir is made to enter through &
mouth-plece, as im the flagoolet.
In others, a reed is axed, as in
the clarinet. In the organ there
is a collection of tubes, similar to
these shown in Figs. 175 and
177. In some instruments, a
the trumpet and the hora, a
conical mouth-piece is used, of
the form shown in Fig. 153,
within whieh the ips of tle amu
sician vibrate in place of the
rapidity of vibration
can be regulated at with.
256. Sounding Flames. —
Whe s-flame fs enclosed in
a tube, open at both emds, the
passage of the air over it is gen-
crally sufficient to produce the
reed.
THE HUMAN VOICE. 207
neeeesary thythmiec netion, and to cause it to give out a
sousi¢al tone, Fig. 194 represents auch a tube firmly held in
position by clamps, which are fastened by screws to a stand.
By means of the paper slider, s, the tube may be lengthened or
shortened. While the flame is sounding, raiso the elider, and the
By pounding tho rame note with the voice or any mosical inst
wera, the singing of the dame inay bo iuterrupted, of eaused to cease
eatirely ; of, when sileat, to begin guia,
257. Sensitive Flames. — Flames are affected by sound-
waves from musical tones even when not cucloaed in tabes,
‘The action of musical sounds upon such flames is shown by
the vibrations of the yuslights in unison with certain pul-
sations of the music at some instrumental concert. This
phenomenon does not take place unless the pressure of gus is
safticiently great to keep the flames on the verge of tlaring.
A long flame mag ba shortened and a short one lengthened by
sonorous vibrations, we have a Jong smoky flane and a
abort, forked, and ‘one, both om the point of flarings and
roth insaing tom « vory small orifice, lke a pin-hole in a tube,
On sounding u whistle, their sensitivencss to tho sound vibrations
is at once apparent, The long flame becomes short, forked, aud
Ueilliant; andthe forked, long and smoky. A flare may bo short-
goed half ite length by striking two pieces of wood or iru together.
as8. The Human Voice.— The most perfect reed in
strument & the haman voice. Across the top of the trachen,
or windpipe, are stretched two elastic bands, called voew!
chords; through the space between the chords the air passes
in anil out of the lungs.
and singing the space betwoon tho ehords is lee
than in ordismey breathing. The voice & produced by the air,
whieh, driven from the Inugs and striking agwins: the chords, eauses
‘them to silirate, “The greiter the tension uf the chords the higher
the piteh.
‘The month, by ite resonance, reinforces tho soand given out by
the vibrating chenla By changing iv shape i can We wade vo
—_
208 ACOUSTICS.
resound to the fandamental tone, or any of the overtones of the voeal
chords.
259. The Human Ear. — A section of the ear is seen
in Fig. 185. It consists of the external ear, so formed as to
enable it to catch the sound-waves. # represents the audilary
canal, about an inch in length, A circular membrane, called
the membrane of the tympanum, closes the lower end of it.
‘The drum of the ear, or the tympanum, is the envity bebied this
membrane, Beyond the drum is the labyrinth, Tt consists of «
Fig. 185,
small rounded chamber, A, called the cevtibule; from it epem three
semicireular canals, D, wud a spiral canal, 2, called the cochlea, frean
its resemblance to a sunil-shell,
‘Through these cunals the axditory nerve is distributed. From the
membrane of tho tympanuin to the membrana of the vestibule «
chain of three bones is stretched, the hamuner attached te the mem~
Urano of tho tympanum, the anvil, and the stirrup conneeted with
the membrane of the vestibule, ‘The vibrations of the wtuiosphere
siriko against the membrane of the tympanum, and are eondueted
through the chain of bones to the second membrane, snd thence, by
the auditory nerve, to the brain, The Luslachian tube, G, admits
air to ihe drum, and thas keeps tho density within the same as the
exterwal as.
THE PHONOGRAPH. 209
a6o. The Phonograph. —The Phonograph is an in-
strument, devised by Epteon, to register sound-yibrations
and to reprodace ther at any time when desired.
It consists (Fig. 136) of a simple, small-sized iron cylinder, C,
snoguted upon a shaft, at ove end of which is a crank, M, for tuning
it, the whole being supported by two iron upright Tn feont of this
cylinder isa movable arm tbat supports a mouth-piece, Ey of gatta-
percha, on the uoder side of which is 1 disk of thin, elastic metal.
Against tke ceatre of the lower side of this disk, a fine steel point,
roanded at the end, is held by a spring attached to the rim of the
southepicce, Au lbdia-rabber cushion between the point and disk
contruls the vibnations of the «pring.
"The cylinder is covered with a fine spiral groove ronning con=
Mienously from enil to end, the threads being about jy of an inch
apart Th works on & screw, A A’, the thread of whieh is the same
Fig. 186.
as that on tho eylinder. Jt iv turnod by the’ handle, M, the motion
boieg mgulated by a heavy tly-whoel, The position of ath
ploce snd ite promure uguiust the tinfoil are adjusted by the arrange-
went, Lom,
Th using the phonograph, a sheet of tinfoil is wrapped
closely around the cylinder. ‘The mouth-piece is then ad-
Justed against the left-hand ond of the cylinder so closely,
that when one speaks or kings into the mouth-piece, and at
the same time turns the crank with a uniform motion, the
disk is made to vibrate, and the stecl point presses upon the
tinfoil in the groove, leaving upon ita scries of minute in-
dentations.
In order to reproduce the words, the cylinder is turned
buck 80 that the steel point may go over the indentations
made by speaking into the mouth-plece.
a
210 ACOUSTICS.
‘On turning the crank again, the point is made to work slong the
indentations in the groove. This sata the disk vibrating, aud the
vibrations, being communicated to the ear, rhproduee the sound,
‘A founol is generally inserted into the mouth-picoe, to be wsed as
au ear-pleee wheu the sound is being reprodaced.
Speech which has been recorded on the tinfuil may be kept for au
indefinite period.
261. Energy of Sound Vibrations.—In order to make
a body rate forve must be applied to it. It then exhibits
energy of motion, or kinetic energy, and this energy is trans-
mitted to other bodies in its vicinity.
Ho bow be drawn arose the wine of the Senometer, the Force
causes it lv vibrate with au enengy whieh is propor
square of the amplitude of the vibrations,
‘Tho vibrating body will come to rest when all its energy has beew
iunparted to the surrounding bodies. ‘This condaction varies accord
ing to the nature of the substance in contast with it; some Daies
conveying away the onorgy much quicker than others.
Ifa tuaiug-fork is set vibrating, and the stem rested on 4 table,
it will not vibrate so long as it would if the stem had bees beld
between the thumb and finger.
Summary. —
Opticad Study of Sound,
Lissajous! Repeosontation of Vibrations:
Experiments with Taning-Pork,
Vibratory Motions at Right Angles
Lissajous’ Figures produced by Pendolim,
Kaleidophona,
Description of Koenig's Apparstas,
1 of Operation.
Musical Instruments.
Stringed Tustruments
Sound from Pipes,
Pipes with Fixed Mouth-pieoes.
Rood Ptpes
Wind Tustraments.
Sirending Flames,
MMARY. 21
Sensitive Flames.
The Human
The Human Ear.
The Phonograph.
Description,
Mode of Operation
Energy of Sound Vibrations.
HAPTER VIL
HEAT.
SRCTION 1. —- GENERAL PROVNITIS OF SURAT,
262. Definition of Heat. — Heat is the physical
agent that produces the sensation we call warmth; the
term /eat is also applied to the sensation itself.
263. Nature of Heat.— We can regurd heat as meleeu-
Jar energy of motion, or molecular kinetic energy. “This motion
consists of very rapid vibrations, or oscillations, of the mole-
cules of substance. ‘Those bodies are hottest whose mole-
cules vibrate with the greatest velocity and throagh the
greatest amplitades
Tho torm cold is used us a conveniont torm to express dlimintion
of heat, Wut not the entire absence of i, for no substance is supposed
to be wl levoid of heat, and henes the moleenles of dvery beady
il to be in continos) motion at all times and under all
ane presuu
ciroumstanc
‘This energy of motion may be transmitted from owe body te am
her through an elastic medium callat ether, that pervades all
matter and infinite epace, in the same way that sound is tramsmitted
ns of waves.
au pass from one bedy to another or be
for any thine, is a measurable quantity.
rt
thre
Heat, then, since it
the alr, that Is, by
a be
The emisecon, or calori
Haid destino of
y supposes it to be a smbedamer,
apable of passing from one body te another
particles repel one another, and -thergtore
ce of cohesion. The entrance of this sb-
10 our bodies prodeces the eeusition of warmth; ie Gere,
the semsatine uf eld
with great velocity
oppose the attraetive f
EXPANSION OF BODIES. 218
‘This theary ia now generally discaried in favor of the one already
given, which is called the undulatory, or wace theory. Tho lattor
atfueds a Letter explanation of the phenomena of heat, and at the
same time serves to ahow the intimute relation betwoen hoat und
ight.
We shall also e8e, further on, that heat may be transformed ints
something which is not a substanen af all, vaanely, mechanical work.
264. General Effects of Heat. —Heat may act on a
body in three ways. One portion may be expended in pro-
mating the warmth of the body, that Ix, by increasing the
energy of motion of the vibrating molecules. A second
portion acts as a repellent power, counteracting the force of
eobesion and enlarging the amplitude of the molecular vibra-
tions. "This latter action causes an increase in the volume of
the body, or completely alters the relative position of the
molecules and produces a change of state; as when a solid
is changed into a liquid, or a solid or liquid into a gus or
‘These two effects may be classed under the head of internal
swork.
‘The third portion is required to overcome the external
pressure of the atmosphere, which must be forced back so
that the body may expand.
‘This may be called external work.
When the body cools, the force of cohesion which was over-
come by the repellent force of the heat, now reasserts its
power and draws together the molecules; Hence we say that
heat expands bodies. and cold cvatracts them.
265. Expansion of Bodics by Heat.— All bodies are
seins but in very different dogroes. As a gen-
eral rule, the most expansible bodies an: gases, then liquids,
and lastly solids.
which have definite flyures, we have three kinds of
at Ainear expansion, that is, expansion ia lengths ewper-
or expansion in two dimensions; cubical, on wdbawa
a
ab
214 HEAT.
expansion, that is, expansion in three dimensions. Aan matter of
fact, however, no ono of these takes place without the other, As
liquids and gases have no definite forms, expansion of volumes i
alone applicable to them.
266. Expansion of Metals.— Fig. 187 rpreseuts the
method of showing and measuring the Linear expansion Of the metals
by moans of an instrument called the pyrometer. A rod of metal, A,
pases through two metallic supperts, being made fast wt ome extret
ity hy a clunp-sorew, 7%, and being free 16 expand at the other ex-
tremity, The freo cud abuts against the short ond, ©, of a lever,
the long end, 0, of which plays in front ofa graduared are.
Fig. 187,
When the rod is heated, by placing firo beneath Ht, as shown im
the figure, the rod, A, expands, and the expansion iy shown by the
motion of tho index, D. When tho rod, A, is of stecl, copper, silver,
ets,, tho amonnt of expansion varios, as ix shown by the different
its of displacement of the index. Brass, for example, @xpainite
inore, for the sane atnonpt of heat, than iron a ateel,
Fig, tho method of demonstrating that bodies mnderge
an expansion in volume when heated. A ring, A, i comstracted
so that a ball, B, passes freely through it when eld. Tf the ball be
heated Jn a furnace, it will no longer uss through the wings; bat if
hows
a
EXPANSION OF LIQUIDS AND GASES, 215
allowed to eval, it again fulle through the ring, ‘The mothod of
raking the experiment is fully shown ia the figure.
267. Unequal Expansion of Metals. — In Fig. 180
we have shown a simple cvuteivance for illustrating the unequal ex~
pansion of ditlerent metals. Two bars of iron and brass are riveted
(ogether at different points along their whole Jength, forning one
compound bar.
Fig. 158.
When such a bar is heated, the brass expands more than the irou,
and the bar carves, as represented in Fig, 189, in order to accom:
inodate the inequality of length which thas results, When the bar
has retorned to its original ternperatary, it assumes tts rectilinear
form, to bend again fu the opposite direction if it be afterwards sube
jected to coating. The unequal expansion of different metals is also
shown in the compensation pendulums, pages 5¢, 59.
a —
Fig. 189.
268. Expansion of Liquids and Gases. — Liquids ani
gases being more expansible than silids, their expansion ie
easily shown Wy experiment. For liquids, wo tako a bollow glass
ephere, terminating fo a narrow tobe, open at the top, and fill the
globe and & portion of the stem with somo fluid Uke morury, a
shown in Fig. 190, If beat be appliod to the globe, the Tiquid will
ice tn the stem from a tomunts 6, indicating on increnee of volames
and If sufficient heat be applied, the liquid will flL the Hem, awd
—
216 HEAT.
will ultimately bo couverted into yepor. If the liquid is allowed
to wol, it again returns to its original
volume,
An analogous experinent shows the
expansion of gases and vapoen. A
bulb of glass is provided with a long
and fine tube of the same suaterial,
which is beut twice pow itself, ms
shown in Fig. 191. Am index of inar-
cury is introduced into the steux in abo
following manner. ‘Tho bulb is heated,
aud a portion of the alr which | com-
tains is driven out, when a drop of
mereury is poured into the fimnel, «
If tho instentnant is allowed to eool, the
air in the bulb contracts, aod the pres-
sure of the atmospher drives the drop
of mercury along the tbe to some
position, m.
‘The instrument having beea pre
pared in this manner, if the bully is heb
in the hand for a few minutos, the ale
Tocomes brated and expands, the ex-
pansion being indicated by the index
moving to some new position, aan Tf
Wig. 190. Fig. 191. allowed to cool, the tide returns Um,
Summary. —
Definition of Heat.
Nature of Heat.
The Undulatory, or Wave Theory of Hoat,
The Emission, or Calorie Theory of Heat.
General Effects of Heat.
Interal Work.
raal Work
ds Bodies.
Cold contracts Bodies.
mn Of Bodies ty Heat.
Expansion of Metals.
eee |
THE THERMOMETER. 217
Expansion of Boilies by Heat (continued).
Experiments,
‘Tneyual Expansion of Metals.
Expansion of Liquids and Gabor,
Experinents.
SOCTION It. — TEMPERATURE. — THK THERMOMETER,
a6g. Temperature. — The temperutyre of a body is that
property that gives it the power, to a greater or less extent,
of imparting sensible heat to other bodies.
By the terea sensible heat is meant that portion of beat that in-
creases the warmth of the body.
Wha one boly gives off sensible heat to another, the former is
said to have a higher temperature than the latter, or to be warmer.
The temperature of a body rust not be confounded with the quan-
tity of Thewt it possesses; a body may have a high temperature and
yet have « very swall quantity of heat, a low temperature and a
Tange amount of heat. Quantity of heat will be treated of under the
subject of Specific Heat.
ajo. The Thermometer. — A ‘Taermooeren is an in-
strument for wessuring temperatures,
‘Oar bodily sensations cannot serve as a sure guide in
meeasaring temperature. A body may seem hot and cold to
the same person at the same time. If we place one hand
into pulverized ice and the other into water at about 100° F.,
amd, after allowing them to stay awhile in this position,
plunge them simultaneously into water at 70°, the hand from
the foe will feel warm, but the one from the hot water will
experience a sensation of cold.
We must have a more accurate and constant standard of
reference, and this ie found in the thormometer.
‘The thermometer epoois upou the principle that bodies expand
when heated, and contract when cooled. Thermometers have been
constructed of groat variety of materiale, For coramaon parpoes,
Ma
218 HEAT,
the merourial thermometer is preferred, on account of the enifurnity
with which both mercury and glass expand when heated.
Tt consists of a bulb of glase, at the upper extremity of which
is a narrow tube of uniform bore, hermetically sealed at ite epper
ood. ‘The balb aud a part of the ube are filled with mercury, mad
tho whole is mttnched to a frume on whieh is a seale fur necusering
the #ise and fall of the meroury in tho tubs-
271. Method of making a Thermome-
ter.—A capillary tube of glass is provided, of
uniform bore, upon one end of which a bath bs
Llowo, and upon the other a fusuel, as shown io
Fig. 19%.
1" anel is nearly Glled with mereary, which te
at first prevented from penetrating inte the bulb by
the resistance of tho air and the smallness of the
tube. ‘The bulb is therefore heated, whan the als
within expands, and » portion eseapes in bubbles
through the mervary. On cooling, the pressure of
the external ntinusphore forees a quantity of merenry
through the tute into the bul By rupeating this
ution a fow times, the Wulb aud a portion of the
tube are filled with meremry.
‘The whole iy thea heated will the mereury baila,
thurs filling the tube, when the funnel is melted off
and the tabe hermetically sealed by means of a jet af
fhune unzed by blow-pipe. On eooling, the mer
cury deecunds to scroe polut uf the the, at shows fa
Pig. 1M, Teaving o vacuum ot the opper end. Te
ouly remains to gneluate i, aud attach a suitable
scale.
Figs 192,
272. Method of Graduation. — Two petwis of the stem
arv first determined, the freesing and the bailing paints. “Thee ane
doternined on the principlo that the teanporstimros st which distilled
fet freezes aml boils ary always constant, that ix, whet these
changes of state take placw onder eqeal atiaoephoris preeemanes
The lustrument i+ fire plunged into a bath of sneliing Jom, ae
chown in Pig. LM, and ie allowed to recnain wutil it takes the ten
THE THERMOMETER. 219
peniture of the mixture, say twenty or thirty minutes. A alight
seratel i then madi on tho stem at tho upper surface of the mer-
‘cary, stal this constitutes the freesing-point.
‘The instrament is noxt plunged into a buth of distilled water, in
8 wiate of ebullition, eure belng taken to surround is with steam by
Fie 104. Fig. 196.
smeaus of iim apparatus like that shown in Fiz. 195. After the mers
eury cease to riso in the tube, which will be in a fow minutes, the
Teval of is sipper sarfice [5 marked on the stem by a seratel, as
before, and this constitutes the boiling-potnt.
Whe space between the boiling and freeding points Ws Yen Bev,
=
220 HEAT.
into a certain number of equal parts, and the graduation is continued
above und below as far as may be desired. "These divisions may be
scratched upon the glass with a diamond, or, as is usually done,
they may be made on a strip of metal, which ie attached to the
fraine, ‘The divisions arw auimbered according to the kind of seale
adopted.
273. Thermometric Scales. —Three principal scales
are used: the Centigrade scale, in which the space between
the freezing and boiling points is divided
into 100 equal parts, called degrees ; Réas~
mur's scale, in which the same space is divided
into SO equal parte, called degrees ; and Fiah-
A a
.
4
renheit’'s scale, in which this space is divkted
into 180 eqnal parts, also called degrees.
In the centigrade scale, the freezing-
point is marked 0, and the degrees are
numbered both up and down, the former
numbers being considered positive, and
designated by the sign +, whilat the Entter
are considered negative, and designated by
the sign —. Of course the boiling point is
marked 100°.
‘Tho sigus ++ ond — are used also in Réfau-
mur’ and Kahrunhoit’s thermometers to indiexto
ogres respectively ubove and below the aero
point.
In Réanmur’s scale, the freezing-point is
marked 0, and the boiling-point 80°. The
s below freezing are marked as fa the
To Fabrenkeit's scale, which is the ome
principally used in the United States, the
zoro point is taken 32° below the freezing-
3 > point, and the divisions are numbered irom
Fig. 18, this point both up and down, The boiling-
point of distilled wator is 212°,
— a
THE THERMOMETER. 221
Fig: 196 represents the thermometric sales, with the freezing
and boiling points Indieatad upon them.
Tt is sual, io stating temperatures, to indicate the seale referred
to by tho initial letter F., C.,
274. Conversion of Centigrade and Réaumur's De-
grees into Fahrenhcit’s. —A degree on the centigrade seule
fs equal to ove and eight twnths of w degree on the Fahrenbeit scale,
and one on Résurnur’s seale is equal to two and a quarter on Fahron=
heit's, Henes, to convert tho roading on a centigrade to an equiva-
Jest ove on Pahrenheit's scale, multiply it by 18 and add to the
result 32°. “I'hus, a reading of 25° contigrade Is equivalent to 25°
13-42%, or 77° F. To convert a reading on Réaumur’s scale to
an oyaivalent one on Fahrwabeit's, multiply by 24, and to the result
wht 22°, ‘Thos, a reading of 24° Réanmar is equivalent w 21° x
2} + B?, or 80° FL
By reversing tho above proceeaos, readings on Fabronheit’s scale
may be converted into equivalent ones on tho centigrade or Réxu-
mnur'e seal.
‘The rofes for the conversion of the throe thermometrie scales may
bo smmmed up in the following formule, in which F, C, and RB
denote equivalent temperstures expressed in degrees of the three
wealos: —
F=jC+W=yR4R «@
c= =i) @)
= —®) @)
a7s. Alcohol Thermometers. — An Atconon Tuxr-
moateret is similar to a mercurial one in all respects, except
that alcohol, tinged red, is uscd in place of the mercury.
Because aleobol docs wot expand regularly with « regular increase
‘of temperature, the wleohol thermometer has tw be graduated by
‘experiment, comparing it degree by dogree with a standard mercurial
therniometer. The degrees, in fict, inernase in Jongth we we mseend
ou the seale.
Ab aleolal therinometer is more easily filled than a mereurial ome,
required. The bulb is heated mntil a portion of the
‘contain’ air is dkiven off, and then the open end of the tube by
longed fhto « vere! of alcohol. Ax the wie'in the Wills coda, Yaw
=
222 HEAT.
pressure of thy external atmosphore forces @ portion of aleobell mp
into the bulb. Af this be boiled, the wapor of aleohol will expel the
remainder of the air, and by dipping the opeu end of the tube laste
the aloohol once more, the bulb will be completely filled, when it
‘agnin becowes cool, ‘The instrument is then treated like the merou~
rial thermometer,
a76. Relative Advantages of Mercurial and Al-
cohol Thermometers. — For ordinary purpows, the merearisl
thermumeter is to be preferred, on account of the uniformity with
whioh the mercury expands with a uniform inerosse of temperatura,
But mercury conseals at 39° below O of the Fabrenhelt scale, and
where a lower temperature than this is to be observed, it becomes
absolntely necessary to cmploy the spirit thermometer. In the
severe cold of the polar regions, mereury ofum congeals, bat no
degree of cold has yet boon obtained that will congeal absolute
alcohol.
For high temporatures, moreury only is capable of being ased :
thie liquid does not boit 1} raised to G62" F., whilst aleohol boils at
174° F, ‘The latier liqeid cannot therefore be used to observe
temperatures higher than 174° F., nor ean it be relied upon even for
temperatures considerably lower than this.
It is to bo observed that mercury cannot be relied upon for teen
poratures Jower than 82° below 0, on account of irregularities fu its
rate of contraction below that limit.
Aloohol has also the disadvantage of being slower in its action
than mereury, on necount of its inferior conducting power:
277- Rules for using a Thermometer. — Before not-
ing the height of the mercarial column, the instrument should
bo allowed to acquire the tomporature of the medinm in which
it is placed. ‘This, in general, will roquire some minutes.
In determining tho tetperatnre of a room, the thermometer
should not be bong against the walls, but should be fiwely: sume
uc of the atmesphers. When
hang against a wall, especially an outer wall, au errur of several do=
greca may rewult. Tn leo mutiner, if hung agaiuet a wall containing
temperature, a similar
a Hee, or adjoining another room of dliffere
error of several dogrees imlght result
=, - |
THR THERMOMETER. 228
‘To determine the temperatare of the atmosphere, the thermomo-
ter should be frecly susponded in the nir, nt some distance from any
building or tem, It should be sheltered fron the dirvet action of the
sun's rays, ax well as from tho influence of rvflecting substances.
Purthermore, it should be protected from winds and currents of
als.
278. The Differential Thermometers.— A Dirren-
SNTIAL Tuxrmoaeren is a thormometer contrived to show
Fig. 197.
the difference of tomperntare between two places near each
other. The two principal forms of the differential thermome-
ter are Ruwvonp’s and Lescrr’s.
"They are Basel on the expansion of air, and are, therefory, etr
thermometers. ‘These instruments are not affeetnd by the varying
presume of the ntmorphere, ae many alr thermometers, and wre, eou~
souontly, Toss innecurate.
279. Rumiord’s Differential Thermometer. — Row-
Forp's Dirvenxxriat. Toxnxomerce is represented in Fig.
197,
=
oa HEAT.
Tt consists of two bulbs of thin glass, A and 2, connected
by a fine tube bent twice at right angles, as shown in the
figure. The whole apparatus is attached to suitable frame,
which supports a scale parallel to the horizontal branch of
the connecting tube. The 0 of the seale is at its middle
point, and the graduation is continued from it in both direo-
tions. The bulbs and a lange part of the connecting tabe are
filled with air; there is, however, in the tube a small drop of
fluid which separates the air in the two extremities.
‘The instrument iy 90 constructed that the index mis at the 0 of
the seale whon the temperature of the two bulbs is the samo. When
one of the bulbs is heated more than the other, the alr in it expands
and drives the index towards the other, until the tensions of the air
in the two bulbs exactly balance each other.
‘The scale ts divided by experiment by the aid of a standard mer-
curial thermometer. s
280. Leslie's Differential Ther-
mometer. — Lrstan’s Dirrenenrian
‘Tuermomeren is shown in Fig. 198,
It differs from Rowvoro’s in having
the bulbs smaller, and in containing =
longer column of liquid in the tube.
‘The scales are placed by the sides of
the vertical portions of the tube, har=
ing their 0 points at the middle
‘There is, then, a double scale, Tho
method of graduating and using thia
thermometer is the same as that de-
scribed in the last article,
But of all instruments for detecting: amd
measuring slight differences of tempera:
ig t08. ture, the most delicate and acourate is the
thermo-eleetric pile, which will bo dosertbed hereafter.
261. Pyrometer. —A Prnowernr is an instrament for
meaassiring higher temperatures than can be observed hy
means of the mercurial thermometer.
P
a —
ABSOLUTE ZERO OF TEMPERATURE. 225
‘The niost important pyrometers are those of Wencrwoop
and Broostarr. The former is founded on the diminution
of the volume of clay at high temperatures, and the latter
(Fig. 187) on the principle of the expansion of metals. ‘Tho
indications of these instruments are very untrustworthy, and
they have gone substantially out of use.
‘The arrangements now used for measuring the higher tempera
tures are based on the expansion of guses and vapors, or on tho
electrical properties of bodies.
82. Absolute Zero of Temperature. — Since a gas
expands for each degree centigrade 9}, of its volume at 0°,
it follows that at a temperature of 273°C. its volume is
doubled, and that the amount of contraction when the tem-
perature is reduced to — 278’ would be equal to the fnitial
volume. The gas then would be redaced to 2 mathematical
point, and would cease to exist.
‘This point ou the centigrade sealo is enlled tho absolute zero af
femperatere, sud temperatures reckoned from this point are called
absolute temperatures. "The lowest temperature that ean thus bo
exprrsed is evidently — 273° C. or— 460" F, We can obtain
absolute toinperatares by ating 273 1 tho temperature on the
centigrade reale, or 400 to that on the Fahrenheit.
An abéclote zero of bent hus never yot been realized experimen~
tally. Evon if matter can exist without heat, whleh there is great
reason to doubt, it ix impossible to predict whut would he its eondi>
ton ander such circumstances.
Tf the enorgy of motion, which wo call heat, should wholly come
g ite power, and the molecules be brought into actual contact,
phenomena of # new nnd nnoxpectod charneter would undoubtedly
{Phe greatest artificial cold prodteod up to the present time ix
WP C, or — 220° F. Tho greatest natural cold recorded in
Arctic expeditions is — $8.7° C., or —73.06° F.
ahd
226 HEAT,
Summary. —
Temperature of Bodies,
Definition of the Term Temperatwre,
Definition of Seasible Hear.
Distinction betweeu Tompemtare and Quantity of Hest,
The Thermometer.
Dofinition of a Thermometer.
Untrustworthy Results of Bodily Sensations.
Principle apon whieh it depends,
Method of making @ Mercurial Thermometer.
Mothod of graduating a Moreurial ‘hermomoter.
Thermometric Seales.
Centigrade,
Reésmour,
Fahrenheit.
Conversion of ove Seale into Another:
Alcohol Thermometers.
Relative Advantages of Mercurial and Alcohol Ther-
momotere
Rules for using a Thermometer,
Differential Thermometers.
Rumford's.
Lealie’s
Absolute Zero of Temperatures
SECTION 111, — LAWS OF EXPANSION OF SOLIDS, LQUING, AND
Gases,
283. Law of Expansion of Solids. — Numerous ex-
periments have been made to determine the exact amount of
expansion whi addition of a given
amount of heat. As in a former article, it will be found éon-
venient to consider, first, dinear expansion, and afterwants,
expansion in colume
h bodies experienoe by th
1, Linear Expansion. —In order to compare the rate of
1 expansion of different bodies, we take, for a term of
comparison, the expansion experienced by a unit of length
<<“ 4
EXPANSION. 237
of cach body when heated from 32° F. to 88° F. This is
callod the coefficient of linear expanvion,
‘The coefficients of linear expansion for a great number of
bodies were determined in the latter part of the last century
by Lavowtex and Lartace. They roduced the substance
to be experimented upon to the form of a rod or bar, then
exposed it for a sulllcient tine to the temperature of melting
ice, and measured its exact length. They next exposed the
bar to a temperatare of boiling water, and again measured
its length. The increased length, divided hy 180, gave the
increase in length of the whole bar for 1° F, ‘This result,
divided by the length of the bar at 32° F., gave the lincar
expansion of a unit of longth, and for an increase of tempora-
tare of 1° F., that is, the coepficient of linear expansion.
‘The following are yome of the latest results; —
From the above table, it is seen that the amount of expan-
sion is always very small,
2. Expansion in Volume. — Tho coefficient of expansion in
volume is the increment which a cubic unit of the subsiance
experiences when its temperature is raised 1° F. This
‘vefiiciont may be determined experimentally, or it may be
foand by multiplying the coeficient of linear expansion by
three. The superficial expansion of « solid is, of course,
‘twice as great as tho linear expansion.
284. Applications.— The principle of expansion explains
many familiar phenomena, rome of which wo will give.
A cold tambler is often broken when {1 ke snideuby ted wit wor
i
228 HBAT.
water. ‘Tho oxplanation is simple. Glass i a bad conduntor of
heat, hence the inside becomes heated by contact with the water
moro mipidly than the outaide, and this inequality of heatiog produces
an inequality of cxpausion that ruptures the glass. ‘The thinner the
glass, tho less will he the inequality of expansion, and consequently
the less will be the dauger of rupture, Iu a metallic vessel euch am
accident is not to be apprehended, becanes metals ar good eondve-
tors, and bat litte, ifany, inequality of expansion cau arise.
When a candle is held too oar a pauo of glass, the gles i
often broken ; the reasou is the sume as before. Sometines « glasw
vessel is broken by suddenly opening a door or window. "This
is due w a cugrent of cold air, which, falling upom the owter
surface of the glum, causes an inequality of contraction thet
may prodaco ruptare, All articlos of glass should be
from sudden changes of temperature, if we would aveld isle of
breakage.
In the art of engineering, it is important to take into account the
expansion and contraction of the metals. Tn laying the trek of =
railroad, for example, the rails ebould not be laid a0 as to took enh
other, otherwise in warm weather the expansion, acting through =
long ling, might produce a foree sufficient either to bond the mile or
to tar thom from their fastenings. In employing iron ties in bnilit-
ing, arrangements should be made by means of nuts and screws to
Ughten them in warm weather, and loosen them in cold weather,
otherwise the forces of evatraction and expansion would weaker and
eventually destroy the building. Very serious necidents have om
carred from ennitting this precaution,
‘The principle of expansion and contraction of metal has beem
utilized In bringing the walls of a building together afier they have
commenced to soparste. A eystem of iron thes ix formed, pasting
through the opposite walls, on the outside af which they are seourtd
by a ‘The alternate rods being heated, they expand, asd the
hula ary screwed up close to the walls, On cooling, the furs of ean
traction brings tho walle noarer together. ‘The remaining rods ane
next heated, and the nuts screwed up. Ou cooling, « further some
tmetion takes place, and so on until the walls are restored to their
proper position. ‘This method was successfully employed to nedtore
the walls of a portion of the Conserratire des Arte et Motiers, ix
Paris, which had begun te separate,
EXPANSION. 229
‘Thore are some apparent exceptions to tho law that heat expamds
borlies and coll contracts them. ‘Thus, bodies capable of absorbing
water, like paper, wood, clay, aad the like, contract on being heated.
‘This contraction i6 ouly apparcnt; it arises from the water which
they contain being vaporized and driven off, which produces an
apparent diminution of volume; after they are thorvaghly dried,
they follow the grneral law, with the exception of clay. This
pomtmeta permanently, by reagm of chemical changes among its
particle
‘Tho property just oxplained is usod for bending absorbent bodies.
‘To effect this they ure heated on one side only, which drives out the
water frean that side, and causes thom te bend in that direction. It
i this priveiplo that causes wooden articles to warp, und therefore
desnande that articles of furvitare and wooden paris of buildings be
coated with vila, paints, or varnishes, 10 prevent the absorption of
water.
‘The principle of expansion and contraction is often utilized fu the
arts. A familiar example is tho proces of sotting tho tire of a
‘The tre is made a litde smaller than the outor
periphery of the wooden part of the wheol. It is thou heated, and
placed around the wheel; on cooling, it contracts powerfully, and
draws the follow firinly together.
a8s. Law of Expansion of Liquids. — Liquids are
much more expansible than solids, on account of their
feeble echosion ; their expansion is also much more irregular,
expecially when their temperature approaches the boiling-
point.
‘The expansion of a liquid may be absolute or relative. The
absolute expansion of « liquid is its actual increase of vol-
ume; the relative expansion is ita increase of volume with
respect to the containing vessel. For example, In a ther-
‘momoter the rise of the liquid in the stem is due to Its rela-
tive expansion with respect to that of the stem. Both
Bot the liquid more rapidly than the glass The
capacity of the bulb inerenses with an increase of heat, but
the volume of its contained mercury incresses more rapidly,
and therefore rises in the stem. The abeclute ia wounds
a
230 HEAT.
greater than the relative expansion, It is the relative expan-
sion that we generally observo-
‘The coefficient of expansion of a liquid is thn expansion of a enit
lume, corresponding 1o an increas» of tenperature of one
‘Taken with reforence to glass, the ecefficlent of expanales fir
mereary is 0.000853; that of water is threo thes as great, umd that
of alechol nearly elght times as great as that of mercury,
286. Maximum Density of Water. — If water is
cooled down gradually, its volume continues to contmct
until it reaches the temperature of 39.2" F., or 4° C., when
it attains its maximum density. If it be still further cooled,
it begins to expand, and at 82° F., or 0° C., it becomes solid,
or freezes.
‘This curious phenomenon 1 shown by osing # water ther-
imetmeter in connection with a mercarial one, As the temnperstare ts
diminished, the liquids descend in.
the stems of both thermorneters
nit the mercurial ope shows
339.2° P., after which, if the eval
ing proceed be continund, the ser
cury will continue to fall, white
the water will begin to rise.
‘The maximum density of
water can be determined more
accarately by another method.
We have represented in Fig.
199 a glass jar having two
Istoral openings, one near the
top, and the other near the
bottom. Into these aportares
= are inserted two thermomo-
Fix. 199. tors. ‘The jr is fillod with
nda freezing mixture placed around its central part
cezing mixture remains long enough about the jar,
Il have the following results.
ie lower thermometer fills to 4° C., or 302° P., amd pemaina wk
of
If the
we al
EXPANSION. 731
that point. "Tho apper one at first changes vory little, but when
ft rvaches the fixed tomperatare, it leyins to fall wntil fv sinks wo
the freeaing-poiut, wheu the water at the surface freezes, The
reason is this: as the water in tho centr grows colder ite den-
shy ineroaees, and it falls to the bottom. This process gocs un
until all the water in the bewer part of the veswel has reached the
temperature of 30:29 F
When this portion of the water has this vempensture, circulation in
it couses, ontil needles of ico are formed, which, being lighter, rise te
the surtioe and start up a new clreulatiou, which cuses the water to
frveze at the surface, while that vear the bottom nmains at 302°,
"This experiment proves that water is heavier at 39.2° than at 22°,
fines it Hinks to the lower part of the verrel
‘This apparent exception to the law of expansion and con-
traction is explained fom the fact that at the temperature
of 39.2° F, the particles begin to arrange themselves in a
new order, preparatory to taking a crystalline form. Some
other substances, such as melted iron, sulphor, bismath, cte.,
exhibit a similar expansion of volume immediately previous
to taking a solld crystalline form. Tt is this property of
expanding at the time of crystallization that renders iron so
valuable a metal for casting. ‘Ihe expansion of the metal
nets to fill the mould, thus giving sharpness and accuracy to
the casting.
The fuct that water has its greatest density at 392° PL causes
‘ice to form at the surface instead of at the bottom of rivers and lakes.
Wore it not that ico is lighter than water, It would sink to the
bottom as fast 4s formed, or rather would form at the bottorn, and in
the colder regions of the globe would soon convert entire lakes [nto
folid masses of let, Ax ice nnd water are bad eondactors of heat,
the sanmer sun would not possess the power to convert them again
Ente water,
Ts’ Bwitorrland 1€ te found Ly experiment thot the temperatar
‘of the water at tho bottam of deep and snow-fod lakes romaine
dering the eutire year at the uniform tempernture of #2" P,
although the surfice ie freaon in winter, and in summer rises to
75° or OUP F,
Tris beenuee water bas Its maxinum deusity a 22° F., Yar W
—
282 HEAT.
is taken at this tempenitury, as the standand ef ceanparison for deter
mining the specific gravity of bodies.
287. Law of Expansion of Gases. — Gases are net
only more expansible than solids and Uquids, but they also
‘expand more uniformly.
"Phe evefficient of expansion of a gus is tho expansion which
a unit of volume experiences when ite temperature is increased
one degree.
Gay-Lvssac supposed that all gases expand equally for
equal increments of temperature; but more recent investi-
gations show that the coefficients of expansion are slightly
different for different gases. This difference is, however, so
small that for all practical purposes we may regard all gases
as haying the eame coefficient. The value of the coeificieat
of expansion for gases is 0.00204, which is about eight thnes
that of water.
288. Applications. — The law of expansion of gases, whon
heated, has many iinportant applications, some of which will be
explained.
When the air of a room becomes warmed and vitinted by the pres
enee of 2 nnmber of persans, it oxpands and becomes Tighter thax
the external air; henoo it rises to tho top of the room, and its place
is supplied by fresh alr from without, which enters thromgh the
cracks of the doors, or through apertures constroctod for the purposn:
Qponings should be made nt the upper part of the roam to permit the
foul air to escape, Such is the theory af eentilation of route.
In large buildings, like theatres, tho spectators im the upper gnl-
leries often exporienco great inconvenicnes from the hot aud sormupt
ir arising from below, ‘To remedy this ev
ventilatens, should
openings should be arrang
e constructed in the ¢
the bottom of the building te supply
to koop up the eireulations
neipto of expansion gives adranght to ourehimueys, "The
ne
hot ainaseonds through the fhe, and its place is supplied DF ope
F > eed air from below, which keeps up the eombaxtion
e
=
DENSITY OF GASES. 238
‘The eae principle is applied in warming buildings by means ef
farnaces. Furnaces are placed in the Jowest story of the building,
and are provided with air-chambera, which communicate with the
external air by means of air-pipes, When the ait becomes heated
in the air-chamber, i rises through pipes, of flucs in the walls, to
the upper stories of the building, and is adinitted to ur exeladed from
the diffireat apartments by valvoe, ealled registers.
The principle of expansion of air explains many metcorologieal
phetiomens. When the air in any locality becomes heated by the
rays of the sum, It rises, and its place is supplied by colder air from
the neighboring regions, thus producing the phenomena of winds.
‘Tho circulation of the atmosphere in the form of winds tends w
equualixe the temporatore, and also, by transporting clouds and vapors,
tends to equalize the distribution of water over the globe.
‘Winds iilso sore to remove tho vitintod air of citios, replacing it
by the pure air of the neighboring places, thus contributing to the
preservation of life and health. Winds alto act to propol veasels
on the ecean, thes contributing to the spread of commerce and
civilization.
Without winds, our cities would become centres of infection, the
elonds woald remain motionless over the localities where they were
formed, the greater portion of the carth would beoome arid nail desert,
‘without rirers or streams to water them, and the whole earth would
sean become uninhabitable.
289. Density of Gases. —The density of a gas depends
upon the pressure to which it is enbjectod, and also upon its
tenn
Tt is for this reason that we select a3 a term of comparison
the density at some particular pressure and temperature,
‘The standard pressure ie that of tho atmosphere when the
barometer stands at 30 Inches, and the standard temperatare
is 32° F., or the freezing-point of water. To determine
the density at any other pressure, we apply Masiorre’s
Taw ; to determine it at any other temperature, we apply the
coefiiciont of expansion, as explained in preceding articles.
‘Suppose it wore required to determine the density of air when the
atemoter indicttes 20 inches, and the thermorncwe (LP. two
ae
234 HEAT.
density being equal to 1 at the étandand temperature and pressure,
‘The pressure being only two thirds the standard pressure, the air in
the easy considered would occupy once and a half He primitive
volame, supporlug the temperature to retnainat 32°F. Bus the
temperature being 62° F., or 30° above the standanl, we multiply
1.5 by 30 tines 0.00204 for the expansion. ‘This product, added te
1.5, gives for a resnit 1.5918, That is, « anit of voluane at the
standard pressure ond temperature becomes 1.5018 units of volume
atthe given pressure and tempersture, Because the density varies
inversely as the volume, we shall have for the required deasity
rosbre, oF 0.0282.
The following table exhibits the donsity of some of the most im-
portant gaara, air being taken as a standard: —
Oa, Dealt, Gan Density.
ee 1.0000 Oxygen. -| 1.1086
Hydrogo 0.00% Carbonicacid . 1.4200
| Nitrogen ort
Hydrogen is the lightest known body, fis density being fourieen
ond a half times | han that of air.
Summary. —
usin of Solids.
‘ocdlicient of Linear Expansion.
Coefflelent of Expansion la Volume.
Practical Applications of the Principle of Expansion,
Law of Expansion of Liquids
Absolute and Relative Expansion.
iclent of Expandion.
Maximum Density of Water
Exporiinents
Apparent
os to the Law of Expansion and
Contre
Tho Fre
Law of
CoefBeient of Expansion.
Practionl Applications of the Expmusion of Gases.
Density of Goses.
=a0C~é‘ (‘N
DIFFUSION. 285
SPOTION 1¥, — DIFFUSDON OF HEAT,
290. Methods of Diffusion. —There are three methods
of diffusing heat, — Radiation, Conduction, nnd Convection.
We shall find tn another article that diffusion of heat inva-
riably tranaters heat from a hotter body to a colder one,
#0 a8 to cool the hotter and warm the colder. The three
methoxls will now be considered in the order named.
agi. Radiation of Heat.—The ctherval medium that
transmits heat extends through space, and is almost per
fectly elastic. 1t penetrates all bodies and occupies the
intervals between their molecules. The heat vibrations of
bodies are thas imparted to the surrounding ether, and by it
are propagated outward in spherical waves similar to sound-
waves In air, Heat propagated in this way is called radiant
Aeot. A. line porpendicnlar to a wave front is called a ray
off heat.
A ray of beat indicates a direction in which hoat i» propagated
and along which t produces its effect. To a homogencous medinm
Deat-rays are straight lines mdiating in every dircetion from a heated
Doty. Radiant heat does not impart warmth to the medium that
trunsmite it, but when intereepted by a body the molecular energy
ef the ether is imparted to the molecales of the body, and the phe-
womena of heat are developed.
‘Whes we speak of radiant heat, it mast be understood that it is
not a wae kind of heat, bat radintion considered in its thermal, or
heat aspect.
To onder to distinguish it from tho ordinnry heat-enerry whied
‘bodies possess, it may be regarded as sndulalory, ar radiant euency
which travels through space with yreat velocity: and when rays of
heat, a+ has been stated, are intercepted by a body, this mdiaut
nergy ls changed to ordinary hent-cnorgy, which in turn ix changed
pia agnin into mdlant energy when heat is given off by any
subatanee,
292. Laws of Radiant Heat.— The radiation of heat
takes place acconting to the following laws :
—
236 HEAT.
1. Heat is radiated equally in all direetions,
‘Vhis law may bo veritied by placing thermometers at equal dis-
tances and in different dircetions frorn a beated body.
2 Rays of heat are straight tines.
‘This law may bo vorified by interparing a sereen anywhere inn
right Line Joining the heated body and the thermometer, when tho
thermometer will cease ty rise.
If a nay pass from one medium to another, it ix bent from ite
course ; this bending is called refraction.
Wo #00 rofmaction of heat when the luminous thermal rays of the
sun, like the rays of light, are refracted to a focus by a conversing
lons. Non-luminous rays of boat, or obscure nays, aa they are
generally called, can be refracted by a lens of rock salt hold before
an iron ball heated bolaw redness.
‘The laws of refraction for heat are the same as for Nght, and will
bo more fally discussed under that subject.
8. The intensity of radiant heat varies directly as the temper-
ature of the radiating body, and inversely as the square of the
distance to which it is transmitted.
‘Tho first part of this law is verified by exposing one of the bulbs
of @ differential thermometer to a bluckened cubical box, filled with
hot water, the other bulb being protected by a sereen, If the water
is in the first Instance of a given temperature, and then falls to
half or a third of that tomporature, the differontial thermomoter will
manifest « half or a third of its origiaal indication, and so on for
any temperature.
‘The second part of the law may also be verified by means of the
differential thermometer. In this ease the hented body is
always at the same tempornture, and «me bulb of the differential
thormomoter is placed at different distances from it. Tt will be fied
that at a double distance the indication is only fourth of the original
indication, at a triplo distance only x ninth, and #0 on.
4. Radiant heat és propagated in « cacunn as well as ta air
The radiation of heat from the sun to the earth prowes this
law.
Tt can bo demonstrated also by the following experiment, Ta the
botrmef a glass globo (Fig. 200) 4 thermometer, f, ie sealed air
REFLECTION. 237
tight, in auch a manner that its bulb occupies the centro of the globe.
‘The apparatus ts thon filled with mereury, und inverted over a cup
of mereury with the end of the neck of the globe under
the surface of the mercury. We get in this way a it
‘Terricellian yaonom,
‘Now molt off the neck with a blow-pipe above the
mereury. If the globe be immersed in bot water, the
moreury is seen at ones to rie. And this must be due
to the radiation of heat through the vacuum.
293. Exchange of Heat between Bodies.
—The process of radiation of heat between
bodies is mutual and continuous, According to (
the laws given in the preceding article, those
bodies which are most heated give off most heat; — Fig. 200.
hence the hottest bodies of a group give off more beat
than they receive, and the coldest ones receive more than
they give off. The consequence is, that there is a continual
tendeney towards equalization of temperature. If all the
bodies are of the same temperature, each will give off ns
much as it receives, and no further change of temperiture
can occur, The process of radiation, however, goes on as
before.
All the bodios i a room, for oxample, tend to come to a uniform
temperature. We may, tend to come to a uniform temperature,
toeunes this condition ta nover fully realized. Bodios nearest the
walls are coutinunlly exehangiog heat with the walls, and as these
aro in communication cither with the outer air or with other rooms,
luenced thereby, and will in turn oxert
in
294. Reflection of Radiant Heat. —When radiant heat
falls upon the surface of a body, some of it is deflected or
ent from its course. This bending is called reflection.
‘The point at which the bending takes place is called the
point of tneidenee. Tho ray before incidence ts called the
facident ray ; aftor incidence, it is called the reflected ray. A
Tine drawn perpendicular to the surface at the yolut of wee
a
238 HEAT. ~
dence is callod the perpendicular. The angle between the
incident ray and the perpendicular is the angie of imeidence >
the angle between the perpendicolar and the reflected ray is
the wngle of reflection, ‘The plane of the incident ray and the
perpendicular ia the plane of incidence; the plane of the
reflected ray and the perpendicular is the plane of reflection.
These plines coincide,
295. Laws which govern the Reflection of Heat.—
‘The following laws, indicated by theory, have been confirmed
by experiment :—
1. The plane of the incident and reflected rinye ¥e perpendicilier
to the reflecting surface at the point of incidence.
Fig. 201.
2. The angles of incidence and reflection are eqial,
‘Tho apparatus employed in establishing these laws is shoven in
201. A in a tin box with ite frees blackened, in whieh bet
water is placed. B is a toflecting surface, and D is w alfferential
thermonetor. BC ina porpendioulat to the reflecting surfiee.
‘Tho surfueo, A, radiates heat in all diretions, tut only a single
ray is permitted te fall upon the reflector, 2 the remainder bein
Intereepted by a sereen, having a small hole in it. By aulmabily
amusing the thermenoeter, und other parte of the apparntus, Tf spay
be shown that the plane A 22 is perpendicular to the refleeting enr-
fice at B, and that tho angles, A BC and CBD, are equal t each
ee, Wee 7
REPLECTION, 239
296. Reflection of Heat from Concave Mirrors. —
A Coscave Minow is a polished spherical or parabolic sur-
fuce, usually of metal, employed to concentrate rays of heat
at a single point.
‘It is a property of such mirrors that all rays which before
ineidenee aro parallel to the axis, ure after reflection con-
verged to a single point, which point is the focus of the
mirror. Conversely, if the rays proceed frow the focus, they
will be reflected in lines parallel to the axis,
he misror, B, is am inflammable substance, ag a piece of
phosphorus The heat nvtiating from the ball is reflected from A,
parallel to tho eummen axis of the rarer, and fi upon BR, is
gain cefléeteed tothe foens m5 the beat, owcentrated at m, is eufli-
amie the phosptiorns, even when the jalerons are several
ftom each other. If the mirror, A, alone is wiod, the
ps Dries porllel mays more accurately t0 a forse
are more diffienlt t constrict, and therefore are
a0 HEAT.
‘The property of concave mirrors, above explained, enables us to
concentrate the heat of the sun'e mys. In this ease the mefleetor is
called a durning mirror. Tt must bo placed so that its axis is pare
allel to the rays of the sun, which, aa they fall upon it, are reflected
tw the fecus, where they produce heat enough to set fnllamenable
substances on fire.
Tt iy easid that Arc IMEDES Was cuablel by means of mirrons te
sot fire to the Roman in the barbor of the city of Symmons.
Borrow showed the possibility uf such an uperation, by setting fire
toa tarred plank, by means of burning mirrors, at a diatasies of more
than 220 fect.
Fig. 208.
297. Reflecting Power of Different Substances. —
Those belies which reflect a largo portion of the incident
heat are called good reflectors ; those which reflect but ttle
are ca bet bard reflectors
shows the method of determining the relative
reflecting powers of different bodies, adopted by Lesint.
He ph vox, filled with water at the heii
polnt, in front « polic reflector. ‘The rays of hent,
falling upon the ee reflected sind tend to came fo
a foes at F, but by interposing a square plate of some sly
Ia cubie
2 =a 5 =
ABSORPTION, 24h
stance between the mirror and its focus, the rays are aguin
reflected, and come to a focus as far in front of the plate
as Fis behind it, The heat thus reflected is received upon
one bulb of a differential thermometer, by means of which
it is measured. By tnterposing plates of different sub
stapces In succession, their relative reflecting powers any
determined.
To this way Leste showed that polishel) brass possessed the
reflecting power; silver retlocta only nine tenths, tin only
eight tenths, oud glass only one teath as much as brass, Plates
Mackened by smoke do not reflect heat at all,
Ji has beou stated that when radiant heat falls upoo the surface of
a bevly, some of ft is reflected, ‘There ix some of it also that is
absorbed by the body, and some transinitted.
A substance that trausmits hoat is called diathermanous, aud ono
that docs wot, athermanous.
Rock salt ix the most diathermanous of all solids, Radiant heat,
both larinous and obscure, will pass through it with about the sue
freility that light passes through glass Glass ix very transparent,
that is, will let light through it readily, but is not specially diather-
wanons.
Tocident rays not transmitted aro elther reflected or absorbed. It
is ouly the rays absorbed that warn a body.
298. Absorbing Power.—In order to determine the
telative powers of absorption, Lesii: employed the apparatus
shown in Fig. 204.
‘The source of heat ani the reflector remaining a before,
he placed the bulb of the differential thermometer in the
focus of the reflector, covering it successively with layers of
the substance to be experimented upon. In thie way he
showed that those substances which reflect most heat absorb
least, and the reverse.
When tho bulb was blackened by smoke, the thermometer indi
ented tlie greatest change of tomperaturo, and when covered with
ieatven of brass, We inieated the Sian change.
ce
42 HEAT,
299. Radiating Power.—Tle Raniarme Pownn of o
body is its capacity to eat, or radiate the beat which it
ing the radiating power, Leseu employed
the apparatus shown in Fig. 204. In this case, instead of
covering the bulb of the thermometer with layers af the
substances to be experimented upon, he covered the different
faces of the cnbie box with layers of the different substances.
Fig. 206
For example, let one fioe be inade of tin, let a second be. blnek=
k, Jet a think be covered by a layer of
paper, and a fourth by a pl umning these different
faces towanla the reflector, the thermometer indicntes different degrees
of temperatare. Tf the bluekenod faeo he turned tevranis the reflen
tor, the thermeimeter rises, showing that this face is a good muiliaters
nest turned towands the refleeter, the
thermometer falls, showing that paper is a pooner mdiaine than
lampebilack ; if th severe fhee be tarued towns the reflgetar,
tho thermometer falls till lower, indicating that glass if a poorer
radiator than paper; flually, if the tinned fice is turned towards the
le still lower, indicating the fact that tin
ov than glue
ened by smoke or lamp-bl
10 of glass, On
if the paper-coverel face
retleetor, the thermometer fi
J 9 poorer rad
i,
THE RADIOMETER, 24s
Leste fonnd, by this ear of proceeding, that the radiating
perrers «if bodies ate tho same ns their abeorbing powers; that ls,»
good radiator is also a good absorber Wot a bad reflector, and the
eNErse.
This commonly supposed that bodies of bright colors radiate heat
to a less extent than those of a dull and dark color, This awa dis
proved by Meloni, at lenst for obscure heut. He found that white
Jeu and lamp-blnck mdinted the earne ainonnt of heat.
300. Modifications of the Reflecting Powers of
Bodies. — The principal causes that modity the reflecting
and absorbing powers of bodies are: polish, density, direction
of the trident rays. nature of the source of heat, and color.
Other things being equal, polished bodies are better reflectors
and worse absorbers than unpoliahed anes.
Other things hing equal, dense bodies are betler reflectors
end worse absorbers than rare ones.
Other things being equal, the nearer the incident ray ap-
proaches the perpendicular, the tess will be the portion reflected
oud the greater the portion absorbed.
The mature of the snirce of heat sometimes modifies the reflect-
ing end absorbing powers. Thus, if a body is painted with
White lead. it absorbs more beat from a cubical box of boiling
water, than thougl the sume heat were emitted by a lamp.
Bot if a body is painted with lamp-black, the ainount ab-
sorbed is the same, whatever may be its source.
Bodies ikworb Toss and reflect more heat than durk~
colored anes. "This fs found to ho true in regard to lurninous hewi,
such axthat of the sun, But in the ex of olsen heat, ec
‘not poem to affect the absorption.
Whother a badly isn good reflector, wbsorbeut, or mudiater, or
Whether it is the rereeer, depends more upou the molceular emdition
wf ite surface than upon its color,
wr doves
gor. The Radiometer. — This consists of o glass tube
(Fig. 205) with a bulb blown in it, which rests on a wooden
support. A fine steel point is fused on n small Woloe exvend-
—
aa HEAT.
ing up into the bulb; on this polut
rests a small vane consisting of four
arms, exch one carrying a disk of mien
‘or pith, white on one side and covered
with lamp-black on the other.
q In order to keep the rane on the steel
pivot, a small tbe extends down from the
x top of the bolb so as to surround the tep of
the cap, whieh rests on the pivot withoat
touching The other end of this tube ix
drawn out, and connected with sume mappa
ratus for exhausting the air. Whee this
done, the bull is hermetically sealed,
If a hot body be brought near the ruil.
‘oueter, or if it be exposed to the sunlight,
tho arms will rotate mere or Jot magridly,
‘The cause of this was formerly supposed to
be dhe to the meehanieall aetion of light, but
it ls uow thonght to be owing to beat nadia-
tions, and the reactive force of the sndlo-
Fig, 205. cules of the rarefied gas in the bulb,
302. Absorbing Power of Gases. — Tho powor of the
different gases in absorbing heat varies greatly. ‘The almple
gases, hydrogen, oxygen, and nitrogen, absorb very Tittle.
Dry alr also is a very poor absorbent. ‘The aqucoas vapor
in the atmosphere, however, has great power of absorption ;
bat it is more manifest in the case of obscure than Ieminous
the compound youses exhibit great capacity for absorbing
ulphurous sell and nia, the former wba
mes as mach as ry alr
ight is eubject to the smo
milecced, reGoted, transmitted,
another modificatioe, also, called
sce ft) aether ehuptur th
viz, it
abe
leurs that radinut hewt is
aad absorbed. ‘They beth
polarization, to be expdainad her
In view of those fact, we are justitio’ in our inforemen thas heat
Wih: are citber identical wr closely allied to cack other,
CONDUCTION. 246
303. Applications of the Preceding Principles. —
Articles of clothing are intended to preserve uniformity of tempera
tere in the human body by excluding the too violent heats of
sammor, and by preventing too mpid radiation of animal heat in
winter,
Loose substances, like woollens and furs, are bad reflectors, and
therefore are saitable for winter clothing. Compact substances, Tike
Finens and cottonr, aro good reflectors, and thoroforo aro suitable for
summer elothing.
Snow Is a good reflector, but a bud absorber and muiater. Hence
{it Is that a layer of snow iu winter acts to protect the plauts which
it covers. Snow and icc, when exposed to the rays of tho sun, melt
bat slowly; but if a brinch of a treo or stone projects through the
sour, it causen the Tattor to melt in its neighborhood, first by abeorb-
ing the heat of the sun, and thon nuliating it to the surrovoding
portloles of loo or anow.
If w stone fa thrown upou a feld of Ice, it soon causes the Teo
xround it 10 melt, forming a hole into which it sinks. A darle cloth
sgread upon snow acts in the saine manuer, wud soon sinks under the
intluenee of the sun's mye.
Water it soonest heated in a vessel whore surfiwe is black and
uupoliahed, beeusse the veesel in thie stato is best adapted to absorb
the hoat which is applied to it, but on removing it from the fire, the
wator cools rapidly. ‘To rotain heat in liquids, thoy should be con-
fined in dense and polished vesols, as these are poor mediators,
Honeo, for boiling avd cooking, rough and black vowels shoull bo
ewployed, but to koep the articles warn, deuse und polished vessels
should be uso It is for this reason that a silver teapot is better
thas on earthen one. But as silver is a good conductor of heat, the
hanille should bo insulated by intorposing betwoen it and the veaol
seane non-eouducting substance, as ivory or bone.
Stoves, being intendod to radiate heat, should be rough and black,
‘but firgplaces, being intended tu reflect heat inte the room, should be
lined with white, dense, and polishod substances, like glaxod carthen-
ware, oF glazed fire-bricks.
04. Conduction is that property of bodies by virtue of
ek sease heat from tnolecule to molecale. When
any body is heated hy conduction. it must be of a \owex Wem
—_
246 HEAT.
perature than the parts of the body through which the heat
comes to it,
‘Those bodies that tranamit heat readily are ealled good comdino:
tors ; those that do not tranmnit it readily are called bad comductora:
IxoxsHonss showed that solid bodies possess different degrees of
ounductivity, by meana of ou apparatas shown So Pig, 206. It coe
sists of an oblong vessel to contain water, from ane gide of whieh
Projects a system of short tubes for receiving rods of different Kinds
of solids, sue as metals, marble, wood, glass, and the Ike
He coated tho difforcut mda with a soft wax that would imelt at
about 140° F., and then filled the vessel with bolling water. pes
Fig. 208,
some of the rods the wax melted rapidly, apen fame mene sianwely,
pot at all. ‘This showed that the reds varied i
and upon ov
thelr
Teh
eames marble, then porcelain, bricks, w
nduetivity
wn that inetale aro the best condactor, after whieh
nj, glass, resin, ote
Liqaide nro had condootors of heat, éxeeit mercury, whtei kal
metal, They are such had conductors that Rusitomt asserted that
ductor at all. Moro earefal expérimeuls Rave
shown that all liquids are conductors, but extremely bad ones.
Gases are had conductors of heat, but on sewount of the extreme
y of their particles, it bs difficult to establish the fuet by dinst
observation.
beer
water
mobi
APPLICATIONS. wT
305. Convection is the motion of the particles of the hot
body carrying the heat with them. When # liquid ie heated
at the bottom if illustrates convection. ‘The heated particles
expand, and as they are then lighter than the cooler ones
above them, they rise to the top of the vessel to give place
to the heavier and cooler particles that supply their placrs-
In this way a double current of par
ticles ia set wp, as shown in the fig:
ure by the arrows, the bot ones rising
and the cool ones descending, This
process of circulation goes on tll a
uniform temperature is imparted to
all of the liquid.
‘The cirealation of particles may bo
shows by putting into tho vessel (Fig,
207) particles of w substance of ueurly
the sane density as the liquid; a» for
‘ook: rawdust. ‘Thos particles
will partake of the motion of the dail,
rising up in tho contre, and doseevding =
alony the walls of the vessel as shown in Fig. 207.
the figere.
‘Gasca sto Kesied by convection, in the sari manner as liquide,
306. Applications of the Preceding Principles. —
If the bund be plived upon different articles iv a eld room, they eon-
Yey different sensations. Motals, stones, bricks, and the Like, feel
cold, whilst carpets, curtains, nnd the like, feel warm, ‘The reason
uf this Is, that the former are good conductors, and readily abstract
the animal heat from tho hand, whilet the latter are bad conductors,
ath dey amt convey away the heat of the hil.
Woesden handles are sometimes fitted to inotallic vossels which aro
fi enutale heated Liquids. This is because wood is a bad conductor,
andl therefor does not convey the heat to the hand. For a sitnilar
Teneon, When we would handle any heated body, we often interposo #
Thick holder af woollen cloth, the latrer being u bad conduetor.
To preseres to in eeiimer, we surmund it with eome bad cons
Avetor, as straw, sawilast, or a layer of confined ake, "Ye acon
=
28 HEAT.
means are adoptod to preserve plants from the action of frost, Tn
this caso the non-conducting substance prevouts the radiation of
heat.
Cellars are protected from frost in winter by a double wall eneee-
ing « layer of air, which is a non-conductor, It is the layer uf eva-
fined air that roulors double windows so efficient in exelading frust
from oar houses.
‘The feathers of birds and the far of animals are not only in them-
selves bad conductors, but they enclose a greutor or leas quantity «f
air, which renders them eminently adapted to the exclusion of old.
‘The bark of trees is « bad conductor, and bo serves to protect thems
from the injarior foots of heat insammer and cold in winter.
One warmest articles of clothing aro composed. of non-conducting
substances, enclosing a greater or Tess quantity of alr. Such are furs,
woollen cloths, and the like. It ia not that these aro warm of thew)-
wives, but they serve ms non-conductors, preventing thé escape of
animal heat from our bodies.
Summary. —
Difiusion of Heat,
Radiation of Heat.
‘Transmission throagh Space.
Radiant Heat. — Ray of Heat,
Laws of Radiant Heat.
Exchange of Heat betwoen Bodies,
Reflection of Resdinnt Heat.
Dofinition of Terms.
Laws of Refleetion,
Reflection of Heat from Concave Mirrors.
Rotleeting Powor of different Substances,
Lealic’s Experiment
Diathermanous and Athermanour Substances.
Teslie's Method to ascertain the Relative Atsorting
Powers of Substances.
Leslie's Method to ascertain the Relates Hadioting
Powers of Set
Comses that modify the Leflecting cmd Atwarting Powers
of Bodies
et aa
PUSION. 249
The Rodiometer,
‘Deseription,
Explanation of its Action.
Absorbing Power of Gases.
‘Connection between Light and Radiant Heat,
Practical Applications of preceding Principles.
Conduction.
Definition,
Experiment to illustrate Conduction of Solids,
Liquids Bad Conductors of Meat.
‘Gases Bad Conductors ef Heat.
Convection,
Definition.
Experiment to illustrate Convection of Liquide,
Convection of Gases.
Practical Application of preceding Principles.
SuCTION ¥.— CHANGE OF STATE OP BODIES HY FUSION aND
CONGELATION,
307. Fusion.—It 4as been stated that heat not only
causes bodies to expand, bat that it may in certain circam-
stances canse them to change from the solid to the liquid
state, or from the liquid to the gascous state.
When a body passes from a solid to a liquid state, it is
sald to melt, or fuse, and the act of changing state in this case
is called fuston,
If a melted body is suffered to cool, it gencrally becomes
solid at the same temperature at which it melted. Hence the
melting-point is tisunlly the same as the freezing-point.
‘The freeving-point may be lowered in various ways That of
water has been lowered several degrees below 2° P. A slight jar,
however, will canes tho water to freero, and the temperature will in=
tantly rise 10 32°.
‘Fusion takes place when the foree of cohesion, which holds the
particles of « body together, is exactly balanced by the heat whieh
foude to sepmmte them The temperature at which fishom wien
—
250 MEAT.
Mereury
lee at rn
Tallow Antimony...) SMe
White wax Ze. sel or
Sulphur Silver . ress?
Tin Gold. 2 ne
All bodies are not melted by the action of heat, Some are decam-
posed, such as paper, wood, bone, marble, ete. Simple bodies — that
is, bodios which ure composed of but one Kind of matter —always melt
if sufficlently heated, with a single exception. Even carbon, the most
refractory of all known bodice, has been brought to x state of bneip=
int Fasio
‘The passage from the solid to the liquid stute is generally sbeept,
but not always. Some hodies show no definite melting-potuts fir
and row gradually become softer and softer until the
ndition is reac
example, glo:
quia
308, Latent Heat of Fusion.— Bodies which can be
melted always present the remarkable phenomenon that when
they are heated to the temperature of fusion, they eannot he
heated ny higher until the fusion is complete, For example.
if ice be exposed to heat, it begins to melt at $2°R., and if
more heat be spplied, the melting ix necelerated, but the tem-
perature of the mixture of ice and water remaing at $2° until
all the Ice is melted.
‘The heat that is applied during the process of fision enters
into the body without raising its temperatare, and Is said to he-
come latent, When the body returns to Its solld state, all the
given out, and once more becomes semeifle,
‘Those who first used the term datent heat noticed That the ther
fmaneter did not reepond to the host that was eommuniegted dma
the process of inelsing, and eupposnd that it wae biddem away ia the
molecular epaces {a state of inaetion ; henee the mane Jatent,
Intentheat is ays
LATENT HEAT. 251
Aceonting to the present theory, the beat is expended in conferring
poteatial evergy upon the melocales, and performing the interior
work of moving them into new positions. When the heat is with:
drawn this potential enerzy beeoince kinctio, and the molecules rush
Yack again to their former condition with the sate forve used in sep
arating them, ‘Tho heat that was consumed now reuppears, ae hae
been maid, In its original form of sensible heat.
‘The expression latent heat, although not in strict accordance
with modern ideas, is nevertheless generally used by physi-
cists as & matter of convenience.
‘There can be no confusion in its use if we understand it to
mean simply the amount of heat that must be communicated fo a
tody in a giren state in order to convert it fio another state with-
ont changing its temperoture.
Tf we consider sensible heat to be Avnetic molecular eneray
(Art. 263), then latent heat may be regarded as potential
molecelur energy.
The phenomenon of latent heat may be illustrated by the follow:
ing experiinont, Ifa pound of polrerized feo wt 32° Fo he mixed
with a pound of water at 174P,, the beat of the water will be just
‘sufflelent to mele the fer, and there will reaalt two poonde of water nt
the temperature of 32°F. During the prooms of molting, 149° of
heat have been absorbed and become latent: heuce wo sy that the
beat required to molt ico at 22° F. is 142°; or, in «ther words, the
arent heat of water at 22° is 142°.
The euormous amount of heat which becomes latewt when ine
melty explains why ft is that large masses of ler remain unmelted
for = cousidorable time aftor tho temperature of the air x raised
above (2° FL Conversely, the tinmense quintity of heat evolwed
when witer passes to the state of ioe explains why it is that ior
firms so slowly in extremely cold weathor. ‘The absorption of heat
in melting and tho production of heat in froceiny tend to eq
the temperature of climates in the ouighborhued of large masses of
water, Hike bales and rivers.
309. Congelation. — Solidification. — Regelation. —
Any! Mist can be melted by the application of beat can,
aa
_——
252 «HEAT.
be bronght back to 1 solid state by the abstraction of heat.
‘This passage from a liquid to a solid state is called congetiation,
‘or solidification, D
Tn every body the temperature at which congelation com:
‘menees is generally the same as that at whieh fusion begins.
Thus, if water be cooled, it will begin to congeal at $2" F.
and, conversely, if ice be heated, it will begin to melt at
32°F. Furthermore, the amount of heat given out, or ren
dered sensible, in congealing is exactly equal to that ab-
sorbed, or rendered latent, in melting.
‘That this is really the case may be proved by the following ex-
periment. If we wke two vessels, the finst containing one pound of
water at 174° F., and tho eeoond one pound at 32° F,, and expose
them to the nir daring a cold winter day, so that equal amocnts of
heat shall cecapo from beth during a givun thine, we shall fied that
the temperature of the water in the first vessel will Tinmediately Gill,
whilo that in tho eecond will remain stationary.
To the mean time the water in the second wessel will begin to
freeze, bat a» long as tho water keope its liquid state the temperature
will stay at G2". When the last particle of water has frozen, and
before the temperature falls, if
firat vessel, we shall find it to bo 22°. We sor, therefore, that 12"
of heat bave boon given oat in the firet vearel,
‘The same amount ust also have escaped from the water im the
second, but the temperature ja not changed, hecnume it i the host of
fusion given up by the wator In changing into toe
Some Haquids cannot be congealed by the griatest ecld to whieh we
cau subject them; such are aleohol and ether, Pare water eongeals
at 32>; the salt water of the oecan congeals at 27°; ollvo-oll as
21°} linseed and nut olle wt 17%
Water r is maxim density at &.2°, and as ite tempers
ture is diminished frou this limit, it» volume continues te tnerosse
until congelation i completed.
liquid to « solid state the expansion fe aad-
don and irresistible, ‘The immense power of this expansion is seen
in the bursting of weter-pipes during « freet, the breaking of plteh-
ors, tumblers, Yates, ¢to., im which water has heen ofl, when the
temperature falls to 32°
When it parses from
al
CRYSTALLIZATION, 253,
The following experiment illustrates this expansive force
in a till more striking manner :—
Aux ofticur of the Artitlory in Qnoboe fillod « 12-inch shell (Pi. 208)
with wenter; wad dosed the fiiseo hole with a wooden plug driven In
with o mallet, It wos
then exposed to intense ge
frst. When the water 7
froze the plog was pro-
joeted! to m distance of sov-
eral bundred feet, and a
Tong cylinder of ico issued
from the hole,
Th another experiment
the bomb aplit open and a
sheet of fee was forced
through the crack,
Tf two stnooth pieces Fig. 208.
of melting ice be pressed against each other, they are soon
frozen together, This phenomenon is enlled regelation.
Reqgelation is exphined by enpposing the interior of the iew colder
Hin tho outer Iyer just jrssing into tho state of water, When
tho pilecos sire prossed toyether tho layer of watur at 32°F. has a
colder body ow each side, The latent heat of fusion of this layer ix
soon absorbed und conducted away, and tho water is eonvertod into
joe. Tho formation of a snow-ball depends on regelation, Below a
Semmperatore of 32° F. the particles of snow aro dry and mgolation
exunot take place. Eouce # coherent encw-ball can only be mate of
melting snow.
310. Crystallization.—When bodies pass slowly from the
liquid to the solid state, their particles, instead of arrang-
ing themselves in » confused manner, tend to group them
selves into regolar forms. Those forme are called crystals,
and the process of forming them Ix called erystallization.
Flakes of snow, sugar candy, alum, common salt, and
the like offer examples of crystallized bodies. ‘Phe forms of
‘tie erystals are best seen under a magnirying-gluss.
Bodies may he exystaltized in two differen wage. Wa Yue tors
(ali
254 HEAT.
ease, we melt them, aud then allow them to enol slowly. Ifa yewel
of aulphur bo melted und allowed to cook slowly, it will comanenes
crystallizing about the surface, and if we break the crust thes
formod, and pour out. the interior liquid sulphur, we may. obtain
freautifl erystals of sulphur.
Tn the eecont cuse, we dissolve the ody to be erpsballived, sud
then allow the solution to evaporate slowly. ‘The dissolved body
ia then deposited at the bottom and om the sides of the vessel im the
form of erystala. ‘The slower the process, the finer will be the ery»
tals It is in this manner that wo erystallize candy and Varios salts.
11. Freezing Mixtures. — The absorption of beat
which takes place when a body passes from a solid to a ligaid
state ia often utilized in the production of intense cold, ‘This
result is best obtained by mixing certain substances. and
these mixtures are then called frnezing mixtures,
A mixture of one part of common salt and two parts of
pounded ice forms a mixture that is used for freezing eream.
The salt and ice have an affinity for each other, but they
cannot unite until they pass to the Tiquid state. Tn orler te
pass to this state they absorb a great quantity of heat from
the neighboring bodies, asd this causes the Intter to freeze.
By means of « mixture of salt and snow the thermometer may
Definition.
Table of Fusion for different Substances,
Latent He
Explanation of the Term Latent,
Origin of te Use
What Latent H.
Exanples,
of Busion.
t really accomplishes,
Comgeintion,
Detisition.
Heat given out in Freezing,
Experiment,
Expansive Power of Water in Freezing.
__ lll
VAPORIZATION. 26
SECTION Vi. — VAPORIZATION. — ELASTIC PORCE OP VAPOMS.
312. Vaporization. — Volatile and Fixed Liquids, —
When saffictent heat is applied to a Nquid, it is converted
into a gaseous form and is called a vapor, The change of
state from a liquid to a gaseous state is designated by the
general term raporization.
Tf vaporization takes place slowly and from the surface, at
ordinary temperatures, it is called evaporation ; but if vapor is
prodaced rapidly in the mass of the liquid itself, the process
is termed boiling.
Some solids are capable of passing directly to a state of
yapor without firet becoming liquid. Iodine, arsenic, and
camphor are examples of this class. This is called sublimea-
tion. Feyen the vapor of ice can be detected far below the
freezing-point,
‘The nember of yapors that exist at ordinary temperatures is very
small. Of these, watery vapor ie the most familiar, ag well he
sioat important, ov account of the part which it plays in many nat-
tend phengmens.
Liquids arp divided into two classes, with respect to the readiness
with which they pass from the liquid 10 the vaporons state, viz
cobutile liquide and fixed biquiels,
Volatile Jiquids are those which havo = natural tendency to pase
fatoa state of vapor oven ut ordinary temperatures, such 1s ether,
alcohol, and the Uke. Ifa vessel of water, alcohol, ether, or chlaro-
form bo Ieft exposed to the air, the liquid ix slowly converted into
vapor and disappear; in ether wonls, it evaporates, “To the sans
lam
255 HEAT.
of volatile Hiquide belong essences, essential oils, volatile cls,
amongat which may bo inentioned spirite of turpentine, vil of laven-
der, attar of roses, oil of orange, and the Tike.
Fixed liquids are those which do not pase into vapor at any tem:
perature, as, for example, fish oils, olive offs, and the files, At high
temperntares they aro docomporod, giving rise to wurious kinds uf
gnves, but to no true wipors that can be condensed Into the origi
nal form of the liquid. Some oils, like linkeed eal, harden on expos
ur to the air: but it in vot by evaporation, bat by alworbing oxygen
from the air, aud thus passing to a solid state.
313. Elastic Force of Vapors. — Vapors are generally
colorless, and are endowed with an expansive foree, Or lension,
which, when heated, may become very great.
‘This property may be illustrated by means of an apparatus shoo
in Fig. 200. Tt consists of a carved
tobe, the short ranch of which is
closed and filled with mereury; the
mercury also fills a portion of rhe
Jong branch, A ssnall quantity of
other i trodaced into the abert
Dranch, whea it at enew rises to the
top, B, of this branch. At ordinary
texoperaturco, the pressure of the ex-
ternal atmosphere exerted throtigh
the mercury is eufficient to prevent
the ether from forning waper,
If, however, the tube is plunged
into a vessel of water heated to 112%,
the ether will be converted into Ya
por, and will eceupy & certain pare
tion, AB, of the tube, holding is
equilibrium the presse of the wt
mosphere, together with the weight
of the merenrial column, whowe
height is AC.
If the tube te withdrawn and
allowed to col, the vapor of ether
will be condensed, and will appear
EVAPORATION. 267
as 9 Hquld at B If snore heat be applied, it will agnia be cons
verted into vapor, and the mereury will rise in the branch, C, as
loog as any ether rniains to bo evaporated, ‘his shows that the
tension of the eapor angtnenta with the temperatare, ‘This prin-
éiple holds true for all hinds of vapor.
‘The tension aequired by the vapor of water, or steam, often be-
cones so great by being cated us to burst the strongest vessels, and
thos ts the conse of frightful accidents The canse of wood snap-
ping when bumed in a fireplace is the expansion of the water in the
pores, giving rige at last to an explosion. Wher a chestuut is
réasied fi the ashes, the moisture within the shell expands into
steam, and explodes with sufficient force to throw the ont from the
fire. Henec it is that 0 small puncture is usually made in tho shell,
which pernits the eseape of the steam and prevents explosion.
314. Instantaneous Evaporation in a Vacuum. —
Vapors formed apon the:
surface of a liquid ca-
cape by virtue of their
tension, Under ordi-
ary circumstances, the
pressure of the air pre.
vents a very rapid es-
cape of yapor at ordi-
hary temperatures, but
when the atmoaphoric
pressure is diminished
in any way, evaporation
takes place with great
rapidity. Tf the. pres-
sure is entirely removed,
258 HEAT,
iNustrated by moans of the apparatus shown in Fig. 210, Tt eomsists
of several baromoter tubes, 4, B, C, D, Glled with inereury, and
inverted in a common cistern of wereury, ax shown in the fycere.
‘The whole apparatus is supported by o frame, t which is attached
4 graduated senle. ‘Tho mercury will stand at the sume height ia
all of the tubes, —ot the height in A, for esumple.
Hm fow drops of water be introdaced into the tube, B, they will
riee through the moreury in the tube, and on rénching the yaequm
will be instantly converted into vapor, as is shown by the depression
that takes place in the column of mereury. If a little aleohol be
Introduced into the tube, C tt will, in, tke manner, be conversed
into vapor, and will prodore a still greater depression of the eolust,
If a amall quantity of ether be introduced into the tube, 22, a sill
greater depression of the sterenry will be observed.
‘This experiment shows that the tension of the vapor of ether br
greater than that of aloohol, and that éf aloohol greater thas that of
water. By carefil measurement, it is found that the teusion of the
vapor of ether is twenty-five times as great a that of water, and
six tines as great as that of aleohol.
315. Limit of the Tension of Vapors.—If a suf
clont quantity of each of the liquide in the Isat experiment be
introduced into the tubes, vapor will finally cease to form,
and a portion will remain in the Hquid state. Tn this Gee
the tension of the vapor already formed is sufficient to bak
ance the tendency of the liquid to pass into 9 state of vaper
In this state of affairs oo more vapor ean foem without =
change of temperatare. This is the case supposed im the
last article.
3:6. Causes that accelerate Evaporation. — The
slow evaporation of water on the surface of oar globe ie
accelerated by many causes, some of which are Endjented
Ielow : —
1. Temperature. — Increase of temperature also ineremees
the tension of the vapor formed, and accelerates evaperm
tion.
This peuperty is viilized in the arts in the manufactere of exteaess
a =a
EBULLITION. 259
"The evaporation is carried on in chambors kopt at temporaturos of
frou 80 to 140° F., the ale being continually renewed to carry off
the vapor ms fret ne formed.
2. Pressure. —Diminution of pressure facilitates evapora-
tion,
‘This prineiple has been wiilized in the arts for the concentration
<f syrups, This application is illustrated by the mothod of concen-
trating «yrups in sugar refining. The syrups are placod in lange
spherical boilers, froin which the air is extracted by reaus of alr-
pomps worked by steam.
3. Change of Air.—A continual change of the alr in con-
tact with the liquid facilitates evaporation, by carrying off
Wie vapor which would otherwise saturate the layer in contact
with the fquid, and effectually eheck the formation of nddi-
thonal vapor.
1; fs for this reason that the surfiee moisture of our fields ant
rodods disappears wore rapidly when there is 6 breeze than in calm
wather. In the arts, the principle is applied by keeping n current
of nie playing across the surface of the liquid to bo evaporated, by
means of blowers of atherwite,
As Kartent of the Liquid. —A large surface ia favorable to
rapid evaporation, by affording a great pumber of points
from which vapor may be formed,
‘This principle is orilized in the arts by employing shallow and
‘read evaporating pans This application is illustrated by the pro-
cous of snaking salt from seawater, ‘The water is spreul out in
Jange pans, which are very shallow, and then exposed to the influence
of the sun's rays, when the water slowly evaporates, leaving the salt
ia the form of erystals.
$17- Ebullition.— Evuturrox, or Hoiro, ts a rapid
evaporation, in whieh the vapor eseapes in the form of bub
Wes. The bubbles are formed in the interior of tho liquid,
‘ani, rising to the surface, they collapse, permitting the vapor
to aks into the sir.
Ts Ledting water, the first bubbles aro due to the small quantitie
of nit contained tn the liquid, whieh expand and tive to tan w-
ee
260 HEAT,
face. Afterwards, a the heat is kept op, particles of water are
converted into vapor and rise through the liquid, becoming eon-
densed by the colder lay
ors of water above them.
‘The formation and con-
doasing of these first
babbies eanee the sings
sng noticed in liquide be-
fore they begin to buil,
When all of the layers
become suitably heated,
the bubbles are uo long-
er condensed, bat rise to
the surface, and eseape
with = commotion that
wo eall boiling, ws shown
in Pig. 20).
Fig. 211
ters into ebullition at a ized temperature.
‘The temperature at which « liquid boils is called its Botling-
point, When the barometer stands at 30 inches, the botling-
point of pure water is 212° F.; the boiling-point of ether is
108 F; the boiling-point of alcohol is 174° P., and the boil-
ing-point of mercury is 660° P.
2. The pressure remaining the same, a Wqutd ecoinol be Rested
higher than the boiting-point.
For oxample, if water be heated to 212°, it will begin to
boil, and no matter how much may be applied, it will
continue to boil, but will never become hotter than 232°;
all the applied heat passes into the vapor and becomes
latent. It becomes latent, because it docs not beat either
the water or the steam above 21
EBULLITION. 261
318. Causes that modify the Boiling-Point of
Liquids.—The principal causes that influence the boiling-
point of liquids are: the presence of foreign bodies, varia
tions of pressure, anil the nature of the vessels in which the
boiling is effected.
Fig. 212
1, Presence of Foreign Bodies. — Matter in solution gener-
‘ally raises the point of a Liquid. Thus, a solution or
‘salt does not boil so readily ns pure water. If, however, the
body dissolved is more volatile than water, then the boiling-
point is lowored. Fatty matters combined with water mise
its Doiling-point. Honce it fs that boiling soup ix hotter
2. Variations of Pressure. — Increnso of poosanre Tain.
~—
262 HEAT,
and diminution of pressure depresses, the holling-point
When the pressure is great, the vapor, In order to escape,
must have a high tension, and this requires e high tem-
perature, When the pressure is stall, the reverse is the
case,
‘This principle may be illustrated by the apparatus shown tn Pig,
212. Te consists of a bell-glass, connected with an air-pump. Te
neath tho gliss isa vessel of water. If the air be exhausted from the
boll-glass, tho water enters into ebullition, even at ordinary teen pera~
tures, This ls because the pressure f dim!
If it is desirable to continue the ebullition for some time, a=
armangoweat must be inade to remove the vapor as fast ius formed
‘This can bo etfooted by placing a dish of sulphuric acid andor the
bell-glass, The acld absorbs the vapor with great avidity. Per
thermore, there is no incrosse of temperature in the water, but, em the
coutrary, the temperature eouthun.
ally falls, and the water may eves
De frozen.
“The influence of pressure on the
boiling-point can also be Hostrsted
by the following experiment. ‘Take
a tlask (Fig. 219), about half full
of water, expel the air by boiling,
and wheo the steam is ¢seaping
cork it
steam, by
the boiling
= it, the steam will bo comdemsed,
— 4 and, the pressure being remowed,
- the boiling will bogin agate, whieb
in its tuen will cease Hf hot water
> —— Se be poured overt
‘Tho height of « mogttals ens
be approximately ascertaknel hy
observing the diferencs between
the boiling-point at its summit and at its base. "The higher we
nountain, the less the pressure and tho lower the bolle
Fig.
neoend the
Ing-potut.
EBCLLITION. 263
8. Nature of the Vessel. — When the interior of the vessel
is rough, the projecting points form centres for developing
vapor, and the boiling-point is lower than when the surface is
smooth. Water boils at a lower temperature in an iron than
in a glass vessel. Tn fixing the boiling-point of thermome=
ters, a metallic vessel should always be employed to boil the
water in, On necount of the fret just mentioned.
319- Papin’s Digester. — When water is heated in opon
‘vessels, its termpernture cannot be raised beyond « certain limit, bur
fo closed weesels both the water and its vapor tay bo raised to very
high tomperatanes, 20 that the teasion of the vapor may reach several
‘Tho instrument employed to show this fact js eallod
Parny's Digester, #0 called because Pavix invented it for extract-
ing the nutriment from bones. ‘The high temperature dissolves the
gelatine.
At ix represented in Fig. 214,
and consists of w thick brane
passing
Vhroagh & strong fraroe. It is
shout two thirds filled with
By moving the weight, p, aloug the lever, wo
‘Tony Yary the force with whick tho valve, m, is kept in place.
‘tension of the vapor within the digester excreta Yow
204 HEAT.
weight exerted upon the valve by the lever, the valve will be foreed
open, and a portion of the steam will ossape with a whistling sound
Thiet indicates reat compress Tf the valve be left opon, the
tomperature can ouly be raised to 212°, and wo have the phonom-
ena of slinple boiling.
If water be heated in a well-corked bottle, the tension of the
vapor will finally cause the cork to spring from ite pkico with »
loud explosion, It fs the high tension of confined vapors that giver
rise to the oxplosion of steain-boilors, Hence the necessity of eon-
stmeting them of strong materials, and of providing them with
proper safety=valves.
320. Measure of the Elastic Force of Vapor. —
Darron measured the clastic force of watery vapor at every
temperature, from 32° F. up to 212° F.
Hie method, howe ix wanting in precision, bot Reoxacur,
with a more complicatod apparatus, obtained resulis of greater
wey
‘Two mothods havo been devised for determining the teasion of
por above 212°, one by Duroxe and Amago, fo 1830,
and the other by Ruoxaue, in 1864.
All the results that were reached prove that the tension Increases
vory mpidly with the temporature,
aqueous ¥:
321. Latent Heat of Vapors. — When a liquid beging
to boil, all the heat that is added enters into the vapor and
becomes latent. ‘The amount of heat that becomes latent is
ditforont for different liquids. It ia eallod the fatent heat of
oporization.
What was said about the term latent in the case of fiestom
may be repeated concerning vaportzation, namely, itis a con-
venient word to nse,
Tt was also stated that this heat was really expended in oom-
ferring potential eneryy upon the molecules, and performing the
y atoms inte new yrisitions. A. greater
is conferred upon the molecules im the
eof vapors; and more work is t be done, for besides the in
terior work of pulling apart the liquid molecules, there fie the exe
Interior work of mov
amount of potential ener
a. & al
LATENT HEAT, 265
ternal work of pashing back the atmosphere ro that the vapor can
expan,
Whon the heat i withdrawo, the molecules rush back again
to thelr former condition, with a Kinetle cucrgy equal to that em=
ployed in separating them. ‘The heat that was consumed now
reappears.
322. Latent Heat of Steam.— When the source of
beat is the same, it takes about 54 times as long to change
water into steam as to raise the same quantity of water from
the freezing to the boiling point, 180°. We find the latent
heat of steam to be 1805}, or 990°; that ix, it takes
64 times us much heat to convert any quantity of water into
steam as to raise the same quantity from 32° to 212°,
This may be verified by mixing Lb, of steam at 212° with 5} Ths.
of water at 32° The result is 6) lbs, of water at 212° The ex-
orient can be porfurmed by putting tho 1 Ib. of water into a flasks,
and connecting the flask by a tube with a beaker containing the
54 The Then ploco the flask over the spirit-lamp or gas-jet, oo
that the steam shall pase through the tube into the water. The
Intent heat of the steam is given out, when it is condensed, and raises
the temperature of the water to the boiling-polnt.
323- Examples of Cold produced by Heat becoming
Latent. — If few drops of ether be poured upon the hand and
‘allowod to evaporate, a eensation of cold will be felt. Tho ether in
evaponiting extracts the host from the hand, which becomes latent.
‘Damp linen foels cold when applied to tho body, beeaueo the mois-
‘tere in passing to a state of vapor extracts the animal heat, which,
entering the vapor, becomes latent.
‘Tho warm wind of sunmer is refreshing, because it eanses a more
mpid evaporation of the porspiration, which abstracts animal heat
from the body to. become latent in the vapor thns prodneed. ‘The
codlaess that reanlte from sprinkling the floor «f an apartment in
summer arises from the passage of hrat from a sensibly to a litent
state, in consequence ef the evaporation of the water. For the
Tike renson, a shower of rain is generally followed by n diminished
temperature,
‘Water may bo cooled by putting it in porows voasle A went
—
266 HEAT.
quantity escapes through the pores, and in evaporating mbstracte »
Portion ef heat from the remaining liquid, thus reducing ite tempers
ture. This ia the process of cooling water einployed in many Gop
eal countries.
324. Spheroidal State. —If a metallic disk he heated
red-hot, and a little water be dropped upon it, the liquid does
not wet the disk, but takes the form of a flattened globule,
and rotates rapidly about on the bettom,
As the disk cools, It reaches a point where the spheroidal
state cannot be maintained, and the water moistems the metal
and goes off instantly in a cloud of steam.
‘This pecaline action of tho water can be explaiued ax follows:
When it comes near the hor disk, steam is genenited beneath i,
which acts as a sort of cushion to keep it from the smetallie
surface.
That the globule of Liquid is not in contact with the vessel was
alearly proved by Boutiasy, He heated a silvor plate and pilseed
it in a horizontal position ; then dropped upon it» Tittle dark-eoloend
Whon tho wator assuried the spheroidal condition, tho Haewe
andle placed at a little distance could be distinetly seem Between
ate,
325. Congelation of Water and Mercury. — When
evaporation is rapidly increased, the absorption of heat is
proportionally fncreascd, and as it is taken from the sar
rounding objects, these are sometimos frozen. It has been
stated that water may be frozen under the reeelver of the mir
pump by absorbing the vapor as rapidly as it fs gencrated,
liquid more volatile than water, ®
greater degree of cold is produc By using salphorons
acid, which boils at 14° F., 2 sulficient degree of cold is pro-
duced to freeze mercury. ‘This is effected by sumounding »
thermometer bulb with cotton, saturated with sulpharous acid,
and then placing it under a receiver and exhausting the alr,
The rapid vaporization ubstracts so much boat from the mereery
that it freezes in a few minutes. If wo break the bull, The meres
is found in» solid mass, Tike'a leaden ballet. To this form mereary
By operating with
— |
SUMMARY. 207
can be drawn aut into sheets, or stamped like a coin; batit soon ab-
sorbe beat from neighboring bodies, and again passcs ts a liquid
state.
The tempernture of a liquid in the spheroidal state, explained in
Art. 324, is always below ite boiling-point. ‘This property has
deen applied by Bourioxy in frvczing water in a red-hot crucible.
He brated a platinnm disk ton bright redness, and placed a small
quantity of liquid sulphurous acid in it. "The ncid assumed the sphe-
roldal stare, and water dropped upon it wae instantly frozen.
By vwing Hiquid nitrogen protoxid teat of sulphurous acid,
rareniry enn be freaen.
‘The boiling-point of the protoxido is about —94° P,
Summary. —
Vaporization. .
Definition.
Volatile und Fixed Liquids.
Elastic Force of Vapors
Experiment.
Instantancows Evaporation in a Vacuum.
Experiment.
Limit of the Tension of Voy
Causes that accelerate Evaporation.
1. Temperature.
2 Preesum
B Change of Air,
4. Extent of tho Liquid.
Ebultition.
Definition.
Experiment.
Laws of Ebollition.
Camses that molify the Boiting-Point of Ligwids
J. Presence of Foreign Bodios.
2 Variations of Pressure.
Experinents,
3. Natare of the Vessel.
Papiata Digester.
Deseription and Cee.
Principle Mustrated.
HEAT.
Mensure of the Elastic Force of Vapor.
Dalton’s Method.
Rognanlt’s Method.
Latent Heat of Vapors,
Origin of the Term Latent.
Dotinition of Latent Heat,
Its Real Action on the Molecales.
Latent Heat of Steam.
Experiment,
Examples of Cold produced by Heat tecoming Latent.
Spheroidat State of Liquide,
Experiments.
Congelation of Water and Mercury.
Water by Sulphuric Acid in a Vacaumm.
Mercury by Liquid Sulphurous Acid ina Vaewnm,
Water by Liquid Sulphuroas Acid in the Spho-
roldal State,
Mercury by Liquid Nitrogen Protoxide in the
Spheroldal State.
SNOTION WI, — CONDENSATION OF GASES AND VAPORS. — SPROIFIO
MEAT. — SOURCES OF HEAT AND COLD,
326. Causes of Condensation. — The Coxprxsiniox of
a vapor is its change from a vaporous to a liquid state. This
change of state may arise from chemical aclion, pressure, Or
diminution of temperature,
1, Chemical Action. —The affinity of certain substances
for the vapor of water is so strong that they absorb it from
the air, even when the latter is not saturated ; sue, for ex-
ample, are quick-lime, potash, sulphuric seid, and many
others, When placed in a closed space, they in a short
time abstract all the moisture that is in it,
2. Pressure, —If a closed cylinder be filled with yapor, and
this be compressed by a piston, 96 600 a8 the space occupied
CONDENSATION, 269
by the vapor is eaturated it will begin to condense, and if the
pressure be continned all the vapor will be reduced to the
liquid state,
Tatil the space becomes saturated, the pressure must be contion-
ally incroased on account of the augmentod tousion of the vapor; but
after liquiftetion begins v6 farther augmentation of tension twkes
place, and the preaure mquired to complete tho liquefuetion remains
uniform.
3. Diminution of Temperature. —When the tempernture of
‘ny space is diminished, the amount o° vapor required for
saturation is diminished. After the point of saturation is
_ reached, any further diminution of temperature causes a de-
posit of the vapor in a liquid form,
Stoam is colorless, but when allowed to eseape into the eold air,
condensation takes place in the form ef drops, which become visible,
Por the same reason, the moisture contained in the breath beeomos
visible in cold weather.
In winter tho las of onr windows often becomes coated with
drops Whe dow. ‘This arises frum the fact that the glass is colder
than the sir of the room, and thus acts continually to produce oon-
densation of the vapor in the air. If the difforence of temperature is
sufficient, the particles of vapor are frozen as they are deposited, pro-
i eryetallizations. When the external air is warmer
than that within, the deposit takes place on the outside of the glass.
If & veswol of cold water be placed in a warn room, a deposition of
midistiire takes plice on its extorior surface.
327. Heat developed by Condensation. — When a
Tiquid passes to a state of vapor, a great quantity of heat Is
absorbed from neighboring bodies, and becomes latent.
When the vapor returns to a liquid state, an equal amount of
heat 1s given out und becomes capable of affecting our senses ;
in other words, it becomes sensible.
328. Heating by Steam. — Buildings are heated by
means of steam conveyed from « boiler in the lower story,
through iron pipes im the walls. The steam, by ite beak and
———
270 BEAT:
by the heat given out on condensation, serves to warm the
apartments through which it isanade to pass To this end,
coils of pipes are placed in the rooms to be warmed.
329. Distillation. — Dieriiation is the process of sep
arating liquids from each other by means of bent. .
‘The most volatile of the liquids. is most ensily evaporated,
and its vapor is then condensed. ‘The heat should be kept
above the boiling-point of the liquid that we wish to obtein,
Fig. 216,
hut below that which we wish to leave behind. "The boiling.
point of alcohol bein and that of water 212°, if a
mixture of alcohol and water be heated np to some temperi=
ture between these Limits, the alcohol will all be vapartzed,
whilst most of the water will a behind,
330. Method of Distillation.—An Axsarmc, or Still,
fy an apparatus for distillation.
The most usual form of an alembie is represented: tn
Fig. 215. It ix composed of « boiler, 4, with a cover, #
el
LIQUEFACTION OF GASES. 21
called the dome. From the top of the dome a metallic tube,
Cy passes: into a vessel, S, called the condenser, and Is then
ten to a leat or ‘This tube is called the worm, and after
passing through the condonser, 5, it leads to a receiver, D.
‘The condenser, S, is kept fall of cold water hy an arrange-
ment shown in the figure.
‘The wabstance to be fistilled is placed in A, and a suitable
heat is then applied, The more volatile portion ix converted
into vapor, rises into the dome, and, passing through the
worm, is condensed, and escapes in a liquid form into the
receiver, D.
Wine ia composed of water, alcohol, and a coloring matter, 1
this Hiqeid be placed in tho alembic und heated to any temperature
between 1747 and 212°, the alcohol is separated from the other in-
portion of water is evapurated, the aleuhal thus
and will require to be distilled agnin, At eoch
“strength is inerrused, bat no sinount of distillation ean
pure,
, pure water may be obtained from the brine of the
wc welle and springs,
faction of Gases. — All of the gases have
either by preesure alone, or hy a combination
h a diminution of temperature. An immense
had by utilizing the tension of the gases
therwelven by generating large quantities in confned
et ftlerenting examples of tho liquelacthm of gas
a togue For this purpose two very strong cylinders are
both being hermetically eealed, and communicating
of these eslinders is the generator, and the other the
‘Benenitar aro placed the ingredionte necessary to
‘avid, watally Licarbonate of soda and sulphuric
ps carefully closed, these materials are brought
=_ onde
272 HEAT.
avd, being unable to expand, its tension becomes so great that a
portion ix condensed ioto « liquid form, The tension, at the temper
ature of 60° F., is equal to 50 atmospheres, or 730 ths. on eseh
squaro inch. Ae tho use of this apparatus is attended with danger,
it haa come into genera) disfavor,
Another mothod is to draw the gue by a condensing-pump from a
generator and to force it into « receiver.
Aftor liquefaction has coased, if a atopeock be tured so ax te
allow & part of the confined gus to escape, a portion of the Kiet
acid poeses to a state of vapor with immense rapidity, and im doing
80, absorbs so much hext from the remaining portion as tor freee it.
‘The frozen acid ie thrown out by the gasoous fot in flakes Hike mow.
Tt in very white, and so cold as to freeze mercury instantly Te
ovaporates very slowly, and when tested with a spirit thermometer,
its temperature is found to be 106° below the 0 of Panntormer's
thermometer,
If the solid acid be mixed with ether, it changes into a
vapor rapidly, and intense cold is the result. If the mix-
tare be placed under the reeeiver of an ainpump, the evapo-
ration is more rapid, and greater cold is produced.
AMADAY obtained a tomperatore in this way of 166° FA
perature of —220° F, was obtained by Narremen by svapo-
rating under the exhansted rooeiver a mixture of Bismlphide of ear
bon and liquid nitrogen proteside.
My powerful and Ingenious appliances all the gases hawe been
liquefied, but a detailed description of the apparatus cannot be given
here.
332. Specific Heat of Solids and Liquids. — Experi-
ment shows that different bodies reqaire different amounts
of heat to elevate their temperatures through the same nem-
ber of degrees.
Tf equal weights of water, iron, and mercury have the same
amount of heat communicated to them, the mercury will be
most heated, the iron next, and the water least of all,
When heated to a certain temperature, water absorbs ten
tas iron, and thirty-three times as much
times as much hea
— 4
i
_ as
oT4 HEAT,
is contained in 115, which gives we a reeult, 083 of por tnik.
‘This decimal expresses the specific hewt of mercury. ‘This imethed is
simple and reasonably accurate, if proper exre be aaod.
335- Method by Melting Ice. —In this method the
bodies to be experimented upon are taken of equal weights,
brought to a standard temperature, say 212° F,, amd thea
brought into contact with ice. The amount of tee melted
makes known the quantity of heat given off by the bodies in
passing from 212° to $2*, from which the relative specific
heats may be determined.
An instrument called the calorimeter (Fig. 216) is used in
this method. / contains the heated body, 4 the fee to be
melted, D the outlet for the water of the
melted ice, Tce is also placed at 2 to
prevent the heat of the airdrom melting
the ice at A. There is an outlet at & for
tho water which comes from the Hquefine~
tion of the feo In B, We can tell how
much ice is melted by the different bodies
by measuring the respective quantities of
water that ran off at 2.
Tr will be found that equal weights of from,
culphur, and mercury will melt, respectively, $4.
and gly as mnuch leo as tho sumne weight of water.
Calling the specific heat of water touily, these
fractions oxpress the specific heat of the substances: JBither of thes
methods may be aves fo find the specific heat of solids and Tquite
ts of different substances differ wory widely
clearly seen from the following experiment.
‘Toko five bails of cual weights, made of iron, tim, eopper, lea, asd
Viewuth. Heat them to the same tesnpenstury, say 00°F. 3 thew:
place them (Pig. 217) on a disk of wax. Every ball gives sp somo
ef Its heat to the wax, cuusing it to elt.
The iron goes through the disk fleet, the copper next, then the tin,
while the Jend and bismath are slower Sn their notion, maid will re
tnain in the sheet of wax unless very thin
Big. 206.
‘That the spe
from one another ean
SPECIFIC HEAT. 278
336. Specific Heat of Gases ix determined by puxs-
ing a current of gas at a given temperature through o spiral
glace tabe placed in water. By noting the increase of tom-
perature of the water, and knowing also the weight of the
gas and the temperature to which it has been cooled, its spe-
eille beat can be calculated by a process similar to that given
onler the method of mixtures.
The same body has in the Hauid state w greater specific heat than
im the polid or gaseous, Thue, for instance, the +pocitic heat of water
is double that of ice aud more than double that of steain.
Fig. 217.
Hydrogen is the only known substance that has greater specific
heat than water.
"The following tables ehow the specific heat of « fow of the moxt
Snportant substances, water being represented by unity.
‘The uumbers express the averago values for temperatures between
2° and 112° F,
TABLE FOR SOLIDS,
‘Specie Hest. | Submtane. | Space Moat
7 |) Silver. , ost
AU) Platinum . one
06 1. ae i
005 Lead ss At
2 Antimony 080
a) Sulphur . on
276
| Satwetance,
Alcohol... -
Benzine . -
Mercury. -
‘Substance, ‘Specific Heat, Bubetanes,, ‘Specie Hear.
Hydrogen Steam. 2... a0
Nitrogen... Al. Di Spel ST
Oxyien aa
4937. Sources of Heat. — The principal sources of beat
are: the sun, electricity, combustion by chemical combination,
pressure anil percussion, and friction.
1. The Sun. —The sun is the most abundant source of
heat. We are ignorant of the cause of heat in the sun's
rays.
Je has been computed that the heat roecived from the wan By the
earth in w year ix sufficient to melt a In
entire globe, and 100 feet in thieknone
distance of the earth from the san, and ite comparatively small siae,
it can receive only tho minutest portion of the heat which the ean
radintes in all directions.
2. Blectricity.—The subject of heat due to electricity will
be treated of under the heud of Electricity,
- Combustion by Chemicel Combin
hinations are generally accompanied: by
heat. When they take place slowly, the heat is inappreeiable :
but when they take place rapidly, there is often prodticed an
intense heat, and sometimes a development of light,
‘ombustion is one form of chemical combination ‘The forma of
he combustion exhibited in our Sreplaces awd on loge te a combine:
id a sal
SOURCES OF HEAT. 217
‘tiem of the carbon and hydrogen of the wood nnd oil with tho oxygen
cf the sir. The produets of soch forms of combustion are watery va
por, Gerbonle acid, with gases and volatile products that appear under
the form of smoke. Combustion i a decomposition of certain sab-
stances, accompanied by « composition of new products. In this
change no element is lost, simply a ehange of form takes place,
‘The Hame produced in combustion is a mixture of gaseous and
‘volatile matters, heated red-hot by the beat disengaged in the procoss
cof combnetion.
‘The process of respiration is a specios of slow cabustion, fn which
the earbon and other watter of the blood unites with the oxygen of
the air. This species of combustion gives riss to the het of the
body of men and animals. This heat is called animal heat,
Fermentation is a chemical process thit gives rise tu heat.
4. Pressure and Perewssion. —Whenever a body is com-
pressed (Fig. 218), the heat
generated fs sufficient to set
fire to inflammable bodies.
Percussion ia a source of
Fig. 28,
i ail
278 HEAT.
body offers to another when they are rubbed together. ‘This
resistance is necompanied with & great development of beat
In this way many savage tribes procure fire, by revolving the
end of one piece of dry wood in the cavity of another.
Pieces of ice, when rubbed together, genemte heat enough to
melt them, In machinery, the friction on axles often sets
them on fire, especially when lubrication has been neglected.
‘The development of heat by friction can be strikingly shaven with
the apparatus devised by Tyndall,
Fig. 219,
‘A brass tube, about 7 inches in length and 9 of an fueh in dinmee=
ter, Is nearly filled with water and corked. ‘This is atlashod fo «
whinli Jo, ax represented in Fig, 219. When the tube ts
rotated rapidly and pressed with a wooden clamp, the frietion ppro-
duced heats the water in a few minntes te the boiling-pelnt, and the
cork &s driveu out by the atestn
338- Sources of Cold. —The principal sources of vold
are: fusion, vaporization, expansion of gases, and radiation of
beat.
1. Fusion. — When « body melts, it absorbs heat from the
snrrounding bodies, which becomes latent in the melted
body.
280 HEAT.
Definition of Speesfic Heat.
Illustration.
Methods of ascertaining the Specijie Heat off Trades
1, Method of Mixtur,
Mustration and Experinem.
2 Method by Melting Ice.
Mlustration.
Method of showing Relatiee Specific Heat,
Exporimout.
Specific Heat of Gases.
Experiment.
Tables showing Relative Specific Heat
Of Solids.
Of Liquid.
Of Gases.
Sources of Heat.
1, The Suu.
2 Electricity
3% Combustion by Chemical Combination.
4. Proesure and Pereussion,
5. Friction,
Experimont illustrating Heat by Friction,
Sources of Cold.
1. Fuslov.
2. Vaporization.
4. Expansion of Gases,
0
|
ation,
SECTION VIL, —~ THERMO DENAMICS,
339. Definition of Thermo.dynamics.— The selonce
which treats of the connection between heat and the mechanl-
cal work it can perform,
nd determines, by means of sium=
bers, the relation between the qnantity of heat supplied and
the quantity of work done, Is called Thermoedymanvies.
340. Conservation of Energy. — Knengy, as previously
defined, is the power of doing work, and com
THERMO-DYNAMICS. 281
types. Kinetic and potential. ‘Ther ean be no destruction or
creation of energy, in uny of its varied forms, by any means
at our command.
As the quantity of matter in the universe is invariable, so is the
quastity of onergy. Neither can be annihilated. Heat, we have
seon, isn form of ouergy. If pat out of existence cs heot,
appears iu some other form of energy; but the energy itself, the
power «f doing sowe Wind of work, of everouiing some kind of
resistance, remains anditaluisher.
Fig, 220,
The prineiple of the conservation of energy when appiled
to hoat i commonly called the First Law of Thermo-dynam-
tes, which may be stated ae follows: Whew how! fe transformed
fnto work, or work tuto heat, the quantity of heat ts equivalent
te the quantity of work,
34%, Mechanical Equivalent of Heat. —The law
giver! in the last article was established in a large measure
hy the following experiment of Jour,
The we wed by iin coneinted Vruss paddlo-welheel
(Pig: 220), furaistied with eight sets of revolving arms worklag
Tretineon four seta of stationary vane. The vanes, FV‘, are ween in
‘tho eulangod seetion at the left; alse the yuulilos, PY
=—
282 HEAT.
‘Theso parts of the apparatus are enclosed in a cylindrical copper
or brass vessel, B, which is filled with water The vanes prevert
1 wator from being carried round bodily in the direction of rotates.
‘Tho descent of the weight, W, causes the paddles to turn hy means
uf'the eon, 7
The friction of the pales against the water raises its teupers
ture, which is measured by the thermometer, & Tt was Sout
JovLe with this machine that the quantity of heat which would raise
une pound of water LY P. is exuotly what wowkl be produced fa
pound weight, after having fallen through u height of 772 feet, Ras
ita rootion arrested hy collision with the earth ‘The same offvet
would be produced by 772 pounds falling oue foot.
Conversely, the amount pf heat necessary to raise a pound of wa-
ter 1° would, if it could be all otilized, be enpable of raising a poured
weight 772 feet high, or 772 pounds one foot high,
Now, the foree nseeseary to raise une pound ono foot is culled «
Joot-pound. "Then 772 foot-pounls are equivalent to due enit of
heat, Physicists now eall 772 foot-pounda the meckanical equivalent
the experiment with othor liquids, and by using a
swonller apparatus sith an iron paddle-wheel revolving in serury,
Jove obtainest results similar te thove whero water was mad
342. Transformation of Energy. — The great charac-
teristic of energy Is its capability of being, a¥ a general rule,
readily transformed, and yet. in all its transformations, the
quantity present remaining precisely the ame,
We ean explain this jirinciple beat by examples. "The sndtion of
r when brought dows upon a plece of metal is changed:
in ; and could we gather ap the heat produced by the shock
of the hamtmer, and apply it without loss, it would Wf It te the
height from which it fell
Pouring mereory from ane cup to another raises fix tethyperitiine,
"The water at the tae ef n cataract hos « higher temperatsre than
that at the top. ‘Tho heat is these two Instunees Is generated by thet
oy of the mercury wad water, and the feletion of thelr
ast the alr. When a train of cam Is stopped the
ls changed into bent. A ballet going thromgh the alr te
warmnad by frietion. If the narth’s motion should be suddenly ire
jp frase heat would be devcloped.
the bamn
arrested 0
m0 y
=
THERMO-DYNAMICS, 283
We have on exsinple of the conversion of heat into me-
chanical energy in the case of the steam-engine. The leat
changes the water Into steam, and this, by means of the ex-
pansive force it also receives from the beat moves a piston.
We bave here a change of invisiblo molecular motion to
visible motion of the mass.
‘Pho heat produced in the body by the various changes the ful
undergoes, Jt digestion and assiuilation, is expended io muscular
‘The heat energy of the sunbeam is stored mp in coal in the form
of petoutial energy.
‘We might rnultiply examples indefinitely if there were space fur
further Ulastration of tho principle.
343. Dissipation of Energy. — We find it a compara-
tively easy matter to convert mechanical energy into heat,
Dut we cannot get all the heat back again into work. During
the process of converting heat into mechanical effect, there is
always a transfer of a large quantity from a body of a bigher
to one of a lower temperature, without any work being
done,
‘Take, for instance, the stenm-engine. Some ef tho heat, tt i
true, is doing urefial work in conferring expansive power upon the
steam; but a lange portion of tis lost, s0 far us conversion inty mn=
chanteal energy is concerted, in heatlug the mnuchivery aul by radia~
tion into the air,
‘Tt & Aalmed that meehunical energy is changing more and more
into Heat, and that all bodies will, by conduction and nidintion of
this heats eventually acquire the same temperature.
‘And since we cannot get any work ont of heat unless we have
belies of differeut temperatures —for hont passes frow hotter to colder
substances, — thorefore, when the whole univers has
temperature, all forms of lifo and snotion will ecase, and the «
will be no longer babitable by man. Al! the energy that exists
he in the form ef diffused heat. This principle, ealled Diesipsition,
OF Diffusion, of Koorgy, wax first pointed out by Sir Winnsase
‘Puomson.
—
284 HEAT.
344 The Steam-Engine. — A Steam-Exorxe 1s a com-
bination of pleces for utilizing the expansive foree of steam
and converting it into a motive power.
Tt consists essentially of two parts: first, the boiler, in
which the steam is generated ; secondly, the eylinder, where
the expansive force of the steam is applied.
345. The Power of Steam. —Lot 4B (Pig. 271) reqar-
seut n gliss tabe of auiform bore, and C, a piston, fitting it steam
tight, and suppose a little water to be in the tube
below the piston. If heat be spplied to the bution:
yy Of the tube by means of a spirit-lainp, the water
will be converted into steam, and the pe
be driven to the top of the tabe, If the lamp be
removed, and the tube allowed to eoul, the steam
will be eondensed, und the pressing of the stance
phere will drive the piston back to its original posi~
tion. By ngain applying heat, and withdrawing it,
the operation may bo ropesiod inl at Sa
This simplo experiment involves the fundamental
idea of the steamn-engine.
Pig. 231 Under the ordinary pressure of the atineephers, a
cuble inch of water gives 1,700 cubic inches, or nearly a euble foot,
of stein. In this ease the expansive force of the stenm is im equilib=
rum with the pressure of the atimoephers, and it is said to have =
fensiow of 15 pounds te the sqaam inch, 1f enbie inch Of water te
vonrerted into steain, under a prossure of two atmosphenisy & gall
yield bat 850 cabic inches of steam, bat the fensiou will sow be 30
pounils te the ine
In general, the volume of steam yleldod by a given volame ef wa-
ter varies inversely as the pressure under whieh it is generated, and
in all cases the fension of the steam ix equal to this presume. Th
round numbers, we inay say that the conversioe af a cable find of
water into steam produce a quantity of work saleiont to Faken a
weight of one ton through a height of ove forte
346. Varicties of Steam-Engine. — Steam-engines inay
bo cither condensing ov now-comdensing. Tn tho former, the
steam, after having acted upon the piston, is condensed, anil
em |
2
THERMO-DYNAMICS. 285
the warm water returned to the boiler; in the latter, the steam
is not condensed, but, after haying acted upon the piston, is
blown off into the air, In condensing engines steam may
bo, and often is, used of a lower tension than 15 pounds to
the Inch, in which case the cugines are culled fow-pressure en~
gives. In non-condensing engines steam is always nsed of a
tension greater than 15 pounds to the inch, and the engines
are then called high-pressure engines.
Condeaxing engines are more economical of fuel, but ane heavier
and tnoge complex in their eoustruction. Hence they are generally
need as stationary engines. Non-condensiug engines are used for
locomotives, anil where fuel is ebeup aro often employed as stationary
sugrace.
‘The effdency of a stoarn-engine is moasared in tenna of a unit
called a horse-power, that is, a force which is capable of raising a
swelght of 33.000 pounds through a height of ane foot in one minute.
‘Thes, an engine that exn perform a work equivalent to raising 33,000
poowls through 10 foot in one minute is eaid to bo an engine of 10
347. Boilers and their Appendages. —The Boren is
a shell of metal, generally of wrought iron, but sometimes of
copper, in which steam is generated.
Boilers arm made of varions shapes. One of the simplest has the
form of n eylinder with ronnded ends. Sometimes two smaller oyl-
inders, also with manded enils, called heaters, are placed below tho
mak shell, and coanceted with it by suitable pipes Tho object of
‘Vhls arrangement bs to increase the heating surface. Iu the Cornish
boiler the oylindrieal shel! ine a large flue passing throngh it, eou-
talulng an intornal farnace. Somotimes two such flues oxist. The
tubular boiler bas a great number of tubes, or tlacs, piaesing through
it, for transmitting the flame and heated gases from the furnace.
‘The boiler and ite appendaxes are variously arranged in different
eaxines, the olject in all cuss Wing to obtain the greatest amountet
stearh With & given quantity of fuel. In stationary engines the furnaen
is usually made of brick of tome other bad conductor of heat, and the
‘thoes are so arranged as to being the Name and heated gosee va exact
=
286 HEAT:
with as large a portion of the boiler us porwible. In locomotive ex
tines the flre-box is made of boiler-iron, and is so comstractesk that it
is nearly eurrounded by the water in the boiler.
Fig. 222 represents a side view, and Fig. 223 cross
section of a cylindrical boiler with the heaters attached, such
as are used for stationary engines.
‘These heaters, indicated in the figure by 20, are filled with
watcr, and conuseted with the boiler by the tbes, PP, while the
is only about half full.
‘Tho flame of the farnace, ¢, plays dincetly against the heaters;
the heated gases and smoke are sutarned under the soain cylinder
in the flue, O (Fig. 223), and finally discharged into the ebiinner
through the sido dues, 2. The hext is thus atilited toa greater
extent.
The principal appendages of the boiler are the following, as rep
resentéd in Fig. 222,
Furnace, or fireph
The alarny-whisth ro arranged as to bo operied by the feat, f,
when the level of the water falls too low.
Anothor kind of indicator of the level of the water im the Daler i
repevsented at f" Tt consists of a float connected with a tommters
poise by a wire jeseing over a pulley, nnd through « pmekiags iene in
the top of the boiler, The position of the coanterpaise fells tee
height of the water
Still ancther indicator, which is sometines wed, it seen atay Tt
bg ad
THERMO-DYNAMICS, 287
oonaiste of « thick glass tubo, beat wrice at right angles, the lower
end belng ander the water and the upperend above. ‘The water will
stand mt the eaxne Iovel in the tube as in the boiler.
P represents the safoty-valve (see Art. 319),
©, the pipe that conducts the steam to the stearn-chest.
1, the pipe for the admission of feod-wator to the boiler; it reaches
nearly te the bottom.
A, the inag-hole, an aperture by which the boiler can be repaired
and ebeansed.
LR, tho dampor to regulate the draught.
©, the fluo leading t the chimney. The chimney is uxunlly of
great height, so as to secure « goud draught.
348. The Manometer.— The Maxomerrr, or pressure-
gauge, for measuring the tension of steam in the boiler, i
not shown in the figure.
‘These are not all based upon the
same principle. Some are simply
siphon barometers whose long branch
fs open, the short branch connecting
directly with the boller, ‘The steam
from the boiler forces the mercury
up the long branch, and the highcr
the colume the greater the pressure
of steam.
‘This manometer, which is called
the open manometer, answers well
enough for low pressures; but for
higiv ones the length of tube neces-
sary renders it very inconvenient,
‘The closed manometer is shown
in Fig, 224, and differs from the one
Just deseribed in having its vertical
tube closed at the top. It is gradu-
ated on the principle enunciated in
Maniorm’s law.
Fig. 234.
‘Whion the pressure fn the boiler is one atmosphere, the wereury
a
288 NEAT,
in the cistern and tabe are ot the game level, the tension off the
steam and the elastic force of the air just balancing eel: other.
When the premsure becomes two, three, four, ete, atmospheres, the
air in the closed tube will oveupy one half, one third, ome fourth,
éto,, tho space it did bofore, allowance being made for tho weighs of
the merenry which is forced op Inte the tube. The instrument
having been gradoated, its ase is evident. When it ie desired te
uscertain the tension of the steam in the bedler, the cock i+ turned,
und the height to which the mercury asqerde in the tobe indleatos
the tension in atmospheres. Any number of eubdivisions may be
anade in either of the two manometers described,
The lability of glass tubes to break, and to lose thele trans-
paroney by the merenry clinging to their sides, rondens them scene-
what objectionable, ‘They ure not adapted, either, to tachines ia
motion.
‘The cheapness of metallic manometers has caused them to
bo nsed for a great number of boilers, We
only the one
this: If we allow the
from the boiler bs!
will tend to uncoil it, Shut
off the steam, and the tale,
by virtue of its elasticity, re
sumos ita original position.
Pig. 223 repesents soe
manometer. One end ef the
Fig. 235 tube is connected with a pipe
loading to the boilers to the
other ond is attached a steel vecdle, whieh traverses a seule. As the
coils, and the h
When the yroesare removed the needle retume to its former
pesitiens
i ail
THERMO-DYN AMICS. 280
249. Mechanism of the Condensing Engine. —
‘The essential parts of a condensing engine are shown in
Fig. 226, The figare is only intended to illustrate the prin-
Giples of the engine, and, for the purpose of illustration, the
parts ane arranged In such « manner ws will best exhibit them
ata single view.
‘The principal parts of the condensit
‘The cylinder, shows ov the left, with a portion broken away.
‘The piaton, P, which receives the action of the steam, alternates
engine are the
290 HEAT.
‘on its apper and lower fies, and ie thereby moved ap and down ia
tho cylinder.
The steam-cheat, 6, into which tho steam foom the boiler enters
Hirongh the stzam-pipe ato, and from which it passes thremgh the
iteam-passages, alterautely to the upper and lower enda of the
eylinder.
Tho slidting-ralre, moved up and down by tho red, m,
alternately opens a communication between the stoaui-chest aed
the two steun-paseauyges Jeading to the top aud bottian of the
eylinter.
‘The eduction-pipe, U; connecting with the eylinder at @, by which
the steaus, after having acted upon the piston, i+ coudiucted inte the
conslenser, On
‘The piston-rod, A, working through « packing-loe, a, which
transits the inotion of the piston to the working-beam, Za
"Tho parallel bars, DD, aus the radial bars, CE, whitch Ioeep the
plston-rod from pressing against the sido of the packingslas, ‘This
armngement is called Watt's paralle! motion,
Tho connecting-rod, I, whieh transmits the wotion of the workitgy-
‘beam to the crank-arm, K, and through it imparts @ motion of
ion to the #haft of the engine,
The ply-wheel, V, which obviates to & corlain extent the itera
larities of motion in the engine,
When the eraok is at ite highest or lowest position the steam has
ho power to move it. In either of these positions, ealled the ead
points, the suchine would come to rest if it were mot for the sy-
wheel, whieh, by its tnortin, curries the pleton and crank over these
points, and brings them again under the power of the steam. "The
steamboat aud locomotive need no fly-wheel, inanueh as the iner-
tia of the moving inaxs suffices
‘The eccentric, « which, acting like » eran, produces » baeleward
and forward wotion in the connecting-rod, Z, “This rod, meting om
tho ew! lecer, ¥, cwuses tho rod, om, of the sliding-valve, to anave my
and down.
The cold-rater pump, I,
water from a
wked by the rod, HZ, whieh dws cold
ss it through the pipe, 7 fute the
‘Thia pips, terminating within the condenser fm nese,
the water in the form of a shower, and condenses the
servuir, and fo
THERMO-DYNAMICS. 291
‘The air-pump, M, worked by the rd, F, which draws the hot
water and tho air that te mized with it from the condenser, and forces
it imto the hot well, NW.
‘Tho feed-pump, Q, worked by the rod, G, which dnuwes the water
frow the hot well and forces it into the boiler.
To explain the action of the engine, let the position of the parte
bo as represented in the figure, ‘The steam catering the steam-chest
finds the oppor passage open, and, flowing through It, acts upon the
apper face of the piston and drives it to the bottom nf the eylinder,
‘The steam below the piston meanwhile flows through the lawor pause
sage, and, entering the eduction-pipe at a, is conveyed to the eon-
denser, where it is condensed, When the piston reaches the bottom
of tho cylinder, the cecontelc acts upon the bent lever 10 open the
lower and close the upper passage. “Tho steain from the stenta-ahest
cow flows through the lower passage, and, acting upon the lower
{hee of the piston, forces it to the top af the cylinder. Meantime the
steam above the piston, flowing down the upper passage, enters the
‘eluetion-pipe, aud is conveyed to the condenser. When the piston
reaches the top of the eylinder, the eccentric again acts to change the
position of the sliding-malve, and thus the motion of the piston. is
continued indefinitely,
350. The Governor.—J1n many engines the supply of
steam to the cylinder is regulated by an apparatus called the
goversor. One form of this contrivance is shown in Fig. 227.
A Bis a vertical axis, connocted with the machine noar its worle-
fog point, and revolving with a velocity proporsional to that of the
working point; FE und GD aro anus
tarning with the axis, and Dearing heavy
halls, D and KH, at their oxtremities; the
Arms are atiached by hinge-joints at @ and
Ft two bars, CG and CF, and these bare
are counceted by hinge-joints with the axis
at @, The arins, PE and GD, sre also con-
nected by hinge-joints with a ring, 2, which
ta free 10 slide nprand down the asic, AF
Whew the axis revelves, the centrifuzal
force developed in the halle causes them w- Fig. 227.
recede from A 2, and depresses tho ring, H. "This cases Yao Weven,
Mle
.
202 HEAT.
BK, to turn about its falernm, A, and when the velosity has become
sulliciently great, the lever uperates to close « valve and slut off the
motive power. When the velocity again diminishes, the Dalle ap-
preweh the axis, the ring, d, rises, and the valve is opened. The
governor may be adjusted so x8 to seoure any desirable webosity at
the working point.
351. Action of the Eccentric. — The automatic move:
ment of the sliding-valve by means of the eccentric needs a
more detailed explanation than is given in the preceding
article,
‘Tho eecontric (Fig. 228) consists of 1 cirealar piece af metal, 6 60
attuched to the shaft of the engine that Sts contre does mot coincite
with the axis of rotation.
‘The cecentric fy surrounded with w ring of metal which does set
rotite, but fullows the motion of the eecontrle, themby receiving a
Fig. 298,
motion back and forth in a horisontal direction. "This movement ix
transtnitied by the arp, Z; to the bent lever, ab ¢, casing it te tire
about the point, b. ‘This rotation of the lever ralees aud Towers
ly the rod, d, which is connected with the sliding-wales >
upicard and downward motion is slay ieoparted to thie
alternate
thus
valve.
352. The Locomotive. — Fig. 220 represents & seetion af
comotive, the principal paris of whieh are the followltige: —
Tho boiler, BB, with ite flues, pp, and safely-ralee, A The
dotted Tine represents the height of the water in tho boller,
The fire-bor, A, communienting with the smoke-box, OC hy meate
of the flues, pp. ‘The fire-box has a doable wall, the interval beling
filled with water and communicating with the boiler. Avis the grata,
and D) the door for the supply of fuel.
onveys the
The steam-pipe, S
tron the stemae—doue ts
THEBMO-DYNAMICS.
204 HEAT.
the steam-chest. It may bo closed by « valve, F, worked ly a
lever, L.
‘The steam-dome is an olevated portion of the boiler, thie object of
which ix to permit the steam to enter the taum-pipe without any
admixture of water, as might be the eat wore the steam taken from
4 Iewer level
The cylinder, the piston, P, and the piston-rodl, J, aro similar t
the corresponding parts af the condensing engine.
The blast-pipe, Zi, through which the steam in blown off afver
having acted upon the piston, terminates in the swoke-bax, and the
Dlaet of stoain from it serves 0 inereaze the draftof air through the
flues, and thng promotes the combustion of fuel.
The connecting-rod, G, trangmits tho motion of the piston to
the erank-arm, by means of which a rouuy motion ts linparted to
of the locomotive,
the driving-whe
The
the sam
anner in which steam act to impeurt motion to the piston is
tho ongine ulroady doseribed.
Summary. —
Thermo-dynamice.
Definition,
Consercation of Energy.
Explanation
First Law of Thermo-
Mechanical Equivalent of Heat.
Description of Joule's Apparntus
Modo of Oper
Results of th
Transformation of Energy,
Mastration by Exwumples
Dissipation of Ewergy.
Experiment,
Explanation,
Mlustration.
Possible Results of Dissipation.
The Steam-Engine.
Definition.
The Power of Steam
Mlnstration by Experiment.
Varieties of Steaw-Engines,
mdensing and Nou-condensing.
Definition,
HYGROMETRY. 295
Boilers awd their A ppondages.
Boilers of varias Shapes.
Boiler, with Appondages, of Stationary Eupine, il-
fustrated by Figure.
‘Open Manornetor.
Closed Manometer,
Bourdon’s Manometer.
Mechaniom of the Condensing Engine.
Mlostrated by Figure.
The Governor,
Hloscrated by Figure.
The Locomotive,
Diustration of the Principal Parta by Figure.
SDCTION IX. — BYGROMETRY. — Itaty. — rw, — WrxDs, —
SIGNAL sHVICR.
383: Hygrometry. —Hyrcnownrny is the process of
measuring the amount of moisture in the air with Teepect to
the amount necessary to saturate it.
When a given space has taken all of the vapor that it can
contain, it is said to be sutwrated. For example, if water be
poured into a bottle filled with dry air, and the bottle be her
metically sealed, 2 slow evaporation will go on until the ten-
slon of the vapor given off is equal to the tendency of the
remaining water to pass info vapor, when it will cease. In
this ense the space within the bottle is sutursted.
Tf the temperature varies, the amount of vapor required to saturate
given space will vary also. The higher the temperature, the
greater will be the quantity of vapor req to saturate the given
‘space; amd the lower tho temperature, the
for saturation.
‘The quantity of watery sper in the atmosphere varies with the
woasoms, temperature, climate, wait different, local causes; but not-
withstanding tho eontinaot evaporating that is taking place from
lakes, rivers, and oceseis, the air in the lower reginws of Oye sascuee
Ue
jess the quantity required
a
296 HEAT.
phore is never saturated. The reason is, that the vapor, being Tne
dense than the air at the surface, rises inte the higher regions, whew
it is condensed by the greater oold existing ther, and falls to the
earth in tho form of rain.
‘The object of hygrometry i« not to devermise the ahsolute amaurt
of moisture in the attwosphore, but simply to find out ite degree uf
saturation, or, in other words, its hremidity. When the air is eom-
pletely saturated, its humidity is suid to be 100; when half exturated,
50; and 20 on, ‘The absolute amount of moister remaining the
samo, the atmosphere might at ono temperature ‘be muturated, wikilet
at some other termperature it would be far frata saturation.
Tn winter tho air is gonerally damper than in snenmer, though in
the latter season it generally contains a greater absolute amount of
vapor than in the former. ‘This tx due to differmnes of
For the same reason the alr is damper at night than in the daytime
and a cold room is damper than # warm one.
354. The Hygroscope.— A Hycroscorr is an instra-
ment for showing the amount of moisture in the air.
Any substance capable of absorbing moisture may be em-
das a hygroscope. A great number of animal and
getable substances, such as paper, parchment, hair, catgat,
are elongated by absorbing moisture, and are shortened when
dricd, and are therefore adapted to the construction of a
hywroscope.
Instromoents of this kind are vory uncertain in their action, and
are therefore used ax inatters of curiosity rather thas for any seleutliie
value they may pomogs
pl
ve
355. The Hygrometer. — A Hyonowernat ix an instra
ment for measuring the amount of moisture ih the air,
Several kinds have b invented, the moat portant of
which - hygrometers of absorption; 2. dew-point lip=
grometers; 8. wet and dry bulb by
The hygrometers of the first class are sally liygroscopes.
‘The hair dygrometer is the most trustworthy of this clas Tt
rly which ongunie substances have of
at, and contracting when dry.
is based on the pr
dongating when me
==
HYGROMETRY. 207
‘The hair is connected with a needle, and by its expansions and
contractions causes it to move over an are, thus indicating that the
aie is more of leas moist. To this class belong those chimney orva-
soents that indicate inoistare in the air, They are founded on the
property which twisted strings or pieces of catgut possess of unteist-
tng when moist and twisting when dry.
356. Daniell’s Dew-Point Hygrometer.— The tem-
peratore at which vapor is deposited in the form of dew is
called the dew-point. Davicll’s hygrometer cnables us to de-
termine the amount of vapor in the atmosphere by indicating
the dow-point.
Tt consists (Fig, 230) of two bulbs connected by a sipbon-
tuibe, from which the air has been expelled by hormetically
sealing the bulb, 2, when the
instrument is filled with ether fp
vapor. The bulb, 4, is about
half filled with ether, and con-
tains the bulb of a small ther-
momoter, Ais made of black
glass, so that the deposition
of dew may be more readily
perceived.
The bulb, B, is eovernd with
tnuelin, and ether is dropped apon
it, This evaporates. from the
ineslin, cools the bulb, B, eon
denses the vapor of ether in it,
anid cases rapid evaporation from
the gurfaee of the quid in the
hulk, A. This is coolet untit the
air im contact with it sinks below
the daw-point und Inoisture eol-
fects on the bull, At the moment of dep of the
mereary in A noted. Tho addition of ether tw tho bulb, B, ia
hen diseontinded, the temperature of A rises, and the dew disap.
pears Whee this takes plsoe, read the thermometer ix A agave.
fants
208 HEAT.
‘The two observations should not differ much from ewcl ether, att
their moan ts the dow-point. ‘The thermenneter in the eemtey of the
etand gives the temperntare of the alr,
‘The nearer the dow-point is to the ternperstare of the alr, the
nearer the air is to being sntarated with waper.
357. The Wet and Dry Bulb Hygrometer. — This
instrument consists of two similar thermometers, pliced om a
stand a short distamee from each
other, as shown in Fig. 231, The
bulb of one is covered with meslin,
and is kept moist by means of =
wick dipping in water. The bulb
of the other i¢ kept dey, and indi-
cates the temperatare of the air.
‘The evaporation thattakes place from
the wet bulb lowers ity temperature be
Jow that of the ether thermometer,
‘The greater the difference between
the readings of the twe thermenueters,
the dryer ie the alr, of the further fern
complete saturation.
‘The evaporation will go om wales
the air is folly saturated.
‘This hygrometer, on account of the
facilities of ebservation Jt affenls, i
toore generally used than say other.
—_— — 358. Mists, Fogs, and Clouds.
Wig. 251 — Murs, Foos, and Crowns are
muxses of vapor condensed into drops or vesicles by coming
in contact with cokler strata of the atmosphere. The term
fog or mist upplies when these masses are in contact with the
earth, and the term cloud when they are suspended in the
air. A fog differs from a mist more in degree than in Kine,
We generally call a very thick mist m fog.
The alr at all times contains a greater of bess quantity
= mal
MISTS, FOGS, AND CLOUDS. 209
of invisible vapor, and if at any time the air becomes cooled
below a certain limit, a portion is condensed and becomes
Visible; the result is either a fog or a cloud,
‘One of the mast common causes of clouds is the cold generated by
un aseending current of air, When the air becomes heatod it ex-
pands and secends, ani, being continually subjected to a dimlulshing
pressure, it expands rapidly, and a largo amount of heat must beeotne
Intent. This absorption of heat produces cold enough to condense
the vapor into clouds. When a cloud floats into a warmer etratam
of the atrnusphere, it is often converted into invisible vapor and dis-
appears. Tis
treat the Wiads Blowing fidim the plainn, and furwe
oe, ascend their sl sides. in
te) loping Coming in contact with the
eee te atcenter, the moisture is converted jute douds
and fogs. Hence we often seo the mountain-tops covered with fogs
and loads when the other portions of the sky are clear. ‘The con-
donsation of wator on the sides of mountains is the moet fruitful
eoures of our steains. When a cold wind meets with a warn and
(eedet exirront of air, the cooling process is #9 great as to genenite
chvods.
‘Two theorins have been advanced to explain the reason
why clonds remain suspended In the alr. Acconting to the
first theory, the particles of moisture are hollow spheres of
wenter, like soap-bubbles, filled with air less dense than that
without, Consequently the little vesicles float in the air like
so many minnie balloons. According to the second and
favorite theory, the particles are oxtremely small, and float in
the air in the same way that particles of dust and other small
bodies are seen to be borne along by the atmosphere.
and mists forin over belles of water and moist grounds,
when the air nbove them is coolor than the water or carth.
‘They are frequent along the course of rivers and upon inland
lakes The cause of the donee fogs that prevail in the neighborhood
of Newfemniland is the Gulf Steam. The water brougit by the
Gulf Stream. te warmer thun that of tho surronndivg ocean, and as
athe vapor rises from It, it ls emverted by the culd alr frou: the weigh
to fog:
—_—
800 HEAT.
359. Varieties of Clouds, — Clouds have heen divide)
accorling to Howard, into four principal kinds: nimbus, sénx
tus, cumulus, and eirrus. Chose four kinds are represented ix
Fig. 232, and are designated, respectively, by one, twa, Unter,
and four birds on the wing.
HMowanl calls any cloud mimbus from which rain is déseending,
although it is not strictly «ne of the fundamental varieties, but «
combination of several.
Fig, 292.
‘The stratus clouds consist of horizontal sheets. ‘hey
lore position in the atmosphere. ‘They are frequently formed ot
J dicappear at xumrise.
jouds ase rounded sasses that look Tike anouastales
pled nme on the other, They are summer clouds,
The cirrur clouds are light, feathery clouds, and oeempy the Iikeh=
est regions of tho atmosphere. ‘They are probably sumposed wf
frozen particles
It sonst not be supposed that these four fundaneutal forme ane
The cumulus
be bt el
RAIN, DEW, AND Prost. Sot
always distinetly outlined in the atmosphere, ‘They frequently pass
into one anothor and form intermediate types
360. Rain. — Rats is « fill of drops of water from the
atmosphere. When several particles of a cloud unite, the
weight becomes too great to be supported by the air, and
‘the drop thas formed falls to the ground.
When % cload Hoats into a colder stratom of the atmoephere, it
Decomes more condensed, aud we have a fall of rain, When it Howes
into a net it dinsolves. Henoe we often see the clouds
jdixsclve tider the influence of the sua, which acts to
regione of the atmosphere.
untity of rain that falls in any country depends upon
to the ocean or other bodies of water, upon
the temperature, and upon the prevailing
More rain falls near the consts than
r; more rain falls in summer than in winter;
in tropical climates than in temperate and.
and, finally, more rain falls in those countries
dling winds are from the occan than where
tulle indicates the amber of inches of rain that
atthe ston ‘nated : —
eh See 18 Inches.
sae BD *
i
aH
m
‘Prom this we seo that the quantity of rain fucrenses rapidly as we
approach the equatorial regions.
361. Dew and Frost. — Dnw is a deposition of watery
particles that takes place upon the soil and plants during the
calm nights of summvr,
‘The true theory of dew was first established by Wenn,
According to his theory, dew results from the earth aud
plauts becoming cooled hy radiation, Usus yroxluelug a de
—
‘The water loses its heat by radiation, and
an equivalent supply from the earth em
ing power of the stray, ite temperature
nd ice is formed. (The drops of water:
‘on the glass of our windows in winter,
‘Tho nearer the wir is to saturation, the
posit of dew. Hence, before a rainy the
dant. Stone walls aud the Tike, being evole
fare often in summer eovernd with moisture,
mireut. ‘The mcistume iu this ease i 6
etances aa ave favorable to the formation of
that frost may occur, the earth must be cooled by
Tris often said that it freexes harder whee the mess
when it is concealed by clouds. ‘This is the case, batt
nothing to do with tho freozing. The true expll
nomena is this: When the moon shines, it is ge
and the radiation gees on mone rapidly, and of eourss
gree of cold is producol, On the coutracy, whem the
scared, it is generally cloudy ; anid the clouils ax
beck the heat, and the heat they send back to the earth,
SNOW AND MAIL 303,
exeegh to compensate for that radiated frm the earth; hence the
process of freezing iv cither eetanled ve entirely prevented.
Planta arm good radiators, henoo they are more likely to be affected
by Froet. thas ether objects. protect them froin frost we corer
them with mats, whieh prevent radiation, or rather weilect back the
heat that the plants throw oif
362. Snow and Hail. — Sxow is formed by the freezing
of vapor in the npper regions of the atmosphore, whonce it
falls to the ground in fakes.
Snow-flakes are made up of crystals, arranged in star-like
forms, with three or six branches, differently arranged, but
always remarkable for thelr resw When
snow falls, the temperature of the If the
temperature is much lower, the snow is leas abundant, be
cause the amount of vapor in the air is loss,
Fig. 253 shows srno of the forms as seon through « ti
‘The quantity of svow thot falls in any place is generally the
greiter as the plies is nearev tho pole, or as it is higher above the
Herel of the cowan. At the poles, and ou the somumits A Wig waren
204 HEAL.
tains in all latitudes, snow remains through the entire year, An wr
approach the equntar, the region of perpetual now rises higher ani
higher above the level of tho ocean. In the Andes, under the equs-
tor, the limit of perpetaal snow is between 15,000 and 16,000. et
above tho level of the ocean; in the Alps it is only 10,4) feot abe
tho lovol of the ocoan ; toward the northem extremity of Norway 8
is but 3,000 feet above the ceean level.
Hau. is composed of layers of compact ioe, arranged com
centrically about nuclei of snow. The formation of hailstones
has never been satisfactorily explained, especially the great
size of some of them,
Hil in wupposed by eome to be dae to the freezing oF raindrops ie
their passage through strata of air cokler than those in whiiels they
wore formod.
Others suppose # cold current of air flrrees Its way Into a mam of
air tnch warmer than itself and nearly saturated, the temperstere
being reduced below 2° P.
363- Winds. —Wixps aro currents of air, moving with
greater or less rapidity. ‘They aro generally named from the
quarter whence they blow; thus, a wind that blows from the
east is called an east-wind, and so for other winds. Wits
are sometimes named from some local peculiafity, “Thus, we
have tradewinds, monsoons, siroceas, and the Hike. “The pre-
vailing directions of the wind are different in different eoun-
tries, for reasons that will be explained bervafler.
364. Causes of Winds. — Winds ore caused iy varia
tions of temperature in the atmosphere; these variations
produce expansions and contractions, thus distarbing tse
equilibriom of the atmosphero, causing currents. These enr-
ronts aro winds. For example, if the sir is more heated over
one country than over the neighboring coontries, it dilates
and rises, its place being supplied by the colder air which flows
in from the serrounding regions. ‘The susphis of alr ume
brought im flows over at the top of the ascending eolumia.
Hence there ix a current near the earth in one dingetion, whitet
=
WINDS. 305
ata higher elevation there is a current flowing in a contrary
direction.
365. Regular, Periodic, and Variable Winds.—
Winds are divided into three classes: Reguean Wixps,
Prasopie Wixps, and Varianie Wixps.
L. Regular Winds. — Regular winds are those which blow
throughout the year in the same direction, They occur in
the neighborhood of the equator, extending on each side
about $0 degmes. From their advantage to commerce they
are called frareswinds. Qn the north side of the equator they
‘low from the northeast; on the south side they blow from
the southeast.
‘Tho trwle-winds arise froin currents of air flowing from the polar
regions towands the equator; the yolocity of the earth about its axis
being greater ns we ajprosch the equator, these winds lag behind, as
it were, and become inclined to the westward, giving northeast
winds on the north sido, und southcust ones on the south side of the
equator.
2. Periodic Winds. — Periodic winds are those which, at rog-
ular intervals of time, blow from opposite directions. Snel
‘are the monsoons that prevail in the Indian Occan, blowing
one half of the year from northeast to southwest, and the
other half in the opposite direction, When the sun is on
the north of the equator, the southern portion of the Asi-
atic continent is warmer than the southern part of Afkica,
and the winds blow from southwest to northeast; when the
sun 1s on the south side of the equator, the reverse is the
CARO.
The sinwoom is a hot wind that blows from the deserts of
Africa. [tie folt in the northern and northeastern parte of
the Afficun continent. During its prevalence the thermome-
ter offen rises to 120° FP. In the desert this wind beoomes
‘suffocating from its heat and dryness, Travellers exposed to
It covor thelr faces with thick cloths, and their cumels turn
thelr backs to escape its injurious eifects.
—
306 HEAT,
‘The sirnero Is a hot wind that sometimes ts felt In Italy.
When it blows people remain in their houses, taking eare to
close every door and window. Some suppose this to be #
continuation of the simoom from the African desert.
‘The land and sox breezes are winds What blow on the sea-
coast. During the day the land becomes heated to a higher
degree than the sea; consequently the air resting on the laud
becomes more heated ond rarefied than that on the water;
henee it ascends, and the cooler air from the sea flows in to-
wards the Inud to take its place, constituting the seubreese.
During the night the Jaad coola more rapidly than the sea and a
contrary effect Is produced. The air over tha sea benomes wanner,
and race to make way for the cooler and denser ale coma frou the
land. ‘his current Is ealled the land-breeze,
3. Variable Winds. — Variable winds are those which blow
sometimes in one direction and sometimes in another, without
any opparent law of change. The further we recede from the
equatorial regions, the more variable are the winds in their
character.
‘This is undoubtedly due to the fact that the two grest enrrents
of gir thot form the trade-winds gradually approach each other
io temperature, at a distance from the equator, od Tose that
rogularity of activo that marke their movements in the tropieat
regions,
‘The curtoat corning from the poles grows warmer, and that goteg
towards the poles grows cooler, so that In the tempentie zones the
disparity of tenperntare is not sufficiently great to heep the eorrvnte
distinet, and therefore there is « constant tendency te mingles and to-
twrehange their positions
366. Tornadoes. —A Tonsano is a violent whirlwind,
attended with rain, thunder, and lightning. ‘They are sdp-
posed to be canwd ly currents of alr encountering one ain
other when moving in <itferent directions, thereby itapartiog
to the atmoapher® a whirling motion, “Tornadoes often trvel
considerable distances, overturning buildings ant uprooting
s =
WINDS. 307
trees; they are accompanied with a noise like that of heavily
loaded carts driven over a stony road,
‘Two species of turnudo ure recognized, terrestrial aud marine, ac
cording we they take place on land or on water. ‘The latter class
present renmrkable phenomena. The rotary force of the wind raises
the water in the form of & coup, while a socond cone forms in the
cloud, having ite apex downwanls. These omes move to meet each
other, forming « column of water reaching from the ocean to the
dood. To this form the column of flaid is called a water-spout,
When # water-spout strikes a ship it docs iinmense damage.
367. Velocity of Winds.— The velocity of winds ix
exceedingly variable. The velocity is measured by instru-
menta called anemometers, ‘These consist of a species of
windmill attached to a train of wheel-work, by means of
whic the number of revolutions per minute can be regis-
tered. From the number of revolutions the velocity can be
computed. *
Fig. £34 represents thin form ef ancmomoter. It consists of four
hemispheriral cups attached to hur-
leontal ‘arms of eqnal length.
These tura freely about a verti-
cal nxin,
‘This axis curries an endless
forew, which sets in motion a }
train of wheel-work. The nam- 1
ber of revolutions ia registered on
a dial by means of pointers con- ~
neeted with the whecl-work,
The velocity of the gentlet
heeese, cr zephyr, is not mere
Yhas one amile por hour; a mod~
eente wind travela at the rate of
45 to S miles per hour, a brisk
wind 20 miller per hour, a tom.
pest 40 to 50 niles por hour, wend Fig. 204.
i hurricane from 90 to 100 wiles por hour.
_
[a
308 HEAT.
368. The Signal Service. — Attempts to predict im-
portant changes in the weather, so as to give timely warniog
of the approach of storms and tempests, have been made ley
civilized communities from time immemorial, These al
tempts, however, have of necessity been, fo a great extent.
crude and ineffectual. ‘The coming storm could not be fore-
told in sufficient season to adit of making preparations for
averting its violence.
By means of the electric telegraph the Signal Service of
the present day has reached a high state of efficiency, and f&
of great value to commerce and agriculture. By its aid in-
telligence of storms and approaching weather-changes can be
travamitted from point te point many hours in advance.
That the Signal Servico is a part of the regular army tn-
spires confidence in its work and gives trustworthiness to. its
reports. ‘The thorough discipline of the army is essential to
the successful working of the corps of weather-observers.
There must be, on the part of its members, panetunlity, prompt
obedience, and the closest attention to the mingtest detatls.
Thore must also be the power to enforce these requirements,
and this can be perfectly secured in the army.
Every man of the sigual corps is thoroughly instructed and prac
tised in the use of the telegraph oni ether instruments that are em-
1 in overy branch of the service,
‘Tho total uamber of stations of observations within the Lenits of
the United Stites is beowoen two and three hundred. Each station
is eqalpped with the following instrusnenta: baromoter, thermome=
ter, hygrometer, anemoseope, anemoneter, and rait-gange, AM the
stations communicate with thé central office at Washington.
‘Three observations are taken daily, Washington thne; this instnes
the reading of the instraments by all the observers at the same time.
The instruments are read in the order given abowe,
‘Tho reports from the differnt stations are transmitted in lipber to
the contra office and coterot on weather-maps Prom the study of
these maps the probable weather changes for the next trenty-fowr
rything wust be eutered on the snaps atl
The weather dtoetious wre then fur-
hours are deduced. E:
rt
minut
=
SUMMARY. 309
nished to the press for publication, also telegraphed in bulletin form
to different centres for the wee of farmer, beeidee being given to the
Associated Press for distribotion throughout the country.
Not ovly is the state of the weather ia tho various great districts
of the country given and a brief synopsis of the probabilities, but also
‘a insight knto the manner by which the probabilitica are determined
and the reasons for the predictions.
‘When sovere storms are approaching the Jakes or the sea-const, cau-
tiomary signals are ordered at the central office to be displayed al the
Jakes and seaports and along tho eea-coast as a warning to marinone.
Por fuller details of this important and interesting topic the sta-
dent is referred to the annual reports of the Chief Signal Officer and
te other decuments bearing on the subject, which gan be obtained on
application to the War Department.
Summary, —
Hygrometry.
Definition,
Saturation
Real Object of Hygrometry.
The Hygroscope.
Definition.
Examples of Hygroseopic Substances.
The Hygrometer.
Definition,
Different Kinde of Hygrometere.
Hygromoters of Absorption.
Hale Hygrometer.
Prineiple upon which it depends.
Deseription,
Daniel's Dew-Point Hyygrometer.
Construction.
Method of Action,
Wet and Dey Bulb Hygromoter.
Coustruction.
Method of Action.
Mists, Fogs, and Clouds,
Explanation of these Terma.
Cunss of Clouds.
‘Theuries to explain thei
Suspemdun in Noe
310 HEAT.
Varintics of Clouds.
‘The Division made by Howank,
Nlustration of the Different Kinda,
Rain.
Definition.
Hilustention.
nncitions that alfvet the Quantity of Rain
Tab!
Dew and Frost.
Definition of Dew.
Wells's ‘Theory of Dew.
Hlasteations,
Definition of Froet.
Hilustrations and Esplanatinga
Snow and Hail.
Formatic
Snow Crystals
Mhostration hy Figaro,
Quantity of Snow in Different Places,
Dofinition of Hail.
Theortes of its Formation.
f Snow
Winds
Definition and [lustration.
Causes of Winds.
Explanation.
Different Classes of Wintts
1. Regular Winds
‘Trule Winds Explained.
‘oriodio Winds
‘The Mons
The Sitnoom:
The §
I
4. Variable Winds
Explanation of thelr Causes
ad and Sea Broorem,
Tor naior.
Definition,
Came
Terrestrial and Marine
SUMMARY. 311
Velocity of Winds.
‘The Anemometer.
Description.
Mode of Operation.
The Signat Service.
Valoo of the Telegraph.
Sigual Service « Part of the Army.
How Weasther-Prodictlons are made,
CHAPTER VIII.
oprics.
SECTION 1. —GENERAL PRINCILES.
369. Definition of Optics. — Orcs is that branch
of Physics which treats of the phenomena of light
370. Definition of Light. —Light is that physical agent
which, acting upon the eye, produces the sensation of sight.
371. Two Theories of Light.—Two theories have
ccoant for the phenomena of light: the
ission Theory, and the Ondulatory ov Ware
According fo the emission theory, light consiats of Infinitely
smell particles of matter, shot forth from Tnminous bodies
with immense velocity, which, falling on the retina of the
eye, produce the sensation of sight
According to the undulatory sheary, ght, like heat, ts
caused by the vibrations of the molecules of bodies, Tt ix
by a highly elastic medium called Jiuninifereste
ether. ‘This medium, which also transmits radiant bent, ex-
tends through space, penetrates all bodies, and exists In the
intervals between thelr molecules. The molecular vibrations
1 to the neighboring ether,
ail ave propagated through it by a succession of spherient
waves; these waves, falling on the retina of the eye, excite
the sensa
Light and radiant beat are very closely related to exch other, bei
farus of radiant enoree: they ure weveented in the saxo wake AIH
been advanced to
&
transmi
of a luminous be imps
on Of sight.
SOURCES OF LIGHT. 318
are propagated through the same medium, but thoy differ from each
other in their wave-length, amd, as a consequence, in thelr mode of
notion on bodies,
Heat is prodiiced by: waves of greater Iengih than those which
cue light. ‘The vibratious of ether also ary wore rapid in the ease
of light,
In sound the particles of air vibrate to and fro in tho dirvotion of
propagation ; in Tight and radiant heat the particles of ether vibrate
toand fro in a dircetion perpendicular to that of prepagution,
sound the vibrations are fongitudinat, ur ia the direction of the mayx;
in Tight and radiant best they arw (ransrersal, oF porpondicular wo tho
rays.
‘The iden of transversal vibrations may bo illustrated by a rope
imade fast at one end end held by the haud at the uther. If the free
end be moved rapidly to and fro, at right ungles to the rope, a sue-
cession of waves will run aloug the rope, while the particles uf the
rope simply vibrate buck and forth in porpondiculars to the rope. If
Fig. 228.
4 stone be drupped into a pool of still water, a series of waves will be
outwant, while the particles of water simply rise and fall,
thele soution belng perpendicular to the direction of propagatio
‘The endulatory theory is now generally accepted by physicists
‘This kind of wave motion is shown in Fig, 235. The white dots
Tepresest molocules of ether, and the light is supposed to fuse in the
direstion AB. ‘Tho distances t! ¢ and ed! aro called wave-length,
Pest de foes the’ crest of onc. wave ta tho crest of the next. The
betancee BOY 17", ce", and a! d” repreeent omplitrvier of vitration,
‘Throngh these distances the molecules of wither ovciliate back and
fowth.
972 Luminous Bodies.— Sources of Light. — Boil
fes that emit light are anid to be huminows: those that are
seem by light derived from others are said to be illuminated.
—=
3th OPTICS. —
Luminous bodies gencrate light; luminated bodies reflect
and diffuse it. The sun is 0 darlgie ee
Gmninated by it.
‘The principal sources of light are the sum, the steers, heat,
chemical combination, phosphorescence, and electricity.
‘The ultimate couse of the sun's light is unknown, (eke, ae &
sorrunndesl by a gasoous envelope, called the phatogphere, whieh
pears to be ina state of intense iguition, ‘The idsedln pualaas
of this envelope are undoubtedly the Sinmedinte sources of solar Fight
tind solar heat. ‘The stars are aimnilar to the eau, but on wecoaut of
thole enonmons distynces from us, they send os but a small amount
of light and heat.
If a body be heated its anolecules are thrown into
whon ite temperature revchow 900? or 1000" F., mes ae
nous in the dirk, Beyond that its Brightness inerrases ae fs temper
ature rises
‘The fight developed by ehemleal pesmi oh
the heat that accompanies them. Comba down
affinity Yetwoon the oxygea of the ale amd
causes them to rush together under favorable
geneniting beat and ultimately Hight felt,
Phosphorescenoo is the property that «ome ba
out Tight ander certain conditions, without heat ol
iu decaying animal and vogotable matter, and in some mimeada
the fire-tly is an example of this
Elvetricity is tho source of a species of light that tivala tn intaoaity
that of the sun itself. Tt will be treated of hereaéior,
373. Media. — Opaque and Transparent Bodies. —
A Meprem is E + thus, free space,
nir, water, and glass are medio.
A tnedinm is said to be hotnogenoons when the stoenteak Sonia
tion and density of all its parts are the sunae.
A Traxsranesr Boy is one that permits Tight to pass
throngh it freely; as glass, diamonds, rock-crystal, and
water.
When bodies permit light to puss through them, ‘but nat in
such guautity a8 to allow objects to be seen te
ABSURPTION OF LIGHT. 316
they are called franalircent, Thus, scraped horn, ground
glass, olled paper, and thin porcolain are transincent.
An Oragur Bony is one that does not permit light to pass
through it. ‘Thus, iron, wood, and granite are opaque bodies,
No bodies are perfectly opaque; when cut into sufficiently
thin leaves, they are more or loss translucent,
374- Absorption of Light. — No boily Is perfectly trans
parent; allintercept or absorb more or less light, but some
absorb much more than others. If light be transtnitted
through great thicknesses of media which in thin layers are
transparent, a quantity of light is absorbed, and it often hap-
pens that the tranamitted light is not of sulficient intensity to
produce the sensation of sight.
‘The atmosphere svoms perfetly transparent, but it is a known
foct that much of the light of the sun is absorbed in reaching the
earth, a8 ix shown by the grewter brillianey of the stars in the higher
ae on mountain-tops. In tho high regione of the atmon-
phere ure more clearly seen than nearer the earth ; indeed, so
great is the elsarnees of vision in theee regions, that it becomes ex-
cevdingly gifllenlt to jude of distances, Opaque: bodies alsorb all of
the light falling upon thom which is uot rolfected.
‘The physical cause of alsorption of light hy bodies is some peen~
lsrity of molecular constitution which breaks up and neutralizes the
waves of light that enter them.
375- Rays of Light. — Pencils. — Beams. — Propa-
gation of Light. —A Kar ow Liar fs a lino along which
Tight is propagated. [i ix perpendicular to the advancing
wave-fromt. When the source is very distant the wave-fronts
are sensibly plane and the rays parallel.
A Pexon. of Rars is a small group of rays meeting in a
common point, such ms the rays proceeding from a candle or
a lamp,
When the rays proceed from a common point, they arc said
to he divergeat. Whom they proceed towards « common point,
they ure said to be coavergrnt.
316 OPTICS.
A Beam ov Rays is a small group of parallel rays, euch
as enter a sinall hole in a shutter, frous # distant body, as the
aun
To» homogenoous medium light 5+ propagated in etraight Hoes,
This is proved by placing an opaque body iu the straight Time that
joins tho eye on the luminons body; the light i intercepted. "Te
rays of light that pass foto a dark room by a small apertere are
sen to be straight by the particles of floating dust whieh they
Marinate,
376. Visual Angle.—The angle formed by two Tacs
drawn from the centre of tne eye to the two extremities of the
object is called the wiswal angle.
Fig. 236 represents the visual angle. ‘The size uf this angle va~
ries with the distance of the body. AB and AUR are of the same
Fig 2%, =
length, yot the angle A OB is larger than tO BY hence the ap-
parent of A’ B is lows than thatof AB CD has the sane
vieval angle ns A’ BF, yet 4’ HF is the larger. “Tho viswal angle, then,
not indicate the real size of a body, —we must Know ite die
Kuowing the size of a body, we eam eethmate ita distames by
ita visnal angle, wod knowing the distance we cam gut its aeo.
can be varied by ineremsinge ar de
ereasing tho visual angle. Tn the formation of feimges bir jairnies
avd leesses this
The apparent sim of a be
neiple will be Hlnstrated
377. Shadows. — When li
2 the rays are
hit fills upon an opaque body,
wanitted in straight lines, the
pt behind the body from which the light is excluded ix
called a sbadine,
If the
defined ; if it be lary
inasinne
ree of Hy
ithe o point. the shaclow will be sharply
than a point, the perfeot shadow silt
ae =
VELOCITY OF LIGHT. S17
be surrounded by a fainter one called the penumbra. The
darker shadow is culled the umbra.
In Fig. 287 we have these two shailows represented, both the
Juminoas nnd opaque bodies being spheres, If the Lnminous surface,
B, be larger than the opaqne body, tho umbne will terminate in a
point, as in the caso of the chadow of C. ft will be fringed ly a
peoumbra, DD.
Bat if the opaque body is larger than the luminous, the umben will
ho divergent, us seen in the shadow of A. ‘This Is also fringed by
penutabm DD.
Vf the luminous sphere be of the swune size as the opaque, the
ambra will be « cylinder, with a penumbra for a border,
‘The penumbra is less dark than the wnbea, because only « part
of the mys from the luminous body are cut off frown the space It
cecapins,
Fig. 297.
378. Velocity of Light. — Light moves with such ve-
loeity that for all distances on the earth it is practically in-
stantaneous.
Tiwas shown by Romer, a Danish astronomer, in 1678,
that light occupies nearly 84 minutes in coming fram the san
to the earth, which gives a velocity of 186,000 miles per
second,
He ascertained the velocity of Ught by a succession of ob-
servations on the celipses of Jupiter's first satellite. In
Fig. 238, & represents the sun, T the earth, J Juyiter, ao
818 OPTICS.
e¢ Jupiter's first satellite, that is, the one nearest to Jupiter,
The darkened portion of the figure beyond Jupiter represents
the shadow of that planet cast by the gun. Itis Known br
computation that Jupiter's first satellite revolves about that
planct once in 42 hours 28 minutes and 36 seconds, and by
entering the shadow of Jupiter is eclipsed at each revelation.
Roemer found that as the earth moved from 7, its nearest
position to Jupiter, towards ¢, its most remote position, the
interval between the consecutive eclipses of the satellite grad-
ually grew longer, whilet in moving from ¢ back agnin to 7;
these intervals grew shorter, ‘The total retardation in pase
ing from 7’ to ¢ was found to be nearly 165 minutes, and the
total acceleration in the remaining half of the earth's revela-
tion was also found to be 164 minutes. “This was accounted
for by the fact that the earth was moving away from Japiter
Fig. 238.
in the first cnse, and therefore the light had to travel farther
ch the observer, while ip tke
penod.
and farther at each eclipse to rv
sccond case the roverse ha
MEK therefore inferred that it required 16) minutes for a may
light to traverse the diameter of the earth's orbit, ar Sf sminnbes
it to pass over the rudiax of that orbit, that ity Onee m dixtamee
‘equal to that of the ea
It ie difficnlt to oon
ad, a spec that would eaery
ive a velocity so erent ax 180,000 intles per
ray of light onvand the earth
cight times In a single second ef time. Some idea, howener, teay be
had of the velocity of rom the faet that it would neqaine more
2 oe of GE Tone mgt expEREE
than two and a half centr
»
kek
INTENSITY OF LIGHT. 319
traing if cars to run a distanes over which light passes In Sf
pwinetes.
379. Intensity of Light. — Photometry. — The in-
tensity of light 1s the amount of disturbance it imparts to the
eter. It is proportional to the square of the amplitude of the
eibration of the ether particles ; that is, a8 the amplitude in-
creases the intensity increases, as |t decreases the intensity
also deereases, The intensity also eurves inversely as the square
of the distance from its source.
Fig, 230
Hence we see that light follows the samo law with regard
to itt intensity that is observed for gravity (Fig. 23) and
sound. ‘The law of variation of intensity can be verified,
eee, hy means of an instrument called a pho-
Traian fs an inetroment for comparing the intensi-
tos of different lights.
Several different instruments have been devised for this
inpose, one of the simplest being that shown Ww Fy. 28.
820 OPTICS.
It consists of a vertical screen of ground glass, A, aod a
vertical solid rod, #, situated a short distance in front of it,
If two equal lights are placed at equal distances fewin J, it is
found tht the shadows whieh H easts upon A are of the samo tie,
If ono Light be placed at any distunee, and four equal lights be
placed at twice the distance, the shoilows will be of the antee tint ;
thin is the cae ehown in the figures It will require nine equal Tights
at three times the distance, #ixteen at Himes the distance, and so
1 to produce the samo affect. This experiment confirms the law of
variation of intenalty aeconding to the inverse sqmury of the Uistaser
To use the photometer to compare the jutensitics of umy two
lights, let them be placed, by trial, at such distances from ZF that the
thidows cast on A arv of exactly the samo tint; thin will their in
her as the squares of their distamees from the
‘twuritios be to each
rod, B.
Summary. —
Definition of Optics.
Definition of Light
Two Theories of Light
Esnission Theory.
planation
Undalatory Thoory.
Explanation,
‘Tmesveree Vibrations of Ether in Hont and Light
Tlustrations
Explanation with Figure.
Definition of Terms.
Luweiinous Bodies
Taminatod Bodies
The Principal Sources of Light.
Explanations
Diefinition of Terme.
Medium
Tornsparent Be
iy
Translaceat Body.
Opaque Body
Adsorption of I
REFLECTION OF LIGHT. 321
Definition of Terms,
‘A Ray of Light.
A Pencil of Rays.
A Beam of Rays
Propagation of Light im Homogeneous Medium.
Exporiment.
Visual Angie.
Definition.
Explanation by Figure.
Shailoues,
DeGnition.
Definition of Umbra and Penumbra,
Tilustrated by Figure.
Velicity of Light.
Tnstantancous on the Earth
Roemer’s Method by Jupiter's Satellitos.
Anternity of Light, =»
‘Laws that govern the Totensity.
Photometer.
Detinition,
Method of aring the Photometer.
SRCTION 11, — REFLECTION OF LIGHT. — MIRRORS.
380. Reflection of Light.—When light passes ob-
liquely from one medium to another, it ix separnted Into two
parts, one of which is driven back ond remains in the first
medium, while the other passes on and enters the second
medium. The part that is driven back {s said to be reflected,
and the deviating surface fs called a reflector.
Reflection of light is explained in the same way us reflection of
svmnd. Tn ease of light the wavo-lengths are so amall that the most
highly polished surfuces aro comparatively rwugh. Henee only a
part af the reflected light appenrw to follow the regular Taws; the
risk is inmgalarly reflected or diffused. ‘Che amount of light reflected,
fe well as the relition between that whieh is regularly ava Ww
2 OPTICS.
whieh is irregularly refeeted, depends on the oliiquity of iseidemee,
wediumy, 2ud the polish of the deviating
ularly reflected enables us to e6e objects; thus,
the light falling on a shoot of paper it seattered oF diffused so ms te
it visible in all directions. If a reflector were perfectly sanouth
uld be invisible; we should simply see in it the images of other
objects.
Vig. 240,
Tt bs the diffused light reflected by the dood, the air, the enrth,
jorts upon jt, that ilbsminates cet rosens, and fenders aijeeta
tisible which do uot receive the direct rays wf the sam.
If we look Gut from our o
this diffimed E Wweacen they 1
rellost much; but if we
objects clearly by means of
touch Tight apd theredane
from without into a house we met
vise they receive bet Bittle Mabe,
1s with teas distinetwess
£ therefore thay reticet bet little
Ti ly now proposed to explain the hows of reeiar feflectiom:
REFLECTION, 823
381. Definition of Terms. — The ray that fills upon a
reflecting surface is called the incident roy; thus, CD (Pig,
240) is am incident ray.
The point where the incident ray meets the reflecting sur-
face is ealled the point of incidence; thus, D is a point of
incidence.
‘The angle that the incident ray makes with the perpendicu-
lar to the reflecting surface at tho point of incidence ix
called the angle of incidence; thus, CDA is an angle of
incidence.
‘The plane that passes through the incident my and the
perpendicular is called the plane of fneidence : thus, the plane
through CD and DA is a plane of incidence.
‘The ray driven off (rom the reflecting surface is called the
reflected ray: thus, 2 J? is a reflected ray,
‘The angle that the reflected ray wakes with the perpendic-
ular bs called the angle uf reflection; thus, BDA is an angle
of
of the reflected my and the perpendicular is
called a plane of reflection ; thus, the place of BD and DA
is a plane of reflection.
382. Laws of Reflection. —The following laws are
shown by theory, and confirmed by experiment : —
L. Mhe planes of incidence anc reflection coincide; both
are perpendicular to the reflecting surface at the point of
Incidence.
2. The amngles of incidence aud reflection are equal; this is
trae whatever may be the angle of incidence.
"Those two laws are illustrated on page 82 (Fig, 18) ax regards
snotion s but the ilusteation will sorre equally well for Light with w
fow changes. Let B represent a mirror, and let a ray of light pase
along the Hine A; ix will be rflocted at B to C.
Tk will be seen that tho incident and retlocted rays lie in the same
lune with the perpendicular, 22, or, in other words, that the
planes of each coincide.
MIRRORS, 825
of alloys, or mixtures of hard metals, which admit-of a high
polish, Such a mirror is eallod a specudun,
385. Plane Mirrors.— A Piaxe Minnor is one in
which the reflecting surface is planc.
Wo have an example of pline mirrors in the ordinary
looking-glassea of our houses. The surface of still water,
which reflects surrounding objects, and the surface of qnick-
silver, whet at rest, are additional examples,
Fig 242
986. Images formed by Plane Reflectors. — An
IwAce of an object is a picture or representation of that ob-
fect, formed by a reflector, or by a lens.
The manner of forming images by plane reflectors is flus-
trated fn Fig. 242. A poncil of rays coming from a point is
reflected 45 as reach the eye. Because the angles of inel-
dence and reflection are equal (Art. S82), each ray wi Yowe
POE
MIRRORS. 827
front surfuce of the glass, and the metallic surface at the back
of the glass. An image is formed by cach of these surfaces,
bat that formed by the latter is the more striking, bocause the
first surface reflects only small portion of the light.
This formation of two images by glass mirror renders
them wnfit for many optical purposes, as previously staved
(Art, 354). The double image, formed by placing a point
against the glass, enables us to Judge of the thickness of the
glass.
Fig. 243,
If w randle (Fig. 243) be plaeod botireou two plane mirrors which
form an angle with each other, images of the objects are formed. If
the angle ie 90°, there will be three images; if 60°, five images; and
woven, if It Is 45°.
‘The number of images increoaos xs the angle diminishes, When
it becomes zero, that is, when the mirrors are parallel, the number
would be infinite, on account of the increasing number of roticetions
from one iuirrur to the other. Tho lnages, however, become more
and more disn as thoy recede, since cach reflection involves a Toss of
Night.
989. The Kaleidoscope depends on this property of In-
clined mirrors. Tt consists of a tube containing usually three
iirrors inclined to one another 60°. Ope end of the tube
328 OPpTIcs.
closed by a cap provided with an aperture for the eye;
it the
other end there are two plates, one of ground and the other
of clear glass, the former being more remote from the eye:
Between these two plates of glass small irregular pieces of
colored glass are loosely placed.
When we look throih the tube, holding the groupid-ghise end
tenrards the light, tho objects und thelr inages are seen arranged in
forms of great beanty, which show an cnilless varity of shapes as
wo tarn the tubo.”
390. Reflection by Transparent Bodies. — We bare
Just seen that glass, notwithstanding its irausparency, reflects
light enough to form an image. ‘The same ib the case with
other transparent bodies, of which water forme # conspicuous
example. Images seen in
water are symupeteloally dis.
posed with respect to the
surface of the water, but
inverted.
The case is precisely the
sainne ws though the fnages Bead
heen formed by a Weeizomtal
tuirror, MEN, as represemted tix
Fig: 3H. Fig. 244, The iinnge, ab, ts
seon to be inverted, and us fir bekvw the mirror ax the olijeet, a B,
is above it
Fi 15 reyersents the phenomenon of reflection from the surface
ef still wator
391. The Heliostat. — It is necessary, in the Hlnetra-
tion of many of the properties of Hight, to have a beam of
sunlight enter a darkened room. This mast be direct suo-
light, or soulight reflected from « tirror placed ontakde the
window-shw
to have
light reflected: in amy
any th of time. To seenre
an lnstrnment called n Aefiostat ie emnloved,
reqatn
this advan
= ee
MIRRORS, 320
‘This usually consists of a mirror, which is movable, and can
bo adjusted to the position of the sun at ull times, by means
of the hand or by clock-work arrangement. The direction of
the reflected beam is thus kept unchanged.
A simple and tnexpensive hellostet can be made by using
two mirrors, one movable, to receive the sun's rays aod te
refloct them upon a second inclined mirror, which in turn ne»
thects them through an aperture into the darkened room.
‘The method of constricting a heliostat of this forme is gives in
detail in Mayer and Barvand’s book on Light.
Dolbear’s * Art of Projecting” also giver dimetions for making ene
Of w trifling ent that will answer every purpose.
‘This apparatus is of croat use in many oxperiments in physica.
Tho mime Neliostat is grucrnlly given to the fastrument when it hes
8 Clockwork arrangement for moving the mirror, and porte Iumitre
to the simpler form, where the mirror it adjusted by the hand.
4392, Concave Mirrors. —A Coxcave Mmaon is one in
which the reflection takes place from the coacave side of a
curved surface,
a
330 OPTICS.
We shali consider the casein which the reflecting surface ix
o segment of « sphere.
‘The following definitions apply equally to concave and con-
vex smirtors : —
‘The middle polut of the mirror Is catled ita verter. ‘The
nitre of the sphero, of whieb the mirror forms a part, i
indefinite straight line
through the centre of enrvature and the vertex fe called the
principal axis, or sometimes simply the aris. Any plane see
tion through the axis is called a principal section.
‘Thus, WN (Vig. 246) represents » principal seetion of a
oe tmirror, al is its vertex, © its cuntre of ecievature, ated
lod the centre of cureature. Thy
Fig, 246,
393. Principal Focus of a Concave Mirron =A
Focus is a point at which devinted rays meek PARE NEE
dent rays are parallel to the axis, the foous t called the
principal focus, as F's and Ue distance from the wirtex to thie
principal focns is called the principal fooal distemee, as FAL
6G, ani rays parallel to the axis.
ol © Af are perpendicular to the kurfase of
lrays, 4, Gland 2, are
neidence equal to those
being rvili. ‘The poral
so as to make the angles of
of rellection, that is, OB HW equal to CBF, ODGte ODF,
as St aR own that the principal focus is om the
axis, snd midway between the vertex and centr: Gf curva
ture. We shall always designate the principal focus lige tise
letter P.
hut =
MIRRORS, O31
If the Iumninous pofat is not situated on the principal axis of the
mirror, # lino draw ftom this point through the centre of curvature
will constitute a secondary axis, ausl the focus of the reflected rays
will be on this axin
Ic is to be observed that in practice the surface of a curved milr+
ror is only » vey small part of the xnrface of the sphere of which it
forms a pnt,
‘Unless this be the case we shall not secure accuracy of refleetion,
Decause the rays rellected frvin the borders of the mirror and those
from portions nearer the vertex will not be brought exactly to tho ,
Big. 247.
some fens. Tho outer rays are reflected neurer to the mirror than
the inner ones. This inacenracy ta called spherical aberration by
reflection,
Parabolio thimors refleet without aberration, aud aro veel where
intense Hight ts desired at a grent distance, as in the headlight of a
Joeomotive.
Fig. 247 shows the manuer of determining the y
experiment, making use of « beam of light coming from the wun, Tn
this firm the concave rellector way be used to collect the rays fur
the purpase of developing a great aynouwi of \wat,
neipal focus by
332 OPTICS.
394. Conjugate Foci.—If the rays of light emanate
from some poitt of the nxis not infinitely distant fram the
mirror, they will be brought to a focus at some point of ter
axis, generally different from F. ‘Thus, in Fig. 248, the pen-
cil of rays coming from the point 2 is brought te a focus
at 6, between Fond C. Had the rays emanated from 4, they
would have been brought to a focus at 8, ‘These poinis are
so related as to receive the name of coujugote foct, Hence
we have the following definition: —
Fig. 248,
CoxsvoaTe Foct are any two points so related that a per-
cil of light emanating from either one is brought to a foeus
at the other.
‘That one from which the light actually proceeds is called
the radiwat ; thus, in Fig. 248, 2 is the radiant,
The following are some properties Of conjugate fel oF Gon-
cave mirrors
If the radiant is on the axis and at an infinite distance
mm the mirror, the rays will be parallel and the correspond:
foous is at F ( 246),
As the mdinnt approuches the mirror, the foeus Feoedes
from it
Tf the radiant Is beyond the centre of eurvatare, @, the focus
', the focus is at CO also.
idiant is betwoen © and F, the focus is beyond
ja the direction CL.
MAS eal
MIRRORS. 883
If tho radiant is at J, tho focus ia at an infinite distance;
that is, the reflected rays are parallel
If the radiant is between # and A, as shown in Fig. 249,
Fig 0.
the rays are reflector so as to diverge, and on being pro-
doced backwards, meet at p. To this ease the foous is behind
the mirror, and is said to be wirtuat.
If the radiant is at A, the focus coincides with it.
If the radiant ix on a secondary axis, the pencil of rays ks
oblique, bat it is still brought to a focus on that axis, and the
radiant and focus enjoy properties entirely analogous to those
just explained.
Fig. 200.
395. Formation of Images by Concave Reflectors.
If an object be placed in front of a concave mirror, « p
cil of rays will proceed from each point of the doy, wae
o34 oPprTices.
after reflection will be brought to # focus, either real or vir-
tual. The collection of foci thus formed make ap the fmege
of the objoct.
Let AB (Fig. 250) be an object in front of a concave mir-
ror beyond the centre of curvature, All the ruys that diverge
from A will be reflected to its conjugate focus, a, whieh is on
the secondary axis, Az. This point can be found by drwe-
Big. 2
4% parallel to the principal axis: it will past afer re-
through # and cut A x at a, the point required,
By similar process we ean find the eomjugate foous, b, for the
B, or for any other paint of the abject. ‘The eotleetion oF feel
tho image, af.
Afwor the refleetel mys fonn tho image, a, they come fron thi*
to the eye, just as if it wero a real object. That the fing ike
real roay be shown by throwing Hon a screen (Pig. 251)3 St sell
nlso be accu thit the rays by crossing Invert He
Tho diteetion which the mays assume after reflection twhes the
MIRRORS. 385,
As the object approaehee tho mirror, the image recedes from It;
when the object is as the sentra of curvature, the image will be the
ratno bizo ns the object; whou it is between tho centre and prine}pal
foous, the image is langer; in both these Instances we shall find
the {mage real and inverted.
When the object is at the principal focus, there will be no image,
sineo the reflected raya aro parallel.
396. Virtual Images. — When the object is between the
Principal focus and the mirror, the image i8 virtoal and erect,
and larger than the object, or maguified.
Fig 262.
Pig. 352 shows the course of the in forming a virtual ond
erect image. The face is between the prineipnl focus, ¥°, und
the mirror, Tho pencils of rays from @ and ate reflected ro a to
appenr to diverge from the virtual foci, A and B. It |» easily seen
that the image is linger than the object, by « comparison of the
virual angles of both.
397- Formation of Images by Convex Reflectors. —
Th convex mirrors the reflection takes place from the outer or
convex surface,
From what has been said of concave mireom, \\ will venting
526 OPTICS.
be seen how images are formed by convex mirrors. ‘The
images formed in this
case are always virtual,
always erect, and always
smaller than the object,
as ix shown in Fig. 253.
‘Tho parallel myo, AD
and BK, aro reflected as
the divergent rays, £D and HA. When these rye enter the eye,
nat ab.
Fig
he image Is a
Summary. —
Keflection of Light.
Explanation,
Regul
Diffused 1
Definition of Terme.
Laws of Reflection.
Direction in which Objects ave seen.
Mlustrated by Figures
Mirror
Definition
Materials of whieh Mirrors are mada.
Plane Mirrors
Detinition
Examples of Plane Mim
Images formed by Plune Mirra
od Trrewolar Refleetion,
t-
Delinition of the Tenn Tinage.
Illustration by Fi
Pormation 0
Nature of the Images fu
Virtual Image
Real [mage
Mubtiple Im
F lage Mirrors.
Fr an Angle with ench other.
D
lection by Transparent Bodies
iption and Manner of ust
vhe Kalebiloscopwe.
Wustration by Pigures
REFRACTION, 887
The Heliostat.
Use ard Description.
Comewee Mirrors.
Definition.
Explauation of Terms by Figure.
Secandary Aais.
Spheriral Aberration.
Parabolic Mirrors,
Conjugate Foc.
Explanation by Figure.
Different Positions of tho Focns and Radiant.
Formation of Images by Concave Reflectors.
Image formed by Collection of Foci
‘Method of finding the Conjugate Foci.
Formation f Real Images illustrated by Figure.
Fopmagjon of Virtual Images iMustrated by Figure.
Formation of Images by Conver Reflectors.
Mlustrated by Figure,
—THHRACTION OF LOOMT. — Lass.
SEOTION
398. Tt was stated under Reflection of Light, that when
tight passes obliquely from one medium to another, it is sep
arated into two parts, one of which is driven back or reflected,
and remains in the first medium, while tho other passes on
and enters the second medium. If the substance that forms
the second medinm is opaque, itis absorbed, but, if transparent,
some is absorbed and some transmitted. The transmitted
rays change direction nt the point of incidence. ‘This change
of direction is called refraction, Its amount depends on the
nature of the media, and also on the obliquity of incidence.
If the incident my is perpendicular to the second medium,
itis not bens from its course.
‘Tho cause of this change of dirortion ix a change |» the elastleity
and demity of the ether in passiug from one medium inte the other,
which causes a change in the volocity of tho yay. Voows, Woe Armas,
888 OPTICS.
and elasticity of ether in water aro different from what they are
in the atmosphere, ao that light travels considerably Eater in the
latter smediusn than i the Sormer,
‘This causes a ray, 08 paswinig From alt
Into water, to bend towards the
dicular at the point of ineidenes, ms
shown in Pig. 254, Thus, ZA ie bent
fran its course #0 a8 to take the direction
AK. Ty passing from water to air, the
my is bent awny from the perpomdicular,
Just the reverse of what happens whee
Fig. 254, Fight passes from air into water.
399. Definition of Terms.—‘The ray before refraction
is enlled the incident ray ; ths, L-A (Fig. 264) is an incident
rays
‘Tho point at which tho ray is devisted or bont is called the
point of incidence; thus, A is 8 point of incidence.
The ray after deviation is called the refracted ray; thos,
AK isn refracted ray
‘The angle that the incident ry makes with the perpendica-
Jar at the point of incidence is ealled the angle of ineidence,
and the plane of this angle is the plane of énctdence. Tis,
LA Bis an angle of incidence, and the plane, £42, the
plane of incidence,
‘The angle that the refracted ray makes with the perpendic-
ular at the point of incidence is called the angle of refraction,
and the plane of this angle is the plane of refraetion ; thas, the
angle, AA C, is an angle of refraction, and the plane of this
angle is a plane of refraction.
400. Refractive Power of Bodies.—In the case of
two media through whieb light is parsing, that in whieh the
ray makes tho smaller angle with the perpenticular is said to
have greater refractive power than the other,
As @ general rule, the incident ray, when passing olliguely from
@ rarer to a denser meciivin, bends towards the perpendientcer s
when passing from a denser to a rarer, it bends from the perpen
fam
=|
REFRACTION. 830
diewlar ; or, in other words, the denser of two substances has the
greater refracting power,
Newron observed that, as a general rule, the refmaetive power
sens greatest for combustible bodies, or bodies containing combustible
elemonta, such as aleohol, ether, vils, ete, which contain both hydro-
geo und earbou, He found that tho diamond was more highly re-
fractive than any other bady, and hence inferred that it waa a
combustible hod's,— un inference that has since been confirmed. Its
to its high refractive power that the diamond owes its brillianey as
jewel Gases aro not sa highly refractive us Liquids, but their ros
fractive power may be increased by compression, which augments
their density,
401. Laws of Refraction. —When light passes from any
given medium [nto another, no matter what may be the an-
gle of incidence, it always conforms to the following laws : —
1. The planes of incidence and refraction coincide, both being
perpendicular fa the swrface separating the media, at the point of
tucidence.
2. The sine of the angle of incidence divided by the vine of the
angle of refraction constant quantity for the same two media,
but varies for different reedia,
‘This constant quantity is called the index of refraction,
Tho second Taw way wr iostrated by Pig. 255, Let Z be the
paint of ineldones on a sartice
separating ulr from water, With
Tnsa contre, describe » cirele,
TEP S. Let TR bo an incident
ray, and ST the rofmeted ray.
Draw #8 and SP porpondie-
nlar to the line YP. Then will
these lines be the sincs of the
angles of incidence xnd refrae~
tion, amd we ehall have for the
index of refraction wheo light
fein air into water the ra-
‘te f, feom alr into ghiss, §. Tho
reciprocals of these fractions will Fig BS.
a
340 OPTICS.
give the indices of refraction when light gore in the opposite dinse-
tion; thus, from water to air it ts §, and fron glass to alr. “Thowe
fractions represent the relative indices of refraction for the two
media.
When a ray passes from a vacuum into any median, the ratio of
the sino of the angle of incidence to the sine of the angle of refrietion
isulways greater than unity, and la called the absolute indesr of re
JSraction, or sitmply the indee of refraction fur the given tediin. ‘Chie
index is goverally expressed decimally. ‘Thus, for Joo, H is L290;
for aleohol, 1,372; and so om.
Fig 206.
402, Experimental Proofs of Refraction. — If 9
team of light be introduced through a hole In a shutter ofa
dark room, and allowed to fall upon the surface of water in =
ulnes vessel, as shown in Fi the bending of the beam
as it enters the water may be seen by the eye. ‘The course
ray in the air may be rendered more apparest By filling
REFRACTION. 341
the air with fine dust or smoke, as, for example, the smoke
from gunpowder.
Let a piece of money be placed at the bottom of an empty
vessel, and then take a position such that the coin shall just
be hidden hy the side of
the vessel. While in
this position, if water be
poured into the vessel,
the rays from the coin
will be refracted 50 as to
render it visible. The
effect of refraction in this
and similar eases is to
make the bottom of the Fig. 267
vessel appear higher than it is in reality, as shown in Fig. 257.
403. One of the effects of refraction was explained in the
fast nrticle. ‘The principle has numerons applications. ‘To
a person standing on the shore, a fish in the water ap-
pears higher than hie real position, If » stick be partially
plunged into water, the portion immersed will be thrown up
by refraction, and the stick will appear bent, howk in
Refraction has the effect to make the Weavenky ‘lies
342 OPTICS.
appear higher than they are, and thereby eauses them to rise
earlier and set Inter than they wonld do were thore ne at
mosphere.
‘This can be soon by inspecting Fig. 259. ‘The layers of the at-
masphere are denser as they are nearur the earth, and wa the refiue
tive power of a gaa increas with ft
density tho mys arp bent in. enrwod
Hine 10 the eye. The bearenily body,
S, is seen in tho pesition, 5% ‘The
eye refers ite position alongs the lkoe
A
To understand the apparent changes
|u position of bodies when refraction
tukes place, wo moat remenber that
= 250 the ofject i seen in the direction of
the refracted ray as it emtore the eye.
404. Total Reflection. — Critical Angle. — If light
fall on a surface that separates a medium from one that ix
leas refuctive, there is a limit beyond which if will not pass
om the first mediuen foto the
second, at that limit light is
fotally reflected.
Let BMC (Pig. 200) be a glues
globe half fall of water. "The ray;
LA, being perpendicular 10 the
lobe, is not refimeted In entering,
but if the angle, CAL, te email
enough, it is refracted at Ay taking
the direction, AR. If the anabe
of incidences be increased, the
gle of evfrastion will alto ey tne
angle, or 90° "Lhe refmeted ayy
4M, then emerges parallel tu of the water. The intel
dent angle in this case is called the critical angle, sine foe muy
as FA C, tho incident ray ean no looger pues Himotigh:
1M, bet ix totally reflec and remains i the first
erensed wotil it becomes a
ww surf
& =a
REFRACTION. 348
From water to air the critieal auglo
ie 48°35'; from glass to air, about
AW.
495. Examples of Total
Reflection. — The phenomenon
‘of total reflection may be shown
in various ways. If a glass of
water with a spoon in it be hell
above the level of the eye, and
we look up obliquely at the sur-
faoe of the water, the under side
of the surface will shine like a pol-
ished mirror; the lower portion of
the spoon will be totally reflected
in it, 3 seen in Fig. 261.
Lot & ray of light (Fig. 262) fall
tho glass priam, A CA; ie will form an
angle of 43° with the side, AD. This boing greater than the eriti-
eal angle of gliss, the my will be totally reflected in the direction,
0.
‘The prism represented in the figure
hus the form of a right-anglet imsceles
triangle,
406. Mirage is on atmospheric
phenomenon dependent on extraondi-
nary refraction and total reflection, Pig. 02.
Somotimes « layer of atmosphere next the earth becomes a
reflector, and in that case portions of the extth appear to the
traveller like fakes and ponds; such appearances are frequent
in desert countrios when the heat is intense. ‘To heighten
the iMlusiom, trees are often soon reflected from the any
fuces of these apparent ponds. An example of this kind Is
shown in Fig. 263, ‘The layers of air near the ground are
more heated than those higher op, and therefor: less dense.
‘The mays coming from the top of the iree on Ye Wh. ot Yee
eee
se, ad mach te of he are a th a
‘The observer refers the position of the |
along the direction ef the dotted line, which os the tree
to appear inverted. ‘In this case both the tres: A its image
are seen,
Images of distant shores or ships are somatimes seen in tho alr
at sea, "Tha fer of lenge a the sores ot ee
the Layers near the water are denser than those abore,
Fig. 263.
‘The phenomenon of mimge may be shown in a
way. If we lock along tho side of a red-hot paler
glowing charcoal at an object a few feet off, we shall see
Aistanee from cither an inverted image.
Summary.—
Refraction of Light,
Explanations.
Cans of Refraetion.
Trefinition of Terms.
Refroctioe Power of Bodies.
Rules for the passage of Light Into Modis of Ditkeeot
Dondlty.
Comparative Refractive Power of Dificreut Belem
:
a
REPRACTION. 45
Lanes of Refroction.
Mustration of the Second Law by Figure
Explanation of the Indices of Refraction.
Kaperimental Proofe of Refraction.
Beam of Light entering a Darkened Room.
Rays of Light from a Coin in Water.
Rays of Light from un One ini Water.
Effect of Refraction on the Heavenly Buaties.
Direction in which the Object is sen in Kefroction.
otal Reflection.
Thaxteated by Figure.
Critieal Anglo
Exvawples of Total Reflection.
With Spoon ond Turobler.
With Prism,
In Cases of Mirage.
47. Media with Parallel Faces. — When « ray of
Night, SA, Fig. 264, falls upon a medium bounded by plane
faces, as a plate of glass, for example, it is refracted towards
the perpendicular and pasecs through the plate; as it emerges
at D, it is refracted as much from the perpendicular as it was
towards it fn the first instance, and the my emerges in the
direction, DB, parallel to SA, but pot in the same straight
line with it, The two refractions
do not change the direction of
the ray, but simply shift it slightly
to one eile ortho other. Hence,
in looking throngh « window, we
flo not see the direction of ob-
Jects changed by the intervening
glass.
Fig. 204.
GA end DE reqrosent the perpendiculars, ¢7 the angles of inei-
dence, and ¢7 the angles of refraction,
48. Prisms.—A Pris is 2 refrnctive medium bounded
ly plano faces intersecting each other,
Fig. 265 represents o prism mounted for oeal exyere
345 “OPTICS.
monts. It consists of a picce of glass with three plane faces,
ineeting in parallel Hines called edges. It is placed on a
order to follow the course of a ray of fightin pin
a prism, let nmo (Pig. 266) represent a section prise
iT] the prism
Fig. 26.
falls upon the second thee, 0, and 14 again
—_ _
LENSES. 7
this time from the perpendicular, and emerging into the air,
takes the direction, bc. An eye situated atc refers the ob-
ject, L, backwards along the ray, eb, 80 that it appears to be
situated at. The total deviation is the angle between its
original direction, La, and its flnal direction, er.
We sea from the figure that tho ray is beot from the edge in
which tho refracting faces moet; that bs, it ie bent towards the thick
part of the prism; this deviation has the effect to make the object
appear ue though thrown towards thut edge. ‘Tho ungle, nm, is
called the refracting angle of the prism.
gto. Lenses. — A Luss is a refracting medium, bounded
by carved surfaces, or by one curved and one plane enrface.
Lenses are usually made of glass, and are bounded by
spherical surfaces, or by one spherical and one plane surface,
The surfaces aro made spherical, because they are more easily
wrought by the glass-grinder.
M x r 9
Fig. 257 Fig. 268.
4:3. Classification of Lenses. — Lenses are divided
into six classes, according to the nature and position of the
hounding surfaces, sections of which are shown in Figs. 267
and 268.
‘The first three, represented in Fig, 267, are thicker in the
middle than at their edges. These converge or collect rays of
light, and are called convergent lenses.
‘The best three are thinner in the middle than at thelr edges.
‘These diverge or seattor rays of light, and are called divergent
6
Ik The dowNe-consex lens, Af, bounded by two convex sure
faces; 2, The plano-coaver lens, NV, bounded yy ove cones
LENSES. Sao
Is called the optical centre, and is of much use in the constrne-
tion of images.
In practice it is usaal to make the surfaces which bound
doubleconyex and double-concave lenses equally curved.
When this is the case, as we shall suppose in what follows,
the optical centre is on the axis, and midway between the
two surfaces of the lena; thus, in Fig. 269, O ix the optical
centre, and any ray, 27, passing through it, is not deviated
by the lens,
‘To find « normal at any point of the surface of a lens, wo dye i
Tine from that point to the corresponding centro of curvature; thus,
mC ond we are normals at the points m and m
413. Action of Convex Lenses on Light.—Whena my
of light falls upon one surface of a double-conves lens, it is
refracted towards the normal, passes through the lens, ls again
fneident upon the second surface, and is refracted from the
normal ‘This action is entirely analogous to that of a prism,
the deviation being towards the thicker portion in both cases.
Tn fact, if we suppose planes to be drawn tangent to the amr
faces ut the points of incidence and emergence, they may be
regaried as the faces of a prism through which the ray
passes.
Fig. 270.
350 OPTICS.
‘The course of the mys is indicated in Fig. 270, im which
the rays parallcl to CX are bronght to a fens at M Here
JF is the principal focus.
Since the riya that pass throagh the edge of a ephecioal lens ay
refracted more thin these passing dewer the centre, they exumet be
Drought accurately to the mune focus, éxeept in the ease in whiel the
surface of the leus is suull, when compared with that of the whole
ephere of which it form part, ‘This seatteriog of the cays from «
focns is called spherical aberration by refraction, Tt is remedied &
pnwtice by covering up « part of the surface on which Tight falls, by
paper osver with an mperture in ita contre.
Had the zaya fallen upon the other sida of the Bees, world
have been brought to a focus as far to the right of the lens a Fis to
the left of ft. i
Wig zi. o
Wig. 272
415. Conjugate Foci are any two points: it
the axis of a lens that 9 pencil of light col pms ome [a
brought to a focus at the other, That from whieli the Tight
actually comes fs called the radiont
To Fig, 271 a pencil of raps is from Z ts broaglit te a
focus at I; had tho light come from /, it would have bees
ought to a focus at L: Zand] aro conjugate fool, and ta
the cuse figured, Z is the mdiant.
When the radiont is ot an inflnite distance, the rays ane
— =|
LENSES. 851
| parallel, and the corresponding focus is at F; this is the
| principal focus. As we have alroady soon, thoro arw two such
foci, one on each side of the lens. Itwill be snfficient for our
purpose to suppose the light to come from the right, in which
ease the principal focus ix on the left, at /.
‘When the radiant is anywhere on the axis at a greater dis-
tance than the principal focal distance, the corresponding
focus will also be at a greater distance from the lens than the
principal focal cistance, as shown in Fig. 271.
Af the mdiant approach the lens, the corresponding focus
will recede from it, as is shown in Fig. 272.
If the radiant is at the principal focal distance, the re-
Fig. 278,
Fig. 274.
fmcted rays will be parallel ; that is, the corresponding focus
will be at an infinite distance, as fs shown In the upper dine
gram (Fig. 273).
Tf the radiant is atill nearer the lens, the rays will diverge
after doviation, and will only meet the axis on being produced
backwanis, fn which case the focus is virtual, as is shown in
the lower diagram (Fig. » Tn this dingram Z is the
radiant, and / the virtoal focus.
‘This far we ave sipposed the radiant Lo Wwe ehuoated om
(ae
352 OPTICS,
the principal axia; if itis om any lino through the optical cen-
tre not much inclined to the axis, the corresponding foens
will be on that Tine, and the laws which regulate the posi-
tions of conjugate foci, alrendy considered, will be applicable.
Such a line is called a secondary axis,
‘The principles just Ulustrated are of nse in the discussion
of images formed by lenses.
416. Formation of Images by Convex Lenses. —
If an object be placed in front of a lens, each point of it
may be regarded a4 a radiant sending out a peneil of rays.
Each pencil is brought to a focus somewhere bebind the lens.
‘The assemblage of these foci makes up a picture of the object,
which is called {ts fmage. When the object is at a greater
Fig. 270,
distance from the lens than the principal focal
image will be real and inverted.
The course of the mys ix shown in Fig, 275. ‘Tin tage
is real, as may be shown by throwing it npon @ screen; so
long as the image is real it ie inverted, as may be seen by
allowing it to fall upon a sereen; or it may otherwise be
shown from the fact that the axis of each penell passes
through the optical centre; hence the image of each point
on the opposite sido of the axis from the point.
With respect to the size of the image In this ease, it may
be cither greater or smaller than the object, When the ob-
Ject is farther from the lene than twice the principal focal dis-
tance, the image is smaller than the object; when the object
is at twice the focal distance, the tuage is of the same size
__h =
LENSES 853
a the object; when the distance is less than twiee the
principal focal distance, and greater than the principal focal
distance, the image is greater than the object.
‘These principles may be shown experimentally as follows :—
Lot a convex Ions be placed in a dark roen, and suppose its prin-
cipal focal distance w have boen deterinined by means of a bean of
solar rays. Let a candle be placed in front of the lens, and a serven
Lchind it-to receive ita {roage, as shown in Fig, 276.
Vig. 276.
Whoo the distance of the eindle from the lens is more than wis
tho principal focal distance, ita imago will bo less than the object;
and the more renote the candle the lees will bo its time.
If the candlo be moved towards the lens, its image will grow
larger, until, at twlee the principal focal distance, the sie of the
image and object will be equa
Tf the candle be moved still newror, the sixe of the image will be
increased ; that is, it will bocome greater than tho object, as is shown
in Pig. 277.
354 OPTics.
If tho distance of the object does not Leccene atnallee than the
Principal foeal distance, the image will be inverted, as is shown in
Fige. 276 and 277,
If the object approach still nestor the Inns that im, if its distance
Becomes lees than tho princlpal focal distance, the kena will in-
creas, it will become ervet, and furshernore it will be vleweal, ‘The
course of the raysin thie caso is shown in Fig. 278. HereABis the
object, and ab |p its im which can yoly be seen by looking
through the lens
Fig. 27.
Tn this ease the lens beccanes what is called a single micnamonne
When the object is at the principal focal distance from the iam
the image is infinite ; that is, i disnppenre
The phonoinena just decribed may be observed ly booking thaw
A conver bens at the letters on a printed page When the letiew ane
at a short divtanee fron the Wes, they are mageified sped wreeks we
Temering the lous farther fre
He pare, they disappear at the pete
reappear inverted eral diuskwisled da aise
ral Real distance, and fi
“ae =a
LENSES. 855
417. Formation of Images by Concave Lenses.—
Coneave lenses, being thinner in the middle than at the edges,
have the effect todiverge parallel rays. If the rays are already
divergent, these lenses make them still more so.
Fig 278.
‘This ix shown in Pig. 279, in which n pencil of rays, coming from
the radiant, Z, is mado to divergo, ns though they proceeded from
a point, L mentor the Jens. This point, J, is the virtual fooux, eurre-
sponding to the radiant, Z. To an ayo situated on the loft of the
lous, the light, 1, appears to be sitoated at
Fig. 270.
From what has been said, it is plain thet the images
formed by concave lenses are virtual, ‘They
ny in Fig. 279.
"The course of the rays, in forming an image in the case of
® conoaye Jens, is shown in F In that figure 4B
represents the object. A pencil of rays, coming from A, is
deviated so as to appear to come from a, tote ou aor
e nléo ervet,
356 OPTICS.
drawn from A to the optical centre of the Jens, 0. A pencil,
coming from #, is deviated so as to appear to come from 6,
on the line Ho. Hence a6 is the image of the object, AB,
and is, as we sce, smaller than the object, being nearer the
optical centre, and furthermore it is erect.
418. Burning-Glasses. — Rays of heat are subject to
the same Jaws of reflection and refraction as rays of light.
When a beam of solar light falls upon s convex fens, there
is not only 4 concentration of light at the focus, bat of heat
also.
Fig. 280.
cctvat a to intlume combustible bodies,
e like. In the caso of Large lenses
nes mificiontly powerful to fuse metals. ‘This prop-
the lens in this caso fa
expoeed may scenctitmes
0 fnflamenable materials.
wenels of lave filled with wa-
f lentes,
The
such as pape
the heat t
erty of Tenses tins beon used
called a Durning-glaee, Leve
as results, by
This fect may réenlt from. «phe
ter, which poss
all the prope
419. Lighthouse Lenses.— Parabolic mirrom were
formerly used in lighthouses. These, wowever, on became
LENSES, 857
tarnished by the influence of sea-fogs, and have been sup-
planted by plano-convex lenses. In the case of reflectors,
the lamp itself cats off considerable light. In the principal
foeci-of the lenses powerful lamps are placed so that the emer-
gent rays form a parallel beam, which enables the light to be
seen ata distance of many milos,
‘The difficulty of constructing large plano-convex lenses, together
with their great abserption of light, led finally 1 the adoption of a
particalar aystem of lenses, known an échelom lenses.
Fig. 231 Wig 2
Pig. 281 shows a front view, and Fig. 252 a section or profile of
an Geholon lens.
‘A lens of this kind conaists of a plano-convex lena, 4, about a foot
fn diameter, around whieh are disposed several annular lenses, which
are also planio-conyex, and whooe enrvature ix vo caleuhited that each
fone ball have the mame principal focus as the ceateal lens, A,
A lamp, Z, being placed at the principal focus of this refracting
system, ns shown fn Fig. 222, the light emanathg from it is refracted
fate on immenee boain, RC, of parallel rays
Besides this refracting: system, several ranges of veRhedsare me, WS
DECOMPOSITION OF LIGHT, 359
Formation of Lnages by Concave Lenses.
Mlnsteated by Figure.
Explanation of Burwing-Glaxses,
Lighthouse Lenses.
Deweription.
Mlasteated by Pigare.
Arrangement for illuminating the whole Horizon,
Use of the Electric Light
SRCTION IV. — DRCOMPORITION OP LIGHT, — COLORS OF BODIES.
420. Solar Spectrum.—If a beam of sunlight pnss
through: a prism, it fs bent from ita course and at the same
time is spread out into a brilliantly colored band called the
solar spectrum. The spreading of the rays is called dispor-
sion; it is caused by unequal refrangibility of the different
colored rays. ‘The angular dispersion of rays is different for
different media.
Fig. 26,
The method of forming a spectrum is shown In Fig. 253. ‘Tho
heain Of Tight that enters a hole in the shutter of a darkened room
falls on a prism whose refracting edge ix torned downward; the
whole bears fs beng opward, aud at the sume time its elements are
dispersed #0. to formn the clongutedd spectrum scon on the screen,
When w lignid is weed it ie cuclosod in w beAlow ylieeytoun.
860 OPTICS.
Af the beam of lyght were unobstructed fu its course, it would Gil
upon the floor at X, forming a clreular spot ef white light. In order
Ww have the culors distinet, the opening through whieh the ight wnters
should bo very uarrow. ‘The refracting angle of the prista de tsgally
Gor.
‘Thie spectrum consiste of almost an infinite munber of rays of
different tint, but it is customary to consider only seven, and thee
am called primary colors. These, it the onder of least refrumibility,
are ae follows: rod, at rs orange, ato; yellow, at y> greem, mtg =
blue, at bz indigo, at i= and wiolet, at e,
Tf a colored ray of the spectrum pass through « hole in a screen,
and then fall on a second prism, it is deviated as before, bot there je
uo farther change of color; henee the colors of the spectra are
said to be simple,
Tho wave-leugths correspovding to diferent colored mys bave
been measured, and it ix i that for red rays they dre about yyfyy
of am inch each, and for vielet rays no more than gybey of am inch
thea, gradoally diminish in longth from the red to
, phenomena of dispersion indicate that shorter waves
are inorw retarded thin longer ones in passing through a snedium ¢
hence the rays at the red ead of the spectrum are least refnacted, aud
those ut the violet end are most refracted.
Color in light corresponds to pitch in sound. ‘The color near the
red end of the spectrum correspond to the graver sounds, and those
ucar the vivlet end to the more seule sounds: "The waves of the
let end of tho spectra strike the retina with doabbe the
od. While, therefsre, the mnge of audible sotieds
aves, the rangn of visible eulors is searenly owe
rapidity of
is nearly clenes oe
oetave
421. Recomposition of Light. — That white solar light
is composed of rays of different colors can be proved in an-
other way. When we recom-
bine the colors of the spectran:
white light will be reprodiaced.
This can be done im several
ways,
Fig. 234. 5 Fy Ir it be mote on by aise
ond prism exactly like the fiys\, with is retracting edge
ve -£ —!
COLOR OF BODIES. $61
turned in the opposite dircotion, it will be recomposed and
will emerge a8 white tight (Fig. 254)-
‘This amounts to nothing more than passing ght through a»
medium bounded by parallel plane faces.
‘2. If it be received on a donble-convex lens, as shown in.
Fig. 285, it will be recomposed,
and an image will be formed
free from color. r
8. If the decomposed light
be received upon a concave
mirror (Fig. 286), it will in Fig. 285.
like manner be recomposed and a colorless image pro-
duced.
4, If a circular disk of cardboard be painted as shown
in Fig. 287, in sectors, the colors
being distributed according to
intensity and tint, as in the spec
trum, it will be found, on rotating
the disk rapidly by a piece of
mechanism shown in Fig. 287, Fig. 266.
‘that the separate colors blend into a single one, which Is
a grayish white.
‘The color from any sector produces npon the eyo an impression
that Jonts for an appreciable Iongth of time. In the experiment the
rotation {x so rapid that the impressions from all the colors coexist
‘at the same instant, and the effect is the same aa though the colors
were mixed.
‘That tho impression produced by light Insts for an appreeiablo
length of xime may bo shown by whirling a lighted stick round in
a drelo; it will proseut the appearance of # continuous circle of
fire.
422. Color of Bodies. — The natural color of bodies is
dae to the fact that some of the colored rays in white light
are absorbed when the light enters them. If the unabsorbed
portion is transmitted, the body is colored and transparent,
—_
362 OPTICS.
if reflected, it ix colored and opaque. In both eases the
light that is not absorbed gives the color.
Ifa body absorbs all the colors, it ia black ; if it retleets or
transmits all, it is white or colorless. A body appears red
when it absorbs all the colors except the red, yellow when it
absorbs all but the yellow, ete.
Water when peen in masses hy trausmitted light appears of =
greenish hac, Air appears blue; hence the eolor of the tky. As
we ascend, the mast above us becomes smaller and loses its bie
tint, Tt is probable that the bluish tint of the heavens tx also in x
measure due to reflection from the actial molectles, At sanirise and
sunsot, the tays ef the sun have to travers’ a great Gedy of thé
atrnosph hich absorbs most of the rays exeept the red Gon
Hence it is that the sun appears red at euntiee and wanaote
eel
COLORS. 363
Some bodies transmit a color different from thar which they
reflect. Thus, gold appears yellow by reflected light and green by
light transmitted through the leaf.
423. Complementary Colors.—Nuwrox calls two colors
complementary when by their mixture they produce white.
‘Tf all the rays of the spectrum except the red ones be re~
composed by a convex lens, a greenish blue color will result ;
hence rod and greenish bine aro complementary. In like
manner it may be shown that Prussian blue and orange are
complementary, as nre also violet and grecnish yellow, and
Sellow and indigo blue.
424. Subjective Colors.—If a wafer upon a black ground
be viewed intently for some time, until the nerve of the eye
becomes fitigued, and the eye be then directed to a sheet of
white paper, an image of the wafer will be seen upon the
paper, whose color is complementary to that of the wafer.
‘Thos, if the wafer is red, the image will be green; if the
wafer is orange, the image will be blue; and so on.
If the setting sun, which fs red, be viewed for some time,
and then the eyes be directed to « white wall, a green image
of the sun will be son, which will last for some moments,
when a red image will appear; a second green image suo-
coeds it, and so on till the effect entirely ceases,
Ifwo look for some thno ut a colored object on a white ground,
wo shall finally observe the object surrounded by a fringe, whose
color is complementary to that of the body; thus, if a red wafer be
Placed upon a sheot of white paper, the fringe will be green.
Shadows cast apun a wall by the rising or setting sun are tingod
green, tho tint of the sun eing red at that timo.
TE wo examine several pivces of cloth of the samo color, the eye
Tecomes wenried, and fn consequence of the accidental complemen
tary color belng formol, the Last picces examined appear of a different
shade from those first viewed.
‘Tyndall explains these phenomena as follows: tho eye, by looking
at one color, the red wafer for instance, for some tan, 4 condoned Vow.
364 OPTICS.
sensitive to that color, in fiet partially blinded to ite perception j
hence, when the wafor is removed, the white light, falling mpon the
spot of the retina on which the image of the wafer rested, will have
its red constituent virtually removed, and will therefore appear of the
complementary color, Colors of this kind are called subjection caloen,
‘since they depend upon the condition of the eye.
425. Fraunhofer's Lines.—The solar spectrum is not
continuous; rays corresponding to certain degrees of
refrangibility are wanting ; hence it is crossed at intervals
by dark lines, These are seen to best advantage in a
spoctram formed by passing a beam of sunlight through «
narrow elit, and then decomposing it by a prism whose
: cncecas Rave
tHEST
Fig, 288,
edges aro parallel to the slit. The prism should be of flint
glue und free from flaws. If the slit be wide the color
will overlap one another, but in a pure spectrum this must
not be. A pure epectram is obtainod by making the elit
very narrow,
‘The dark lines of the solar xpectram wer noticed by
Wortasron as early as 1802, but they were first studied and
mapped by Fraunnover in 1814; from that fhet they have
been called Fraunhofer's lines.
Pnavsuoren’s chart contains between five and six hundred fines
irregularly distributed, In it the most preminent lines are designated
by lotters, and these tervo as points of comparison to whidh others
may be referred. ‘The line marked A (Pig. 258) is at the beginning,
und B is near the middle of the red ape
near the boundary of the red and orange
THE SPECTROSCOPE. 865
B, in the yellow ; and F, G, and H aro well-marked lines, F being
in the greon, G in the indigo, and AT in tho violet,
PRauntioren counted nine lines botweeu Band Cs thirty between
© and D, eighty-four between D and E, seventy-five botwoon K
and P, one hundred and eighty-five botween Band G, and one hundred
and winety between @ and H. Recent obvervations have iucreusd
the number of dark lives till they are now cuunted by thousands,
Fnacxnorer found tho spectra of the fixed stars to be crossed by
dark lines, but the lines are differently arranged in the diffrent stars,
and in none are they arranged as in the solar spectrum. ‘The
spectra of the moon and planets whose light is reflected from the sun
give the same lines as those of tho wun. Recently the range of
observation has been vastly incressed, and on the results of these
exuminations a new branch of scieneo bas been founded, called
spectrum analysis,
426. The Spectroscope.— The instrument used for form-
ing and examining the spectra of hodies is calle’ w wpectrorceye
Ue
(Fig: 289). Tt hy
Biya prism, P, oF a
thrown upon the prrisin nd
In planed in front of the tube,
relative distanoos of the lines of |
‘The substance whose spoetr
in the flame at @,
hofer's Lines. — Metals and
acteristic colors to flames: thus, sodi
impart a yellow color to a Bunsen:
copper render it green, the compounds
and the compounds of strontian give it
colors are due to the vapors of the con
THE SPECTROSCOPE, 867
exist Ifa mineral substance coutaining many differeat metals be
volatilized, the apectrurn will show tho bands charaeteriatic of enchs
Bunsen and Kirchoff discovered the uew metals Rubidiam and Cor
sium, by wesns of bands shown by the spectroscope, whieh difforod
from those of all the metals provyiously kuown ; aud in like mauner
Mr. Crookes discovered tho new metal ‘Thallium,
‘Tho method of spectrum analysis is exceedingly delicate; the
presence of tho minutest portion of any substance in the form of in-
candescent vapor Is instantly made manifest by its characteristic
ines in the spectrum.
Tt has been shown that an incandescent solid or liquid
gives o continuous spectrum. Lf light from such a source be
transmitted through the vapors of any substances, and then
eXamiined with the spectroscope, the resulting spectrum will
be crossed hy dark lines having the same position as the
bright lines belonging to the spectra of the vapors. Hence
it appeurs that every body in a state of vapor is opaque to
the elass of rays that it emits when rendered incandescent.
‘Tho principlo just clucidated hs boen applied to explain the dark
Tinos of the slur spectram. Tt is supposed that the body of the sun
is an incandescent eolid, or perhaps » glowing Liquid, and eonso-
quently that it emits white light, It is further supposed that the
body of the wan ie surrounded by a layer of gaseous matter coutain-
ing vapors of various substances, including many of the known
metals. This envelope, called tho photospherv, being at a lowor
temperature than the nucleus, is in a condition to absorb the very
‘maze that it would iteelf emit if it wore incandessent, ‘The nbsorbed
‘or tidsing rays form the dark lines of the spectrum, Were the cen=
teal nuelons abolished, tho solar spectrum wonld be transformed ioto
aaystem of brilliant bands, These would correspond wo the bands
of o spectrom given by n flame charged by metallic vapors: ‘They
would gonatitate the spectram of the solar photoaphere.
Sodium, caleiuin, magnesinm, iron, chromium, wickel, copper, zine,
and gther metals hare been found in the solar atmosphere.
‘The spectra, of the fixed stars indicate that thase bodies are similar
in coustitution to our sun, but the number and position of the dark
Tines shew that their photospheres do not contain the same elements
that are found in our carn Juminary.
368 OPTICS.
‘The nebulo, where they can be observed, give out spectra like
Ignited gases instead af spectra like the sun and stars
‘Tho permanent gases, when heated to a muificient semperature by
means of electricity, exhibit bands in thelr spectra.
Tt has long been known that the sun is surrounded during the
lime of a total eclipse by a great number of irregular rose-colored
protuberances. Thoso have beea shown by «pectrum analysis to
consist, for the most part, of incandescent hydrogen; vith i ane
mixed vapors of sediam and magnesiam. The form
yurt of un irregular envelope surrounding the entire body of the sem,
and lying outsido of its photosphore. ‘This layer constitutes what
haw been named the chromosphere, and within a few years a method
haw been discovered for observing ite spectrum without the nevessity
cof waiting for a total eclipse,
428. Interference of Light — If two waves of light
move in such « way that the crest of one coincides with the
crest of the other, and the depression of one with the depres
sion of the other, the resultant will be a wave of double am-
plitude of vibration.
But when the crost of one corresponds to the depression of
the other, they neutralize each other and there ix no light.
429. Newton's Rings are explained on the same princi-
ple. Upon a flat, smooth piece of glass let the convex ete of
a plano-convex lens having a small curvature be placed and
=e firmly pressed down, as shown in
== Fig. 290. Suppose a beam aflame
Fig. 200. gencous light, that is, light of one
color, is allowed to fall perpendicularly upon the upper glass ;
a portion will be reflected from the lower surface of the lens
and a portion from the upper surface of the lower glass.
‘The coutro, which is the paint of contact of the toro glass surfisns,
fe a dark circular spot; at a cortain distance from it, the two sets of
reflected waves, as they go Wogether to the eye, will have the orest of
‘one coinciding with tho dopresston of another, and the effect will Te
darkness, or there will be a black ring formed. A Hutle farther oat,
the ervets will coincide, and wo shall have « bright rug Of the mish
nl —-
‘color as tho beam of light. Farther still from the contro the crosta
‘and depressions will again correspond, and we shall have a dark ring,
and #9 on,
‘The appearance presented to the eye will be a series of
rings, dark and bright alternately, as represented in Fig. 291,
If yellow light be nsed, we shall have alternately dark and yel-
tow rings; if red light, dark and red rings; and
other colors will produce similar results,
Tfa beam of solar light ts used, each ring will take
tho colors of tho spectrum, — violot on the innor edgo,
and red on the outer, in order of their refrangibilitios,
By finding the thickness of the layer of air between FB 201.
the two glasses, the wave-lengths have been determined,
‘Tho colors of finély grooved snrfaces are doe to interference.
‘Theso colors are independent of the physiatl sonstitution of the body,
and depend solely on the fineness and shape af the grooves.
‘The play of colors npon inother-of-pearl ia duc to fine grooves or
strim, as may be shown by taking an impression of a piece of Ht in
white wax; the colors of the wax, thns prepared, aro entirely analo-
ons with those of the mother-of-pearl from whieh the impression
was taken,
‘Tho brilliant colors of sonp-bubblo are dan to the interference of
the two sets of rays that are reflocted frou the outer end inner sur-
faces of the tilm that constitates the bubble.
‘Tho colora of thin plates, like the fil ef oil on water, the splen~
did colors of the skimmings of melted lead, the iridescent displays of
fractured oryetals, and the like, aro all due to interforeneg of light.
430. Diffraction. — When light paseca the edges of
opaque bodies, the luminous rays appear to become bent
and to enter the shadow of the body.
If 4 ray of light pass by a very small aperture into a dark-
‘ened room, and an opaque body be placed in it, the shadow
‘that it casts will be surrounded with colored fringes.
Ifthe body bea hair or fine metallic wine, thers will not only be
exterior fringes, but also @ series of dark and colored bands In the
‘shader iteclf, which aro called interior fringes. Thes phenomena
ave due to the interference of light.
a
370 OPTICS,
Summary.—
ion.
Llustration by Figure.
Wave-Lengths aud Color,
Recomposition of Light.
1. By two Prinns.
By Doublo-Convex Lens.
3. By Concave Mirror.
4. By Revolutions of Cantboard.
Color of Bodies.
Explanations of the Natural Color of Batlies.
Examples to illustrate Color.
Bodies that tranainit Color different from that whiek they
refleot,
Complementary Colors.
Definition and Manner of Production.
Subjectioe Colors
Examples.
Eeplanation of Tyndall.
Prawnhofer's Lines.
Method of producing these Lines.
Hlustration by F
The Speetresrope.
Description and Musteation by Figures
Spectrum Analysis.
Characteriat
C
Plawes of different Metals and thelr
inpounds
Colored Flarocs due to their Vapors
New Metals discovernt by the Speetrun.
Bodies Opaque to Rays they omit whee Tnoandoscemt.
Coustitution ef tho Heavealy Bodies indicated by their
Spectra
Interference of Light.
+ Rings explained hy Figures.
xanples of Interferenoe of Light.
nation of Diffraction of Light.
Los,
REFRACTION. ami
43t- Double Refraction. — Certain crystalline sub-
stances have the power of separating a transinitted beam into
‘two parts, 80 that objects
seen through them ap-
pear double, as shown
In Fig. 292. This phe-
nomenon, called double
refraction, depends on
the moleenlar arrange-
ment of the body, which >
causes the contained ether Neliced
to have different degroes of elasticity in different directions,
Terland spar, which is crystallized carbonnte of limo, is an example
of double refracting bodies. Its orystals ean be reduced by cleavage
to the form of an equilateral rhomnb,
as shown in the figure. ‘The parti-
cles are aymmetzically arrangod gs;
about the shortest diagonal (ab, Pig.
29), and this is called the axis. On
acoovatof the inequality i the are
rangement of the moloeulos, tho
surrounding ether is endowed with Fig. 8,
different degroes of elasticity. To
of thes unequal elasticities, the transmitted wave i
divided tote two, which advance with unequal velocities; hence the
phenomena of double refraction. Whero the elasticity is the grest-
est, the velocity is the greatest and the refmetion the least, and the
revere aleo is trae.
‘The two ports into which n roy is divided do not move according
to the same lav, One follows both the laws of refraction alrady
‘explained ; it is called tho ordinary rmy. ‘Tho other does not, aa a
‘genoral thing, follow either of thoso laws ; it is called the extraordi-
nary ray. When transmission takes placo in tho direetion of tho
axis the two mys colnclde, and this direction of no-double refraction
ix eallod tho optic axis of tho crystal; whon in « plane perpendicular
to the axis, the two rays are most reported. If we turn the spar
round (Fig. 253), the image made by the extraordinary ray will re
volve about the ober, whily that remaiue stationary.
a
372 opries.
‘The class of bodies to which Icaland spar belongs lave bet ctw
optic axis; these are called walacial. There are bodies that have
two optic axes; theee are culled biaxial,
Tn all crystals where the molecules are not grouped alike, the elas,
ticity of the other is not the samo, and double refraction occur tee
‘will cause double refraction, but water will not, (hus showing a dit
feronce of molecular arrangement.
432. Polarization of Light.—If a beam of light be
transmitted through a crystal of Jocland spar, the parts inte
which it is divided are of equal intensity. Jf one of these
parts be transmitted through # second crystal, the parts into
which it is divided are of unequal intensity, and the degree of
inequality depends on the relative positions of the crystals.
Hence light that has been doubly refracted differs from common
light ; it te polarized, or, in other words, it has aequired sides
‘The vibrations that constitute tight are transeersal; that is, they:
are perpendicular to the direetiou of propagation, Tn eommnem Hight
: pes
every possible:
with this law ; in polarized light they:
take place in only une dinvetion, or
aw all in one plane, called the
plane of polarization.
Pig. 204. Cortain eryetals have the power
of arranging these transverse vibrations of ordinary light into two
sots at right angles to exch other (Fig. 295),
—_—$.
Fig. 206,
Ono of tho sots is more retarded than the other in passing thromgh tire
crystal, and is generally the ordinary eny, which ‘haa boon deserted.
433- Polarized Light and Tourmaline. — Light is est
studied by allowing it to fall perpendicularly on a plate of tour
maline, cut parallel to the axis of the crystal. Sucli m plate
— al
POLARIZATION, 873
allows no vibrations to past except they be parallel to the
axis, Hence the emergent beam is polarized. Let such a
beam fall perpendicularly on 2 nec
‘ond plate, similar to the firet. If
the axes of these plates aro parallel
(Fig. 296), the entire beam is wholly
transmitted; if the axes are per
pendicular to each other, the beam
Fig. 200.
is wholly intercepted ; if the axes
are oblique to each other, the beam is partially transmitted
and partially intercepted.
‘This can be further illustrated by Fig. 297. A and © rep-
resent two gratings with parallel bars, corresponding to the
plates of tourmaline. £ is a :
cardboard corresponding to A
the transverse vibrations of a
light-wave.
* Tecan be readily seen that
‘the vertical portion paxses Fig mr.
throngh the bars at 4d. This
is the polarized ray, the vibrations being all in one plane.
It is evident also that it cannot pass through the bars at C in
their present position.
‘That which polarizes light is called a polarizer, and whnt-
ever is used to examine polarized Hight is called an analyzer.
Of the two tourmaline plates mentioned, the first ts a polar-
izer, the second an analyzer. ‘To test whother light is polar-
ized, it is usual to observe it through an analyzer, and to notice
whether there be any change of brightness as the analyzor Is
rotated.
If tho myethat have pased through « orystal of Tocland spar be
tosted by a plato of tourmaline, it is found that they are polarized in
Planes which aro porpendiculur to cach other.
Light may be polarized’ by relleetion and refraction. We have
‘seen, when a my of light, A C, falls ou a surface separating two
anedia (Fig. 298), that it is separnted into two parts, one of whidas
Va
aT4 OPTICS.
CD, in refracted, and the other, CB, ie ruflected, When these two
parts are perpendiculsr to each other, the reflected tay ix polariaal
iu a plane at right angles te
the reflecting surface.
‘The rofmeted ray in also po-
larized, and will contain just. as
mach polarized light we the re-
Hected nay.
‘Tho angle at which the r-
Fig. 208, flected ray is completely polar
ined in called the angle of polarization.
For glass this angle is 4° R¥. At any other angle the retleeted
ray is ouly partially polarizod.
By means of tho interference of polriged light many bewutifel
effets are prodises
If we place a thin disk of Iealand spar bo-
twoon the tourmaline plates,
aod have the axes of the
plates perpendicnlar to each
other, there will be seen a
we
sores of colored rings trav-
ersed by a black cro. If
tho axes are parallel, oe
have a white ervss instead off Fig 0
black, and the coiors of the rings are changed to thelr eamplementary
ones. Fi 0, represent these resalts.
Fig, 2090,
434. The Tourmaline Pincette. —The best method of
observing the varied colors of polarized light is by means of
Fig. 20
an apparatas called the tourmaline pineette. This is a email
instrument (Fig. 301), consisting of two tourmaline plates emt
parallel to the axis, each being fitted in a metalliedisk. "The
POLARIZATION. 816
tourmalines torn with the disks, and can be rotated and ine
clined to each other at any angle.
The disks are perfvestod in the centre, blackened, and mounted
fn a frame of metal eviled at one end so 48 10 fonn a spring and press
tognther the tourmalines.
The subetanes to be exatnioed js fixed upon a cork disk, Mf, and
then placed betwoon the tourmalines. The pineetto is held before the
eye a0 as to view diffused light, ‘The tourmaline farthest from theese
‘ects a9 a polarizer, and the other as an amalyzer.
435 Applications of Polarized Light.— Polarization
enables us to know whether the light that comes to us from
asubstance is reflected from its surface. We can determine
the light of the heavealy bodies in this way, like the moon and
plancts, which send the sun's rays. Polarization is also use~
ful in ascertaining the nature of precious stones and in study~
ing crystals,
Ma beam of polarized light bo passed through & solution of eano-
sugar, the plane of polarization will be mutated towards the right; if
throagh frult-sogur, towurds the left. By this mothod the amount
of pure sagar in siraps or solutions cau be discovered.
436. The Rainbow is a brilliantly colored arc, formed
by reflection, refraction, and dispersion of solar light by rain-
drops.
Tt f# necessary to the formation of the bow that the sun
should shinc when the drops are falling, and that the ob-
server should stand with his back to the san, between the
drops and the sun.
Two rainbows are often observed at the same time: the
inner and brighter one is called the primary; the outer and
fainter, the secondary.
Fig: 802 shows the course of the rays in the formation of
arninbow. Itwill be observed that in the case of the see-
ondary bow the raye coming from SS suffer two refrac-
tions and two reflections in the drops, eand r, before reaching
the eye, In the primary drops, r and v, the rays from StS"
816 OPTICS.
suffer two refractions and one reflection; hence not so much
light is lost, and the bow is brighter. ‘The result is, that the
emergent light is resolved into the acven prismatic colors for
each bow, only those of the secondary are in the reverse onler
of the primary on account of the additional reflection.
In tho primary bow, violet occupies the inside, red the outelde;
in the secondary, violet the outside anil red the inside, the interme.
diate colors taking their proper order
437. The Manner in which the rays come to the eye
from the seren ae to form the primary bow is shown in
Fig. 308.
The secondary ia formed
in 4 similar way oxcept that
the eye catches the red ray
from the first drop and ylo-
lot from the seventh, the
intermediate drope furnish-
-—— ing thelr respective rays,
Fig. 909. OF course the seven drops
of the secondary bow sre above the seven of the primary,
THE SPECTRUM. 87
The colored rays from cach drop that do not reach the eye are
shown in the figure.
‘The eye occupies a position on n line whieh, if produced, parses
‘throngh the son and the centre of the rainbow circle.
‘Tho red rays of the primary bow as they emerge from the drops
make an angle with the sun's tays of 42°, the blue rays 40°, and the
other colors between these. ‘The different colors will be goon ta arce of
concentric circles, the emergeut rays making the constant angles just
given.
‘The angles which the rays of the secondary make are Larger than
‘thowe of the a
As the sun goes towards the horizon the bow rises; when it is in
tho horizon it forms a somicirelo.
If the sun is below the horizon and the observer on an elevation,
‘the whole bow may be seen.
‘The primary bow disappears if the sun is more than 42° above the
horizon; the secondary, if more than 54°,
Since the position of the rainbow depends upon the direc
tion of the sun's rays and the position of the observer, no
two persone see precisely tho eame bow, although, if they
are near together, the bows very nearly coincide.
‘The rainbows of any two successive moments are not the
same, for the drops that form them are constantly succeeding
one another in rapid succession.
We often sve the colors of the rainbow In the dewdrop, in Icicles,
in tho ice that often clothes tho twigs and branches of trees in winter.
‘The entire cirele of rainbows may be seen fu the spray that arises from
cataracts. The halos often seen aroand tho moon and sometimes
around the sun are suppoved to be due to reflections and refractions
of the Tight.
438. The Properties of the Spectrum.—The seven
mys enumerated differ in illuminating power, the middle rays
being those which possess the greatest illuminating power;
‘that i#, the most powerfully illuminating rays lie midway be-
‘tween the heat rays and the actinie rays, namely, in the yellow.
‘Aa thermometer be held for a tine Wn the A\ferent raya,
878 OPTICS.
beginning at the violet, it will show an increase of heat till it
comes outside of the red rays, where it is greatest.
‘The actinic rays are those that produce chemical changes.
Tf a strip of paper, prepared with nitrate of silver, be placed
in the spectrum, it will be least changed in the red, and fn
passing towards the violet end this change will increase till it
becomes the greatest beyond the violet.
In Fig. 288 wo have represented by means of curves the relative
intensities of the three properties of the spectrmm.
The mys below the red of the spectrum, or ultra-red. shee
thosw above the violet, or ultraviolet mys, are ealled
distinguish them from the colored portions of the spectrum, whieh are
called the visible says. Strictly speaking, however, uo nays are visS-
ble or invisible; it ie not the rays that aro eeen, bat the objects they
iMuminate.
439. Fluorescence and Calorescence.—If the ultra-
violet rays are permitted to fall upon certain substances, as
sulphate of quinine, for example, or common paralline oil, their
refrangibility is lowered and they become laminous. "This
change is called fluorescence, the name having been originally
suggested by a variety of fluor spar which produces the effect.
‘Tyndall has succeeded in raising the refrangibility of the
ultra-red rays and in making them visible. He brought the
rays of the cloctric lamp to « focus by means of a reflector,
and then stopped the laminous rays by foterposing a vessel
of rock-salt containing a solution of iodine. He found that
a plece of platinum foil when brought into the focus was
heated to incandescence, and thus emitted light as well ay
heat. This transformation of dark heat-rays to light he called
calorescence. Sunlight will produce similar effects, bat the re
sults are not 30 marked,
440. Chromatic Aberration. —The light that falls on a
lens is decomposed into colored rays of different degrees
of refrangibility. These rays are brought to different foci
alors _° axis, giving rise to 0 wultitude o€ partial images
a. Sone =
SUMMARY,
of different colors, which by superposition produce a single
image slightly indistinct, and fringed with all the colors of
the spectrum, This acattering of the colored ruye to differont
foci is called chromatic aberration.
Fig. 304 shows the phenomenon of chromatic aberration. ‘The red
rays, being loss dovinted
than theothersare brought
to a focus beyond then at
7, while the violet rays,
Being more rofrangiblo
than the others, are
Fig. 004.
brought to a foeus within
them at c Between 0
and the intermediate colors aro also brought to foet.
441. Achromatic Combinations.— An Actnomatic
Commixarion consists of two or more lenses of different
kinds of ginss, so constructed as to neutralize the effect of
dispersion.
‘The combination usually consists of two lenses: a convex
Tens made of crown glass, and a concave Jens made
of flint glass, as shown in Fig. 305. Flint glass dis-
perses light more than crown glass. The combina-
tion, having its thickest part at the middle, is
convergent. The dispersion of the rays by one of
the Iensos is) exactly neutralized by a dispersion of
them In an opposite way, 80 that the image is nearly
colorless.
Sach combinutions of lensea aro called achromatic, and
are the ones used in the construction of telescupes.
Big. 205
Summary.—
Double Refraction.
Definition and Mlustration by Figure.
Cause of Double Refraction.
‘Onlinary and Extraond
OPpTics.
Polarization of Light.
How produced.
Vibrations of Common and Polarized Light shown by
Figure,
Separation of Common Light into two Sets at Rigtt
‘Angles to cach other.
Polarized Light and Tourmaline.
Ilusteated by Figure,
Definition and Explanation of Terms.
Test uf Polatlaed Light.
Bountiful Effects of Pelarized Light,
Mustrated by Figure,
‘The ‘Tourmatine Piueotte.
Description and Method of Using.
Applications of Polarizod Light.
In determining the Light of the Heavenly Bodies.
In studying Procions Stones and Crystals.
In determining the Purity of Sagar.
The Rainbow.
Definition and Conditions of Formation
Primary and Secondary Bows explained by Figure.
‘The Manner in whieh the Rays reach tho Bye explained
by Figu
Why the Bow is Cireular.
No two Persons ace the sane Bow,
Rainbow Colors xeon in Dewdrups, Tolcles, ete.
Properties of the Spectrum.
Heat, Luminous, and Actinie, or Chemical, Raye
Positions determined in the Spectrum,
Relative Intensities iusteated by Figure.
Fluorescence and Calorescence.
Explanations by Experiments.
Chromatic Aberration explained by Figure.
Achromatic Combinations explained by Figure.
MICROSCOPES. 331
SROTION V.—THEORY AND CONSTRUCTION OF OPTICAL INSTRUMENTS.
442. Optical Instruments. — The properties of mirror
and Jonses lave led to the construction of a great variety of
instruments, whieh, by Increasing the limits of vision, have
‘opened t our senses two new worlds that had clse remained
unknown to us, the one on account of its minutencss and the
other on account of its immensity.
Of the optical instruments, the most useful and interesting,
are microscopes and telescopes.
Besides these a great variety of other instruments have
been devised, such as the magic lantern, the photo-eleetric mi-
croseope, the solar microscope, the camera obscura, and the
stercoscope.
443. Microscopes. —A Macnoscorr is used for viewing
near objects.
Microscopes may consist of a single Tens or a combination of lenses,
‘Wo shall deseribe the two kinds, the simple and the compound.
444. The Simple Microscope, or magnifying-glass,
consists of a double-conyex lens of short focal distance. It
is usually set in a frame of metal or of hora, and held in the
hand,
‘Tho ohjcet ts placed between the lens and its principal foeus.
‘The imago is croet, virtaal, and magnified (Fig. 278). ‘Tho visual
angle subtended by the iamage is greater than that subtended by the
object ; henee the enlargement of tho image.
445- The Compound Microscope consists essentially
of a double-convex lens called the olject-lens, and a secon
double-convex lens called the eye-piece.
Fig. 806 shows the instrument in section, and makes
known the course of the rays.
‘The object to be observed is placed at «, between two
Plates of glass upon a support, ¢ is the object-lens, and 0 the
eye-piecs, Tho object, a, being placed a Wile WeyeoA Yoo
a
382 oprics.
principal focns of the object-glass, this lens
3 pr real
image, dc, which is inverted aud enlarged. The ey
really is, it is said to magnify
100 diameters, the surface being
magnified 100*=10,000 times.
Ccmmponnd microscopes are een~
stracted whose magnifying power ix
1,800 diameters; but what is gulied iu
power ia often Jost fn diatinetmess AL
good magnifying power ix 600 diame-
ters, which gives 360,000 in surtnee.
‘Tho magnifying power depeods up-
~~ on the object-lens "This poner is in-
me creased by combining twe or three
Tenses, as shown at JZ, on the right of Fig.906, ‘Tho eye-piece and
object-glaxs often consist of two ur none Jenne, sett
nalngle lens, for the purpose of remedying the defect arising fren
spherical and chrowatic aberrations.
‘The magnifying power of the compound microscope is eqaal to
the magnifying powers of the two glasios.
As there is no more light on the magnified image than on the ob-
ject itself, the object mast bo strongly illuminated, so Alificsed
light may bo sufficient to weet the eye. To secare this, thes hy
when rrensparent, is iitaninated ‘by © wnivror, MC CPE i
os = ||
TELESCOPES. 283
concententes the light upon it. When the ebject is opaque, it can be
iMayinnted by «lens, which concentrates the rays upon it from abore.
‘The microscope is used in the study of botany to diseover the
laws of the vegetable world; In entomology, to study the habits of
minute insects ; in anatomy and medicino, to study the laws of ani-
mal physiology; In the arts, to discover the composition of mixtures 5
in eonmerce, to detect tho natare of stuffs; and soon. Its use is
almost universal, either as wn instrament of research or of curiosity.
446. Telescopes. — A Texescore is an optical instrument
for viewing objects at a distance,
‘Telescopes may be divided into two classes, refracting tele-
scopes and reflecting telescopes.
In the first class a lens, called the objectens, is employed
to form an image; in the second class a mirror or speculum
is employed for the same purpose ; in both, the image formed
is viewed by lens, or combination of lenses, called the oye-
piece. The manner of arranging these component parts,
together with the nature of the auxiliary pieces employed,
determines the particular kind of telescope. We will first
vonsider the refracting telescopes.
447- The Galilean Telescope, named from its illus-
trions discoverer, Ga1iino, consists essentially of a commer
object-glass, which collects the rays from an object, and a con-
eave eyepiece, by means of which the rays from each point of
the object are rendered parallel, and capable of producing
distinct vision.
Fig. 30%,
Fig. 807 shows the course of tho rays In the Galllean telo-
scope. Pencils of rays from points of the object, 4 2, falling
Bpon the object-lens, 0, are converged by it, and tend to
form a real and inverted image beyond the eye-pisee, @, The
concave eye-piece is placed so as to intercept the rays coming
from the object-glass, being at a distance in front of the in-
verted image equal wo its own principal foral distance. In coa-
sequence of this arrangement, the peneil of light coming from
A is converged by the object-glass, and, falling upon the eye
piece, is diverged and refracted #0 as to appear to the exe to
come froma. In like manner the peneil from 2 appears te
the eye to come from b.
‘The image is ercet and virtual, and beeasse the visual angie
(Art. 378) undor whieh tho iinago is soon is greater than that ander
which the object would be seen without the telescope, it appenrs
magnificd.
Opera-glasses aro simply Galilean telescopes. The leugth of this
telossope is equal to the difference of the fosal lengths of the
tww glasses, and therefore has the advantage of being short and
portable.
448. The Astronomical Telescope consists oxsontially
of two convex lenses, the one, o, being the object-lens, snd
the other, O, tho eye-picce, The objeot-giass forms an in-
verted image of the object, which is viewed by the eye-piece.
Fig. 808 represents the course of the rays in this insten-
ment. A pencil of rays coming from 4 is converged bye
to a focus, a, while a poncil from 2 és brought to the focus, 6.
In this manner the lens, 0, forms an image, a6, of an object,
Fig. 008.
AB, which image is real and inverted. ‘The eye-plece, O, i=
placed ata distance from a6 a little Jess than its principal
focal distance, The pencil coming from the points «and 6 of
the image are refracted #0 as to appear to come from the polats
=> § — |
TELESCOPES, 385
eandd, ‘The visual angle is greater than it would be in view-
ing the object without the telescope, and consequently the
object appears to be magnifled.
Tn this, as in all other telescopes, the eye-picce is capable of being,
pushed in or drawn out, to coable the observer to accommodate it to
tiene os well wa distant objects,
‘The object-lass is made aa largo as pmeticablo, to iuminate the
inage as tnnch as possible, und should be achromatic (Art. 441).
‘Tho sian of tho imag increases with its distaneo from the object
gluse; it should therefore be of small convexity, that its focal dis-
tanoe may bo as great as possible. ‘The eye-pices should have
teat ennvexity, and consequently short focal length, as it does the
To find the magnifying power of a telescope, we divide the focal
Jength of the object-glies by that of the eye-slass-
This telescope differs froin the microscope in these respects; the
cbject-glass of the latter ie as small as possible, very convex, and
aloo has the object to be examined very near it, so that the image
formed is much beyond the prinelpal focus, and greatly magnified.
Consequently both object-gliss and cye-glass magnify. Whereas,
in the teloscope, the heavenly bodies being at an innmense distance,
the incident rays are parallel, and the image formed in the principal
foens of tho object-glass 1s xmaller than the object itaclt. Tha objoet-
glasd also, as has beon stated, in as large as poreible, has very Little
convexity, and does no magnifying, the eye-piece doing that.
"Tho length of the astroncmical telescope equals the sum of the
focal lengths of the two glasses.
449: The Terrestrial Telescope differs from the astro-
nomical telescope in having two additional lenses, which
4
Fig. 900.
together conatitate what is called an crecting-piece. Tho
object of the ereating-piece is to invert the image formed by
the object-lens, s0 that objects may appear erect when viewod
through the telescope.
ell
386 OPTICS.
Fig. 309 ehows the course of the rays in a terrostrial tele-
scope, A Bis the object, o is the objectlens, m and mn, two
convex lenses, constitute the erecting-piece, amd @ is the
eyepiece.
The erecting-picce is so placed that the distance of the
image, /, shall be at a distance from m eqoal to ite principal
focal distance.
A pencil of rays from 4, falling upon the object-lems, i
converged to a focus at the lower end of the image, J; the
pencil proceeding from J is converted into a beam by the
lens, m, directed obliquely upwards, which beam is converged
to a focus at’. In this manner an erect image, #¢, is formed,
which is then viewed by the eyepiece, 0. ‘The eyepiece re-
fracts the pencils coming from the image, 4, seas to make
them appear to come from a.
‘The angle under which aé is seen is the efewal angle, and,
being greater than the angle under which 4 2 would be seen
without the telescope, the object is magnified.
‘The magnifying power is the same as in the astronemieal tele
scope provided the correcting glasses, m and m, have the sane eon
verity; the loss of light, howewwr, is greater,
The terrestrial telescope is used at sex and on Bal for viewing
objects at a distance.
450. Reflecting Telescopes.—A Revtzctexgo Tetr-
x is one in which the image of a distant object fi
formed by means of a reflector or speculum, which image
is then viewed by an eye-piece. The eye-plece is either a
single lens or a combination of lenses.
One of the first telescopes of this description was con-
structxl by Newrox, and this is the only one of the kind
Which we shall describe in detail.
451. Newtonian Telescope. — Fig, 310 shows the tele-
scope of Newrow in section, and indicates the course of the
rays of ligh
Al is a parabolic mirror placed at the bottom of a long
=
& ==
TELESCOPES, 387
tube. This reflector tends to form a small image of an object
atthe other end of the tube, Bot before the rays reach the
image they are intercepted by a prism of glass, mn, se ure
ranged that the rays enter its first face without deviation,
and strike its second face so as to be totally retlected, which
causes the image to be formed at ab, ‘The prism, mn, re-
places the inclined mirror used in the old form of Newtonian
telescope. The image thus formed is viewed by an eyepiece
Fig. 810.
through the side of the telescope. ‘Tho eyepiece in this tele-
scope is inade of two plano-convex lenses, as shown in the
figure, the combined effect of whieh is to enuse the image to
appear in the position BA, giving a great power to the tole-
scope.
Fig. a1,
452 Hetschel’s Telescope. — Sir Wintiam Henscuen,
of London, modified the Newtonian telescope by inclining
the mirror, Mf, 80 as to throw the image to ono side of the
tube (Fig, 311), where It could by viewed by a wagnityiog,
eye-pivoe, the observer's back being turned towards the
object.
Tho largest reflecting telescope ever made fa that of Land Rosse,
which bas” diameter of 6 feet arafoed Jangil Sad tise
present usod as a Newtonian telescope, but can be used like Horschel's.
453- The Magic Lantern is an apparatus for forming
upon a sereen enlarged images of objects painted on glass.
Fig. 312 represents a section of the Iantern. It is om
posed of a box, in which a lamp is placed before a reflector,
4M; the light is reflected upon a Jens, Z, and is converged so as
to illuminate strongly the plate of glass, «6, upon which the
picture ix painted. Finally, a combination of bwo lenses, a,
Fig 312.
acting as a single-convex lens, is placed so that the plate, a5,
shail be a little beyond its principal focus, Ab this distance
the lenses produce (as shown in Fig. 277) a magnified amd
inverted image of the picture painted on the glass. ‘The pic-
ture on the glass should be inverted, in order that Its image
may appear crect,
Tho Lmige on the screen will be the more magnified as the plate, af,
approaches the principal focus of tho compound lena, mi. Et will
also bo tho more magnified as the compound Teas inerenses in
power.
‘The magnifying power of the lantern is found by diviling the
=|
THE POLYRAMA, 889
distance of the Jens, m, from the image by its distance from the
object,
454- The Polyrama and Dissolving Views. — The
Pournama consists of a double magic-lantern, with two cut-
off screens. Dissonvixe Virws are obtained by using both
lanterns. ‘Thus, if a picture of a daylight scene be painted
on one of the slides, and of the same scene by moonlight be
paloted on the other, the first pleture is thrown pon the
screen strongly illuminated, the other one being entirely ex-
cluded by 4 screen that cuts off the second lens. By an
arrangement operated by the exhibitor, the light is gradually
cut off from the first picture and admitted upon the sccond.
the first fading away insensibly while the second as gradu-
ally grows brighter. In this way all the effects intermediate
between full daylight and full moonlight may be obtained in
succession. ’
A voleano, calm, and only surmounted by a light cloud of sinoke,
may be followed by a pictaro of the sue voleano sending forth vol-
umes of flane and mnoke. A storm may be made to succeed a
smiling landscape, and eo on, ‘The illusion is complete.
Since tho brightness of the image diminishes as we enlarge it, our
Momivating power must bo yery great. Instead, therefore, of oil
lamps, the magnesium, calcium, and electric lights aro axed to intensify
the Hight.
‘The magnesium light is nade by burning a narrow ribbouof the
metal; it gives » brilliant and daezding light.
Ifa piceo of tinslaked limo is placod in a flame of mixed hydemgen
aud oxygen gases ftom a blow-pipe, a vivid light fs the result this
is called the exlcium light.
he electric light is the brightest of artificial lights, and is briefly
described in the next article,
455- The Photo-Electric Microscope is constructed
on the same optical principles us the magic lantern, except
that the light employed is obtained by passing an electric
current between two chareoal points.
Fig. 315 represents in detail the arrangementof this instra-
890 OPTICS.
ment, At the foot of the apparatus Is a battery for gen-
vrating cleetri¢ity, which will be described hereafter. The
electricity is conveyed to the charconl points in the box, J
Ly means of bwo Copper Wires, ene going to the upper and the
other to the lower point. The points being slightly sepa-
ratod, the cireuit is completed only by the electricity passing
aterval, whieh gives rise to a light of extreme
ig
rabolic reflector for compen-
X. through a Jens, @. Dts
of t vinute Object on
a screen, The tube in which the lens, 0, is pacha be
. J represents ay
At upon the slic
a lens whieh forms a magnifled im
THE SOLAR MICROSCOPE. 891
drawn out or pushed in to vary the magnifying power of the
apparatas,
‘The maguifying power of this instrument may bo made extremely
grent, and by snitable rnanagement it sereee to show to a lange com=
pany the wonders ef the inlcruscopie world. One of tho tnost re-
matleable experimonts made with it is to show the eirealation of the
bled. Tostend of a picturo on the alide, Ict the tail of tadpole be
placed between two plates of ylass and introdvced. ‘There will ap-
pear open the screen, what secs an illuminated map, all of whose
streams flow with a mpid current. It is but the blood circulating
with groat velocity through the arteries and veing,
‘The phenomena of crystallization are exceedingly beautiful when
s00n by this microscope. Ifa drop of a solution uf sal ammoniag, for
‘example, be poured upon a plate of glass, and then introduced into
the instrument, the heat will eauso the water to ovaporate, producing
one of the most Beautiful examples of crystallization that can be ex
hibited. ‘The minute animaloula of solotions and stagnant water ean
be shown by this microscope,
When the magvesiam, calcium, or oleetric light is axed, the lan-
tern is called a stereopticun,
To the oil-lanwen the nanos magic lanters, Lampascope, and
bea ane Saag
458. The Solar Microscope. — When the light of the
son ix used instead of the clectric light, the apparatus is called
the solar microscope. M (Fig. 314) ia av inclined mirror
which throws the solar rays into the tube of the microscope
‘through the lenses, A and %, which concentrate them upon
the object, O. ‘The tens, £, thon brings therm vo a forur ak ab.
Herschel’s explained by Fipael
Magic Lantern.
Construction and Method of using
CAMERA OBSCURA, 393
Photo- Electric Microscope.
Its Pmotieal Value in the Microseopie World.
Different Names gicen to the Lantern.
Solar Microscope.
‘Construction and Method uf using it explained by Figure.
457. Camera Obscura.—The camern obscura (dark
chamber) is, a3 its name indicates, closed spnee, as, for ox-
ample, & room shut off from the light, with the exception of
the Jeminous rays that are allowed to enter through a small
aperture, as shown in Fig. $15,
‘The rays proceeding from external objects and entering
through this aperture form
on the side opposite the ——-
aperture an image of the
object, inverted and di-
minished In size, but re- Fig. $15.
taining the colors of the object. ‘The inversion of the image
is duo to the crossing of the rays.
If the apertare is a large one, the ray® are scattered indis-
ctiminately over the whole picture, and the image is not so
distinct as when the aperture is small. The image will be
distorted if the screen is not perpendicular to the direction of
the rays.
‘Tho images formed by » carne obscurs posters the reanarkable
peoaliarity of being entirely indopondent of the shape of the openiaye,
in the box, prewided ft be quite stall. ‘Phe shape af the images is the
‘eame, whother the opening be square, round, triangalar, or oblong,
‘To show this, let as consider the case of a beam of solar light en-
toring a dark room through a hole in a shutter (Fig. 316), With
respect to the sim, the hole in the shutter is bot @ point; henee the
group of mays which enter it form in reality a cone whoee base is the
by a soreen perpenilicular to the line joining the hole with the centre
of the aun, the image formod will bo a circle. If the rays aro inter
eepled by an oblique plane, as in the figare, the image is elliptical,
“But ft never takes the form of the hole when that % wall,
—
BLS Opries.
In accordance with thie principle, wo find the illuminated patches
ofearth formed by light passing between the leaves in a forest of a
cireular or elliptical ehapé. bn an eolifes of the #un, whew the yisi-
bie portion of the sun is of crescent shape, the patebes of glt all as
wumo tho crescent forut ; that is, they ave images ef'the wisible part of
ie sun,
458. Camera and Lens. —If a double-convex Jens be
placed in the aperture and'a sereen in the focus, the image
will be brighter and more sharply defined.
Fig. 816,
If now, i
tead of the room, we substitute a box, we ball
ry camera used in sketching the outlines of a
landseape or buikling, and also employed in the Warious
branches of photography. ‘This latter ose constitutes tte
principal importance at the present time,
Wher the mys of light passing into the exmera trough
the Jons are allowed to strike upon a mirror inclined atan
have the or
SS
CAMERA OBSCURA. 395
angle of 45°, they are reflected to the top of the box, and ifa
plate of ground glass be inserted there an upright image will
be formed.
‘This image can very easily be copied by means of trcing-
paper laid upon the glass,
‘A camem arranged in this way Is very convenient for artists in
aketching landscapes, It may also bo wied as azourse of amusement
in repreneuting street scenes with all their life and motion, ‘The box
containing the mirror is generally made to slide in the box to which
the lens is fitted, so that the focus can radily be found.
Fig, 817.
459. Portable Camera for Artists. — For taking views
the camera obsctra should be light and portable. The best
form is that shown in Fig. 517. It consists of a sort of portable
tent of black cloth, within which isa table for receiving the
image, and at the top of which is a tube bearing a prismatic let
that produces the combined effect of the mirror and lens.
figure projected upon the table may be traced out with a pon
cil on a sheet of white paper.
396 OPTICS.
Fig. 418 shows the course of the rays in forming the image.
‘The rays coming from the object, AB, fall upon the convex
Jace of the lens and are converged. and In this state they reacts
the plane surface, m, which is inclined to the horizon. Being
totally reflected from the surface, m, they emerge through the
slightly concave surface below, and go to form an image, a4,
on the table, P. A sheet of paper is spread on P to receive
‘the image, and on it the outlines may be traced,
Fig- 318
460. The Photographer's Camera, —Fig. 319 repre-
sents the form of camera need in the process of -
ing. It consists of a rectangular wooden box, ©, te
of which is attached a tube, A, beariog & Jems. whet
the Image. ‘The opposite face of the box consists of a alidling
drawer, B, holding a plate of ground glass, upon which the
image, #, is thrown, and by drawing itout or sliding it im, the
picture may be rendered distinct upon the glass. “The Gnal
addjustinent in getting the plate of glaas in the focus is made
by means of the pinion, D. When the image is clearly de
fined, the plate of glass Is removed, and a plate of metal or
glass introduced which bas previously been prepared: by cor
tain chemical processes so a8 to be sensitive to the actinic
property of the sun. ‘Tho image is then imprinted on thir
plate.
‘There are two kinds of photographic pictures, positing abd
negative. Positive pictures are those that have their lights
ais. al
THE EYE. 897
and shades in their proper relative position ; negative pictures
aro those in which the lights and shades are reversed in
position.
Fig. 819.
A nogative picture is taken on glass in the way described; it is
then placed upou papor chemically propared, and exposed to the wan's
rays, thus prodaciag a positive picture. ‘The full dotails of the pro-
cones involved in the art of photography belong to the province of
chemistry rather than physics, and will wot be considered here.
Fig, 820,
46t. The Eye is a collection of refractive media, by
menns of which we are made acquainted with the external
world through the sense of sisht.
As au optical instrament the eyo fs not, ax generally supposed,
theoretically perfect; it has faults, to some extent, of apherical
and cliromatic aberration, but its remarkuble properties ul wAGwlorgon-
898 OPTICS.
tion and self-adjustient make ita practical instrument of marvellous
power,
‘The shape of the eye ts spherical, with a slight protuber-
ance In front; the average diameter of the human eye isa
little less than nine tenths of an inch. Fig. $20 represents
a aoction of an eye, with some of the coverings thrown back
80 a% to show the position of the parts.
‘The front part of the eye is limited by a perfectly trans-
parent membrane, ¢, called the cornea, The remainder of the
exterior coating is an opaque white membrane, S, called the
sclerotic cont; this is a tongh, white, opaque, flbrous mem-
brane. The cornea is set in the sclerotic cont, as a watch-
glass is set in its frame.
Immediately behind the cornea is a transparent flaid, tim-
pid as water, called the aqueous humor, Tu this Moats a
circular curtain, Ai, attached by its outer edge to the sclerotic
coat, and having small circalar opening at its middle. ‘Tho
curtain is called the iris, and the hole in its centre fx eallict
the pupil. The iris gives color to the eye, being black, bite,
gray, cto, It is muscular, and by the contraction and ex-
pansion of the fibres, the pupil may be enlarged or dimin-
ished ; it is throngh the pupil that rays of light enter the
eye.
Behind the iris is a double-convex lets, 6 ealled He ery
talline lens ; it ia of the consistence of gristle, perfectly trans-
parent, more curved behind than in front, and ts denser
towands its middle than at the edges, ‘This lens, with the
cornea, serves to converge the rays to foci behind it, Imme-
diately behind the crystalline lons is a mediom wéerly Gilling
the remainder of the cavity of the eye, called the witreous Am
mor; it is of the consistence of Jelly, and perfectly transpar-
ent, permitting the rays to pass through it. “These Lumors
keep the eye symmetrical.
Immediately behind the vitreous humor is a thin white ex-
pansion of the optic nerve, N, lining ncarly all of the sele-
rotio cont; this is called the retina, and is the sest of vision.
-
WAlies" 2
THE BYR. 399
Behind the retina, and between it and the sclerotic cont, ia
a fine volvety conting enlled the choroid cont, covered with a
binck pigment, which absorbs the rays that pass the retina,
preventing internal reflection, The sensation of sight is
conveyed fo the brain by the optic nerve, which goes to the
brain.
462. The Mechanism of Vision.— The action of the
eye is similar to that of the camera obscura, except more per
fect: the pupil corresponds to the hole in the abutter, the
crystalline lens and cornea form tho imago, and the retina is
the scrven on which the image falls. ‘The iris corresponds to
the diaphragm, which is used in the ordinary camera to mod-
erate the light by cutting off all the rays except those which
fall upon tho central part of the lens,
‘The image om the retina is inverted, as shown In Fig: 920, foe
the ray cross as in the onliuary camera. .'This ean be proved by
taking the eye of an ox and paring off the back of it so as to nearly
expose tho retina ; thon hold én front of the eye a eandlo, ite inverted
nage ean be seen in the back of the eye,
Many theories have been propesod to explain why we do not seo
foverted Images of objects. The fact thut we always sco Images
erect seems to be duc to the interpretation by the mind of the sensntion
earried'to'the ‘brain by the opti ncrre. ‘The sense of touch-is aled
suppored to arsist in detoruiining correetnoss of pesitina.
463. Distinct Vision. — ‘The oye adapts itsolf'to different
distances by changing the convexity of the erystalline lens by
muscular contraction and relaxation. For distant objects
‘the lens is made less convex, as the rays are more readily
brought to a focus upon the retina; but for near objocts the
Jens ig rendered more convex on account of the greater dill
culty of securing the focas.
‘The eye adjusts itself to different dogrees of intensity by
varying the eize of tho pupil. If the light is too intense, the
fris contracts the pupil so tlint less will enter; if too weak, it
expands the pupil, thus admitting more ight.
400 OPTICS,
Each improssion mado upon the retina no wasaeene fn
sceand j Eilat a lene tt Gan Ca (ha io ote
Tine, When the impressions snocead one another with greater
ity than this, ono continuous impreasion will be produced. Tey
drope of rain appear like liquid threads; a stick whirled round pap.
idly with a spark of firo at one end gives a circle of Light, as men-
tioned In Art. 421. Tho spokes of a earringe-wheol revolving with
great velocity cannot bo distinguished,
464. Near-sightedness and Farsightedness.— Per
sons who see distinctly only at very short distances are said
to be near-sighted ; and those who can only sce distinctly at a
long distance, far-sighted.
Nran-siontepyess comes from too great convexity of the
cornea or crystalline lens, or both; also from too an
elongation of the eyeball, so that the retina is too
‘The effect is to bring the rays to focl before reaching the ret-
ina, giving an indistinctness to vision. This defect is remedied
by holding the object very close to the eye, or by using spec-
tacles with concave lenses, which diverge the rays before
falling upon the cornea, and thus enable the media of the eye
to bring them to foci upon the retina. If the eyes arc mulike,
the lenses should be of ditforant power,
Far-sicnrepyrss is a defect just the reverse of
edness. It arises from too great flatness in the cornea or
crystalline lens, or it is due to the retina being too near the
cornea on account of the flatness of the whole eyeball, so
that rays of light are brought to foci behind the retina. ‘This
defect is remedied by using spectacles with convex lenses.
465. Vision with two Eyes. — An image of every ob-
ject viewed is formed in each eye; yet vision is not double,
but single.
‘This is undoubtedly owing to the way the eyes are com
nected with the brain and with each other by means of the
optic nerve. They are not so much two distinct organy as
one double organ, both parts of which ars associated for the
purpose of performing 1 single act. 7
— =|
THE STRREOSCOPE. 401
466. The Stereoscope. — Simultaneous vision with two
eyes is supposed to give us the ides of relief, or form of ob-
Jects, —a view which receives confirmation from the action of
the stereoscope,
‘This is an apparatus employed to give to flat pictures the
appearance of relief, that is, the appearance of having three
dimensions.
When we look at an objoct with both ayes, each eye sees a
slightly different portion of it, ‘Thus, if we look at a small
cube, as a die, for example, first with
one eye and then with the other, the
head remaining fast, we shall observe
that the perspective of the cube ix dif.
forent in the two cases. This will be
the more apparent the nearer the
Tf the cube has one face directly in
front of the observer, and the right
eye is closed, the other eye will sco
‘the front face and also the left-hand
fuce, but not the right; if, however, \]
the left eye is closed, the other eye 4
‘will eee the front face and also the 4
Tight-hand face, but not the left. 7
Hence we know that the two images
formed by the two eyes are nob abso- la chad
Tntely alike, It is this difference of images which gives the
idea of relief in looking at a solid body.
Tf, now, we suppose two pictures to be made of an object,
the one as it would appear to the right eye and the other as
it would appear to the left cye, and then look at them with
both eyes through lenses that cause the pictures to coincide,
the Impression is precisely (he same as though the object itself
were before the eyes. The illusion is so complete thi is
almost impossible to believe that we are simply viewing gic
wires on a fut surface.
i
SUMMARY. 403
Distinct Vision.
Aadjustinent of the Eye to Distance,
Adjustinent of the Eye to Different Degrees of Intensity.
Duration of the Jinpressious on the Retina.
Examples.
Near-sightedness and Far-vightedness.
Definition of the Terms.
Causes.
Vision sith tivo Eyes.
Explanation.
The Stereoseope.
Definition.
Mlustrations of the Principle.
Covstruction explained by Figures
el dss
CHAPTER IX.
ELECTRICITY,
Part 1. —MAGNETISM.
SROTION L — NATURE OP ELECTRICITY. — GENERAL PROPERTIES OF
MAGNETS,
467. Nature of Electricity. — The real nature of eleo-
trivity is difficult to determine. It manifests itself chiefly in
attractions and repulsions, but itis also recognized by its
luminous and ‘beating effects, by its power in chemical de-
compositions, and, at times, by the violence of its action.
All electricity has the chmmeteristic of polarity, or two-
sideduess, und is uow generally conceded te the dae to moloo~
ular motions. Several theories have been advanced In regard
to its nature, some of which will be considered hereafter.
We may conveniently separate ft into three divisions:
Magnetism, whieh, althongh formerly ascribed to a special
force, is now identified with electricity ; Frictional Electricity ;
and Dynamical Electricity.
468. Natural and Artificial Magnets. — Natural mag-
nets are certain ores of iron, and are generally known under
the name of loadstones,
The magnet is so called from the town of Magnesia, in
Lydia, where it was first noticed by the Grocks. It is known
in chemistry as magnetic oxide of iron. It is now found in
coneiderable quantitics in Sweden aud Norway, as well as in
many other countries,
=|
MAGNETISM. 405
Artificial magnets ase bara of tempered steel, to which the
property of the natural magnet has been imparted. Th
artificial magnet is far more valuable and powerful than the
nataral magnet, and is generally used in practice,
Steel is. mixture of iron with a small quantity of carbon, and
when heated and then plunged Into water, it becames exceedingly
hard, and capable of retaining the magnetism that may be imparted
to ft. Stoel magnets are permancat magnets.
Fig. 322.
‘Magnets may be rnado of soft iron or untempered steel, but they
do not retain their magnetism when the exciting cause is removed.
Such magnets nre called femporury magnets,
Aniificinl inaguete for experiment are made of oblong barr, from
twelve 1 fifteen foches in length, as represented io Figs S32, SER.
‘They aro somotiines made in the form of a horwe-dhwoe, we vheree Na,
aco
406 ELECTRICITY,
Fig. 834. Sometimes they are mado in the forn of thin loo
ueedle, as shown ia Pig. 224. This is the forn i whieh they are
constracted for puinting ont the direction of the magnetic weridan,
a in compasses, In this form thoy are also axed im maay magnetio
experiments.
469. Distribution of Force in Magnets. — The foree
with which a magnet attracts Iron is not the same in all of
its parts, The attraction is strongest at its extremities, from
which it docreases towards its middle, where it is nothing.
Fig. 2%
This may be shown by planging one end of m tangnetized
dar into iron filings; on withdrawing it, the filings will be
ecen adhering to it in long filaments, as shown in Fig. $22,
If the entire bar be rolled in the filings, it will be found that
they adhere to both ends, but not to the middle.
The two ends, where the attraction is strongest, are called
poles, and the central part, where the attraction is nothing, fy
ealled the eguetor, or the neufra! fine, and the magnet is said
to exhibit polarity.
Every magnet has two poles aud one neutral Ine, whether the
magnet bo natural or artificial. Semetimes, besides the two prim=
cipal poles, there are other ininur poles, called secondary poles, Tey
Ss
MAGNETISM. 407
artificial magnots these arise from inoquality of temper in the steel
bara, ot from want ef proper care in magacticing thom. Wo shall
suppose each mugnet to have but two poles.
We shall presently see that a magnet when freely snspended
always assumes a position with ove pole pointing towards the north
and the other towards the south. ‘Tho end puinting towards tho
‘north is called the north pole, and the other end the south pole,
‘To dintinguiah between the two poles of an artificial magnet,
the north pole end iy geuorally marked with a + sign or with the
letter N
Fig. 224
‘Tho dotion of & magnet npon iron takes place through intermediate
bodies. If a magnetized har be cavered with a sheet of paper, and
then fine from filings bo sifted uniformly over tho papor, they will be
seou arranging themselves in regular eurves around each pole, ux
shown in Fig. 323. No netion is observed about the neutral line,
the filings falling there as on any other surface.
479. Action between Magnets. —If we compare the
action of the two poles upon soft iron, we observe the same
phenomena, — both will attract ordinary iron. It is not 20,
however, when we compare the action of two mnaguets upon
each other. Ifto the same pole of a magneric needie.ab<
a
408 ELECTRICITY,
balanced on a pivot (Fig. $24), we present in succession the
two poles of a magnetized bur, held in the hand, we observe
the curious phenomena that if the pole, a, of the needie
attracted by the pole, ZB, of the bar, the pole, 6, will he re-
pellod by it; if the pole, a, is repelled, the pole, 6, will be
attracted. .
471. Hence the following law: Like poles repel, and wutihe
aatiract cach other.
472. Effect when a Magnet is broken. —If we break
a magnet into pieces, every plece becomes a perfect magnet
with its two poles and neutral line, as sown in Fig, 525. If,
now, these pieces are still further divided, the number of mag-
nets will be equal to the number of divisions, and so on in-
definitely. Thus, we cannot resist the conclusion that éxeh
molecule is a maguet complete in all its parts.
26 we have a maguct, VS, showing the polarized molo-
cules, the white halves repro-
senting ono pole, the north or
positive pole, and the blsel the
south or negative pole,
‘Tho opposite polarities neutralize each other at the oettey, bat
strongly manifest themselves at the ends of the
All the molocules exact a positive foree towards V and « negative
towanls S.
473. Magnetic and Diamagnetic Bodies. — Magnetic
substances are those which are attradted by a magnet, a
from, steel, nickel, and cobalt. By using very powerfal
magnets Faraday found that certain substances are repelled
by magnets, such as bismuth, antimony, zine, tim, meneury,
lead, silver, copper, gold, and arsenie. These are called
diamagnetic,
MAGNETISM. 409
‘Tho greatest degree of repulsion is seen in bismuth, and
attraction in iron. But the repulsion between the magnet
and bismuth is not so strong as the attraction between the
‘maguet and fron,
474- Magnetism by Induction. — Ifa ring of soft iron
be presented to a mag-
net, as an ivon ring, it
converts it into a mag
net. Tf a second ring
be presented to the first,
it is in Tike manner con-
verted into a magnet,
and so on for a third, s
fourth, ete, The mag- Fig. 827,
nots thus formed adhere to one another, as shown in Fig.
827. If the bar be removed, the rings cease to be magnets,
the chain falls to pieces, und the rings separate. ‘This mode
of exciting magnetic phenomenn is called magnetizing by
induction.
Tnduction ean bo explained by supposing that in the unmagnetized
tings the two opposite ur polar forces neutralize each other, and no
tmaynetie action is oxhibited; but when they aro brought near the
tnagnet these forces separate, and each ring becomes a magnet, and
unlike polos attract ono another, as soon in the figure. ‘The inducing
tungnet loves none of its mnguetic force.
475. The Coercive Force. ~ Sof iron brought in con
tact with a bar magnet becomes a magnet instantly, and on
being removed returns to its neutral condition, ceasing to be
a magnet. With hardened steel the reverse Is the case: it
takes considerable force and some time to render ita magnet,
‘and on being removed from the bar it continues to be a mage
net. To make the magnetism complete in steel, it must be
rubbed with one of the poles of a magnet.
‘This foree which alfers a realsuunce to the sepurition of the two
polrities ia magnetic bodice, and also tends to prevent a recombina-
when ouce seperated, ix called tlie coercive forces
a
MAGNETISM. 411
If, instead of mounting the needle on a pivot, it be at
tached to a piece of cork and placed in a vessel of water, so
that the needle may float in a
horizontal position, it will turn
itself slowly around and come
to rest in the same general
direction us though it were
balanced on a pivot. In this
experiment it will be found
that the needle ence in the
neni does not advanes
either towards the north or
south. Hence we infer that
the force exerted upon the
needle is shnply a directive
one.
‘The foree which causes a movable magnet to direct itself
north and south is called the directive force.
Since the phenomenon deseribed takes place at all points of the
earth's surface, the earth has been regarded a4 an jmencnse taguot,
having its north and south poles near the north and south poles of the
earth, anda neutral Iine near the equator, This immenso magnet,
acting upon the sinaller maguets described, would produce all of the
effects observed. Whea we come to explain the action of electric
currents, it will be seen that there is another explanation of the diree-
tive power of the earth.
Acconting to the law that like poles repel and unlike attract, the
pole, A, in the figure ia really the south polo, and tho pole, B, the
north pole of the needle.
But in practice it is gonorally customary to call the end of the
magnet pointing towards the vorth, the north pole, and the one point
ing towards the eouth, tho south pole,
N
Fig. 023,
477. Magnetic Meridian— Declination.—Variations.
— When a balanced magnetic needle comes to a state of rest,
it points out the line of magnotic north and south. Ifa plane
‘be passed throug! the needle in this position and the centre
Charleston, 5. C., along which the ne
north ; this is called a line of no
‘The lino of no declination ix tra
a rato whicl would earry it around:
For all points of the Taioet States est,
the declination of the needle is to thew
‘of it, the declination \s to tho east ; th
in all casos is inclined towards tho line of
For all points in the United States
Acetination, the declination is slowly
to the weat of it, the declination is slowly d
goes slight changes, some of whieh are
others yery irregular, In our latitude the
needle moves towards the west during the ene
day, through an angle of ten or fifteen minute
back again during the latter part of the day. 1
the diurnal variation. To the southern | ly
is reversed. There is also a stall change o
which takes place every year, called the:
Irregular changes are called perturbations.
Pe
MAGNETISM. 413
placo during thonder-storms, during the appearanen of the ausura
porcalis, aod in general, when there is any sudden chango in tho
.glectrieal condition of the atmosphere.
478. The Compass.— The property possessed by mag-
nota of arranging themsclyes in the magnetic meridian has
boon utilized in the construction of Compasses.
Fig. 829,
Fig. 329 represents a compass. It consista of a compase-
box, having « pivot at its centre, on which is poised a delicate
magnetic needle. Around the rim of the box is a graduated
circle, whose diameter is somewhat leas than the length of
the needle, and of which the pin is the centre. The pin is
‘of hard stecl, carefully pointed ; a piece of hard stone is let
Into the needle, in which is a conical hole to rest upon the
Pivot, to diminish the friction between the needle and its
support. In addition to the graduation on the circle, the
bottom of the box ix divided into sixteen equal parts, indi-
oatlag the points of the compass.
a
414 ELECTRICITY.
‘This invtrumont undor various forms is used for a great variety
of purposes. It is used in navigation, In surveyings aid ix of
finportance to tho tmveller aud explorer, to. say nothing off 34 me
in mining.
ihe ingot anion 08s eT
tho true meridian is known. This is found by astronomical methods,
‘by taking observations of tho north polar star, or the sun, and au io=
atroment called the declination compass is used. "This form of com-
pass has a telescope turning on a horizontal axis ina vertieal plane.
Let the compass be eo placed that the line, X'S, coincides with the
true meridian; then when the needle eomes 16 rest, tho reading
cic oki oe
is 19° west.
479. The Dipping Needle.—When « steed needle,
mounted as shown in Big. 828, is carefully b
compass is remedied by making the
other end of the needle a little
heavier, by adding a movable weight,
as a plece of wire wound rouned the
needle and capable of sliding along
it.
‘To show the dip and to measure:
it, the needle is mounted in tho way
indicated in Fig. 830. "The nowdle bs
suspended on a horizontal axis, so.
that it car move up and down freely,
and the amount of the dip is indik
cated by a graduated cirele or quad
rant. The dip indicated in the:
— _ |
MAGNETINM. 415
figure Is 54°, which is the angle made by the needle with the
horizon. At any place the dip will be the greatest possible
when the needle vibrates in the plane of the magnetic
meridian.
‘Tho dip varies in passing from place w place, inercasing as we
approach the magnetic poles of the earth, whero the dip is 90°; that
is, the noodle is perpendicular to the horizon. At the anagnetic
equator it is horizontal,
Action similar to that exerted by the earth on the needle is
shown in Fig. 331, Wo have here three positions of the dipping
necdle ropreewuted apon a bar magnet. At tho onds of the mag-
ict the positions of the needle are the sane as when over tho
Fig. 331
magnetic poles of the earth, ‘The centro position corresponds to the
position of the needle when over tho magnetic equator, "The dipping
needle follows the law that unlike poles attruct and like repel.
Summary. —
Directice Force of Magnets.
Hlustrated by x Noodlo toning on a Pivot.
Mustrated by a Neolle attached to u Picee of Cork
which i# floated on Water.
Earth aa n Magnet.
Poles of the Needle.
Magnetic Meridian.
Definition.
True Meridicen,
Definition.
Declination of the Needle,
Definition.
Bast and West Declination
MAGNETISM, ai
equal to the dip. In this position the earth acts upon it by
induction, the lower end manifesting south polarity (in our
latitude), and the upper end, north.
‘The maguetism thus induced is only temporary; for if the
bar be moved from its position, tho opposite polarities neu-
tralize each other. If, however, when the bar is in position,
it be struck smartly by a hammer, or if it be violently twisted,
sufficient coercive force may be developed to retain the ine
duced magnetism for a time.
Fig. a2.
481. Magnetizing by Friction. — Bare of steel, and
needles for compasses, are usually magnetized by rubbing
them with other magnets. The three methods are called the
methods by single touch, by separate touch, and by double
touch.
‘To magnetize a steel bar by single touch, we hold the body
to be magnetized in one hand, and with the other we pass
over it a powerful bar magnet, as shown in Fig. 332. After
several repetitions of this process, always in the eame direo-
tion, the steel is found to possess all the properties of a mag-
net, These properties are the more durable in proportion
to the hardness of the steel,
‘To magnetize a steel bar by separate touch, we bring the
Via
418 ELECTRICITY.
two opposite poles of two magnets of equal force fi the middle
of the bur to be magnetized, and then move them simulta-
neously to the opposite ends of the bar,
‘To magnetize a body by double touch, we muke use of tro
magnetized bars, which are placed with their opposite poles
in contact with tho bar at its middle point, being kept at a
fixed distance ly a piece of wood placed between, as shown
in. Fig. 383; the combined bars are then moved alternately
Fig. 238.
fn opposite directions to the two ends of the bar, and the
operation is repeated several times, finishing in the middie
of the bar, Care must be taken to apply the sane number of
touches to each end of the bar.
The method of magnetizing by dynamical electricity will be
reated of under th ad of Ei ical Currents.
482. Magnetic Battery. —Armatures.— A Boxpir
or Macxers, consisting of a group of magnetized bars united
so that their polos of the same names may be coincident, is
called a mognotic battery.
Sometimes these bundles are composed of straight bars,
=|
MAGNETISM. 419
like that shown in Fig. 332, and sometimes they are carved
in the shape of a horse-shoe, as shown in Fig. 334.
Magnets, if nbandoned to themselves, would lose ina short
time much of their power; hence
it is that armatures are employed.
An Anmatore Is a piece of soft
Tron placed in contact with the poles
of amagnet. Thus, ad, in Fig. 334,
is an armature.
‘The poles. acting by induction
upon the armature, convert it into a
magnet whose poles are of the oppo~
site kind to those with which they
come in contact. Those two poles,
reacting upon the poles of the mag-
net, 4 4, prevent the neutralization
of the two polar forces, and thus
preserve its magnetism. ‘The arma-
tare is sometimes called a Leeper.
If weights be attached to the keeper
All it separates from the magnet, wo can,
from the number of pounds applied,
Judge of the power of the maxnet,
For many kdods of magnetic experi+
mont tho horse-shoo form is preferable,
Tk is also the form Dest adaptod to the
application of an arnntare ot kooper.
Wheu the maguets aro in the form of Mg. 56.
ams they are arranged in pair, and the armatures placed at the ends,
os shown in Fig. S34.
Pigg 35.
‘The power of a maguct is liable to be lessened by heat or rough
i
ELECTROSCOPE, 42%
acquired the power of attracting light bodies, on being rubbed
with woollen cloth or cat's skin.
‘To repeat theso exporitnents, rab a tube of glass or a stick of
sealing-wax with a piece of woollen cloth, then present them to light
Bodies, ax shreds of gold-leuf, burbs of quills, or fragments of paper,
and the latter will be seen to approach and adhere tothe excited glass
br sealing-wax. Tho glass and pealing-wax are then sald to be
electrified. "Ihe manner
‘of making these experi
mento ig Indicated in
ua
6.
At will be seen here-
afer that resin and other
wabstances named above
not only develop fore-
es of attraction whon
rubbed, but also thoy
become luminous, emit
sparks, and display a
number of other prop- Fig. 886,
erties, all of which aro known as clecttieal phenomena,
Sineo tho beginning of tho soventcenth century the progress of
discovery in electricity has been rapid, and a multimdo af new frets
‘have boen developed, which have beon so well studied aa to form o
vory extensive brauch of uatural selene.
‘The Greeks-appliod the namo elektron to amber, and henee the
name electricity was given w the power of attraction exhibited by
‘this substance,
484. Electroscope. — Electrical Pendulum, —-An
Exrecrnoscore is an apparatus for showing when a body Is
electrified.
‘The most simple clectroscope is the Ennernica, Pexpo-
LEM, Which consists of a small ball of elder pith, suspended
by a fine sitk thread, us shown in Fig. $37. The thread is
fastened to the upper end of a stem of metal, which stem bas
@ enpport of glass.
‘To ascertain whether a body is electrified or not, the pendalurm ie
a
422 ELECTRICITY.
presented to ft; if it is electrified, the pith ball will be attracted,
otherwise nol, When the quantity of electricity ts too senall to gre
duce sonsible attraction upon the pith ball, more dellexto inatrarmente
are sometiines employed.
485. Two Kinds of Electricity. —That there are two
kinds of electricity may be shown by the action of glass and
resinous bodies, after being rubbed, upon pith balls.
If a tube of glass be rubbed with a piece of sill, and then
predented to the electrical pendulum (Fig. 337), the pith hall
\a
Fig. 337, Fig. 3
will at first be attracted, and after a short time it will he re
pelled, as shown in Fig. 338, ‘The ball is then cluarged with
the same kind of electricity as that in the glass.
If now a piece of a resinous body, a6 seallog-wax, be
rubbed with flannel and brought near the excited plth ball,
the Intter is ime: attracted to the former: Tn Lice
manner, if the sealing-wax be first presented to the penda-
lam, it will be attracted and then repelled. If then the ginas
be brought near the pith ball, attraction will be observed.
This shows that the action of electrielty, as developed In glass
and resin, is different, the one repelling when the other
attracts.
b |
BLECTROSCOPE, 423
‘The electricity devoloped in rubbing glass with a piece of
sili has been named vitreous electricity; that developed by
rubbing resin or scaling-wax with the flannel has been named
resinous electricity. We now use the term positive (+) to
designate vitreous electricity, and negative (—) to designate
resinous,
486. The Gold-Leaf Electroscope.—When the quantily
of electricity is too sual to produce sensible attraction upon
the pith ball, more delicate instruments are sometimes cm-
ployed, like the gold-leaf electroscope.
Tt cofiaists of a glass bottle or jar, olosed ut the top with a cork,
miuates at the top in a
ball of metal, ant at ite
Jer extremity iu too
slips of gold-louf. The
beth Ld
in Fig. 30.
Tho cork and the
whole top of the bottle
aré covered with a kind
Ini on with a bruch,
and serves to make the
‘bottle a better aon-con-
dactor. This kiad of
varnieh jis often used in
Ley experiments w
render glise won-oon-
ducting. Gloss iu a dry
Mate isa good pon-conductor, but it is apt to condense moiatuse frat
the air so as to become a conductor. When covered with way rvnin=
008 ‘this troulde ip removed.
487. ‘Method of using the Gold-Leaf Electroscope.—
Toa H whether a body is electrified, we Weing the Wall of en
Fig. 309,
HYPOTHESIS OF TWO FLUIDS. 425
Into-contact with the earth, or when pluced upan supports of metal,
charcoal; or any molest iubstanco whatever, They remain in an
electrified condition for a long time when placed upon supports of
glass, resin, sulphur, or-whon suspended hy silken cords.
From these fucts we conclude that metals, charcoal, and the like,
permit the electricity t pass freoly through thom, while glass, resin,
aalphur, ete. oppose its passage. ‘Tho latter class of bodies are
not entitely inenpablo of conducting cloctricity, but they are ex-
twemely poor condactors. Wheu an electrified body is surrounded
by nom-condactors it is said to be insulated, und any non-conducting
support of an electrified body is therefore called an insulator,
The best conductors of electricity are the metals; afer
these come plumbago, well-caleined carbon, acid and saline
solutions, water either in a liqdid or vaporous form, the
homan body or animal tissues, vegetable substances, and in
general, all moist ov humid substances,
The worst conductors, or best non-conductors, are resins,
gums, india-rubber, silk, glass, precious stones, spirits of
turpentine, oils, air, and guses when perfectly dry.
490. Hypothesis of Two Electrical Fluids. —To
account for electrical phenomena several theories have been
proposed. The two principal ones are the one.fluid theory of
Frawxcrs and the two-fluid theory of Syxnter,
The former maintains the existence of only one electric fluid, whose
particles are eclf-repellont. This fluid exists in all bodies in vary~
ing proportion, Tn ite natural state every substance has exactly ite
«own quantity; but when electrical excitement occurs, it is positicey
electrified if it has an exress of its natural quantity, and negatively
cloctrified if thero fv a deficioney. Equilibrinin is restored in positive
bodies by parting with the excess, and in negative bodies by supply-
ing the doficioney from surrounding bodies.
the Peart theory maintains the existence of two electric fluids
whidh exist in noxcited bodies in equal quantitivs in a stato of neu-
tralization, When separated they attract each other, but the particles
of either fluid repel one another.
‘Thess two fluids wore at first named the vitreous and the rerinows
fluids, but more recently they have been called the positine atid the
METHODS OF ELECTRIFYING BODIES, 427
of bodies, A crystal of Iccland «par prowsed between tho fingers
becomes positively electrified. When a pice of sugar is broken sud~
only in a dark room, a feeble light is observable, which is due to the
of electricity at the moment of separating the molecules,
Ifa plate of mica be quickly split, cleetricity ix developed. Some
minerals, particularly tourmaline and topaz, manifest electrical phe=
peer on being beated.
This fact was first discovered in the caso of tourmaline, which first
attracts and then repels hot ashes when placod among thom. ‘The
éleetricity produced’ by the methods just mentioned is similar in its
action to that produced by friction. Frictional electricity 8 somo-
‘times called station! electricity because it can be retained for some
‘Hine ou excited bodies. Electricity produced by chemical composi=
tions and decompositions of bodies will be considered under Dynami-
eal Electricity.
493- Methods of electrifying Bodies. —Non-con-
ducting bodies nre electrifled only by friction, but conductors
may be electrified cither by friction, by contact, or by
induction.
In order to electrify a metal, it must be insulated ; that is,
it must be surrounded by non-conducting bodies, and it must
Ve rubbed by an insulated body.
This may be offected by mounting the metal upon a stand of glass:
and rubbing it with a non-conductor, such as a pines of silk, Were
‘tho metal not insulated, the electelelty would go to the earth ws fast
as generated, and were the rubbing body not a non-canductor, the
eleetsielty would pass off through the bands and arms of the experi-
menter.
‘The method of eleetrifying by contact depends upon the property
of conduetibility. If a conductor is bronght in contact with au elec
tified body, a portion of the electricity of the latter ix at once im-
parted to the former body. If the two bodies arn exactly alike, the
electricity will be equally distributed over beth. If they differ in ize
or in shape, the electricity will not be equally distributed over both,
‘Tho method of éleetrifying bodies by indvetion is similar to that
of magnetizing bodies by induction, aad will be treated hereafter:
_494- Accumulation of Electricity on the Surface
— Experiment shows that when a body is clectei-
Mi
428 ELECTRICITY.
fied, the electricity all goes to the surface of the body, where
it exists in a thin layer, tending continaally to escape. It
actually doce escape as soon as it Onds an ontlet through =
conducting body.
Of the various experiments intended to show this fhet, we
select one that was first performed by Cocroms. He mounted
‘4 copper sphere upon an insulating rod of glass, as shown in
Fig. 310,
Fig. 340. He then provided two hallow hemispheres also of
copper, which, when put together, exactly fitted the first
sphere, and these he insulated by attaching them to glass
handles. Having placed the hemisphere 80 08 to cover the
solid sphere, be brought the whole apparatas in contact with
an electrified body till it was fally charged.
On removing the apparatus from the electrified bedy, be soparnted
tho two hemispheres abruptly, and applied to emehs fn tee thee eles.
& il
TENSION. 429
trical pendulum, when he found that both were electrified. On
testing the solid sphere a like wanaer, be could diseover no trace of
fu other words, it was perfoetly neutral. In taking away
from the body its outer coating, he had removed every particle of
ite olectricity, which proved that the electricity was entirely upon the
surface.
Another fact which indicates the #sime conclusion 1, that a hollow
wod a solid sphero of the same sizo aud of the same material will be
charged with exactly the samo quantity of eleetrilty when made to
communicate with the sawe electrical source.
‘The following experiment was invented by Farapay to
prove that electricity is confined to the surfice of bodies. A
metallic ring (Fig. 341) is fixed
vpon an insulating stand; attached
‘to this is a conical linen bag, A
silk thread passes through the apex
of the cone, so that the bag can be
turned inside out as often a8 neces-
sary without discharging the elec-
tricity. When the bag is electrified
the electricity is found to be on the
outside, and if we turn it inside out
the same is true,
‘Thers aro two exceptions to thia rule. Fig, StL.
A hollow wire will not conduet electricity as well ax a solid one of
the mame diameter. Electricity may be induced on the innor surfxco
‘ofa bollow conductor, if we place within it an electrified body inau-
lated frown the conductor.
495- Tension of Electricity. Whon electricity is no-
cumulated upon the surface of a body, it tends to escape with
8 certain foree, which is named the tension,
‘The tension augments with the quantity of electricity acoamulated.
Bo long as ft docs not pass a certain limit, it ix held hy the resistance
‘of the air, bot if the tonsion pases this Limit, the olectricity oscapea
swith w crackling noise and a brilliaut light called tho electric spark. Tu
‘moist wir the tension is not as grat asin dry wir, Leanne wane «fh Yom
Mi
SUMMARY. 431
at every point of the sphere, and consequently it is inferred
that the distribution is uniform over the whole surface.
When the body is elongated and pointed, as in Fig. 342,
different results are obtained. In this case the proof-plane is
more highly charged at the sharp end of the body than at any
other point, showing a larger amount of electricity at the
point than elsewhere.
Tu general, it may be shown that the greater the curvature of a
surface ot any part, that ia, the nearur it approaches a point, the
greater will bo the accumulation of electricity ther,
‘This shows that electricity tends to accumulate at, or to
flow towards the pointed portions of bodies,
Summary. —
Discovery of Etectrical Propertica.
By Thales of Miletos, in Amber.
By Dr. Gilbert, in Glass, Resin, Silk, ote.
Mothod of developing Electricity by Friction illustrated
by Figur.
Origin of the Name,
The Electroscope.
Definition,
Electrical Pendulum.
Description.
Method of ascertaining whother a Body is eloctrified.
Tico Kinds of Blectricity,
Shown by the Electrical Pendulum and illustrated by
Figure.
Vitroons, or Positive Electricity
Electricity.
Gold-Lenf Electrosenpe.
Description.
Mothod of using the Gold-Leaf Electroscope.
Dlustrated by Figure.
Law of Electrical Action.
Conductors and Insulators.
Definitions.
Moustrutions.
Exainples of Good and Poor Conductors.
Resinous, or Negutive
INDUCTION. 133
Fig. 343. On the right of tho figure is the prime conductor
of an electricnl machine, which, a8 we shall see hereafter, is
charged with positive electricity. On the left is a metallic
eylinder with spherical ends, and supported by a rod of glass.
Attached to its lower surface, at intervals, are pairs of pith-
ball pendulums, supported by threads of some conducting
substance, fs ne has
When the cylinder is a
brought slowly towards
the electrical machine,
we see the pith balls re-
pel exch other and di-
verge. ‘This divergence
js unequal at different
points, being greatest
near the extremitios of
the cylinder; towards
the middle of the eylin-
der the pith balls remain
in contact without repel- Re, B48
Hing each other. We conclude from these facts that the elec
tricities are driven towards the extremities of the cylinder,
while the central portion remains in a neutral state, thas
showing polarity as in the action of 2 magnet on soft iron,
If a stick of resin be rubbed with silk and brought near the pith
balls towards tho electrical machine, thoy will be repelled, showing
that that end of the oylinder is negatively electrified, If it ix brought
none the pith balle at the remote extromity of the eylinder, they are
attracted, showing that that end of the cylinder is positively elvctri-
fied. Finally, the olectricitios in tho two onda are equal in quantity,
as may be shown by removing the eylinder, when they neutralize
eve other,
‘Tho positive electricity of the machine, then, simply acts to sep-
arate the two flaids, attracting the nogative Muid to the end nearest
it, and repelling the positive Huid to the opposite end of the cylinder,
No oloctricity passos from the eloetrifiod body to the one in a nontral
state when Induction takes place.
oe
INDUCTION. 435
nets upon the disk by induction, drawing the positive elec-
tricity: to the tin-foil on its lower face, and repelling the nega-
tive eloctricity to the foil on the upper facg.
In this jrdition, if the uppor face be touched with the tloger, as
shown in Pig. SHG, the negative electricity will be drawn off lato the
body, and the disk will be charged with positive electricity. If tho
disk be raised from the resinous plate by ite handle, aud touched
Fig. 046. Fig. 947.
with the knoekle, as shown in Fig. 347, 4 spark will pass, which iw
flue to tho negutive electricity passing fen the body to.the pasitively
electrified plate.
Tf now we continue to repent the manipulation, exhibited in Figs.
HG, BAY, a succession of spurks may be obtained without the neces
sity of rubbing the resin again with the eat's skin. If the air is dry,
the resin will continue in an electrified state for a very long time,
goo. The Electrical Machine. — The
cure is a machine by means of which an unlimited amount
of electricity may be generated by friction.
‘This machine was invented about two hundrod youre age by Orta.
‘rein a i re
he ball, a quantity of frietional elotricity was develope,
‘One of the best machines for ordinary p
machine represented in Fig. S48,
‘The principal piece of the machine is a cirendar plate of
glass, mounted upon # horizontal axis and turned by a crank.
At the right of the plate, but 0 constructed as to embrace a
portion of ft as we turn the crank, are two rublers, aaually of
leather covered with an amalgam (a mixture of tin, zine, apd
mercury) which by their friction develop 1
‘The brass cylinder in front of the plate is ealled the
conductor ; it ts insulated by a glass standard to the
electricity from escaping to the earth, At the end of the
conductor nearest the plate is @ picce called a “comb, from
the fact that a great number of projecting teeth are Beek!
its side noxt the plate, but not to touch it.
The silk bag serves to keep the electricity on Pr
> i
ELECTRICAL MACHINES. 437
The negative conductor Is the brass «phere at, the: right in-
sulated by a glass standard,
Finally, wll of the ends of the cylinders in the machine are
wrought Into spherical forms, to prevent the dissipation of
electricity a8 much as possible.
sor. Use of the Electrical Machine.— When the
plate {s turned rapidly, the friction of the rubbers develops
& gront quantity of positive clectricity on the glass, and nexn-
tive om the rubbers, which is conveyed along the chain to the
earth, and thus disappears.
The positive electricity on the plate acts by induction on
tho prime conductor, attracting its noyative electricity. ‘This
collects on the teeth of the combs, and neutralizes the positive
on the glass plate. ‘The prime conductor, thus haying given
up its negative, remains charged with positive electricity.
Whea we want negative clectzicity we can take the chain from
thw rubbers and place it on the primeconductor, ‘The electricity will
thou collect on the nogative oouductor.
If both conductors are insulated there is yery little electrical action,
‘ve the two eleetricities hol wach other in check. Phe plate gives up
‘Ho electricity t the prime conductors it only attencts its negative.
502. Holtz's Electrical Machine.— The Hore ma-
chine is based on the principle of continuous induction, It
consists of two circular glass plates (Fig. 349), about one
tenth of an inch apart. The larger one, A, is fixed and ine
salated, but the smaller one, 4, can be made to revolve very
near it. In A are two openings, or windows. Across these
and partly covering them on the back of the plate, 4, are
glavd two varnished papers, or armatures, with tongues, (/",
which project into the windows. Two metallic combs, PP,
are placed in front of the armatures, on the other side of the
plate, B. These combs are connected by insulated con-
ductors with the knobs mm, which may be called the poles of
the machine.
‘Tho distance between the knobs is regulated by the sliding
rod attached to the knob, m. which has a wooden handle,
238 ELEOTRICITY.
Tn operating tho machine the two knobs are first brought
together; one of the armatures, /, for instance, is
charged by holding agninst it a piece of valeanite, which has
previously been excited by rubbing it on « cat's skin; (thes
induces positive electricity on the face of B next to it, and
negative on the opposite face, ‘The latter attracts the posi-
tive from the comb, /, together with that of the comiuctor amd
Fig. 210.
knob, #, and leaves them charged negatively. ‘The tongue,
JS, facilitates the passage of electricity.
When we turn the plate, B, which ow charged with
positive electricity, and bring it opposite the armature, 7%
induction again tnkes place, the positive glass attracts nega~
itive electricity from f', leaving it positively changed, at the
same time negative clectricity is drawn through the comb,
P’, leaving m positively charged.
After the plate is tumed a few seconds, the charges of the
knobs and armatures are strengthened, and the two Knobs,
being the negative pole and m the positive, are then gradaally
lat i =|
ELECTRICAL MACHINES. 439
‘separated. A torrent of eparke will pass between the two
knobs. If-we connect one of the poles with the ground by
a chain, the other may be need as a prime conductor.
This machine is very much alfocted by tho moisture of the air,
although its power is very much greater thu the plave machine, the
Tength of the spark being nonrly equal to tho radiue of the re-
volving plate.
503. Carre’s Dielectric Machine has much to recom-
mend it. It is @ combination of the Holtz and the plate ma-
chine. Its power is greater than the plate, but much less
than the Holts. Moisture in the air aifects it about the sume
‘ag the plate, but loss than the Holtz machine.
Besides theso methods for producing electricity, many other ar-
rangemonts have boon devised. ‘Tho hydro-electrie machine gener>
ates clectcielty by causing atean charged with rericles of water to
issue forth from jets attached to a steam-beiler. ‘The frietion of
these globules of water aguinat the surface of the jets genenstes the
cletricity.
504- Precautions in using the Machine. — After the
prime conductor is electrified, if we cease to turn the plate, anit the
air is dry, apith ball attached to the prime conductor will descend
slowly, showing a gradual dispersion of the eloctricity. If the air
in damp, the Dall doacends rapidly, showing a rapid loss of electrioity.
Electrical experiments seldom succeed ia a datop day. Ta order that
they should bo successful, the instrument, as woll as the surrounding
atmosphere, ought to bo perfectly dry.
Only « certain amount of electricity oan be retained on the prime
conductor, after which, If the plate is turned, the teuxion becomes: so
grout that it esenpes throngh the earth or along the glass logs of the
conductor, and all that is goverated continues theuceforth to be dissi
pated. ‘The pith ball tes that the instrament is fally charged
Dy céstsing to rise, aud remaining stationary ns the plate is tumek
505. Electrical Condenser. — An Execrnican Coxpex-
St is an apparatua employed for the accumulation of elec-
tricity. They are of various forms, but are all essentially
composed of two conductors, separated by an insulator.
Fig. 0. n
n large quantity of positive electricity
and of negative clectrieity on the outsid
After the jar has heen charged, if it be
other is brought in contact with the bation,
through the arms and body, called: the electric shi
roturn to ite neutral state, When it is desirable:
without tho shock, the discharger is used, as
‘One ball of the discharger ix made to touch
the other is then broaght in contact with the: on
there is A spark emitted, and the jar returns to ite
507. Electrical Battery. —An E
consists of an assemblage of Leyden ors, #0 00
wet like a single condenser. a8 shown in Fig.
are placed in a box whose bottom is lined
ELECTRICAL MACHINES. 441
serves to connect their outside surfaces, Their inside sur
faces are bronght into communication by connecting the sev-
‘eral buttons with metallic rods.
To batteries the jars aro made large, and aro covered within and
without with tin-foil, the futerior lining being brought into commu-
nication with the button of cach jar by a wetallie chain. Upon one
Fig. 351.
of the butions Is placed an electrical pendalam, which indicates the
‘oxeess of the flaid on tho inner over that én the onter eurfaco.
‘The battery iv charged by attaching » bar, « portion of which is
seen in the figure, or chain te the knob of one
of the Jars, and also to the priine eondoetar.
08. Leyden Jar with Movable
Coatings. — The tin-foll coatings of the
Leyden jar act morely a8 conductors, and
the opposite electricities reside chiefly on
the opposite surfaces of the glass. Fig.
G2 representa a jar with movable coat-
Ings. When the jar is charged it is placed
‘on an insulating stand,
The pices aro taken apart, as shewu
in the figure, nnd the two coatings are found
To eontain little or no electricity, But when
the parte are jut together again, a charge
May be roceived from it almost as great as it
would have given if the coatings had not been
Fg
litt
ELECTRICAL MACHINES. 443
shock felt by the experimenter when it is done with the hands,
were described in treating of electrical condensers. A simi~
lar spark, but not eo brilliant, can be drawn from the prime
conductor of an electric machine whon the finger is presented
to it. A shock will also be felt, but not so violent as that
from the jar, It isa sharp, prickly sensution, —_
‘The spark arises from the combination of the two opposite lee-
tricitics. The positive electricity, acting at o distance by induction,
drives the positive electricity of the band to the earth, and attimcte
‘the negative; consequently the bedy of the experimenter becomes
togativoly electrified. Whon the tensions of tha positive electricity
of the machine and the nogative cleetelelty of the body overcome the
resistance of the alr, they rush together with n sharp emok and a
bright light which constitutes the spark. When the electrical ma~
chine is powerful, the sparks take a xigaye course, like lightning
from a storm-cloud,
sto. The Electrical Stool. —A spark may be drawn
from the human body when properly electrified. For this
purpose an Exneriicat Soot, that is, a stool insulated by
means of glass legs, is used. A person standing on the
stool, and taking hold of the prime conductor, becomes,
when the plate is tarned, positively clectrified. If a sec-
‘ond person now attempts to shake hands with the first, a
shock will be experienced,
and a spark will pass between
them.
sur. The Electrical
Chime is 4 collection of
bells that are made to ring
hy means of electrical attrac-
tlons and repulsion.
‘Tt consists, in the case
shown in Fig. 853, of three
bells suspended from a hori-
zontal bar of wood, m. The
a
d
ELECTRICAL MACHINES. a5
523. The Effect of Points in Electrical Action. —
‘The aceumulation of electricity at points gives rise to a high tension,
which is sulficlent to overcome the resistance of the alr and to give
rise to au escaping current. In fact, metallic bodies of a pointed
rhape soon lese tho electricity imparted to them, und often the eseap-
ing curreut may be felt by placing the hand in frout of the poim. Uf
a candle-flame ie held near the point, it will be blown away {roe it.
Uf the flow takes place in a darkened room, it umy be discovered
by a feathery jot af faint light,
Tho current {s formed by the repulsion of the elcctrified air ta the
vieinity of tho point. "Tho molecules aro polarized, give up eloetri-
ety opposite to that with which the polat Is charged, which unites
Te
Fig. 356.
with the electricity of the point to neutralize it, and consequently, be-
coming themselves charged with tho eame kind an the point, are re~
pellod, and new ones take their places ; henea the current.
In working an clectrie machine, all cbjcets with points, aa angular
objects, should be avoided. The prime condoctor toxds to alsstrart
from surrounding objecta their negative clectricity, and to retura to
ita neutral eundition.
Tho effeot of ueighboriog bedics may be illustrated by bringing a
metallic point near a eharged prime conductor. When the polat is
at a considerable distance from the conductor, the pit
prime conductor begins to fall, showing a loos of elect
It ie kometines aid Chat the point draves off tho electricity from
the conductor, but this ix not the ease; the polot abstracts none of
ELECTRICAL MACHINES. 447
‘The duration of the electric spark is exceedingly brie If we
divide @ elrele into black and white
sectors (Fig. 357), and then eause i¢
to rotate so rapidly that the sectors
Blend into a uniform gray, if the cvom
bo durkened and the eirele {Timinated
by @ spark from the Leyden jor, it will
appear perfectly still, and every iudi~
vidual oectoe will be distinctly seen
516. The Electrical Egg is
nn eggeshaped light, produced by
the passage of electricity through a vacuum,
The method of exhibiting this light, and the apparatos em-
ployed, ate stiown in Pig. 358, ‘The apparatus consists of a
hollow globe or oval of glass, con-
taining two swaall metallic spheres
at some distance apart. The upper
one communicates with the prime
vonductor, and the lower one with
the carth.
‘The globe may be deprived of its ine
toraul oir by moans of the sir-pump.
Then, if the plate of the machine be
turned, cleetrivity will escape from the
machine to the earth throagh the two
balls, and bocanve tho bolle are in a
vacomn there will be uo obstruction
to ite posse, If the experiment is
made in a darkened room, « beautifal
violet-colored Light will be seen be-
tween the tuo balls, of the shape Fig. S64
shown in the Byure.
517. The Electrical Square consists of a square plate
of glass, pan one surface of which a thin strip of tin-foll ta
fastened, ronning hackwards and forwards across the plate,
as shown by the black line in Fig. 859, One end of this
448 ELECTRICITY.
stip of tin is made to connect with the prime conductor of
the electrical machine, and the other end is made to com-
manicate with the earth by
achsin. ‘The square is insa-
Inted by legs of glass.
When the plato ix tured,
au current of electricity flows
through theatrip af tin from the
machine to the carth, asd po
spark Is given out. Tf, however,
the tin is brokea at any point,
there will be a successlon of
«parks ut that point, which will
be eo close tngether ax te pro=
doco & contingows light. Tf,
now, the tia be broken by a pen-
Fig. 89 Knifo, so that the points of rop-
ture are arranged in a definite figure, ax that of a flower, for in-
stanes, a continuous light will be seen at ench of these points, nod
the figure will appear as if 4
traced upon the glass with
fire. Any kind of figure
inay be drawn, of words
inay bo written on the glass.
Tho experiment is inoro
striking fn a darkened room.
518. Heating Power
of Electricity. — The
heat developed by elec
tricity Is snilicient not
only to inflame ether,
gunpowder, coal gas,and
the like, but also to melt
andl volati
P
the manner of inflany
Ing other. It ty poured
he metals.
360 represents
BLECTRICAL MACHINES. 449
into a glass vaso, through the bottom of whielt passes a metal-
Me wire terminating in a button. ‘The wire is connected by
‘a chain with the outer covering of a Leyden Jar, When the
circuit is completed by touching the button of the apparatus
with that of the jar, a spark ix given off, and heat enongl
developed to inflame: the ether.
‘This experiment succeeds with a very small jar, or even a simple
kpark from the prime conductor. The oxporiinent may be nade
more interesting by standing upou the clectrieal stool, and indlaming
the ether with the finger, ‘The ether nay be intlamed by a spark
from « piece of ioe held in tho hand.
Fig. 961.
When an electrical tavery is discharged through a fine metallic
wire, It may be melted of oven volatilized, according to the power
of the buttery.
Tn performing this exporiment it will be best to use the universal
Wischarger. ‘This Sustrument and the manner of using it are shown
fn Pig. 261. The divcharger wonsiate of Wo copyor wives, A anh By.
Ue
ELECTRICAL MACHINES. 451
ductors. They consist of violent expansions, with tearing,
fracturing, and the Ike.
‘These effects ure generally exhibited by placing the body upon
the plate, M, of tho universal discharger (Pig. 361), and then pass-
ing a powerful charge from a battory throagh it. In this way a
sinall block of wood may be torn to splinters in an instant,
Pig. 862 reprosonte un apparatus by means of which a hole may
‘be torn in a cani by using a single Leyden jar. A card is placed at
the top of a glass cylinder, beneath which is a wire projecting from
a metallic plate, Tho plate couneets by a chain with the exterior
coating of the jar. Above the cand is a second wire, whieh fs insa~
lated in the manner shows in the figuro, When the circuit is coun-
pleted, by wouching the npper wire with the button of the jar, a shook
follows, and the cand is found to have boca picreed aa if run through
by a needle or pin.
520. Chemical Effects of Electricity. —The electric
spark Is capable of producing chemical reactions. Por exainply,
water is fonned of oxygen und hydrogen gnees,
in the proportion of ove volume of the fonner to
‘two volomes of the latter, Now, if these two
gases be inixed in this proportion, and an elec
trical park be passed throngh the mixture, the
gases instantly uuite and form water. Moreover,
the combination takes place with a brilliant flash
of light and w Tond report, the report being dve
to the expansive force of the vapor which is pro-
duced at the momont of combination. Tt is upon
these principles thit the cletrical pistol ropre- Fig. 268,
sented in Fig. 36:5 is constructed.
Nitric acid i formed by the passage of electric sparks through
tmoist alr,
Sulphuretted hydrogen, aumnonia, and carbonic acid are decoua
posed by the electric spark.
‘Tho chemical -ellocts of frictional electricity are not a powerful or
varied as those of dynamical, whieh will be considered wider that
subject.
§21. Physiological Effects of Electricity. — The
Parsioioaican Errecrs or Ececraterry are the effects which
a
ATMOSPHERIC ELECTRICITY. 453
Effect of Points in Electrical Action (continued).
Loss of Electricity from the Prime Conductor whea pear
Pointed Objects.
Current formed. .
Action of Points on a Flame illostrated by Figure,
Rotution of the Electric Wheel explained.
Velocity of Klvctricity. — Duration of the Spark.
Velocity through Copper Wire.
Duration of Spark Wustrated by Figure,
The Electrical Fag.
Method of producing this Light exphined by Figure.
The Electrical Square,
Method of illuminating th Square explained by Figure.
Heating Power of Electricity.
Tiustrated with the Leyden Jur and Ether.
Ilusteated with Battery and Wire.
Mechanical Effects of Electricity
Shown by the Battery and Block.
Shown by the Leyden Jar and Cant
Chemical Effects of Electricity,
Iu combining Oxygen and Hydrogen by tho Elvetrical
Pistol.
Tn decomposing certain Compounds
Physiological Fifects of Electricity.
THastrations,
SECTION IY. — ATMOS!
$22. Identity of Lightning and the Electric Spark.
—The complete identity between lightning and electricity
was established by Dr. Fanti, at Philadelphia, in 1752,
He raised a silken kite, provided with a metallic point, jast
before a coming thinder-storm, ‘The string of tho kite was
of hemp; attached to the lower end of it was a small key,
and fastened to the key was a silken cond, by which the
kite might be insulated. It wos only after the string became
damp from the falling rain that the key showed signs o€ being,
IC RLRCTRICITY,
THUNDER. 455,
A tlash of lightning ia often of great length, and as it takes placa
along the line of least resistance, it genorally follows o zigzag path,
us is often tho eas with the spark from a Leyden jar. Whon we seo
ito entire length we call it chain-lightning. When a flash of lightning
fs seen in the lower regions of the atmosphere, it has a brillinnt
white color; but in the higher regions, where the air is rarefied, it
assumes x violet hue, similar to that of the eloctrie ee (Art. 516),
Shoet-lightwing ix that which tlasbee through the clouds, eausing
‘extensive iIluinination.
Heat-lightning is supposed to bo the retleetion of the lightning of
‘distant storms.
526, Thunder is the sound which follows a flash of light-
ning. Tt is due to vibrations caused by the passage of the
spark through the air, and the clashing together of the mole-
cules of nir in filling the vacuum caused by the lightning.
‘Thunder is wot heard tll an appreciable time after the flash is
perceived. This arises from the fact that light travels with immense
‘Yelocity, maching the eye instantancously, while sound wavels more
slowly, and roaches the car only after « sousiblo interval of time.
The distance of a clap of thunder inay be ascertained by counting the
number of seeands between the Hash and the roport, and allowing
five seconds to a tile.
‘The intensity of the sound diminishes as the distance becomes
greater: near by, it is sharp aod rattling, like boants falling ove
upon the other; at a greater distance, it ix dell, and prolonged in «
Tow romble of varying intensities.
The rattling or rolling of thunder ts differently explained. Ry
nome it is said to be duc to a succession of echoes from the clouds
and the earth. Others regan! lightning, not as a single spark, bat as
a suecdewion of eparks, cach giving rise to separate oxplosions that
mnoened cach other so rapidly ax to prodoce n continuous rumbling
sound. Otherg again attribute the rolling of thunder to the zigeag
conrse of the lightning, the sound fram differwnt points of the risen
path roaching the ear in times proportional tw their distances. Tu
this way the sounds from different points are superposed irregularly,
giving rito to irregularity in the resulting sand.
§27. Effects of Lightning. — When an electrified cloud
passes near the earth, it acts upon it by induction, repelling
LIGHTNING-RODS. 487
§29. Lightning-Rods. —A Liouryixe-Rov is a rod of
metal, placed upon a ling or ship to preserve it from the
effect of lightning. Gulvanized iron or copper is now gener-
ally used.
A lightning-rod should fulfil the following conditions : —
1. It should be of sufficient size so as not to be melted
while carrying the charge off.
A copper rod of half an inch in diametor, or an iron one of threo
fourths of an inch in diameter, is large enough tw protect any
building.
2. They should be of one piece throughout.
%. ‘They should terminate in points to give roadler egross
for the electricity that is set free by Induction.
4. The rod should be carried down into the earth till it
meets with a good conducting medium, such as a layer of wet
or moist earth,
When no such medium can be renched, « pit #hould be dug, and
after the lower end af the rod las been carried to the bottom, it
shoal be nearly filted with same good conductor, as coke. ‘This will
also prevent rusting.
A rod is supposed to protect # circular space about it, whowe radius
is about twieo the length of that portion of the rod that extends above
the bailding. Tho lightning-rod was invented by PRawaLix, who
thought that its protective action consisted in drawing off the elec
ticity from the cloud, and condacting it to the earth.
‘Tho real explanation of its utility is just tho reverse. The cloud
neta by induction upon the earth, repelling the electricity of the asiuo
ame aa that In the cloud, and attracting that uf an opposite name,
which securnulates upon the bodies undor the cloud. Now, by arming
a body with metallic points communicating with the earth, we permit
‘a pasenge of electricity frum tho earth to the elond, This not only
prevents the accumulation of electricity upon the body, but it tends
gradually to neutralize the olectricity of tho elond itself, and thus tho
rod nets io a double way to prevent the body from being struck.
Whon the electricity vet froo ix morn than the conductor cam dixe
charge the lightning strikes, but the rd receives the discharge, owing
tu ite higher conducting power, and proteets the building.
458 RLECTRICITY,
530 The Aurora Borealis. —The Avkoka is = Temi-
nous phenomenon, which appears inost frequeatly about the
poles of the earth, aud more particularly about the boreal or
northern pole, whence ite name.
At the chee of twifight a vague nod dite Hight appenes tts the
borizem in the direction of she magaetic weridkus. "This Hight jerade-
ally awumes tho fonu of an arch of a pule yelluwiah cobor, Iuving its
ecuocsre side turned towunls the carth, Frou this sreh stresue of
Pig, 264
Tight shout forth, passing fran yellow to pale grocty amd thew to the
most brillinnt violet purple. “These ray
converge to th nt of the heavens whieh
ping needle hey then appear to form a fragment of ai iinevessn
cupola, as show
Since the antvra ys aeccenpanted by = disturtianen ef the
J is geocrally arranged bn the direction Of the
dip, and acts upon te oh wires, It is fuferned that Ht i die to
eeotrical action, Serh in at present the generally received belie
magnetic nealle,
SUMMARY, 459
Summary. —
Identity of Lightwing and the Electric Spark.
Discovered by Dr, Franklin
Method of its Diseovery.
Atmospheric Electricity,
Found in the Clouds and in the Atmosphere when five
from Clonds.
Method of detes
Causes of Almospheric Electricity,
Friction of the Air.
Evaporation and Condensation of Water,
Vogetation,
‘Combustion.
Lightning.
Definition,
Ditforent Kinds.
Thunder.
Definition,
Mothod ef ascertaining the Distance of Thunder.
Rolling of Thunder explained.
Effects of Lightning.
Why Lightulng strikes
Examples of the Deetructive Effects of Lightuing.
The Teturn Shack,
Definition and Cause,
Experiment with Frog.
Lightring-Rods,
Dofiuition
Conditions of a Good Rod.
Explonation of the Action of a Lightulng-Row
The Aurora Borealis.
Definition.
Mlustrated by Figure
pining the Electrical Condition of Clouds.
CURRENTS. 461
thea touch the lege of the frog with tho other end. At overy contact
tho tmuseles contract, reproducing all the motions of life.
Gavraxr attributed the phenomena observed to the electricity
existing in animal tissnes, which, passing from the nerves to the
muscles, through the metals, produced the muscular contruction».
532. Volta’s Theory of Contact. —Vorra repeated
the experiment of Gatvant, and after much stady advanced
the theory of contact. According to this theory, when two
metals or other dissimilar substances are simply “brought in
contact, there i always a decomposition of the natural elec-
tricity of both bodies, the positive electricity going to one
and the negative to the other.
In the case of the frog the electricity was supposed to be devel-
oped by the contuct of the copper hook and xine plate, the nerves
and muscles serving imply as conductors,
533- Fabroni's Chemical Theory. — Fanon first
suggested that the phenomena of the pile (Art, 540) were
due to chemical action. He observed that zine became
oxidized in contact with water containing acid when joined
with copper, and thonght that this oxidation was the prin-
cipal cause of the electric action.
It sceme now ta be generally acceptad that the separation of the
oleetricities is eansed by the contact of two difforeut metals, but that
the constant supply of elustricity is kept up by ehemteal action.
934 Current Electricity. —If a plate of zinc, Z, and
ane of copper, 0, be placed in a mixture of water and weak
sulphuric acid (Fig. 366), a slight chemical change takes place
in the ense of the zinc, and bubblos of hydrogen gas will col-
lect on its surface und escape to the surface of the liquid.
The zine will gradually waste away. Connect the plates with a
metallic wire. The chemical action is more violent; the zine
wustes away more rapidly than before; a greater amount of
hydrogen is set free, but it is disengaged at the surface of the
copper instead of the zi iectrical action is now manifest.
This apparatus ix called a simple voltaie element, or couple.
ELECTRODES, 465
536. Action of the Acid. Amalgamation of the
Zinc. —If zine Is placed in water, It decomposes it, forming
zine oxide, and setting the hydrogen free. This action coos
‘not Jast long, as the zine becomes coated with a film of the ox-
ide, whieh is insoluble. The sulphuric acid, however, seizes the
oxide of zine, and forms sulphate of zine, which is dissolved
in the ligaid, thereby leaving a clear surface on the zine.
Chemically puro zine is not attacked by dilute sulphurle neld wutil
tho dloctrio current begins. Cowmercial xine, however, is usually
impure, mud is acted on rapidly by the acid, und consequently wasted.
‘The impurities in the aine, usually consisting of iroa or lead, also
ennee local currents, and this accelerates the chemical action and wastes
tho aine, without adding to the quantity of eleotrieity in the general
current that passes over the wires, ‘To prevent this waste, the zine
in galvanic battorios is usually amalgatnated, that ia, rubbed over
with inereury, after it has first bean cleaned in dilate acid,
537- Electrodes. — Poles. — If we cut the wire connect-
ing the two plates in the liquid (Fig. 366), positive electricity
will tend to accumulate at the end of the wing attached to the
copper, or negative plate, aud negative on the wire connected
with the zinc, or positive plate. ‘These ends are called the
poles of the battery, Sometimes pieces of platinum are at-
tached to the ends of the wires, as the ordinary metals would
suffer corrosion in many experiments.
"Tho term electrode is now often used instead of pole, Joining the
two electrodes is culled closing the efreuit ; separating them, breaking
the cireuit. Care inust be exercised not to confound the poles with
the plates of the couple. ‘The positive pols ix joined to the negative
plate, and the negative pole to the positive plate.
538. Electrical Potential.—The Exrcrncat Porextiar
is that property ofa body by means of which clectricity tends
to pass from it and flow to another body,
Tn order that water may flow there rust be a difference of graviti~
tion level, and we notice olso # flow of heat when there is a difference
oftemperntare level; und so we may say that to get a Dow of elec=
trlelty there must be » difference uf electrical lowel, or, ka other words,
BATTERIES, 465
‘cach couple being separated from the next by a layer of eloth moist-
eued with dilute eulphurio acid, which acts spon the metals aud the
Tiquid in the eases already mentioned, ‘The couples are all disposed
fu the same order, the zinc of each couple belug always on the sane
side of theeorresponding disk of capper. When the pio fs completed
there will be a disk of xine at one end and a disk of copper at the
other. A connection is made between them by means of the wires, a
and }, one being attached to cach of the extreme plates.
In the pile shown in Pig. 367 there are twenty couples, the copper
disk being at the bottom of each couple, and the inc one wt the wp.
Fig. 807.
‘The pile ls supported by a suitable framework. ‘These disks are
opt in placo by glass rods.
The pile is insulated by placing it on glass or resin. The positive
electrode, a, eouneets with the copper plate, and the negative Jy with
‘the zine,
541. Constant Batteries. — Batteries constructed on the
Dineiple of the voltaic couple have sabstantially gonp out of use om
necount of the rapid enfeoblement of their cavrents. In order to pe
enre & eonstint current, the permanent depcsition of hydrogen on the
inactive metal inuct be prevented, as this interferes with the current.
(hi
BATTERIES. 467
deaited. A: sinall quantity of nitric acid whled to the solution in-
croasea the constancy of the battery.
544. The Mercury-Sulphate Battery. — A buttery,
small in #820 but of considerable power, ean be sade by itnmersing
alue plates in x solution of sulphate of inereury coftalued in aubun
cops, ‘Tho ze takes axygen from the water, forming oxide of zine;
the hydrogen escapes, and decompeses the mereury sulphate into aul-
phurle noid and mereary. ‘The latter amalganates the xine, and the
sulphuric acid dissolves the zine oxide.
545- Daniell's Battery, — This was the first form of the
constant battery; in respect to the coustancy of its action it ia, in all
probability, the best of the constant batteries. Fig. 870) representa
f alagle couple of this battery. ‘There is an outer vessel of glam
or porvelain, filled with a solution of sulphate of eopper (loo
vitriol), which is kept saturated by some crystals of the sulphate
placed at the bottom af the vessel. A copper eylindor is tumnersed
fo this, perforated with holes. Inside this eylinder is a thin porous
‘vee! of nnglazed earthenwarg filled with dilute
sulphuric acid, ia which ia 1 cylinder of
ins, t
When this battery is in action, water is
decomposed: the oxygen goes to the xine,
forming oxide of zinc, which is dueolved by
the sulpharie acid, giving salphate of xine.
Tho hydrogen of the water coos to the sul-
phate of copper, aud desompesos it into me-
tallle copper and sulpburle acid; the former us
deposited on the copper plate, while the latter gore to the zine to
replace that already used in forming sulphate of zine. Tho result of
these deeompositions and recomporitions Is to keop up a current of
clectricity, which will continue as long ns the outer yossel is kept full
‘of the saturated solution of sulphate of copper.
546. Grove’s Buttery. — Fig. a71 represents one of the
elements of this form of battery. The outer Jar, which s wade
‘of glass, 18 partially fillod with dilute sulphurte nel, and in thls in
placed w eylinder of ano with m sht at the side for the preage of
the liquid. The ioer versel is made of porous curthenware, and
BATTERIES. 469
current; and the intensify of the clectricity, or ite power of
traversing a condactor with marked effect. Intensity may
be more accurately defined as the quantity of electricity which
passes through a conductor in a unit of time.
‘The law established by Ono is expressed as follows: The ine
tensity of the current equals the electromotive force divided by’ the
‘The resistance of a conductor depends upon threo things ite eon-
ductivity, its cross-section, and leagth. ‘The less the couductiag
power, the groater the resistance, the greater the eroes-«cction, the
Jess the resistance; and the greater the lougth, thegreater the resist~
ane, ‘The larger the wire, the less obstruction to the paseage of the
current, and tho longer the wire, the greater obstruction,
Tnan ordinary cell there are two resistances that offered by the
Liquid conductor between the two phites, ealled the infernal rvsistance,
and that by the conductors ovtside, eulled the external resistance.
‘The resistance of the liquid conductor is vastly greater than that of
any motal, ‘The distance between the plates ix the length of the
liquid condoctor, aud the size of the plates the arva of ite cross
section, When the internal and external resistances are equal, we
get the most satisfactory resulta
‘The unit of resistance is callod an ohm. Tho resistance of an
‘ordinary Dauiell's cell is about half an olin; of a mile of submarine
telegraph eable, from four to twelve ohms. Copper wire yy of an
inch i diameter has a resistance of about one ohm for sixty feet.
549 Quantity and Intensity.—A battery may de-
velop a large amount of electricity with Httle intensity, or
A small amount with great intensity. The intensity de-
pends upon the number of cells, the quantity upon the extent
ofsurface. If the external resistance is great compared with
the internal, increasing the number of colls adds to the inten-
sity; a8 in the case of the electric light, since the current most
puss between the charcoal points through the sitspace, the
resistance must be great and the number of cells should be
large.
To seeure great intensity we can form a battery of couples, Bun-
en's for example, by connecting the zine eylinder af one eouple with
SUMMARY. 47
frictional electricity ; the current begins and continues
steadily with the chemical action in the cells, whereas frie-
tional electricity accumulates and is discharged with instan-
taneous explosive power; voltaic electricity also clings to
conductors with more pertinacity than frictional, which makes
it available for telegraphing.
‘Tho electricity of the machine is small in quantity, but of enor-
mous intensity ; that of the buttery, of enorinous quantity but alight
intensity. It Is the intense energy of the former that cuables it ty
pase through poor conductors, as the lightning through the inter=
‘voning air, while the fecblo energy of tho latter allows it to pass
through only the smallest interval of air, but makes it fallow the
conducting wire with fulthful accuracy from cuntinent to continent,
‘Trxpatt compares frictional electricity 10 a cuble inch of alr,
which, if compressed with sufficient power, may be able to rapture
a very rigid envelope; and voltaic eleetricity to cuble yunt of alr,
which, if not #o coinpreseed, may exert Dut a feeble pressure upon the
surfaces which bound it.
‘Phe pusitive conductor of au electrical machine eorreeponds to the
positive pole of a galvunie battery, and the negative conductor tw
the negutive pole, and the friction ou the plates to tho chemical action
in the couples.
Summary. —
Voltaic Batteries.
Definition,
‘Voltaic Pile.
Pile Mustrated by Phare.
Constant Batteries.
Disuse of Voltaic Pile
Action of Coustunt Buttery.
Smee’s Battery.
Potassium Bi-chieomate Battery.
Mereary-Sulphate Battery.
Daniell's Battory.
Grove's Dattery.
Bunpen’s Battory.
Pomes of Grove’s and Bunsen’s Batteries,
HEAT AND ILLUMINATION, 473
The effect of galvanic electricity upon the bodies of dead animals
is pooulinrly striking. It produces violent contractions of the muscles,
causing inctions ehuilar to those of the living being.
553: Heating Effects. —When current of galvanic
electricity is passed through 2 conductor, it becomes heated,
and often to such a degree as to produce fusion or even va-
porization. When a powerful current is passed through a wire
of very small diameter, it soon becomes incandescent, and
then melts or is dispersed in vapor, and burns with splendid
Urillianey.
‘The emaller the wire and the less the conducting power, the
jgrvater the resistance to the current, and the more iutensy the Kear.
Silver burs with o grecninh light, much smoke arisiug from the
vaporization of the metal. Goll buras with a bluish white light.
Platinum, which is infusible in the most intense heat of our furnaces,
imelts Into spherical globules with « dazzling Tight. Carbon is the
only body which has wot been fused by gulvanie electricity. Dns
prerz, however, by pussing a current throagh suall rods of pure
carbon, succeeded in soft them so much that they could be bent
sani made to adhore, whieh indicates an approach to fasion,
‘The heat thus developed is used in fring nitro-glycerine and gun-
power blasts even under water. ‘The explosive substance is placed
ina tightly clusod vessel, and through it a fine platinum wire is con~
nected at cither end with the wires frum a battery. On account of
the fineness ani poor conductivity of tho platinum it offers great re
sistanes to the passage of the current, and, becoming nwl-hot, ignites
the chance. We can show that the hent produced is proportioned to
the resistance it pacounters in the conductor by passing a strong eur
rout of electricity through n chai composed wf alternate links of silver
aud plativam; the platinum beemmes red-hot, while the silver ne
santine dank.
554- Illuminating Effects. —The heating effects just
described, are accompanied with a disengagement of move or
Jess light; but to obtain the most brilliant electrical light pos-
sible, dense carbon points are employed. They aro at first
placed in contact, one being connected with the positive, and
the other with the negative pole of a powerful galvanic bate
ELECTROTYPING, 416
quantity of sulphuric acid is wided to improve its conducting power,
for pury water is a very imperfect cooducter. Two narrow belle
glusses, Af and Q, are filled with wator and inverted over the two
platinum wires. ‘Tho tubo, a is then connected with the positive
pole of the buttery, and tho tube, &, with the nogativo pole. A cur=
rent is eet op from oue wire to the other through the water, aud
clecompasition begins, as is shown by bubbles of gus zisiog in the twa
bell-glansos.
By testing tho gusen thas obtained, wa find that in the glass, O,
‘currveponding to the positive pole of the battery, is pure oxygen,
while that in the glass, Jf, corresponding to tho wegative polly ie
pare hydrogen, We sce ulav that the volume of hydrogen is twive
Fig, 378,
that of the oxygen. This experiment shows that water is composed
of one volume of
of oxygen aul hydrogen, mixal in the proporti
the former to two of the latter.
‘The bodies soparated at the positive pole are electro-negative, ns
they are supposed to be charged with uegativo electricity, aud thee
soparated at the negative ary electro-positice. Moat of the metabe wo
to the negative pole, and the non-snctallle substances to the positive,
when the eleetraiee are plunged fute salutions uf eomnpuands like
chlorite uf copper, iodide of potassinn, sulphide of iron, ete.
556. Application of Electricity to Electrotyping.
—Exxerrorreixo fs the operation of copying metals, wood-
cuts, types, and the like, in metal, by the aid of galvanic
electricity.
‘The first step is the preparation of a mould of the object
v6 ELECTRICITY.
upon the accuracy of which depends the success of the entine
operation, An impression of the object is taken in wax.
The surface of the mould to be copied is brushed with
powdered graphite, to increase its conducting power.
Fig, 377 shows the method of depositing the metal mpoo the
imould, Af is a vessel filled with » solution of salphate of coppers A
and B aro metallic rods communicating with the t%e polos of the
battery ; the mould is suspended freon the rod, BB, amd daekng it ke a
plate of pare copper suspended (rom the rod, 5 these constlnete the
electrodes, the mould being the negative one.
Fig. S17.
The corrent which is set up throngh the solation of
es decomposes the sulphate into salphurke
and pure copper. The snlphurie neid goes to the
and, uniting with it, produces sulphate ef coppers the
e de that Is, te the mond, st
© hours, or four owen: with
ines thiek enough to
toved from the monld, and it then presents m= fu
object ug medals, enel Cane fe
y, nod tho two arv united by moans of some Susie
2 them.
i
if
trees the ele
iF
i}
F
f cupper ber
Ht
He
to te copied. In cop
ES =
ELECTRO-PLATING. Ww
557- Electro-plating and Electro-gilding. —'The pro-
‘cess of covering bodies with thin coatings of goli or silver
is analogous to that of clectrotyping. The perfection of the
process consists in making the coating of gold or silver not
only of uniform thickness, but also closely adherent.
‘The method of silvering, or electro-plating, is shown In Pig. 378,
Tho object to be silvered is suspended iu a bath of a silver solution by
i metallic rod which conneets with the negative pole of a battery.
Immediately below it is a plate of pure silver, which is connected with
the positive pole of the battery, ‘The object to be silvered aud the
Fig. 378,
silver plate, a, constitute the electrodes, « being the positive one.
The explanation of the proces bs analogous to that fo the preceding
article.
The salt of silver generally employed is a eyanide of silver, which
ie diesotved in cyanide of potamium. The thickness of the costing
Mopasited will depend upon the power of the battery aud upon the
tine of immersion.
The proces of electro-gilding ts the same as that of silvering,
except that we nse a eynnide of gold, dissolved in eyanide uf potar-
sium, and a plate of golf at a, instead of a silver one.
A vessel may Iie“ gold-linod” by filling it with » solution of gold,
surpending in it v slip of gold from the positioe yale of Noe Wwdvers
—
ACTION UPON A MAGNET. 479
Between these avalogies and dissimilarities nothing positive could:
‘ho affirined with respect to the identity of magnetiam and electricity,
until, in 1519, Oxmernn wade a discovery which showed that these
physical agonta aro most intimately allied, if not Montiel. They
are now rogarded, as previously stated, by physicists generally, to be
Mdentical.
559» Action of an Electrical Current upon a Mag-
net. — Oxieren discovered the fuct that an electrical current
has a diretive power over the magnetic needle, tending al-
ways to direct it at right angles to its own direction.
Fig. 879.
This action may be shown by theapparatus represevted in Fig. 979,
Tfa wire be placed purallol to. and protty near a magnetic noedle, and
then a earrent of electricity be passed throagh it, the needle will turn
around, apd after n few oscillations will come to reet in» position
sensibly mt right angles to the carrent. That it does not take a
position absclitely perpendicalar to that of the current is because of
the directive force of the earth, which partially counteracts that of
the enrrent.
‘The direction towards which the sorth ond of the neolle will
tum depends upon the direction of tho current, If that Sows drum
touth to north, and ubove the neelle, the north pole of the needle
deviates towards the weet; if it ows towards the south, and wbave
THE HELIX. 481
2, The earth, which acts lke a huge magnet upon a mag-
‘netic needle, nets in the same mannor upon movable currents ;
that is, it directs them so that they are perpendicular to the
mugnetic meridian.
This nay be shown by the apparatus of Pig. 380. Ifthe commn-
nication with the battery be cat eff, and the hoop be turned till ite
pline coincides with the magnetic weridian, it will rémain in teat
position, If now a current be passed through it, wo eee it turn
slowly around the pivots, 20 as to luke « position at right angles to
tho meridian. It will turn in such a direetion that the current in
the lower part of the hoop will flow from east to weat,
3. The wires of two parallel
currents attract each other
when the currents How in the
anime direction, if there is free
dom of motion for the wires,
and repel each other when they
flow in opposite directions. Fig 381,
4. If n wire be coiled as represented in Fig, 481, and thea
be suspended by its steel points in the eups of mercury (Fig.
Fig S82
880), it will, when a current i# passed throngh ft, arrange
itself in the meridian like n magnotie needle.
When the ovrrent takes the direction of the arrows, the end.
GALVANOMETERS.
563. The Galvanometer, — Galvanic Multiplier.—A
Garvaxomeree is an instrument for measuring the foree of an
e@ootrical current. In its sim
plest form it consists of a
magnetic needle (a4, Fig.
381) with a conducting wire
passed around it in the dinec-
tion of its length.
When a current of electricity
is paseed through the wire, Ite
presence will be indicated by a mation of the needle, its force by the
amount of deviation of the needle, und the dirvetion of the current
will be indicated by the direction towards which the north end of the
noedle deviates,
Fig, 35
The Gatvante Muutirrien is» galeanometer of great seusitive-
nest, Dnt constructed on tho sate principles as the ono alrendy
Th is represented in Fig. 385. It consists of a copper stand, M,
SUMMARY. 485,
If the enrrent conse, tho iru bar at onen loses its magnetism,
Wo tay in like manner form a permanent magnet by asing « bar of
steel instead of a bar of lun.
Rete ASSES )
Pig, 386,
‘The bar of stool may also be magnetized by passing through the
wire n spark from a Leyden jac. To do thi
made to touch the external covering of the jar, aud the other
broughs into ountact with the batton of the jar. The steel bar
is magnetized instantaneously, thus showing the identity between
the electricity of the galvanic current and that of the Leyden jar.
Summary. —
Relation between Magnetism and Electricity.
Action of aw Electrical Current upon a Magnet.
Tastented by Figure.
Ampares Love.
Action of Magnets upon Currents, and of Currents upon
Corrente,
1, Magnets exorcise a Dircetive Force upon Carrenta.
2, The Earth acts like « huge Maguet upon Movable
Currents.
Illustrated by Figure.
B, Action of Parillel Currents upon each other.
4. Action of the Current upon a Helix suspended in Cups
of Moreury.
Ilustrated by Pigur
Action of two Solenoids upon euch other ilastmated by
Figure.
Ampére’s Theory of Magnetism.
Iilastrations,
Like Poles repel and Unlike attnict, explained by Figure,
Galoanometer. 7
Action illustrated by Figure.
Gateanie Multiplier
Description by Piguro.
Use and Mode of Action.
Magnetizing by means of an Electrical Current.
Method illustrated by Figure.
THE TELEGRAPH. 487
567. The Electrical Telegraph. —An Execrrican
‘Teikorarn is an apparatus for transmitting intelligence to
a distance by means of electrical currents. Monsn’s tele-
graph is more extensively used than any other, and the prin-
ciple on which it is operated is very simple,
At the station from which a telegrain is deepatched is an clee-
tieal battery, and at the one where tt is tw be received Is an
clectro-magnet. The two are connected by a wire eanning be-
tween the stations. When the current Ss transmitted through
the wire, the iron becomes mngnetiaed ond attracts an armature of
soft iron, whieh in tarn imparts motion to other pieces, by menns
‘of which the signals aro imparted. When the current eens, the
iron Jowes tte snagnetian, and a spring forees the armature ‘back
to ite primitive position. By successively broaking and restoring the
current, the telegram is transmitted. As a matter of fet, hawever,
cach station has the transmitting and receiving apparatus,
Fig: 988,
568. The Register, — One forin of the receiving npparatas ix
the register represented in Fig. 389, which is composel of an eleetro-
magnot, F, which, whenever n current is transmitted, ax at A, acta
by attraction upon an armature of soft irun,m, fixe at the extretity of
0 lover, mn, and movable about an axis. At ite extromity, m, the
Tover carries « point, st, which may be made to press
able slip of paper, ab. When the cnrrent does not pass through
the electro-magnet, the point, x, does not pros against the paper;
Dot na soon as the current passes, tho point is pressed against the
paper, and tnaces upon it either a point or a fine 1orw oF Tess elon
gatod, recording to the length of time during whieh the earrent ie
uninterrupted,
THE TELEGRAPH. 4189
lie plate below. Cand D are the wires through which the
current passes.
"Tho operator, to cleo the elreuit
and send the message, presses the
rent will then pass through the
metallie connections out at the wire,
D, to the next station. Y is # nov
ablo brass arin that slides under a lip for the purpose of closing
tho cireuit when the key is not in usc. A spring under the lever
Keeps the platinuin points separated when the pressure is removed
from the knob. ‘Tho knobs, ¥and X, aro both non-eouductors to
Fig a0.
protect the operator frutn electrie shocks.
570. The Relay. —It is only when the stations are #
short distance apart, generally less than fifty miles, that the
receiving instrument Is operated directly by the line current,
In long distances this becomes too feeble to do this etfee-
tively, but by allowing the main current to enter an instru-
ment called the relay, a local current ix generated to work the
register or sounder.
Fig, 3.
‘The line wire enters wt 2 (Pig. 201), traverses tho helix aud passes
‘out at @ to the ground, or if (t tea way-statlon to the iain Tine. A
wire from A connects with the positive pole of m local battery of two
or three cells A wire froin B gves to the mgister or founder, wud,
THE TELEGRAPH. 41
relays should be cut off from the main line, bat in such a manner
as uot to break it,
572. The Circuit. — In what has been sald, only a single
wire has been spoken of as running from station to station,
‘This is gonerally an iron wire which passes over glass insu-
lators attached to tall wooden posts. When the wires are
laid under ground or in water, they are insulated by a coat-
ing of gutta-percha. Copper wires are commonly used in
offices.
Tt would seem necessary, in order to complete the circuit, that a
second wiro should bo emplosed. Such, however, is not the eas,
‘The employment of a second wire is avoided by connecting the two
ends of the singlo wire with the «arth. Wher gus or water pipes
enter an office the ground wire is attached te them.
If thore.are no such couvenieneds, copper plates several foot square
ateach station are buriod in a perpendicular position, nt sufficient
dopth 0 a to be always in contact with molst earth. Tho circuit
is thus completed. At the station where the message is sent the
Vino is connected with the positive pole of the battery, and the eur
rent passes over the wire down through the earth back to the uega-
tive pole. This simple device saves not only half the expense in
constructing wires, but greatly inereases the power of electrical
transmission, the resistance it offers compared with the wire being
practically nothing.
Sivoo tho earth ie the common reservoir of neutml electricity the
clectrle current from the wire is really dissipated when it communi-
cates with it ‘hero is aot supposed to be any real pastage of the
electricity back to the’ battery from which it started. Tho inter-
modiate offices aro suppliod with ground wires, to be used only in
case of trouble on the line.
573- Plan of a Way-Station.—In Fig. 392 wo have
represented a plan of tho instruments and connections of 4
way-station, The line enters at /, passes through the light
ning arrester, X, traverses the coil of the relay, Af, and then
passes through the key, Ay back to the lightning arrester,
and then to the next station by the tine, Z'. ‘The dotted lines
SUBMARINE CABLES. 498
ido of potassium, ond which rests mpon a metallic plates Whoo
the point touchex the paper the chemical preparation is decomposed,
apd bla inarks aro left on the paper, due to the formation of Pras-
tian blue,
Of the three printing telegraphs, that of Prmeues is the most ser=
vierable, and is a combination of House's and Huames’s with the
itoproverents of Puxtos,
‘The sending instrument has twenty-eleht keys areanged like those
of % piano; upon those are printed the twenty-six lettcra of the
alphabet, and two punetuation points, Whou the operator depressos
tho koys, the cirenit is closed, and tho morage is printed at the other
end of the line in ordinary letters. ‘This ayatem works fuster than
Monsn’s, and the message does not have to be transeribod.
575- Duplex and Quadruplex Telegraphy. — Duplex
telegruphy refers to that system of telegraphing by which inessages
are simaltancously sent in opposite directions on cue and the same
wire, thereby doubling the working eapacity of the line. Quadroplex
telegrnphy refers to the system of telographing whereby four mee~
sues, two [n each direction, may be simultaneously tranknitied over
one acd the sane wire. Tho quadruples system has been exten~
sively employed within 3 fow years bythe Western Union Telegraph:
Company, and is at present in use between almost all the principal
cities in the country.
A iletailed description of theo systems, however, would be beyond
the scope of the present work,
576. Submarine Cables. —Since the invention of the
telegraph, a complete network of lines has
been established over both continents. Not
only have thousands of miles of wires been
stretched on land, but submarine wires
have been laid, connecting places separated
by thousands of miles of water. Tele=
graphic wires connect England and Ireland,
England and France, France and Algiers,
Earope and Americn.
The Atlantic cables (Fig. 398) consist of Fig. aa.
(1) a central conducting strand, O, of seven copper wines ; (2)
ELECTRO-MAGNETIC MOTOR. 493
INDUCTION.
The Relay.
Object of the Relay.
Deseription.
Method of working illustrated by Piguees
Lightning Avresters.
“Atmospheric Electricity taken from the wiros by meane
of Metallic Teeth.
Water as a Method of relieving the Wires.
The Cirewit.
Earth as a part of tho Circuit.
Advantages.
Circuit ofa Way-Station.
Miostrated by Figure.
Other Forms of Telegraphs.
Batn's, Honse’s, Hughes's, and Phelps's.
Duplex and Quaskruplex Telegraphy.
Explanation of Each.
Submarine Cables.
Fire-Alarm Telegraph,
Blectro-magnetic Motor.
Explained by Figure.
SECTION ¥.— INDUCTION. — MAGNETO-ELUCTRICITY. — THERMO=
ELPOTRICITY,
§79- Induction by Currents. — We havescen that the
electricity of the machine acts upon bodies by induction,
‘The clectricity of the battery acts in a similar manner, but
only when the currents begin to flow and when they cease.
To show this, take two cupper wires, covered with silky and wind
them side by side upona bebbio. Then fasten the two ends of the
firat wire to the two binders, m and a, of the galvanoweter (Pig. 985).
Next connect one end of the second wire with one pole of a feeble
galvanic Battery. If the other end of the second wire be brought
Inte contact with the seeond pole of the battery, wt the Instant of
contnel, the neeille of the galvanometer will ladicate the production
INDUCTION. 499
tncrease its infonsity, an induced current, inverse anc momentary, te
developed in a neighboring eirouit,
2 A primary current approaching a conductor gives rise to an in-
duced current, inverse and momentary.
S. At the moment the primary current coases, or when its intensity
diminishes, or when it ix removed from an adjacent coil, an induced
current begins, direct and momentary.
58. Induction Coils. — An arrangement for producing
an induced current in a secondary coil by breaking and clos-
ing, in rapid succession, the circuit of the primary, ix called
an induction oot.
Induced currents aro the more powerful, the Ionger the wires em-
ployed. Heneo in prerica it is asual to wind the wires apo bob-
Ving, #8 chown in Pig. 306,
Fig. 398,
‘The coil chown in Fig, 396 consists first of a cylinder of several
hundred coils of coarse coppor wire, ‘This is the inducing coil. Over
it is @ finer wire, making several thousand coils, ‘These wires aro
not only covered with silk, but leo with an insulating varnish of
gumnlac, At the extrome left of the etand on which the coil reste,
are two biodurs in eemnection with the two poles of a battery,
A banch of iron wires Js inserted as a cone in the primary,’ or lence
coil. The eurrent-breaker consists of a small armature, at the left
of the figure, attmeted by an elvetro-magnct, When the primary
current paves, the armature is attracted aud immediately breaks the
current. It then instantly tlios back by means of a spring, and eom=
plotes the cireult. By the passage ef the current theoagh the prisary
coil the bunch of frou wires is magnetized, and helps to strengthen
MAGNETO-ELECTRICITY, 501
when tho current passes through Goiteler’s tubes, These aro eealed
eluss tubes filled with rarefied vapors or gases; platinum wires are
sealed into the onds of the tabes to conduct tho eurrunt. Fig. 387
repreacuis the curreut passing through a tube of hydrogen; ia the
bulbs tho ight is Whito, but in the couneeting links it ia red.
Fig. 207.
583. Magneto-electricity. — We have seen that a cur
rent of electricity passing through wires which surround a
piece of soft iron magnetize it, and, conversely, a magnetized
bar introduced into a coil of wire develops a current of eloc-
tricity In the wire. Electricity prodaced by a magnet is called
nuagneto-electricity.
Fig. a.
Tf'we substitute for the primary coll represented in Fig.
395.4 permanent magnet, we shall obtain results like those
given in Art. 679.
THE ELECTRIC LIGHT. 508
wires made incandescent, If a break-piece be addod, tho eirenit will
i rapidly broken and closed, and a series of shocks will be folt by
person grasping the handles at ZZ, Tho shocks will be more
tuarhed Wtho bunds are ft maitaned with eedalsted water,
Within the last few years magnoto-electrical machines have
largely increased in number and power. By ineans of these con-
trivances mechanical work is transformed into powerful electrical
currents, which bave been utilized in eleetro-plating and telograph-
ing, but expecially are they sucecssful in obtaining the electric light.
With one of these powerful machines driven by steam, an electric
Light of remarkable brilliancy is produced,
g85- Electric Lighting by Magneto-electricity. —
Tn Art. 554 we considered the electric light as produced by
a voltaic battery, but experience has proved that to make this
light of practical benefit and at the same time economical, the
clectrical energy must be derived from cdynamo-electric ma-
chines, All these machines embody the general principle
of a revolving armature, wrapped about with coils of wire, in
front of the poles of a magnet, a& described in the article on
Magneto-clectricity. —*
Probably the best machine for this purpose is tho Brush magneto-
electric generator, invented by Cutances FP. Buwsu, of Cleveland, 0.
For industrial use and Momianting large areas the Brush system of
clectrio lighting is no longer an experiment but a substantial sucr
eves, and 8 more extnsively adopted than any other,
‘There are two kinds of cleetric lamps in use, the incandescent and
the voltaic are. Tho incandescent consists of a strip of platinarm,
carbon, of bamboo, placed in the cireuit, which becomes white-hot
when the current passes, and emits a brilliant light. ‘The voltaic are
was described in Art. 554,
‘The Brush system uses the voltaic are in preference ta the inean-
deeeont, a4 being more econctnical and powerful for lighting streets,
large parks, buildings, manufactories, halls, vtec.
Gas-carbonk in the are are now, on necount of their impuriticn.
generally superseded by pure carbon, specially prepared and pressed ;
and to improve their conducting power they are eometines coated
with precipitated copper or nickel ; this i the ease with tho Brush
carbons,
THE MICROPHONE, 606
587. Action of the Telephone. — Whon a person spealce
into the inoath-picee of the telephone the sound-waves of air stelle
against the diaphragm and cause it to vibrate. ‘These vibrations
produce an alteration in the magnetism of the permanent magnet,
which indaces electric currents in the wire coil, These cleetrio pul-
ations, being transmitted through the ling-vwire to the distant helix
in the second station, canse the diaphragm there to vibrate exactly
like that at the sending station.
‘The waves of uir that strike the ear frem the second vibrating
dinphragin, being complete reproductions of thooe that etrike the
first, give the same sounds. The sound-wares are uot earried over
the lino-wire, but tho pulsations of the electric ourrent.
‘Tho sound that is reproduced in the receiving instrument becomes
somewhat fooble, but ptill the characteristics of the person epealdug:
‘are faithfully reproduced.
588. The Microphone consists of a small battery con-
nected by means of wires with a telephono-reeeiver, and with
the apparatus represented in Fig. 401. ‘This apparatus con-
slats of a vertical rod of carbon
fitted loosely into two blocks, also
of carbon; these are securely fas-
tened to an upright framework ;
the wires that connect the carbon
with the telephone and battery
are acen at the left of the figure.
‘The sound produced by the walh-
ing of a ly on the base-boand, oF
bruehing of the softest feather, or
faint ticking of a wateh, are magnified
to such an extent that they may be
heard with distinctness miles away by Fig. 401,
the listener iat the telephone. If the carbon be impregnated with
inereury the inierophone is eonsidert moro effective, ‘To get the
maxiinumn effect with avy particular instrament, the position of the
eathon rod must bo esrofully adjusted hy repeated trialk. To prevent
the interference of external vibrations the lyeo-board — reat
upon a cushiou of wadding or indlu-rubiber,
SUMMARY. 507
‘The mnltiplior was usod by Muntoxt with grat succeas in de-
moosiniting the phenomena of ra
diaat heat. Por tho purpose of
concentrating the heat-mys upon the
pile « cone is employed, as repre-
vented in Fig. 404.
591. Animal Electricity. —
Cortain fishos possess the powor of
imparting a shock that compares
in Intensity with that of a power-
ful Leyden Jar. Such fishes are
called electrical fishos, the inst
interesting of which ary the electri=
cal ool of South America, and tho
wrpedo, which Is a native of the
Mediterranoan.
‘The shocks given by electrical fishes are dao to electricity gener~
ated in the body of the fish. Marrruce showed thit aparks could
Je obtained from the fish, and also that the gulvanometer is alfected
when one of its wires is brought into connection with the luck of the
fish and the other with its abdomen, In all eases the shock is vol~
untary, and serves as a moans of defence against enemies,
Summary.—
Induction by Currents.
Illustrated by the Galvanometer.
Induced Currents prodoced by Primary and Secondary
Coils,
TMustrated by Figure.
Lawes of Induced Currents.
Induction Coils,
Definition.
Construction explained by Figure.
Mody of Operation.
Use in Treatinont of Diseases.
Raliwkorif's Coil, — [ts Powur.
Geissler's Tubes.
ELECTRICITY. '
Me icity (continued).
Produced by a Coil and Magnet.
Produced by Coil containing Soft Iron Ber and Maguot,
Power of giving Sparks and Shocks.
‘Uses of these Machines.
Electric Lighting by Magneto-clectricity.
Brush System.
‘Lumnpe formed by tho Voltaic Arc.
Lampe formed by Ineaudescont Platinum and Carbon.
Construction of Carbon Pencils.
The Telephone.
Description by Figure.
How Used.
Explanation of its Action.
The Microphone.
Description by Figuro.
Thermo-electricity.
How Produced.
‘Thermo-clectric Couple.
Thermo-electric Pile, or Battery.—Llustrated by Figures.
How the Battery works.
Animal Electricity.
PROBLEMS
WEIGHTS AND MEASCRES,
1. Mow many wiles in 3) Kilometers Tne cuble meter Of waler bow pusny gations?
To 10 basbols, how many Liters! What isthe #do of m equnee that contsloe 278,788 mpuan
erimwters?
‘2. Find the wright in kilograsa of 10 gallons of water. In 8 militmeters, how many
neti!
3. Abos wnasurlog 10 centimeters ln eoch direction will Leki how many les, and lt
what poriion of a ouble meter?
A. Tartare 6 plate (o Yters and eube centimeters.
UNIFOUM MOTION.
5. A raieny trnla Se moving sniforwnly at tho rate of a mallee yer Recars what te the
‘velocity tn foet pee second T
Ge A tocountire rune MO Ailometers In 2} Bouse, wad Is Ite velonihy per ssocaad x
meters
7. From two places, m and», kilomators apart in a stexlght tine, two persons, A gen
1A, start ab Lhe mime fhe towanis each other ; A toores with & rolocity of @ metas jer aee=
‘ond, 1 with velocity of 0 meters 4B what dietauce frau wt and wm will Sey 1aees, word
‘after wha Ulmne ?
MOMENTUM AXD STRIKES PORCH
An irom bal) walghing 3) pounds moves wtih a velcity of 20) fret per mead, and 8
‘ecoot ball welghing G pounds mov with » velocity of 400 fet per mend ; reyuird the
mcnernins sort otriRing fare of eae all
1. A boy weighing 29) pounds moves with a velacty of mile fn 34 socom; what
0st i the welghE of 4 tealy moving G feet per seowed to hase the ante meeaentis Mt fee
former?
VO, A tocomotive weighing 30 tows bs meving with « velacity wf A Ailmaters heme
what tiltsmomentom? How dew copa with © slp eighing 0 tat a
‘Nils reloity of a dectinetar per seco ?
11, Which wil caus the uvt deetruotiow 9 62pm mena severing
per second, ora taitering-raan webghing 11,03) pours worring wh 9. ele of
teconilt x
12. If. pile driver weighing 1.000 puna, rained 96 et, 96mg
‘uv what hight must it be ratoed to prodes an feet threw Hieann a
PROBLEMS. ou
ARS, The longth of an tnetined plane 4s 30 fet, the height 15 feet what time ls re-
plane?
WD, Aatove ls thrown verealy dowowari from & beight of 200 motere with « veloc
of WS etare por send; how loo lH ein tlt?
‘CRNTUK OF GRAVITY.
40, 1 wre ban, wing, repetioly, 2 and 1 pocyare conned by ber,
‘whe ln the common contre of gravity
[iat i ane t's entities knead 24 Hale BE
SER tie ag tran ae, of mio Pt
43. How will the times of witraions of to penduluins compare whom lengths are,
A pendulim fbi (vlee Jo} of a meond ; how long le tt
If, Des peedulem vine fe Hey ft ana rend what oy ie agen
MO mo soca cas acs dig ee
‘ts lengtD, how many seconds would | howe ench diay f
‘EXEROY,
49. How any bilgram-netve ary repre Ym mig G0 Agrame 1) metre
“30 Yih haste grater ener : «ty svn 60 pode snd Mang ely
Soe reo oe wire pene ‘with a ralosity Of 100 fivt? Repasaeut the
SBE ai ee xr a et ent wad te pound
toot
5B. A ocomativewughing 9 tun, wovlag ate ria of mallet an Dour aa bo
SERBS Se ne pore tm engin sas tt exe 30,0 pt, 8 eB
54, What the hormeyover of su engive that can rate 10,000 pounds 10 feet In
6 sevenda
ve Leven,
BS, Poow s lever of the first chau 3 fort In leagth, « weight of 10 pounds We meapemtied
24 (oebes from the fulcrum; what weight at the ther «od will Koop the wer tm
t
‘equubeiune
SW. fo = lever of tho meccest claw 12 Set Joop, where must the fuleres be places ta
piatersbe oweu fo that a power of half ® peaind may Dakiace = weight of 10
PROBLEMS. 513
S11. Three seconds elapee between a fash of lightning and a corresponding peal of
hander; what le the distance of the place of origin ?
82. How many milee will sound travel in an hour? Tow long will It take it to go
round the earth?
‘SS. A tuningfork gives sound-wares 1 meter In logth ; bow many vibrations per
srcond does it make ?
‘SA, A shot is fred before a cliff, and the echo fe heard in 7 seconds; what Is the dis-
tance of the elle?
5. The density of oxygen fe about rixteen nes that of hydrogen; sbow that the
‘velocity of sound in hydrogen ought to be about four times that in oxygea.
REVIEW QUESTIONS. 515
86. On what ate the principio of mechanics hasnt ? 187. Give Newton's Birt Law of Mow
Hon. Muscrie, 38, tire Newioa's Second Law. What thrve elements deteruiine a force?
Define each. How represented? Me Define almple and compoutd motion. Duflue re
roltant, lustrote Tedive compounds. 40, Kaplan tho poralislagram of forvox. De-
‘ine composition And resolution of forces. tituaale by figure. 42. Kaplato the Might of
a bird. 4%, Explain the sailing of a boat 43, Kxplain the reealtant of paraltl Barco,
When the forces act In the sae an opponite Dirvetinns. 8s Kaplaln the compesition of
nore than te forces. 45, Define momentuss. Tilustrate, Rate for fmling momentum.
Examples. 46. Explain collision of bodies, Hlusteste, The efitet is proportional to what?
Mlustraie, 47. Deflve stetking foree, Proporddousl wo what ? ihiserwle the diference
Letwcen momentum and siriing ferwe. 48 Dedine wethow and revesion. What by New
tow's Third Law! 41%, Bivstrate resetion lo Hou-elntie bation 50, Ilustrsie weton
In elasto Ceding. Give anime familiar examples SH. Kxpinin teflerted motion, Dene
lige and angles of lacilence and retleetion, Give the lay Of reflected motlon.. Taxa
bby figure. 2, Hxplaln the cootrifugal aad cuntrtpetal forces, Tlustrute by exampler aod
‘igure. How does tho telly more when the eentrijetal force lx dostacywd | Explain the we
periment with trory ballk. 334. Give some oflets of the eentifial force bet on the
‘marth. Baplain the experiment Kaylaia te tuloury of boiles to revolve about tole
shortest axie, 54, Delne the gyreeeope. Kapiniv hyure,
BB, Detine the forew of gravity; weight | universal gravitation, Replain (he lw of
univers gravitation, Gir the law of Newton. Explain further by fure, Why do not
vo beads come together resting oo a table? BG. Explain the eflee of gravitation on the
planets, 2. What le the law of the foe of gravity? Why be gravity differents diferent
Dlaves on the earth's surfuce? 3S. Define a vertica! lino. itustrate by figure. Define &
horimmtal fine. Iiiustrate Wnt instruments are tmoes upoa thes tines? Sifts What fe
the didlorence betwown weight abd gravicy? How Is eich determined 60, DeGne the
deere of graviiy. Rxplaln. Whur le the Woe of direction t Where ie the eeatee of
agravity In sods of gular figure and wnlform devalty ? Rxamples, Tn shea of wobforen
thickness and dewslty? How ls the centre of greeity fund in surfsees of frregulse ott
line? Mow fund in any volhi? When aot within the boty, bow bet and? GL. When
Jem bey In equilibrium? When 6 bly rests on a polut, where muust the centre of irr
‘ty le When It rete on tro peiot#? Reample. When on three points? Xaample,
6. What are the three enue of equllibrium? What i stable equilibrium ? Lshvsteate,
Reamplen What le gustable equiiorian filwstewie What i neutral equilibria?
iusto, Heamples 6f che three Mads vf mqullibeiom wlth the comes Bib What bodies
‘are the mont stable? Rplain the ataility of the treves of Pisk wil Boligns.
ng nd animals maintain a stable position? natrete, GB, Clive the drew
falling boulon. How Uy the fire law vorited? explain the eeuson of the
Third law, What ts tho rule for Ouding the velovity acqulnet hy » tilting
snd of any given tice? ‘Temple. What Ts the rule for fading the #pnce
‘over daring nuy dren second of the descent? Keample, What ls the rule for
Ing the whole distance trareesed Dy a falling testy in a giewn time? Keampie. 3,
plain Ganille'awettiod for verlying the laws of falling Dodien. GW What ts
‘en a Yealy Vhrown perpeadleularly upward? How do we fiat the wamber
We wilt continue to rise? example. How do we fd the whole ditanos fe will
tunple, G7. DeGoe & projectile. lurtrate by figure whom a ball Us thrown
tally. Tilveteate the atts uf m Yosll by gure, fred obliyuety, at diferent angler
GS. Wher will a tall fied heriavotally roach the groand? When Af @rek ebiiquety wp
want? GD. Detine the pendutam, What eanses the persalian to vitwate? Keplain the
ation tn detail What i ovetiazory motion? What is an oseiation ot vibeation ? nak
4 Ss nonplltode? What ether hes the air on vibration t Qs Whist i shiple peoxtar
om? J+ Herel or ideal? What Is & compound peudutum) Rylan ioe wonstraction.
71. Give the four lame of the eTbrasinns of che pondtutam. Thaw arw thew Ixwe die
duced? How te the fret Jaw verifled? Sieond law? Limitation, Define thochro
lem, When are sibrations fwcctironiralt Who di revered thie peralulinn, and whee t
‘FR Kxplin the evstres uf suspension wud oelllavion, 73. What in the prinelpal ume
iT
ae
2 i
HOE
REVIEW QUESTIONS. * 617
Aloe? How demonstrated? 12. Repinin equiltbrium of beterogencous tiqaide Mow
shown?
ESS. Ksplald the waterberel. Mow ured? 154, Explain the spirit-evel. How
Janed T Appliaations. 13%. Explain »priogy, fountains, aul clvers, Ai}, Kaplain arte
Mac walla, “Finite. Keamplet. Orwell.
BT. How arv eubmerped betes promal? Thastraie Give the principle of Aree
‘oat oa water? LAE. Tilusteste the principles ef Motation by experiments
142, Kspiain the reining blader of che fat. Whas e Kes setiout Habe Explain
LAA, Define speriie gravity. Hioctrate, Whats taken as & standard? Mow do we
‘wit the specific gravity ofa’ benly? HAS. Mow co we find the specifi rarity of w soit
‘by tho ytromtatio Dalanee? Mle, Keainple. Mow do we find the specific gravity of
sold at floats on the water? Kxammple. My Nicholoon’s hydromerer® Dy w Mash ?
IAG. How do w+ Bud the opeeitc gravity of Liquids by Fuhrmnbolt's bydrometer? Ly
‘Mask? “Application of specite grasity. 147. Demeribe Meuumd's arwometor. Wow ix it
14S, Dowrite the alcoboleeter, How gradumied? Cre?
ume of w Tigakd dlaciserped equal to what? Exampa Kxplain the von rontracta.
- epilale the ow of quis throug pipes. Iustrate. 19, Rapin the tow of
the redstanes of frietloa,
‘LB. Rxplain tho enengy poenomed by water cofhetod tn rvecrwoiry, ete What arw the
forces that tara watorehools? “154. Brpiain the aadershoe wheal. 195, Ite power,
Replain the overshot wheel. te power, — 106. Kxplain the broaat-wheel, Its power,
yf. Maplain-the turbine wbert Tiartrate. ow great lie power
SS. aplald Archimedea!-scwew. 168. Rxplaln the ebalergump LOO, Txplala
the hydrialle rami, Illustrate te netion,
PNROMATICR
‘G1. What are pares and vapors! low do they differ from liqahis? What tthe dif
ference between 6 gus anda vapor? 168, The aumemphere x the iype of vhost What ie
‘Ms calee ? Componed of what? Seurees of carbonls ankl inthe wir? ‘The relaihen of plants
to cxygee and rarbonte whi? TEE. Hinstrato the exzansive fowre of air 164, Prove
Ghat air hax weight. 163. Explain acmospheric presure iustrsne, LOG, Show the
Gubalanced force of the ait by burting a membrane and by ruretoblng rubber, EOF. ih
huntrate the foree of the air with the Magleburg hemispheres. 1G, Mhustrate the ap-
‘want prewure of the alr by experiments with tumbler xnd pleton wlth weight attarhet.
‘16M, What te the promure of tho atmosphese on a ayasry inch? Deseribe Torrie"
Gapsriment. How shown that the premure ts 19 pounds on am tach? What unit
of premare be adopted for all gues and vapors? Example, 170, Drsortbe Pascnl'y
experiments tn detail and bis mede of resswoning What eonslusion le derived them
‘Pascal's exportinents? 299. Whar ise barometer? What W ite principle! ETB, Be
seritecthe cistera taroweter. Whore ls the sero point of the scale? Mow is it regulates im
sccursi tmrometers! How tx the beight of the barometer determined! 27%. Dewwrite
tho siphon barometer, How do we fed the height of the barometer? Mow are onefliations
obviated? 174; Desertbe the wueet barogier. tNhustrate ite action. Why Inarearate ?
175, What ts the prinwiple uf the averehd berometer | iptain tie ection. 27G. What
are che ennnes of barwteetrie Huctuasions? Iidietrnte LFF. Expialo the barceneter ae a
waathor indleator, What rules are genorsliy Srastworthy? 19S On «tat privetpte te
he tarceneter amd for mesworing heights! Give role, 279. Whnt Ie the prewure of
the miesompbets in Uie human Bete! How rwletek? iow be M shown tha) the tau
ef the body contain game Principle of capping?
REVIEW QUESTIONS. 519
‘ana acute wus, QOD. What is the wee of the siren! Deveribe it im detail. Hxplalo fix
ction. \230. Explain how we determine the rapidity of the vibrations of the sonoroue
Explain how we fod be length of @ and-ware. BAZ. Mow are cords
i
fi
Egy
i #
Ff i
SF tl
ee
i
{Late what Gr clamer aro séringed =
B52. How bs round produced ia vip?
2 25S. What are
‘ines with fixed mouth-pleces Give examples. section of one, Rxpiain the
ction of tie air tu causing the sound. Whal is tbe diflrence between the nodes of an
‘open ongxe-pipe and » cloed omet Expinin the a0 orgse-pipe. Krove with
tant. How shown with Koenig's enprule| rewl-pipes! Give examples.
ive the to kinds of rveds. Deseribe the arrangrment of a reed of the firit Mod. Ea
iat Ita setlom, Kaplaia tie secon of 0 ual Wostrummenseoasteh of
what? Tustrate their action, 26, Kyplain seandi Mastrate by expert:
ment. 237. Explain sensitive flames. Ilostrate. 23M. What kind of an instrument
‘the aman Foieet What are the Yoeal chords” ‘reduced? 3585 De
scribe the yarts of the ear,
phonograph? Desrrtbe ii. Explain tt sation, 206N. What bx meant by energy
sound vibrations? Kilustrate.
mxat.
262, Defive beat. GE, Kapinio heat wr a form oCemerey What feeuld? Replafn
the two theories of heat, Went an te changed (nto wha form? 26%. Deseribe Whe eet
‘ema effete of heat What is interns work t exserualt flow do hea sist coht ales
Vanties? 265. 10 pres, thywide, and sulkds, what bs the order of expansion? Nase aud
eneie the Riess of expaniion. 266, Tow lt Tone erpansicn af metals showe ? Ke:
pension tn voluiwe?) 207, owls unequal expansion cf meals ahown' 26%. Now be
REVIEW QUESTIONS. 521
{nthe Tqahiforwseowspare wih that of the saune beky Iw a alld oF gaseous frm * What
abstance hax the greatest ryewitiy heat? What weas? ERY. What are the principal
Hxplaio ita working. $90, Dewribe
scorernor, Whatls [ts we? B31. Ilustrate the setion of the eccentric, Sie Deweribe
Nocorotl re.
{in detail Che structore of the
‘BSS. Deflae hygremetey. When be spare saturated? Kenmnple. thet of
ives
Veunpersture on mturation. Causes that vary the amount-of watery ey Waa Oma
REVIEW QUESTIONS. 528
refraction, 400, What mesot by the rtrsetive power of Medhee? That te the pene
‘eral rule of retract? {iro exampird of the tolsetive yower of ditfreot sabwmices.
ADL» Give tne ive of rofevetion, Wael be wieant by Ue iodex of refevetion tT Hlietrwe
‘ho second nw by fecure> Iiluetrae lites of retrvetion, LOB, Cire seine eayprimesad
root af rvinvetinn, 403, Give mew ensniphes of refenetion tn water, What floes dies
avfraetion Hake on the heavenly Wafies? The otjert ts seem An the dirgetion of wnt ray P
‘AOA. Hixpiain and ilustrove Wetal eeteetion sna te eriteal anghe, 403, Give woe ex-
‘unpies of Golal reCvetion, —Hiasteste eotal veflestion by figure, 406. Drow wiragn
How produred? lustre hy figure. Gire prectieal exsmplen. 407. Explain and iam
trite retraction with motia having Yaretiel fires. AUN. Defines prim, Mow do price
fake Highs? 40% Llastrate the cour of luminous raye To prio, ATO. Define w
ous. How mate? ALT Give the claslfieation of lousns, Es Dollos eaten of eurvie
Aare asiey option erates. Ruplain bow weftnd the perpendicalse. ALB. 2xplain the
action of convex lenses an light. 4BM. Define principal forte) principal foeal Mtaniee
‘mpherien! abermation by refraction. &13- Explate aad \wtrate combate foct. Wheat ds
he radiant? Give position of thw fock mlwn the radiant has difereot poritiona Mow are
‘the fort situated In case of woondaryaxte? 416, How Ivan image formed? LMustrate
Aw dota the formation of Tages by convex irnses, wit dilleent poaitions of the ohjeet.
‘Whew doer the lene becouse w atngie micrescope? 427+ Uunirate the formation. of ieee
age by coccave looms 418s Explain burning games. Cire emimplen 42M. Wast
Kinds cf mirrors ware formeety wel iu lighthiowse } What are the ahjecthoos $e tnlrewes
ilustrate the lenses red (a lighthouses How are ifierent lighibouses distinguished
ror one another
A420, Define the solar spocteum. plato tu detail, Explain colar a+ compared lsh,
pitch In sound. AA. What tr recompoattion of tight! Explain the wwetbade top
‘whileti ran be peotucet 4:22. Explain fally how the color of beste is jroduend:
423. Define complementary colors, Uuwirsta AZ. Win are ealjective collrs?
Wustrate, Give Tyndall's explanation 43k. Rapiain mod ilusteste Prewsbotee's
Hiner 4:26, Dowrtbe Im dvtail tho sptctemoops, 427. Whnt bs spectrum aaljuls?
Uhutste. Tow yore new metals diecovyred ' How do we doteeraiow tbe exinwenes of
tals tn the hexrenty bodies! 4328, What ts interference of light? 4:20, Replatn
and illustrate Nerton'e riage Kaunploe of incerftermre of Might 490. Kxpiin
Aiton of Night. Lxamples, 42024 Wak te double netracthnn? Mavtvate faltye
422. Rephain polartanion of light. Wewtrets. 420. Iustente polar
tourmaline; by gratings; by reflection amd rofracsion. —Ueautifiul effete peo
Anterferonee of polarised Light. ible Xaplaln the pincotee. Ake ive rome
tions of polarized Light, 4idthe What ls » rlakow? Conditions of Me forwathoat Zw
Made? Heplain by Sgure, 4387. Flow the primary formed frean sereo droyt fete
~
“435. What tne the tree properties of the spectrum! Alow determlond Mluatrate
Agure. 430, Explain Quoreceuce and ealorerceuoy. 440. Expiain chromate wbeera-
tha, AMlystesto, 441, What ie an webromatie combinatien } Wasirate,
AAR. Kame some vuretion of optical Instrumente 44. What bem uderservpe?
Kinds? A644 Whit tm singe microsnpe? uaiithes of the lmage? 44S, OF weet
oe tie cetn pound iokerveope cous? Rapiain fu cbeadll. How I) he ming ifying pone
‘expromed! How ls tne object ihonmiuatol! Uren? 4G. Whanit a tlaoupe? Chasen
Kxpinin the frvt-clam. 447. Replain in detail the Galilean telenrage, 4-48, xpiale be
it
ae
lal Heewebet'e 455. What be the rege etre? Kxplin fo detail 44. What Me
ue payrana? How ane iusalvine lows o&taived? uaniples, What our thts are
‘ave instil of etbbuiny 55. Whit le the ydin-eheeie nieve Kapil i Oe
Lai), Wert, 40. Beylela nod iMoetrate Um shee mleromope 45% Prdive the vee
‘ecm ohweara. Tlustrate. The tiuagee are Voileywedent of what shape? Reaingire
45%. Kxplate theeamers and tens. Hilustrate Cele wethou. And wie. AV. Waoyatn om,
REVIEW QUESTIONS. 625
mechanical fects by cant and Laydon je. 9:20, Show ehemeal eee by plbtol.
EEL. What arw tho physlologia! effets of eluctricty * ivy examples,
BEL. how the Wenity of Nghtnlog with the electzlo spars, BBB Explain atsnoe
pherie electricity. How daterminel! S24. Give cua of atmonplerts electricity.
‘SUS. What is lightning? Name soe of the diferent kinds. 6:26, Wha ie tuner?
‘To what ee dvet Heplain the peculiarities of thonder. 2. Dewelbe the ellets of
NeMtalog AEs Hplain the reiurM shock. DAM. What wre lltalinerate? Whds
conditions whould sie OuiBi? Whot le their real utility? 330, What is the aurora
Aorwalia Deveribe it
‘SEN. What fe dynamical elecurelty? Why 0 called? Origie of the terms pxleanie
and Foltale? Deveribe Gsivanl's experiment. What wae his explanation? S32. (ive
Yolta’s theory. $33, Give Pabronl's theory. SA. Yeplain and liuetewle ewerent
eeteeity, What is 9 volisle couple or element? GU. Explain the dicortiow of the
‘current, Define the terms stect=n-fouitivn, elestro-negatlve, ail elevtromotive. 586, Ra-
pain the action of the nek and the amalgamation of the wine. S57. What le meant Ry
‘rewtevies To wuss plates uxp the positive and tegacive electrodes Joined? BS. Whak
e waeant by cloetrhsl poteatilT Tlustiate. GA. What ie» voltae battery t 40s Dre
serite the voltaic pile, S42. What are constant batteret 54:2. Deveribe Smee’
tattery, Sdy Describe the pomatam bivhirumate battery S44. What isthe monary
culphate Daltery? SLD. Descrite Danieitx tatty. xphain itasetion. dit. Kxpiain
Grove's Wathers. S47 Kxplain Dunaea's ations. GAN. Defiuw electromotive frre j
walatavies | Sutensity, What le Ohen’s lam? Define external nod Internal nevletaween.
What Seam obm? 49 explain batterie of high and low redxtances. 30. Compare
Metional with gulraule slectriety. Give Tyndall's Uiartration,
SO» Name to eeotsof the galvanic battery. GBs Raplain and Mustrate the plryslo-
glen! offvts. 55%. Kxplainantilivstrate the heating efecte. iA. Explaly and ine
trate the iluminatiog wflests, Explan the oltalo are. 35D. Wastrabe the ober
effects by the analssis of water. Kxplala the terms oloetro-cegative and
55G. Defie electrotyping. Describy the pryyaration of Ybe mould. Deseribe the
Hon of eopper vo thy would. 5G%. Esplalo eiecteo-plating and gildings
‘53S. Flow tho elation between magnetiam and electricity. $50. Exploln and flue
trate the aetan of the sevtri eurwot npan x magnet. DEO. What le Ampére’s Ise
1. tinstrate the force magnets have on currents; the earth. How do two parallel
ceorreoie fies each ether ? How die a helix uct wheo supendod to caps of morewry?
Utes solenobhe are browght tegpther, whnt rents? SO, Explain Ampirw's theory of
magnetion, 563. Define & galvancmeter. Deeribe It. Deseribe the extvanie multl-
pier. What isn astatie newio? Gd. Yxplala and situstrate tbo wees ef the galvanke
ulUpter. $05. How exn wo magnetias Vy au eecteiccurreat
B66. Define mu elwtro-nngost. ow made? What property bee » voftiroo arma:
tore? Alvow that the Kelle Inalso ringnethet S07, Whit t the elertrle telngraph ?
Give & prorat description of Morse’s. AGS. Descrtbe the meter, Describe the sounder.
‘Write Morw's slpbatet, GGD. Eaplala the iranmliting bey, 5FO- Raplsio ihe wey.
TL. Replain ightaing sxrywterr. SPQ. How are wires arrange fn a cirenit? What
‘the pluse of & wseond wim? Where must cho emis of the single wire be placed?
ST. Deseribe the plan ofa waystation, 37 fe Explain wave other forms of telegraphs.
575. Kxvladn duplex aint quatruplex telegraphs. $76. Wat are wubsuarioe cables?
Resplala the Atlantic cables. 577. Deseribe the Orealarc talegeaph. 7%. Explain In
otal the slestrl-tsaguetic motor.
‘S7W. Kxplain and ilivetrato lnuetion by currents, GSO. Girv tho Ise of Induced
‘carrents. GST. What tema toductlon exih? Deseribe ihe eopatraction and action. 358+
Desciite Hubmkoriy coll. Hew unk? SSB. What ir magoato-clontrelty | 1artrate
BSA. Deportbe the construction and setive of the magnetonelwtrie machine. BN. Kx
Wiain sotrie lighting Ly magnetoclecsriity. 3, Bxplain the eoustractioa of Well's
Wwiephons. S87. Explain lis setion, GSS Rsplalw the wilerophone. S619. What +
hermo-ectrieliy? 50, Eaplalu the Gerworvlecttle pile, SOL. What le animal
slectriehiy? Tlusteate,
INDEX.
‘THE raves REFER To THE PAGES,
Aberration, chromatic, 3:8.
spherical, 331, 350.
Absorption, 16.
‘Achronatic combinations, 379,
Acousties, 109.
‘Action and re
Auvesion, 13.
of ig
Agents, physical,
Air, compressed, 151.
condensed, 149
expansion of, 128.
pressure of, 138
upward, 129.
weight of, 127.
Air-pump, 142.
Alcoholwerer 1
Ampére’s law of eletro-raaguet
theory of maguiets
‘Angle, critical, 342
incidence and reflection, 33, 238, 323
visual, 316.
Archimedes, principle of, 104-106
serew of, 121
Arcometer, Beaumé’s, 114.
Armature, 418.
“Artesian Wells, 102
‘Atmoephere, 125,
buoyant effort of, 162.
Atmospheric inkstand, 153,
Atean, 3.
‘Aurora borealis, 458.
toa, 20.
jilsand gases, 161.
0, 480.
43d
Balance, 69.
bydrestatie, 106,
Balloon, W4-165,
Harometer, 12.
celstern, 132.
sipbon, 133.
used in measuring height
2137
Barometer, weather-indicator, 136.
wheel, 134.
Raroscope, 163.
Battery, electrical, 440.
nuagnetic, 48.
voltaic, of galva
Beats, 173.
Dellows, hy drostat
Bodies, aeriform, 4
brittle, 19.
collision of, 29
sfeneral properties of, 6.
Hq, 4
solid, 4
Body, 3.
Rollers, 285.
Boiling, 259,
Buroing-classes, 35.
wwirrore, 331.
461-470
0.
Calorescence, 378
Camera, artlst's, 6,
obser, 38.
ity 4
Capstan, 74
dielectric machine, 439.
tripetal foree
Chindni's figures
Chords, 196.
Clouds, 300.
scoustic, 177.
Coercive foree, 409.
Color and piteh compared, 300,
of Water AN
Compass, ANB. ‘
‘Composition of forces, 5.
Compound lever, 0%
Compressbiity, 10.
‘Currents, eleettie, 481.
Declination of wewille, ALL
Honaiey, 4
Dew, 301
Dinkyele, 18.
Dinnapnetie bees, 408.
[Difraction of (ugh, 3,
Discord, 106.
Disslving wees, 2
Distitiarion, 270,
Divbbtity, 2
Ductltiny, 20.
Dynauieat etectrieity, 409
a, 8
Yer trumpet, 180
Woalticion, 280
Wreenirie, 02
Raines, 175.
Hlasticicy, 1
Rleette Night, 478, nh
Haerent batters, 440.
10.
current and magnets, 470-481,
re. M7.
anes, 4849
pendulum, #21,
tential, 45
snare, 47.
Riervicity, Wk
Anko, 7
‘xtanonphverio, A
by tndoction, 420.
‘ehecolen) effects of 46, AH
‘conductors Wf 424
evelopment of, 42h, AK
Aywntotesd, 30)
‘ees of points in, 48)
Yranklia’s theory of, 4.
frletionsl,
weaving power of, WS, «70
nds of, #22
aot of, 4
-merbanieal ethers of, 404.
on vurtace of beatin,
Phyniegheeflets of, VL, 42
Bruumer’s wreory of, A
527
qubtorions, 42-4, 16 20,
reporation, i.
‘causes that acrelorate, 28,
ns rapunm, 255,
Exonuene, 17.
Exyaribity, 10
xj, tw of, Ror gunna, ED
Mgubiia, E20
lll, 230,
ch Vagal ak geen, 215,
‘of metals, 214,
Ratenson, 6.
Kye,
Pahront's theory of eoetrielty, #61.
Paling edly te 9
Prbetion, Bt
Pronk, aL
| Gatemais expert, MA
Magnets, Law of 3.
pole of, 448
Magultode, 6
Matloabiitis, 2
Manonsler, 257
Marenvetiie fates
Mariotte's law, 19.
“0
Meine BV
Metosy, Wt
Miercscope, 1
Mrmr, 313,
Mirrow, 234
Mists, 2.
Motewote. 3
Stonnentun, 38
Motion absolute, 22
sacenteratint, 25
taws of, 23
wellectn, 22
rolative
simple st
‘untiorm, 22
he, 29
Moen,
Mobo, 18
erly 106.
1,
soand, 182
Optical instruments, 281
sudy of sound, 137
Optics 3
Overtones, 18.
Maple digeator,
INDEX.
629
Parehate, 168
Paratielograan of foreen, 23.
Voorn, experinent of, 02, 18%,
peinefpte of, $8
Phiocogre pile casey, 30,
Physi, 6.
Pipos, reed, 26
seand from, 2
‘ith fond snout piece, BL
Pawonatier, 15,
Hnieowatie babes, M7
Tolarhartion of Kgl, 3
Hotgrama, 230
Hore,
Forenity,
Power, (2, 6
rewire, transiioa of, UL
rina, B15,
Dirge, 62
Pulley,
Praumps, i, 143
clisio, 122
fowwing, 180,
ining, Et
renunts
raters 1,
Pyrometer, 224
PM
Quabity, 100
Krustion bored, 9
Recompanttion of Tight 30
Retleetou wf beat, 397
sof Ba,
of mun 16,
total wf Dg,
Radrmccton, hy parade! surinews, 36
ty WA
oud, of tgat, 74
Faden of,
ws of 0
=
wmtranrent, 189
Kesatutian of forees,
Kemmance, 18
Rent, abmlute, 22
wets
Meeantasst 2,30,
1 Wrens, 101.
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