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current at right angles to it - 368
2013. Case in which the indefinite cur-
rent is circular - 369
2014. Experimental verification of these
principles ib.
2015. To determine in general the ac-
tion of an indefinite rectilinear
current on a finite rectilinear
current - - - 370
2016. Experimental illustration of these
principles - - - 373
2017. Effect of a straight indefinite cur-
rent on a system of diverging or
converging currents - - - ib.
2018. Experimental illustration of this
action 374
2019. Consequences deducible from this
action ib.
2020. Action of an indefinite straight
current on a circulating current 375
2021. Case in which the indefinite
straight current is perpendicular
to the plane of the circulating
current - - - 376
2022. Case in which the straight current
is oblique to the plane.of the cir- .
culating current - 377
2023. Reciprocal effects of curvilinear
currents - - - - - ib.
2024. Mutual action of curvilinear cur-
rents in general ... 373

CHAP. IX.


currents produced upon revolv-
ing metallic disks : researches of
Arago, Herschel, Babbage, and
Faraday 351

CHAP. VII.


OX VOLTAIC CURRENTS.

1985. Direction of the earth's magnetic


1986. In this part of the earth it corre-
sponds to that of the boreal pole
of an artificial magnet - -354
1987. Direction of the force impressed
by it upon a current - ib.
1988. Effect of terrestrial magnetism on
.1 vertical current - 355
19S9. Effect upon a horizontal current
directed north and south - - ib.
1990. Case of a horizontal current di-
rected east and west - - - ib.
1991. Case of a horizontal current in
any intermediate direction - ib.
1992. Effect of the earth'smagnetism on
a vertical current which turns
round a vertical axis - - - 356
1993. Effect on a current which is ca-
pable of moving in an horizontal
plane ib.
1994. Experimental illustrations of these
effects ; Pouillet's apparatus - ib.
1995. Ils application to show the effect
of terrestrial magnetism on a
horizontal current- - - - 358
1996. Its effects on vertical currents
shown by Ampere's apparatus - 359
1P97. Its effects on a circular current


1998. Its effect on a circular or spiral
current shown by Delarive's
floating apparatus - ib.
1999. Astatic currents formed by Am-
p&re's apparatus - - - 360
2000. Effect of earth'smagnetism on spi-
ral currents shown by Ampere's
apparatus ib.
2001. Effect on horizontal current shown
by Pouillet's apparatus - - 361
2002. Effect of terrestrial magnetism on
an heliacal current shown by
Ampere's apparatus - - 362


2025. Circulating currents have the mag-
netic properties - - - ib
2026. Magnetism of the earth may pro-
ceed from currents - 379
2027. Artificial magnets explained on
this hypothesis - - - - ib.
2028. Effect of the presence or absence
of coercive force - - -380
2029. This hypothesis cannot be admitted
as established until the exist-
ence of the molecular currents
shall be proved ... ib.



CONTENTS.



CHAP. X.

BEOSCOPES AND REOMETER8.

Sect. Page

2030. Instruments to ascertain the pre-

sence and to measure the inten-
sity of currents ... 380

2031. Expedient for augmenting the ef-

fect of a feeble current - - 381
032. Method of constructing a reoscope,

galvanometer, or multiplier - 382
2033. Nohili's reometer - - - 383

20o4. Differential reometer - - - 384
2035. Great sensitiveness of these instru-
ments illustrated - ib.



THERMO-ELECTRICITY.

2036. Disturbances of the thermal equi-
librium of conductors produces
a disturbance of the electric
equilibrium ... - ib.
>7. Thermo-electric current - - 385
203H. Experimental illustration - - ib.

2039. Conditions which determine the

direction ot'current - - - ib.

2040. A constant difference of tempera-

ture produces a constant current 386
20H. Different metals have different

thermo-electric energies - - ib.
012. Pouillufs thermo-electric appa-
ratus - - - - - ib.
2<H3. Relation between the intensity of
the current, and length and sec-
tion of the conducting wires - 388
044. Conducting powers of metals - 389
045. Current passing through a com-
pound circuit of uniform in-
tensity - - - - - ib.
046. Equivalent simple circuit - - 390

2047. Ratio of intensities in two com-

pound circuits - - - - ib.

2048. Intensity of the current on a given

conductor varies with the ther-
mo-electric energy of the source ib.

2049. Thermo-electric piles - - - 391
2U50. Thermo-electric pile of Nobili and

Melloni 392



ELECTRO-CHEMISTRY.

2051. Decomposing power of a voltaic

current - 393

2052. Electrolytes and electrolysis - - ib.

2053. Liquids alone susceptible of elec-

trolysis ib.

2054. Faraday's electro-chemical nomen-

clature ib.

055. Positive and negative electrodes - 394
2053. Only partially accepted - - ib.

2057. Composition of water ... ib.

2058. Electrolysis of water - 395

2059. Explanation of this phenomenon

by the electro-chemical hypo-
thesis 396

2060. Method of electrolysis which sepa-

rates the constituents - - 397
2C61. How are the constituents trans-
ferred to the electrodes - . 398



Sect. Page

20H2. Solution of the hypothesis of Grot-

2063. Effect of acid and salt on the elec-

trolysis of water - - - 400
Cases in which the matter of the
electrodes combines with the
constituents of the electrolyte - ib.

2064. Secondary action of the hydrogen

at the negative electrode - - 401

2065. Its action on bodies dissolved in

the bath 402

2066. Example of zinc and platinum

electrodes in water - ib.

2067. Secondary effects of the current - ib.
1. Compounds which are susceptible

of electrolysis - id.

2069. Electrolytic classification of the

simple bodies - - - - 403

2070. Electro-negative bodies - ib.

2071. Electro-positive bodies - - ib.
072. The order of the series not cer-
tainly determined - - - 404

2073. Electrolytes which havecompound

constituents - ib.

2074. According to Faraday, electrolytes

whose constituents are simple
can only be combined in a single
proportion - ib.

2075. Apparent exceptions explained by

secondary action ... 405

076. Secondary effects favored by the
nascent state of the constituents.
Results of the researches of Bec-
querel and Crosse - - - ib.

2077. The successive action of the same
current on different vessels of
water 406

078. The same current has an uniform

electrolytic power - - - 407

079. Voltameter of l-'araday - - 16.

OSO. Effect of the same current on dif-
ferent electrolytes - ib.

2081. It comprises secondary results - 408

OS2. Practical example of its application ib.

083. Sir H. Davy's experiment?, show-
ing the transfer of the constitu-
ents of electrolytes through in-
termediate solutions - - 409

2083*. While being transferred they are
deprived of their chemical pro-
perty 410

2084. Exception in the case of producing

insoluble compounds - - 411

2085. This transfer denied by Faraday - 412

2086. Apparent transfer explained by

him on Grotthus' hypothesis - ib.

2087. Faraday thinks that conduction

and decomposition are closely
related 413

2088. Maintains that non-metallicliquids

only conduct when capable of
decomposition by the current - i'6.

2089. Faraday's doctrine not universally

accepted ; Pouillet's observa-
tions ib.

2090. Davy's experiments repeated and

confirmed by Becquercl - - 414

2091. The electrodes proved to exercise

different electrolytic powers by
Pouillet - - - - -415

2092. Case in which the negative elec-

trode alone acts - 416

093. Cases in which the electrodes act

unequally^- ... - ib.



CONTENTS.



XVII



Sect. Page

2094. Liquid electrodes ; series of elec-

trolytes in immediate contact - 416

2095. Experimental illustration of this - 417

2096. Electrolysis of the alkalis and

earths' 418

2097. The series of new metals - - ib.

2098. Schonbein's experiments on the

passivity of iron - - - 419

2099. Other methods of rendering iron

passive 420

2100. Tree of Saturn - ... ib.

2101. Pavy's method of preserving the

copper sheathing of ships - - 421

2102. Chemical effects produced in vol-

taic batteries - ib.

2103. Effect of amalgamating the zinc - 422
210*. Effects in Smee' battery - - ib.

2105. In Wheatstone's battery - - 423

2106. In the two fluid batteries - - ib.

2107. Grove's battery - ... 424

2108. Bun?en's battery - ... ib.

2109. Daniel's battery - ib.



CHAP. XIII.

ELECTRO-METALLURGY.

2110. Origin of this art - - - -425

2111. The metallic constituent deposited

on the negative electrode - 426

2112. Any body may be used as the ne-

gative electrode - ib.

2113. Use of a soluble positive electrode ib.

2114. Conditions which affect the state

of the metal deposited - - ib.

2115. The deposit to be of uniform

thickness - - - 427

2116. Means to prevent absorption of the

solution by the electrode - - ib.

2117. Non-conducting coating used

where partial deposit is required ib.

2118. Application of these principles to

gilding, silvering, &c. - - ib.

2119. Cases in which the coating is in-

adhesive 428

2120. Application to gilding, silvering, or

bronzing objects of art - - ib.

2121. Production of metallic moulds of

articles ib.

2122. Productionof objects in solid metal 429

2123. Reproduction of stereotypes and

engraved plates - ib.

2124. Metallizing textile fabrics - - ib.

2125. Glyphography - - 430

2126. Reproduction of Daguerreotypes - ib.

CHAP. XIV.

ELECTRO-TELEGRAPHY.

2127. Common principle of all electric

telegraphs - - - - 431



Sect. p aee

2128. Conducting wires - ... 432

2129. Telegraphic signs - 453

2130. Signs made with the needle system 434

2131. Telegraphs operating by an elec-

tro-magnet - 435

2132. Morse's system - ... 435

2133. Electro-chemical telegraphs - 437

CHAP. XV.

CALORIFIC, LUMINOUS, AND PHYSIOLOGICAL
EFFECTS OF THE VOLTAIC CURRENT.

2134. Conditions on which calorific

power of current depends - - 439

2135. Calorific effects Hare's and Chil-

dren's deflagrators ... if,.

2136. Wollaston's thimble battery - 440

2137. Experimental illustration of the

conditions which affect calorific
power of a current -

2138. Substances ignited and exploded

by the current -

2139. Application of this in civil and

military engineering

2140. Jacobi's experiments on conduc-

tion by wat



2141. Combustion of the metals -

2142. Spark produced by the voltaic cur-

rent - - ..

2143. The electric light -

2144. Action of a magnet on the electric

flame -

2145. Incandescence of charcoal by the

current not combustion -

2146. Electric lamps of Messrs. Fou-

cault, Deleuil, and Dubosc-
Soleil

2147. Method of applying the heat of

charcoal to the fusion of refrac-
tory bodies and the decompo-
sition of the alkalis - - .

2148. Physiological effects of the current

2149. Medical application of the voltaic

shock

2150. Effect on bodies recently deprived

of life

Effect of the shock upon a leech -

2151. Excitation of the nerves of taste -

2152. Excitation of the nerves of sight -

2153. Excitation of the nerves of hearing

2154. Supposed sources of electricity in

the animal organization -

2155. Electrical fishes -

2156. Properties of the torpedo Obser-

vations of Walsh - - .

2157. Observations of Becquerel and

Breschet -

2158. Observations of Matteucci -

2159. The electric organ -



HAND-BOOK

OF

NATUBAL PHILOSOPHY

AND

ASTRONOMY.



SECOND COURSE.
BOOK THE FIRST.

HEAT.



CHAPTER I.

PRELIMINARY PRINCIPLES AND DEFINITIONS.

1304. HEAT, like all other physical agents, is manifested and
measured by its effects.

1305. Sensible heat. One of the most familiar of these
effects is the sense of more or less warmth which a body, when
it receives or loses heat, produces upon our organs.

When the heat received or lost by a body is attended with
this sense of increased or diminished warmth, it is called
sensible heat.

1306. Insensible heat. But it will occur in certain cases
that a body may receive a very large accession of heat without
any increased sense of warmth being produced by it, and may,
on the other hand, lose a considerable quantity of heat without
exciting any diminished sense of warmth. The heat which a
body Avould thus receive or lose without affecting the senses, is
called latent heat.

1307. Dilatation and contraction. "When a body receives

II. *B



2 HEAT.

or loses heat, it generally suffers a change in its dimensions,
the increase of heat being usually attended with an increase,
and the diminution of heat with a diminution of volume.

This enlargement of volume due to the accession of heat is
called dilatation, and the diminution of volume attending the
loss of heat is called contraction.

There are, however, certain exceptional cases in which heat,
whether received or lost, is attended with no change of volume,
and others in which changes take place the reverse of those
just mentioned ; that is to say, where an accession of heat is
accompanied by a diminution, and a loss of heat with an in-
crease of volume.

1308. Liquefaction and solidification. If heat be imparted
in sufficient quantity to a solid body., it will pass into the liquid
state. Thus, ice or lead, being solid, will become liquid by
receiving a sufficient accession of heat. This change is called
fusion or liquefaction.

If heat be abstracted in sufficient quantity from a body in
the liquid state, it will pass into the solid state. Thus, water
or molten lead losing heat in sufficient quantity will become
solid. This change is called congelation or solidification ; the
former term being applied to substances which are usually
liquid, and the latter to those that are usually solid.

1309. Vaporization and condensation. If heat be im-
parted in sufficient quantity to a body in the liquid state, it
will pass into the state of vapour. Thus, water being heated
sufficiently will pass into the form of steam. This change is
called vaporization.

If a body in the state of vapour lose heat in sufficient quantity,
it will pass into the liquid state. Thus, if a certain quantity of
heat be abstracted from steam, it will become water.

This change is called condensation ; because, in passing from
the vaporous to the liquid state, the body always undergoes a
very considerable diminution of volume, and therefore becomes
condensed.

1310. Incandescence Heat, when imparted to bodies in a

certain quantity, will in some cases render them luminous.

Thus, if metal be heated to a certain degree, it will become
red-hot; a term signifying merely that it emits red light.
This luminous state, which is consequent on the accession of
heat, is called incandescence.

The more intense the heat is which is imparted to an incan-



PRELIMINARY PRINCIPLES AND DEFINITIONS. 3

descent body, the more white will be the light which it emits.
When it first becomes luminous, it emits a dusky red light.
The redness becomes brighter as the heat is augmented, until at
length, when the heat becomes extremely intense, it emits a
white light resembling solar light.

A bar of iron submitted to the action of a furnace will
exhibit a succession of phenomena illustrative of this.

1311. Combustion. Certain bodies, when surrounded by
atmospheric air, being heated to a certain degree, will enter into
chemical combination with the oxygen gas which forms one of
the constituents of the atmosphere.

This combination will be attended with a large development
of heat, which is accompanied usually by incandescence and
flame.

This phenomenon is called combustion, and the bodies which
are susceptible of this effect are called combustibles.

The flame, which is one of the effects of combustion, is gas
rendered incandescent by heat.

1312. Thermometers and pyrometers. The degree of sen-
sible heat by which a body is affected, is called its temperature,
and the instruments by which the temperature of bodies is in-
dicated and measured are called thermometers and pyrometers ;
the latter term being applied to those which are adapted to

'the measurement of the higher order of temperatures.

Changes of temperature are indicated and measured by the
change of volume which they produce upon bodies very suscept-
ible of dilatation. Such bodies are called thermoscopic bodies.
The principal of these are, for thermometers, mercury, alcohol,
and air ; and, for pyrometers, the metals, and especially those
which are most difficult of fusion.

1313. Conduction. When heat is communicated to any
part of a body, the temperature of that part is momentarily
raised above the general temperature of the body. This ex-
cessive heat, however, is gradually transmitted from particle to
particle throughout the entire volume, until it becomes uni-
formly diffused, and the temperature of the body becomes
equalized.

This quality, in virtue of which heat is transmitted from
particle to particle throughout the volume of a body, is called
conductibility.



4 HEAT.

Bodies have the quality of conductibility in different degrees ;
those being called good conductors in which any inequality of
temperature is quickly equalized, the excess of heat being
transmitted with great promptitude and facility from particle to
particle. Those in which it passes more slowly and imperfectly
through the dimensions of a body, and in which, therefore, the
equilibrium of temperature is more slowly established, are
called imperfect conductors. Bodies, in which the excess of
heat fails to be transmitted from particle to particle before it
has been dissipated in other ways, are called non-conductors.

The metals in general are good conductors, but different
metals have different degrees of conductibility. The earths
and woods are bad conductors, and soft, porous, and spongy
substances still worse.

1314. Radiation. Heat is propagated from bodies which
contain it by radiation in the same manner, and according to
nearly the same rules, as those which govern the radiation of
light. Thus, it proceeds in straight lines from the points
whence it emanates, diverging in every direction, these lines
being called thermal rays.

1315. Diathermanous media. Certain bodies are per-
vious to the rays of heat, just as glass and other transparent
media are pervious to the rays of light. They are called dia-
thermanous bodies. Thus atmospheric air and gaseous bodies
in general are diathermanous.

The rays of heat are reflected and refracted according to the
same laws as those of light. They are collected into foci by
spherical mirrors and lenses, they are polarized both by reflection
and refraction, and are subject to all the phenomena of double
refraction by certain crystals in a manner analogous to that
already explained in relation to the rays of light.

Bodies are diathermanous in different degrees.

Imperfectly diathermanous bodies transmit some of the rays
of heat which impinge on them, and absorb others ; the portions
which they absorb raising their temperature, but those which
they transmit not affecting their temperature.

1316. Reflection of heat. The surfaces of bodies also reflect
heat in different degrees ; those rays which they do not reflect
they absorb. The processes of transmission, absorption, and
reflection vary with the nature of the body and the state of its
surface with respect to smoothness, roughness, or colour.



THERMOMETRY. 5

1317. Refraction of heat. Rays of heat, like those of light,
are differently refrangible.

1318. Different senses of the terms heat and caloric. The
term heat is used in different senses : first, to express the
sensation produced when we touch a heated body or are sur-
rounded by a hot medium ; secondly, to express the quality of
the body by which this sensation is produced ; and thirdly, to
express the physical agent, whatever it be, to which the quality
of the body is due. Notwithstanding these different senses of
the same term, no confusion or obscurity arises in its use, the
particular sense in which it is applied being generally evident
by the context ; nevertheless it were to be desired that writers
on physics could agree upon a nomenclature more definite.

The term caloric has been proposed, and to some extent
adopted, to express the physical agent to which the effects of
heat are due.

1319. Hypothesis to explain thermal phenomena. Two
hypotheses have been proposed to explain the phenomena of
heat. The first regards heat as an extremely subtle fluid
pervading all space, entering into combination in vai-ious pro-
portions and quantities with bodies, and producing by this
combination the effects of expansion, fusion, vaporization, and
all the other phenomena above mentioned. The second hypo-
thesis regards it as the effect of the vibration or undulation,
produced either in the constituent molecules of bodies them-
selves, or in a subtle impenetrable fluid which pervades them.

In the present Book the effects of heat will be explained
independently of hypothesis ; and, when they have been fully
developed, the different theories proposed for their explanation
will be stated.



CHAP. II.

THERMOMETRY.



1820. Measures of temperature. Of all the various effects of
heat, that which is best adapted to indicate and measure tem-
perature is dilatation and contraction. The same body always
has the same volume at the same temperature, and always



6 HEAT.

suffers the same change of volume with the same change of
temperature.

Since the volume and change of volume admit of the most
exact measurement and of the most precise numerical expres-
sion, they become the means of submitting the degrees of
warmth and cold, or, which is the same, the degrees of tem-
perature, to arithmetical measure and expression.

1321. Thermoscopic substances. Although all bodies what-
ever are susceptible of dilatation and contraction by change of
temperature, they are not equally convenient for thermoscopic
agents.

For reasons which will become apparent hereafter, the most
available thermoscopic substance for general purposes is mer-
cury.

1322. Mercurial thermometer. The mercurial thermometer
consists of a capillary tube of glass, at one end of which a thin
spherical or cylindrical bulb is blown, the bulb and a part of
the tube being filled with mercury.

When such an instrument is exposed to an increase of
temperature, the glass and mercury will both expand. If they
expanded in the same proportion, the capacity of the bulb and
tube would be enlarged in the same proportion as the mercury
contained in them, and, consequently, the column of mercury in
the tube would neither rise nor fall, since the enlargement of
its volume would be exactly equal to the enlargement of the
capacity of the bulb and tube. If, however, the expansion of
the bulb and tube be different from that of the mercury, the
column in the tube will, after expansion, stand higher or lower
than before, according as the expansion of the mercury is
greater or less than the expansion of the bulb and tube.

It is found that the dilatability of mercury is greater than
the dilatability of glass in the proportion of nearly 20 to 1,
and, consequently, the capacity of the bulb and tube will be
less enlarged than the volume of the mercury contained in
them in the proportion of nearly 1 to 20 ; consequently, for the
reason above stated, every elevation of temperature by which
the mercury and tube would be affected will cause the column
of mercury to rise in the tube, and every diminution of
temperature will cause it to fall.

The space through which the mercury will rise in the tube
by a given increase of temperature will be greater or less ac-



THERMOMETRY. 7

cording to the proportion which the tube bears to the capacity
of the bulb. The smaller the proportion the tube bears to the
capacity of the bulb, the greater will be the elevation of the
column produced by a given increase of temperature ; for a
given increase of temperature will produce a definite increase
of volume in the mercury, and this increase of volume will fill
a greater space in the tube in proportion to the smallness of the
tube compared with the capacity of the bulb.

Such an instrument, without other appendages or prepar-
ation, would merely indicate such changes of temperature in
a given place as would be sufficient to produce visible changes
in the elevation of the column of mercury sustained in the tube.
To render it useful for the purposes of science and art, and in
domestic economy, various precautions are necessary, which
have for their object to render the indications of different
thermometers comparable with each other, and to supply exact



Online LibraryDionysius LardnerHand-book of natural philosophy and astronomy (Volume 2) → online text (page 3 of 45)