LONDON

WALTON AND MABERLY,

UPPER GOWF/

Price Eighteenpence.

EDITED BY

DIONYSIUS LAEDNEE, D.C.L.,

Formerly Professor of Natural PMlosophy and Astronomy in University College, London.

*

ILLUSTRATED BY ENGRAVINGS ON WOOD.
YOL. III.

LONDON :
WALTON AND MABERLY,

UPPER GOWER STREET AND IVY LANE, PATERNOSTER ROW.
1854.

LOAN STACK

LOVDON :
BRAUBCRY AND 3V.\XS, PKINTSR9, WHITEFRIARH.

,37

CONTENTS.

LOCOMOTION AND TRANSPORT, THEIR INFLUENCE AND
PROGRESS.

PAOK

CHAP. I. INFLUENCE OP IMPROVED TRANSPORT ON CIVILISATION. —

1. Art of transport essential to social advancement. — 2. Its
rapid advancement in modern times. — 3. Commerce mainly
dependent on it. — 4. Its conditions. — 5. Its advantages, its
influence on price. — 6. Example of cotton. — 7. Agricultural
products. — 8. Reciprocal advantages to rural and urban popu-
lation.— 9. Absence of good means of transport injurious to
France. — 10. Renders -worthless or injurious articles serviceable
and valuable. — 11. Stimulates both production and consumption.
— 12. Increases the demand for labour. — 13. Effects of rail-
ways.— 14. Advantages of increased speed. — 15. In the transport
of cattle. — 16. Steam vessels not so well adapted to this. — 17.
Supply of milk to towns. — 18. Advantages to farmers and land-
lords.— 19. Advantages of steam navigation. — 20. Advantages of
personal locomotion. — 21. In the case of the working population.
— 22. Influence on the value of land. — 23. Advantages to the
population of large cities. — 24. Relative speed of horse coaches
and railways. — 25. Military advantages. — 26. Offers induce-
ments to peace and the means of abridging war. — 27. Influence
on the diffusion of knowledge. — 28. The electric telegraph. —

29. Journalism 1

CHAP. II. RETROSPECT OF THE PROGRESS OF TRANSPORT. — 1. Of the
first construction and improvement of roads and carriages. —

2. Roads do not exist in more than two-sevenths of the inhabited
parts of the globe. — 3. Roman and Egyptian roads. — 4. Roads
constructed by order of Semiramis. — 5. Internal communication
in ancient Greece. — 6. Roads of the Phoenicians and Carthagi-
nians.— 7. Roman military roads. — 8. Commercial intercourse
during the middle ages. — 9. Influences of the crusades on the art
of transport. — 10. Roads and intercommunication on the Con-
tinent to the middle of the seventeenth century. — 11. System of
roads projected by Napoleon. — 12. Improvement in internal
communication after the peace of 1815 — Roads of France — 13.
First roads in England, those made by the Romans. — 14. Watling
Street, Ermine Street, Fosse-way and Ikenald. — 15. First
attempts to improve roads in Great Britain in reign of Charles
the Second. — 16. Transport in Scotland to the middle of the
eighteenth century. — 17. Slowness of travelling in Scotland. —

377

iv CONTENTS.

PAGE

18. Arthur Young's account of the roads in England in 1770. —

19. Comparison between cost and speed of former and present
modes of transport. — 20. Origin of railways in England. —
21. Their immediate effects. — 22. Progress of the construction.
—23. Their extent in 1852.— 24. Capital absorbed by them.—

25. Labour employed by them 17

THE MOON.

1 . Interest with which the moon is regarded, and influences with which
it has been invested by the popular mind. — 2. Its distance.
— 3. Its orbit. — 4. Its magnitude. — 5. Its rotation. — 6. Con-
junction.— 7. Quadrature. — 8. Opposition. — 9-11. Tests of an
atmosphere. — 12-13. None exists on the moon. — 14. No liquids.
— 15. No diffusion of solar light. — 16. Appearance of earth seen
from moon. — 17. It would have belts. — 18. Geographical features
and its rotation would be visible through the clouds. — 19. Moon-
light neither warm nor cold. — 20. Moon's physical condition.
— 21. Thickly covered with mountains. — 22. Selenographical
discoveries of Beer and Madler. — 23. Vast extent and diameter of
the lunar mountains. — 24. Circular chains. — 25. Description of
Tycho. — 26. Heights of lunar mountains. — 27. Observations of
Lord Rosse. — 28. Moon not inhabited 33

COMMON THINGS.— THE EARTH.

1. Difficulty of observing the earth as a whole. — 2. It appears at first
an indefinite flat surface. — 3. This disproved by travelling round
it. — 4. Proof of the curvature of its surface by observation of dis-
tant objects at sea. — 5. By the Earth's shadow projected on the
Moon. — 6. Inequalities of surface, such as mountains and valleys,
insignificant. — 7. Magnitude of Earth, how ascertained. —
8. Length of a degree of latitude. — 9-10. Illustrations of the
Earth's magnitude. — 11. Is the Earth at rest? — 12. Apparent
motion of the firmament. — 13. Origin of the word " Universe."
— 14. This apparent motion may not be real — may arise from the
rotation of the Earth. — 15. How such a rotation would produce
it. — 16. Poles. — 17. Equator. — 18. Hemispheres. — 19. Meri-
dians.— 20. Which of the two rotations is the more probable ? —
21. Rotation of the universe impossible. — 22. Simplicity of the
supposed rotation of the globe. — 23. Direct proofs of this motion.
— 24. Foucault's experiment. — 25. Its analogy to the planets. —
26. Conclusion as to the globular form of the earth requires
modification. — 27. All human knowledge tentative and approxi-
mative.— 28. Rotation not compatible with the exact globular
form. — 29. Centrifugal force of the Earth's rotation. — 30. The
globe rotating would assume the form of an oblate spheroid. —
31. The degree of ellipticity would vary with the velocity of
rotation. — 32. Experimental illustration. — 33. Ellipticity corre-
sponding to the diurnal rotation. — 34. How these circumstances
affect the actual state of the Earth. — 35. Form of a terrestrial

CONTENTS. v

PAGE

meridian. — 36. Dimensions of the terrestrial spheroid. — 37. Its
departure from an exact globe very small. — 38. Its density and
mass. — 39. Determined by Cavendish and Maskelyne. — 40. Its
total weight. 49

TERRESTRIAL HEAT.

CHAP. I. — 1. Heat an important agent. — 2. Its local variations. —
3. Diurnal period. — 4. Annual period. — 5. Mean diurnal
temperature. — 6. Mean monthly temperature. — 7. Mean annual
temperature. — 8. Temperature of a place. — 9. Isothermal lines.
— 10. Isothermal zones. — 11. Thermal equator. — 12. Second
isothermal zone. — 13. Third. — 14. Fourth. — 15. Fifth and
Sixth. — 16. Polar regions. — 17. Climate varies on the same
isothermal line. — 18. Constant, variable, and extreme climates. —
19. Classification of climates. — 20. Extreme temperature in
torrid and frigid zones/ — 21. Elevation affects temperature. —
22. Snow line. — 23. Thermal conditions below the surface. —
24. Stratum of invariable temperature. — 25. Varies with the
latitude.— 26. Its form.— 27. Conditions above it.— 28. Con-
ditions below it. — 2 9 . Temperature of springs. — 30. Temperature
of greatest density of water. — 31. Thermal condition of seas and
lakes. — 32. Thermal condition of a frozen sea. — 33. Process of
thawing. — 34. Depth of stratum of constant temperature. — 35.
Superficial agitation extends only to a small depth. — 36. Great
utility of the state of maximum density. — 37. Variations of
temperature of the air. — 38. Interchange of Equatorial and
Polar waters. — 39. Polar ice. — 40. Ice-fields. — 41. Icebergs. —
42. Their forms and magnitude. — 43. Sunken icebergs. — 44.
Curious effects of their superficial fusion. — 45. Depth of Polar
Seas.— 46. Cold of Polar regions 65

CHAP. II. — 47. Sources of external heat. — 48. Solar heat. — 49. Its
quantity ascertained. — 50. Heat at sun's surface. — 51. Tempe-
rature of celestial spaces. — 52. Quantity of heat supplied by
them. — 53. Summary of heat supplied. — 54. Winds. — 55.
Produced by rarefaction and compression. — 56. Sudden con-
densation of vapour. — 57. Hurricanes. — 58. Their cause. —
59. Waterspouts. — 60. Evaporation. — 61. Saturation of air. —
62. May arise from intermixing strata. — 63. Effect of pressure.
— 64. Dew. — 65. Hoar frost. — 66. Artificial ice. — 67. Fogs and
clouds.— 68. Rain.— 69. Its quantity.— 70. Snow.— 71. Hail.—
72. Hailstones. — 73. Extraordinary hailstones . . . .81

THE SUN.

1. An object of great interest. — 2. Its distance. — 3. Magnitude.
— 4. Illustrations. — 5. Its volume. — 6. Mass or weight. — 7.
How ascertained. — 8. Application of this principle. — 9. Its
density. — 10. Form and rotation. — 11. Determined by the
appearance of spots. — 12. Discovery of Solar spots. — 13. Their

vi CONTENTS.

PAGE

great magnitude. — 14. Their rapid changes. — 15. Hypotheses to
explain them. — 16. They are excavations in the luminous
coating. — 17. Their prevalence varies. — 18. Observations upon
them. — 19. Their dimensions. — 20. Facules and Lucules. — 21.
Physical state of the Solar surface. — 22. Luminous coating is
gaseous. — 23. Gaseous atmosphere outside it. — 24. Effects of
such an atmosphere on radiation. — 25. Hypothesis of Sir J.
Herschel. — 26. Intensity of heat at Sun's surface. — 27.
Supposed source of heat 97

THE ELECTRIC TELEGRAPH.

CHAP. I. — 1. Subjugation of the powers of nature to human uses. —
2. Locomotion twenty years since. — 3. Circulation of intelligence
then. — 4. Supposed prediction of succeeding improvements —
Railway locomotion. — 5. Electric telegraphy. — 6. Fabrication of
diamonds — sun-pictures — gas-lighting — electro-metallurgy. — 7.
Such predictions would have been deemed incredible. — 8. Electro-
telegraphy the most incredible of all. — 9. Remarkable experiment
by Messrs. Leverrier and Lardner. — 10. Velocity of electric
current. — 11. No limit to the celerity of telegraphy. — 12.
Physical character of electricity. — 13. Not essential to the
explanation of electro-telegraphy. — 14. Electricity a subtle fluid.
— 15. Properties available for telegraphy. — 16. Voltaic battery.
— 17. It is to the electric telegraph what the boiler is to the
steam-engine. — 18. Means of transmitting the fluid in required
directions. — 19. Conductors and insulators. — 20. Conducting
wires. — 21. Voltaic battery. — 22. Transmission and suspension
of the current. — 23. Current established by earth contact. —
24. Theories of earth contact. — 25. The return of the current
through the earth. — 26. Various bodies evolve electricity. —
27. Common plate battery of zinc and copper. — 28. Why zinc
and copper are preferred. — 29. Charcoal substituted for copper.
— 30. Elements not essential. — 31. Various chemical solutions
used. — 32. Daniel's constant battery. — 33. Same modified by
Pouillet. — 34. Grove's and Bunsen's batteries. — 35. Necessary
to combine many elements 113

CHAP. II. — 36. Common plate battery. — 37. Combination of
currents. — 38. Loss of intensity by imperfect conduction. — 39.
Cylindrical batteries. — 40. Pairs, elements, and poles defined. —
41. Origin of term voltaic pile. — 42. Use of sand in charging
batteries. — 43. To vary intensity of current. — 44. Batteries used
for English telegraphs. — 45. Amalgamating the zinc plates. — 46.
The line-wires, material and thickness. — 47. Objection to iron
wires. — 48. Manner of carrying wires on posts. — 49. Good
insulation. — 50. Expedients for obtaining it. — 51. Forms of
insulating supports. — 52. Dimensions and preparations of the
posts. — 53. Forms of support used in England. — 54. Winding
posts. — 55. Supports in France. — 56. In America. — 57. In
Germany. — 58. Wire insulated by superficial oxydation. — 59.
Leakage of the electric fluid by the conduction of the atmosphere.

CONTENTS. yii

PAGE

— 60. Effects of atmospheric electricity on the wires. — 61.
Lightning conductors. — 62. Those of Messrs. Walker and
Breguet. — 63. Conducting current into stations. — 64. Under-
ground wires. — 65. Methods of insulating them. — 66. Testing
posts . 129

CHAP. III. — 67. Wires of Magneto- electric Telegraph Company. —
68. Mr. Bright' s method of detecting faulty points. — 69. Such
failure of insulation rare. — 70. Underground method recently
abandoned in Prussia. — 71. Underground wires of the European
and Submarine Company. — 72. Imperfect insulation in tunnels. —
73. Mr. Walker's method of remedying this. — 74. Overground
system adopted through the streets of cities in France, and in
the United States. — 75. Telegraphic lines need not follow rail-
ways.— 76. Do not in America. — 77. Submarine cables. — 78.
Cable connecting Dover and Calais. — 79. Failure of first attempt
— Improved structure. — 80. Table of submarine cables and their
dimensions. — 81. Dimensions and structure of the Dover and
Calais cable. — 82. Holyhead and Howth cable. — 83. First at-
tempt to lay cable between Portpatrick and Donaghadee — its
failure. — 84. Dover and Ostend. — 85. Portpatrick and Donagha-
dee.— 86. Orfordness and the Hague 145

CHAP. IV. — 87. Cable between Spezzia and Corsica. — 88. Other
cables, European and American. — 89. Objections brought by
scientific authorities to the submarine cables. — Answers to these
by practical men. — 90. Example of a cable uninjured by the
action of the sea. — 91. Precautions necessary in laying the cable.
— 92. Accident in laying the Calais cable. — 93. Imperfection
attributed to the Belgian cable. — 94. Transatlantic Ocean Tele-
graph.— 95. Underground wires between the Strand and Loth-
bury. — 96. Effect of the inductive action of underground or
submarine wires. — 97. Possible influence of this on telegraphic
operations. — 98. Examples of overground wires extended to great
distances without intermediate support — between Turin and
Genoa. — 99. Telegraphic lines in India. — 100. Difficulties arising
from atmospheric electricity — height and distance of posts — mode
of laying underground wires — extent of line erected to April
1854.— 101. Intensity of current decreases as the length of wire

increases. — 102. Also increases with the thickness of the wire.

103. And with the number of elements in the battery. 104.

Result of Pouillet's experiments on the intensity of current. —
105. Intensity produced by increasing the power of the battery.
: — 106. How the current produces telegraphic signals. — 107.
Velocity of the current. — 108. Transmission of signals instan-
taneous lg^

CHAP. V. — 109. Current controlled by making and breaking the contact

of conductors. — 110. Instruments for controlling the current.

Commutators. — 111. General principle of the commutators.

112. Its application to telegraphic operations. — 113. To trans-
mit a current on the up-line only. — 114. On the down-line only.
— 115. On both lines. — 116. To reverse the current. — 117. To
suspend and transmit it alternately. — 118. How to manage a

viii CONTENTS.

»•

PAGE

current which arrives at a station. — 119. To make it ring the
alarum. — 120. Station with two alarums. — 121. Notice of the
station transmitting and receiving signals. — 122. When signals
not addressed to the station the current is passed on. — 123. How
to receive a despatch at the station, and stop its farther progress.
— 124. How several despatches may be at the same time sent
between various stations on the same line. — 125. Secondary lines
of wii-e then used. — 126. Recapitulation. — 127. Signals by com-
binations of unequal intervals of transmission and suspension. —
128. Key commutator. — 129. Horological commutator for a
current having equal and regular pulsations. — 130. Case in which
the pulsations are not continuous or regular. — 131. No limit to
the celerity of the pulsations. — 132. Application of a toothed
wheel to produce the pulsations. — 133. By a sinuous wheel. —
134. Method of diverting the current by a short circuit, its
application to the alarum. — 135. Effects of the current which
has been used for signals. — 136. Deflection of magnetic needle. 177

CHAP. VI. — 137. Relation of the deflection to the direction of
the current. — 138. Galvanometer or multiplier. — 139. Method
of covering the wire. — 140. Method of mounting the needle. —
141. Method of transmitting signals by the galvanometer. — 142.
How the current may produce a temporary magnet. — 143.
Electro-magnet constructed by Pouillet. — 144. Electro-magnets
formed by two straight bars. — 145. They acquire and lose
their magnetism instantaneously. — 146. Magnetic pulsations as
rapid as those of the current. — 147. How they are rendered
visible and counted. — 148. Extraordinary celerity of the oscil-
lations thus produced. — 149. They produce musical sounds by
which the rate of vibration may be estimated. — 150. How
the vibrations may impart motion to clock-work. — 151. Their
action on an escapement. — 1 52 . How the movement of one clock may
be transmitted by the current to another. — 153. Hew an electro-
magnet may produce written characters on paper at a distant
station. — 154. How the motion of the hand upon a dial at one
station can produce a like motion of a hand upon a dial at a
distant station. — 155. How an agent at one station can ring an
alarum at another station. — 156. Or may discharge a gun or
cannon there. — 157. Power of the bell or other signal not
dependent on the force of the current. — 158. Mechanism of
telegraphic alarum. — 159. Various alarums in telegraphic oifices.
— 160. Magneto-electricity. — 161. Method of producing a
momentary magneto-electric current. — 162. Application of an
electro-magnet to produce it 193

LOCOMOTION AND TRANSPORT,

THEIE INFLUENCE AND PROGRESS.

CHAPTEE I.

INFLUENCE OF IMPROVED TRANSPORT ON CIVILISATION.

Art of transport essential to social advancement. — 2. Its rapid
advancement in modern times. — 3. Commerce mainly dependent on it.
— 4. Its conditions. — 5. Its advantages, its influence on price. — 6.
Example of cotton. — 7. Agricultural products. — 8. Reciprocal
advantages to rural and urban population. — 9. Absence of good
means of transport injurious to France. — 10. Renders worthless or
injurious articles serviceable and valuable. — 11. Stimulates both
production and consumption. — 12. Increases the demand for labour.
13. Effects of railways. — 14. Advantages of increased speed. — 15.
In the transport of cattle. — 16. Steam vessels not so well adapted to
this. — 17. Supply of milk to towns. — 18. Advantages to farmers and
landlords. — 19. Advantages of steam navigation. — 20. Advantages
of personal locomotion. — 21. In the case of the working population.
— 22. Influence on the value of land. — 23. Advantages to the popula-
tion of large cities. — 24. Relative speed of horse coaches and railways.
25. Solitary advantages. — 26. Offers inducements to peace and the
means of abridging war. — 27. Influence on the diffusion of knowledge,
— 28. The electric telegraph. — 29. Journalism.

LARDNER'S MUSEUM OP SCIENCE. B 1

No. 27.

LOCOMOTION AND TRANSPORT.

1. THE art by which the products of labour and thought, and
the persons who labour and think, are transferred from place to
place, is, more than any other, essential to social advancement.
"Without it no other art can progress. A people who do not
possess it cannot be said to have emerged from barbarism. A
people who have not made some advances in it, cannot yet have
risen above a low state of civilisation. Nevertheless, this art has
been, of all others, the latest in attaining a state of perfection, so
late, indeed, that the future historian of social progress will
record, without any real violation of truth, that its creation is one
of the events which have most eminently signalised the present
age and generation. For, although transport by land and water
was practised by our forefathers, its condition was so immeasurably
below that to which it has been carried in our times, that a more
adequate idea of its actual state will be conveyed by calling it a
new art, than by describing it as an improvement on the old one.

2. But if human invention has been late in directing its powers
to this object, it must be admitted to have nobly compensated for
the tardiness of its action by the incomparable rapidity of
advancement it has produced, when once they have been brought
into play. Within a hundred years, more has been accomplished
in facilitating and expediting intercommunication, than was effected
from the creation of the world to the middle of the last century.
This statement may, perhaps, appear strained and exaggerated,
but it will bear the test of examination.

3. The geographical conditions of the world, the distribution of
the people who inhabit it, and the exclusive appropriation of its
natural productions destined for their use to the various countries
of which it consists, have imposed on mankind the necessity of
intercommunication and commerce. Commerce is nothing more
than the interchange of the productions of industry between people
and people. Such interchange presupposes the existence of the
art of transport by land and water. In proportion to the per-
fection of this art will be the extent of commerce.

A people incapable of communicating with others must subsist
exclusively upon the productions of its own labour and its own
soil. But nature has given us desires after the productions of
other soils and other climates. Besides this, the productions of
each particular soil or country are obtainable in superfluity.
They are infinitely more in quantity than the people by whom
and amidst whom they are produced have need of; while other
and distant peoples are in a like situation, having a superfluity of
some products and an insufficiency or a total absence of others.
The people of South Carolina and Georgia have a superfluity of
cotton, the people of the West India Islands have a superfluity of
2

ADVANTAGES OF TRANSPORT.

coffee and tobacco, the people of Louisiana have a superfluity
of sugar, the people who inhabit the vast valley of the Upper
Mississippi and Missouri have a superfluity of corn and cattle, the
people of civilised Europe have a superfluity of the products of
mechanical labour, those of France have a superfluity of silk
goods, those of England of manufactured cotton, pottery, and
hardware. Each of these various peoples is able and willing to
supply the others with those productions in which themselves
abound, and to receive in exchange those of which they stand in
need, and which abound elsewhere.

4. But, to accomplish such interchanges, means of transport must
be provided, and this transport must be sufficiently cheap, speedy,
safe, and regular, to enable these several productions to reach
their consumers, and be delivered on such terms and conditions
as will be compatible with the ability to purchase them.

5. Among the advantages which attend improved means of
transport, one of the most prominent is that of lowering the price
of all commodities whatever in the market of consumption, and
thereby stimulating production. The price paid for an article by
its consumer consists of two elements : 1st, the price paid for the
article to its producer at the place of its production ; and, 2ndly,
the expense of conveying it from that place to the consumer. In
this latter element is included the cost of its transport and the
commercial expenses connected with such transport. These last
include a variety of items which enter largely into the price of the
commodity, such as the cost of transport, properly so called, the
interest on the price paid to the producer proportionate to the time
which elapses before it reaches the consumer, the insurance against
damage or loss during the transport. This insurance must be
paid directly or indirectly by the consumer. If it be not effected
by those who convey the commodity to the consumer, the value of
the goods which may be lost or damaged in the transport will neces-
sarily be charged in the price of those which arrive safe. In either
case the consumer pays the insurance. There are also the charges
for storage, packing, transhipment, and a variety of other com-
mercial details, the total of which forms a large proportion of the
ultimate price.

In many cases, these expenses incidental to transport amount
to considerably more than half the real price of the article ; in
some they amount to three-fourths or four-fifths, or even a larger
proportion.

6. Let us take the example of raw cotton produced on the plains
of South Carolina or Georgia. This article is packed in bales at
the place of production. These are then transported to Charleston
or Savannah, whence they are exported to Liverpool. Arriving

B2 3

LOCOMOTION AND TRANSPORT.

at Liverpool, they are transferred upon the railway, "by which they
are transported to Manchester, Stockport, Preston, or some other
seat of manufacture. The raw material is there taken by the
manufacturer, spun into thread, woven into cloth, bleached and
printed, glazed, and finished. It is. then repacked, and again
placed on the railway and transported once more to Liverpool,
when it is re-embarked for Charleston or Savannah, for example.
Arriving there, it is again placed on a railway or in a steam-boat,
and is transported to the interior of the country, and finally returns
to the very place at which it originally grew, and is repurchased by
its own producer. Without going into arithmetical details, it will be
abundantly apparent how large a proportion of the price thus paid
for the manufactured article is to be placed to the account of the
transport and commercial expenses. The article has made the
circuit of almost half the globe before it has found its way back in
its manufactured state.

7. The products of agricultural labour have, in general, great
bulk with proportionately small value. The cost of transport has
consequently a great influence upon the price of these in the market
of consumption. Unless, therefore, this transport can be effected
with considerable economy, these products must be consumed on
the spot where they are produced.

In the case of many animal and vegetable productions of
agriculture, speed of transport is as essential as cheapness, for
they will deteriorate and be destroyed by the operation of time
alone. "Without great perfection, therefore, in the art of trans-
port, objects of this class must necessarily be consumed in the
immediate neighbourhood of the place where they are raised.
Such are, for example, the products of the dairy, the farm-yard,
and the garden.

8. In countries where transport is dear and slow, there conse-
quently arises great disadvantage, not only to the rural, but also
to the urban population. While the class of articles just referred
to are at a ruinously low price in the rural districts, they are at a
ruinously high price in the cities and larger class of towns. In the
country, where they exist in superfluity, they fetch comparatively
nothing : in the towns, where the supply is immeasurably below
the demand, they can only be enjoyed by the affluent.

But if sufficiently cheap and rapid means of transport be pro-
vided, these productions find their way easily to the great centres
of population in the towns, and the rural population which produces
them receives in exchange innumerable articles of use and luxury
of which they were before deprived.

9. France, one of the most civilised states of Europe, exhibits a
deplorable illustration of this. Notwithstanding the fertility of

ITS INFLUENCE ON PRICES.

her soil, the number, the industry, and intelligence of her popu-
lation, the products of every description, animal and vegetable,
which abound in her territory, yet, from the absence of sufficiently
easy means of intercommunication, these advantages have been
hitherto almost annihilated. All these productions, in the place
•where they are raised, can be obtained at a lower price than in
most other countries; and yet, in consequence of the cost of
transport, they would attain, if brought to the place where they are
in demand, a price which would amount to a prohibition on their
consumption. From this cause the industry of France has long
been to a great extent paralysed.

10. In some cases the price of an article at the place of consump-
tion consists exclusively of the cost of transport. An article has
frequently no value in the place where it is found, which never-
theless would have a considerable value transported elsewhere.
Numerous instances of this will occur in the case of manures used
in agriculture. Every reduction, therefore, which can be made in
the cost of the transport of these, will tend in a still greater
proportion to lower their price to those who use them.

Cases even occur in which the cost of transport is actually
greater than the price paid for an article by the consumer. This,
which would seem a paradox, is nevertheless easily explained.
An article in a given place may be a nuisance, and its possessor
may be willing to pay something for its removal. This article,
however, transported to another place, may become eminently
useful, and even be the means of stimulating profitable production.
The cleansing the common sewers of a city affords a striking
example of this. The filth and offal which are removed are a
nuisance where they exist, and may even be the cause of pestilence
and death. Transported, however, to the fields of the agriculturist,
they become the instruments of increased fertility. Cases may be
cited where the whole cost of transport will be more than
covered by the sum paid for the removal of the nuisance.*

1 1 . Every improvement in the art of transport having a tendency
to diminish cost, and augment speed and safety, operates in a
variety of ways to stimulate consumption and production, and
thereby advance national wealth and prosperity. When the
price of an article in the market of consumption is reduced by this
cause, the demand for it is increased : 1st, by enabling former
consumers to use it more freely and largely ; and, 2ndly, by
placing it within the reach of other classes of consumers who were
before compelled to abstain from it by its dearness. The increase of

* In Aberdeen the streets were swept every day, at an annual cost of
1400Z., and the refuse brought in 2000Z. a-year. In Perth the scavenging
cost 1300Z. per annum, and the manure sold for 1730J.

5

LOCOMOTION AND TRANSPORT.

consumption from this cause is generally in a larger ratio than
the diminution of price. The number of consumers able and
willing to pay one shilling for any proposed article is much more
than twice the number who are able and willing to pay two
shillings for the same article.

But consumption is also augmented in another way by this
diminution of price. The saving effected by consumers who,
before the reduction, purchased at the higher price, will now be
appropriated to the purchase of other articles of use or enjoyment,
and thus other branches of industry are stimulated.

12. The improvements which cheapen transport, necessarily in-
cluding the expenditure of less labour in effecting it, might seem,
at first view, to be attended with injury to the industry employed
in the business of transport itself, by throwing out of occupation that
portion of labour rendered superfluous by the improvement. But
experience shows the result to be the reverse. The diminished
cost of transport invariably augments the amount of commerce
transacted, and in a much larger ratio than the reduction of cost ;
so that, in fact, although a less amount of labour is employed in
the transport of a given amount of commodities than before, a
much larger quantity of labour is necessary by reason of the vast
increase of commodities transmitted. The history of the arts
supplies innumerable examples of this. When railways were first
brought into operation, it was declared, by the opponents of this
great improvement (for it had opponents, and violent ones), that
not only would an immense amount of human industry connected
with the business of land carriage be utterly thrown out of
employment, but also that a great quantity of horses would be
rendered useless. Experience was not long in supplying a striking
proof of the fallacy of this prevision.

13. The moment the first great line of railway was brought into
operation between Liverpool and Manchester, the traffic between
those places was quadrupled ; and it is now well known that the
quantity of labour, both human and chevaline, employed in land
carriage where railways have been established, has been increased
in a vast proportion, instead of being diminished.

In 1846 there were seventy-three stage-coaches or lines of
omnibus employed in the transport of passengers to and from the
several stations of the North of France Railway, which supplied
176 arrivals and departures, had 5776 places for passengers,
and employed daily 979 horses. In the six months ending 31st
December, 1846, these coaches transported 486948 passengers.

Improvements in transport which augment the speed, without
injuriously increasing the expense or diminishing the safety, are
attended with effects similar to those which follow from cheapness.

ADVANTAGES OF RAILWAYS.

14. A part of the cost of transport consists of the interest on the
cost of production chargeable for the time elapsed between the
departure of the article from the producer and its delivery to the
consumer. This element of .price is clearly diminished in the exact
proportion to the increased speed of transport.

But increased speed of transport also operates beneficially on
commerce in another way. Numerous classes of articles of pro-
duction become deteriorated by time, and many are absolutely
destroyed, if not consumed within a certain time. It is evident
that such articles admit of transport only when they can reach the
consumer in a sufficiently sound state for use ; various classes of
articles of food come under this condition.

While the Houses of Parliament were occupied with the numerous
railway acts which have been brought before them, a great mass
of evidence was produced illustrating the advantages which both
producer and consumer would obtain by the increased cheapness
and expedition of transport which railways would supply. It
was shown that the difficulties attending transport by common
roads affected, in an injurious manner, the grazier who supplied
the markets with veal and lamb. Lambs and calves were generally
sent by the road ; and when too young to leave the mothers for so
long a time as the journey required, the producer was obliged to
send the ewes or cows with them for at least a part of the way.
This also rendered it impossible to send them to market sufficiently
young, which it would have been advantageous to do, that the
mothers might feed off earlier.

15. But, independently of this, the animals of every species driven
to market on the common roads were proved to suffer so much
from the fatigue of the journey, that when they arrived at market
their flesh was not in a wholesome state. They were often driven
till their feet were sore. Sheep frequently had their feet literally
worn off, and were obliged to be sold on the road for what they
would fetch. Extensive graziers declared that, in such cases, they
would be gainers by a safe and expeditious transport for the animals,
" even though it cost double the price paid to the drovers."

Butchers engaged in large business in London proved that the
cattle driven to that market from considerable distances sustained
so much injury that their value was considerably lessened, owing
to the inferior quality of the meat, arising from the animal being
slaughtered in a diseased state ; that the animal being fatigued
and overdriven " became feverish, his looks became not so good,
and he lost weight by the length of the journey and the fatigue."

16. It was shown further, that even steam-vessels, when they
could be resorted to, did not altogether remove this objection. Cattle
arriving from Scotland in steam-vessels are found in London to be

7

LOCOMOTION AND TRANSPORT.

in an nnnatural state ; " they seem stupified, and in a state
suffering from fatigue."

It is not merely the fatigue of travelling which injures the
animal, but also the absence from its accustomed pasture. The
injury from this cause is more or less, under different circum-
stances, but always considerable : in order to obviate this, a large
portion of the meat supplied to the London market was slaughtered
in the country, and came in this state, in winter, from distances
round London to the extent of one hundred miles. In warm
weather a large quantity of it was spoiled. The transport of calves
and lambs from a distance greater than thirty miles is altogether
impracticable by common roads, and even from that distance is
attended with difficulty and injury.

To convey these and other live cattle from a great distance, not
only speed but evenness of motion is indispensable. Now these
two requisites cannot be combined by any other means than the
application of steam-engines upon a railroad.

The whole of the evidence showed that the supply of animal
food to the metropolis was not only defective in quantity, but of
unwholesome quality — comparatively, at least, with what it might
be, if the tract from which it could be supplied were rendered more
extensive.

17. But, forcibly as the evidence bore on this species of agricul-
tural produce, it was still stronger respecting the produce of the
dairy and the garden. Milk, cream, and fresh butter, vegetables of
every denomination, and certain descriptions of fruit, were usually
supplied exclusively from a narrow annulus of soil which circum-
scribes the skirts of great cities. Every artificial expedient was
resorted to, in order to extort from this limited portion of land the
necessary supplies for the population. The milk was of a quality
so artificial, that we know not whether, in strict propriety of
language, the name milk can be at all applied to it. The animals
that yielded it were fed, not upon wholesome and natural pas-
turage, but, in a great degree, on grain and similar articles. It
will not be supposed that the milk thus yielded is identical in
wholesome and nutritious qualities with the article which could be
supplied if a tract of land, of sufficient extent for the pasturage of
cattle, was made subservient to the wants of such cities. Add to
this that, inferior as must be under such circumstances the quality
of the milk, there exist the strongest temptations to the seller
who retails it to adulterate it still further before it finds its way to
the table of the consumer.

Since the introduction of transport by railways, we see attached
to the fast trains, morning and afternoon, numerous waggons
loaded with tier over tier of milk-cans for the supply of the metro-

ADVANTAGES TO FARMERS AND LANDLORDS.

politan population. Milk is thus brought from pastures at great
distances from the cities where it is consumed. In Paris the
benefits of this have been very conspicuous.

18. The benefits to farmers and landlords, as well as to the inha-
bitants of towns, by carrying extensive lines of railroad through
populous districts, connecting them with those places from which
supplies of food and other necessaries might be obtained, are
always considerable. The factitious value which tracts of land
immediately surrounding the metropolis and large towns acquire
from the proximity of the markets, is thus modified, and a portion
of their advantages transferred to the more remote districts ; thus
equalising the value of agricultural property, and rendering it, in
a great measure, independent of local circumstances. The profit
of the farmer and the rent of the landlord are augmented by the
reduced cost of transport, while the price paid by the consumer is-
diminished ; the advantages of centralisation are realised without
incurring the inconvenience of crowding together masses of people
within small spaces, and the whole face of the country is brought
to the condition, and made to share the opportunities of improve-
ment which are afforded by a metropolis and by towns of the larger
class.

19. Steam navigation affords many striking examples of like
advantages obtained in the transport of perishable productions.

Pines are now sold in the markets of England which are brought
from the "West Indies ; various sorts of fruits are likewise brought
from the countries on the coast of Europe which could not be
transported in sailing vessels, as they would not keep during the
voyage. Oranges are sent in large quantities from the Havannah
to New Orleans and Mobile, in the United States : when they are
brought by sailing vessels, a large proportion of the cargo is lost by
the destruction and deterioration of the fruit; when sent by
steamers, they arrive sound.

The utility of an article often depends on its place. Thus, what
is useless at one part of the world will become eminently valuable
if transmitted to another. "We have already given examples of
this in the case of agricultural manures. Others present them-
selves. Ice at mid-winter in Boston, Halifax, or St. John's, has
no value ; but this ice, properly packed and embarked, is trans-
mitted to the Havannah or Calcutta, where a price is readily
obtained for it which pays with profit the cost of the voyage.

Like all the other effects of improved transport, this reacts and
produces collateral benefits. The ships thus enabled to go to
Calcutta laden with a cargo which costs nothing and produces a
considerable profit, instead of going in ballast, which would be
attended with a certain expense, return with cargoes which again

9

LOCOMOTION AND TRANSPORT.

become profitable in the port from which they sailed, and which
they could not have brought with profit unless aided by the
expedient just mentioned.

20. Important as are improvements in the transport of the pro-
ducts of industry, they are less so than those which facilitate the
transport of persons. Here speed becomes of paramount importance.
In the case of the products of industry, the time of the transport
is represented only by the interest on the cost of production of the
article transmitted.

In the case of the transport of persons, the time of transport is
represented by the value of the labour of the travellers, and their
expenses on the road ; and as travellers in general belong to the
superior and more intelligent classes their time is proportionally
valuable.

21. When cheapness can be sufficiently combined with speed,
considerable advantage is gained by the operative classes.

The demand for labour in the several great centres of population
varies from time to time, sometimes exceeding, and sometimes
falling short of the supply. In the latter case, the operative
having little other capital save his bodily strength, is reduced to
extreme distress, nay, often even to mendicancy.

In the former case, the producer is compelled to pay an excessive
rate of wages, which falls disadvantageously on the articles pro-
duced, in the shape of an undue increase of price, and thereby
checks consumption. But although the equilibrium between supply
and demand in the labour market is liable to be thus deranged, it
rarely or never happens that it is subject to the same derangement
in all the centres of population. Supply is never in excess every-
where at once, nor is it in all places at once deficient. Improve-
ments in transport, which will render travelling cheap, easy, and
expeditious, so as to bring it within the means of the thrifty and
industrious operative, will enable labour to shift its place and seek
those markets in which the demand is greatest. Thus, the places
where the supply is in excess will be relieved, and those where the
demand is in excess will be supplied.

22. The extent of soil by which great cities are supplied with
perishable articles of food, is necessarily limited by the speed of
transport. A ring of country immediately about a great capital, is
occupied by market gardens and other establishments for supplying
the vast population collected in the city with their commodities.
The width of this ring will be determined by the speed with whic«i
the articles in question can be transported. It cannot exceed such a
breadth as will enable the products raised at its .extreme limit to
reach the centre in such a time as may be compatible with their
fitness for use.

10

ADVANTAGES TO LARGE CITIES.

It is evident that any improvement in transport which, \viil
double its speed will double the radius of this circle ; an improve-
ment which will treble its speed will increase the same radius in a
threefold proportion. Now, as the actual area or quantity of soil
included within such a radius is augmented, not in the simple
ratio of the radius itself, but in the proportion of its square, it
follows that a double speed will give a fourfold area of supply, a
triple speed a ninefold area of supply, and so on. How great the
advantages therefore are, which in this case attend increased
speed, are abundantly apparent.

23. So far as relates to the transport of persons, the advantages
of increased speed are equally remarkable. The population of a
great capital is condensed into a small compass, and, so to speak,
heaped together, by the difficulty and inconvenience of passing
over long distances. Hence has arisen the densely populated state
of great cities like London and Paris. With easy, cheap, and
rapid means of locomotion, this tendency, so adverse to physical
enjoyment and injurious to health, is proportionally neutralised.
Distances practically diminish in the exact ratio of the speed of
personal locomotion. And here the same arithmetical proportion
is applicable. If the speed by which persons can be transported
from place to place be doubled, the same population can, without
inconvenience, be spread over four times the area ; if the speed be
tripled, it may occupy nine times the area, and so on.

Every one who is acquainted with the present habits of the
population of London, and with those which prevailed before
the establishment of railways, will perceive the practical truth of
this observation. It is not now unusual for persons whose place
of business is in the centre of the capital, to reside with their
families at a distance of from fifteen to twenty miles from that
centre. Nevertheless, they are able to arrive at their respective
shops, counting-houses, or offices, at an early hour of the morning,
and to return without inconvenience to their residence at the usual
time in the evening. Hence in all directions round the metropolis
in which railways are extended, habitations are multiplied, and a
considerable part of the former population of London has been
diffused in these quarters. The same will, of course, be applicable
to the country which surrounds all other great towns. It is felt
at Paris, Brussels, Berlin, Dresden, Vienna, and other capitals of
Europe, just in the same proportion in which they are supplied
with railway communication.

This principle of diffusion, however, is not confined to the
towns only. It extends to an entire country when well inter-
sected by lines of easy, rapid, and cheap communication.

The population, instead of being condensed into masses, is

11

LOCOMOTION AND TRANSPORT.

more uniformly diffused ; and the extent of the diffusion which
may be thus effected, compatibly with the same degree of inter-
course, will be, to use an arithmetical phrase, in the direct
proportion of the square of the speed of locomotion.

24. The common average of the speed of diligences in France and
other parts of the Continent is two leagues, or about five miles, an
hour. The speed of stage-coaches in England, before the esta-
blishment of railways, did not average eight miles an hour.
According to the principle just explained, it would follow that the
same degree of intercourse could be kept up in England in a space
of sixty-four square miles, which in France could be maintained
only within twenty-five square miles. Since the establishment of
railways the average speed upon these lines of communication, on
most parts of the Continent and in America, is fifteen miles an
hour. By this improvement, so far as it has been carried, as
compared with diligences, the area of practical communication, or,
what is the same, of the diffusion of the population compatible
with a given degree of intercourse, has been augmented in the
ratio of the square of five to the square of fifteen ; that is, in a
ratio of twenty-five to two hundred and twenty-five. In other
words, the same degree of intercourse can 1;3 maintained by means
of the present railways within an area of two hundred and twenty-
five square miles, as could be previously maintained by diligences
within an area of twenty -five square miles.

But in England, where the average speed of railway transit is
much greater, this power of diffusion is proportionally increased.
Assuming the average speed on English railways at twenty-five
miles an hour, which is less than its actual amount, the power of
intercommunication thus obtained will bear to that obtained on
the Continent of Europe where railways are in operation, the
ratio of the square of twenty-five to the square of fifteen ; that
is, of six hundred and twenty-five to two hundred and twenty-
five, or of twenty-five to nine.

Thus, the English railways afford the same facilities of commu-
nication within an area of twenty-five square miles as is afforded
by the continental railways within an area of nine square miles ;
and thus, by augmenting the speed from fifteen to twenty-five
miles an hour, the practical convenience to the public is aug-
mented in the ratio of twenty-five to nine, or very nearly as three
to one.

25. The importance of good internal communications in military
affairs has long been acknowledged. By the possession of such
means of transport as may enable a body of troops, with their
arms and ammunition, to be transported promptly and rapidly
from one part of the country to another, the standing army,

12

MILITARY AND COMMERCIAL ADVANTAGES.

maintained as well for the purposes of order at home as for the
defence of the frontiers, may be diminished in proportion to such
facilities.

Instead of maintaining garrisons and posts at points of the
country within short distances of each other, it will be sufficient
to maintain them at such points that they can, at need, be trans-
ported "with promptitude to any other point that may be desired.
In case of invasion, or any foreign attack on the frontier, by good
internal communications, the troops quartered throughout the
interior can be rapidly transferred and concentrated upon the
point attacked.

If, however, such improvements in the art of transport facili-
tate the means of maintaining order at home and of defence
against a foreign enemy, on the one hand, they also happily,
on the other, greatly diminish the probability of a necessity for
such expedients. " The natural effect of commerce," says Mon-
tesquieu, " is to tend to and consolidate peace." Two nations who
trade with each other soon become respectively dependent. If
one have an interest to buy, the other has an interest to sell, and
a multitude of ties, commercial and social, spring out of their
mutual wants.

26. Nothing facilitates and developes commercial relations so
effectually as cheap and rapid means of intercommunication.
"When, therefore, all nations shall be found more intimately con-
nected with each other by these means, they will inevitably multiply
their exchanges, and general commerce will undergo great
extension, mutual interest will awaken moral sympathies, and
will lead to political alliances. After having for ages approached
each other only for war, peoples will henceforth visit each other
for purposes of amity and intelligence, and old antipathies,
national and political, which have so long divided and ruined
neighbouring states, will speedily vanish.

But if, in spite of this general tendency towards pacific progress
and peace, war should occasionally break out, the improved
means of intercommunication will aid in bringing it to a prompt
close. A single battle will decide the fate of a country, and the
longest war will be probably circumscribed within a few months.

27. The advantages of good means of communication in the diffu-
sion of knowledge, and the increase of civilisation by intellectual
means, are not less considerable. While the means of intercom-
munication are slow, difficult, 'and costly, great cities have a
tendency to monopolise intelligence, civilisation, and refinement.
There genius and talent are naturally attracted, while the rural
districts are left in a comparatively rude and almost barbarous
state. "With easy and rapid means of locomotion, however, the

13

LOCOMOTION AND TRANSPORT.

test part of the urban population circulates freely through the
country. This interfusion improves and civilises the rural
population. The highest intelligence will be occasionally found,
both in public and in private, diffusing knowledge and science in
the remotest villages. We cannot now take up a London journal
without observing announcements of men distinguished in the
various branches of knowledge and art, visiting the various towns
and villages of the provinces, and delivering their lectures on
science, and entertainments and exhibitions in the fine arts. So
rapid are the communications, that it is frequently announced that
this or that professor or artist will, on Monday evening, deliver a
lecture or entertainment in Liverpool, on Tuesday in Manchester,
on Wednesday in Preston, on Thursday in Halifax, on Friday in
Leeds, and so forth.

28. Nor is this all. The aspirations of the present generation
after the spread of knowledge and the advancement of mind, unsatis-
fied with a celerity of transmission so rapid by the railway, which
literally has the speed of the wind, has provoked from human
invention still greater wonders. The Electric Telegraph for the
transmission of intelligence, in the most literal sense of the term,
annihilates both space and time. The interval which elapses
between the transmission of a message from London and its
delivery at Paris, Brussels, or Berlin, provided the line is unin-
terrupted, is absolutely inappreciable.

This system is now spreading throughout the whole civilised
world. The United States of Am erica are overspread with a net-
work of electricity, The President's message delivered at Wash-
ington, was transmitted from thence to St. Louis, on the confines
of the state of Missouri, a distance of about 1200 miles, in an hour.
The news from Europe arriving at Boston by the Cunard steamers,
is often transmitted to New Orleans, over almost the entire terri-
tory of the United States from north to south, a distance of nearly
2000 miles, in less time than would be necessary to commit
it to paper. Even the small delay that now exists arises, not
from any imperfection in the instrument of transmission, but
merely from the line of electric communication being inter-
rupted from point to point, and transferred from one system
of telegraphs to another, at several intermediate stations.
After improvements shall remove such delays as these, we shall
probably see intelligence conveyed in an instant over a quadrant
of the globe.

29. But if we would seek for a striking illustration of the effects
of the rapid transmission of intelligence by the combination of all
the various expedients supplied by science to art, it is in the practice
of Journalism that we are to look for them, and more especially in

H

JOURNALISM.

the great enterprises of the London newspapers. The proprietors
of a single morning journal are able to maintain agencies, for
the transmission of intelligence to the central office in London, in
all the principal cities of Europe , besides roving correspondents
wherever the prevalence of war, revolution, or any other public
event excites a local interest. These various agents or " corre-
spondents " as they are called, not only transmit to the centre of
intelligence in London regular despatches by the mails, but also,
on occasion of emergency, by special couriers.

These despatches are first received by an agent at Dover, by
whom they are forwarded to London by a special messenger.
But in cases where intelligence arrives of adequate importance, it
is transmitted from the principal continental cities direct to
London, in an abridged form, by the electric telegraph, thus
anticipating the detailed despatches by many days. Within two
hours of its arrival the intelligence is in the hands of tine London
public.

That portion of the journal intended for the provinces is sent to
press at 3 A.ir. ; and by the activity of the editors, reporters, and
compositors, all of whom work during the night, it includes not
only the detailed reports of the Houses of Parliament, which often
sit to a late hour in the morning, but also the foreign news, as
above explained, .by electric telegraph. This earliest impression
is printed and delivered to the newsvenders, in sufficient time to
be despatched to the provinces by the early railway trains, and it
is thus delivered at all the stations along the road.

The part of the impression intended for London circulation is
worked off and delivered later.

Thus we see that, by these combinations of enterprise, intel-
lectual and material, the intelligence which arrives in London at
3 A.^r., is written, composed, printed, and distributed within a
radius of one hundred miles round London, and in the hands of
the population before their customary hour of breakfast.

Even before the present improved methods of transport were
brought into operation, wonders in this way were effected.

Thus, in some cases where debates of adequate public interest
took place in Parliament in the evening, the evening mails (for
there were then no other) carried to the provinces the first part of an
important speech, reported and printed before the remaining part
was spoken. Thus it was related that the commencement of Mr.
(since Lord) Brougham's celebrated speech on the reform of the
laws was read at tea-tables twenty miles from London before he
had pronounced the peroration.

Few of the numerous readers of newspapers have the least idea
of the immense commercial, social, and intellectual powers wielded,

15

LOCOMOTION AND TRANSPORT.

and benefits conferred, by these daily publications, a large portion
of which influence is to be ascribed to the cheapness, promptitude,
and rapidity with which they are transmitted from the capital to
all parts of the country.

It is well known that the average number of copies of the most
•widely circulating London journal, which are daily issued, amounts
at present to more than forty thousand. Each of these forty
thousand copies, according to common estimation, passes under the
eyes, upon an average, of at least ten persons. Thus we have
four hundred thousand daily readers of one organ of information
and intelligence. But the effects do not end there. These four
hundred thousand readers, long before the globe completes a
revolution on its axis, become four hundred thousand talkers, and
have vastly more than four hundred thousand hearers. Thus
they spread more widely by the ear the information, the argu-
ments, and the opinions they have received through the eye. We
shall certainly not be overstating the result if we assume, that this
influence of a single journal, directly and indirectly, reaches daily
a million of persons.

13

LOCOMOTION AND TRANSPORT,

THEIR I^FLUEJSCE AtfD PROGRESS.

CHAPTEE II.

RETROSPECT OF THE PROGRESS OP TRANSPORT.

Ot the first construction and improvement of roads and carriages. —
2. Roads do not exist in more than two-sevenths of the inhabited
parts of the globe. — 3. Roman and Egyptian roads. — 4. Roads con-
structed by order of Semiramis. — 5. Internal communication in
ancient Greece. — 6. Roads of the Phoenicians and Carthaginians. —
7. Roman military roads. — 8. Commercial intercourse during the
middle ages. — 9. Influences of the crusades on the art of transport. —
10. Roads and intercommunication on the Continent to the middle of
the seventeenth century. — 11. System of roads projected by Napoleon.
— 12. Improvement in internal communication after the peace of
1815. roads of France. — 13. First roads in England, those made by
the Romans. — 14. Watling Street, Ermine Street, Fosse-way and
Ikenald.— 15. First attempts to improve roads in Great Britain in
reign of Charles the Second. — 16. Transport in Scotland to the middle
of the eighteenth century. — 17. Slowness of travelling in Scotland. —

18. Arthur Young's account of the roads in England in 1770. —

19. Comparison between cost and speed of former and present modes
of transport. — 20. Origin of railways in England. — 21. Their
immediate effects. — 22. Progress of the construction. — 23. Their
extent in 1852. — 24. Capital absorbed by them. — 25. Labour
employed by them.

LARDNER'S MUSEUM OF SCIENCE. 0 17

No. 30.

LOCOMOTION AND TRANSPORT.

1. IN the first attempts at an interchange of the products of
industry, which mark the incipient commerce of a people emerging
from barbarism, human labour and the strength of the inferior
animals, applied in the most rude and direct manner to transport,
are all the means brought into play. The pedlar and the pack-
horse perform all the operations of interchange which take place
in an infant society. Pathways are formed over the natural
surface of the ground, in a course more or less direct, between
village and village. The beds of streams following, by the laws
of physics, the lowest levels, serve as the first indication to the
traveller how to avoid steep acclivities, and, by deviating from the
most direct and shortest course, to obtain his object with a
diminished amount of labour.

As industry is stimulated and becomes more productive, inven-
tion is brought more largely into play, and these rude expedients
are improved. "Wheel carriages are invented, but the earliest
theatre of their operations is the immediate surface of the soil
from which the products of agriculture are raised. They are used
to gather and transport these to a place where they may be
sheltered and secured.

But to enable wheel carriages to serve as the means of transport
between places more or less distant, the former horse-paths are
insufficient. A more uniform and level surface, and a harder
substratum, become indispensable. In a word, a ROAD, constructed
with more or less perfection, is necessary.

These roads, at first extremely rude and inartificial, and rendered
barely smooth and hard enough for the little commerce of an infant
people, are gradually improved. The carriages, also, which serve
as the means of transport undergo like improvement, until, after
a series of ages, that astonishing instrument of commerce, the
modern road, results, which is carried on an artificial causeway,
and reduced, at an enormous expense, to a nearly level surface by
means of vast excavations, extensive embankments, bridges,
viaducts, tunnels, and other expedients supplied by the skill and
ingenuity of the engineer.

Between the pack-horse, used in the first stages of growing
commerce, and such a road with its artificial carriages, there is a
prodigious distance. The first step, from the pack-horse to the
common two-wheel cart, was, in itself, a great advance.

It is calculated that a horse of average force, working for eight
or ten hours a day, cannot transport on his back more than two
hundredweight, and that he can carry this at the rate of only
twenty-five miles a day over an average level country. The
same horse, working in a two-wheel cart, will carry through the
same distance per day twenty hundredweight, exclusive of the
18

ANCIENT AND MODERN ROADS.

weight of the cart. By this simple expedient, therefore, the art
of transport was improved in the ratio of one to ten ; in other
words, the transport which before was effected at the cost of ten
pounds, was, with this expedient, reduced to the cost of one
pound.

2. The adoption of expedients for the maintenance of commerce so
obvious as roads, would seem to be inevitable among a people who
are not actually in a state of barbarism. Nevertheless, we find
that not only was the construction of good roads for commercial
purposes of comparatively recent date, but that, even at the
present day, a very large portion of that part of the world called
civilised, is unprovided with them. With the exception of certain
parts of Europe, the French colony of Algeria, and the United
States, the entire surface of the world is still without this means
of intercourse.

It is calculated that, of the entire inhabited part of the globe,
roads do not exist in more than tico-sevcnths. The extensive
empire of Russia, with the exception of one or two main com-
munications, such as that between Petersburg and Moscow, is
without them. In general, the only practicable communications
through this vast territory are effected in winter on the surface of
the frozen snow by sledges. On the return of summer, when the
snow has disappeared, the communications become extremely
difficult, slow, and expensive. Spain is scarcely better supplied
with roads than Russia, nor do we find much improvement in the
practice of transport in Italy. Until recently, Corsica possessed
no communications of this sort; horses and mules were the
common means of communication and interchange in that island
until the French government constructed some roads.

3. The roads constructed by the Romans and Egyptians will
probably be referred to as instances of an early advance in this
art. But these great monuments of antiquity, though serving
incidentally, to some extent, as means of commerce, were
constructed for exclusively military purposes.

4. The most ancient roads which are recorded in history, are those
constructed by order of Semiramis, throughout the extent of her
empire. It would seem, however, that the commerce of that day
did not find these communications suitable to its objects ; for it is
certain that, at the epoch at which Tyre and Carthage were
signalised for their enterprise, their commerce was almost exclu-
sively carried on by the coasting navigation of the Mediter-
ranean.

5. Notwithstanding the advanced stage to which civilisation had
arrived in Greece, the means of internal communication in that
country remained in a state of great imperfection. This may in

o2 19"

LOCOMOTION AND TRANSPORT.

part be explained by the multitude of small states which formed
that confederation, by their conflicting interests, and their want
of any moral or social sympathies. The common sentiment of
nationality slumbered, except when it was awakened by the strong
stimulus of foreign attack. The intercourse between one centre
of population and another was then very restrained, and although
the public ways were placed under the protection of the gods, and
the direction of the most considerable men of the respective
states, they were suffered to fall into neglect. The exigencies of
internal commerce were never sufficiently pressing to excite the
people to contribute to the maintenance of good means of inter-
communication and exchange.

6. The earliest roads which were really rendered conducive to the
purposes of commerce, on any considerable scale, were those con-
structed by the Phenicians and Carthaginians. To the latter is
ascribed, by Isidore, the invention of paved roads.

7. When imperial Rome attained the meridian of her power, and
her empire extended over a large portion of Europe and Asia,
colossal enterprises were entered upon for the construction of vast
lines of communication, extending over the immensity of her
territory. These roads, however, like those of the Egyptians,
were constructed without the slightest view to commercial objects.
It concerned imperial Rome but little, that her provinces should
be united by commercial or social interests. What she looked to
was to be enabled to convey with celerity her powerful legions at
all times from one extremity of her dominions to another. With
this purpose, she availed herself of her vast resources to construct
those military roads, intersecting her territory, the remains of
which have excited the admiration of succeeding generations.

The first of these great monuments of the enterprise and art of
the Roman people were those so well known by the names of the
Via Appia, the Yia Aurelia, and the Yia Flaminia. Under
Julius Caesar, communications were made by paved roads between
the capital of the empire and all the chief towns. During the last
African war, a paved road was constructed from Spain, through
Gaul, to the Alps. Subsequently similar lines of communication
were carried through Savoy, Dauphine', Provence, through
Germany, through a part of Spain, through Gaul, and even to
Constantinople.

Asia Minor, Hungary, and Macedonia were overspread with
similar lines of communication, which were carried to the mouths
of the Danube. Nor was this vast enterprise obstructed by the
intervention of seas. The great lines which terminated on the
shores of continental Europe were continued at the nearest points
of the neighbouring islands and continents. Thus, Sicily, Corsica,
20

LOCOMOTION IN MIDDLE AGES.

Sardinia, and England, and even Africa and Asia, were intersected
and penetrated by roads, forming the continuation of the great
European system.

These colossal works were not paths rudely prepared for the
action of the feet of horses and the wheels of carriages, by merely
removing the natural asperities from the surface of the soil.
They were constructed, on the contrary, on principles in some
respects as sound and scientific as those which modern engineering
has supplied. Where the exigencies of the country required it,
forests were felled, mountains excavated, hills levelled, valleys
filled up, chasms and rivers bestridden by bridges, and marshes
drained, to an extent which would suffer little by comparison with
the operations of our great road-makers of modern times.

On the fall of the Empire, these means of communication,
instead of subserving the purposes of the commerce of the people
through whose territory they were carried, were, for the most
part, destroyed. When the barbarians conquered Rome, and a
multitude of states were formed from its ruins, the victors shut
themselves up and fortified themselves in these several states, as
an army does in a citadel ; and, far from constructing new roads,
they destroyed those which had already existed, as a town
threatened with siege breaks those communications by which the
enemy may approach it.

8. From this epoch through a long series of ages, the nations of
Europe, animated only by a spirit of reciprocal antagonism,
thought of nothing but war, and entered each other's territories
only for the purposes of conflict. The history of the intercom-
munications of nations during the middle ages is only a history of
their wars.

When Europe emerged from this state, and when commerce
began to force itself into life, its operations were in a great
measure monopolised by Jewish and Lombard merchants, who
carried them on subject to the greatest difficulty and danger.

The provincial nobles and lords of the soil, through whose pos-
sessions the merchant necessarily passed in carrying on the
internal commerce of the country, were nothing better than high-
way robbers. They issued with their bands from their castles and
arrested the travelling merchant, stripping him of the goods which
he carried for sale.

The sovereigns of France endeavoured in vain, by penal enactr
ments, to check this enormous evil. Dagobert I. established a.
sort of code to regulate the public communications through his
dominions, and decreed heavy fines against such provincial lords
as might obstruct the freedom of communication, by interrupting
or plundering travellers. These decrees, however, remained a

21

LOCOMOTION AND TKANSPOKT.

'dead letter, no adequate power in the state being able to carry
them into practical effect.

Under the successors of Charlemagne, this abuse, which it
was found impossible to repress, was, in some measure, recog-
nised and regularised. Tolls of limited amount were allowed
to be exacted by the local proprietors from those who passed
through the provinces for purposes of trade, on the condition
that such travellers or merchants should be otherwise unmo-
lested.

The prevalence of all these vexatious impediments soon rendered
intercommunication by land almost impracticable. The roads,
such as they were, became accordingly deserted, and were suffered
to fall into utter disrepair. During a series of ages, internal com-
munication and internal commerce became almost suspended ; a
journey even of a few leagues being regarded as a most serious
and dangerous undertaking.

9. The Crusades had a favourable influence on the art of trans-
port. The population of Western and Northern Europe became
by them acquainted with the productions and arts of the East.
New desires were excited and new wants created. Commerce was
thus stimulated, and greater facility of intercourse becoming
necessary, governments were forced to adopt expedients for the
security of the traveller.

The same difficulties and dangers did not, however, affect
navigation. We find this art developed in a much higher
degree than that of internal commerce. Hence arose the dis-
proportionate commercial opulence of maritime people. The
British, the Dutch, and the Portuguese rose into immense com-
mercial importance, as well as the Genoese, the Tuscans, and the
Yenetians.

10. Even so late as the middle of the seventeenth century, the
roads throughout the Continent continued in a condition which
rendered travelling almost impracticable.

They are described by writers of this epoch as being absolute
sloughs. Madame de Sevigny, writing in 1672, says, that a
journey from Paris to Marseilles, which by the common roads of
the present day is effected in less than sixty hours, required a
whole month,

Besides the material obstacles opposed to the growth of internal
commerce on the Continent by the want of roads in sufficient
number, and the miserable state of those which did exist, other
impediments were created and difficulties interposed by innumer-
able fiscal exactions, to which the trader was exposed, not only in
passing the confines of different states, but even in going from
province to province in the same state, and in passing through
22

FRENCH ROADS.

almost every town and village. Hence the cost of every com-
modity was enormously enhanced, even at short distances from the
place of its production.

11. The disorganisation of society and the destruction of the
institutions of feudalism which followed the French Revolution of
1789, caused some improvement in the means of internal commerce
in Europe, and would have caused a much greater development
in this instrument of civilisation, hut for the wars which imme-
diately succeeded that political catastrophe, and which only
terminated with the hattle of Waterloo.

Indeed Xapoleon, conscious of the vast importance of a more
complete system of roads, had actually projected one, which he
intended to spread over Europe. His fall, however, inter-
cepted the realisation of this magnificent design, and the
Siu^on remains as the only monument of his glory in this
department of art.

After the re-establishment of peace, the nations of Europe,
directing their activity to industry and commerce, soon became
impressed with the necessity of effecting a great improvement in
the means of internal communication. Western Europe, accord-
ingly, soon began to be covered with roads and canals.- The
obstructions arising from fiscal causes, if not removed, were greatly
diminished.

The advance made by France especially in this department, is
deserving of notice. That country possesses at present four or five
times the extent of roads which were practicable under the Empire ;
a sum of nearly four millions sterling was, until lately, expended
annually upon the completion and maintenance of these great
lines of communication.

The roads of France consist of three classes ; the first, until the
late revolution, were called royal roads, and are now called
national roads. These are the great arteries of communication
carried from one chief town to another throughout the' territory,
and being used indifferently, or nearly so, by the whole population,
are constructed and maintained at the general expense of the
nation. The second class are departmental roads, or what would
be called in England county roads. These are chiefly the branches
running into the royal roads, by which the local interests of the
departments are served, and are accordingly maintained at the
expense of the departments. Finally, the third class is called
vicinal roads, which would correspond to our parish roads.

The rate at which these improved communications have con-
tributed to augment the internal commerce and national wealth,
may be estimated in some degree from the statistical results which
have been published. In 1810, the various stage-coach establish-

23

LOCOMOTION AND TRANSPORT.

ments in Paris transported each day from the capital into the
departments, two hundred and twenty passengers, and twenty-one
tons of merchandise. Before the establishment of railways, they
transported nearly one thousand passengers and forty-five tons of
merchandise. Thus the passengers were augmented in a fourfold,
and the merchandise in a twofold proportion.

12. In 1815, the length of roads in operation in France was as
follows : there were three thousand leagues of royal roads, and two
thousand leagues of departmental roads. In 1829, there were
four thousand two hundred and five leagues of royal roads, and
three thousand leagues of departmental roads. In 1844, there
were eight thousand six hundred and twenty-eight leagues of
royal roads, and nine thousand one hundred and forty-six leagues
of departmental roads, independently of twelve thousand leagues
of vicinal roads. Thus, it appears that between 1815 and 1844,
the total length of roads of the first and second classes was aug-
mented from five thousand leagues to nearly eighteen thousand, or
in the proportion of three and a half to one.

13. Although the practice of road-making in England attained a
certain degree of perfection at a much earlier period than in other
parts- of Europe, and the United Kingdom was overspread with a
noble network of internal communications, while continental
Europe remained in a comparatively barbarous condition, the art
of transport nevertheless, even in England, remained for a long
series of ages incalculably behind what would seem to be the com-
mercial wants of the population.

The first English roads of artificial construction were those
made by the Romans, while England was a province of that
empire. The island was then intersected by two grand trunk
roads running at right angles to each other, the one from north to
south, and the other from east to west.

These main lines were supplied with various branches, extending
in every direction which the conquerors found it expedient to
render accessible to their armies.

14. The Roman road called Waiting Street commenced from
Richborough, in Kent, the ancient Rutupial, and, passing
through London, was carried in a north-westerly direction to
Chester. The road called Ermine Street commenced from
London, and, passing through Lincoln, was carried thence through
Carlisle into Scotland. The road called the Fosse-way passed
through Bath in a direction N.E., and terminated in the Ermine
Street. The road called Ikenald extended from Norwich in a
southern direction to Dorsetshire.

But these great works, at the date of their construction, ex-
ceeded the wants of the population, who, unconscious of their
24

BRITISH ROADS.

advantage, allowed them to fall into neglect and disrepair. Nor
were any new roads in other or better directions constructed. For
a succession of ages the little intercourse that was maintained
between the various parts of Great Britain was effected almost
exclusively by rude footpaths, traversed by pedestrians, or at best
by horses.

These were carried over the natural surface of the ground,
generally in straight directions, from one place to another. Hills
were surmounted, valleys crossed, and rivers forded by these rude
agents of transport, in the same manner as the savages and settlers
of the backwoods of America or the slopes of the Rocky Mountains
now communicate with each other.

15. The first important attempt made to improve the communi-
cations of Great Britain took place in the reign of Charles II. In
the sixteenth year of the reign of that monarch was established
the first turnpike road where toll was taken, which intersected the
counties of Hertford, Cambridge, and Huntingdon. It long
remained, however, an isolated line of communication ; and it was
little more than a century ago that any extensive or effectual
attempts were made, of a general character, to construct a good
system of roads through the country.

16. Until the middle of the eighteenth century, most of the
merchandise which was conveyed from place to place in Scotland
was transported on pack-horses. Oatmeal, coals, turf, and even hay
and straw, were carried in this manner through short distances ;
but when it was necessary to carry merchandise between
distant places, a cart was used, a horse not being able to transport
on his back a sufficient quantity of goods to pay the cost of the
journey.

17. The time required by the common carriers to complete their
journey seems, when compared with our present standard of speed,
quite incredible. Thus, it is recorded that the carrier between
Selkirk and Edinburgh, a distance of thirty-eight miles, required
a fortnight for his journey, going and returning. The road lay
chiefly along the bottom of the district called Gala-tcater, the bed
of the stream, when not flooded, being the ground chosen as the
most level and easy to travel on.

In 1678, a contract was made to establish a coach for pas-
sengers between Edinburgh and Glasgow, a distance of forty-four
miles. This coach was drawn by six horses, and the journey
between the two places, to and fro, was completed in six days.
Even so recently as the year 1750, the stage-coach from Edinburgh
to Glasgow took thirty- six hours to make the journey. In 1849,
the sair>e journey was made, by a route three miles longer, in one
hour and a half !

25

LOCOMOTION AND TRANSPORT.

In the year 1763 there was but one stage-coach between
Edinburgh, and London. This started once a month from each of
these cities. It took a fortnight to perform the journey. At the
same epoch the journey between London and York required
four days.

In 1835 there were seven coaches started daily between London
and Edinburgh, which performed the journey in less than forty-
eight hours. In 1849, the same journey was performed by railway
in twelve hours !

In 1763, the number of passengers conveyed by the coaches
between London and Edinburgh could not have exceeded about
twenty-five monthly, and by all means of conveyance whatever
did not exceed fifty. In 1835 the coaches alone conveyed
between these two capitals about one hundred and forty pas-
sengers daily, or four thousand monthly. But besides these,
several steam-ships, of enormous magnitude, sailed weekly
between the two places, supplying all the accommodation and
luxury of floating hotels, and completing the voyage at the same
rate as the coaches, in less than forty-eight hours.

As these steam- ships conveyed at least as many passengers
as the coaches, we may estimate the actual number of passengers
transported between the two places monthly at eight thousand.
Thus the intercourse between London and Edinburgh in 1835 was
one hundred and sixty times greater than in 1763.

At present the intercourse is increased in a much higher ratio,
by the improved facility and greater cheapness of railway
transport.

18. Arthur Young, who travelled in Lancashire about the year
1770, has left us in his Tour the following account of the state of
the roads at that time. " I know not," he says, "in the whole
range of language, terms sufficiently expressive to describe this
infernal road. Let me most seriously caution all travellers who
may accidentally propose to travel this terrible country to avoid it
as they would the devil, for a thousand to one they break their
necks or their limbs by overthrows or breakings down. They
will here meet with ruts, which I actually measured, four feet
deep, and floating with mud, only from a wet summer. What,
therefore, must it be after a winter? The only mending it
receives is tumbling in some loose stones, which serve no other
purpose than jolting a carriage in the most intolerable manner.
These are not merely opinions, but facts ; for I actually passed
three carts broken down in these eighteen miles of execrable
memory."

And again he says (speaking of a turnpike road near "Warring-
ton, now superseded by the Grand Junction Railway,) " This is a
26

TRAVELLING IX ENGLAND IN 1770.

paved road, most infamously bad. Any person would imagine
the people of the country had made it with a view to immediate
destruction! for the breadth is only sufficient for one carriage;
consequently it is cut at once into ruts; and you may easily
conceive what a break-down, dislocating road, ruts cut through a
pavement must be."

Nor was the state of the roads in other parts of the north of
England better. He says of a road near Newcastle, now super-
seded by a railway, " A more dreadful road cannot be imagined.
I was obliged to hire two men at one place to support my
chaise from overturning. Let me persuade all travellers to
avoid this terrible country, which must either dislocate their
bones with broken pavements, or bury them in muddy sand.
It is only bad management that can occasion such very miser-
able roads in a country so abounding with towns, trade, and
manufactures."

Now, it so happens that the precise ground over which
Mr. Young travelled in this manner less than eighty years
ago is at present literally reticulated with railways, upon which
tens of thousands of passengers are daily transported, at a
speed varying from thirty to fifty miles an hour, in carriages
affording no more inconvenience or discomfort than Mr. Young
suffered in 1770, when reposing in his drawing-room in his
arm-chair.

19. Until the close of the last century, the internal transport of
goods in England was performed by waggon, and was not only
intolerably slow, but so expensive as to exclude every object
except manufactured articles, and such as, being of light weight
and small bulk in proportion to their value, would allow of a high
rate of transport. Thus the charge for carriage by waggon from
London to Leeds was at the rate of 131. a ton, being 13$d. per
ton per mile. Between Liverpool and Manchester it was forty
shillings a ton, or lod. per ton per mile. Heavy articles, such as
coals and other materials, could only be available for commerce
where their position favoured transport by sea, and, consequently,
many of the richest districts of the kingdom remained unpro-
ductive, awaiting the tardy advancement of the art of transport.
Coals are now carried upon railways at a penny per ton per
mile, and, in some places, at even a lower rate. Merchandise,
such as that mentioned above, which was transported in 1763 at
from I4d. to lod. per mile, is now carried at from 3d. to 4c?.,
while those sorts which are heavier in proportion to their bulk are
transported at 2|(/. per ton per mile.

But this is not all : the waggon transport formerly practised
was limited to a speed which in its most improved state did not

LOCOMOTION AND TKANSPORT.

exceed twenty-four miles a day, while the present transport by
railway is effected at the rate of from twelve to fourteen miles
an hour.

20. When we look back upon the state in which every part of
the civilised world was placed in relation to this vital element of
social and commercial progress, this standard and test, as it may
be justly called, of civilisation at an epoch so recent as the first
year of the present century, and compare it with the present con-
dition not of England only, but of Europe and North America, we
cannot fail to be struck with the incalculable amount of benefit to
the human race that must result from the extraordinary energy
with which the discoveries and resources of science have been
applied to the improvement of this instrument of civilisation
within the brief interval of twenty-four years, for it is not more
since the date of the commencement of railway transport in this
country which took the lead in that, as in so many other improve-
ments in the arts of life.

21. In 1830, the first railway for general traffic in passengers
and goods between Liverpool and Manchester was opened ; and
immediately, of the thirty stage-coaches which had previously
run daily between Liverpool and Manchester, one only remained
on the road; and that was supported solely by passengers to
intermediate places not lying in the direction of the railway.

The comparatively low fares and extraordinary expedition
offered by the railway had the effect which might have been
expected. Previously, the number of travellers daily, by the
coaches, was about five hundred ; it was immediately augmented
above three-fold. Sixteen hundred passengers per day passed
between these towns. If the traffic in passengers exceeded all
anticipation, the transport of goods, on the contrary, fell short of
what was expected. The canal lowered its tariff to the level of
the railway charges and increased its speed and its attention to
the accommodation of customers. The canal, moreover, winding
through Manchester, washed the walls of the warehouses of the
merchants and manufacturers. At the other end it communi-
cated directly with the Liverpool docks. The goods were there-
fore received directly from the ship, and delivered directly to the
warehouse, or vice versd ; without the cost, delay, and inconve-
nience of intermediate transhipment and cartage. These
considerations went far to counterbalance the superior speed
of the railway transit for goods ; yet, notwithstanding this
inconvenience and obstruction, the company soon found them-
selves carriers of merchandise at the rate of a thousand tons
per day.

Thus, the problem of the rapid transport of passengers by steam
28

CONSTRUCTION OF RAILWAYS.

on railways was solved in 1830, and the profitable character of the
enterprise soon became apparent. Dividends of 10 per cent, were
declared, and the shares were greedily bonght up at 120 per cent,
premium. Then followed in rapid succession those results which
must necessarily have ensued. Other lines of railway, connecting
the chief centres of population and industry with the metropolis,
and with each other, were projected. In the four years which
elapsed from 1832 to 1836, about 450 miles of railway were com-
pleted, and 350 miles were in progress of construction.

22. From 1836 to the present time the construction of these
great lines of intercommunication in the United Kingdom has
proceeded at a rate of progress of which no previous example has
ever been recorded in the history of the industrial arts in any
country. From the official reports presented to Parliament, it
appears that the whole extent of railway communication open for
traffic in the United Kingdom at the end of 1852 was 7336 miles,
which were distributed in the different portions of the kingdom in
the following proportions : —

In England and Wales .... 5650 miles.

In Scotland 978

In Ireland 708

Total in the United Kingdom . . 7336 miles

open for public traffic.

It further appears from these reports that, at the close of 1852,
the legislature had authorised the construction of a total length
of railway (including the above 7336 miles) amounting to 12561
miles, of which 676 miles had been abandoned by the companies
which had originally undertaken them. Thus the account of the
total amount authorised by Parliament, to the end of 1852,
stood thus : —

Constructed and in operation. . . 7336 miles.
In progress or intended to be commenced 4549
Abandoned 676

12561 miles.

23. The following table, taken from the report of the Committee
of the Privy Council, dated August, 1853, will exhibit 'the rate at
which the railway projects were sanctioned by Parliament, and
the rate at which their execution has progressed up to the end of
1852 :—

29

LOCOMOTION AND TRANSPORT.

!

1 •»!

!

OOOOOOGCGOGOCCGOOO 3 0

bO

0

Previously to Decem-
ber, 1843.

LENGTH OF LINE OPENED.

«

I

10

During 1844.

£

§

cr.

t-" I-"

During 1845.

p

1

During 1846.

^0 0»

§

During 1847.

ta *• o> ta to

s

During 1848.

O Oi 4* 00 M

1

tO -T Ox i^ I-" W

During 1849.

1

. • • CO fcO
bO I-1 ' OJ O 05 rfk

During 1850.

1

... i_i . .

During 1851.

*> -J.-'tOOl

1

«::ss8S= :

During 1852.

1

(-• U> O> CO O O ^4 S tO O

Total Length of Line opened to
December, 1852.

M

rf*-C^OOOSt— '^-OOOCX O

Length of Line authorised at end
of 1843, and during each sub-
sequent year.

O

OS

C* O 00 W '

Decrease by Abandonment, De-
viation, &c., under authority
of subsequent Acts.

!

M *> tO fcO

tOh-« CO t— * O O CO CO

Length of Line after Reductions
made in consequence of Aban-
donment, Deviation, &c., under
the authority of Acts passed
• subsequent to 1843.

I

gg-tiggi* :

Length of Line remaining to be
made.

30

PROGRESS AND EXTENT OF RAILWAYS.

24. Nothing in the progressive development of this vast national
enterprise is more surprising than the amount of capital raised
and expended upon it, and the rapidity and facility with which it
was obtained.

The following statement, also taken from the official reports,
will illustrate this : —

Total capital raised by shares and loans up to

the end of 1848 £200,173058

Total capital similarly raised in 1849. . . 29,574720

Ditto. . . 1850. . . 10,522967

Ditto. . . . 1851. . . 7,970151

Total capital raised up to the end of 1851 £248, 240896

Of the sum of 248 millions, which had been expended before
the 1st January, 1852, a part had been absorbed by the lines
which were in process of construction, but had not yet been
opened. Against this, however, there remained an amount of
capital still to be expended on the lines already open. On most of
the more recently opened railways, the stations were still incom-
plete ; in some cases, depots, workshops, and other permanent
buildings had not even been commenced. The full complement
of the locomotive and rolling stock had not been provided. In
the absence of exact data then, if these latter expenses be placed
against the former, the entire capital of 248 millions may be placed
to the account of 7336 miles open for traffic ; which would give an
average expense of construction, including the locomotive and
carrying stock, and the workshops and depots for its repair, &c.,
of 33S40Z. per running mile.

25. The extent to which these enterprises employed the industry
of the country may be judged from the following results of the
reports : —

It appears that in 1848 a quarter of a million of persons were
employed on the railways of the United Kingdom ; and if it be
considered that each of these must have contributed to the support,
on an average, of one or more other persons, it will follow, that
this vast enterprise must have, at that epoch, supplied means of
living to at least two per cent, of the entire population of these
countries.

It further appears that, on the 30th June, 1852, there were
employed

On the railways open for traffic 67601

On the railways in progress of construction . . . 35935

103536

It follows, therefore, that from 1848, to June, 1852, about

31

LOCOMOTION AND TRANSPORT.

150000 persons have been dismissed from the direct employment
of the railway companies, and who must now he obtaining support
from other occupations. It is, however, certain that a large
increase of the demand for labour has been produced by the
creation and operation of railway traffic, such as that which arises
and must arise from the establishment of founderies, carriage, and
engine building, and other branches of railway business, not
only in the United Kingdom, but in other countries which are to
a great extent supplied by British industry.

We shall on another occasion notice the progress of locomotion
by railway in other countries.

32

TELESCOPIC VIEW OF THE REGION OF THE MOO* SURROUNDING THE CIRCULAR
MOUNTAIN CHAIN* CALLED TYCHO, MEASURING ABOUT 375 MILES NORTH AND
SOUTE, ASD ABOUT 200 MILES EAST AND WEST.

THE MOON.

Interest with which the moon is regarded, and influences with which it
has been invested by the popular mind. — 2. Its distance. — 3. Its
orbit. — 4. Its magnitude. — 5. Its rotation. — 6. Conjunction. — 7.
Quadrature. — 8. Opposition. — 9-11. Tests of an atmosphere. — 12-13.
None exists on the moon. — 14. No liquids. — 15. No diffusion of solar
light. — 16. Appearance of earth seen from moon. — 17. It would have
belts. — 18. Geographical features and its rotation would be visible
through the clouds. — 19. Moonlight neither warm nor cold. — 20.
Moon's physical condition. — 21. Thickly covered with mountains. —
22. Selenographical discoveries of Beer and Miidler. — 23. Vast extent
and diameter of the lunar mountains. — 24. Circular chains. — 25.
Description of Tycho. — 26. Heights of lunar mountains. — 27.
Observations of Lord Rosse. — 28. Moon not inhabited.

LABDKER'S MUSETJH OF SCIEKCE.
No. 28.

33

THE MOON.

1. ESTIMATED merely by its magnitude, the moon is among the
most inconsiderable of the bodies which compose the Solar
System. It has not, as will presently appear, even that interest
which must attach to a globe adapted for the habitation of
organised races, analogous to those for whose dwelling the earth
has been appropriated. Nevertheless it has ever been regarded by
mankind with sentiments of profound and peculiar interest, and
has been invested by the popular mind with various influences,
affecting not only the physical condition of the globe, but also
directly connected with the organised world. It has therefore
been as much an object of popular superstition as of scientific
observation. These circumstances are doubtless owing in some
degree to its striking appearance in the firmament, to the various
and rapid succession of changes of apparent form to which it is
subject, and above all to its proximity to, and close alliance with
our planet. We propose on the present occasion to give a general
account of its motion, magnitude, and physical condition ; and
to explain more particularly those circumstances which lead to
the conclusion that, unlike the planets, the moon presents none of
the analogies to the earth which would render it at all probable or
even possible that it can be a habitable world.

2. It has been ascertained, that its distance is very little less
than 240000 miles ; and since the semidiameter of the earth is
4000 miles, it follows that the moon's distance is about sixty
semidiameters of the earth. The method of ascertaining this dis-
tance differs in nothing that is essential, from that by which a
common surveyor ascertains the distance of an object on the earth
which is inaccessible to him.

3. Now the least reflection will render it apparent that the
moon must move round the earth, in a path which cannot differ
much from a circle of which the earth is the centre. This
follows from the fact with which every one is familiar, that its
apparent magnitude is always nearly the same. It is, therefore,
always at the same or nearly the same distance from the observer.
The earth must consequently be placed in the centre of its path,
and that path must be nearly a circle.

4. When the distance of a visible object is determined, its
magnitude may easily be ascertained by comparing it with any
other object of known magnitude at a known distance. Let us
take, for example, a halfpenny, which measures about an inch
in diameter, and let it be placed between the eye and the moon.
It will be found on the first trial that the coin will appear larger
than the moon ; it will, in fact, completely conceal the moon from
the eye, and produce what may be termed a total eclipse of that
luminary. Let the coin be moved however further from the eye,

DISTANCE — ORBIT — MAGNITUDE.

and it will apparently diminish in size as its distance is increased.
Let it be removed until it becomes equal in apparent magnitude to
the moon, so that it will exactly cover the moon, and neither more
nor less. If its distance be then measured, it will be found to be
about 120 inches, or 240 half inches. But it is known that the
distance of the moon is about 240000 miles, and consequently it
follows in this case, that 1000 miles in the moon's distance is
exactly what half an inch is in the coin's distance. Now under
the circumstances here supposed, the coin and the moon are
similar objects of equal apparent magnitude. In fact the coin is
another moon on a smaller scale, and we may use the coin to
measure the moon's distance, provided we know the scale, exactly
as we use the space upon a map of any known scale to measure a
country. But it has been just stated that the scale is in this case
half an inch to 1000 miles ; since, then, the coin measures two
half inches in diameter, the moon must measure 2000 miles in
diameter. The moon is then a globe whose diameter is about one-
fourth of that of the earth.

This may be rendered still more clear by reference to the
annexed diagram (fig. 1), where E is the eye, c the coin, and M the
moon. It will be evident on mere inspection, that the triangle
formed by the distance EC of the coin from the eye, and the
diameter cc of the coin, is similar to the triangle formed by the
distance EM of the moon from the eye and the diameter aim of the
moon, and that consequently the proportion of EC to cc is exactly
the same as that of EM to x;«. But as has just been stated, it is
found that when cc exactly covers the moon, and neither more nor
less than covers it, EC is 120 times cc. It follows, therefore, that
EM is 120 time* iim. But since it has been ascertained that EH is
240000 miles, that is 120 times 2000 miles, it follows that MW is

2000 miles.

Fig. 1.

5. While the moon moves around the earth, we find by observa-
tions of its appearance, that the same hemisphere is always turned
toward us. We recognise this fact by observing that the same
marks always remain in the same place upon it. Now, in order
that a globe which revolves around a centre should turn continu-
ally the same hemisphere toward that centre, it is necessary that

D2 35

THE MOON.

it should make one revolution upon its axis in the time it takes so
to revolve. For let us suppose that, in any one position, it has
the centre round which it revolves north of it, the hemisphere
turned toward the centre is turned toward the north. After it
makes a quarter of a revolution, the centre is to the west of it,
and the hemisphere which was previously turned to the north
must now be turned to the west. After it has made another
quarter of a revolution the centre will be south of it, and it must
be now to the south. In the same manner, after another quarter
of a revolution, it must be turned to the east. As the same
hemisphere is successively turned to all the points of the compass
in one revolution, it is evident that the globe itself must make a
revolution on its axis in that time.

It appears, then, that the rotation of the moon upon its axis
being equal to that of its revolution in its orbit, is 27 days, 7
hours, and 44 minutes. The intervals of light and darkness to the
inhabitants of the moon, if there were any, would then be alto-
gether different from those provided in the planets ; there would
be about 13 days of continued light alternately with 13 days of
continued darkness ; the analogy, then, which prevails among the
planets with regard to days and nights, and which forms a main
argument in favour of the conclusion that they are inhabited
globes like the earth, does not hold good in the case of the moon.

6. While the moon revolves round the earth, its illuminated

Fig. 2.

hemisphere is always presented to the sun; it therefore takes
various positions in reference to the earth. The effects of this
are exhibited in the annexed fig. 2. Let E s represent the direction
36

CONJUNCTION — QUADRATURE, &c.

of the snn, and E the earth ; when the moon is at N, between
the sun and the earth, its illuminated hemisphere being turned
toward the sun, its dark hemisphere will be presented toward the
earth ; it will therefore be invisible. In this position the moon is
said to be in coN-rracxiox.

When it moves to the position c, the enlightened hemisphere
being still presented to the sun, a small portion of it only is
turned to the earth, and it appears as a thin crescent, as repre-
sented at c.

7. When the moon takes the position of Q, at right angles to the
sun, it is said to be in QTTADRATITRE : one half of the enlightened
hemisphere only is then presented to the earth, and the moon
appears halved as represented at q.

When it arrives at the position G, the greater part of the
enlightened portion is turned to the earth, and it is gibbous,
appearing as represented at g.

8. When the moon comes in OPPOSITION to the sun, as £ een at
r, the enlightened hemisphere is turned full toward the earth, and
the moon will appear full as at f, unless it be obscured by the
earth's shadow, which rarely happens. In the same manner it is
shown that at G' it is again gibbous; at <j' it is halved, and at c7
it is a crescent.

If the moon or the planets be supposed to be viewed by an
observer placed on the one side or the other of the general plane
in which they move, they will appear to move either in the
direction of the hands of a clock, or in the contrary direction,
according to the side of the general plane from which they are
seen. If the observer be supposed to be on the north side of that
plane, their motion will be contrary to that of the hands of a
clock. If he is placed on the south side of that plane, their
motion will be in the direction of the hands of a clock.

In the case represented in fig. 2, and also in the astronomical
diagrams in the first volume of the Museum, pp. 5, 11, &c., the
observer is supposed to be placed at the south side of the general
plane.

9. In order to determine whether or not the globe of the moon
is surrounded with any gaseous envelope like the atmosphere of
the earth, it is necessary first to consider what appearances such
an appendage would present, seen at the moon's distance, and
whether any such appearances are discoverable.

10. According to ordinary and popular notions, it is difficult to
separate the idea of an atmosphere from the existence of clouds ;
yet to produce clouds something more is necessary than air. The
presence of water is indispensable, and if it be assumed that no
water exist, then certainly the absence of clouds is no proof of the

37

THE MOON.

absence of an atmosphere. Be this as it may, however, it is certain
that there are no clouds upon the moon, for if there were, we
should immediately discover them, "by the variable lights and
shadows they would produce. If there be an atmosphere upon tl}e
moon, it is therefore one entirely unaccompanied by clouds.

11. One of the effects produced by a distant view of an atmo-
sphere surrounding a globe, one hemisphere of which is illumi-
nated by the sun, is, that the boundary, or line of separation,
between the hemisphere enlightened by the sun and the dark
hemisphere, is not sudden and sharply denned, but is gradual —
the light fading away by slow degrees into the darkness. It is
to this effect upon the globe of the earth that twilight is owing,
and as we shall see hereafter, such a gradual fading away of the
sun's light is discoverable on some of the planets, upon which an
atmosphere is observed. Now, if such an effect of an atmosphere
were produced upon the moon, it would be perceived by the naked
eye, and still more distinctly with the telescope. When the moon
appears as a crescent, its concave edge is the boundary which
separates the enlightened from the dark hemisphere. When it is
in the quarters, the diameter of the semicircle is also that boun-
dary. In neither of these cases, however, do we ever discover
any gradual fading away of the light into the darkness ; on the
contrary, the boundary, through serrated and irregular, is never-
theless perfectly well defined and sudden. All these circumstances-
conspire to prove that there does not exist upon the moon an
atmosphere capable of refracting light in any sensible degree.

But it may be contended that an atmosphere may still exist,
though too attenuated to produce a sensible twilight. Astro-
nomers, however, have resorted to another test of a much more
decisive and delicate kind, the nature of which will be understood

by explaining a simple principle
of optics. When a ray of light
passes through a transparent
medium, such as air, water, or
glass, it is generally deflected
from its rectilinear course, so as
to form an angle. A simple and
easily- executed experiment will
render this intelligible. Let a
visible object, such as a coin, be
placed at c, in the bottom of a
bucket. Let the eye be placed at E (fig. 3), so that the side of the
bucket, when empty, shaU just conceal the coin, and so that the'
nearest point to the coin visible shall be at A, in the direction of
the line E B A. Let the bucket be now filled with water, and the

NO ATMOSPHERE.

coin will become immediately visible ; the reason of which is, that
the ray of light c B proceeding from the coin is bent at an angle
in passing from the water into the air, and reaches the eye by the
angular course c B E. Thus it appears that the coin will be visible
to the eye, notwithstanding the interposition of the opaque side of
the bucket.

Let us see how this principle can be applied to the case of the
moon's atmosphere, if such there be.

Let m m' (fig. 4) represent the disk of the moon. Let a cf
represent the atmosphere which surrounds it. Let s m e and
s m' e represent two lines touching the moon at m and m', and
proceeding towards the earth. Let s s be two stars seen in the
direction of these lines. If the moon had no atmosphere, these
stars would appear to touch the edge of the moon at m and m',
because the rays of light from them would pass directly toward
the earth; but if the moon have an atmosphere, then that
atmosphere will possess the property which is common to all
transparent media of refracting light, and, in virtue of such pro-
Fig. 4.

*.*'

perty, stars in such positions as s' &*, behind the edge of the moon,
would be visible at the earth, for the ray s' m, s' m ', in passing
through the atmosphere, would be bent at an angle in the
direction m e', and m' e', so that the stars s' s' would be visible
at e' e', notwithstanding the interposition of the edges of the
moon.

This reasoning leads to the conclusion that as the moon moves
over the face of the firmament, stars will be continually visible
at its edge which are really behind it if it have an atmosphere,
and the extent to which this effect will take place will be in pro-
portion to the density of the atmosphere.

12. The magnitude and motion of the moon and the relative
positions of the stars are so accurately known that nothing is
more easy, certain, and precise, than the observations which may
be made with the view of ascertaining whether any stars are ever
seen which are sensibly behind the edge of the moon. Such
observations have been made, and no such effect has ever been
detected. This species of observation is susceptible of such extreme
accuracy, that it is certain that if an atmosphere existed upon the

39

THE MOON.

moon a thousand times less dense than our own, its presence must
he detected.

13. The earth's atmosphere supports a column of 30 inches
of mercury: an atmosphere 1000 times less dense would support
no more than the thirtieth of an inch. It may therefore he con-
sidered as proved that the space around the surface of the moon
is as exempt from an atmosphere as is the receiver of a good air-
pump after that instrument has exhausted it of air to the utmost
limit of its power. In fine for all practical purposes it is demons-
trated that the moon has no atmosphere.

14. The same physical tests which show the non-existence of
an atmosphere of air upon the moon are equally conclusive against
an atmosphere of vapour. It might, therefore, be inferred that
no liquids can exist on the moon's surface, since they would be
subject to evaporation. Sir John Herschel, however, ingeniously
suggests that the non-existence of vapour is not conclusive against
evaporation. One hemisphere of the moon being exposed con-
tinuously for 328 hours to the glare of sunshine of an intensity
greater than a tropical noon, because of the absence of an atmo-
sphere and clouds to mitigate it, while the other is for an equal
interval exposed to a cold far more rigorous than that which
prevails on the summits of the loftiest mountains or in the polar
regions, the consequence would be the immediate evaporation of
all liquids which might happen to exist on the one hemisphere,
and the instantaneous condensation and congelation of the vapour
on the other. The vapour would, in short, be no sooner formed
on the enlightened hemisphere than it would rush to the vacuum
over the dark hemisphere, where it would be instantly condensed
and congealed, an effect which Herschel aptly illustrates by the
familiar experiment of the CRYOPHOROUS. The consequence, as he
observes, of this state of things would be absolute aridity below
the vertical sun, constant accretion of hoar frost in the opposite
region, and perhaps a narrow zone of running waters at the
borders of the enlightened hemisphere. He conjectures that this
rapid alternation of evaporation and condensation may to some
extent preserve an equilibrium of temperature, and mitigate the
severity of both the diurnal and nocturnal conditions of the
surface. He admits nevertheless, that such a supposition could
only be compatible with the tests of the absence of a transparent
atmosphere even of vapour within extremely narrow limits ; and
it remains to be seen whether the general physical condition of
the lunar surface as disclosed by the telescope be not more com-
patible with the supposition of the total absence of all liquid
whatever.

It appears to have escaped the attention of those who assume
40

SOLAR LIGHT AND HEAT.

the possibility of the existence of water in the liquid state on the
moon, that, in the absence of an atmosphere, the temperature
must necessarily be, not only far below the point of congelation
of water, but even that of most other known liquids. Even
within the tropics, and under the line with a vertical sun, the
height of the snow line does not exceed 16000 feet, and never-
theless at that elevation, and still higher, there prevails an atmo-
sphere capable of supporting a considerable column of mercury.
At somewhat greater elevations, but still in an atmosphere of
very sensible density, mercury is congealed. Analogy, therefore,
justifies the inference that the total, or nearly total, absence of air
upon the moon is altogether incompatible with the existence of
water, or probably any other body in the liquid state, and neces-
sarily infers a temperature altogether incompatible with the
existence of organised beings in any respect analogous to those
which inhabit the earth.

But another conclusive evidence of the non-existence of liquids
on the moon is found in the form of its surface, which exhibits
none of those well understood appearances which result from the
long-continued action of water. The mountain formations with
which the entire visible surface is covered are, as will presently
appear, universally so abrupt, precipitous, and unchangeable, as
to be utterly incompatible with the presence of liquids.

15. The general diffusion of the sun's light upon the earth is
mainly due to the reflection and refraction of the atmosphere,
and to the light reflected by the clouds ; and without such means
of diffusion the solar light would only illuminate those places into
which its rays would directly penetrate. Every place not in full
sunshine, or exposed to some illuminated surface, would be
involved in the most pitchy darkness. The sky at noon-day
would be intensely black, for the beautiful azure of our firmament
in the day-time is due to the reflected colour of the air. Thus it
appears that the absence of air on the moon must deprive the
sun's illuminating and heating agency of nearly all its utility.

16. If the moon were inhabited, observers placed upon it would
witness celestial phenomena of a singular description, differing
in many respects from those presented to the inhabitants of our
globe. The heavens would be perpetually serene and cloudless.
The stars and planets would shine with extraordinary splendour
during the long night of 328 hours. The inclination of her axis
being only 5°, there would be no sensible changes of season. The
year would consist of one unbroken monotony of equinox. The
inhabitants of one hemisphere would never see the earth : while
the inhabitants of the other would have it constantly in their
firmament by day and by night, and always in the same position.

41

THE MOOff.

To those who inhabit the central part of the hemisphere presented
to us, the earth would appear stationary in the zenith, and would
never leave it, never rising nor setting, nor in any degree
changing its position in relation to the zenith or horizon. To
those who inhabit places intermediate between the central part
of that hemisphere and those places which are at the edge of the
moon's disk, the earth would appear at a fixed and invariable
distance from the zenith, and also at a fixed and invariable
azimuth, the distance from the zenith being everywhere equal to
the distance of the observer from the middle point of the hemi-
sphere presented to the earth. To an observer at any of the
places which are at the edge of the lunar disk, the earth would
appear perpetually in a fixed direction on the horizon.

The earth shone upon by the sun would appear as the moon
does to us; but with a disk having an apparent diameter
greater than that of the moon in the ratio of 79 to 21, and an
apparent superficial magnitude about fourteen times greater, and
it would consequently have a proportionately illuminating power.

Earth light at the moon would, in fine, be about fourteen
times more intense than moonlight at the earth. The earth
would go through the same phases and complete the series of
them in the same period as that which regulates the succession
of the lunar phases, but the corresponding phases would be
separated by the interval of half a month. When the moon is
full to the earth, the earth is new to the moon, and vice versa :
when the moon is a crescent, the earth is gibbous, and vice versd.

17. The features of light and shade would not, as on the moon,
be all permanent and invariable. So far as they would arise from
the clouds floating in the terrestrial atmosphere they would be
variable. Nevertheless, their arrangement would have a certain
relation to the equator, owing to the effect of the prevailing atmo-
spheric currents parallel to the line. This cause would produce
streaks of light and shade, the general direction of which would
be at right angles to the earth's axis, and the appearance of which
would be in all respects similar to the BELTS which are observed upon
some of the planets, and which are ascribed to a like physical cause.

18. Through the openings of the clouds the permanent geogra-
phical features of the surface of the earth would be apparent, and
would probably exhibit a variety of tints according to the prevail-
ing characters of the soil, as is observed to be the case with the
planet Mars even at an immensely greater distance. The rotation
of the earth upon its axis would be . distinctly observed and its
time ascertained. The continents and seas would disappear in
succession at one side and reappear at the other, passing across
the disk of the earth as carried round by the diurnal rotation.

42

HEAT OP MOONLIGHT.

19. It has long been an object of inquiry among philosophers
whether the light of the moon has any heat, but the most
delicate experiments and observations have failed to detect this,
property in it. A thermometer of extreme sensibility, called
a differential thermometer, was the instrument applied to this
inquiry.

This instrument consists of two glass bulbs, A and B (fig. 5),
connected by a rectangular glass tube. In the horizontal part of
the tube a small quantity of coloured liquid (sulphuric acid, for
example) is placed. Atmospheric air is contained in the bulbs
and tube, separated into two parts by the liquid. The instrument
is so adjusted that, when the drop of liquid is at the middle of the
horizontal tube, the air in the bulbs has the same pressure ; and
having equal volumes, the quantities at each side of the liquid are
necessarily equal. If the bulbs be affected by different tem-
peratures,* the liquid will be pressed from that side at which the

Fig. 5.

50 40 30 20 "10 O ID 20 30 40 So

temperature is greatest, and the extent of its departure from the
zero or middle is indicated by the scale. This thermometer is
sometimes varied in its form and arrangement, but the principle
remains the same. Its extreme sensitiveness, in virtue of which
it indicates changes of temperature too minute to be observed by
common thermometers, renders it extremely valuable as an instru-
ment of scientific research. By this instrument, changes of
temperature not exceeding the 6000th part of a degree are
rendered sensible.

The light of the moon was collected into the focus of a concave
mirror of such magnitude as would have been sufficient, if exposed
to the sun's light, to evaporate gold or platinum. The bulb of
the differential thermometer was placed in its focus, so as to receive
upon it the concentrated rays of the moon. Yet no sensible effect
was produced upon the thermometer. We must therefore conclude
that the light of the moon does not possess the calorific property
in any sensible degree.

This result will create less surprise when the comparative

43

THE MOON.

intensity of sunlight and moonlight are considered. It may be
assumed, without sensible error, that the intensity of the sun's
light on the surface of the moon and on the earth is the same ; it
follows from this, that supposing no light whatever to be absorbed
by the moon, but the entire light of the sun to be reflected from
its surface undiminished, the intensity of moonlight at the earth
would bear to the intensity of sunlight the same proportion as the
magnitude of the moon bears to the magnitude of the entire
firmament, that is, the proportion very nearly of 1 to 300000 ;
but there is no reflecting surface, however perfect, which does not
absorb the light incident upon it in a very considerable degree,
and the rugged surface of the moon must be a most imperfect
reflector. It may then be considered as demonstrated that the
intensity of moonlight is much more than 300000 times more
feeble than that of sunlight. We shall not, then, be surprised at
the absence of its heating power.

But if the rays of the moon be not warm, the vulgar impression
that they are cold is equally erroneous. We have seen that they
produce no effect either way on the thermometer.

20. Curiosity will doubtless be awakened in a very lively
manner regarding the physical condition of our moon : what part
has the Maker of the solar system destined this body to play in
the economy of His creation ? Is it a globe teeming with life and
organisation like the earth ? Is that orb, which rolls in silent
majesty through the midnight firmament, the abode of life and
intelligence ? The beauty of her appearance naturally leads the
mind to conjectures of this kind. Yet the circumstances which
I have unfolded regarding the total absence of air and water
appear to exclude the possibility of any such supposition. How,
may it be asked, can it be conceived that a globe can have upon
it an organised world which is destitute of fluid matter in every
form ? How can growth, which implies gradual change, increase,
and diminution, and all the various effects in whicli fluidity is an
agent, go on there ? How can they proceed upon such a solid,
arid, unchangeable, crude mass ? Let it be remembered what a
multitude of purposes in our natural and social economy are sub-
served by the combination of the water and the atmosphere of our
globe. None of these purposes can be fulfilled upon the moon.
Perhaps, however, our notions on such questions may be cleared up
to some extent by a careful examination of the facts that scientific
research has collected respecting the physical condition of the
surface of our satellite.

21. If, when the moon is a crescent, we examine with a tele-
scope, even of moderate power, the concave boundary which is
that part of the lunar surface where the enlightened hemisphere

PHYSICAL CHARACTER OP THE SURFACE.

ends and the dark hemisphere begins, we shall find that it is not
an even and regular curve, which it undoubtedly would be if the
surface of the globe of the moon were smooth and regular, or
nearly so. If, for example, the lunar surface resembled in its
general characteristics that of our globe ; granting the total
absence of water, and that the entire surface is land, but that land
had the general characteristics of the continents of the globe of
the earth ; then I say, that the inner boundary of the lunar cres-
cent would still be a regular curve, broken or interrupted only at
particular points. Where great mountain ranges, like those of
the Alps, the Andes, or the Himalaya, might chance to cross it,
these lofty peaks would project vastly-elongated shadows along
the adjacent plain ; for it will be remembered that, being situated
at the moment in question at the boundary of the enlightened and
darkened hemispheres, the shadows would be those of evening
and morning; which are prodigiously longer than the objects
themselves. The effects of these would be to cause gaps or
irregularities in the general outline of the inner boundary of the
crescent ; with these rare exceptions, the inner boundary of the
crescent produced by a globe like the earth would be an even and
regular curve.

Such, however, is not the case with the inner boundary of the
lunar crescent, even when viewed

by the naked eye, and still less ^

so when magnified by a telescope.
It is found, on the contrary,
rugged and serrated, and bril-
liantly illuminated points are seen
in the dark parts at some distance
from it, while dark shadows of
considerable length appear to
break into the illuminated sur-
face. The inequalities thus ap-
parent indicate singular cha-
racteristics of the surface. The
bright points seen within the dark
hemisphere are the peaks of lofty
mountains tinged with the sun's
light. They are in the condition
with which all travellers in Alpine
countries are familiar ; after the
sun has set, and darkness has set in over the valleys at the foot of
the chain, the sun still continues to illuminate the peaks above.
The sketch (fig. 6), of the lunar crescent, will illustrate these
observations.

45

THE MOON.

22. The visible hemisphere of our satellite has, within the
last quarter of a century, been subjected to the most rigorous
examination which unwearied industry, aided by the vast im-
provement which has been effected in the instruments of telescopic
observation, rendered possible ; and it is no exaggeration to state
that we now possess a chart of that hemisphere, which in
accuracy of detail far exceeds any similar representation of the
earth's surface.

Among the selenographical observers, the Prussian astronomers,
MM. Beer and Madler, stand pre-eminent. Their descriptive
work, entitled " Der Monde," contains the most complete collec-
tion of observations on the physical condition of our satellite, and
the chart, measuring 37 inches in diameter, exhibits the most
complete representation of the lunar surface extant. Besides this
great work, a selenographic chart was produced by Mr. llussel,
from observations made with a seven-foot reflector, a similar
delineation by Lohrmann, and, in fine, a very complete model
in relief of the visible hemisphere by Madame Witte, a Hanove-
rian lady.

23. The surface of the visible hemisphere is thickly covered
with mountainous masses and ranges of various forms, magni-
tudes, and heights, in which, however, the prevalence of a
circular or crater-like form is conspicuous. The various tints of
white and gray which mark the lineaments observed upon the
disk arise partly from the different reflecting powers of the matter
composing different parts of the lunar surface, and partly from
the different angles at which the rays of the solar light are incident
upon them. The more intensely white parts are mountains of
various magnitude and form, whose height, relatively to the
moon's magnitude, greatly exceeds that of the most stupendous
terrestrial eminences ; and there are many characterised by an
abruptness and steepness which sometimes assume the position of
a vast vertical wall, altogether without example upon the earth.
These are generally disposed in broad masses, lying in close con-
tiguity, and intersected with vast and deep valleys, gullies, and
abysses, none of which, however, have any of the characters which
betray the agency of water.

24. There are circular areas, varying from 40 to 120 miles in
diameter, enclosed by a ring of mountain ridges, mostly con-
tinuous, but in some cases intersected at one or more points by vast
ravines. The enclosed area is generally a plain on which moun-
tains of less height are often scattered. The surrounding circular
ridge also throws out spurs, both externally and internally, but
the latter are generally shorter than the former. In some cases,
however, internal spurs, which are diametrically opposed, unite

46

LUNAR MOUNTAINS.

in the middle so as to cut in two the enclosed plain. In some rare
cases the enclosed plain is uninterrupted by mountains, and it is
almost invariably depressed below the general level of the sur-
rounding land. A few instances are presented of the enclosed
plain being convex.

The mountainous circle enclosing these vast areas is seldom a
single ridge. It consists more generally of several concentric
ridges, one of which, however, always dominates over the rest,
and exhibits an unequal summit, broken by stupendous peaks,
which here and there shoot up from it to vast heights. Occasionally
it is also interrupted by smaller mountains of the circular form.

25. The most remarkable of the class of lunar mountains, called
ring mountains, is that called TYCHO. This object is distinguish-
able without a telescope on the lunar disk when full ; but, owing
to the multitude of other features which become apparent around
it in the phases, it can then be only distinguished by a perfect
knowledge of its position, and with a good telescope. The enclosed
area, which is very nearly circular, is 47 miles in diameter, and
the inside of the enclosing ridge has the steepness of a wall. Its
height above the level of the enclosed plain is 16000 feet, and
above that of the external regions 12000 feet. There is a cen-
tral mountain, having the height 4700 feet, besides a few lesser
hills within the enclosure.

This region of the moon is represented in the engraving
at the head of this tract, copied and reduced from the chart
of MM. Beer and Madler. The volcanic character observed
in the mountain formations loses much of its analogy to like
formations on the earth's surface when higher magnifying powers
enable us to examine the forms of what appear to be craters, and
to compare their dimensions with even the most extensive terres-
trial craters. Numerous examples may be produced to illustrate
this. Tycho, which, viewed under a moderate magniiying power,
appears to possess in so eminent a degree the volcanic character,
is, as has been stated, a circular chain enclosing an area of 47
miles in diameter. Gassendi, another system of like form, and of
still more stupendous dimensions, as seen with high magnifying
powers, consists of two enormous circular chains of mountains, the
lesser, which lies to the north, measuring 16^ miles in diameter,
and the greater, lying to the south, enclosing an area 60 miles
in diameter. The area enclosed by the former is therefore 214,
and by the latter 2827 square miles. The height of the lesser
.chain is about 10000 feet, while that of the greater varies from
3500 to 5000 feet. The vast area thus enclosed by the greater
chain includes, at or near its centre, a principal central mountain,
having eight peaks and an height of 2000 feet, while scattered

THE MOON.

over the surrounding enclosure upwards of a hundred mountains
of less considerable elevation have been counted.

It is easy to see how little analogy to a terrestrial volcanic crater
is presented by these characters.

26. In the work of Beer and Madler a table of the heights of
above 1000 mountains is given, several of which attain to an eleva-
tion of 23000 feet, equal to that of the highest summits of terres-
trial mountains, while the diameter of the moon is little more than
a fourth of that of the earth.

27. By means of the great reflecting telescope of Lord Eosse,
the flat bottom of the crater called Albategnius is distinctly seen
to be strewed with blocks, not visible with less powerful instru-
ments ; while the exterior of another ( Aristillus) is intersected with
deep gullies radiating from its centre.

28. In fine, the entire geographical character of the moon, thus
ascertained by long-continued and exact telescopic surveys, leads
to the conclusion that no analogy exists between it and the
earth which would confer any probability on the conjecture
that it fulfils the same purposes in the economy of the Universe,
and we must infer that whatever be its uses in the solar system,
or in the general purposes of creation, it is not a world inhabited
by organised races, such as those to which the earth is appro-
priated.

48

Fig. 2.

COMMON THINGS.

THE EARTH.

Difficulty of observing the earth as a whole. — 2. It appears at first an
indefinite flat surface. — 3. This disproved by travelling round it. — 4.
Proof of the curvature of its surface by observation of distant objects
at sea. — 5. By the Earth's shadow projected on the Moon. — 6. In-
equalities of surface, such as mountains and valleys, insignificant. —
7. Magnitude of Earth, how ascertained. — 8. Length of a degree of
latitude. — 9-10. Illustrations of the Earth's magnitude. — 11. Is the
Earth at rest ? — 12. Apparent motion of the firmament. — 13. Origin
of the word " Universe." — 14. This apparent motion may not be real
— may arise from the rotation of the Earth. — 15. How such a rotation
would produce it. — 16. Poles. — 17. Equator. — 18. Hemispheres. — 19.

LARDNER'S MUSEUM OF SCIENCE. s 49

No. 29

COMMON THINGS — THE EARTH.

Meridians. — 20. Which of the two rotations is the more probable ? —
21 . Rotation of the universe impossible. — 22. Simplicity of the supposed
rotation of the globe. — 23. Direct proofs of this motion. — 24. Foucault's
experiment. — 25. Its analogy to the planets. — 26. Conclusion as to the
globular form of the earth requires modification. — 27. All human
knowledge tentative and approximative. — 28. Rotation not compatible
with the exact globular form. — 29. Centrifugal force of the Earth's
rotation. — 30. The globe rotating would assume the form of an oblate
spheroid. — 31. The degree of ellipticity would vary with the velocity
of rotation. — 32. Experimental illustration. — 33. Ellipticity corre-
sponding to the diurnal rotation. — 34. How these circumstances affect
the actual state of the Earth. — 35. Form of a terrestrial meridian. —
36. Dimensions of the terrestrial spheroid. — 37. Its departure from
an exact globe very small. — 38. Its density and mass. — 39. Deter-
mined by Cavendish and Maskelyne. — 40. Its total weight.

1. LOCKE somewhere observes, with his usual felicity of illustra-
tion, that the "mind, like the eye, while it makes us see and
perceive all other things, can never turn its view with advantage
upon itself." We encounter something similar to this in our
researches through the universe ; for of all the objects which
compose it, one of the most difficult of which to obtain a com-
plete and accurate knowledge is the planet which we inhabit.
The cause of this is our proximity to it, and intimate connexion
with it. We are confined upon its surface, from which we cannot
separate ourselves. We cannot obtain a bird's-eye view of it, nor
at any one time behold more than an insignificant portion of its
surface. We have the same difficulty in obtaining an acquaintance
with it that a microscopic animalcule would have in acquiring
a perfect knowledge of the form and dimensions of a terrestrial
globe twelve inches in diameter, on the surface of which it
creeps.

Still, by a variety of indirect methods supplied by the ingenuity
of scientific research, we have been enabled to ascertain its form,
dimensions, and physical constitution, with a considerable degree
of accuracy.

2. The first impression produced upon the eye of an observer,
who has not carried his inquiries further, is, that the surface of
the earth is a flat plane, interrupted only by the inequalities of
the land. A little careful observation, however, upon the many
phenomena which are easily accessible to every observer, will
correct this erroneous impression.

3. It is well known that if a voyage were made upon the earth,
continually preserving one and the same direction, or doing so as
nearly as circumstances will permit, we should at length arrive
at the place from which we departed. If the earth were an
indefinite plane, this could not happen. It is evident, then, that
whatever be the exact form of the earth, it is a body which is on

50

CURVATURE.

every side limited, and one which must therefore have such a
surface that a traveller or navigator can completely surround it in
one continuous course.

4. Let us see, however, whether we may not obtain evidence
more distinct as to its form. If we stand on the deck of a ship at
sea, and out of sight of land, the view being bounded only by sea
and sky, and look at the horizon when a ship (A, fig. 1) approaches,
we shall at first see its topmast rising out of the water like a pole.

Fig. I.

As it gradually comes nearer to us (as at B), more of the mast will
become visible, and the sails will be seen — cut off, however,
horizontally, by the line at which the water and sky unite. Upon
the nearer approach of the ship (as at c and D), the hull will at
length become visible. Xow since this takes place on all sides
around us, it will follow that when the ship is at a distance, there
must be something interposed between the eye and it which inter-
cepts the view of it ; but as the surface of the water is generally
uniform, and not subject to sudden and occasional inequalities like
that of the land, we can only imagine its general form to be
convex, and that its convexity is interposed between the eye and
the object so as to intercept the view.

Since the same effects are observed from whatever direction the
ship may approach, it will follow that the same convexity must
prevail on every side.

If, on the contrary, the surface extending from the eye to the
ship were a plane, the ship would be rendered invisible only by
reason of its distance ; whereas it is ascertained that a ship
frequently is invisible at a distance at which it must be seen but
for the interposition of some other object; this may be tested, and
in fact is frequently tested at sea by mounting to the masthead,
whence the seaman being enabled to overlook the convexity, sees
vessels which are invisible from the deck, although, strictly
speaking, he is nearer to those vessels on the deck than at the
masthead.

When the mariner, after completing a long voyage, discovers by
his observations and reckonings that he is approaching the desired
coast, he ascends to the topmast and looks out for the appearance
of mountains or other elevated land, and he invariably sees them
from that point long before they are visible from the deck. He

E2 51

COMMON THINGS — THE EARTH.

afterwards sees them from the deck long before the general level of
the country will be observed by him. All these are natural and
necessary consequences of the convexity of the surface of the
ocean. The same effects would be seen in any part of a continent
which is sufficiently free from mountains and other inequalities.

5. But we have a still more conclusive and convincing proof of
the general form of the earth even than those which have been
explained. "When the moon passes directly behind the earth, so
that the shadow which the earth projects behind it in the direction
opposite to the sun shall fall upon the moon, we invariably find
that shadow to be, not as is commonly said, circular, but such
exactly as one globe would project upon the surface of another
globe. Now, as this takes place always, in whatever position the
earth may be, and while the earth is revolving rapidly with its
diurnal motion upon its axis, it follows that the earth must either
be an exact globe or so little different from a globe that its devia-
tion from that figure is undiscoverable in its shadow.

We may, then, consider it demonstrated that the earth may
be practically regarded as globular in its form. "We shall here-
after see that it slightly departs from the spherical figure, but
our present purpose will be best answered by regarding it as a
globe.

6. The objection will doubtless occur to many minds that the
inequality which exists on the surface of that portion of the globe
that is covered by land, especially the loftier ridges of moun-
tains, such as the Andes, the Alps, the Himalaya, and others, are
incompatible with the idea of a globular figure. If the term
globular figure were used in the strictest geometrical sense, this
objection doubtlessly would have great force. But let us see the
real extent of this presumed deviation from the globular form.
The highest mountain on the surface of the globe does not exceed
five miles above the general level of the sea. The entire diameter
of the globe, as we shall presently see, is eight thousand miles.
The proportion, then, which the highest summit of the loftiest
mountains bears to the entire diameter of the globe will be that
of five to eight thousand, or one to sixteen hundred. If we take
an ordinary terrestrial globe of sixteen inches in diameter, each
inch upon the globe will correspond to five hundred miles upon
the earth, and the sixteen hundredth part of its diameter, or the
hundredth part of an inch, will correspond to five miles. If, then,
we take a narrow strip of paper, so thin that it would take one
hundred leaves to make an inch in thickness, and paste such a
strip on the surface of the globe, the thickness of the strip would
represent upon the sixteen-inch globe the height of the loftiest
mountain on the earth. "We are then to consider that the highest

52

MAGNITUDE.

mountain-ranges on the earth, deprive it of its glohular figure only
in the same degree and to the same extent as a sixteen-inch globe
would be deprived of its globular figure by a strip of paper pasted
upon it the hundredth part of an inch thick.

It is supposed that the greatest depth of the ocean which covers
any portion of the globe does not exceed the greatest height of the
mountains upon the land. If this be true, the ocean upon the
earth might be represented by a film of liquid laid with a camel's
hair pencil upon the surface of a sixteen-inch globe.

It is apparent, therefore, that depths and heights which appear
to the common observer to be stupendous, are nothing when con-
sidered with reference to the magnitude of the earth ; and that, so
far as they are concerned, we may practically regard the earth as
a true globe.

7. Having ascertained satisfactorily the form of the earth,
our next enquiry must be as to its magnitude ; and since it
is a globe, all that we are required to know is the length of its
diameter.

If a line were described surrounding the globe, so as to form a
circle upon it, the centre of which should be at the centre of the
globe, such a circle is called a great circle of the earth. Xow if
we know the length of the circumference of such a circle, we could
easily ffclculate the length of its diameter, for the proportion of
the circumference to the diameter is exactly known. But we
could calculate the circumference if we knew the length of one
degree upon it, since we know that the circumference consists of
three hundred and sixty degrees ; we should therefore only have
to multiply the length of one degree by three hundred and sixty
to obtain the circumference, and should thence calculate the
diameter.

8. In our tract upon latitudes and longitudes, it was shown how
the latitude of a place can be ascertained. Now, let us suppose
two places selected which are upon the same meridian of the earth,
and therefore have the same longitude, and which are not very
far removed from each other. Let them, moreover, be selected
so that the distance between them can be easily and accurately
measured. Xow let the latitude of these two places be exactly
determined, and let us suppose for example that the difference
between these two latitudes is found to be one degree and a half ;
and supposing also that on measuring the distance between them,
that distance is found to be one hundred and four miles and thirty-
five hundredths. We should thence infer that such must be the
length of one degree and a half of the earth's surface, and that
consequently the length of one degree would be two thirds of this,
or sixty-nine and a half miles. Having thus found the length of

53

COMMON THINGS — THE EARTH.

a degree, we should have to multiply it by three hundred and
sixty, by which we should obtain the circumference of the earth.
This would give twenty-five thousand and twenty miles, and we
should then find by the usual mode of calculation the diameter of
the earth, which would prove to be a little under eight thousand
miles.

The fact that a degree of the earth's circumference consists in
round numbers of just so many thousand feet as there are days in
the year, supplies a very convenient aid to the memory.

We have made these calculations chiefly with a view of render-
ing the principles of the investigation intelligible. The more
exact dimensions of the earth will be explained hereafter.

"We conclude, then, that the earth is a globe eight thousand
miles in diameter.

9. To enounce this stupendous arithmetical result is much
easier than to obtain any distinct notion of the actual magnitude
which it expresses. Such a globe has a circumference of twenty-
five thousand miles. A locomotive engine travelling incessantly
night and day, at twenty-five miles an hour, would take about
forty-two days to go round it.

10. When the diameter of a globe is known, its surface and
volume or cubical bulk can be easily determined. To find the surface
we have only to take three hundred and fourteen hunditedths of
the square of the diameter, and to find the volume, five hundred
and twenty-four thousandths of the cube of the diameter. In this
way we find that the surface of the earth measures two hundred
millions of square miles, and that its cubical bulk is about two
hundred and sixty thousand millions of cubic miles.

If the materials which form such a globe were built up in the
form of a vertical column, the base of which would have the mag-
nitude of England and Wales, its height would be nearly four
and a half millions of miles !

11. Such being the dimensions of the globe we inhabit, we are
next to consider what is its condition as to motion. Is it, as it
appears, at rest ? For several thousand years in the history of
the human race, it was not only so considered, but he that would
have ventured to call in question its stability and quiescence
would have been deemed insane. Certain expressions in the sacred
Scriptures being erroneously supposed to affirm its immobility, it
was deemed heretical to deny it ; and Galileo, who did so, was
put to the torture by the ecclesiastical authorities of the day, and
compelled to admit its quiescence. This verbal admission was,
however, so utterly opposed to his convictions, that, on quitting
the presence of the inquisitors, he stamped on the ground, and
muttered the words, " It moves for all that."

54

ROTATION.

12. A few hours' attentive contemplation of the firmament at
night will enable any common observer to perceive, that although
the stars are, relatively to each other, fixed, the hemisphere, as a
whok, is in motion. Looking at the zenith, that is the point
directly above our head, constellation after constellation will
appear to pass across it, having risen in an oblique direction from
the horizon at one side, and, after passing the zenith, descending
on the other side to the horizon, in a direction similarly oblique.
Still more careful and longer continued observation, and a com-
parison, so far as can be made by the eye, of the different directions
successively assumed by the same object, creates a suspicion, which
every additional observation strengthens, that the celestial vault
has a motion of slow and uniform rotation round a certain diameter
as an axis, carrying with it all the objects visible upon it, without
in the least deranging their relative positions or disturbing their
arrangement.

When these loose impressions of the senses are submitted to the
more exact means of observation which are at the disposition of
astronomers, it is found that all the appearances of the heavens,
the rising and the setting of the stars, the sun and the moon, their
apparent motion in ascending to, passing, and descending from,
their several points of culmination, is that of a sphere revolving
with an uniform motion round the diameter which is directed to
the pole.

The world we inhabit therefore would, to judge from these
phenomena, seem to be fixed in the centre of a hollow sphere of
vast magnitude. On the concave surface of this hollow sphere
thus surrounding us at an immeasurable distance all the stars
appear to be placed. This sphere, carrying the whole creation,
upon it, appears to revolve round our world. It makes a complete
'revolution in twenty -four hours.* By this rotation, the diurnal
appearances of the rising and setting of all the heavenly bodies are
perfectly explained.

13. The ancients who, as has been stated, affirmed the reality
of this motion of the celestial sphere, gave to the whole creation
around the earth, the name UNTVEESE ; from two words, Uxus, one,
and VEBSTTM , turning or rotation ; because they assumed that by
an imaginary force, called the PEmrM MOBILE, or first impulse,
this rotatory motion had been imparted to the firmament, which
ever afterwards retained it.

14. It is easy to perceive that the apparent diurnal rotation of
the firmament round the earth may arise indifferently from either
of two causes : 1st, from such a real rotation of the firmament

* More exactly 23h 56m 4'09§, but for the present the cause of this
difference need not be noticed.

55

COMMON THINGS — THE EARTH.

once in twenty-four hours ; 2ndly, from the rotation of the globe
of the earth in the same time round that diameter which is in
the direction of the axis round which the firmament appears to
revolve.

There is absolutely no other supposition possible but one or
other of these. The rejection of either necessarily throws us upon
the adoption of the other.

But it may be required that we should show how the rotation of
the earth upon an axis passing through the poles would cause the
apparent diurnal rotation of the firmament.

15. Let us assume that the earth is a globe revolving uniformly
on its axis in twenty-four hours. The universe around it is
relatively stationary, and the bodies which compose it being at
distances which mere vision cannot appreciate, appear as if they
were situate on the surface of a vast celestial sphere in the centre
of which the earth revolves. This rotation of the earth gives to
the sphere the appearance of revolving in the contrary direction,
as the progressive motion of a boat on a river gives to the
banks an appearance of retrogressive motion; and since the
apparent motion of the heavens is from east to west, the real
rotation of the earth which produces that appearance must be from
west to east.

How this motion of rotation explains the phenomena of the
rising and setting of celestial objects is easily understood. An
observer placed at any point upon the surface of the earth is
carried round the axis in a circle in twenty-four hours, so that
every side of the celestial sphere is in succession exposed to his view.
As he is carried upon the side opposite to that in which the sun is
placed, he sees the starry heavens visible in the absence of the-
splendour of that luminary. As he is turned gradually towards
the side where the sun is placed, its light begins to appear in the-
firmament, the dawn of morning is manifested, and the globe con-
tinuing to turn, he is brought into view of the luminary itself,
and all the phenomena of dawn, morning, and sunrise are
exhibited. "While he is directed towards the side of the firmament
in which the sun is placed, the other bodies of inferior lustre are
lost in the splendour of that luminary, and all the phenomena of
day are exhibited. When by the continued rotation of the globe
the observer begins to be turned away from the direction of the
sun, that luminary declines, and at length disappears, producing
all the phenomena of evening and sunset.

Such, in general, are the effects which would attend the motion.

of a spectator placed upon the earth's surface, and carried round

with it by its motion of rotation. He is the spectator of a gorgeous

diorama exhibited on a vast scale, the earth which forms his station

56

EQUATOR, ETC.

being the revolving stage by which he is carried round, so as to
view in succession the spectacle which surrounds him.

These appearances vary with the position assumed by the observer
on this revolving stage ; or, in other words, upon his situation on
the earth, as will presently appear.

16. That diameter upon which it is necessary to suppose the
earth to revolve in order to explain the phenomena is that which
passes through the terrestrial poles.

17. If the globe of the earth be imagined to be cut by a plane
passing through its centre at right angles to its axis, such a plane
will meet the surface in a circle, which will divide it into two
hemispheres, at the summits of which the poles are situate. This
circle is called the TERRESTRIAL EQUATOR.

18. That hemisphere which includes the continent of Europe is
called the XOETHEEX HEMISPHERE, and the pole which it includes
is called the XOETHEEX TEEEESTEIAL POLE ; the other hemisphere
being the SOUTHEEX HEMISPHERE, and including the SOUTHERN

TEEEESTEIAL POLE.

19. If the surface of the earth be imagined to be intersected
by planes passing through its axis, they will meet the surface
in circles which, passing through the poles, will be at right
angles to the equator. These circles are called TERRESTRIAL
MEEIDIAXS, and will be seen delineated on any ordinary terrestrial
globe.

These observations will be more clearly comprehended by
reference to fig. 2, in which x is the north, and s the south pole of
the earth, and & Q the equator. The firmament surrounding the
earth is represented by the circle ncesq. The axis s x of the earth
being supposed to be prolonged to the heavens will meet the firma-
ment at n and s, the celestial north and south poles ; and in like
manner the plane of the terrestrial equator JE Q being continued
to the heavens, will meet the firmament at <z q, the celestial
equator.

If an observer be stationed at o, his zenith will be at z, and his
horizon at h h'. As the globe revolves from west to east, the
heavens will be successively brought into view on the east, and
will disappear continually on the west.

20. Assuming then that all the diurnal changes of appearance
presented by the firmament, the risings and settings of the sun,
moon, and stars, and their varying appearance in diiferent lati-
tudes, admit of being explained with equal precision and com-
pleteness, either by supposing the universe to revolve daily round
the earth, or the earth to revolve daily on its axis, the only
question which remains to be decided is, which of these two
suppositions is the more probable ?

57

COMMON THINGS — THE EARTH.

The fixity and absolute repose of the globe of the earth being
assumed by the ancients as a physical maxim which did not even
admit of being questioned, they perceived the inevitable character
of the alternative which the apparent diurnal rotation of the
heavens imposed upon them, and accordingly embraced the hypo-
thesis, which now appears so monstrous, and which is implied in
the term TTNTVERSE, which they have bequeathed to us.

21. But with the knowledge which has been obtained by the
labours of modern astronomers respecting the enormous magnitudes
of the principal bodies of the physical universe, magnitudes
compared with which that of the globe of the earth dwindles to a
mere point, and their distances under the expression of which the
very power of number itself almost fails, and recourse is had
to colossal units in order to enable it to express even the smallest
of them, the hypothesis of the immobility of the earth, and the
diurnal rotation of the countless orbs of magnitudes so incon-
ceivable filling the immensity of space once every twenty-four
hours round this grain of matter composing our globe, becomes
so preposterous that it is rejected, not as an improbability, but as
an absurdity too gross to be even for a moment seriously enter-
tained or discussed.

22. But if any ground for hesitation in the rejection of this
hypothesis existed, all doubt would be removed by the simplicity
and intrinsic probability of the only other physical cause which
can produce the phenomena. The rotation of the globe of the
earth upon an axis passing through its poles, with an uniform
motion from west to east once in twenty- four hours, is a suppo-
sition against which not a single reason can be adduced based on
improbability. Such a motion explains perfectly the apparent
diurnal rotation of the celestial sphere. Being uniform and free
from irregularities, checks, or jolts, it would not be perceivable by
any local derangement of bodies on the surface of the earth, all of
which would participate in it. Observers upon the surface of our
globe would be no more conscious of it, than are the voyagers shut
up in the cabin of a canal boat, or transported above the clouds in
the car of a balloon.

23. It has been shown that a body descending from a great
height does not fall in the true vertical line, which it would if the
earth were at rest, but eastward of it, which it must, if the earth
have a motion of rotation from west to east..

24. An ingenious expedient, by which the diurnal rotation of the
earth is rendered visible, has been conceived and reduced to
experiment by M. Leon Foucault. This contrivance is based upon
the principle, that the direction of the plane of vibration of a
pendulum is not affected by any motion of translation which may

58

FOUCAULT'S EXPERIMENT.

be given to ita point of suspension. Thus, if a pendulum suspended
in a room and put into vibration in a plane parallel to one of the
walls, be carried round a circular table, the plane of its vibration
will continually be parallel to the same wall, and will therefore
vary constantly in the angle it forms with the radius of the table
which is directed to it.

Now, if a pendulum, suspended anywhere so near the pole of
the earth that the circle round the pole may be considered a plane,
be put in vibration in a plane passing through the pole, this plane,
continuing parallel to its original direction as it is carried round
the pole by the earth's rotation, will make a varying angle with
the line drawn to the pole from the position it occupies. After
being carried through a quarter of a revolution it will make an
angle of 90° with the line to the pole, and so on. In fine, the
direction of the pole will appear to be carried round the plane of
vibration of the pendulum.

The same effects will be produced at greater distances from the
pole, but the rate of variation of the angle under the plane of
vibration and the plane of the meridian will be different, owing to
the effects of the curvature of the meridian.

This phenomenon, therefore, being a direct effect of the rotation
of the earth, supplies a proof of the existence of that motion,
attainable without reference to objects beyond the limits of the
globe.

25. Another evidence of the rotation of the earth upon its axis
is derived from the ascertained fact that the planets which hold
places in the solar system similar to that of the earth, do revolve
on axes, in times not very different from that of the earth's
rotation, as has been shown in our tract upon the Planets.

It may, then, be taken as proved that the earth is not fixed and
quiescent, but that it has a rotatory motion round the diameter
which passes through its poles, completing a revolution in a day.

26. Having explained the proofs by which we have arrived at
the knowledge of the globular form of the earth, it may occasion
some surprise that we shall now have to reconsider and modify
that conclusion. In this there is nevertheless nothing unusual.
It is quite in harmony with all the labours of those who devote
themselves to the discovery of the laws of nature.

27. It is the condition of man, and probably of all other finite
intelligences, to arrive at the possession of knowledge by the slow
and laborious process of a sort of system of trial and error. The
first conclusions to which, in physical enquiries, observation
conducts us, are never better than very rough approximations to
the truth. These, being submitted to subsequent comparison with
the originals, undergo a first series of corrections, the more

59

COMMON THINGS — THE EARTH.

prominent and conspicuous departures from conformity being
removed. A second approximation, but still only an approxima-
tion, is thus obtained ; and another and still more severe com-
parison with the phenomena under investigation is made, and
another order of corrections is effected, and a closer approximation
obtained. Nor does this progressive approach to perfect exactitude
appear to have any limit. The best results of our intellectual
labours are still only close resemblances to truth, the absolute
perfection of which is probably reserved for a higher intellectual
state.

These observations will be illustrated by the process of inves-
tigation and discovery in every department of physical science,
but in none so frequently and so forcibly as in that which now
occupies us.

The first conclusions at which we have arrived respecting the
form of the earth is, that it is a globe ; and with respect to its
motion is, that it is in uniform rotation round one of its diameters,
making one complete revolution daily.

28. The first question then which presents itself is, whether this
form and rotation are compatible ? It is not difficult to show, by
the most simple principles of physics, that they are not; that
with such a form such a rotation could not be maintained, and
that with such a rotation such a form could not permanently
continue.

The conclusion that the earth revolves on its axis with a motion
corresponding to the apparent rotation of the firmament, is one
which admits of no modification, and must from its nature be
either absolutely admitted or absolutely rejected. The globular
form imputed to the earth, however, has been inferred from
observations of a general nature, unattended by any conditions of
exact measurement, and which would be equally compatible with
innumerable forms, departing to a very considerable and measurable
extent from that of an exact geometrical sphere or globe.

29. It is a fact familiar to every one that when a body is whirled
round in a circle it has a tendency to fly from the centre. This is
called CENTRIFUGAL FORCE. If a stone be whirled round in a
sling, this tendency is sensibly felt.

By reason of the rotation of the earth on its axis all the matter
composing it, solid and fluid, being carried round the axis in
circles of greater or less radius, has this tendency to fly from the
axis round which it is thus whirled ; and this tendency is stronger
for those parts which are more distant than for those which are
nearer to the common axis.

30. If the globe thus revolving were composed altogether of
matter capable of yielding to the action of such forces, it would

(0

FORM.

obviously assume a form departing from that of an exact sphere.
The parts near the eqiiator would extend themselves to a greater
distance from the axis, those more remote from the equator to a
less distance, and so on, until, at the pole, the matter would not
he at all affected by the rotation. This would be the case if the
globe were formed of matter in a liquid or even in a semi-liquid
or soft state, or if its materials were elastic.

The form it would take would be one resembling an orange or a
turnip. Thus, if N s, fig. 3, be its axis, the equatorial diameter,
q q, will be stretched out to the increased length, Q Q, while the
parts between q q and the poles will be less and less extended the
nearer they are to the poles, 3

The globe would therefore be
changed from the form N q s q.
of a true sphere, to the form
M" Q, s Q, of a flattened globe,
called in geometry an OBLATE
SPHEROID.

31. The elliptic form would
depart more and more from a
true circle as the motion of
rotation is more rapid, so that

between the time of rotation and the degree of ellipticity there is a
fixed relation, such that when the time of rotation is given, the
oval form, or what is the same, the proportion of the equatorial
to the polar diameter, can be computed.

32. It is certain, then, that if the earth were composed of fluid,
soft or elastic matter, it could not continue to retain the form of a
globe, but would become a spheroid, having that degree of ellip-
ticity which would correspond to a motion of rotation, at the rate
of one revolution per day, and it is shown by calculation that this
ellipticity would be such that the equatorial diameter would be
greater than the polar diameter by one three-hundredth part.

33. But the earth, in its present state, is not composed of such
yielding materials, and it becomes a question, what, in that case,
must be the effect of the diurnal rotation on the distribution of land
and water, if the earth were an exact globe.

34. The solid parts of the earth would resist by their cohesion the
tendency of the rotation, to cause them to be accumulated and
heaped up around the equator ; but this would not be the case
with the waters composing the seas and oceans. These, by reason
of their freedom and mobility would yield to the centrifugal force,
and would heap themselves up around the equator, flowing in that
direction from the polar regions of either hemisphere, so that the
necessary consequences of the earth having a form exactly

61

COMMON THINGS — THE EARTH.

globular, and a diurnal rotation, would be that the surface would
consist of two vast polar continents separated by an extensive
equatorial ocean.

Such not being the distribution of land and water on the earth,
it follows that its form cannot be that of an exact globe.

35. It remains, then, to find means to ascertain by direct
measurement and observation, what is the actual form of the
earth.

If a terrestrial meridian were an exact circle, as it would neces-
sarily be if the earth were an exact globe, every part of it would
have the same curvature. But if it were an ellipse, of which the
polar diameter is the lesser axis, it would have a varying curva-
ture, the convexity being greatest at the equator, and least at the
poles. If, then, it can be ascertained by observation, that the
curvature of a meridian is not uniform, but that on the contrary
it increases in going towards the Line, and diminishes in going
towards the Poles, we shall obtain a proof that its form is that of an
oblate spheroid.

To comprehend the method of ascertaining this, it must be
considered that the curvature of circles diminishes as their
diameters are augmented.

If, therefore, a degree of the meridian be observed, and
measured, at different latitudes, and it is found that its length is
not uniformly the same as it would be if the meridian were a
circle, but that it is less in approaching the equator, and greater
in approaching the pole, it will follow that the convexity or curva-
ture increases towards the equator, and diminishes towards the
poles ; and that consequently the meridian has the form, not of
a circle, but of an ellipse, the lesser axis of which is the polar
diameter.

Such observations have accordingly been made, and the lengths
of a degree in various latitudes, from the Line to 66° N. and to
35° S., have been measured, and found to vary from 363000 feet
on the Line to 367000 feet atlat. 66°.

From a comparison of such measurements, it has been ascer-
tained that the equatorial diameter of the spheroid exceeds the
polar by r^th of its length.

Now this is precisely the form, precisely the degree of ellipticity,
which a globe, composed of fluid or soft materials, would assume if
it had a rotation on its axis once in twenty-four hours.

Thus it appears, that the form of the earth, ascertained by
observation, supplies another proof of its diurnal rotation.

36. It is not enough to know the proportions of the earth. It
is required to determine the actual dimensions of the spheroid.
The following are the lengths of the polar and equatorial diameters,

62

DIMENSIONS.

according to the computations of the most eminent and recent
authorities : —

BESSEL.

AIRY.

Miles.
7899-114
7925-604
26-471

1

Miles.
7899-170
7925-648
26-478

1

Equatorial diameter
Absolute difference
Excess of the equatorial expressed in a frac- )
tion of its entire length . • • )

2yy-4u7

299-330

The close coincidence of these results supplies a striking example
of the precision to which such calculations have been brought.

37. The departure of the terrestrial spheroid from the form of an
exact globe is so inconsiderable that, if an exact model of it
turned in ivory were placed before us, we could not, either by
sight or touch, distinguish it from a perfect billiard ball. A
figure of a meridian actually drawn on paper could only be
distinguished from a circle by the most precise measurement.

38. The magnitude of the earth being known with great preci-
sion, the determination of its mass and that of its mean density
become one and the same problem, since the comparison of its
mass with its magnitude will give its mean density, and the
comparison of its mean density with its magnitude will give its
mass.

The methods of ascertaining the mass or actual quantity of
matter contained in the earth are all based upon a comparison of
the gravitating force or attraction which the earth exerts upon an
object with the attraction which some other body, whose mass is
exactly known, exerts on the same object. It is assumed, as a
postulate or axiom in physics, that two masses of matter which at
equal distances exert equal attractions on the same body, must be
equal. But as it is not always possible to bring the attracting and
attracted bodies to equal distances, their attractions at unequal
distances may be observed, and the attractions which they would
exert at equal distances may be thence inferred by the general law
of gravitation, by which the attraction exerted by the same body
increases as the square of the distance from it is diminished.

39. To solve this celebrated problem, it is necessary to bring
the whole mass of the globe into direct comparison with some
object whose mass is exactly known. This was accomplished first
by Dr. Maskelyne, and afterwards by Cavendish. The former
compared the attraction of the earth with that of a mountain in
Perthshire, called Schehallion; the latter compared it with the
attraction of a large ball of metal. Both obtained nearly the

63

COMMON THINGS — THE EARTH.

same result, showing that the earth is a mass of matter about 5|
heavier than an equal volume of water, or, what is the same, that
the mean density of the earth is 5|, or, more exactly, 5*67 times
the density of water.

Among the substances which have nearly the same density as
the earth may be mentioned, arsenic, chromium, chloride of silver,
oxides of copper and zinc, and peroxide of iron.

40. The average weight of each cubic foot of the earth being
5-67 times the weight of a cubic foot of water, is 354-375 Ibs., or
0-1587 of a ton. It follows, therefore, that the total weight of
the earth is more than 6000,000000 billions of tons.

TERRESTRIAL HEAT.

CHAPTER I.

Heat an important agent. — 2. Its local variations. — 3. Diurnal
period. — 4. Annual period. — 5. Mean diurnal temperature. — 6.
Mean mouthly temperature. — 7. Mean annual temperature. — 8.
Temperature of a place. — 9. Isothermal lines. — 10. Isothermal
zones. — 11. Thermal equator. — 12. Second isothermal zone. — 13.
Third. — 14. Fourth. — 15. Fifth and Sixth. — 16. Polar regions. —
17. Climate varies on the same isothermal line. — 18. Constant,
variable, and extreme climates. — 19. Classification of climates. —
20. Extreme temperature in torrid and frigid zones. — 21. Elevation
affects temperature. — 22. Snow line. — 23. Thermal conditions below
the surface. — 24. Stratum of invariable temperature. — 25. Varies
with the latitude. — 26. Its form.— 27. Conditions above it. — 28.
Conditions below it. — 29. Temperature of springs. — 30. Temperature
of greatest density of water. — 31. Thermal condition of seas and
LARDKER'S MUSEUM OP SCIENCE. v 65

No. 32.

TERRESTRIAL HEAT.

lakes. — 32. Thermal condition of a frozen sea. — 33. Process of
thawing. — 34. Depth of stratum of constant temperature. — 35.
Superficial agitation extends only to a small depth.— 36. Great
utility of the state of maximum density. — 37. Variations of tempe-
rature of the air. — 38. Interchange of Equatorial and Polar waters —
39. Polar ice. — 40. Ice-fields. — 41. Icebergs. — 42. Their forms and
magnitude. — 43. Sunken icebergs. — 44. Curious effects of their
superficial fusion. — 45. Depth of Polar Seas. — 46. Cold of Polar
regions.

1. OF all physical agents, heat is the most intimately connected
with the terrestrial economy, the most important to the well-being
of the organised tribes which inhabit the earth, and that upon the
play of which the most remarkable revolutions which our planet
has undergone have been more or less dependent. Since, in some
future numbers of this series, we propose to explain these revo-
lutions, and the traces they have left upon the crust of the globe,
it will be useful to supply at present some preliminary information
as to the laws which regulate the distribution of heat, and the
periodical vicissitudes of temperature, on and below the surface of
the earth, and in the superior strata of the atmosphere.

2. The superficial temperature of the earth varies with the
latitude, gradually decreasing in proceeding from the equator
towards the poles.

It also varies with the elevation of the point of observation,
decreasing in proceeding to heights above the level of the sea, and
varying according to certain conditions below that level, but in
all cases increasing gradually for all depths below a certain
stratum, at which the temperature is invariable.

At a given latitude and a given elevation the temperature varies
with the character of the surface, according as the place of
observation is on sea or land ; and if on land, according to the
nature, productions, or condition of the soil, and the accidents of
the surface, such as its inclination or aspect.

3. At a given place the temperature undergoes two principal
periodic variations, diurnal and annual.

The temperature falling to a minimum at a certain moment
near sunrise, augments until it attains a maximum, at a certain
moment after the sun has passed the meridian. The temperature
then gradually falls until it returns to the minimum in the
morning.

This diurnal thermometric period varies with the latitude, the
elevation of the place, the character of the surface, and with a
great variety of local conditions, which not only affect the hours
of tie maximum, minimum, and mean temperatures, but also the
difference between the maximum and Tm'nJTmim, or the extent of
the variation.
66

THERMAL PERIODS.

4. The annual thermometric period also varies with the latitude,
and with all the other conditions that affect the thermal phenomena.

In order to he enabled to evolve the general thermal laws from
phenomena so complicated and shifting, it is above all things
necessary to define and ascertain those mean conditions or states,
round which the thermometric oscillations take place.

5. The mean diurnal temperature is a temperature so taken
Dehveen the extremes, that all those temperatures which are
superior to it shall exceed it by exactly as much, as those which
are inferior to it shall fall short of it.

This mean temperature may always be obtained by taking the
sum of the temperatures at sunrise, at 2 P.M., and at sunset, and
dividing the result by 3, or more simply still, by adding together
the maximum and minimum temperatures, and taking half their
sum. Whichever of these methods be adopted, the same result
very nearly will be obtained.

6. The mean temperature of the month is found by dividing the
sum of the mean diurnal temperatures by the number of days.

7. The mean temperature of the year may be found by dividing
the sum of the mean monthly temperatures by 12.

It is found that in each climate there is a certain month of
which the mean temperature is identical with the mean tempera-
ture of the year, or very nearly so. This circumstance, when the
month is known, supplies an easy method of observing the mean
temperature of the year.

In our climate this month is October.

8. The mean annual temperature being observed in a given
place for a series of years, the comparison of these means, one with
another, will show whether the mean annual temperature is subject
to variation, and if so, whether the variation is periodic or pro-
gressive. All observations hitherto made and recorded tend to
support the conclusion, that the variations of the mean annual
temperature are, like all other cosmical phenomena, periodic, and
that the oscillations are made within definite limits and definite
intervals.

But even though the period of these variations be not known, a
near approximation to the mean temperature of the place may be
obtained by adding together any attainable number of mean annual
temperatures, and dividing their sum by their number. The pro-
bable accuracy of the result will be greater, the less the difference
between the temperatures computed.

Thus it was found by a comparison of thirty mean annual tem-
peratures at Paris, that the mean was 51°'44, and that the
difference between the greatest and least of the mean annual
temperatures was only 5° '4. It may therefore be assumed that

*2 67

TERRESTRIAL HEAT.

51°'44 does not differ by so much as two- tenths of a degree from
the true mean temperature of that place.

Observation, however, has been hitherto so limited, both as to
extent and duration, that this thermal character has been deter-
mined for a very limited number of places. Indications, never-
theless, have been obtained sufficiently clear and satisfactory to
enable Humboldt to arrive at some general conclusions, which we
shall now briefly state.

9. In proceeding successively along the same meridian from the
equator towards the pole, the mean temperature decreases generally,
but not regularly nor uniformly. At some points it even happens
that the mean temperature augments, instead of decreasing. These
irregularities are caused partly by the varying character of the
surface, over which the meridian passes, and partly by the atmo-
spheric effects produced by adjacent regions, and a multitude of
other causes, local and accidental. As these causes of irregularity
in the rate of decrease of the mean temperature, proceeding from
the equator to the poles, are different upon different meridians, it
is evident that the points of the meridians which surround the
globe, at which the mean temperatures are equal, do not lie upon
a parallel of latitude, as they would if the causes which affect the
distribution of heat were free from all such irregularities and
accidental influences.

If, then, a series of points be taken upon all the meridians
surrounding the globe, having the same mean temperature, the
line upon which such points are placed is called an isothermal line.

Each isothermal line is therefore characterised by the uniform
mean temperature which prevails upon every part of it.

10. Isothermal zones. — The space included between two iso-
thermal lines of given temperatures is called an isothermal zone.

The northern hemisphere has been distributed in relation to its
thermal condition into six zones, limited by the six isothermal
lines, characterised by the mean temperatures, 86°, 74°, 68°, 59°,
50°, 41°, and 32°.

The first zone is a space surrounding the globe, included between
the equator and the isothermal line, whose temperature is 74°.

The mean temperature of the terrestrial equator is subject to
very little variation, and it may therefore be considered as very
nearly an isothermal line. Its mean temperature varies between
the narrow limits of 81|° and 821°.

11. If, iipon each meridian, the point of greatest mean tempe-
rature be taken, the series of such points will follow a certain course
round the globe, which has been designated as the thermal equator.
This line departs from the terrestrial equator, to the extent of ten
or twelve degrees on the north, and about eight degrees on the

68

THERMAL LIXE3 AXD ZONES.

south side, following a sinuous and irregular course, intersecting
the terrestrial equator at about 100° and 160° east longitude. — It
attains its greatest distances north at Jamaica, and at a point in
Central Africa, having a latitude of 15°, and east longitude 10°
or 12°. The greatest mean temperature of the thermal equator
is 86°.

The isothermal line having the temperature of 74° is not very
sinuous in its course, and does not much depart from the tropics.

12. The second zone, which is included between the isothermal
parallels characterised by the mean temperatures of 74a and 68° is
much more sinuous, and includes very various latitudes. At the
points where it intersects the meridians of Europe, it is convex
towards the north, and attains its greatest latitude in Algeria.

13. The third zone, included between the isothermal parallels
which have the mean temperatures of 68° and 59°, passes over the
coasts of France upon the Mediterranean, about the latitude 43°,
and from thence bends southwards, both east and west, on the
east towards Xangasaki and the coasts of Japan, and on the west
to Xatchez on the Mississippi.

14. The fourth zone is included between the parallels of mean
temperatures 59° and 50°. It is convex to the north in Europe,
including the chief part of France, and thence falls to the south
on both sides, including Pekin on the east, and Philadelphia, New
York, and Cincinnati on the west. It is evident from this
arrangement of the fourth thermal zone, that the climate of
Europe is warmer than that of those parts of the eastern and
western continents which have the same latitude.

15. The fifth and sixth zones, included between the mean tem-
peratures of 50° and 32°, are more sinuous, and include latitudes
more various even than the preceding. The thermometric
observations, however, which have been hitherto made in these
regions, are too limited to supply ground for any general inferences
respecting it.

16. The circle whose area is comprised within the isothermal
parallel whose mean temperature is 32% is still less known.
Xevertheless, the results of the observations made by arctic
voyagers within the last twenty years, afford ground for inferring
that the mean temperature of the pole itself must be somewhere
from 13° to 35° below the zero of Fahrenheit, or 45° to 67° below
the temperature of melting Ice.

17. AVhen it is considered how different are the vegetable
productions of places situate upon the same isothermal line,
it will be evident that other thermal conditions besides the mean
temperature must be ascertained before the climate of a place can
be known. Thus London, New York, and Pekin are nearly on

09

TERRESTRIAL HEAT.

the same isothermal line, yet their climates and vegetable pro-
ductions are extremely different.

18. One of the circumstances which produce the most marked
difference in the climates of places having the same mean tem-
perature is the difference between the extreme temperatures. In
this respect climates are classed as constant, variable, and extreme.

Constant climates are those in which the maximum and minimum
monthly temperatures differ but little ; variable climates are those in
which the difference between these extremes is more considerable,
and extreme climates are those in which this difference is very
great.

Constant climates are sometimes called insular, because the
effect of the ocean in equalising the temperature of the air is such
as to give this character to the climates of islands.

19. Examples of the classification of climates. — The following
examples will illustrate this classification of climates : —

Places.

Mean
Temp.

Highest
Mean
Monthly
Temp.

Lowest
Mean
Monthly
Temp.

Difference.

Funchal .

6*9

75°56

62°96

12°60

London ....
Paris ....
St. Malo

50-36
51-08
54-14

66-92
65-30
64-40

41-72
36-14
37-76

25-20
29-16
26-64

New York .
Pekin ....

53-78
53-86

SO -78
84-38

25-34
24-62

55-44
59-76

Funchal offers the example of a constant or insular climate ;
London, Paris, and St. Malo, of a variable ; and New York and
Pekin of an extreme climate.

20. The highest temperature of the air which has been observed
within the torrid zone is 130°, which was observed by MM. Lyon
and Ritchie, in the Oasis of Mourzouk. This, however, is an
extreme and exceptional case, the temperature even in this zone,
rarely exceeding 120°.

The lowest temperatures observed by arctic voyagers in the polar
regions range from 40° to 60° below zero of Fahrenheit, which is
from 70° to 90° below the temperature of melting ice. Thus it
appears that the air at the surface of the earth ranges between
— 60° and + 120°, the extremes differing by 180°.

21. Innumerable phenomena show that the temperature of the
air falls as the elevation increases. The presence of eternal snow

70

SXOW LIXE.

on the elevated parts of mountain ranges, in every part of the
globe, not excepting even the torrid zone, is a striking evidence of
this.

It appears, from observations made upon the declivities of the
vast mountain ranges -which traverse the equatorial regions, that
the decrease of temperature is neither uniform nor regular.

The observations made in temperate climates give results equally
irregular. Gay-Lussac found ascending in a balloon, that the
thermometric column fell one degree for an elevation of about 320
feet. On the Alps the height which produces a fall of one degree
is from 260 to 280 feet, and on the Pyrenees from 220 to 430 feet.
It may be assumed, that in the tropical regions, an elevation of
300 feet, and in our latitudes from 300 to 330 feet, corresponds to
a fall of one degree of temperature on an average, subject, however,
to considerable local variation.

22. It might appear that in those elevations at which the tem-
perature falls to 32°, water cannot exist in the liquid state, and
we might expect that above this limit we should find the surface
invested with perpetual snow. Observation nevertheless shows
such an inference to be erroneous. Humboldt in the equatorial
regions, and M. Leopold de Buch in Norway and Lapland, have
shown that the SXOW-LINE does not correspond with a mean
temperature of 32° for the superficial atmosphere, but that on the
contrary, within the tropics, it is marked by a mean temperature
of about 35°, while in the northern regions, in latitudes of from
60° to 70°, the mean temperature is 26|°.

It appears that the snow-line is determined not so much by the
mean annual temperature of the air as by the temperature of the
hottest month. The higher this temperature is, the more elevated
will be the limit of perpetual snow. But the temperature of the
hottest month depends on a great variety of local conditions, such
as the cloudy state of the atmosphere, the nature of the soil, the
inclination and aspect of the surface, the prevailing winds, &c.

23. At a given place the surface of the ground undergoes a
periodical variation of temperature, attaining a certain maximum
in summer and a minimum in winter, and gradually, but not
regularly or uniformly, augmenting from the minimum to the
maximum, and decreasing from the maximum to the minimum.

The question then arises as to whether this periodic variation
of temperature is propagated downwards through the crust of
the earth, and if so, whether in its descent it undergoes any and
what modifications ?

To explain the phenomena which have been ascertained by
observation, let us express the mean temperature by M, and let the
maximum and minimum temperatures be T and #.

71

TERRESTRIAL HEAT.

If we penetrate to depths more or less considerable, we
shall find that the mean temperature M of the strata will be very
nearly the same as at the surface. The extreme temperatures
T and t, will, however, undergo a considerable change, T de-
creasing, and t increasing. Thus the extremes gradually approach
each other as the depth increases, the mean M remaining nearly
unaltered.

24. A certain depth will therefore be attained at length, when
the maximum temperature T, by its continual decrease, and the
minimum temperature t, by its continual increase, will become
respectively equal to the mean temperature M. At this depth,
therefore, the periodical variations at the surface disappear ; and
the mean temperature M is maintained permanently without the
least change.

This mean temperature, however, though nearly, is not precisely
equal to the mean temperature at the surface. In descending, M
undergoes a slight increase, and at the depth where T and t become
equal to M, and the variation disappears, the mean temperature is
a little higher than the mean temperature of the surface.

25. The depth at which the superficial vicissitudes of temperature
disappear varies with the latitude, with the nature of the surface,
and other circumstances. In our climates it varies from 80 to
100 feet. It diminishes in proceeding towards the equator, and
increases towards the pole. The excess of the permanent tem-
perature at this depth above the mean temperature at the surface,
increases with the latitude.

The same thermometer which has been kept for sixty years in
the vaults of the Observatory at Paris, at the depth of eighty-eight
feet below the surface, has shown, during that interval, the tem-
perature of 11° '82 cent., which is equal to 53£° Fahr., without
A-arying more than half a degree of Fahr., and even this variation,
small as it is, has been explained by the effects of currents of air
produced by the quarrying operations in the neighbourhood of the
Observatory.

26. We must therefore infer, that within the surface of the earth
there exists a stratum of which the temperature is invariable, and
so placed that all strata superior to it are more or less affected by
the thermal vicissitudes of the surface, more so the nearer they
are to the surface, and that this stratum of invariable temperature
has an irregular form, approaching nearer to the surface at some
places, and receding further from it at others, the nature and
character of the surface, mountains, valleys, and plains, seas,
lakes, and rivers, the greater or less distance from the equator or
poles, and a thousand other circumstances, imparting to it varia-
tions of form, which it will require observations and experiments

INVARIABLE STRATUM.

much more long-continued and extensive than have hitherto been
made, to render manifest.

27. The thennometric observations on the periodical changes
which take place above the stratum of invariable temperature are
not so numerous as could be desired ; nevertheless, the following
general conditions have been ascertained, especially in the middle
latitudes of the northern hemisphere : —

1. The diurnal variations of temperature are not sensible to a
greater depth than 3| feet.

2. The difference between the extreme temperatures of the
strata decreases in geometrical progression for depths measured in
arithmetical progression, -or nearly so.

Thus, at the depth of twenty-five feet the difference between the
extreme temperatures T and t, is reduced to two degrees ; at fifty
feet it is diminished to the fifth of a degree, and at sixty or eighty
feet to the fiftieth of a degree.

3. Since the effects of the superficial variation must require a
certain time to penetrate the strata, it is evident that the epoch at
which each stratum attains its maximum and minimum tempera-
tures will be different from those at which the other strata and the
surface attain them. The lower the strata the greater will be
the difference between the times of attaining those limits as com-
pared with the surface.

28. The same uniformity of temperature which prevails in the
invariable stratum is also observed at all greater depths ; but the
temperature increases with the depth. Thus, each successive
stratum, in descending, has a characteristic temperature, which
never changes. The rate at which this temperature augments
with the depth below the invariable stratum is extremely different
in different localities. In some there is an increase of one degree
for every thirty feet, while in others the same increase corresponds
to a depth of 100 feet. It may be assumed, in general, that an
increase of one degree of temperature will take place for every fifty
or sixty feet of depth.

29. The permanency of the temperatures of the inferior strata is
rendered manifest by the uniformity of the temperature of springs,
of which the water rises from any considerable depths. At all
seasons of the year the water of such springs maintains the same
uniform temperature.

It may be assumed that the temperature of the water proceeding
from such springs is that of the strata from which they rise. In
these latitudes it is found in general to be a little above the
mean temperature of the air for ordinary springs, that is from
those which probably rise from strata not below the invariable
stratum. In higher latitudes the excess of temperature is

TERRESTRIAL HEAT.

greater, a fact which, is in accordance with what has been already
explained.

It has not been certainly ascertained whether the hot springs,
some of which rise to a temperature little less than that of
boiling water, derive their heat from the great depth of the strata
from which they rise, or from local conditions affecting the strata.
The uniformity of the temperature of many of them appears to
favour the former hypothesis ; but it must not be forgotten that
other geological conditions besides mere depth may operate with
the same permanency and regularity.

30. It is well known that bodies in general expand when they
are heated, and contract when they are c*ooled. Water, when its
temperature falls below 40°, presents a most remarkable exception
to this general law. It continues in accordance with the law to
contract, though in a continually diminished degree, from 40° to
38° *8, and when it arrives at the latter temperature the contraction
ceases altogether. "When its temperature falls below 3S0tS, instead
of contracting, it expands, and it continues to expand until it is
frozen, which takes place at 32°.

It follows from this that the density of water, or its weight
bulk for bulk compared with itself at different temperatures is
greatest when it has the temperature of 380<8, which is therefore
called the temperature of greatest density.*

31. This anomalous quality of water when its temperature falls
below 38° '8 Fahr. and its consequent maximum density at that
temperature, is attended with most remarkable and important
consequences in the phenomena of the waters of the globe, and in
the economy of the tribes of organised creatures which inhabit
them. It is easy. to show that, but for this provision, exceptional
as it feeems, disturbances would take place, and changes ensue,
which would be attended with effects of the most injurious
description in the economy of nature.

If a large collection of water, such as an ocean, a sea, or a lake,
be exposed to continued cold, so that its superficial stratum shall
have its temperature constantly reduced, the following effects will
be manifested.

The superficial stratum falling in temperature, will become
heavier, volume for volume, than the strata below it, and will
therefore sink, the inferior strata rising and taking its place.
These in their turn being cooled will sink, and in this manner
a continual system of downward and upward currents will be
maintained, by means of which the temperature of the entire mass
of liquid will be continually equalised and rendered uniform from

* See Tract on Water (5).
74

SEAS AND LAKES.

the surface to the bottom. This -will continue so long as the
superficial stratum is rendered heavier, volume for volume, than
those below it, by being lowered in temperature. But the super-
ficial stratum, and all the inferior strata, will at length be reduced
to the uniform temperature of 38°'8. After this the system of
currents upwards and downwards will cease. The several strata
will assume a state of repose. When the superficial stratum is
reduced to a temperature lower than 38° '8 (which is that of the
maximum density of water), it will become lighter, volume for
volume, instead of being heavier than the inferior strata. It will
therefore float upon them. The stratum immediately below it,
and in contact with it, will be reduced in temperature, but in a
less degree ; and in like manner a succession of strata, one below
the other, to a certain depth, will be lowered in temperature by
the cold of those above them, but each stratum being lighter than
those below, will remain at rest, and no interchange by currents
will take place between stratum and stratum. If water were a
good conductor of heat, the cooling effect of the surface would
extend downwards to a considerable depth. But water being, on
the contrary, an extremely imperfect conductor, the effect of the
superficial temperature will extend only to a very limited dep{h ;
and at and below that limit, the uniform temperature of 38° '8,
that of the greatest density, will be maintained.

This state of repose will continue until the superficial stratum
falls to 32° *, after which it will be congealed. When its surface
is solidified, if it be still exposed to a cold lower than 32°, the
temperature of the surface of the ice will continue to fall, and this
reduced temperature will be propagated downward, diminishing,
however, in degree, so as to reduce the temperature of the stratum
on which the ice rests to 32°, and therefore to continue the process
of congelation, and to thicken the ice.

If ice were a good conductor of heat, this downward process of
congelation would be continued indefinitely, and it would not be
impossible that the entire mass of water from the surface to the
bottom, whatever be the depth, might be solidified. Ice, however,
is nearly as bad a conductor of heat as water, so that the super-
ficial temperature can be propagated only to a very inconsiderable
depth ; and it is found accordingly, that the crust of ice formed
even on the surface of the polar seas, does not exceed the average
thickness of twenty feet.

32. The thermal condition, therefore, of a frozen sea, is a state
of molecular repose, as absolute as if the whole mass of liquid were
solid. The temperature at the surface of the ice being below the

* For sea water the freezing point is 284°.

75

TERKEST111AL HEAT.

freezing point, increases in descending until it rises to the freezing
point, at the stratum where the ice ceases, and the liquid water
commences. Below this the temperature still augments until it
reaches 3S°'8, the temperature of maximum density of water, and
this temperature is continued uniform to the bottom.

33. Let us now consider what effects will be produced, if the
superficial strata be exposed to an increase of temperature. After
the fusion of the ice, the temperature of the surface will gradually
rise from 32° to 38°-8, the temperature of greatest density. When
the superficial stratum rises above 32°, it will become heavier
than the stratum under it, and an interchange by currents, and a
consequent equalisation of temperature, will take place, and this
will continue until the superficial stratum attain the temperature
of 38° -8, when the temperature of the whole mass of water from
the surface to the bottom will become uniform.

After this a further elevation of the temperature of the super-
ficial stratum will render it lighter than those below it, and no
currents will be produced, the liquid remaining at rest ; and this
state of repose will continue so long as the temperature continues
to rise.

Every fall of the superficial temperature, so long as it con-
tinues above 38°'8, will be attended with an interchange of
currents between the superficial and those inferior strata whose
temperature is above 38°*8, and a consequent equalisation of
temperature.

34. It appears, therefore, to result as a necessary consequence
from what has been explained, and this inference is fully confirmed
by experiment and observations, that there exists in oceans, seas,
and other large and deep collections of water, a certain stratum,
which retains permanently, and without the slightest variation,
the temperature of 38° '8, which characterises the state of greatest
density, and that all the inferior strata equally share this tempera-
ture. At the lower latitudes, the superior strata have a higher,
at the higher latitudes a lower temperature, and at a certain mean
latitude the stratum of invariable temperature coincides with the
surface.

In accordance with this, it has been found by observation that
in the torrid zone, where the superficial temperature of the sea is
about 83°, the temperature decreases with the depth until we
attain the stratum of invariable temperature, the depth of which,
upon the Line, is estimated at about 7000 feet. The depth of this
stratum gradually diminishes as the latitude increases, and the
limit at which it coincides with the surface is somewhere between
53° and 60°. Above this the temperature of the sea increases as
the depth of the stratum increases, until we sink to the stratum
7G

TEMPERATURE OF OCEAN.

of invariable temperature, the depth of which at the highest
latitudes at which observations have been made, is estimated at
about 4500 feet.

35. It might be imagined that the temperature of the surface
would be propagated downwards, and that a thermal equalisation
might therefore be produced by the intermixture of the superior with
the inferior strata, arising from the agitation of the surface of the
waters by atmospheric commotions. It is found, however, that
these effects, even in the case of the most violent storms and
hurricanes, extend to no great depth, and that while the surface
of the ocean is furrowed by waves of the greatest height and
extent, the inferior strata are in the most absolute repose.

36. If water followed the general law, in virtue of which all
bodies become more dense as their temperature is lowered, a con-
tinued frost might congeal the ocean from its surface to the
bottom, and certainly would do so in the polar regions ; for in that
case the system of vertical currents, passing upwards and down-
wards, and producing an equalisation of temperature, which has
been shown to prevail above 38°*8, would equally prevail below
that point, and consequently the same equalisation of temperature
would be continued, until the entire mass of water, from the
surface to the bottom, would be reduced to the point of congela-
tion, and would consequently be converted into a solid mass, all
the organised tribes inhabiting the waters being destroyed.

The existence of a temperature of maximum density at a point
of the thermometric scale above the point of congelation of water,
combined with the very feeble conducting power of water,
whether in the liquid or solid state, renders such a catastrophe
impossible.

37. The air is subject to less extreme changes of temperature at
sea than on land. Thus, in the torrid zone, while the temperature
on land suffers a diurnal variation amounting to 10°, the extreme
diurnal variation at sea does not exceed 3£°. In the temperate
zone the diurnal variation at sea is limited generally to about 5|°,
while on continents it is very various and everywhere consider-
able. In different parts of Europe it varies from 20° to 25°.

At sea as on land the time of lowest temperature is that of
sunrise, but the time of greatest heat is about noon, while on
land it is at two or three hours after noon.

On comparing the temperature of the air at sea with the super-
ficial temperature of the water, it has been found that between the
tropics the air, when at its highest temperature, is warmer than
the water, but that its mean diurnal temperature is lower than
that of the water.

In latitudes between 25* and 50° the temperature of the air is

77

TERRESTRIAL HEAT.

very rarely higher than that of the water, and in the polar
regions the air is never found as -warm as the surface of the
water. It is, on the contrary, in general at a very much lower
temperature.

38. Much uncertainty prevails as to the thermal phenomena
manifested in the vast collections of water which cover the greater
part of the surface of the globe. It appears, however, to be
admitted that the currents caused by the difference of the pressures
of strata at the same level in the polar and equatorial seas, produce
an interchange of waters, which contributes in a great degree to
moderate the extreme thermal effects of these regions, the current
from the pole reducing the temperature of the equatorial waters,
and that from the line raising the temperature of the polar waters
and contributing to the fusion of the ice. A superficial current
directed from the line towards the poles carries to the colder
regions the heated waters of the tropics, while a counter current
in the inferior strata carries from the poles towards the line the
colder waters. Although the prevalence of these currents may be
regarded as established, they are nevertheless modified, both in
their intensity and direction, by a multitude of causes connected
with the depth and form of the bottom, and the local influence of
winds and tides. ,

39. The stupendous mass of water in the solid state which forms
an eternal crust encasing the regions of the globe immediately
around the poles, presents one of the grandest and most imposing
classes of natural phenomena. The observations and researches of
Captain Scoresby have supplied a great mass of valuable informa-
tion in this department of physical geography.

40. Upon the coasts of Spitzbergen and Greenland vast fields of
ice are found, the extent of which amounts to not less than twelve
to fifteen hundred square miles, the thickness varying from twenty
to twenty-five feet. The surface is sometimes so even that a
sledge can run without difficulty for an hundred miles in the
same direction. It is, however, in some places, on the contrary,
as uneven as the surface of land, the masses of ice collecting in
columns and eminences of a variety of forms, rising to heights of
from twenty to thirty feet, and presenting the most striking and
picturesque appearances. These prodigious crystals sometimes
exhibit gorgeous tints of greenish blue, resembling certain varieties
of topaz, and sometimes this is varied by a thick covering of snow
upon their summits, which gives them the appearance of cliffs of
chalk or white marble, marked by an endless variety of form and
outline.

41. These vast ice-fields are sometimes suddenly broken, by the
pressure of the subjacent waters, into fragments presenting a

78

ICE-FIELDS — ICEBERGS.

surface of from 100 to 200 hundred square yards. These being
dispersed, are carried in various directions by currents, and
sometimes by the effect of intersecting currents they are brought
into collision 'with a fearful crash. A ship, which might chance
in such a case to be found between them could no more resist their
force than could a glass vessel the effect of a cannon ball. Terrible
disasters occur from time to time from this cause. It is by the
effects of these currents upon the floating masses of broken ice
that these seas are opened to the polar navigators. It is thus that
whalers are enabled to reach the parallels from 70° to 80°, which are
the favourite resort of those monsters of the deep which they pursue.

42. Sometimes after such collisions new icebergs arise from the
fragments which are heaped one upon another, " Pelion on Ossa,"
more stupendous still than those which have been broken. In such
cases the masses which result assume forms infinitely various,
rising often to an elevation of thirty to fifty feet above the surface
of the water; and since the weight of ice is about four-fifths
of the weight of its own bulk of water, it follows that the
magnitude of these masses submerged is four times as great as
that which is above the surface. The total height of these floating
icebergs, therefore, including the part submerged, must be from
150 to 250 feet.

43. It happens sometimes that two such icebergs resting on the
extremities of a fragment of ice 100 or 120 feet in length, keep it
sunk at a certain depth below the surface of the water. A vessel
in such cases may sail between the icebergs and over the sunken
ice ; but such a course is attended with the greatest danger, for if
any accidental cause should detach either of the icebergs which
keep down the intermediate mass while the ship is passing, the
latter by its buoyancy will rise above the surface, and will throw
up the ship with irresistible force.

44. Icebergs are observed in Baffin's Bay of much greater magni-
tude than off the coast of Greenland. They rise there frequently
to the height of 100 to 130 feet above the surface, and their total
height, including the part immersed, must therefore amount to
500 or 650 feet. These masses appear generally of a beautiful
blue colour, and having all the transparency of crystals. During
the summer months, when the sun in these high latitudes never
sets, a superficial fusion is produced, which causes immense
cascades, which, descending from their summit and increasing in
volume as they descend, are precipitated into the sea in parabolic
curves. Sometimes, on the approach of the cold season, these
liquid arches are seized and solidified by the intensity of the cold
without losing their form, and seem as if caught in their flight
between the brink from which they were projected and the surface,

79

TERRESTRIAL HEAT.

and suddenly congealed. These stupendous arches, however, do
not always possess cohesion in proportion to their weight, and
after augmenting in volume to a certain limit, sink under their
weight, and, breaking with a terrific crash, fall into the sea.

45. The depth of the seas off the coast of Greenland is not con-
siderable. Whales, being harpooned, often plunge in their agony
to the bottom, carrying with them the harpoon and line attached
to it. "When they float they bear upon their bodies evidence of
having reached the bottom by the impression they retain of it,
and the length of line they carry with them in such cases shows
that depth does not exceed 3000 or 4000 feet. About the middle
of the space between Spitzbergen and Greenland the soundings
have reached 8000 feet without finding bottom.

46. The degree of cold of the polar regions, like the temperature
of all other parts of the globe, depends on the extent and depth of
the seas. If there be extensive tracts of surface not covered by
water, or covered only by a small depth, the influence of the
water in moderating and equalising the temperature is greatly
diminished. Hence it is that the temperature of the south polar
regions is more moderate than that of the north. After passing
the latitude of the New Orcades and the New Shetlands, which
form a barrier of ice, the navigator enters an open sea, which,
according to all appearance, extends to the pole. Much, however,
still remains to be discovered respecting the physical condition of
these regions.

TERRESTRIAL HEAT.

CHAPTEE II.

47. Sources of external heat. — 43. Solar heat.— 49. Its quantity ascer-
tained.— 50. Heat at sun's surface. — 51. Temperature of celestial
spaces. — 52. Quantity of heat supplied by them. — 53. Summary of
heat supplied. — 54. Winds. — 55. Produced by rarefaction and com-
pression.— 56. Sudden condensation of vapour. — 57. Hurricanes. —
58. Their cause. — 59. Waterspouts. — 60. Evaporation. — 61. Satura-
tion of air. — 62. May arise from intermixing strata.— 63. Effect of
pressure. — 64. Dew. — 65. Hoarfrost. — 66. Artificial ice. — 67. Fogs
and clouds. — 68. Rain.— 69. Its quantity. — 70. Snow. — 71. Hail. —
72. Hailstones.— 73. Extraordinary hailstones.

47. WHATEVER may be the sources of internal heat, the globe
of the earth would, after a certain time, be reduced to a state of
absolute cold, if it did not receive from external sources ths
quantity of heat necessary to repair its losses. If the globe were

LARDXER'S MUSEUM OF SCIENCE. o 81

No. 36.

TERRESTRIAL HEAT.

suspended in space, all other bodies from which heat could be
supplied to it being removed, the heat which now pervades tlio
earth and its surrounding atmosphere would be necessarily dis-
sipated by radiation, and would thus escape into the infinite
depths of space. The temperature of the atmosphere, and those
of the successive strata, extending from the surface to the centre of
the globe, would thus be continually and indefinitely diminished.

As no such fall of temperature takes place, and as, on the con-
trary, the mean temperature of the globe is maintained at an
invariable standard, the variations incidental to season and climate
being all periodical, and producing in their ultimate result a
mutual compensation, it remains to be shown from what sources
the heat is derived which maintains the mean temperature of
the globe at this invariable standard, notwithstanding the large
amount of heat which it loses by radiation into the surrounding
space.

All the bodies of the material universe, which are distributed
in countless numbers throughout the infinitude of space, are sources
of heat, and centres from which that physical agent is radiated in
all directions. The effect produced by the radiation of each of
these diminishes in the same proportion as the square of its
distance increases. The fixed stars are bodies analogous to our
sun, and at distances so enormous that the effect of the radiation
of any individual star is altogether insensible. When, however,
it is considered that the multitude of these stars spread over the
firmament is so prodigious that in some places many thousand
are crowded together within a space no greater than that occupied
by the disc of the full moon, it will not be matter of surprise
that the feebleness of thermal influence, due to their immense
distances, is compensated to a great extent by their countless
number; and that, consequently, their calorific effects in those
regions of space through which the earth passes in its annual
course is, as will presently appear, not only far from being insen-
sible, but is very little inferior to the calorific power of the sun
itself.

"We are, then, to consider the waste of heat which the earth
suffers by radiation as repaired by the heat which it receives from
two sources, the sun and the stellar universe ; and it remains to
explain what is the actual quantity of heat thus supplied to the
earth, and what proportion of it is due to each of these causes.

48. An elaborate series of experiments were made by M. Pouillet,
and concluded in 1838, with the view of obtaining, by means
independent of all hypothesis as to the physical character of the
sun, an estimate of the actual calorific power of that luminary.
A detailed report of these observations and experiments, and an
82

SOLAR HEAT.

elaborate analysis of the results derived from them, appeared in
the Transactions of the Academy of Sciences of Paris for that
year.

It would be incompatible with the elementary nature and the
consequent limits of this work, to enter into the details of these
researches. We shall, therefore, confine ourselves here briefly to
state their results.

When the firmament is quite unclouded, the atmosphere absorbs
about one-fourth of the heat of those solar rays which enter it
vertically. A greater absorption takes place for rays which enter
it obliquely, and the absorption is augmented in a certain
ascertained proportion, with the increase of obliquity. It results
from the analysis of the results obtained in the researches of
M. Pouillet, that about forty per cent, of all the heat transmitted
by the sun to the earth is absorbed by the atmosphere, and that
consequently only sixty per cent, of this heat reaches the surface.
It must, however, be observed that a part of the radiant heat,
intercepted by the atmosphere, raising the temperature of the air,
is afterwards transmitted, as well by radiation as by contact, from
the atmosphere to the earth.

By means of direct observation and experiment made with
instruments contrived by him, called pyrheliometers, by means of
which the heat of the solar radiation was made to affect a known
weight of water at a known temperature, M. Pouillet ascertained
the actual quantity of heat which the solar rays would impart per
minute to a surface of a [given magnitude, on which they would
fall vertically. This being determined, it was easy to calculate
the quantity of heat imparted by the sun in a minute to the
hemisphere of the earth which is presented to it, for that quantity
is the same which would be imparted to the surface of the great
circle which forms the base of that hemisphere, if the solar rays
were incident perpendicularly upon it.

49. In this manner it was ascertained, that if the total quantity
of heat which the earth receives from the sun in a year were
uniformly diffused over all parts of the surface, and were com-
pletely absorbed in the fusion of a shell of ice encrusting the
globe, it would be sufficient to liquefy a depth of 100 feet of such
shell.

Since a cubic foot of ice weighs 54 lb., it follows that the
average annual supply of heat received from the sun per square
foot of the earth's surface would be sufficient to dissolve 5400 lb.
weight of ice.

This fact being ascertained supplies the means of calculating
the quantity of heat emitted from the surface of the sun, inde-
pendently of any hypothesis respecting its physical constitution.

o2 83

TERRESTRIAL HEAT.

It is evident from the uniform calorific effects produced by the
solar rays at the earth, while the sun revolves on its axis exposing
successively every side to the earth in the course of about twenty-
five days, that the calorific emanation from all parts of the solar
surface is the same. Assuming this, then, it will follow, that the
heat which the surface of a sphere surrounding the sun at the
distance of the earth would receive would be so many times more
than the heat received by the earth as the entire surface of such
sphere would be greater than that part of it which the earth
would occupy. The calculation of this is a simple problem of
elementary geometry.

But such a spherical surface surrounding the sun and con-
centrical with it, would necessarily receive all the heat radiated
by that luminary, and cue result of the calculation proves that the
quantity of heat emitted by the sun per minute is such as would
suffice to dissolve a shell of ice enveloping the sun, and having a
thickness of 38^ feet ; and that the heat emitted per day would
dissolve such a shell, having a thickness of 55,748 feet, or about
10| miles.

50. The most powerful blast furnaces do not emit for a given
extent of fire surface more than the seventh part of this quantity
of heat. It must therefore be inferred that each square foot of the
surface of the sun emits about seven times as much heat as is issued
by a square foot of the fire surface of the fiercest blast furnace.

51. When the surface of the earth during the night is exposed to
an unclouded sky, an interchange of heat takes place by radiation.
It radiates a certain part of the heat which pervades it, and it
receives, on the other hand, the heat radiated from two sources, —
1 st, from the strata of atmosphere, extending from the surface of
the earth to the summit of the atmospheric column ; and 2nd,
from the celestial spaces, which lie outside this limit, and which
receive their heat from the radiation of the countless numbers of
suns which compose the stellar universe. M. Pouillet, by a series of
ingeniously contrived experiments and observations, made with the
aid of an apparatus contrived by him, called an actinometer,
has been enabled to obtain an approximate estimate of the pro-
portion of the heat received by the earth which is due to each of
these two sources, and thereby to determine the actual temperature
of the region of space through which the earth and planets move.
The objects and limits of this work do not permit us to give the
details of these researches, and we must therefore confine ourselves
here to the statement of their results.

It appears from the observations, that the actual temperature of
space is included between the minor limit of 315° and the major
limit of 207° below the temperature of melting ice, or between
84

SUPPLY OF HEAT.

—283° and —175° Fahr. At what point between these limits the
real temperature lies, is not yet satisfactorily ascertained, but
M. Pouillet thinks that it cannot differ much from — 224° Fahr.

52. It is proved from these results, that the quantity of heat
imparted to the earth in a year, by the radiation of the celestial
space, is such as would liquefy a spherical shell of ice, covering
the entire surface of the earth, the thickness of which would be
85 feet, and that forty per cent, of this quantity is absorbed by
the atmosphere.

Thus the total quantity of heat received annually by the earth
is such as would liquefy a spherical shell of ice 185 feet thick, of
which 100 feet are due to the sun, and 85 feet to the heat which
emanates from the stellar universe.

The fact that the celestial spaces supply very little less heat to
the earth annually than the sun, may appear strange, when the
very low temperature of these spaces is considered, a temperature
180° lower than the cold of the pole during the presence of the
sun. It must, however, be remembered that while the space
from which the solar radiation emanates, is only that part of the
firmament occupied by the disc of the sun, that from which the
celestial radiation proceeds is the entire celestial sphere, the area
of which is about five million times greater than the solar disc.
It will therefore cease to create surprise, that the collective effect
of an area so extensive should be little short of that of the sun.

The calorific effect due to the solar radiation, according to the
calculations and observations of M. Pouillet, exceeds that which
resulted from the formulae of Poisson. These formulae were
obtained from the consideration of the variation of the temperature
of the strata of the earth at different depths below the surface.
M. Pouillet thinks that the results proceeding from the two
methods would be brought into accordance if the influence of the
atmosphere on solar heat, which, as appears from what has been
explained, is very considerable, could be introduced in a more
direct manner into Poisson's formulae.

53. In fine, therefore, the researches of M. Pouillet give the
following results, which must be received as mere approximations
subject to correction by future observation :

1st. That the sun supplies the earth annually with as much
heat as would liquefy 100 feet thick of ice covering the entire
globe.

2nd. That the celestial spaces supply as much as would liquefy
85 feet thick.

3rd. That forty per cent of the one and the other supply is
absorbed by the atmosphere, and sixty per cent received by the
Httfa.

85

TERKESTEIAL HEAT.

4th. That of the heat radiated by the earth, ninety per cent,
is intercepted by the atmosphere, and ten per cent, dispersed
in space.

5th. That the heat evolved on the surface of the sun in a day
would liquefy a shell of ice 10^ miles thick, enveloping the sun,
and the intensity of the solar fire is seven times greater than that
of the fiercest blast furnace.

6th. That the temperature of space outside the atmosphere of
the earth is 256° below that of melting ice.

7th. That the solar heat alone, constitutes only two-thirds of
the entire quantity of heat supplied to the earth to repair its
thermal losses by terrestrial radiation ; and that without the heat
supplied by stellar radiation, the temperature of the earth would
fall to a point which would be incompatible with organic life.

54. No meteorological phenomenon has had so many observers,
and there is none of which the theory is so little understood, as
the winds. The art of navigation has produced in every seaman
an observer, profoundly interested in the discovery of the laws
which govern a class of phenomena, upon the knowledge of which
depends not only his professional success but his personal security,
and the lives and property committed to his charge.

The chief part of the knowledge which has been collected
respecting the causes which produce these atmospheric currents
is derived, nevertheless, much more from the comparison of
the registers of observatories than from the practical experience
of mariners.

55. Winds are propagated either by compression or by rarefac-
tion. In the former case they are developed in the same direction
in which they blow ; in the latter case they are developed in the
contrary direction. To render this intelligible, let us imagine a
column of air included in a tube. If a piston inserted in one end
of the tube be driven from the mouth inwards, the air contiguous
to it will be compressed, and this portion of air will compress the
succeeding portion, and so on ; the compression being propagated
from the end at which the piston enters toward the opposite end.
The remote end being open, the air will flow in a current driven
before the piston in the same direction in which the compression is
propagated.

If we imagine, on the other hand, a piston inserted in the tube
at some distance from its mouth, to be drawn outwards toward
the mouth, the air behind it will expand into the space deserted
by the piston, and a momentary rarefaction will be produced. The
next portion of air will in like manner follow that which is next
the piston, the rarefaction which begins at the piston being pro-
pagated backwards through the tube in a direction contrary to the
$6

HUBBICANES.

motion of the piston and that of the current of air which
follows it.

What is here supposed to take place in the tube is exhibited on
a larger scale in the atmosphere. Any physical cause which
produces a compression of the atmosphere from north to south will
produce a north wind ; and any cause which produces a rarefac-
tion from north to south will produce a south wind.

56. Of all the causes by which winds are produced, the most
frequent is the sudden condensation of vapour suspended in tho
atmosphere. In general the atmosphere above us consists of a
mixture of air properly so called, and water, either in the state of
vapour, or in a vesicular state, the nature and origin of which has
not yet been clearly ascertained. In either case its sudden con-
version into the liquid state, and its consequent precipitation to
the earth, leaves the space it occupied in the atmosphere a vacuum,
and a corresponding rarefaction of the air previously mixed with
the vapour ensues. The adjacent strata immediately rush in to
re-establish the equilibrium of pneumatic pressure, and winds are
consequently produced.

The propagation of winds by rarefaction manifested in directions
contrary to that of the winds themselves, is common in the North
of Europe. Wargentin gives various examples of this. When a
west wind springs up, it is felt, he observes, at Moscow before it
reaches Abo, although the latter city is four hundred leagues west
of Moscow, and it does not reach Sweden until after it has passed
over Finland.

57. The intertropical regions are the theatre of hurricanes. It
is there only that these atmospheric commotions are displayed in
all their terrors. In the temperate zones tempests are not only
more rare in their occurrence but much less violent in their force.
In the circumpolar zone the winds seldom acquire the force which
would justify the title of a storm.

The hurricanes of the warm climates spread over a considerable
width, and extend through a still more considerable length. Some
are recorded which have swept over a distance of four or five
hundred leagues with a nearly uniform violence.

It is only by recounting the effects produced by these vast com-
motions of the atmospheric ocean, that any estimate can be formed
of the force which air, attenuated and light as that fluid is, may
acquire when a great velocity is given to it. In hurricanes such as
that which took place at Guadaloupe on the 25th July, 1825, houses
the most solidly constructed were overthrown. A new building
erected in the most durable manner by the government was razed
to the ground. Tiles carried from the roof were projected against
thick doors with such force as to pass through them like a cannon

87

TKllRESTItlAL HEAT.

hall. A plunk of wood 3| feet long, 9 inches wide, and an incli
thick, was projected with such force as to cut through a branch of
palm wood 18 inches in diameter. A piece of wood 15 feet long
and 8 inches square in its cross section, was projected upon a
hard paved road, and buried to a depth of more than three feet
in it. A strong iron gate in front of the governor's house was
carried away, and three twenty-four pounders erected on the fort
were dismounted.

58. These effects, prodigious as they are, all arise from mechani-
cal causes. There is no agent engaged in hurricanes more subtle
than the mechanical force of air in motion, and since the weight
and density of the air suffer no important change, the vast momen-
tum manifested by such effects as those described above, must be
ascribed altogether to the extraordinary velocity imparted to the
air by the magnitude of the local vacuum produced, as already
stated, by the sudden condensation of vapour. To form some
approximate estimate of this it may be observed that, in the inter-
tropical regions, a fall of rain often takes place over a vast extent
of surface, sufficient in quantity to cover it with a stratum of
water more than an inch in depth. If such a fall of rain were to
take place over the extent of a hundred square leagues, as some-
times happens, the vapour from which such a quantity of liquid
would be produced by condensation would, at the temperature of
only 50°, occupy a volume of 100000 times greater than that of
the liquid: and, consequently, in the atmosphere over the surface
of 100 square leagues it would fill a space 9000 feet, or nearly two
miles in height. The extent of the vacuum produced by its con-
densation would be a volume nearly equal to 200 cubic miles, or
to the volume of a column whose base is a square mile and whose
height is 200 miles.

59. The phenomena, called water or land spouts according as
they are manifested at sea or on land, consist apparently of dense
masses of aqueous vapour and air, having at once a gyratory and
progressive motion, and resembling in form a conical cloud, the
base of which is presented upwards, and the vertex of which
generally rests upon the ground, but sometimes assumes a contrary
position. This phenomenon is attended with a sound like that of a
waggon rolling on a rough pavement.

Violent mechanical effects sometimes attend these meteors.
Large trees torn up by the roots, stripped of their leaves, and ex-
hibiting all the appearances of having been struck by lightning,
are projected to great distances. Houses are often thrown down,
unroofed, and otherwise injured or destroyed, when they lie in the
course of these meteors, llain, hail, and frequently globes of fire,
like the ball lightning, also accompany them.
83

WATEUSroUTS.

Fig. l.

The various appearances exhibited by water-spouts are repre-
sented in fig. 1.

Xo satisfactory theory has yet connected these phenomena with
the general laws of physics.

60. If the surface of a sea, lake, or other large collection of
water were exposed to the atmo-
sphere consisting of pure air

without any admixture of vapour,
evaporation would immediately
commence, and the vapour de-
veloped at the surface of the
water would ascend into and mix
with the atmosphere. The pres-
sure of the atmosphere would then
be the sum of the pressures of the
atmosphere, properly so called,
and of the vapour suspended in
it, since neither of these elastic
fluids can augment or diminish
the pressure of the other.

The vapour developed from the surface of the water thus
mingling with the atmosphere, acquires a common temperature
with it. This vapour, therefore, receiving thus from the air with
which it is intermixed more or less heat, after having passed into
the vaporous state, is superheated vapour. It has, therefore, a
greater temperature than that which corresponds to its density, or,
what is the same, it has a less density than that which corresponds
to its temperature. Such vapour may therefore lose temperature
to a certain extent without being condensed.

61. But if the same atmosphere continue to be suspended over
the surface of water, the process of evaporation being continued,
the quantity of vapour which rises into the air and mingles with
it will be continually increased until it acquires the greatest
density which is compatible with its temperature. Evaporation
must then cease, and the air is said to be saturated with vapour.

If the temperature of the air in such case rise, evaporation will
recommence and will continue until the vapour shall acquire the
greatest density compatible with the increased temperature, and
will then cease, the air being, as before, saturated.

But if the temperature fall, the greatest density of vapour
compatible with it being less than at the higher temperature, a
part of the vapour must be condensed, and this condensation must
continue until the vapour suspended in the air shall be reduced to
that state of density which is the greatest compatible with the
reduced temperature.

TEilEESTHIAL HEAT.

A fluid so light and mobile as the atmosphere, can never remain
long in a state of repose, and the column of air suspended over
the surface of any collection of water however extensive, is suhject
to frequent change. In general, therefore, before any such
portion of the atmosphere becomes saturated by evaporation, it is
removed and replaced by another portion. It happens, conse-
quently, that the atmosphere rarely becomes saturated by the
immediate effect of evaporation.

62. The state of saturation is, however, often attained either by
loss of temperature, or by the intermixture of strata of air of
different temperatures and differently charged with vapours.
Thus, if air which is below the point of saturation suffer a loss of
heat, its temperature may fall to that point which is the highest
compatible with the density of the vapour actually suspended in it.
The air will then become saturated, not by receiving any increased
quantity of vapour, but by losing that caloric by which the vapour
it contained was previously superheated.

If two strata of air at different temperatures, and both charged
with vapour to a point below saturation, be intermingled, they
will take an intermediate temperature, that which had the higher
temperature imparting a portion of its heat to that which had a
lower temperature. The vapour with which they were previously
charged will likewise be intermixed and reduced to the common
temperature. Now, in this case it may happen that the common
temperature to which the entire mass is reduced, after inter-
mixture, shall be either equal to or less than the greatest
temperature compatible with the density of the vapour in the mass
of air thus mixed. If it be equal to that temperature, the mass
of air after intermixture will be saturated, though the strata
before intermixture were both below saturation ; and if less, con-
densation must take place until the density of the vapour
suspended in the mixture be reduced to the greatest density
compatible with the temperature.

It might be supposed that air and vapour being mixed together
without combining chemically, would arrange themselves in
strata, the lighter floating above the heavier as oil floats above
water. This statical law, however, which prevails in liquids, is
in the case of elastic fluids subject to important qualifications.
The latter class of fluids have a tendency to intermingle and
diffuse themselves through and among each other in opposition to
their specific gravities. Thus if a stratum of hydrogen, the lightest
of the gases, rest upon a stratum of carbonic acid, which is the
heaviest, they will by slow degrees intermingle, a part of the
hydrogen descending among the carbonic acid, and a part of the
carbonic acid ascending among the hydrogen, and this will continue
90

DE\V.

until the mixture becomes perfectly uniform, every part of it
containing the two gases in the proportion of their entire
quantities.

The same law prevails in the case of vapours mixed with gases ;
and thus may be explained the fact, that although the aqueous
vapour suspended in the air, and having the same temperature, is
always lighter bulk for bulk than the air, it does not ascend to
the upper strata of the atmosphere, but is uniformly diffused
through it.

63. It may be stated generally, that the effect of a column of
air superposed upon the surface of water is only to retard, but not
either to prevent or diminish, the evaporation. The same quantity
of vapour will be developed as would be produced at the same
temperature if no air were superposed on the water ; but while in
the latter case the entire quantity of vapour would be developed
instantaneously, it is produced gradually, and completed only
after a certain interval of time when the air is present. The
quantity of vapour developed, and its density and pressure, are
however exactly the same, whether the space through which it ia
diffused be a vacuum, or be filled by air, no matter what the
density of the air may be. The properties of the air, therefore,
neither modify nor are modified by those of the vapour which is
diffused through it.

Since, at the same temperature and pressure, the density of the
vapour of water is less than that of air in the ratio of 5 to 8, it
follows that when air becomes charged with vapour of its own
temperature, the volume will be augmented, but the density
diminished. If a certain volume of air weigh 8 grains, an
equal volume of vapour will weigh 5 grains, the two volumes-
mixed together will weigh 13 grains, and, consequently, an
equal volume of the mixture will weigh 6^ grains. In this
case, therefore, the density of the air charged with vapour is
less than the density of dry air of the same temperature in the
ratio of 6| to 8.

64. The evaporation produced during the day by the action ot
solar heat on the surface of water, and on all bodies charged with
moisture, causes the atmosphere at the time of sunset to be more
or less charged with vapour, especially in the warm season. On
hot days, and in the absence of winds, the atmosphere at sunset is
generally at or near the point of saturation.

Immediately after sunset the temperature of the air falls. If it
were previously in a state of saturation condensation must ensue,
which will be considerable if the heat of the day and the con-
sequent change of temperature after sunset be great. In such
case, the vapour condensed often assumes the appearance of a fine

91

TERRESTRIAL HEAT.

rain or mist taking the liquid form before its actual deposition on
the surface.

The deposition of dew, however, also takes place even where the
atmosphere is not reduced to its point of saturation. "When the
firmament is unclouded after , sunset, all objects which are good
radiators of heat, among which the foliage and flowers of vegetables
are the foremost, lose by radiation the heat which they had
received before sunset without receiving any heat from the firma-
ment sufficient to replace it. The temperature of such objects,
therefore, falls much below that of the air, on which they produce
an effect precisely similar to that which a glass of very cold water
produces when exposed to a warm atmosphere charged with
vapour. The air contiguous to their surface being reduced to the
dew point by contact with them, a part of the vapour which it
holds in suspension is condensed, and collects upon them in the
form of dew.

It follows from this reasoning, that the dew produced by the
fall of temperature of the air below the point of saturation will be
deposited equally and indifferently on the surfaces of all objects
exposed in the open air, but that which is produced by the loss of
temperature of objects which radiate freely, will only be deposited
on those surfaces which are good radiators. Foreign writers on
physics accordingly class these depositions as different phenomena,
the former being called by French meteorologists serein, and the
latter rosee or dew. We are not aware that there is in English
any term corresponding to serein.

Dew will fail to be deposited even on objects which are good
radiators, when the firmament is clouded. For although heat be
radiated as abundantly from objects on the surface of the earth as
when the sky is unclouded, yet the clouds being also good
radiators, transmit heat, which being absorbed by the bodies on
the earth, compensates for the heat they lose by radiation, and
prevents their temperature from falling so much below that of the
air as to produce the condensation of vapour in contact with
them.

Wind also prevents the deposition of dew by carrying off the
air from contact with the surface of the cold object before con-
densation has time to take place. Meanwhile by the contact of
succeeding portions of air, the radiator recovers its temperature.

In general, therefore, the conditions necessary to insure the
deposition of dew is, 1st, a warm day to charge the air with
vapour ; 2nd, an unclouded night ; 3rd, a calm atmosphere ; and,
4th, objects exposed to it which are good radiators of heat.

In the close and sheltered streets of cities the deposition of
dew is rarely observed, because there the objects are necessarily
92

HOAH FEOST.

exposed to each other's influence, and an interchange of heat by
radiation takes place so as to maintain their temperature ; besides
which, the objects found there are not as strong radiators as the
foliage and flowers of vegetables.

60. When the cold which follows the condensation of vapour
falls below 32°, what would otherwise be DEW becomes HOAR FEOST.
For the same reason that dew is deposited when the temperature
of the air is above the point of saturation, hoar frost may be
manifested when the temperature of the air is many degrees above
the point of congelation ; for in this case, as in that of dew, the
objects on which the hoar frost collects lose so much heat by their
strong radiation, that while the atmosphere may be above 40° they
will fall below 32°. In such cases, a dew is first deposited upon
them which soon congeals, and forms the needles and crystals with
which every observer is familiar.

The hoar frost is sparingly or not at all formed upon the naked
earth, or on stones or wood, while it is profusely collected on
leaves and flowers. The latter are strong, the former feeble
radiators.

Glass is a good radiator. The panes of a window fall during
the night to a temperature below 32°, although the air of the room
be at a much higher temperature. Condensation and a profuse
deposition of moisture takes place on their inner surfaces, which
soon congeals and exhibits the crystallised coating so often
witnessed.

The frosts of spring and autumn, which so frequently are
attended with injury to the crops of the farmer and gardener,
proceed generally not from the congelation of moisture deposited
from the atmosphere, but from the congelation of their own proper
moisture by the radiation of their temperature caused by the
nocturnal radiation, which in other cases produces dew or hoar
frost. The young buds of leaves and flowers in spring, and the
grain and fruit in autumn, being reduced by radiation below 32°,
while the atmosphere is many degrees above that temperature,
the water which forms part of their composition is frozen, and
blight ensues.

These principles, which serve to explain the cause of the evil,
also suggest its remedy. It is only necessary to shelter the object
from exposure to the unclouded sky, which may be done by
matting, gauze, and various other expedients.

66. In tropical climates the principle of nocturnal radiation has
supplied the means of the artificial production of ice. This process,
which is conducted on a considerable scale in Bengal, where some
establishments for the purpose employ several hundred men,
consists in placing water in shallow pans of ivnglazed pottery in a

93

TERRESTRIAL HEAT.

situation which is exposed to the clear sky and sheltered from
currents of air. Evaporation is promoted by the porous quality
of the pans which become soaked with water, and radiation takes
place at the same time both from the water and the pans. Both
these causes combine in lowering the temperature of the water in
the pans, which congeals when it falls below 32°.

67. When the steam issuing from the surface of warm water
ascends into air which is at a lower temperature, it is con-
densed, but the particles of water formed by such condensation are
so minute, that they float in the air as would the minute particles
of an extremely fine dust. These particles lose their transparency by
reason of their minuteness, according to a general law of physical
optics. The vapour of water is transparent and colourless. It is
only when it loses the character and qualities of true vapour, that
it acquires the cloudy and semi-opaque appearance just mentioned.

Fogs are nothing more than such condensed vapour produced
from the surface of seas, lakes, or rivers, when the water has a
higher temperature than the stratum of air which rests upon it.
These fogs are more thick and frequent when the air, besides
having a lower temperature than the water, is already saturated
with vapour, because in that case all the vapour developed must
be immediately condensed, whereas, if the air be not saturated, it
will absorb more or less of the vapour which rises from the water.

Clouds are nothing but fogs suspended in the more elevated
strata of the atmosphere. Clouds are most frequently produced
by the intermixture of two strata of air, having different tempera-
tures and differently charged with vapour, the mixture being
supersaturated, and therefore being attended with partial conden-
sation as already explained.

68. When condensation of vapour takes place in the upper
strata of the atmosphere, a fog or mist is first produced, after
which the aqueous particles coalescing form themselves in virtue of
the attraction of cohesion into spherules, and fall by their gravity
to the earth, producing the phenomenon of rain.

69. The quantity of rain which falls in a given time at a given
place, is expressed by stating the depth which it would have if it
were received upon a plane and level surface, into which no part
of it would penetrate.

At Paris, the average annual quantity of rain which falls,
obtained from observations continued for thirty years at the
Observatory,' is 23*6 inches. There is, however, considerable
variation in the quantities from which this average is deduced ;
the smallest quantity observed being 16 -9 inches, and the greatest
27-9 inches.

The greatest annual fall of rain is that observed at Maranliam,
94

85OW.

lat. 2V S., which is stated by Humboldt to amount to 277 inches,
more than double the annual quantity hitherto observed elsewhere.

70. The physical conditions which determine the production of
Know are not ascertained. It is not known whether the flakes as
they fall are immediately produced by the congelation of con-
densed vapour in the cloud whence they first proceed, or whether
being at first minute particles of frozen vapour, they coalesce with
other frozen particles in falling through the successive strata of
the air, and thus finally attain the magnitude which they have on
reaching the ground.

The only exact observations which have been made on snow
refer to the forms of the crystals composing it, which Captain
Scoresby has observed with great accuracy in his " Polar Voyages,"
and of which he has given drawings. The flakes appear to consist
of fine needles, grouped with singular symmetry. A few of the
most remarkable forms are represented in fig. 2.

Fig. 2.

71. The physical causes which produce that formidable scourge
of the agriculturist hail are uncertain. Hypotheses have been
advanced to explain it which are more or less plausible, but which
do not fulfil the conditions that would entitle them to the place of
physical causes.

72. In the absence of any satisfactory explanation of the pheno-
menon, it is important to ascertain with precision and certainty
the circumstances which attend it, and the conditions under which
it is produced.

It may then, in the first place, be considered as certain that the

95

TEKRESTFJAL HEAT.

formation of hail is an effect of sudden electrical changes in clouds
charged with vapour ; for there is no instance known of hail which
is not either preceded or accompanied by thunder and lightning.

Before the fall of hail, during an interval more or less, but
sometimes of several minutes' duration, a rattling noise is gene-
rally heard in the air, which has been compared to that produced
by shaking violently bags of nuts.

Hail falls much more frequently by day than by night. Hail
clouds have generally great extent and thickness, as is indicated
by the obscuration they produce. They are observed also to have
a peculiar colour, a gray having sometimes a reddish tint. Their
form is also peculiar, their inferior surfaces having enormous pro -
tuberances, and their edges being indented and ragged.

These clouds are often at very low elevations. Observers on
mountains very frequently see a hail cloud below them.

It appears, from an examination of the structure of hailstones,
that at their centre there is generally an opaque nucleus, resem-
bling the spongy snow that forms sleet. Hound this is formed a
congealed mass, which is semi-transparent. Sometimes this mass
consists of a succession of layers or strata. These layers are some-
times all transparent, but in different degrees. Sometimes they
are alternately opaque and semi-transparent.

73. Extraordinary reports of the magnitude of hailstones, which
have fallen during storms so memorable as to find a place in
general history, have come down from periods of antiquity more
or less remote. According to the "Chronicles," a hailstorm
occurred in the reign of Charlemagne, in which hailstones fell
which measured fifteen feet in length by six feet in breadth, and
eleven feet in thickness ; and under the reign of Tippoo Saib,
hailstones equal in magnitude to elephants are said to have fallen.
Setting aside these and like recitals, as partaking rather of the
character of fable than of history, we shall find sufficient to
create astonishment in well authenticated observations on this
subject.

In a hailstorm which took place in Flintshire on the 9th April,
1697, Halley saw hailstones which weighed five ounces.

On the 4th May, 1697, Robert Taylor saw fall hailstones
measuring fourteen inches in circumference.

In the storm which ravaged Como on 20th August, 1787, Yolta
saw hailstones which weighed nine ounces.

On 22nd May, 1822, Dr. Noggerath saw fall at Bonn hailstones
which weighed from twelve to thirteen ounces.

It appears, therefore, certain that in different countries hail-
storms have occurred in which stones weighing from half to three
quarters of a pound have fallen.

m\

SOLAR SPOTS OBSERVED IK 1826 AKD 1828 BY MM. CAPOCCI AXD PASTORFF.

Capocci— 1. Sept. 29 ; 2. Sept. 2 ; 3. July 1, 1826.
Fastorn— i. Sept 27, 1826 ; 5. May 21 ; 6. Jiiue 21, 1828.

THE SUN.

1. An object of great interest. — 2. Its distance. — 3. Magnitude. — 4.
Illustrations. — 5. Its volume. — 6. Mass or weight. — 7. How ascer-
tained.— 8. Application of this principle. — 9. Its density. — 10. Form
and rotation. — 11. Determined by the appearance of spots. — 12. Dis-
covery of Solar spots. — 13. Their great magnitude. — 14. Their rapid
changes. — 15. Hypotheses to explain them. — 16. They are excavations
in the luminous coating. — 17. Their prevalence varies. — 18. Observa-
tions upon them. — 19. Their dimensions. — 20. Facules and Lucules.
— 21. Physical state of the Solar surface. — 22. Luminous coating is
gaseous. — 23. Gaseous atmosphere outside it. — 24. Effects of such aa
atmosphere on radiation. — 25. Hypothesis of Sir J. Herschel. — 26.
Intensity of heat at Sun's surface. — 27. Supposed source of heat.

1. AiTHorGH perhaps the moon is the object among the heavenly
bodies which presents the subject of most interesting inquiry to
the world in general, yet, to the thoughtful and contemplative
LARDNER'S MUSEUM OP SCIENCE. H 97

No. 34.

THE SUN.

mind, the sun is undoubtedly one of vastly superior interest.
The sun — the fountain of light and life to a family of circum-
volving worlds — the inexhaustible store of genial warmth by
which the countless tribes of organised beings that people these
globes are sustained — the physical bond whose predominating
attraction gives stability, uniformity, and harmony, to the move-
ments of the entire planetary system : to collect together in a
brief compass the information which modern scientific research
has supplied relating to this body, cannot be otherwise than an
interesting and agreeable task.

2. When we direct our inquiries to any object in the heavens,
the first questions which present themselves naturally to us are,
"What is its distance, magnitude, motion, and position ?" When
we say that the distances of the bodies composing the solar system
can be measured with the same degree of relative accuracy with
which we ascertain the distances of bodies on the surface of the
earth, those who are unaccustomed to investigations of this kind
usually receive the statement with a certain degree of doubt and
incredulity ; they cannot conceive how such spaces can be
accurately measured, or indeed measured at all. Thus, when
they are told that the sun is at a distance from the earth
amounting to nearly 100,000000 of miles, the mind revolts from
the idea that such a space could be exactly ascertained and esti-
mated. Yet, let us ask, why this difficulty ? whence this incre-
dulity ? Is it because the distance thus measured is enormously
great, — greater transcendently than any distance we are accustomed
to contemplate upon our own globe ? To this we reply that the
magnitude of a distance or space does not constitute of itself any
difficulty in its admeasurement. Nay, on the contrary, it is often
the case that we are able to measure large distances with greater
relative accuracy than small ones ; this is frequently so in the
surveys conducted on the surface of our own globe. If, then, the
greatness of the magnitudes does not constitute of itself any
difficulty, to what are we to ascribe the doubt entertained by the
popular mind in regard to such measurement ? It will, perhaps,
be replied that the object, whose distance we claim to have
measured, is inaccessible to us ; that we cannot travel over the
intermediate space, and therefore cannot be conceived to measure
it. But again, let us ask whether this circumstance of being
inaccessible constitutes any real difficulty in the measurement of
the distance of an object ? The military engineer, who directs
his projectiles against the buildings within a town which is
besieged, can, as we well know, level them so as to cause a shell
to drop on any individual building which may have been chosen.
To do this, he must know the exact distance of the building from

ITS DISTANCE.

the mortar. Yet the building is inaccessible to him ; the walls
of the town, the fortifications, and perhaps a river, intervene.
He finds, however, no difficulty in measuring the distance of this
inaccessible building. To accomplish this, he lays down a space
upon the ground he occupies, called the base line, from the
extremities of which he takes the bearings or directions of the
building in question. From these bearings, and from the length
of the base line, he is enabled to calculate by the most simple
principles of geometry and arithmetic the distance of the building
in question. Now imagine the building in question to be the sun,
and the base line to be the whole diameter of the globe of the earth,
in what respect would the problem be altered? The building within
the town is inaccessible — so is the sun; the base line of the
engineer is exactly known — so is the diameter of the earth ; the
bearings of the building from the ends of the base line are known
— so are the bearings of the sun's centre from the extremes of the
earth's diameter. The problems are, in fact, identical ; they differ
in nothing except the accidental and unimportant circumstance of
the magnitudes of the lines and angles that enter the question.
In short, the measurement of distances of objects in the heavens
is effected upon principles in all respects similar to those which
govern the measurement of distances upon the earth ; nor are they
attended with a greater difficulty, or more extensive sources of error.
By such means of observation and calculation it has been
ascertained that the sun's distance from the earth is a little less
than an hundred millions of miles. Although such calculations
supply results having surprising arithmetical accuracy, the ordinary
student will always find it convenient to register in his memory the
results in the nearest round numbers, and it is not easy to forget
that the distance of the sun, the most important of all astro-
nomical measurements, is very nearly an hundred millions of miles.
But while this round result is remembered, it will also be useful
to explain the more exact numerical measure of this distance, and
the limits of the error to which it is subject. The result of the
most exact observations made upon the different bearings of lines
drawn from opposite sides of the earth to the sun, gives as the
distance of that luminary,

95,293452 miles,

and it has been proved that this result cannot be greater or less
than the true distance by more than its three hundredth part.
We are, therefore, enabled to affirm absolutely that the distance
of the sun cannot be greater than

95,293452+317645 = 95,611097 miles;
or less than

95,293452—317645 = 94,975807 miles.

H2 99

THE SOT.

Since the sun moves over 360° of the heavens in 365| days, its
daily apparent motion must be 59' '14, or 3548", which being
about twice the sun's apparent diameter, it is easy to remember
that the disk of the sun appears to move in the firmament daily
over a space nearly equal to twice its own apparent diameter. Its
hourly apparent motion is

^=147-8.

3. Having explained the distance of the sun, let us now see how
its magnitude can be ascertained. There is one general principle
by which the magnitudes of all the heavenly bodies can be ascer-
tained when their distance is known. This is, in fact, accom-
plished by the device of comparing them with some object of
known magnitude and which at any known distance will have the
same apparent size. As this is important, considered as a general
principle applied to all objects in the heavens, it may not be
uninteresting to develop it somewhat fully in its application to the
present object, the sun.

The common observation of every one who directs his view to
the heavens, will inform him of the fact that the sun and full
moon appear to be of the same size. The mere effect of ordinary
visual observation is, perhaps, enough to establish this ; but if
more be desired, instruments expressly adapted to measure the
apparent magnitudes of objects may be applied. We are also
confirmed in the fact by the consideration of the well-known
phenomena of solar eclipses. A solar eclipse is produced by the
interposition of the globe of the moon between the eye and the
globe of the sun. The eclipse is said to be central when the
centre of the moon is directly in line between the eye and the
centre of the sun. When this takes place we find that the globe
of the moon generally covers pretty exactly that of the sun.
Owing, however, to a slight variation in the apparent size of these
bodies, from a cause that we shall explain on another occasion,
the moon at one time a little more than covers the sun, and at
another time a little less. In short, the average apparent magni-
tudes of these bodies are the same, the one exactly covering or
concealing the other.

But we have already stated that the distance of the moon is
only a quarter of a million of miles. And since that of the sun is
an hundred millions of miles, it appears that the distance of the
sun is four hundred times greater than that of the moon ; yet
these two globes appear to the eye to be of the same magnitude.
The sun, notwithstanding its being four hundred times farther
off, appears just as large as the moon. What, then, are we to
infer respecting its real magnitude ? If the sun were really
100

MAGNITUDE.

equal in magnitude to the moon, it would assuredly appear fou%
hundred times less at four- hundred times a greater distance: but
since at that greater distance it does not appear less or greater, but
of the same magnitude, the irresistible conclusion, level to the
apprehension of any understanding, is, that the sun must in reality
be four hundred times greater in its diameter than the moon. If
it were less, at four hundred times the moon's distance, it would
appear less than that of the moon ; if it were greater, at that dis-
tance it would appear greater. It follows, then, that whatever
be the magnitude of the diameter of the moon, the diameter of the
sun must assuredly be four hundred times greater. Now it has
been ascertained by absolute measurement that the diameter of
the moon measures about 2000 miles. If we multiply this by four
hundred we shall obtain 800000 miles, which is, therefore, the
diameter of the sun.

These calculations have been made roughly and in round num-
bers ; more accurately, the diameter of the sun measures 882000
miles, but as we recommend the adoption of round numbers, we
shall call the sun's diameter 900000 miles. Such is the stu-
pendous mass placed in the centre of the system which, by its
attraction, coerces the movements of the planets.

4. Such magnitudes and distances are so far beyond all the ordi-
nary standards with which we are familiar, that the imagination
is confounded and falls back upon itself after any effort to form
a distinct conception of them. Let us see whether we cannot
discover some expedient or some means of illustration by which a
more distinct notion can be obtained of the distance and magnitude
of this stupendous globe.

A railway-train moving at thirty-two miles an hour would take
three millions of hours or an hundred and twenty-five thousand
days, or three hundred and forty-two years and three months to
move from the earth to the sun, supposing it to travel incessantly
night and day for that time !

A cannon ball moves fifty times as fast as such a railway train.
It would therefore move to the sun in a little less than seven
years !

To give some idea of the dimensions of the sun we are to con-
sider that having a diameter of 882000 miles, its circumference
will be about 2,770000 miles. Such a railway-train would take
nine years and ten months to travel round it.

We know that the moon revolves in a circle round the earth at
the distance of nearly a quarter of a million of miles. Now let us
suppose the earth to be placed at the centre of the sun. The
distance of the outer surface of the sun from the centre of the
earth would be 441000 miles. Now the circle in which the

101

THE SUN.

moon revolves round the earth, is at a distance of 240000 miles
from its centre, consequently it follows that the earth and moon
would be not only contained within the globe of the sun, but
the moon would be a couple of hundred thousand miles within
the sun's surface.

5. But we have hitherto only spoken of the diameter of the
sun ; let us now consider its bulk. When we know the diameters
of two globes we can always, by an easy operation of arithmetic,
estimate their bulks. Thus, if one globe have a diameter double
another, the bulk of the former will be eight times that of the
latter. If the diameter be ten times greater, the bulk will be a
thousand fold greater, and so on. Now we know that the diameter
of the sun is about one hundred and twelve times greater than
that of the earth, from which we infer, by the same principles of
arithmetic, that the bulk of the sun must be very nearly one
million four hundred thousand times the bulk of the earth. To
make a globe like the sun, it would then be necessary to roll one
million four hundred thousand globes like the earth into one ! It
is found by considering the bulks of the different planets, that if
all the planets and satellites in the solar system were moulded
into a single globe, that globe would still not exceed the five
hundredth part the globe of the sun : in other words, the bulk of
the sun is five hunolred times greater than the aggregate bulk of
all the rest of the bodies of the system.

6. The astronomer, however, is called upon to execute processes
more difficult and yet no less indispensable than the mere measure-
ment of distances and magnitudes. If we desire to know the
quantities of matter composing those distant orbs, we must not
merely measure their magnitudes and fathom their distances, but
we must wing our flight, in imagination, across those vast dis-
tances which separate us from them and weigh their stupendous
masses. If the popular student finds it difficult to believe and
comprehend how we can measure distances and magnitudes such
as those of the heavenly bodies, how much more will he be con-
founded when he is assured that we have at our disposal a balance
of the most unerring exactitude in which we can place those vast
orbs and poise them ! The globe of the sun itself, transcendently
greater than the earth and all the planets put together, is weighed
with as great relative precision, as that with which the chemist in
his analysis, estimates the weights of the constituents of the bodies
which pass under his hands. As the general principles by which
the weights of the bodies of the universe are ascertained is in spirit
the same for all, it may be worth while here to explain the method,
once for all, in its application to the sun.

7. "When a body revolves in a circle, we know from common
102

GRAVITATION.

and familiar experiments that it has a tendency to fly from the
centre, which tendency is greater the more rapidly the body
revolves and the greater its distance from the centre. The boy
•who whirls a stone in a sling is conscious of this physical truth.
The stone, as it revolves, stretches the string with a certain
definite force ; this force is not in the gravity of the stone, for it
would be equally manifested if the stone revolved in a horizontal
plane. It is that tendency which we have just adverted to, and
which is technically called centrifugal force. If you increase the
velocity with which the stone is whirled round, you will find the
string will be more and more tightly stretched, and you may
augment the velocity to such an extent as to break the string.
If you lengthen or shorten the string, preserving the same velocity
of rotation, you will find that the tendency to stretch the string
will be proportionally increased or diminished ; in short, a fixed
rule or law, as it is called, will be easily discovered by a series of
simple experiments which will enable us to predict how much the
string will be stretched, provided we know the distance of the
revolving weight from the centre of the circle and the time it takes
to make each revolution.

8. To apply this general principle, then, to the case before us,
let it be considered that the moon in its monthly course revolves in
a circle round the centre of the earth. "We know its distance, and
we know the time which it takes to make each revolution, we are
therefore in a condition to declare with what force it would stretch a
string, tying it to the centre of the earth. That the moon exer-
cises such a force cannot then be doubted. But on what, it will
be asked, is that force expended ? There is no string, rod, or any
other material or tangible connection between the moon and the
centre of the earth. And yet the moon is held as firmly and
steadily in its circular cours j round the earth, as if it were tied to
the centre by a string. In the absence of the string there must
then be some physical agency which plays its part ; there must be
something to resist that tendency which the string, if there, would
have resisted. That something was discovered by Newton to be
the attraction of the earth's GRAVITATION exercised upon the
moon and holding the moon in its circular orbit, in the same
manner that it would be held by the string which has been just
described. As we know, by the simple mechanical law above
explained, the force with which that string would be stretched by
the moon in this case, we are enabled by the same principle to say
what is the amount of attractive force which the earth exercises
upon the moon to keep it in its monthly orbit.

In this manner, in general, we are enabled to estimate the force
of attraction which a central mass exercises upon another body

103

THE SUN.

revolving in a circle round it at a known distance, and in a known
time.

While, on the one hand, we know the distance and time of the
moon's revolution round the earth, we also know the distance and
time of the earth's revolution round the sun. We are thus,
allowing for the difference of the two distances, in a condition to
compare the actual amount of attraction which the earth and the
sun respectively exercise upon bodies revolving round them, and
we find, accordingly, that the attraction exercised by the sun
upon any body is greater than the attraction that would be exer-
cised by the earth upon the same body in a like position, in the
proportion of three hundred and fifty thousand to one. But as
these attractions are, in fact, produced by the respective masses of
matter composing the sun and the earth, it follows that the weight
of the sun, or what is the same, the mass of matter composing it,
is three hundred and fifty thousand times greater than the mass of
matter or weight of the earth.

To make a globe as heavy as the sun, it would then be necessary
to agglomerate into one three hundred and fifty thousand globes
like the earth.

9. Having ascertained the weights and bulks of the bodies of the
universe, we are in a condition to determine their densities, and
thus to obtain some clue to a knowledge of their constituent
materials. We have seen that while the bulk of the sun is about
one million and four hundred thousand times greater than that of
the earth, its weight is greater in the much less proportion of
three hundred and fifty thousand to one. Let iis see to what
inference this leads in regard to the nature of the matter that
composes the sun. If the materials of the sun were similar to
those of the earth, its weight would necessarily be greater than
that of the earth in the same proportion as its bulk, and in that
case, of course, the weight of the sun would be one million and
four hundred thousand times that of the earth. But it is not
nearly so great as this ; on the contrary, it is much less. Conse-
quently, it follows that the constituent materials of the sun are
lighter than those of the earth in the proportion of about four to one.
The density of the sun is, therefore, about forty per cent, greater
than that of water, and, consequently, the weight of the solar orb
exceeds the weight of a globe of the same magnitude composed
altogether of water, only in that proportion.

10. Although to minds unaccustomed to the rigour of scientific
research, it might appear sufficiently evident, without further
demonstration, that the sun is globular in its form, yet the more
exact methods pursued in the investigation of physics demand
that we should find more conclusive proof of the sphericity of the

104

SPOTS ON IT.

solar orb than the mere fact that the disc of the sun is always
circular. It is barely possible, however improbable, that a flat
circular disc of matter, the face of which should always be pre-
sented to the earth, might be the form of the sun ; and indeed
there are a great variety of other forms which, by a particular
arrangement of their motions, might present to the eye a circular
appearance as well as a globe or sphere. To prove, then, that a
body is globular, something more is necessary than the mere fact
that it always appears circular.

1 1 . "When a telescope is directed to the sun, we discover upon it
certain marks or spots, of which we shall speak more fully pre-
sently. "We observe that these marks, while they preserve the
same relative position with respect to each other, move regularly
from one side of the sun to the other. They disappear, and
continue to be invisible for a certain time, come into view again
on the other side, and so once more pass over the sun's disc.
This is an effect which would evidently be produced by marks
on the surface of a globe, the globe itself revolving on an axis,
and carrying these marks upon it. That this is the case, is
abundantly proved by the fact that the periods of rotation for all
these marks are found to be exactly the same, viz., about twenty-
five and a half days. Such is, then, the time of rotation of the
sun upon its axis, and that it is a globe remains no longer doubt-
ful, since the globe is the only body which, while it revolves with
a motion of rotation, could always present the circular appearance
to the eye. The axis on which the sun revolves is very nearly
perpendicular to the plane of the earth's orbit, and the motion of
rotation of the sun upon the axis is in the game direction as the
motion of the planets round the sun, that is to say, from west
to east.

12. One of the earliest fruits of the invention of the telescope was
the discovery of the spots upon the sun, and the examination of
these has gradually led to a knowledge of the physical constitution
of the centre of our system.

When we submit a solar spot to telescopical examination, we
discover its appearance to be that of an intensely black irregularly-
shaped patch, edged with a penumbral fringe, the brightness of
the general surface of the sun gradually fading away into the
blackness of the spot. When watched for a considerable time, it is
found to undergo a gradual change in its form and magnitude ; at
first increasing in size, until it attains some definite limit of mag-
nitude, when it ceases to increase, and soon begins, on the
contrary, to diminish ; and its diminution goes on gradually,
until at length the bright edges closing in upon the dark patch, it
dwindles first to a mere point, and finally disappears altogether.

105

THE SUN.

The period which elapses between the formation of the spot, its
gradual enlargement, subsequent diminution, and final disap-
pearance, is very various. Some spots appear and disappear very
rapidly, while others have lasted for weeks and even for months.

13. The magnitudes of the spots, and the velocities with which the
matter composing their edges and fringes moves, as they increase
and decrease, are on a scale proportionate to the dimensions of the
orb of the sun itself. When it is considered that a space upon the
sun's disc, the apparent breadth of which is only a minute,
actually measures 27960 miles, and that spots have been frequently
observed, the apparent length and breadth of which have exceeded
2', the stupendous magnitude of the regions they occupy may be
easily conceived.

14. The velocity with which the luminous matter at the edges of
the spots occasionally moves, during the gradual increase or
diminution of the spot, has been in some cases found to be enor-
mous. A spot, the apparent breadth of which was 90", was
observed by Mayer to close in about 40 days. Now, the actual
linear dimensions of such a spot must have been 41940 miles,
and consequently, the average daily motion of the matter com-
posing its edges must have been 1050 miles, a velocity equivalent
to forty-four miles an hour.

15. Two, and only two, suppositions have been proposed to ex-
plain the spots. One supposes them to be scoriae, or dark scales of
incombustible matter, floating on the general surface of the sun.
The other supposes them, to be excavations in the luminous matter
which coats the sun, the dark part of the spot being a part of the
solid non-luminous nucleus of the sun. In this latter hypothesis
it is assumed that the sun is a solid non-luminous globe, covered
with a coating of a certain thickness of luminous matter.

That the spots are excavations, and not mere black patches on
the surface, is proved by the following observations : If we select
a spot which is at the centre of the sun's disc, having some definite
form, such as that of a circle, and watch its changes of appear-
ance, when, by the rotation of the sun, it is carried towards the
edge, we find, first, that the circle becomes an oval. This, how-
ever, is what would be expected, even if the spot were a circular
patch, inasmuch as a circle seen obliquely is foreshortened into an
oval. But we find that as the spot moves towards the side of the sun's
limb, the black patch gradually disappears, the penumbral fringe
on the inside of the spot becomes invisible, while the penumbral
fringe on the outside of the spot increases in apparent breadth, so that
when the spot approaches the edge of the sun, the only part that
is visible is the external penumbral fringe. Now, this is exactly
what would occur if the spot were an excavation. The penumbral
106

WHAT THE SPOTS ARE.

fringe is produced by the shelving of the sides of the excavation,
sloping down to its dark bottom. As the spot is carried toward
the edge of the sun, the height of the inner side is interposed
between the eye and the bottom of the excavation, so as to conceal
the latter from view. The surface of the inner shelving side also
taking the direction of the line of vision or very nearly, diminishes
in apparent breadth, and ceases to be visible, while the surface of
the shelving side next the edge of the sun becoming nearly per-
pendicular to the line of vision, appears of its full breadth.

In short, all the variations of appearance which the spots
undergo, as they are carried round by the rotation of the sun,
changing their distances and positions with regard to the sun's
centre, are exactly such as would be produced by an excavation,
and not at all such as a dark patch on the solar surface would
undergo.

16. It may be considered then as proved, that the spots on the
sun are excavations ; and that the apparent blackness is produced
by the fact that the part constituting the dark portion of the spot
is either a surface totally destitute of light, or by comparison so
much less luminous than the general surface of the sun, as to
appear black. This fact, combined with the appearance of the
penumbral edges of the spots, has led to the supposition, advanced
by Sir TV. Herschel, which appears scarcely to admit of doubt,
that the solid, opaque nucleus, or globe of the sun, is invested
with at least two atmospheres, that which is next the sun being,
like our own, non-luminous, and the superior one being that alone
in which light and heat are evolved ; at all events, whether these
strata be in the gaseous state or not, the existence of two such, one
placed above the other, the superior one being luminous, seems to
be exempt from doubt.

TTe are not warranted in assuming that the black portion of the
spots are surfaces really deprived of light, for the most intense
artificial lights which can be produced, such, for example, as that
of a piece of quicklime exposed to the action of the compound
blow-pipe, when seen projected on the sun's disk, appear as dark
as the spots themselves ; an effect which must be ascribed to the
infinitely superior splendour of the sun's light. All that can be
legitimately inferred respecting the spots, then, is, not that they
are destitute of light, but that they are incomparably less brilliant-,
than the general surface of the sun.

17. The prevalence of spots on the sun's disk is both variable and
irregular. Sometimes the disk will be completely divested of them,
and will continue so for weeks or months ; sometimes they will be
spread over certain parts of it in profusion. Sometimes the spots
will be small, but numerous ; sometimes individual spots will

107

THE SUN.

appear of vast extent ; sometimes they will be manifested in groups,
the penumbra or fringes being in contact.

The duration of each spot is also subject to great and irregular
variation. A spot has appeared and vanished in less than twenty-
four hours, while some have maintained their appearance and
position for nine or ten weeks, or during nearly three complete
revolutions of the sun upon its axis.

A large spot has sometimes been observed suddenly to crumble
into a great number of small ones.

The only circumstance of regularity which can be said to attend
these remarkable phenomena is their position upon the sun. They
are invariably confined to two moderately broad zones parallel
to the solar equator, separated from it by a space several degrees
in breadth. The equator itself, and this space which thus separates
the macular zones, are absolutely divested of such phenomena.

18. Observations upon the appearances from which these infer-
ences have been made, have been at various times made by astro-
nomers, the most important being those of Sir William Herschel,
Dr. Pastorff, Professor Capocci, and Sir J. Herschel, who have seve-
rally supplied drawings of their appearance, the general similarity
of which, made at different places of observation, at very different
times, and by different observers, offers a strong evidence of their
authenticity.

In the figure at the head of this chapter, we have given copies
of several of the most remarkable of these drawings.

19. The superficial dimensions of the several groups of spots
observed on the sun on the 24th May, 1828, including the shelving
sides, were calculated to be as follows : —

Square Geog. miles.

Group A, principal spot 928,000000

Ditto, smaller spots 736,000000

Group B 296,000000

Group C 232,000000

Group D 304,000000

Total area . . . 2496,000000

20. Independently of the dark spots just described, the luminous
part of the solar disk is not uniformly bright. It presents a
mottled appearance, which may be compared to that which would
be presented by the undulated and agitated surface of an ocean oi
liquid fire, or to a stratum of luminous clouds of varying depth,
and having an unequal surface, or the appearance produced by
the slow subsidence of some flocculent chemical precipitates in a
transparent fluid, when looked at perpendicularly from above. In
the space immediately around the edges of the spots extensive

108

SOLAR SURFACE.

spaces are observed, also covered with strongly defined curved or
branching streaks, more intensely luminous than the other parts
of the disk, among which spots often break out. These several
varieties in the intensity of the brightness of the disk have been
differently designated by the terms facules and lucules. These
appearances are generally more prevalent and strongly marked
near the edges of the disk.

21. Various attempts have been made to ascertain by the direct
test of observation, independently of conjecture or hypothesis, the
physical state of the luminous matter which coats the globe of the
sun, whether it be solid, liquid, or gaseous.

That it is not solid is admitted to be proved conclusively by
its extraordinary mobility, as indicated by the rapid motion of
the edges of the spots in closing ; and it is contended that a fluid
capable of moving at the rate of 44 miles per hour cannot be
supposed to be liquid, an elastic fluid alone admitting of such a
motion.

Arago has, however, suggested a physical test, by which it
appears to be proved that this luminous matter must be gaseous ;
in short, that the sun must be invested with an ocean of flame,
since flame is nothing more than aeriform fluid in a state of incan-
descence. This test proposed is based upon, the properties of
polarised light.

It has been proved that the light emitted from an incandescent
body in the liquid or solid state, issuing in directions very oblique
to the surface, even when the body emitting it is not smooth or
polished, presents evident marks of polarisation, so that such a
body, when viewed through a polariscopic telescope, will present
two images in complementary colours. But, on the other hand,
no signs of polarisation are discoverable, however oblique may be
the direction in which the rays are emitted, if the luminous matter
be flame.

The light proceeding from the disk of the sun has been accord-
ingly submitted to this test. The rays proceeding from its borders
evidently issue in a direction as oblique as possible to the surface,
and therefore, under the condition most favourable to polarisation,
if the luminous matter were liquid. Nevertheless, the borders of
the double image produced by the polariscope show no signs
whatever of complementary colours, both being equally white even,
at the very edges.

This test is only applicable to the luminous matter at or near the
edge of the disk, because it is from this only that the rays issue
with the necessary obliquity. But since the sun revolves on its
axis, every part of its surface comes in succession to the edge of
the disk ; and thus it follows that the light emanating from every

109

THE SUN.

part of it is in its natural or unpolarised state, even when issuing
at the greatest obliquity ; and, consequently, that the luminous
matter is everywhere gaseous.

22. All the phenomena which have been here described, and
others which our limits compel us to omit, are considered as giving
a high degree of physical probability to the hypothesis of Sir "W.
Herschel already noticed, in which the sun is considered to be a
solid, opaque, non-luminous globe invested by two concentric
strata of gaseous matter, the first, or that which rests immediately
on the surface, being non-luminous, and the other, which floats
upon the former, being luminous gas or flame. The relation and
arrangement of these two fluid strata may be illustrated by our
own atmosphere, supporting upon it a stratum of clouds. If such
clouds were flame, the condition of our atmosphere would represent
the two strata on the sun.

The spots in this hypothesis are explained by occasional openings
in the luminous stratum by which parts of the opaque and non-
luminous surface of the solid globe are disclosed. These partial
openings may be compared to the openings in the clouds of our sky,
by which the firmament is rendered partially visible.

23. Many circumstances supply indications of the existence of a
gaseous atmosphere of great extent above the luminous matter
which forms the visible surface of the sun. It is observed that the
brightness of the solar disk is sensibly diminished towards its
borders. This effect would be produced if it were surrounded by
an imperfectly transparent atmosphere, whereas if no such
gaseous medium surrounded it, the reverse of such an effect might
be expected, since then the thickness of the luminous coating
measured in the direction of the visual ray would be increased very
rapidly in proceeding from the centre towards the edges. This
gradual diminution of brightness in proceeding towards the borders
of the solar disk has been noticed by many astronomers ; but it
was most clearly manifested in the series of observations made by
Sir J. Herschel in 1837, so conclusively, indeed, as to leave no-
doubt whatever of its reality on the mind of that eminent observer.
By projecting the image of the sun's disk on white paper by
means of a good achromatic telescope, this diminution of light
towards the borders was on that occasion rendered so apparent,
that it appeared to him surprising that it should ever have been
questioned.

But the most conclusive proofs of the existence of such an
external atmosphere are supplied by certain phenomena observed
on the occasion of total eclipses of the sun, which will be fully
explained in another part of this series.

24. The heat generated by some undiscovered agency upon the
110

RADIATION".

sun is dispersed through the surrounding space by radiation. If, as
may be assumed, the rate at -which this heat is generated be the
same on all parts of the sun, and if, moreover, the radiation be
equally free and unobstructed from all parts of its surface, it is
evident that a uniform temperature must be everywhere 'main-
tained. But if, from any local cause, the radiation be more
obstructed in some regions than in others, heat mil accumulate in
the former, and the local temperature will be more elevated there
than where the radiation is more free.

But the only obstruction to free radiation from the sun must
arise from the atmosphere with which to an height so enormous it
is surrounded. If, however, this atmosphere have everywhere the
same height and the same density, it will present the same obstruc-
tion to radiation, and the effective radiation which takes place
through it, though more feeble than that which would be produced
in its absence, is still uniform.

But since the sun has a motion of rotation on its axis in
25dt 7h* 48"", its atmosphere, like that of the earth, must partici-
pate in that motion and the effects of centrifugal force upon matter
so mobile : the equatorial zone being carried round with a velocity
greater than 300 miles per second, while the polar zones are moved
at a rate indefinitely slower, all the effects to which the spheroidal
form of the earth is due will affect this fluid with an energy pro-
portionate to its tenuity and mobility, the consequence of which
will be that it will assume the form of an oblate spheroid, whose
axis will be that of the sun's rotation. It will flow from the poles to
the equator, and its height over the zones contiguous to the equator
will be greater than over those contiguous to the poles, in a degree
proportionate to the ellipticity of the atmospheric spheroid.

Xow, if this reasoning be admitted, it will follow that the
obstruction to radiation produced by the solar atmosphere is
greatest over the equator, and gradually decreases in proceeding
towards either pole. The accumulation of heat, and consequent
elevation of temperature, is, therefore, greatest at the equator, and
gradually decreases towards the poles, exactly as happens on the
earth from other and different physical causes.

25. The effects of this inequality of temperature, combined with
the rotation, upon the solar atmosphere, will of course be similar in
their general character, and different only in degree from the
phenomena produced by the like cause on the earth. Inferior
currents will, as upon the earth, prevail towards the equator, and
superior counter-currents towards the poles. The spots of
the sun would, therefore, be assimilated to those tropical regions
of the earth in which, for the moment, hurricanes and tornadoes
prevail, the upper stratum which has come from the equator being

111

THE SUN.

temporarily carried downwards, displacing "by its force the strata
of luminous matter beneath it (which may be conceived as forming
an habitually tranquil limit between the opposite upper and under
currents), the upper of course to a greater extent than the lower,
and thus wholly or partially denuding the opaque surface of the
sun below. Such processes cannot be unaccompanied by vorticose
motions, which, left to themselves, die away by degrees, and dis-
sipate, with this peculiarity, that their lower portions come to rest
more speedily than their upper, by reason of the greater distance
below, as well as the remoteness from the point of action, which lies
in a higher region, so that their centre (as seen in our water-spouts,
which are nothing but small tornadoes) appears to retreat upwards.*

Sir J. Herschel maintains that all this agrees perfectly with
what is observed during the obliteration of the solar spots, which
appear as if filled in by the collapse of their sides, the penumbra
closing in upon the spot and disappearing afterwards.

It would have rendered this ingenious hypothesis still more
satisfactory, if Sir J. Herschel had assigned a reason why the
luminous and subjacent non-luminous atmosphere, both of which
are assumed to be gaseous fluids, do not affect, in consequence of
the rotation, the same spheroidal form which he ascribes to the
superior solar atmosphere.

26. It has been shown that the intensity of heat on the sun's
surface must be seven times as great as that of the vivid ignition
of the fuel in the strongest blast furnace. This power of solar light
is also proved by the facility with which the calorific rays pass
through glass. Herschel found, by experiments made with an
actinometer, that 81/6 per cent of the calorific rays of the sun
penetrate a sheet of plate-glass 0*12 inch thick, and that 8o-9 per
cent, of the rays which have passed through one such plate will
pass through another, f

27. One of the most difficult questions connected with the phy-
sical condition of the sun, is the discovery of the agency to which
its heat is due. To the hypothesis of combustion, or any other which
involves the supposition of extensive chemical change in the
constituents of the surface, there are insuperable difficulties.
Conjecture is all that can be offered, in the absence of all data
upon which reasoning can be based. Without any chemical
change, heat may be indefinitely generated either by friction or
by electric currents, and each of these causes have accordingly
been suggested as a possible source of solar heat and light.
According to the latter hypothesis, the sun would be a great
ELECTBIC LIGHT in the centre of the system.

* Herschel's Cape Observations, p. 43-1. t Ibid., p. 133.

112

T ROOM, ELECTRIC TELEGRAPH OFFICE, CHARING CROSS.

THE ELECTRIC TELEGRAPH.

CHAPTEE I.

1. Subjugation of the powers of nature to human uses. — 2. Locomotion
twenty years since. — 3. Circulation of intelligence then. — 4. Supposed
prediction of succeeding improvements — Railway locomotion. — 5.
Electric telegraphy. — 6. Fabrication of diamonds — sun pictures — gas-
lighting — electro -metallurgy. — 7. Such predictions would have been
deemed incredible. — 8. Electro-telegraphy the most incredible of all.
— 9. Remarkable experiment by Messrs. Leverrier and Lardner. —
10. Velocity of electric current. — 11. No limit to the celerity of
telegraphy. — 12. Physical character of electricity. — 13. Not essential
to the explanation of electro -telegraphy. — 14. Electricity a subtle
fluid. — 15. Properties available for telegraphy. — 16. Voltaic battery.
— 17 It is to the electric telegraph what the boiler is to the steam-
engine. — 18. Means of transmitting the fluid in required directions.
— 19. Conductors and insulators. — 20. Conducting wires. — 21. Voltaic
battery. — 22. Transmission and suspension of the current. — 23. Current
established by earth contact. — 24. Theories of earth contact — 25.
The return of the current through the earth. — 26. Various bodies
LARDNER'S MUSEUM ov ScuaiOB. I 113

No. 31.

THE ELECTRIC TELEGRAPH.

evolve electricity. — 27. Common plate battery of zinc and copper.
— 28. Why zinc and copper are preferred. — 29. Charcoal substituted
for copper. — 30. Elements not essential. — 31. Various chemical
solutions used. — 32. Daniel's constant battery. — 33. Same modified by
Pouillet. — 34. Grove's and Bunsen's batteries. — 35. Necessary to
combine many elements.

1. EACH succeeding age and generation leaves behind it a peculiar
character, which stands out in relief upon its annals, and is
associated with it for ever in the memory of posterity. One is
signalised for the invention of gunpowder, another for that of
printing ; one is rendered memorable by the revival of letters,
another by the reformation of religion ; one is marked in history
by the conquests of Napoleon, another is rendered illustrious by
the discoveries of Newton.

If we are asked by what characteristic the present age will be
marked in future records, we answer, by the miracles which
have been wrought in the subjugation of the powers of the material
world to the uses of the human race. In this respect no former
epoch can approach to competition with it.

The author of some of the most popular fictions of the day
has affirmed, that in adapting to his purpose the results of his
personal observation on men and manners, he has not unfre-
quently found himself compelled to mitigate the real in order to
bring it within the limits of the probable. No observer of the
progress of the arts of life, at the present time, can fail to be struck
with the prevalence of the same character in their results as that
which compelled this writer to suppress the most wonderful of
what had fallen under his eye, in order to bring his descriptions
within the bounds of credibility.

2. Many are old enough to remember the time when persons,
correspondence, and merchandise were transported from place to
place in this country by stage-coaches, vans, and waggons. In
those days the fast-coach, with its team of spanking blood-horses,
and its bluff driver, with broad-brimmed hat and drab box-coat,
from which a dozen capes were pendant, who "handled the rib-
bons " with such consummate art, could pick a fly from the ear of
the off-leader, and turn into the gateway at Charing Cross with the
precision of a geometrician, were the topics of the unbounded
admiration of the traveller. Certain coaches obtained a special
celebrity and favour with the public. We cannot forget how the
eye of the traveller glistened when he mentioned the Brighton
"Age," the Glasgow " Mail," the Shrewsbury " Wonder," or the
Exeter " Defiance,"— the "Age," which made its trip in five-
hours, and the " Defiance," which acquired its fame by completing
the journey between London and Exeter in less than thirtv hours.
314

AVOXDEKS OF SCIENCE.

3. The rapid circulation of intelligence was also the boast of
those times. How foreigners stared when told that the news oi
each afternoon formed a topic of conversation at tea-tables the
same evening, twenty miles from London, and that the morning
journals, still damp from the press, were served at breakfast
within a radius of thirty miles, as early as the frequenters of the
London clubs received them.

Now let us imagine that some profound thinker, deeply versed
in the resources of Science at that epoch, were to have gravely
predicted that the generation existing then and there would live
to see all these admirable performances become obsolete, and
consigned to the history of the past ; that they would live to regard
such vehicles as the "Age " and " Defiance " as clumsy expedients,
and their celerity such as to satisfy those alone who were in a
ba?kward state of civilisation !

4. Let us imagine that such a person were to affirm that his
contemporaries would live to see a coach like the j Defiance,"
making its trip between London and Exeter, not in thirty, but in
five hours, and drawn, not by 200 blood-horses, but by a moderate
sized stove and four bushels of coals !

5. Let us further imagine the same sagacious individual to
predict that his contemporaries would live to see a building
erected in the centre of London, in the cellars of which machinery
would be provided for the fabrication of artificial lightning, which
should be supplied to order, at a fixed price, in any quantity
required, and of any prescribed force ; that conductors would be
carried from this building to all parts of tha country, along which
such lightning should be sent at will; that in the attics of this
same building would be provided certain small instruments like
barrel-organs or pianofortes ; that by means of these instruments,
the aforesaid lightning should, at the will and pleasure of those
in charge of them, deliver messages at any part of Europe, from
St. Petersburgh to Naples ; and, in fine, that answers to such mes-
sages should be received instantaneously, and by like means :
that in this same building offices should be provided, where any
lady or gentleman might enter, at any hour, and for a few
shillings send a message by lightning to Paris or Yienna, and by
waiting for a few moments, receive an answer !

Might he not exclaim after the inspired author of the book of
Job:—

" Canst thou send lightnings, that they may go, and say unto
thee, Here we are " ! ! xxxviii., 35.

But, suppose that his foresight should further enable him to
pronounce that means would be invented by which any individual
in any one town or city of Europe should be enabled to take in

1 2 115

THE ELECTRIC TELEGRAPH.

his hand a pencil or pen, the point of which should be in any
other town or city, no matter how distant, and should, with such
pen or pencil, write or delineate in such distant place, such
characters or designs as might please him, with as much prompti-
tude and precision as if the paper to which these characters or
designs were committed lay upon the table before him ; or that
an individual pulling a string at London should ring a bell at
Vienna, or holding a match at St. Petersburgh should discharge a
cannon at Naples !

6. Suppose he should affirm that means would be discovered for
converting charcoal into diamonds ; that the light of the sun
would be compelled, without the intervention of the human hand,
to make a portrait or a picture, with a fidelity, truth and precision,
with which the productions of the most exalted artistic skill
would not bear comparison ; and that this picture should be pro-
duced and completed in its most minute details in a few seconds —
nay, evenii^the fraction of a second; that candles and lamps would
be superseded by flame manufactured on a large scale in the suburbs
of cities, and distributed for use in pipes, carried under the streets,
and into the houses and other buildings to be illuminated ; and
that the precious and other metals being dissolved in liquids,
would form themselves into the articles of ornament and use by
a spontaneous process, and without the intervention of human
labour!!

No authority however exalted, no attainments however pro-
found, no reputation however respected, could have saved the
individual rash enough to have given utterance to such predictioas
some forty years ago, from being regarded as labouring under
intellectual derangement. Yet all these things have not onlv
come to pass, but the contemplation of many of them has become
so interwoven with our habits, that familiarity has blunted the
edge of wonder.

7. Compared with all such realities, the illusions of oriental
romance grow pale ; fact stands higher than fiction in the scale of
the marvellous ; the feats of Aladdin are tame and dull ; and the
slaves of the lamp yield precedence to the spirits which preside
over the battery and the boiler.

8. Of all the physical agents discovered by modern scientific
research, the most fertile in its subserviency to the arts of life is
incontestably electricity, and of all the applications of this subtle
agent, that which is transcendently the most admirable in its
effects, the most astonishing in its results, and the most important
in its influence upon the social relations of mankind, and upon the
spread of civilisation and the diffusion of knowledge, is the
Electric Telegraph. No force of habit, however long continued,

116

REMARKABLE TELEGRAPHIC EXPERIMENT.

no degree of familiarity can efface the sense of wonder which the
effects of this most marvellous application of science excites.

9. Being at Paris some years ago, I was engaged to share with
M. Leverrier, the celebrated astronomer, and some other men of
science, in the superintendence of a series of experiments to he
made before committees of the Legislative Assembly and of the
Institute, with the view of testing the efficiency of certain tele-
graphic apparatus. On that occasion operating in a room at
the Ministry of the Interior appropriated to the telegraphs, into
which wires proceeding from various parts of France were brought,
we dictated a message, consisting of about forty words, addressed
to one of the clerks at the railway station at Valenciennes, a
distance of 168 miles from Paris. This message was transmitted in
two minutes and a half. An interval of about five minutes
elapsed, during which, as it afterwards appeared, the clerk to
whom the message was addressed was sent for. At the expiration
of this interval the telegraph began to express the answer, which,
consisting of about thirty-five words, was delivered and written
out by the agent at the desk, in our presence, in two minutes.
Thus, forty words were sent 168 miles and thirty-five words
returned from the same distance, in the short space of four
minutes and thirty seconds.

But surprising as this was, we soon afterwards witnessed, in
the same room, a still more marvellous performance.

The following experiment was prepared and performed at the
suggestion and under the direction of M. Leverrier and
myself : —

"Two wires, extending from the room in which we operated to
Lille, were united at the latter place, so as to form one continuous
wire, extending to Lille and back, making a total distance of
336 miles. This, however, not being deemed sufficient for
the purpose, several coils of wire wrapped with silk were
obtained, measuring in their total length 746 miles, and were
joined to the extremity of the wire returning from Lille, thus
making one continuous wire measuring 1082 miles. A message
consisting of 282 words was then transmitted from one end of the
wire. A pen attached to the other end immediately began to
write the message on a sheet of paper moved under it by a simple
mechanism, and the entire message was written in full in the
presence of the Committee, each word being spelled completely
and without abridgment, in fifty-two seconds, being at the average
rate of Jive icords and four-tenths per second!

By this instrument, therefore, it is practicable to transmit
intelligence to a distance of upwards of 1000 miles, at the rate of
19500 words per hour !

117

THE ELECTRIC TELEGRAPH.

The instrument would, therefore, transmit to a distance of 1000
miles, in the space of an hour, the contents of about forty pages of
the book now in the hands of the reader !

But it must not be imagined, because we have here produced an
example of the transmission of a despatch to a Distance of 1000
miles, that any augmentation of that distance could cause any
delay of practical importance.

10. Although the velocity of the electric current has not been
very exactly measured, it has been established beyond all doubt
that it is so great that to pass from any one point on the surface
of the earth to any other, it would take no more than an inappre-
ciable fraction of a second.

11. If, therefore, the despatch had been sent to a distance of
twenty thousand miles instead of one thousand, its transmission
would still have been instantaneous.

Such a despatch would fly many times round the earth between
the two beats of a common clock, and would be written in full at
the place of its destination more rapidly than it could be repeated
by word of mouth. When such statements are made, do we not
feel disposed to exclaim —

" Are such things here as we do speak about ?
Or have we eaten of the insane root,
That makes the reason prisoner ?"

In its wildest flights the most exalted imagination would not have
dared, even in fiction, to give utterance to these stubborn
realities. Shakspeare only ventured to make his fairy

*' Put a girdle round the earth
In forty minutes."

To have encircled it several times in a second, would have seemed
too monstrous, even for Robin Goodfellow.

The curious and intelligent reader of these pages will scarcely
be content, after the statement of facts so extraordinary, to
remain lost in vacant astonishment at the power of science, with-
out seeking to be informed of the manner in which the phenomena
of nature have been thus wonderfully subdued to the uses of man.
A very brief exposition will be enough to render intelligible the
manner in which these miracles of science are wrought.

12. The World of Science is not agreed as to the physical
character of Electricity. According to the opinion of some it is a
fluid infinitely lighter and more subtle than the most attenuated
and impalpable gas, capable of moving through space with a
velocity commensurate with its subtleness and levity. Some
regard this fluid as simple. Others contend that it is compound,
118

ELECTRIC FLUID.

consisting of two simple fluids having antagonistic properties
which when, in combination neutralise each other, but which
recover their activity by decomposition. Others again regard it
not as a specific fluid which moves through space, but as a
phenomenon analogous to sound, and think that it is only a series
of undulations or vibrations that are propagated through a highly
elastic medium which produce the various electrical effects just
as the pulsations of the atmosphere produce all the effects of
sound.

13. Happily these difficult discussions are not necessary to the
clear comprehension of the laws which govern the phenomena,
upon which electric telegraphy depends. It will nevertheless for
the purposes of explanation be convenient to use a system of
language, which implies the existence of a certain fluid which we
shall call the electric fluid, capable of moving over certain bodies,
and being obstructed or altogether stopped by others, and which
by its presence or proximity produces certain definite effects,
mechanical and chemical.

14. Whether the electric agency be or be not a material fluid
for our present purpose is unimportant. It is enough that it
comports itself as such, and that the properties or effects which we
shall impute to it are such only as it is ascertained by observation
and experiment to possess or produce.

15. However various the forms may be which invention has
conferred upon electric telegraphs, their efficiency in all cases
depends on our power to produce at will the following effects : —

1st. To produce or develop the electric fluid in any desired
quantity, and of the necessary quality.

2nd. To transmit it with celerity to any required distance,
without injuriously dissipating it.

3rd. To cause it upon its arrival at any assigned point to
produce some sensible effects, which may serve the purpose of
written or printed characters.

16. The electric fluid is deposited in a latent state in unlimited
quantity in the earth, the waters, the atmosphere, and in all
bodies upon the earth, whether solid, liquid, or gaseous. It is
disengaged and rendered active by various causes, natural and
artificial. The mutual friction of bodies, contact and pressure,
the contiguity or contact of bodies having different temperatures,
the chemical action of bodies one upon another, the action of
magnetic bodies on each other, and on bodies susceptible of mag-
netism, are severally causes of the development of the electric
fluid in greater or less quantity.

Founded upon these phenomena, various apparatus have been,
contrived, by means of which the electric fluid may be evolved

119

THE ELECTRIC TELEGRAPH.

and collected in any desired quantity, and with any required
intensity. Among these, that which has proved to be the
most efficient for telegraphic purposes is the GALVANIC or VOLTAIC

BATTEEY.

17. This apparatus is to the electric telegraph what the boiler
is to the steam-engine. It is the generator of the fluid by which
the action of the telegraphic machine is produced and maintained.
It supplies the fluid in any required quantity and of any desired
intensity. As the boiler is supplied with expedients by which
within practical limits the quantity and pressure of the steam
may be varied, according to the exigences of the work to which
the engine is applied, so the voltaic battery is provided with
expedients by which the quantity and .intensity of the electric
fluid it evolves can be varied according to the distance to which
the intelligence is to be transmitted ; and the form, whether
visible, oral, written, or printed, in which it is required to be
delivered at the place of its destination.

18. The electric fluid being thus produced in sufficient quantity,
it is necessary to provide adequate means of transmitting it to a
distance without exposing it to any cause of injurious dissipation
or waste.

If tubes or pipes could be constructed with sufficient facility
and cheapness, through which the subtle fluid could flow, and
which would be capable of confining it during its transit, this
object would be attained. As the galvanic battery is analogous
to the boiler, such tubes would be analogous in their form and
functions to the steam-pipe of a steam-engine.

19. The construction of such means of transmission has been
accomplished by means of the well-known property of the
electric fluid, in virtue of which it is capable of passing freely
over a certain class of bodies called CONDTJCTOES, while its move-
ment is arrested by another class of bodies called NOX-COKDUCTOES

Or INST7LATOES.

The most conspicuous examples of the former class are the
metals; the most remarkable of the latter being resins, wax,
glass, porcelain, silk, cotton, dry air, &c.

20. Now if a rod or wire of metal be coated with wax, or
wrapped with silk, the electric fluid will pass freely along the
metal, in virtue of its character of a conductor ; and its escape
from the metal laterally will be prevented by the coating, in
virtue of its character of an insulator.

The insulator in such cases is, so far as relates to the electricity,

a real tube, inasmuch as the electric fluid passes through the

metal included by the coating, in exactly the same manner as

water or gas passes through the pipes which conduct it ; with this

120

VOLTAIC CURRENT.

Fig. l.

difference, however, that the electric fluid moves along the wire
more freely, in an almost infinite proportion, than does either
water or gas in the tubes which conduct them.

If, then, a wire, coated with a non-conducting substance,
capable of resisting the vicissitudes of weather, were extended
between any two distant points, one end of it being attached
to one of the extremities of a galvanic battery, a stream of
electricity would pass along the wire — -provided the other end of
the wire were connected by a conductor with the other extremity
of the battery.

21. How the fluid transmitted to a distant station is made to
produce the effects by which messages are expressed will be
explained hereafter, meanwhile it will be necessary first to explain
the form and principle of the voltaic batteries used for tele-
graphic operations, and secondly the expedients by which the
current is transmitted and suspended, and turned in one or
another direction at the will of the operator at the station from
which despatches are transmitted.

To comprehend the principle of the voltaic battery, let us
suppose that two strips cut, one z z from a sheet of zinc, and the
other cc (fig. 1) from a sheet of cop-
per, are immersed without touching
each other in a vessel containing
water slightly acidulated. To the
upper edges P and x of the strips let
two pieces of wire P p and N n, be
soldered. In this state of the appa-
ratus no development of the electric
fluid will be manifested ; but if the
ends p and n of the wires be
brought into contact, an electric
current will set in, running on the
wires from p, the point where the
wire is soldered to the copper c c,
to x, the point where the other wire
is soldered to the zinc z z. This
current will continue to flow so long
as the ends j9 and n of the wires are
kept in mutual contact, and no longer. The moment the ends p
and n are separated, the current ceases.

22. The commencement of the current upon the contact of the
wires, and its cessation upon their separation, are absolutely
instantaneous ; so much so, that if the ends^ and n were brought
into contact and separated a hundred times in a second, the flow
and suspension of the current being simultaneous with the

121

THE ELECTRIC TELEGRAPH.

contacts and separations, would also take place a hundred times
in a second.

The existence of the current established in this case is inde-
pendent of the length of the wires P p and N n. Whether their
length be 10 feet, 10 miles, or 100 miles, the current will still
flow upon them when their extremities p and n are brought into
contact. The only difference will be, that the intensity of the
current will be less in the same proportion as the length of the
wires is augmented.

23. There is another condition of great importance, whether
regarded theoretically or practically, 'on which the current will be
established and maintained.

Instead of bringing the wires P p and N n into contact, let
them be continued downwards, as represented in fig. 2, and con-
nected with two plates of metal p' and n't buried in the earth, or

with masses of metal or other good conducting body of any form
whatever thus buried. In that case the current will be esta-
blished as before, flowing along the wire soldered to the copper
from P to p' and along that soldered to the zinc from n' to N.

Thus, in both cases the current starts from the copper, and,
following the course of the wires, returns to the zinc. In the
former case, however, it is continuous ; but in the latter it is
apparently broken, terminating at p', and recommencing at n'.
122

EARTH CONTACT.

24. In the electric theories it is assumed that the course of the
current, when it exists at all, must in all cases be continuous and
unbroken from p to x, as it is in fact under the conditions repre-
sented in fig. 1, when the ends p and n are in contact. It is
therefore assumed that in the case represented in fig. 2, the
stratum of the earth which is interposed between p' and n' plays
the part of a metallic wire joining these points, and that the current
which arrives by the wire P pp' at p flows through the earth, as
indicated by the arrow, to n', from whence it flows along the wire
n' n x to x.

It is found also in this case that the existence of the current is
independent of the lengths of the wires, which do not affect it
otherwise than by diminishing its intensity. Whether the wires
are 10 feet, 10 miles, or 100 miles in length, the current still flows
from P to p' and returns from n' to x.

25. Thus, admitting the generally acknowledged principle that
the stratum of the earth intervening between^' and n' plays the part
of a conducting wire, uniting the ends p' and n' of the wires
buried, it will follow that the current at p', though separated, as it
may be, by a distance of several hundred miles from the point n
of its return to x, finds its way nevertheless through the earth
unerringly and instantaneously to that point.

Of all the miracles of science, surely this is the most marvel-
lous. A stream of electric fluid has its source in the cellars of
the Central Electric Telegraphic Office, Lothbury, London. It
flows under the streets of the great metropolis, and, passing on
wires suspended over a zigzag series of railways, reaches Edin-
burgh, where it dips into the earth, and diffuses itself upon the
buried plate. From that it takes flight through the crust of the
earth, and finds its oicn way back to the cellars at Lothbury ! ! !

Instead of burying plates of metal, it would be sufficient to
connect the wires at each end with the gas or water pipes, which,
being conductors, would equally convey the fluid to the earth ;
and in this case, every telegraphic despatch which flies to Edin-
burgh along the wires which border the railways, would fly back,
rushing to the gas-pipes which illuminate Edinburgh, from them
through the crust of the earth to the gas-pipes which illuminate
London, and from them home to the batteries in the cellars at
Lothbury !

26. To derive all the necessary instruction from what has been
explained above, it will be necessary to distinguish what is
essential from what is merely optional, and which admits of
modification or change without affecting the result.

27. It will be seen that the electric fluid is evolved by the
combination of three bodies, the zinc, the copper, and the acidu-

123

THE ELECTEIC TELEGRAPH.

lated solution in which they are immersed. The production of
the current depends on the chemical action of the solution on the
zinc. That metal being very susceptible of oxydation, decom-
poses the water which is in contact with it. One constituent of
the water combining with the zinc, produces a compound called
the oxyde of zinc, and this oxyde entering again into combination
with the acid which the water holds in solution, forms a soluble
salt. If the acid, for example, be sulphuric acid, this salt will be
the sulphate of the oxyde of zinc, and as fast as it is produced it will
be dissolved in the water in which the slips of metal are immersed.

Meanwhile, the copper not being as susceptible of chemical
action as the zinc, remains comparatively unaffected by the solu-
tion ; but the hydrogen evolved in the decomposition of the water
collects upon its surface, after which it rises and escapes in
bubbles at the surface of the solution.

It is to this chemical action upon the zinc that the production
of the electric current is due. If a like action had taken place in
the same degree on the copper, a similar and equally intense
electric current would be produced in the opposite direction ; and
in that case the two currents would neutralise each other, and no
electric effect would ensue.

From this it will be seen that the efficacy of the combination
must be ascribed to the fact, that one of the two metals immersed
in the solution is more oxydable than the »other, and that the
energy of the effect and the intensity of the current will be so
much the greater as the susceptibility of oxydation of the one
metal exceeds that of the other.

28. It appears, therefore, that the principle may be generalised,
and that electricity will be developed, and a current produced by
any two metals similarly placed, which are oxydable in different
degrees.

Zinc being one of the most oxydable metals, and being also
sufficiently cheap and abundant, is generally used by preference
for voltaic combinations. Silver, gold, and platinum are severally
less susceptible of oxydation, and of chemical action generally,
than copper, and would therefore answer voltaic purposes better,
but are excluded by their greater cost, and by the fact that copper
is found sufficient for all practical purposes.

29. It is not, however, absolutely necessary that the inoxydable
element c c of the combination should be a metal at all. It is
only necessary that it be a good conductor of electricity. In
certain voltaic combinations, charcoal properly solidified has
therefore been substituted for copper, the solution being such as
would produce a strong chemical action on copper.

30. In the above illustration, we have supposed that the
124

VOLTAIC COMBINATIONS.

metallic elements of tlie combination are thin rectangular slips
cut from sheet metal. The form, however, is in no manner
essential to the production of the electric current. So long as
the magnitude of the surfaces exposed to contact with the solution
is the same, the current will have the same force. The pieces of
metal may therefore have the form here supposed of thin rec-
tangular plates, or they may be formed, as is often found con-
venient, into hollow cylinders, that of the copper being so much
less in diameter than that of the zinc, that it is capable of being
placed within it without mutual contact.

The simple arrangement first adopted by Yolta consisted of
two equal discs of metal, one of zinc, and the other of copper or
silver, with a disc of cloth or bibulous card, soaked in an acid or
saline solution, between them. These were usually laid, with
their surfaces horizontal, one upon the other.

The late Dr. Wollaston proposed an arrangement, in which the
copper plate was bent into two parallel plates, a space between
them being left for the insertion of the zinc plate, the contact of
the plates being prevented by the interposition of bits of cork or
other non-conductor. The system thus combined was immersed
in dilute acid, contained in a porcelain vessel.

Dr. Hare of Philadelphia contrived a voltaic arrangement, con-
sisting of two metallic plates, one of zinc and the other of copper,
of equal length, rolled together in the form of a spiral, a space of
a quarter of an inch being left between them. They are main-
tained parallel without touching, by means of a wooden cross at
top and bottom, in which notches are provided at proper distances,
into which the plates are inserted, the two crosses having a
common axis. This combination is let into a glass or porcelain
cylindrical vessel of corresponding magnitude, containing the
exciting liquid.

This arrangement has the great advantage of providing a very
considerable electro-motive surface with a very small volume.

The exciting liquid recommended for these batteries when great
power is desired, is a solution in water of 2 1 per cent, of sulphuric,
o.nd 2 per cent, of nitric acid. A less intense but more durable
action may be obtained by a solution of common salt, or of 3 to 5
per cent, of sulphuric acid only.

31. It is not essential that the water in which the metals are
immersed be acidulated, as we have supposed, by sulphuric acid.
Any acid which will promote the oxydation of the zinc without
affecting the copper will answer. Nor is it indeed necessary that
any acid whatever be used. A saline solution is often found more
convenient. Thus common salt dissolved in the water will
produce the desired effect.

125

THE ELECTRIC TELEGRAPH.

Fig.

Of the various voltaic combinations which have been applied in
scientific researches, four only have been found available to any
considerable extent in the working of electric telegraphs, the zinc
and copper plate combination described above, Daniel's constant
battery, Grove's battery, Bunsen's modification of it, and the
magneto-electric apparatus.

32. Daniel's combination, which is extensively used in
working the telegraphs on the continent, consists of a
copper cylindrical vessel c c, fig. 3, widening near the top
a d. In this is placed a cylindrical vessel of unglazed

porcelain p. In this latter is placed the
hollow cylinder of zinc z, already described.
The space between the copper and porcelain
vessels is filled with a saturated solution of
the sulphate of copper, which is maintained
in a state of saturation by crystals of the
salt placed in the wide cup abed, in the
bottom of which is a grating composed of
wire carried in a zigzag direction between
two concentric rings, as represented in plan

at G. The vessel p, containing the zinc, is filled with a solution
of sulphuric acid, containing from 10 to 25 per cent, of acid when
greater electro-motive power is required, and from 1 to 4 per cent.
when more moderate action is sufficient.

33. The following modification of Daniel's system was adopted
by M. Pouillet in his experimental researches, and is the form
and arrangement used in France for the telegraphs. A hollow
cylinder a, fig. 4, of thin copper, is ballasted with sand &, having

a fiat bottom c, and a conical top d.
Above this cone the sides of the copper
cylinders are continued, and terminate
in a flange e. Between this flange and
the base of the cone, and near the base,
is a ring of holes. This copper vessel
is placed in a bladder which fits it
loosely like a glove, and is tied round
the neck under the flange e. The satu-
rated solution of the sulphate of copper
is poured into the cup above the cone,
and, flowing through the ring of holes,
fills the space between the bladder and
the copper vessel. It is maintained in
its state of saturation by crystals of the
salt deposited in the cup.

This copper vessel is then immersed in a vessel of glazed
126

Fig. 4.

VOLTAIC COMBINATIONS.

porcelain «, containing a solution of the sulphate of zinc or the
chloride of sodium (common salt). A hollow cylinder of zinc A,
split down the side so as to be capable of being enlarged, or con-
tracted at pleasure, is immersed in this solution surrounding the
bladder. The poles are indicated by the conductors p and n, the
positive proceeding from the copper, and the negative from
the zinc.

M. Pouillet states that the action of this apparatus is sustained
without sensible variation for entire days, provided the cup above
the cone d is kept supplied with the salt, so as to maintain the
solution in the saturated state.

In the batteries used for the telegraphs on the French railways,
the liquid in which the zinc cylinder is immersed is pure water,
and this is found to answer in a very satisfactory manner.

The current flows from the copper cylinder and returns as usual
to the zinc.

34. Grove's battery consists of two liquids, sulphuric and nitric
acids, and two metals, zinc and platinum, arranged in the following
manner : —

A hollow cylinder of zinc z z, fig. 5, open at both ends as already
described, is placed in a vessel of glazed porcelain v v. "Within
this is placed a cylindrical vessel v v, of unglazed
porcelain, a little less in diameter than the zinc
z z, so tliat a space of about a quarter of an inch
may separate their surfaces.
In this vessel v v, is inserted a
cylinder c c of platinum, open
at the ends, and a little less
than v vt so that their surfaces
may be about a quarter of an
inch asunder. Dilute sulphuric
acid is then poured into the
vessel v v, and concentrated
nitric acid into vv; p proceed-
ing from the platinum will then
be the positive, and N proceeding from the zinc the negative pole.

Bunsen contrived a battery which has taken his name, and
which, while it retains all the efficiency of Grove's, can be con-
structed at much less expense, the platinum element being replaced
by the cheaper material of charcoal.

In the vessel v v is inserted, instead of a hollow cylinder of
platinum, a solid cylindrical rod of charcoal, made from the
residuum taken from the retorts of gas-works. A strong porous
mass is produced by repeatedly baking the pulverised coke, to
^ liieh the required form is easily imparted. Dilute sulphuric acid

127

Fig. 5.

N '

THE ELECTRIC TELEGRAPH.

is then poured into the vessel v v, and concentrated nitric acid
into v v. The electric fluid issues from a wire connected with the
charcoal, and returns by one connected with the zinc.

Messrs. Deleuil and Son, of Paris, have fabricated batteries on
this principle with great success. I have one at present in use
consisting of fifty pairs of zinc and carbon cylinders, the zinc being
2 1 inches diameter, and 8 inches high, which performs very
satisfactorily.

The chief advantage of Daniel's system is that from which it
takes its name, its constancy. Its power, however, in its most
efficient state, is greatly inferior to that of the carbon or platinum
systems of Bunsen and Grove. A serious practical inconvenience,
however, attends all batteries in which concentrated nitric acid is
used, owing to the diffusion of nitrous vapour, and the injury to
which the parties working them are exposed by respiring it. In
my own experiments with Bunsen' s batteries the assistants have
been often severely affected.

In the use of the platinum battery of Grove, the nuisance pro-
duced by the evolution of nitrous vapour is sometimes mitigated
by enclosing the cells in a box, from the lid of which a tube
proceeds which conducts these vapours out of the room.

In combinations of this kind, Dr. O'Shaugnessy substituted
gold for platinum, and a mixture of two parts by weight of
sulphuric acid to one of saltpetre for nitric acid.

The method of producing the electric fluid by the mutual action
of magnets and bodies susceptible of magnetism will be described
hereafter.

35. Although each of the simple combinations described above
would produce an electric current, which, being transmitted upon a
conducting wire, would be attended with effects sufficiently distinct
to manifest its presence, such a current would be too feeble in its
intensity to serve the purposes of a telegraphic line ; and as no
other simple voltaic combination yet discovered would give to a
current the necessary intensity, the object has been attained by
placing in connection a series of such combinations, in such a
manner that the currents produced by each of them being trans-
mitted in the same direction, on the same conducting wire, a
current having an intensity due to such combination may be
obtained.

Such a series of simple voltaic combinations, so united, is called

a VOLTAIC BATTEBT.

128

CABLE IX THE HOLD OF THE

THE ELECTRIC TELEGRAPH.

CHAPTEE II.

36. Common plate battery. — 37. Combination of currents. — 38. Loss of
intensity by imperfect conduction. — 39. Cylindrical batteries. — 40.
Pairs, elements, and poles denned. — 41. Origin of term voltaic pile, —
42. Use of sand in charging batteries. — 43. To vary intensity of current.
— 44. Batteries used for English telegraphs. — 45. Amalgamating the
zinc plates. — 46. The line-wires, material and thickness. — 47. Objection
to iron wires. — 48. Manner of carrying' wires on posts — 49. Good
insulation. — 50. Expedients for obtaining it. — 51. Forms of insulating
supports. — 52. Dimensions and preparations of the posts. — 53. Forms
of support used in England. — 54. Winding posts. — 55. Supports in
France. — 56. In America. — 57. In Germaoy. — 58. "Wire insulated
by superficial oxydation. — 59. Leakage of the electric fluid by the con-
duction of the atmosphere. — 60. Effects of atmospheric electricity
on the wires. — 61. Lightning conductors — 62. Those of Messrs.
"Walker and Breguet. — 63. Conducting current into stations. — 64.
Underground wires. — 65. Methods of insulating them. — 66. Testing
posts.

LARDNER'S MUSEUM OP SCIENCE. E 129

No. 33.

THE ELECTRIC TELEGEAPH.

36. ONE of the most simple forms of voltaic battery is that
represented in fig. 6, which consists of a glazed earthen-

ware trough, divided by

partitions into a series of

/ + 4- *> 'g"~^_ * x- *• ^fr parallel cells, and a series of

of shape and magnitude cor-
responding with the cells,
attached to a wooden rod,

each c°PPer Plate beins

connected at the top, under
the wood, by a band of
metal, with the zinc plate
which immediately succeeds
it in the series. For brevity, let us designate the first copper plate,
C1} the second C2, the third, C3, and so on, proceeding from A'
towards B', and let the first zinc plate, which is connected with cx
by a metal band, be called z2, the next, which is similarly connected
with C2, be called z3, and so on from A' towards B'. Now, the
intervals between the plates being so arranged as to correspond
with the width of the cells, the series of plates may be let down
into the cells so that a partition shall separate every pair of plates
which are connected by a metal band. Thus, the first partition
will pass between cx and z2, the second between C2 and z3,|the third
between C3 and Z4, and so on. It appears, therefore, that the first
cell proceeding from A towards B will contain only the copper plate
cx, the second will contain c2 and Z2, the third, C3 and z3, and so
on, the last cell at the extremity B of the series containing only
the last zinc plate, which we shall call zn.

Now, it is evident that as the arrangement thus stands, the first
and last cells of the series would differ from the intermediate ones,
inasmuch as, while each of the latter contains a pair of plates,
each of the former contains only a single plate, the first copper
ct and the last zinc zn. To complete the arrangement, therefore,
it will be necessary to place a zinc plate, which we shall call zx, in
the first cell to the left of C1? and so as not to be in contact with it,
and in like manner a copper plate, which we shall call cn, in the
last cell B to the right of zn, and so as not to be in contact with it.
Let wires be soldered to the upper edges of these terminal plates
Zj and cn, and let them be carried to any desired distances, but
finally connected with plates, or any other masses of metal, buried
in the ground at n' and j1/, fig. 7.

These dispositions being made, let us suppose the cells to be
filled with a weak acid solution, such as has been already described,
but so that the liquid in one cell may not overflow into the next.
130

VOLTAIC BATTERIES.

A current of electricity will now be established along the wire
passing as indicated by the arrows, from the last copper plate atP,

to the earth at p', and returning by ri to the first zinc plate zv
at y.

This current is produced by the combined voltaic action of all
the pairs of plates contained in the cells of the trough.

37. The current produced by the combination zx cv in the first
cell, will flow from the plate cx by the band of metal to the plate
Z2, in the second cell. It will follow this course because of the
conducting power of the metals, and the insulating power of the
wood and earthenware, which prevents its escape. From the plate
z2 it will pass through the acidulated water to the plate C2, for
although this water has not a conducting power equal to that of
metal, it has nevertheless sufficient to continue the current to c2.
From C2 it will pass by the band of metal to z3, and from that
through the liquid in the third cell to C3, and from that by the
metal to Z3, and so on until it arrives at the last plate cn of the
series, from which it will pass, by the conducting wire, from P to p'.

It is evident, therefore, that the current produced by the voltaic
combination in the first cell must pass successively through the
plates and liquid in all the cells before it can arrive at P.

In the same manner it may be shown that the current produced
in the second cell containing z2 and C2 must pass through all the
succeeding cells before it can reach P, and so of all the others.

38. !Xow, if the metals and liquid were perfect conductors, each
of these currents would arrive at P with undiminished force, and
then the current upon the wire P p' would be as many times more
intense than a current produced by a single voltaic combination as
there are cells. But this is not so. The metals copper and zinc,
though good conductors, are not perfect ones, and the acidulated
water is a very imperfect one. The consequence is, that the
currents severally produced in each of the cells, suffer a consider-
able loss of force before they arrive at the conducting wire ?p'\ and
mathematical formulae, based on theoretical principles and practical
data, have been contrived to express in each case the effects of this

K 2 131

THE ELECTRIC TELEGRAPH.

diminution of force due to the imperfect conducting power, or the
resistance, as it has been called, of the elements of the battery.

Without going into the reasoning upon which these investiga-
tions are founded, it will be sufficient for our present object to
state, that in all cases, a current of greater or less force is trans-
mitted to the terminal plate of the series from each of the cells, no
matter how numerous they may be, and in some cases batteries
have been constructed and brought into operation, in scientific
researches, which consisted of as many as two thousand pairs of
plates.

39. To simplify the explanation, as well as because the form
described is very generally used for telegraphic purposes, we have
here selected the plate battery to illustrate the general principle
iipon which all voltaic combinations are founded. In fig. 8 is

represented the dispo-
8. sition of the cylinders

in a battery formed on
the principles of Daniel
or Grove, where the
metallic connection of
each copper or charcoal
element of one pair,
with the zinc element

of the succeeding pair, is represented by a rectangular metallic bar

or wire.

40. Each combination of two metals, or of one metal and char-
coal, which enters into the composition of a battery, is usually
called a PAIR, and sometimes an ELEMENT. Thus, a battery is
said to consist of so many PAIRS, or so many ELEMENTS.

The end of the battery from which the current issues is called
its POSITIVE POLE, and that to which it returns is called its
NEGATIVE POLE. Thus, in the batteries explained above, P is the
positive, and N the negative pole.

Since in the most usual elements, zinc and copper, the current
issues from the last copper plate, and returns to the first zinc
plate, the positive pole is sometimes called the COPPER POLE, and
the negative the ZINC POLE.

41. The voltaic battery is sometimes called the VOLTAIC PILE.
This term had its origin from the forms given to the first voltaic
combination by its illustrious inventor.

The first pile constructed by Volta was formed as follows : — A disc
of zinc was laid upon a plate of glass. Upon it was laid an equal
disc of cloth or pasteboard, soaked in acidulated water. Upon this
was laid an equal disc of copper. Upon the copper were laid, in
the same order, three discs of zinc, wet cloth, and copper, and the
132

VOLTAIC PILE.

Fig. 9.

same superposition of the same combinations of zinc, cloth, and
copper, was continued until the pile was completed. The highest
disc (of copper) was then the positive, and the lowest disc (of zinc)
the negative pole, according to the principles already explained.

It was usual to keep the discs in their places by confining them
between rods of glass.

Such a pile, with conducting wires connected
with its poles, is represented in fig. 9.

42. As the batteries used on telegraphic
lines are liable to frequent removal from place
to place while charged with the acidulated
water, or other exciting liquid, it has been
found desirable to contrive means to prevent
such liquid from being spilled, or thrown from
cell to cell. This has been perfectly accom-
plished by the simple expedient of filling the
cells with silicious sand, which is kept satu-
rated with the exciting liquid so long as the
battery is in operation.

43. It is often necessary, in telegraphic
operations, to vary the intensity of the current.
This is accomplished, within certain limits,
without changing the battery, in the following
manner : —

If it be desired to give the full force of
the battery to the current, the wires are
attached to the terminal plates, so that the
entire battery is between them. But if any
less intensity is desired, the wires, or one of
them, is attached to intermediate plates, so
that they shall include between them a part
only of the battery. The part included between them is alone
active in producing the current, all the elements which are outside
the wires being passive. The battery, in effect, is converted into
one of fewer elements.

Provisions are made, which will be explained hereafter, by
which the operator can, by a touch of the hand, thus vary the
force of the battery.

44. The batteries generally used for the English telegraphs
are those described in (36). They are usually charged with
sand, wetted with water mixed with sulphuric acid, in the pro-
portion of about one part of strong acid to fifteen of water. A
more intense current could be produced by using a stronger
solution, but it is found preferable to augment its intensity by
increasing the number of plates in the battery. The dimensions

133

THE ELECTIUC TELEGKAPH.

D£ the plates are generally four to five inches wide, and three to
four inches deep. The thickness of the zinc plates is something
less than a quarter of an inch. The cells are filled with sand to
within an inch of the top, and the parts of the plates above the
sand are varnished as a protection against corrosion, and to keep
them clean. In general, the troughs are made either of glazed
earthenware or some compact wood, such as oak, or teak, made
water-tight by cement or marine glue. When the trough is wood
the partitions of the cells are slate, the width of each cell being
one inch and a quarter to one inch and a half. The troughs
contain, some twenty-four, and some twelve cells.

Batteries of this sort, consisting of twenty-four cells, give a
current of sufficient force for a line of wire of 15 miles. For
50 miles, 48 cells, and for 75 miles, three troughs of 24 cells are
required. Mr. Walker considers that these batteries give super-
fluous force, but that it is necessary to provide against the
contingency of leakage by accidental defects of insulation.

45. The durability of these batteries is increased by amalga-
mating the zinc plates. This is effected by first washing them in
acidulated water, and then immersing them in a bath of mercury
for one or two minutes. The mercury will combine with the zinc
and form a superficial coating of the amalgam of zinc. When they
are worn by use, they may be restored, by scouring them, and
submitting them to the same process, and this may be continued
until the zinc become too thin to hold together.

Mr. Walker states that new batteries, when carefully put
together, will, with care, do duty for six or eight months, when
the work is not very heavy ; and by washing the sand out with a
fiow of water, and refilling them, they have frequently remained
on duty ten or twelve months, or even more, without having been
sent in for re-amalgamation.*

46. Having explained, generally, the manner in which the
electric current is produced and maintained, I shall now proceed to
explain the various expedients by which it is conducted from station
to station, along the telegraphic line, and by which injurious
waste by leakage or drainage is prevented or diminished.

The conducting wires used for telegraphic lines are of iron,
usually the sixth of an inch in diameter. On all European lines
they are submitted to a process called galvanisation, being passed
through a bath of liquid zinc, by which they become coated with
that metal. This zinc surface being easily oxydable, is soon, by
the action, of air and moisture, converted into the oxyde of zinc,
which, being insoluble by water, remains upon the wire, and
protects the iron from all corrosion.

* El. Tel. Manip., p. 8.

LINE WIRES.

When a great length of wire is to be stretched between two
distant points without intermediate support, steel wire is often
preferred to iron, in consequence of its greater strength and
tenacity.

Copper being a better conductor of electricity than iron, as well
as being less susceptible of oxydation, would on these accounts be
more eligible for telegraphic purposes. Its higher price, and the
possibility of compensation for the inferior conducting power of
iron, by using greater battery power, has rendered it preferable
to use that metal.

47. Mr. Highton, the inventor of some important improvements
in telegraphic apparatus, affirms that, when galvanised iron wires
pass through large towns where great quantities of coal are
burnt, the sulphureous acid gas resulting from such combustion
acting upon the oxyde of zinc which coats the conducting wire,
converts it into a sulphate of zinc, which being soluble in water,
is immediately dissolved by rain, leaving the iron unprotected.
The wire consequently soon rusts, and is corroded. Mr. Highton
says, that in some cases he has found his telegraph wires reduced
by this cause to the thinness of a common sewing needle in less
than two years.

The wires used on the American lines are of iron, similar to the
European, but are not galvanised. They soon become coated with
their own oxyde. A pair of galvanised wires have been placed
between New York and Boston, and I have been informed by Mr.
Shafiher, the secretary of the American Telegraph Confederation, that
at certain times during the winter, it has been found that they were
unable to work the telegraph with these wires, while its operation
with the wires not galvanised, was uninterrupted. Mr. Shaflher
also states that several anomalous circumstances have been mani-
fested upon some extensive lines of wire erected on the vast
prairies of Missouri. Thus, in the months of July and August, it
is found that the telegraph cannot be worked from two to six in the
afternoon, being the hottest hours of the day. These circumstances
are ascribed to some unexplained atmospheric effects.

48. The manner in which the conducting wires are carried from
station to station is well known. Every railway traveller is familiar
with the lines of wire extended along the side of the railways,
which, when numerous, have been not unaptly compared to the
series of lines on which the notes of music are written, and which
are the metallic wires on which invisible messages are flying con-
tinually with a speed that surpasses imagination. These are sus-
pended on posts, erected at intervals of about sixty yards, being
at the rate of thirty to a mile. They therefore supply incidentally
a convenient means by which a passenger can ascertain the speed

135

THE ELECTRIC TELEGRAPH.

of the train in which he travels. If he count the number of
telegraph posts which pass his eye in two minutes, that number
will express in miles per hour the speed of the train.

49. Since the current of electricity which flows along the wire
has always a tendency to pass by the shortest route possible to the
ground, it is evident that the supports of the wires upon these
posts ought to possess, in the highest attainable degree, the pro-
perty of insulation ; for even though the entire stream of electrical
fluid might not make its escape at any one support, yet if a little
escaped at one and a little at another, the current would, in a
long line, be soon so drained that what would remain would be
insufficient to produce those effects on which the efficiency of the
telegraph depends. Great precautions have therefore been taken,
and much scientific ingenuity has been expended in contriving
supports which shall possess, in the highest attainable degree, the
property of insulation.

50. To each of these posts or poles are attached as many tubes or
rollers, or other forms of support, in porcelain or glass, as there are
wires to be supported. Each wire passes through a tube, or is
supported on a roller ; and the material of the tubes or rollers being
among the most perfect of the class of non-conducting substances,
the escape of the electricity at the points of contact is impeded.

Notwithstanding various precautions of this kind, a considerable
escape of electricity still takes place in wet weather. The coat of
moisture which collects on the wire, its support, and the post,
being a conductor, carries away more or less of the fluid. Conse-
quently, more powerful batteries are necessary to give effect to the
telegraph in wet than in dry weather.

In England, and on the Continent, the material hitherto used
for the supports of the wires is principally a sort of earthen or
stone ware. In the United States it is generally glass.

51. The forms of these insulating supports are various. Tubes,
rings, collars, and double cones, are severally used. The material
used most commonly in England, a sort of brown stoneware, has
the advantage, besides being a good insulator, of throwing off wet,
as water falls from a duck's wing, leaving the surface dry. A pitcher
of this ware, plunged in water, scarcely retains any moisture upon it.

52. The posts vary generally from 15 to 30 feet in height, the
lowest wire being about ten feet above the ground, except in
cases where greater height is required to allow vehicles to pass
under it, as when the wires cross a common road, or pass from
one side of the railway to the other. The poles are about 6
inches square at the top, and increase to 8 inches at the bottom.
In some cases they are impregnated with certain chemical solutions,
to preserve them from rotting, and are generally painted, the parts

136

POST FOR WIRES.

Fi

which are in the ground being charred and tarred. The manner
of treatment, however, varies in different countries.

53. In figs. 10 and 11 are
represented different forms of
supports used in England.
To cross-pieces of wood, A A',
bolted upon the post (fig. 10),
are attached balls, 6, of stone-
ware, as described above, in
which grooves or slits are
formed to receive and support
the wires. These supports
are protected from rain and
from the deposition of dew by
hoods of zinc-coated iron
placed over them. Glass being
so much better an insulator,
balls of that material are re-
cently being substituted for
the stoneware.

Another form of support,
sheltered by a sort of sloping roof, is represented in fig. 11. On the front
of the post is a wooden arm to which a series of stone-ware rings are

attached, through which the wires pass. These rings have the form
of two truncated cones placed with their larger bases in contact.

It is usual, where the wires are numerous, as on some of the
lines near London, to attach these supports both to the front and

137

THE ELECTRIC TELEGKAPH.

back of the post. So many as thirteen of these supports may be
seen upon some of the posts of the North- Western line near
London. The wires supported on some of these are continued to
Liverpool and Manchester, and some even to Glasgow.

54. If the same wire were carried over a succession of supports
for a certain distance, they would after a certain time become
slack and hang in curves between post and post. This would be
attended with great inconvenience and confusion, inasmuch as
one wire — especially when agitated by wind — would come in con-
tact with another, so that the currents running along them would
pass from one to another, and the proper signals conveyed by
such currents would no longer reach their destination.

To prevent this, apparatus for tightening the wire are on all
such lines provided at convenient distances, such as half-a-mile,
upon posts which are thence called winding posts. These posts
are of larger dimensions than the ordinary posts. A grooved
drum, on which the wire is wound, is attached to them by a bolt,
which passes through the post, but clear of the wood. Upon this
bolt is fixed a ratchet wheel by which the drum may be turned
in one direction, so as to coil the wire upon it, with a catch which
prevents its recoil in the other direction, and therefore maintains
the tension of the wire. The bolt is kept from contact with the
post by passing through a stoneware collar.

The current passes through the winder and the bolt, these
being metallic, but in case of any interruption arising from the

Tig. 12.

oxydation of their surfaces a supplemental piece of conducting
wire is provided, which connects the main wires at points taken
above and below the winding post, as represented in fig. 12.
138

INSULATING SUPPORTS.

55. In France the posts are from twenty to thirty feet high,
placed at distances varying from sixty to seventy yards asunder,
and sunk to a depth of from three to seven feet in the ground.
They are impregnated with sulphate of copper to preserve them
from rotting by damp.

The conducting wire rests in an iron hook, which is fastened
by sulphur into the highest part of the cavity of an inverted
bell, formed of porcelain, from which two ears project, which are-
screwed to the post.

A section of this apparatus is given in fig. 13, and a side view
in fig. 14, the figures being one-fifth of the actual magnitude.

The winding posts are placed at distances of a kilometre (six-
tenths of a mile). The apparatus used for tightening the wire
consists of two drums or rollers,
each carrying on its axis a ratchet
wheel with a catch. These drums
are mounted on iron forks formed
at the ends of an iron bar, which
is passed through an opening
in a porcelain support, and se-
cured in its position by pins, the
porcelain support being attached
to the post by screws passing through ears projecting from it.

A front view of this winding apparatus is given fig. 15 ; a

Fig. 15.

14*

Fig. 16.

side view of the porcelain support showing the opening through
which the iron bar is passed, and the screws by which it is.
attached to the post, is given in fig. 16.
These figures are one-fifth of the real
magnitude of the apparatus.

The conducting wires used in France
are similar to those used on the English
lines.

56. The insulating supports of the
wires used on the American lines are
very various in form.

The supports upon the principal
Morse lines consist of a glass knob,

133

THE ELECTRIC TELEGRAPH.

fig. 17, upon which two projecting rings are raised in the
groove between which the wire is wrapped. This glass knob

Fig. 17

attached to an iron shank

as represented in fig. 18, which
is driven into the post.

Another form of support
used on these lines is repre-
sented in fig. 19, which consists
of two rectangular blocks of
glass, in each of which is a semi-

cylindrical groove corresponding with the thickness of the con-
ducting wire, so that the wire being laid in the groove of one
of them, and the other being laid upon it, will be completely
enclosed within the block of glass produced by
their union. These blocks of glass are surrounded
and protected by a larger block of wood, as repre-
sented in the figure, where the white part represents
the glass, and the shaded part the wood.

The supports are sometimes attached to the sides
of the posts, and sometimes placed upon an hori-
zontal cross bar, as represented in fig. 20.

Fig. 20.

Fig. 19.

The supports used in House's lines consist of a glass cnp about
five inches in length and four inches in diameter, having a
coarse screw-like surface cut inside and out. This glass cap
(2) fig. 21 is screwed and cemented into a bell - shaped iron
cap (1) from three to four pounds, in weight, projecting an
inch below the lower edge of the glass, protecting it from
being broken; this is fitted with much care to the top of
140

INSULATING SUPPORTS.

Tig. 21.

the pole (3), and is covered with paint or varnish. The con-
ducting wire is fastened to the top of the cap by projecting
iron points, and the whole of the iron cap is thus in the circuit, as
the wire is of iron and not insulated. To
prevent the deposit of moisture, the glass is
covered by a varnish of gum-lac dissolved
in alcohol, and the ring-like form of the
glass is to cause any moisture to be
carried to the edge and there drop off.*

The wires on the American lines are
not usually galvanised.

57. One of the forms of insulating sup-
port used on the German lines is repre-
sented in fig. 22, and consists of an
insulating cap placed on the tapering end
of a post T. The post terminates in a
point c, an inch and a half in length
and about six lines in diameter; this
pole is covered with a porcelain cap d d,
a sort of reversed cup ; on its summit e,
with lead, in which the conducting wire

b b enters ; this insulator is then covered
with a roof.

58. It may be asked what prevents
the escape of the electric fluid from
the surface of the wire between post
and post ? In general when wires are
used on a smaller scale for the trans-
mission of electric currents, the escape
of the fluid is prevented by wrapping
them with silk or cotton thread, which
thus forms a non-conducting cover
upon them, but on the scale on which
they are used on telegraphic lines
the expense of this, independently

of the difficulty of protecting such covering from destruction by
weather, would render it inadmissible.

59. The atmosphere, when dry, is a good non-conductor ; but
this quality is impaired when it is moist. In ordinary weather,
however, the air being a sufficiently good non-conductor, a
metallic wire will, without any other insulating envelope except
the air itself, conduct the stream of electricity to the necessary
distances. It is true that a coated wire, such as we have

* Turnbull on the Electric Telegraph, p. 176.

Philadelphia, 1853.
141

THE ELECTRIC TELEGRAPH.

described, would be subject to less waste of the electric fluid en
route ; but it is more economical to provide batteries sufficiently
powerful to bear this waste, than to cover such extensive lengths
of wire with any envelope.

60. Atmospheric electricity having been found to be occasion-
ally attracted to the wires, and to pass along them, so as to
disturb the indications of the telegraphic instruments, and
sometimes even to be attended with no inconsiderable danger
to those employed in working the apparatus ; various expedients
have been contrived for removing the inconvenience and averting
the danger. The current produced by this atmospheric electricity
is often so intense as to render some of the finer wires used in
certain parts of the apparatus at the stations, red hot, and
sometimes even to fuse them. It also produces very injurious
effects by demagnetising the needles, or imparting permanent
magnetism to certain bars of iron included in the apparatus,
which thus become unfit for use.

61. One of the expedients used for the prevention of these
inconvenient and injurious effects is to place common lightning
conductors on the posts. The points of these are shown upon the
posts in figs. 10, 11, and 12.

62. Mr. Walker of the South Eastern Company and M. Bre-
guet of Paris, have each invented an instrument for the better
protection of telegraphic stations from atmospheric electric dis-
charges. Both these contrivances have been found in practice to
be efficacious, and though differing altogether in form they are
similar in principle. In both, a much finer wire than any which
lies in the regular route of the current is interposed between the
line wire and the station, so that an intense and dangerous
atmospheric current must first pass this fine wire before reaching
the station. Now it is the property of such a current to raise the
temperature of the conductor over which it passes to a higher
and higher point in proportion to the resistance which such con-
ductor offers to its passage. But the resistance offered by the
wire is greater in the same proportion as its section is smaller.
The safety wire interposed in these contrivances is, therefore, of
such thinness that it must be fused by a current of dangerous
intensity. The wire being thus destroyed all electric communi-
cation with the station is cut off, and the extent of the incon-
venience is the temporary suspension of the business of the line
until the breach has been repaired.

Expedients are used on the American lines to divert the

atmospheric electricity from the wires, consisting merely of a

number of fine points projecting from a piece of metal connected

with the earth by a rod of metal. These points are presented to

142

UNDERGROUND WIRES.

a metal plate, or other surface, attached to the line wire at the
place where it enters the station. It is found that these points
attract the atmospheric electricity, which passes to the ground by
the conductor connected with them, but do not attract the
electricity of the battery current.

63. The wires extended from post to post are continued in passing
the successive stations of the line. The expedients by which the
current is turned aside from the main wire, and made to pass through
the telegraphic office of the station, differ more or less in their
details on different lines and in different countries, but are founded
on the same general principles. It will therefore be sufficient here
to describe one of those commonly used on the British lines.

The conducting wire of the main line in passing the station is
cut and the ends jointed by a shackle, as represented in fig. 12,
in the case of a winding post. This shackle breaking the
metallic continuity would stop the course of the current. A wire
is attached to the line wire below the shackle so as to receive the
current which the latter would stop, and is carried on insulating
supports into the telegraphic office and put in connection with the
telegraphic instrument. Another wire connected with the other
side of the instrument receives the current on leaving it, and
being carried back on insulating supports to the line wire, is
attached to the latter above the shackle, and so brings back the
current which continues its progress along the line wire.

64. Although the mode of carrying the conducting wires at a
certain elevation on supports above the ground has been the most
general mode of construction adopted on telegraphic lines, it has
been found in certain localities subject to difficulties and incon-
venience, and some projectors have considered that in all cases it
would be more advisable to carry the conducting wires underground.

This underground system has been adopted in the streets of
London, and of some other large towns. The English and Irish
Magnetic Telegraph Company have adopted it on a great extent
of their lines, which overspread the country. The European
Submarine Telegraph Company has also adopted it on the line
between London and Dover, which follows the course of the old
Dover mail-coach road by Gravesend, Rochester and Canterbury.

65. The methods adopted for the preservation and insulation or
these underground wires are various.

The wires proceeding from the central telegraph station in
London are wrapped with cotton thread, and coated with a
mixture of tar, resin, and grease. This coating forms a perfect
insulator. Nine of these wires are then packed in a half-inch
leaden pipe, and four or five such pipes are packed in an iron pipe
about three inches in diameter. These iron pipes are then laid

143

THE ELECTRIC TELEGRAPH.

under the foot pavements, along the sides of the streets, and are
thus conducted to the terminal stations of the various railways,
where they are united to the lines of wire supported on posts
along the sides of the railways, already described.

66. Provisions, called testing posts, are made at intervals of a
quarter of a mile along the streets, by which any failure or
accidental irregularity in the buried wires can be ascertained,
and the place of such defect always known within a quarter of
a mile.

144

1'ig. 34. — LAYISG THE CABLE FROM THE DECK OF THE SHIP.

THE ELECTRIC TELEGRAPH.

CHAPTER III.

67. Wires of Magneto-electric Telegraph Company. — 68. Mr. Bright' s
method of detecting faulty points. — 69. Such failure of insulation
rare. — 70. Underground method recently abandoned in Prussia. —
71. Underground wires of the European and Submarine Company.
— 72. Imperfect insulation in tunnels. — 73. Mr. Walker's method ol
remedying this. — 74. Overground system adopted through the streets
of cities in France, and in the United States. — 75. Telegraphic lines
need not follow railways. — 76. Do not in America nor in certain
parts of Europe. — 77. Submarine cables. — 78. Cable connecting Dover
and Calais. — 79. Failure of first attempt — Improved structure. —
SO. Table of submarine cables and their dimensions. — 81. Dimensions
and structure of the Dover and Calais cable. — 82. Holyhead and
Howth cable. — 83. First attempt to lay cable between Portpatrick
and Donaghadee — its failure. — 84. Dover and Ostend. — 85. Port-
patrick and Donaghadee. — 86. Orfordness and the Hague.

67. THE \vires of the Magnetic Telegraph Company are laid and
protected in the following manner.

LARDNER'S MUSEUM OF SCIENCE. L 145

Ko. 3f.

THE ELECTRIC TELEGRAPH.

Ten conducting wires are enveloped in a covering of gutta-
percha, so as to be completely separated one from another. Thus
prepared they are deposited in a square creosoted wooden trough
measuring three inches in the side, so that nearly a square inch
of its cross section is allowed for each of the wires. This trough
is deposited on the "bottom of a trench cut two feet deep along the
side of the common coach road. A galvanised iron lid, of about
an eighth of an inch thick, is then fastened on by clamps or small
tenter hooks, and the trench filled in.

A section of the trough in its actual size is given in fig. 23.

Fig. 23.— Galvanised Iron Lid, No. 14, Birmingham Wire Gauge.

Creosoted Deal Troughiug.

The method of laying the wires in the streets adopted by this
company is a little different. In this case iron pipes are laid, but
they are split longitudinally. The under halves are laid down
in the trench, and the gutta-percha covered wires being deposited,
the upper halves of the pipes are laid on and secured in their places,
by means of screws through flanges left outside for the purpose.

To deposit the rope of gutta-percha-covered wires in the
trough it is first coiled upon1 a large drum, which being rolled
along slowly and uniformly over the trench, the rope of wires is
payed off easily and evenly into its bed.

So well has this method of laying the wires succeeded that in
Liverpool the entire distance along the streets from Tithe Barn
145

UNDERGROUND WIRES.

Railway station to the Telegraph Company's offices in Exchange
Street, East, was laid in eleven hours ; and in Manchester the
line of streets from the Salford Railway station to Ducie Street,
Exchange, was laid in twenty-two hours. This was the entire
time occupied in opening the trenches, laying down the telegraph
wires, refilling the trenches and relaying the pavement.

68. One of the objections against the underground system of
conducting wires, was, that while they offered no certain guarantee
against the accidental occurrence of faulty points where their
insulation might be rendered imperfect, and where, therefore, the
current would escape to the earth, they rendered the detection of
such faulty points extremely difficult. To ascertain their position
required a tedious process of trial to be made from one testing
post to another, over an indefinite extent of the line.

A remedy for this serious inconvenience, and a ready and
certain method of ascertaining the exact place of such points of
fault without leaving the chief, or other station at which the
agent may happen to be, has been invented and patented by the
Messrs. Bright of the Magnetic Telegraph Company.

Instruments called Galvanometers, which will be more fully
described hereafter, are constructed, by which the relative intensity
of electric currents is measured by their effect in deflecting a
magnetic needle from its position of rest. The currents which
most deflect the needle have the greatest intensity, and currents
which equally deflect it have equal intensities.

The intensity of a current diminishes as the length of the con-
ducting wire — measured from the pole of the battery to the point
where it enters the earth — is augmented. Thus, if this length be
increased from twenty miles to forty miles, the intensity of the
current will be decreased one half.

The intensity of the current is also decreased by decreasing the
thickness of the conducting wire. Thus the intensity, when
transmitted on a very thin wire, will be much less than when
transmitted on a thick wire of equal length ; but the thick wire
may be so much longer than the thin that its length will com-
pensate for its thickness, and the intensity of the current trans-
mitted upon it may be equal to that transmitted on the shorter
and thinner wire.

The method of Messrs. Bright is founded upon this property
of currents. A fine wire wrapped with silk or cotton so as to
insulate it and prevent the lateral escape of the current, is rolled
upon a bobbin like a spool of cotton used for needle- work. A con-
siderable length of fine wire is thus comprised in a very small bulk.

The wire on such a bobbin being connected by one end with the
wire conducting a current, and by the other end with the earth,

L2 147

THE ELECTEIC TELEGRAPH.

will transmit the current with a certain intensity depending on
its length, its thickness, and, in fine, on the conducting power of
the metal of which it is made.

Now let us suppose that a certain length of the wire of the
telegraphic line be taken, which will transmit a current of the
same intensity. A galvanometer placed in each current will
then be equally deflected. But if the length of the line wire be
less or greater than the exact equivalent length, the galvanometer
will be more or less deflected by it than it is by the bobbin wire,
according as its length is less or greater.

It is, therefore, always possible by trial to ascertain the length
of line wire, which will give the current the same intensity as
that which it has upon any proposed bobbin wire.

Bobbins may therefore be evidently made carrying greater
or less lengths of wire upon which the current will have the
same intensity as it has upon various lengths of line wire.

Suppose then a series of bobbins provided, which in this sense
represent various lengths of line wire from 100 feet to 300 miles,
and let means be provided of placing them in metallic connection
in convenient cases.

Such an apparatus is that by which the Messrs. Bright detect
the points of fault.

Let B be the station battery, G a galvanometer upon the line
wire, F the point of fault at which the current escapes to the

Fig. 24. F

earth, in consequence of an accidental defect of
the insulation. Let a wire be attached to the line
wire of the station, at o, and let it be connected
with the first of a series of bobbins such as are
described above ; let a galvanometer, similar to G,
be placed upon it at G'. Let a metallic arm A c,
turning on the point A, be so placed that its ex-
tremity c shall move over the series of bobbins,
and that by moving it upon the centre A, the end
c may be placed in connection with the wire of
any bobbin of the series. Let A be connected by
a conducting wire with the earth at E', the nega-
tive pole of the battery B being connected with the earth at E.

The apparatus being thus arranged, let us suppose that the

wire A c is placed in connection with the first bobbin, representing

10 miles of the line wire, and that the distance G F of the point of

fault is 145 miles. In that case the battery current will be

143

DETECTOR OF FAULTS.

divided at o, between the two wires o G and o G', but the chief
part will flow by the shortest and easiest route, and the galvano-
meter G' will be very much, and G very little, deflected. This will
show that F must be very much more than 10 miles from the
station. The arm A c will then be turned successively from bobbin
to bobbin. AVhen directed to the second bobbin, the current on
o G' will have the same intensity as if it flowed on 20 miles of
line wire, when turned to the third the same as if it flowed on 30
miles of line wire, and so on. The needle of G' will, therefore,
continue to be more deflected than that of G, although the dif-
ference will be less and less, as the number of bobbins brought
into the circuit is increased. When the bobbins included
represent 140 miles, G' will be a little more, and when they
represent 150 miles it will be a little less deflected than G, from
which it will be inferred that the point of fault lies between the
140th and the 150th mile from the station. A closer approxima-
tion may then be made by the introduction of shorter bobbins, and
this process may be continued until the place of the fault has been
discovered with all the accuracy necessary for practical purposes.

69. It appears nevertheless, that in the practical working of the
telegraphic lines, occasions for the application of these expedients
are of extremely rare occurrence. During the four winter
months of November, December, January, and February 1853-54,
distances of 300 miles of underground wire, without any break of
circuit, have been in constant operation under the Magnetic
Telegraphic Company, and notwithstanding an unusual pre-
valence of unfavourable weather, with frequent and continued
snow-storms, no stoppage whatever has taken place.

70. The Prussian underground lines of wire have been attended,
however, with occasional failures, which have produced some public
inconvenience. This circumstance has been ascribed to the faulty
method of laying the wires. The gutta-percha enveloping them
was mixed with sulphur, a process called Vulcanisation. Upon
being deposited in the ground the sulphur was soon abstracted,
leaving the gutta-percha brittle and porous.

71. The under-ground line of the European and Submarine
Company, from London to Dover, is laid down in nearly the same
manner as that of the Magnetic Company. There are six conduct-
ing copper wires encased in gutta percha. To detect the more
easily the place of any accidental breach of continuity, a box
is placed at the end of each mile, in which a few yards of the
continuous line of wire are coiled, so that in case of any accidental
interruption occurring to the flow of the current, the particular
mile in which that interruption exists can always be ascertained
by putting the coils at the end of each successive mile in

149

THE ELECTRIC TELEGRAPH.

connection with, a portable battery. The current will fail at the
particular mile within which, the fault has taken place.

72. In passing through tunnels the overground wires have
been subject to great inconvenience, owing to the quantity of
water percolating through the roof, constantly falling on the wires
and their supports, and thus injuring their insulation. It has
been found that from this cause the current transmitted along one
wire has been subject to leakages, a part of it passing by the
moisture which surrounds the supports to an adjacent wire, so
that being thus divided, part either returns to the station from
which it has been transmitted, or goes on to a station for which
it is not intended.

73. This inconvenience would be removed by adopting for
tunnels the under-ground system. Mr. "Walker, to whom great
experience in the practical business of electric telegraphy, and
considerable scientific knowledge must give much authority on
such a subject, has adopted apparently with very favourable
results a method of covering the wires, which pass through
tunnels, with a coating of gutta-percha. The conducting wire
thus treated is copper wire No. 16. The gum being well cleaned
and macerated by steam, is put upon the wire by means of
grooved rollers. The diameter of the covered wire is a quarter of
an inch. Mr. "Walker states that in all the wet tunnels under his
superintendence he has substituted this gutta-percha-covered wire
for the common line wire, and has thus " accomplished telegraphic
feats which could not have been attempted on the old plan."

74. In France and in the United States the wires, even in the
cities and towns, are conducted on rollers at an elevation, as on
other parts of the lines. In Paris, for example, the telegraphic
wires proceeding from the several railway stations are carried
round the external boulevards and along the quays, the rollers
being attached either to posts or to the walls of houses or
buildings, and are thus carried to the central station at the
Ministry of the Interior.

75. In Europe, the telegraphic wires have until very lately
invariably followed the course of railways ; and this circumstance
has led some to conclude that, but for the railways, the electric
telegraph would be an unprofitable project.

76. This is however a mistake. Independently of the case of the
Magnetic Telegraph Company already mentioned, the wires in the
United States, where a much greater extent of electric telegraph
has been erected and brought into operation than in Europe, do not
follow the course of the railways. They are conducted, generally,
along the sides of the common coach-roads, and sometimes even
through tracts of country where no roads have been made.

150

POSTS AND WIRES OX COMMON ROADS.

It has been contended in Europe that the wires would not be safe
unless placed within the railway fences. The reply to this is,
i hat they are found to be safe in the United States, where there is
a much less efficient police, even in the neighbourhood of towns,
and in most places no police at all. • It may be observed, that the
same apprehensions of the destructive propensities of the people
have been advanced upon first proposing most of the great im-
provements which have signalised the present age. Thus, when
railways were projected, it was objected that mischievous indi-
viduals would be continually tearing up the rails, and throwing
obstructions on the road, which would render travelling so dan-
gerous that the system would become impracticable.

When gas-lighting was proposed, it was objected that evil-
disposed persons would be constantly cutting or breaking the
pipes, and thus throwing whole towns into darkness.
' Experience, nevertheless, has proved these apprehensions ground-
less ; and certainly the result of the operations on the electric
telegraph in the United States goes to establish the total inutility
of confining the course of the wires to railways. Those who have
been practically conversant with the system both in Europe and
in America, go further, and even maintain that the telegraph is
subject to less inconvenience, that accidental defects are more
easily made good, and that an efficient superintendence is more
easilv insured oil common roads, according to the American
system, than on railways.

These reasons, combined with the urgent necessity of extending
the Electric Telegraph to places where railways have neither been
constructed nor contemplated, have led to the general departure
of the telegraphic wires from the lines of railway in various parts
of the continent. In France, particularly, almost all the recently-
constructed telegraphic network is spread over districts not inter-
sected by railways, and even where railways prevail, the wires are
often, by preference, carried along the common road.

77. When channels, straits, arms of the sea, or rivers of great
width intervene between the successive points of a telegraphic
line, the conducting wires are deposited upon the bottom of the
water, protected from the effects of mechanical and chemical
action by various ingenious expedients. A considerable number
of such subaqueous conductors have been fabricated for telegraphic
lines in various countries, and others are in progress or contem-
plated. Before June 1854, wire ropes had been made for the
lines between Dover and Calais, Dover and Ostend, Dublin and
Holyhead, Donaghadee and Portpatrick, England and Holland, the
Zuyder Zee, the Great Belt (Denmark), the Mississippi, New
Brunswick and Prince Edward's Island, and Piedmont and Corsica.

151

THE ELECTRIC TELEGRAPH.

78. The earliest attempt to transmit a voltaic current under
water for telegraphic purposes, is attributed to Dr. O'Shaughnessy,
who is so well known for his successful exertions to establish
the electric telegraph in India. He succeeded in 1839 in de-
positing an insulated conducting wire, attached to a chain cable,
in the river Hoogly, by which the electric current was transmitted
from one bank of that river to the other.

The first important project of this kind which was executed in
Europe, was the connection of the coasts of England and France
by the submarine cable, deposited in the bed of the channel
between Dover and Calais. A concession being obtained from the
French government on certain conditions, a single conducting
wire, invested with a thick coating of gutta-percha, was sunk by
means of leaden weights across the channel, and the extremities
being put into connection with telegraphic instruments, messages
were transmitted from coast to coast. One of the conditions of the
French concession being that this should be effected before
September, 1850, this object was attained, but nothing more ; for
the action of the waves near the shore constantly rubbing the
rope against the rocky bottom, soon wore off the insulating
envelope and rendered the cable useless.

79. It is right to state that the projectors themselves did not
expect from this first trial permanent success, and regarded it
merely as the experimental test of the practicability of the
enterprise. It was, therefore, immediately resolved to resort to
means for the effectual protection of the conducting wires
from the effects of all the vicissitudes to which they would be
exposed. With this view, Messrs. Newall and Co., the eminent
wire-rope makers of Gateshead, were charged with the difficult
and unprecedented task of discovering expedients, by which a
cable of gutta-percha containing the conducting wires could be
invested with an armour of iron, at the same time so strong as to
resist the action of the forces to which it wouli L be exposed, and
yet not too ponderous or too rigid to allow of being deposited in
the bed of the channel. The result was the invention of the form
of submarine cable, which has since been successfully adopted
upon the various lines of international electric communication
which will be presently described.

The conducting wires inclosed in the'se cables are usually
copper wires, having a diameter of the sixteenth of an inch.
Each wire is first separately covered with two coatings of gutta-
percha. Each successive coating increases the thickness by
a certain fraction of an inch. The object of laying on this
succession of coats of the gum, is to guard against accidental
defects which might render the insulation imperfect. If such a
152

SUBMARINE CABLES.

defect happened to exist at any point of the first coat it would be
covered by the second, the chances against a defect occurring at
the same point of both coatings amounting to an impossibility.

80. The conducting wire thus invested, or so many of them as
it is intended to deposit, are then twisted together, and surrounded
with a mass of spun yarn, soaked with grease and tar, so as to
form a compact rope. Around this rope are then twisted a number
of stout iron wires, sometimes coated on the surface with zinc, or
as it has been called, galvanised. The cable is then complete, and
is fabricated in one continued length sufficient to extend from
shore to shore, or from bank to bank. Perspective side views of
the several cables, and transverse sections of them in their full
size, are given in the figures indicated in the first column of the
following table, the number of conducting wires insulated by the
gutta-percha and included within the cables, the number of
surrounding iron wires, the total length from coast to coast, and
the weight of the cables per mile respectively being indicated in
the other columns.

•

Fig.

INo. of cop-
per wires.

1^
S*

II

Weight per
mile — Tons

25,26

4

10

?5

7

Holyhead and Howth ....

27,28

1

12

70

1

Dover and Ostend

31, 32

6

12

70

7

Portpatrick and Donaghadee (Magnetic 1
Comp.) /

35,36

6

12

25

7

Orfordness and the Hague . . .

37,38

1

10

135

2

Across the Great Belt (Denmark) .

41,42

3

9

16

5

Across the Mississippi . . . .

45,46

1

8

2

2

Across the Zuyder Zee

43,44

6

10

5

7|

Newfoundland & Prince Edward's Island

39,40

1

9

150

If

Portpatrick and Donaghadee (British"!
Comp.) J

35,36

6

12

27

7

Spezzia and Corsica ....

35,36

6

12

110

8

Corsica and Sardinia ....

35,36

6

12

8

153

THE ELECTEIC TELEGRAPH.

Fig. 25.

Fig. 26.— Dover and Calais.

81. In the Dover and Calais cable,
which was the first fabricated and
laid, each of the four copper wires
are surrounded by gutta-percha,
which in fig. 26 is indicated by the
light shading round the black central
spot, representing the section of the
copper wire. The four wires thus
prepared were then enveloped in the
general mass of prepared spun yarn,
represented by the darker shading.
The ten galvanised iron wires were
then twisted around the whole, so as
to form a complete and close armour.
The external form and appearance of
this heliacal coating is represented in
fig. 25.

This cable which was completed by
Messrs. Newall and Co., in three
weeks, measured originally 24 miles
in length. Owing to the manner in
which it was laid down this was
found insufficient to extend from
coast to coast, although the direct
distance is only 21 miles. It was
therefore found necessary to manu-
facture an additional mile of cable,
which being spliced on to the part
laid, the whole was completed, and
the electric communication between
Dover and Calais definitively estab-
lished on the 17th October, 1851.

The cost of the cable itself was
9000?., being at the rate of 360?. per
mile. The total cost for cable and
stations at Dover and Calais was
15,000?.

82. The next submarine cable laid
down was that which connected
Holyhead on tke Welsh with Howth
on the Irish coast. While several
companies which had been formed
for the purpose, were occupied in
raising the capital necessary for this
project, they were surprised by the

154

SUBMARINE CABLES.

Fig. 27.

Fig. 29.

announcement that the project was already on the point of being
realised by Messrs. Newall and Co., on their own account.

The distance between the points to be connected being 60 miles,
the cable was made with a length of 10 addition miles, to meet
contingencies. In this cable, which
enclosed only one conducting wire,
the external wires enclosing the in-
sulating rope were made thicker at
the parts near the shores than for
that which lies in deep water, the
former being subject to much greater
disturbing forces. A side view of
the part immersed in deep water is
given in fig. 27, and a cross-section
in fig. 28. A side view of the shore
ends is given in fig. 29, and a cross-
section in fig. 30, all being in their
full size.

The gutta-percha rope was fabri-
cated by the Gutta Percha Company
in the City-road, London, from
whence it was sent ' to Gateshead,
where it received the iron wire
envelope at the works of Messrs.
Newall and Co., in the short space
of four weeks. Loaded on twenty
waggons, it was next sent by rail-
way across England to Maryport,
where it was embarked on board the
" Britannia," and transported to
Holyhead. On the morning of the
1st June, 1852, one of its extre-
mities being established at Holyhead,
it was laid in the bed of the channel.
This was done as follows : — The cable
was very carefully coiled in the hold
of the steamer ; one end was then
passed several times round a brake-
wheel, and was conveyed on shore,
when it was attached to a telegraph
instrument. The other or lower end of
the cable was attached to another in-
strument in the cabin of the steamer,
so that any message passing from
instrument to instrument, was conveyed through the entire

155

Fig. 28.
Holyhead and

Howth.
Deep sea part.

Fig. 30.
Holyhead and

Howth.
Shore ends.

THE ELECTRIC TELEGRAPH.

cable in the hold, and round the brake-wheel as the cable passed
off in the process of submersion. The shore end having been
made fast securely, the steamer was put in motion, and a certain
strain was put on the cable by means of the brake-wheel, so that
it was laid straight on the ground, or bottom of the sea.

The cable is seen as it rises from the hold in the foreground,
(fig. 34, p. 145,) guided between rollers to the drum, and it again
appears in the back ground, as it passes over the stern. A counter
and indicator was applied to the shaft of the drum by which the
length of cable which at any moment had been delivered off into
the sea was shown.

The wind and tides have the effect of drawing the vessel out
of her course, so that the quantity of cable expended must always
be greater than the distance between the two points in a straight
line. In the case of the Holyhead and Howth cable, the quantity
expended was 64 miles. The depth of water is 70 fathoms, being-
more than twice that of Dover.

The entire process of laying it down was completed in 18 hours.
In another hour the cable was brought ashore, and put in connec-
tion with the telegraphic wires between Howth and Dublin, and
immediately afterwards London and Dublin were connected by
means of instantaneous communication.

This cable was lighter considerably than that between Dover and
Calais, its weight being a little less than one ton per mile, and
consequently its total weight did not exceed 80 tons, while the
Dover and Calais cable weighing 7 tons per mile, its total weight
was 180 tons.

From some cause, which could not be ascertained, this cable,
after being worked for three days, became imperfect. It was sup-
posed to have been caught by the anchor of some vessel, for on being
taken up lately, it was found broken near Howth, and the gutta-
percha and copper wire stretched in an extraordinary manner.

83. On the 9th October, 1851, Messrs. JNewall and Co. attempted
to lay a cable across the narrowest part of the Irish channel,
between Port Patrick and Donaghadee. This cable contained six
conducting wires, similar to fig. 43. The distance across is the
same as between Dover and Calais, viz., 21 miles, and 25 miles of
cable were placed on board the " Britannia " steamer. The pro-
cess of submersion was carried on until 16 miles had been
successfully laid down, when a sudden gale came on, which
rendered it impossible to steer the vessel in the proper course, and
Mr. Newall was reluctantly compelled to cut the cable, when
within 7 miles of the Irish coast, and having 9 miles of cable
remaining on board.

The whole of this 16 miles of cable has been recovered in
156

SUBMARINE CABLES.

June, 1S54, after being nearly two years submerged. This proved
a most arduous undertaking. The depth of the water in this part
of the Irish channel is 150 fathoms, or 900 feet, and from this
depth the cable was dragged by means of a powerful apparatus
worked by a steam engine placed on the deck of a steamer. The
operation occupied four days, for from the great force of the tide,
which runs at the rate of 6 miles an hour, it was found impossible
to work except at the times of high and low water. The cable
was also imbedded in sand, so that the strain required to drag it
up was occasionally very great.

The recovery of this cable has so far solved the question of the
durability of submarine telegraphs. It was found nearly as sound
as when laid down. There was a slight corrosion in certain parts
which appeared to have been imbedded in decaying sea weed — the
parts imbedded in sand were quite sound, and on other parts,
which appeared to have rested on a hard bottom, there were a few
zoophytes. The cable on being tested was found as perfect in
insulation as when laid down.

84. The next great enterprise of this kind, of which the accom-
plishment must render for ever memorable the age we have the
good fortune to live in, was the deposition in the bed of the
Channel of a like cable connecting the coasts of England and
Belgium, measuring SEVENTY MILES ix OXE TXBEOZEX LEXGTH I
This colossal rope of metal and gutta-percha was also constructed
at the works of Messrs. Xewall and Co.

The probable extension of these extraordinary media of social,
commercial, and political communication between countries
separated by arms of the sea, may be conceived, when it is stated
that during the winter of 1852-53 Messrs. Xewall and Co. exe-
cuted under contracts not less than 450 miles of such cable.

The cable laid between Dover and Calais includes, as already
stated, four conducting wires. That between Dover and Ostend
contains six wires insulated by the double covering of gutta-
percha, manufactured, under Mr. S. Statham's directions, by the
Gutta Percha Company. The gutta-percha laid into a rope is
served with prepared spun-yarn, and covered with twelve thick
iron wires, of a united strength equal to a strain of 40 to 50 tons
— more than the proof strain of the chain cable of a first rate
man-of-war.

" A side view and section of this cable in its natural size are
given in figs. 31 and 32 (page 158).

The Belgian cable weighed 7 tons per mile, so that its total
weight was about 500 tons. Its cost was 33,000/. It took 100
days to make it, and 70 hours to coil it into the vessel from which
it was let down into the sea, and 18 hours to submerge it.

157

THE ELECTJRIC TELEGRAPH.

Fi si.

Fig1. 32. — Dover and Ostend
158

The form in which it was coiled in
the hold of the vessel is represented
in fig. 33 (p. 129).*

On the morning of the Wednesday,
the 4th May 1853, the vessel called
the "William Hutt," Capt. Palmer,
freighted with the cable, being an-
chored off" Dover, near St. Margaret's,
South Foreland, the process of laying
the cable was commenced. This vessel
was attended and aided by H.M.S.
11 Lizard," Capt. Eickets, E.N., and
H.M.S. "Vivid," Capt. Smithett.
Capt. Washington, E.N., was ap-
pointed, on the part of the Admiralty,
to mark out the line and direct the
expedition.

At dawn of day about 200 yards
of the cable were given out from the
" Hutt," and were extended by small
boats to the shore, where the extre-
mity was deposited in a cave at the
foot of the cliff. There telegraphic
instruments were provided by means
of which, through the cable itself, a
constant communication with the
vessel was maintained during the
arduous process, corresponding tele-
graphic instruments being placed on
board the "Hutt."

At 6 o'clock, the process of laying
commenced, the " Hutt " being
taken in tow by the steam tug
"Lord Warden."

The manner in which the cable was
" payed out," as the vessel pro-
ceeded in its course, is represented
in fig. 34 (p. 145), the cable as
it came up from the hold, being

* This illustration, as well as that of
the deposition of the cable, have been
taken from the Illustrated London Neics
of the 14th of May, 1853, by the consent
of the publishers of that journal.

SUBMARINE CABLES.

TMcr ^"

passed several times round a large

brake-wheel, by means of which the

cable was kept from going out too

fast, and its motion maintained so as

to be equal to the progress of the

vessel. Men are represented in the

figure applying the brake to the

wheel.

On arriving off Middlekerke, on

the Belgian coast, a boat sent from

shore took from 500 to 700 yards of

the cable on board, for the purpose of

landing it. The boats of the British

vessels taking her in tow, the end of

the cable was safely landed, and

deposited in a guard-house of the

Custom House, where the telegraphic

instruments brought in the " Hutt "

being erected, and the communica-
tions made, the following despatch

was transmitted direct to London : —
Union of Belgium and England,

twenty minutes before one, p.m. Qth

May 1853.

85. The next submarine cable laid,

was that of the Magnetic Telegraph
Company, connecting Donaghadee

with Port Patrick, also manufactured
by Messrs. Newall and Co.

This cable, which contains six con-
ducting wires, is represented in its
proper size in figs. 35, 36, and corres-
ponds in weight and form to the
Belgian cable. But in the details of
its construction and composition, some
improvements were introduced. This
rope was manufactured in 24 days,
and cost about 13,0007.

The cable laid down by the British
Telegraph Company between the same
points, is precisely similar to this.

86. It is proposed to connect Or-
fordness, on the Suffolk coast, with
the Hague, by seven separate sub-
marine Cables, each containing a Fig 36 ._Donaghadee and Portpatrick.

159

(Magnetic Telegraph Company.)

THE ELECTRIC TELEGRAPH.

Fig. 37.

single wire. Near
the shore on each
side these will be
brought together
and twisted into
a single great
cable, as repre-
sented in figs. 37,
38.

Of these, only
three have been
laid down. The
distance from Or-
fordness to the
Hague being 120
miles, the cables
were made 135
miles in length.
They were laid
down separately
at a little dis-
tance one from
another. At 3£
miles from the
shore they were
brought together.
When the tele-
graphic business
increases the
other four will be
deposited.

160

Fig. 38.— Orfordness and the Ha^ue.

A B C

1 . 3 4 5 G *

90

Fig. 06. — THE SINGLE SEEDLE TELEGRAPH.

THE ELECTRIC TELEGRAPH.

CHAPTER IV.

r. — Cable between Spezzia and Corsica. — 88. Other cables, European and
American. — 89. Objections brought by scientific authorities to the
submarine cables — Answers to these by practical men. — 90. Example
of a cable uninjured by the action of the sea. — 91. Precautions
necessary in laying the cable. — 92. Accident in laying the Calais
cable. — 93. Imperfection attributed to the Belgian cable. — 94.
Transatlantic Ocean Telegraph. — 95. Underground wires between the
Strand and Lothbury. — 96. Effect of the inductive action of under-
ground or submarine wires. — 97. Possible influence of this on tele-
graphic operations. — 98. Examples of overground wires extended to
great distances without intermediate support — between Turin and
Genoa. — 99. Telegraphic lines in India. — 100. Difficulties arising
from atmospheric electricity — height and distance of posts — mode of
laying underground wires — extent of line erected to April 1854. —
101. Intensity of current decreases as the length of wire increases.
— 102. Also increases with the thickness of the wire. — 103. And
with the number of elements in the battery. — 104. Result of Pouillet's
experiments on the intensity of current. — 105. Intensity produced by

LABDSER'S MUSEUM OF SCIENCE. M 1C1

No. 37.

THE ELECTRIC TELEGRAPH.

increasing the power of the battery. — 106. How the current produces-
telegraphic signals. — 107. Velocity of the current. — 108. Transmission
of signals instantaneous.

87. IT is proposed to connect Europe with the islands of the Medi-
terranean and the African continent, by extending the wires which
already run continuously to Genoa from the United Kingdom and
the Northern States of Europe to Spezzia, and from that point to
lay a submarine cable to Corsica, another between Corsica and
Sardinia, and another between Sardinia and Bona. The latter
place would be connected with Alexandria by underground wires
extending along the coast.

It is even regarded as within the scope of probability that
Alexandria may be put in electrical connection with Bombay ; and
as the latter place is already connected by a telegraphic line witli
Calcutta, a continuous line of communication between London and
Calcutta would thus be established.

The distances between Spezzia and Bona on the coast of Algeria
are: —

Miles.

Spezzia to Corsica (submarine) 76

Across Corsica (underground) 128

Corsica to Sardinia by the straits of Bonifacio (submarine) . 7
Across Sardinia (underground) . . . . .203

Sardinia to Bona, on the coast of Algeria, (submarine) about 125

539

There would thus be 208 miles of submarine cable in three lengths of
76, 7, and 125 miles, and 331 miles of overland wires necessary to con-
nect the southern coast of Europe with the northern coast of Africa.

This is the proposed plan, and the cables from Spezzia to Corsica,
and from Corsica to Sardinia are already laid and in operation ;
but it will be obvious on inspecting the map that the object would
be attainable with a less extent of submarine cable by continuing
the overland line to Piombino, in the Grand Duchy of Tuscany,
connecting that place with the Island of Elba by a submarine cable
of 8 or 10 miles, and connecting the westernmost point of Elba
with Bastia, in Corsica, by another cable of 35 to 40 miles.
This method would have the further advantage of including in
the line several important places on the Italian coast ; such as,
Carrara, Massa, Lucca, Pisa, and Leghorn.

A preference has been given to the course above described in
consideration of the benefit conferred upon the company by the
concession and guarantee granted by the government of Sardinia,
which would not have been given had the other course been followed.

The cable now deposited contains six conducting wires, and is
in all respects similar to that represented in figs. 35, 36.
162

SUBMARINE CABLES.

Figs. 39, 40.

P. Edward's Island
and X. Brunswick.

88. The short sub-
marine cable laid down f7"
between Prince Ed- /
ward's Island, and the
coast of Nova Scotia
(figs. 39, 40), is intended
as part of a more ex-
tended submarine line
connecting Newfound-
land with Canada. The
other sections would
make up a total length
of 140 miles; but the
project is reported to be
arrested for the present
by the refusal of the
House of Assembly of
Xova Scotia to grant a
charter to the company
to cross that province.

The Danish subma-
rine cable (figs. 41, 42),
is carried across the
Great Belt from Nyborg
to Korsoe the nearest
point of the opposite
coast of Zealand.

The cable laid across
theZuyderZee is shown
in its proper size in figs.
43, 44 (p. 164).

Subaqueous cables
have been laid across
several of the American
rivers. The difficulties
supposed to attend the
deposition and preser-
vation of these con-
ductors appeared to
telegraphic engineers
and projectors so for-
midable, that the wires
were at first carried
across the rivers be-
tween the summits of
M 2

Fig. 41.

Fig. 42.— Great Belt.
163

THE ELECTS 1C TELEGRAPH.

Fig. 43.

Fig. 44.— Zuyclcr Zee.

lofty masts erected on their banks.
This method, however, was found to
be attended with such effects as to
render the maintenance of the wire
impracticable. The masts were blown
down by the violent storms and
tornadoes incidental to the climate,
and were not unfrequcntly destroyed
by lightning.

The project of depositing the con-
ducting wires in the bottom of the
river was then resorted to, and has
been carried into effect in several
cases. The Ohio is crossed at
Paducah by a cable containing one
conducting wire, of which the fol-
lowing description is given in the
American journals.

"It is composed of a large iron
wire, covered with three coatings of
gutta percha, making a cord of
about five- eighths of an inch in
diameter.

" To protect this from wear, and
for security of insulation, there are
three coverings of strong Omaburg,
saturated with an elastic composition
of non-electrics ; and around this are
eighteen large iron wires, drawn as
tight as the wire will bear, and the
whole is then spirally lashed together
with another large wire, passing
around at every f of an inch. The
whole forms a cable of near two
inches in diameter."

This cable is 4200 feet in length,
being the longest yet laid down
in the United States. It was con-
structed by Messrs. Shaffner^ and
Sleeth.

Mr. Shaffner has also constructed
and deposited subaqueous cables in
the following places : —

Across the Tennessee river, four
miles above Paducah, near its
164

SUBMARINE CABLES.

junction with the Ohio. Length, 2200 feet ; same
construction ; deposited in 1851.

Across the Mississippi, at Cape Girondeau, in
the State of Missouri. Length 3700 feet ; depo-
sited in 18,53.

Across the Merimmac river, where it falls into
the Mississippi, twenty miles below St. Louis.
Length, 1600 feet ; deposited in 1853.

All these are similar to the Paducah cable.

Across the Mississippi at St. Louis, three cables
for different lines, each enclosed by 14 lateral
external wires. Length, 3500 feet. Deposited in
1852-3.

Across the Ohio at Maysville, Kentucky, a cable
containing two conducting wires, enclosed by 28
lateral external wires, constructed like the former.
Length, 2100 feet. Deposited in 1853.

Across the Ohio at Henderson, Kentucky.
Length, 3200 feet. Deposited in 1854.

Cables constructed by Messrs. Xewall and Co.
have also been deposited in the following places : —

Across the Mississippi at New Orleans, contain-
ing one conducting wire. Length, 3000 feet.
Deposited in 1853. Shown in figs. 45, 46.

Across the Hudson, 10 miles above New York ;
similar construction. Length, 3600 feet. Depo-
sited in 1854.

Across the Straits of Northumberland, at the
mouth of the St. Lawrence ; similar construction.
Length, 10 miles. Deposited in 1853.

At certain places on the great western rivers
serious difficulties have been and are still encoun-
tered in the preservation of these subaqueous
conductors. At St. Louis on the Mississippi, and
at Paducah on the Ohio, for example, several
cables have been successively swept away by
tioods. Large trees carried down the stream are,
one after another, stopped by being caught in the
cable, and the number thus accumulated becomes
at length so great that the force of the current,
acting upon them, breaks it.

Another frequent cause of destruction to these
cables in the Western Continent is the attraction
thev offer to atmospheric electricity. They are
frequently destroyed by lightning. Mr. Shaffher

165

Fig. 45.

Fig. 46.— Mississippi.

THE ELECTRIC TELEGRAPH.

tells me that lie has sometimes found a longitudinal incision
measuring ten feet in length, made in the gutta-percha, by the
lightning, and cut as clean as if it had been done with a razor.
At other times he has^ found the gutta-percha swelled, rough and
porous, and sometimes pierced with countless numbers of openings
like pinholes.

These appearances are supposed by Mr. Newall to arise from
imperfection in the covering of the wire. The slit, he thinks, is
caused, by air getting in behind the arm, which holds the mandril
through which the copper wire passes before leaving the cylinder,
and the porous covering arises from air mixed with the gutta-
percha. Mr. Newall has ascertained that a wet hair, or a hole of
equal size is sufficient to destroy the insulation of the wire.

89. Some eminent scientific authorities express doubts as to the
durability of the submarine cables. In the case of the Dover and
Calais cable it has been observed that the bottom of the channel at
that part of the strait is proved by the soundings to be subject to
undulations, so considerable that the summits of some of its elevated
points rise to such a height that the water which covers them is
not deep enough to secure them from the effects of the tumultuous
agitation of the surface in violent storms. It is here well to remind
the reader that the agitation of the ocean, which seems so awful in
great tempests, has been found to extend to a very limited depth,
below which the waters are in a state of the most profound repose.
The objection we now advert to is, therefore, founded upon the
supposition that the crests of some of the elevations upon which
the submarine cable rests are so elevated as to be within that limit
of depth, and it is feared that such being the case, the violence of
the water in great tempests may so move the cable against the
ground on which it is deposited with a motion to and fro, as to
wear away by frequent friction its metallic armour, and thus
expose the conducting wires within it to the contact of the water,
and destroy their insulation.

But it has been most satisfactorily proved by a part of the
experimental wire which was laid down between Dover and Calais,
in 1850, and which was picked up two years afterwards in as
perfect a state as when laid down, that the action of the waves
does not affect the bottom of the Channel there. The greatest
depth is 30 fathoms, and the bottom shelves regularly from Dover
to near Cape Grinez, where there is a ledge of rocks rising
suddenly from the bottom.

It has been also feared that, notwithstanding the effect of the

galvanisation of the surface of the surrounding wires, the corrosive

action of the sea water may in time destroy them ; and it has been

suggested that some better expedient for protection against this

166

SUBMARINE CABLES,

effect might be contrived upon the principle suggested by Davy,
for the preservation of the copper sheathing of ships, by investing
the cable at certain intervals with a thick coating or glove of zinc,
which would increase the efficiency of the thinner coating of that
metal given to it in the process of galvanisation.*

To this practical men who have had as much experience as is
compatible with the recent date of these novel and extraordinary
enterprises, reply that the results of their observations give no
ground for apprehension of any injurious effects from tidal or
tempestuous action, and that the fine iron used in the wire
is not affected by sea water, as larger masses of coarser iron,
such as anchors, are. They cite as proof of this, the slightly
decayed state in which nails and small fire-arms have been
found when recovered from vessels long sunk. They further
state that the tar contained in the layer of hemp within the
protecting wires acts as a preservative, whether the wires be
galvanised or not. It has been found for example that, in the
case of the submarine conductor between Donaghadee and Port-
patrick, a perfect concrete of tar and sand has been already
formed, upon which masses of shell-fish attach themselves at
all parts that are not buried in sand, and it is apparent that
in a few years a calcareous deposit will be formed around it,
which will cement it to the bottom, and altogether intercept the
action of the sea water.

90. In the deposition of submarine cables great care should be
taken to select suitable points on the shore for beaching them.
Sandy places are always to be sought. If this precaution be taken,
it is affirmed that they are not subject to tidal action. A cable
was partly laid by the Magnetic Telegraph Company in 1852
near Portpatrick (83), but abandoned in consequence of the vessel
employed to deposit it being exposed in the process to a violent
storm. The wire was left exposed upon the beach down to and
beyond low water mark, and was in June, 1854, still in a perfect
state, the galvanised iron wires, even to their zinc coating, being
absolutely in the same state as when they were deposited.

91. It is contended by practical men that the great and only
risk of failure in the submarine cables is from defects produced in
the process of their deposition, or from original faults in the prin-
ciple of their construction.

The greatest care is necessary in conducting the process of
delivering out the cable into the sea, or "paying it out," as it is
technically called. All sudden bending of the cable is to be
especially avoided. "Kinks" or "hitches" are apt to occur in

* Potullet, "Traite de Physique," vol. I p, 799, Ed, 1853.

167

THE ELECTRIC TELEGRAPH,

the process, by which the gutta percha covered wires within the
cable are strained.

92. In laying the Calais cable it was found too short to extend
to the opposite coast, and it became necessary to splice a supple-
mentary piece to it. The joint thus formed afterwards failed, and
it was found necessary to splice it anew, and to insert a fresh
piece. Since this was done the cable appears to have continued in
excellent order.

93. It is said that the Belgian cable has been subject to some im-
perfection arising from the position of the wires within the case.
The sixth wire being in the axis of the cable, surrounded by
the other five (see fig. 32), it was found that when the outer casing
of the protecting wires was laid around it, the pressure on the
centre wire rendered it imperfect, while the five surrounding it
suffered to some extent.

Similar defects are said to exist in other cables constructed upon
the same principle.

A hempen case well tarred in the centre is considered to form
the best safeguard for the gutta percha covered wires in the process
of making the cable, since it will yield to any compression itself
without affecting injuriously the wire.

94. This notice of subaqueous telegraphy ought not to be
concluded without some mention of the project for the deposition
of an electric cable across the Atlantic, so as to put the Old
World in instantaneous communication with the New. Such a
scheme is regarded now pretty nearly as that for the electric
connection of the British islands with each other and with the
European continent was regarded some years ago. The sanguine
consider the project practicable, and its speedy realisation pro-
bable. The more phlegmatic notice it only with ridicule.
Men of science generally admit the possibility of the enterprise
while men of finance more than doubt the possibility of a
remunerative result.

The width of the Atlantic between the nearest points of British
America and the west coast of Ireland is about sixteen hundred
miles. Twelve cables, each as long as those which have been
laid down between Orfordness and the Hague, would be sufficient
to extend from coast to coast. That cable could be spliced to
cable was practically proved between Calais and Dover, such a
splice having been successfully made in the cable near the French
coast.

Lieutenant Maury, of the United States, so well known for his

hydrographical researches, caused a series of regular soundings to

be made with the view of determining the form and condition of

the bed of the ocean between the coasts of British America and

16S

SUBMARINE CABLES.

Ireland. He found that between Newfoundland, or the mouth cf
the river St. Lawrence, and the west coast of Ireland, the bottom
consists of a plateau, which, as he says, " seems to have been placed
there especially for the purpose of holding the wires of a submarine
telegraph, and of keeping them out of harm's way. It is neither
too deep nor too shallow ; yet it is so deep, that the wires but once
landed, will remain for ever beyond the reach of vessels, anchors,
icebergs, and drifts of any kind ; and so shallow that the wires
may be readily lodged upon the bottom.

" The depth of this plateau is quite regular, gradually increasing
from the shores of Newfoundland to the depth of 1500 to 2000
fathoms, as you approach the other side."*

Lieutenant Maury concludes that this line of deep sea soundings
is quite decisive of the question, as to the practicability of a
submarine telegraph between the two continents in so far as the
bottom of the ocean is concerned. A cable laid across would pass
to the north of the great banks, and would be deposited upon the
plateau above described, where the waters of the ocean are proved
to be " as still as those of a millpond."

This inference Lieutenant Maury deduces from the fact, that
all the specimens of the bottom brought up have been found to
consist of miscroscopic shells without the admixture of a single
particle of gravel or sand. Had there been currents at those
depths, these shells would have been thrown about and abraded,
and mixed more or less with the debris of the natural bed of the
ocean, such as ooze, sand, gravel, and other matter. "Con-
sequently a telegraphic cable once laid there, there it would
remain as completely beyond the reach of accident as if it were
buried in air-tight cases."

Imperfectly informed persons have expressed an opinion that
the cable would not sink below a certain depth, at which the
increasing density of the sea water would render it bulk for bulk
as heavy as the cable. The well known physical properties of
water prove such a supposition to be groundless. Although not
incompressible in an absolute sense, water is susceptible of com-
pression, even at the greatest depths of the ocean, in so small a
degree, that the cable must always greatly exceed it in specific-
weight.

Putting out of view the financial part of the question, there
appears then to be no good reason for pronouncing the project to
construct such a cable, and to deposit it in the bed of the ocean,
impracticable in an absolute, sense.

* Report of Lieutenant Maury to the Secretary of the U. S. Navy,
Feb. 22,

THE ELECTRIC TELEGRAPH.

It may be asked whether, if deposited, an electric current could
be transmitted through it so as to produce telegraphic signals ?

There can be only two reasons for doubting this— -first, the
length of the conducting wire, and, secondly, the inductive effects
of the water upon the cable.

The intensity of the current transmitted by a battery of given
power upon a wire, is in the direct ratio of the conducting power
of the wire and the magnitude of its transverse section, and in the
inverse ratio of its length. A length so great as 1500 or 1600
miles, would of course considerably attenuate the current.

But it will be recollected that, in the experiments described in
Chap. I. par. 9, made by M. Leverrier and myself, messages were
transmitted over a space of 1000 miles of wire without inter-
mediate battery power, and with a terminal battery of very
limited power. In that case 336 miles of the wire upon which
the current was transmitted were iron, a very indifferent con-
ductor, and the remaining 746 miles were copper wire of extremely
small diameter. It is certain, therefore, that by reason of the
inferior conducting power of the one part, and of the very small
transverse section of the other part, this length of 1082 miles
offered a much greater resistance to the transmission of the
current than would 1600 miles of copper wire, such as is usually
selected for submarine cables.

But independent of these considerations, nothing would be
easier than to give the copper wire enclosed in the cable such a
thickness, and to apply to it such batteries, as would ensure the
transmission of a current of sufficient intensity.

The effects of the recoil currents produced by the inductive
action of the water upon the cable, cannot be so certainly appre-
ciated with our present knowledge and experience ; but although
the effects of these are sensible in the cases of the submarine and
underground wires already laid down, they have not produced
any obstruction to the efficient performance of the telegraphs, and
the managers of the Magnetic Telegraph Company, which works
well several hundred miles of wire partly subaqueous and partly
underground, assure me that no inconvenience or obstruction
whatever is found to arise from this cause. If no other objection
were raised against the project of a Transatlantic cable save this,
it may be safely pronounced that there would be nothing to be
apprehended which the resources of science and art would not
easily surmount.

It does not appear, therefore, that any part of the great

problem of subatlantic telegraphy remains to be solved, except

that which is involved in the financial view of the question. If

it be undertaken as a commercial enterprise with a view to a

170

RECOIL CURRENTS.

remunerative return, icill it pay ? Or, on the other hand, may it
not be regarded as one of those vast international enterprises to
which the influence and resources of states should be applied?
These are questions which we have neither the space nor the
vocation to discuss.

95. In 1852, the conducting wires which connect the Branch
Telegraph Office, established in the Strand, opposite Hungerfoid
Market, with the General Post-office, were laid down. In this
case the conducting wires are galvanised brass instead of copper.
They are as usual laid in iron tubes, and are carried along the
kerb stones of the foot pavement of the Strand, Fleet-street,
Ludgate-hill, and St. Paul's Church-yard to Cheapside, where
they cross over to Foster-lane, and passing through the branch
office in the hall of the General Post-office, are carried thence
to the central telegraph station in Lothbury, at the rear of the
Bank of England.

From this central office, at all hours by day and by night,
despatches are transmitted to and received from every seaport and
every considerable town in England, Scotland, and Wales ; by the
submarine wires, by Holyhead and Portpatrick, from all parts
of Ireland, and by Dover, from all parts of the Continent of
Europe where electric telegraphs have been constructed.

96. After the underground and submarine wires had been con-
structed and laid upon a considerable scale, the attention of Dr.
Faraday was called by some of the parties engaged in their
management to peculiar phenomena which had been manifested
in the telegraphic operations made upon the lines thus laid. After
experiments had been made upon a large scale with lines of sub-
aqueous and subterranean wires, extending to distances varying
from 100 to 1500 miles, it was found that the electricity supplied
by the voltaic battery to the covered wire was in great quantity
arrested there, by the attraction of electricity of an opposite kind
evolved from the water or earth in which the wire is sunk ; the
attraction acting through the gutta percha covering exactly in the
same manner as that in which the electricity developed by a
common electric machine, and deposited on the inside metallic
coating of an electric jar, acts through the glass upon the natural
electricity of the external coating, or of the earth in connection
with it. The two opposite electricities on the inside and outside
of the coating of the wire by their mutual action neutralise each
other, and under certain circumstances a person placing his hands
in metallic connection with both sides of such coating, may ascertain
the presence of a large charge of such neutralised fluid, by receiving
the shock which it will give like that of a charged Leyden jar.

97. It is apprehended that this unforeseen phenomenon may

171

THE ELECTRIC TELEGRAPH.

interfere more or less with the practical working of all telegraphs
having underground conducting wires ; and I have been informed
by the agents engaged in bureaux of the Paris telegraph, that
they are sensible of its effects in all direct communications between
that capital and London.

On the other hand the Magneto-Electric Telegraph Company, who
at the present time (May, 1S54), have nearly 900 miles of under-
ground wire in operation, report that they sometimes pass their
signals without any difficulty through 500 miles of underground
wire without any break or delay in the circuit, and that they have
in constant operation continuous underground lines connecting
towns above 300 miles apart.

The only defect complained of in the underground wires is that
which proceeds from accidental failures of complete insulation,
produced by defects in the gutta percha or other coating which
allow moisture to penetrate in wet weather and to reach the con-
ducting wire, or it may arise from accidental fracture of the wire.
In any such cases the flow of the current to its destination is
interrupted, and the telegraph conveys no signal.

The use of underground wires, and the discovery of the
phenomenon of inductive action above described, are too recent to
justify any certain inference as to their effects on telegraphic
operations. Time and enlarged experience alone can settle the
questions which have been thus raised.

98. Although as a general rule the overground lines of
telegraphic wire are sustained by supports at intervals of about
sixty yards, many exceptional cases are presented in* which they
are extended between supports at much greater distances asunder.
Every recent visitor to Paris may have observed the long lines of
wire which are in several cases extended along the boulevards
and across the river.

But the most surprising examples of long lines of wires
without intermediate support, are presented on the telegraphic
line passing north and south through Piedmont between Turin and
Genoa. There, according to a report published in the "Pied-
niontese Gazette," in the course of the line passing through the
district intersected by the chain of the Bochetta, the engineer,
M. Bonelli, had the boldness to carry the wires from summit to
summit across extensive valleys and ravines at immense heights
above the level of the ground. In many cases the distance
between these summits amounted to more than half a mile, and
in some to nearly three-quarters of a mile. In passing through
towns, this line is carried underground, emerging from which
it is again stretched through the air from crest to crest of the
Maritime Apennines, after which it finally sinks into the earth,
172

INDIAN TELEGRAPHIC LINES.

passing through Genoa under the streets and terminating in the
Ducal palace.

It is stated that the insulation of the wires on this picturesque
line has been so perfect, notwithstanding the adverse circumstances
of its locality, that although it was constantly at work day and
night during the first winter, no failure of transmission or extra •
ordinary delay ever occurred.

99. Efforts have recently been made to extend the system of
telegraphic intercommunication to India. Dr. O'Shaughnessy of
the East- India Company's medical department, in constructing an
experimental line through a distance of 80 miles from Calcutta,
used, instead of wires, iron rods, being the only obtainable
materials. These were fastened together and supported on
bamboos.

By experiments thus made, he found that the wires employed
in Europe would be quite inadequate to the Indian telegraph. In
England, where the lines are carried along railways, and where
there are no living obstacles to contend with, the thin iron wire,
called No* 8 gauge, answers its purpose well ; but no sooner were
the rods mounted on their bamboo supports in India than Hocks Oi
that largest of all birds, the adjutant, found the rods convenient
perches, and groups of monkeys congregated upon them ; showing
clearly enough that the ordinary wire would be insufficient to bear
the strains to which these telegraphic lines would be subjected.
It was found also that not only must the wire be stronger, but
that it must be more elevated, to allow loaded elephants, which
march, about regardless of roads or telegraphic lines, to pass
underneath.

100. The telegraphic communication thus practically effected, is
subjected to attacks to which the telegraphs in this country are
but little exposed. Storms of lightning destroyed the galva-
nometer coils, and hurricanes laid prostrate the posts. Undaunted
by the opposition of the elements, Dr. O'Shaughnessy contrived a
lightning conductor for the instruments, and strengthened the
supporting props.

Dr. O'Shaughnessy returned to England, and at Warley, near
Brentwood, made arrangements for producing 3000 miles of thick
galvanised wire, to be shipped for India; one of the earliest
lines undertaken, to be from Calcutta to Bombay. One of the
peculiar characteristics of the railway lines intended for India, as
contrasted with the English lines, is the greater distance between
the posts, which are higher and stronger than those generally
used. The thick wire is raised to a height of fourteen feet, on
posts nearly the eighth part of a mile apart. To obtain the neces-
sary strength to bear the strain, the posts are fixed with screw

173

THE ELECTEIC TELEGRAPH.

piles. To show the strength of the wires thus extended, a rope
was, for experiment, hung to the centre of the wire of largest
span, and a soldier climbed up it, the weight of his body pro-
ducing but a slight curvature. The common deflection arising
from the weight of a wire of a furlong span does not exceed
eighteen inches.

Dr. O'Shaughnessy's plan of underground communication,
when such a mode of laying down the wires is desirable, is very
economical. The copper wires coated with gutta percha, instead
of being inserted in iron tubes, are inlaid in wooden sleepers, well
saturated with arsenic, to protect them from the white ants, and
they are then laid in a trench about two feet deep. An under-
ground system of two wires may thus be laid down for 35/. the mile.

The plan adopted for joining the lengths of the thick galvanised
wire is to have the two ends turned, so as to link into one another,
which are then introduced into a mould, like a bullet-mould, and
an ingot of zinc being cast over them, they form a most substantial
joint, and perfect metallic connection.*

It appears from reports received in May, 1854, that at that
date a telegraphic line was in full operation from Calcutta to
Agra, a distance of 800 miles, and it was then expected that the
entire line to Bombay, a distance of 1500 miles, would soon be
completed and put in operation.

This line is reported to have been completed and brought into
operation since the preceding paragraphs were in type.

101. To produce the effects, whatever these may be, by which
the telegraphic messages are expressed, it is necessary that the
electric current shall have a certain intensity. Kow, the intensity
of the current transmitted by a given voltaic battery along a
given line of wire will decrease, other things being the same, in
the same proportion as the length of the wire increases. Thus, if
the wire be continued for ten miles, the current will have twice
the intensity which it would have if the wire had been extended
to a distance of twenty miles.

It is evident, therefore, that the wire may be continued to such
a length that the current will no longer have sufficient intensity
to produce at the station to which the despatch is transmitted
those effects by which the language of the despatch is signified.

102. The intensity of the current transmitted by a given

* Year-Book of Facts, 1853, p. 150.
174

INTENSITY OF CURRENTS.

voltaic battery upon a wire of given length, will be increased in
the same proportion as the area of the section of the wire is
augmented. Thus if the diameter of the wire be doubled, the
area of its section being increased in a fourfold proportion, the
intensity of the current transmitted along the wire will be in-
creased in the same ratio.

103. In fine, the intensity of the current may also be augmented
by increasing the number of pairs of generating plates or
cylinders composing the galvanic battery.

Since it has been found most convenient generally to use iron as
the material for the conducting wires, it is of no practical import-
ance to take into account the influence which the quality of the
metal may produce upon the intensity of the current. It may be
useful nevertheless to state that, other things being the same,
the intensity of the current will be in the proportion of the con-
ducting power of the metal of which the wire is formed, and that
copper is the best conductor of the metals.

104. M. Pouillet found by well-conducted experiments, that
the current supplied by a voltaic battery of ten pairs of plates,
transmitted upon a copper wire, having a diameter of four-
thousandths of an inch, and a length of six-tenths of a mile, was
sufficiently intense for all the common telegraphic purposes. Now
if we suppose that the wire instead of being four-thousandths of
an inch in diameter, has a diameter of a quarter of an inch, its
diameter being greater in the ratio of 62^- to 1, its section will be
greater in the ratio of nearly 4000 to 1, and it will consequently
carry a current of equal intensity over a length of wire 4000
times greater, that is, over 2400 miles of wire.

105. But in practice it is needless to push the powers of trans-
mission to any such extreme limits. To reinforce and maintain
the intensity of the current, it is only necessary to establish at
convenient intervals along the line of wires intermediate batteries,
by which fresh supplies of the electric fluid shall be produced,
and this may in all cases be easily accomplished, the intermediate
telegraphic stations being at distances, one from another, much
less than the limit which would injuriously impair the intensity
of the current.

106. Having thus explained the means by which an electric
current can be conducted from any one place upon the earth's
surface to any other, no matter what be the distance between
them, and how all the necessary or desired intensity may be
imparted to it, we shall now proceed to explain the expedients by
which such a current may enable a person at one place to convey
instantaneously to another place, no matter how distant, signs
serving the purpose of written language.

175

THE ELECTRIC TELEGRAPH.

It may be shortly stated that the production of such signs
depends on the power of the agent transmitting the current to
transmit, suspend, intermit, divert and reverse it at pleasure.
These changes in the state of the current take place for all
practical purposes simultaneously upon all parts of the conducting
wire to whatever distance that wire may extend, for although
strictly speaking there is an interval, depending on the time which
the current takes to pass from one point to another, that interval
cannot in any case exceed a small fraction of a second.

107. Although there is some discordance in the results of
experiments made to determine the velocity of the current, they
all agree in proving it to be prodigious. It varies according to
the conducting power of the metal of which the wire is composed,
but is not dependent on the thickness of the wire. On copper
wire, its velocity, according to Professor Wheatstone's experiments,
is 288000 miles ; and according to those of MM. Fizeau and
Gonelle, 112680 miles per second. On the iron wire used for
telegraphic purposes, its velocity is 62000 miles per second,
according to Fizeau and Gronelle ; 28oOO according to Professor
Mitchell, of Cincinnati ; and about 16000 according to Professor
Walker of the United States.

108. It is evident therefore that the interval which must
elapse between the production of any change in the state of the
current at one telegraphic station, and the production of the same
change at any other however distant, cannot exceed a very
minute portion of a second, and since the transmission of signals
depends exclusively on the, production of such changes, it follows
that such transmission must be practically instantaneous.

176

•If;

Fig. CS.— THE DOUBLE NEEDLE TELEGRAPH.

THE ELECTRIC TELEGRAPH.

CHAPTER Y.

109. Current controlled by making and breaking the contact of con-
ductors.— 110. Instruments for controlling the current — commutators.
— 111. General principle of the commutator. — 112. Its application
to telegraphic operations. — 113. To transmit a current on the up line
only. — 114. On the down line only. — 115. On both lines. — 116. To
reverse the current. — 117. To suspend and transmit it alternately. —
118. How to manage a current -which arrives at a station. — 119. To
make it ring the alarum. — 120. Station with two alarums. — 121.
Notice of the station transmitting and receiving signals. — 122. When
signals not addressed to the station the current is passed on. — 123.

LARDNER'S MUSEUM OF SCIENCE. H 177

No. 38.

THE ELECTKIC TELEGRAPH.

How to receive a dispatch at the station, and stop its farther progress.
— 124. How several dispatches may be at the same time sent between
various stations on the same line. — 125. Secondary lines of wire then
used. — 126. Recapitulation. — 127. Signals by combinations of unequal
intervals of transmission and suspension. — 128. Key commutator. —
129. Horological commutator for a current having equal and regular
pulsations. — 130. Case in which the pulsations are not continuous or
regular. — 131. No limit to the celerity of the pulsations. — 132.
Application of a toothed wheel to produce the pulsations. — 133. By
a sinuous wheel. — 134. Method of diverting the current by a short
circuit, its application to the alarum. — 135. Effects of the current
which have been used for signals. — 136. Deflection of magnetic needle.

109. SIKCE all telegraphic signals depend on the power of the agent
who makes them, to transmit, control, and modify the current at
will, it must be apparent how important it is for those who desire
to understand this interesting subject, to comprehend in the first
instance the means by which this power is obtained and exercised.

It is necessary to remember that the current will now along a
line of conducting wire so long as, and no longer than, a voltaic
battery is interposed at some point on the line, the wire being
attached to its poles, and the remote ends of the wire connected
with the earth, as explained in (23) and (36), and in that case the
current will flow along the wire from earth to earth in such a
direction as to enter the battery at the negative, and to leave it at
the positive pole, and that provided the battery have adequate
force, it does not matter how distant from its poles the points may
be at which the wires are connected with the earth.

If at any point of the line the wire is broken, the current
instantly ceases along the entire line. If it be reunited the
current is instantly re-established. If the connection of the
wire with the poles of the battery be reversed, so that the end
which was connected with the positive is transferred to the
negative pole, and vice versa, the direction of the current along
the entire line is reversed — since it must always flow from the
positive and to the negative pole. If at any point the wire, being
broken, be connected with another wire proceeding to the earth in
any other direction, the current will be diverted to the latter wire,
deserting its former course. If the wire conducting the current
be connected at the same point with two wires both connected with
the earth, it will be distributed between the two, the greater part,
however, following that wire which offers the easier road to the earth.

These few principles, which are clear and simple, supply an easy
key to the whole art of electro-telegraphy.

110. The class of mechanical expedients by which the agent
who desires to transmit signals is enabled to control and modify
the current in the manner here described, are called by the general
178

COMMUTATORS.

name of " coinrcrATOES," and are very various in form and
arrangement according to the purposes to which, and the condi-
tions under which they are applied. Not only do apparatus of
this class differ in different countries where telegraphs have been
established, but they vary upon different lines, and even on
different parts of the same line. Without attempting to follow
these endless variations, many of which are quite unimportant,
and all of which are mere varieties in the application of the
general principles explained above, we shall here confine ourselves
to such an illustration of them as will at the same time render
intelligible their structure and operation, and convey a general
notion of the manner of transmitting and receiving signals.

111. Let us suppose that around the edge of a disc of ivory,
wood, or any other insulating material, are inserted at convenient
intervals pieces of metal, B, r, T, D, &c., fig. 47, which we shall
call contact pieces, their purpose being to make and break the
metallic contact which controls the current. At the back of the
disc near these contact pieces are clamps or tighten ing screws by
which conducting wires can be attached to them.

To an axis in the centre of the disc let two metallic hands, A A'
be attached, so that they can be turned round the disc like the
hands of a clock, but having motions independent of each other.
These hands may be supposed to be formed of elastic strips of
metal bent at the ends towards the surface of the disc, so as to
press upon it with some force : and let one of them move over the
other without disturbing it, as the minute hand of a watch moves
over the hour hand. Let A." be another similar hand, turning on
a centre fixed upon the contact piece E, so that it can be turned at
pleasure upon one or other of the contact pieces p or x.

Xow it is evident that by turning the hands A and A' upon any
two of the contact pieces, they will be put in metallic connection,
so that a current flowing from either of them will pass by the
hands to the other, and in like manner by means of the hand A",
either of the contact pieces P or x can be put in metallic con-
nection with E.

112. To convey a general notion of the application of such an
apparatus to telegraphic purposes, we shall for example suppose
conducting wires connecting the several contact pieces in the
following manner : —

1. P, with the positive pole of the battery.

2. y, with its negative pole.

3. E, with the earth.

4. ~c, with the up-line wire.

5. D, with the down-line wire.

6. B, with a bell or alarum.

K 2 179

THE ELECTRIC TELEGRAPH.

It may be necessary to state here that it is customary to call
the wire which proceeds to the chief terminal station of a line the
up wire, and that which proceeds to the secondary terminal station
the down wire. Thus, if a line of telegraph be extended between

Up. Line

London and Dover, the wire which would connect London with any
intermediate station would at that station be the up wire, and
180

TRANSMISSION OP SIGNALS.

the wire which would connect it with Dover would be the down
'-ire.

The manner in which the current arriving at any station is made
to ring a bell or alarum at that station, will be explained hereafter.

In explaining the manner in which the agent at a station is
enabled to control a current by means of the commutator, two
cases are to be considered — first, when he desires to transmit
signals ; and, secondly, when he expects to receive them.

In the former case, he takes the current from his own battery ; in
the latter, he receives it on its arrival by the up or down line wire.

"We shall first consider the case in which he desires to transmit
signals.

113. To transmit a current on the up line only. — Let the hand
A" be placed on x, A on P, and A' on u. The negative pole x of
the battery being then in connection with the earth E by the hand
A", and the positive pole r in connection with the up wire u by
the hands A and A', while the up wire itself at the station at
which it arrives is in connection with the earth, the current will
flow from r by A and A' along the up wire to the station at which
the wire goes to the earth.

114. To transmit a current on the down line onlu. — Let A" and A
be placed as before, and let A' be moved to D. The current will then
How on the down line, as may be explained in the same manner.

115. To transmit a current along the entire line from terminus
to terminus. — Let A' be turned upon tr, and A upon x, and let two
similar hands at the back of the disc be at the same time turned
upon P and D, the hand A" being removed from both x and r.
In that case, the current will flow from the positive pole P along
the hands at the back of the disc to D, and thence on the down
wire to the terminal station, where it will take the earth, by
which it will pass to the earth plate at the up terminal station,
and from thence by the up wire to r, and from u by the hands A'
and A to the negative pole x.

Thus it appears that it will pass along the entire line from
terminus to terminus, flowing from the up station downwards.

116. To reverse the direction of the current. — To accomplish
this, it is obviously sufficient to reverse the connections with the
poles of the battery. Thus, if the current be transmitted on the
up line only, the hand A' will be upon r, A on P, and A" on x,
when, as already explained (113), the current will flow from r
towards the up station. If A" be removed to r, and A to x, the
direction will be reversed, the course of the current then being as
follows : — From the positive pole P to E by the hand A" ; from the
earth E to the earth plate at the upper station ; from that to
the up wire ; from thence to r, and from u by A' and A to x.

181

THE ELECTRIC TELEGRAPH.

Thus, by alternately moving the hands A" and A between the
contact pieces p and K, the current may be changed from one
direction to the other on the up wire as often and as rapidly as
may be desired.

The same reversion may be made in exactly the same manner
on the down wire, if the hand A' be turned upon D.

The reversion may be made with equal facility and rapidity if
the current be established along the entire line by merely inter-
changing the position of the hands directed upon P and N, as
described in 115.

117. To suspend and transmit alternately the current during
any required intervals. — Whether the current be established on
the up line or on the down line, or on both, this is easily accom-
plished by removing any one of the hands from the contact piece
on which it rests, and restoring it to its place after the required
intervals. When it is withdrawn, the current is suspended;
when restored, the current is re-established. The intervals of
such suspension and transmission may be as long or as short as
may be desired. They may be equal or unequal. They may
succeed each other with any degree of rapidity whatever. Thus
there may be ten thousand intervals of suspension and ten
thousand of transmission in a minute. The instantaneous cha-
racter of the propagation of the electric fluid already noticed will
sufficiently explain this.

118. Having thus explained how the agent controls the current
in transmitting signals to a distant station, we shall now show
how he treats the current which arrives from a distant station, so
as to allow it to produce before him the intended signals.

The current must arrive either by the up wire or by the down
wire, and therefore at either of the contact pieces, u or D.

119. To make the arriving current give the alarm. — When the
agent at a station is not engaged in transmitting signals, he must
always be prepared to receive them. A contrivance called an
alarum is provided, to give him notice when signals are about to
be transmitted. The alarum, which will be fully explained here-
after, is an apparatus so constructed, that whenever the current
passes through it, a bell is rung, by which the attention of the
agent is called.

The contact piece B is here supposed to be connected with a
wire leading to such an apparatus.

When not engaged in transmitting signals, the agent connects
both the up and down wires with his alarum. To accomplish
this, he turns A' upon u, and A upon B. The contact piece B
being supposed to be connected with the wire which enters the
alarum, the wire which issues from it is connected with B'. Two
182

PJXGIXG THE ALARUM.

hands, which are behind the disc, are placed one on B' and the
other on D. In this case, if a current comes down the line to tr,
it will pass by the hands A and A' to B, and thence through the
alarum wire to B', whence it passes by the hands at the back of
the disc to D, and thence along the down wire.

If, on the other hand, the current arrive by D, it passes in the
same manner through the alarum to r, and so along the up wire.

From whatever part of the line the current may be transmitted,
whether on the up or the down line, it must therefore pass through
the alarum, and give notice.

120. In some cases a station is provided with two distinct
alarums, one for the down and the other for the up line, having
different tones, so that the agent, on hearing them, knows from
which direction the signals are about to come.

In that case the wire of the up line alarum is attached to B, and
that of the down line to B', the wires which issue from the two
alarums being always in such case connected with the earth.

"When the agent is not engaged in transmitting, he places the
hands A' and A on u and B, and the hands behind the disc on D
and B'. If a current arrive by r, it passes by B through the alarum
to the earth, and gives notice. If it arrive by D, it passes in like
manner through the alarum B' to the earth, and gives notice.

It is, however, more usual to have a single alarum at each
station, acting as above described.

The connections being so arranged that the current shall pass
along the entire line from terminus to terminus, all the alarums
at all the stations will be rung the moment the current is trans-
mitted. General notice is therefore given that a dispatch is about
to be sent from some one station along the line to some other.

121. It is necessary, however, to inform the agents at each
station of the place from whence the dispatch is about to be sent,
and the place to which it is to be addressed. To learn this, the
agent transfers the connections from the alarum to his telegraphic
instrument. This is accomplished by removing the hand A from
B to T, and connecting the wire coming from the telegraphic
instrument by the hands at the back of the disc with D. By this
change the current passes from u to T, from T through the
telegraphic instrument to D, and from thence down the line.
The signals transmitted appear upon the telegraphic instrument,
informing the agent whence the dispatch will come, and where it
is desired to transmit it.

122. If he find that it is not to be addressed to himself, his
arrangements will depend on the position which his own station
holds in relation to the two stations between which the dispatch
is about to be transmitted. If his station lie between them, he

183

THE ELECTRIC TELEGRAPH.

turns the hands A and A' upon the contact pieces u and D, so as to
allow the current to pass between the up wire and the down wire,
along the hands without interruption, and also without spending any
part of its force in needlessly working his telegraphic instrument.

123. If he find that the dispatch is intended for himself, and
that it proceeds from a station on the up line, for example, he
places the hand A' upon u, A upon T, and by the two hands behind
the disc he connects the wire issuing from the instrument with E.
By this arrangement, the current arriving at TJ passes by the
hands A' and A to T, thence through the telegraphic instrument to
E by the hands behind the disc and to the earth.

In this case the course of the current is limited to the part of
the line wire which is included between the station from which it
is transmitted and that to which it is addressed. By connecting
the telegraphic instrument with the earth by E, the down
line wire is free ; so that while the up line wire is employed in
conveying the dispatch in question, other dispatches may be
transmitted between any stations on the down line.

124. If we express for example the chief terminal station by s,
and the series of stations upon the line proceeding from it down-
wards by s1} S2, S3, s4, &c., we can conceive various dispatches to
be at the same time transmitted between them by the arrange-
ment here explained, being made at each station which receives a
dispatch. Thus, if s sends a dispatch to sx, and sx cuts off its
communication with the down wire by putting its telegraphic
instrument in connection with the earth, the current transmitted
from s stops at sx. A dispatch may therefore be at the same
time sent between sa and S3, another between S4 and S5, and so on.

Thus, the same line of conducting wire may be at the same
time engaged in the conveyance of several dispatches, the only
limitation ' being that when a dispatch is being transmitted
between two stations, no other dispatch can at the same time be
transmitted between any of the intermediate stations.

It follows from this as a necessary consequence that if, as generally
happens in thickly peopled tracts of country, the terminal and
one or two of the most populous of the intermediate stations keep
the telegraph in constant work, separate and independent wires,
and instruments must be provided to serve the secondary inter-
mediate stations, just as upon railways, second and third-class
trains are provided to serve those lesser stations on the line, which
are passed by the first-class trains without stopping.

Every great telegraphic line presents an example of this. Thus

upon the Dover line separate wires and instruments are appropriated

to the transmission of dispatches between the terminal stations,

London and Dover, and the intermediate stations, Tonbridge,

3 84

TELEGRAPHIC STATIONS.

Ashford, and Folkestone. The conducting wire passes tkrough
the telegraph offices at these three intermediate stations, but does
not enter any of those of inferior importance, such as Godstone,
Penshurst, Marden, Staplehurst, &c., to the service of which other
conducting wires and instruments are appropriated.

125. Since, however, telegraphic communication must be pro-
vided between all the intermediate stations, and since the chief
wires passing the chief intermediate stations do not enter the
secondary ones, it follows that the wires of the secondary stations
must be carried not only to the terminal stations, but also through
all the chief secondary stations. Thus the wires, which pass through
the stations of Godstone and Penshurst, must also pass through
those of Tonbridge, Ashford, and Folkestone, since otherwise there
could be no communication between the latter and the former.

From what has been already explained, it will be understood
that every two secondary stations along the line can communicate
at the same time with each other, no stations being compulsorily
silent, except such as may lie between two communicating ones.
To illustrate this, let us suppose the secondary stations from ter-
minus to terminus of the line to be expressed by the small letters,
and the chief stations, terminal and intermediate, by the capitals,
in the following order :

A, b, c, (I, c, F, </, h, t, K, /, m, n, 0.

Xow, by the secondary wires A and b, b and c, c and d, and so on,
may at the same moment hold communication. But if A and d
communicate, b and c can communicate neither with each other,
or with any other station. They are compulsorily silent. In like
manner, if A and m communicate, b, c, d, e, g, h, i and I are all
eompulsorily silent.

Hence it will be apparent how necessary it is to put chief inter-
mediate stations like F and K on the primary wires, since if they
eould communicate with A and o only by the secondary wires,
frequent interruptions to the communications of all the secondary
stations with each other would take place.

It will be also apparent that on lines of great intermediate
business, a third or even fourth system of wires would be necessary.

This will render it easily understood why such a multiplicity of
wires are seen stretching along the parts of the lines near London.

Lines of telegraph, like lines of railway, often have branches
which are connected either with the primary or secondary wires of
the main line, or with both, according to their importance. For
example, on the main line between London and Dover, there are
branches which go to Maidstone on the one side, and to Tonbridge
Wells on the other. Sometimes these branch wires are provided
with means of connection with the main line wires, so that the

185

THE ELECTRIC TELEGRAPH.

stations on the main line can communicate directly with those on
the branch line. Sometimes no such connection is provided, and
a dispatch from the main line must be repeated at the branch
station. This is a defect which ought never to be allowed to remain,
inasmuch as simple and efficient commutators may always be
provided for connecting the branch and main lines, which in the
telegraph play a part similar to the switches by which trains are
turned from the main to the branch line, or vice versa.

It will be evident from what has been said that a dispatch
transmitted upon the secondary line of wires may be delivered at
the same time at all the stations from terminus to terminus along-
the line, or it may be allowed to pass any one or more stations
without entering them, by the mere management of the commu-
tators provided at the stations severally.

126. In what has been said, we have adverted to signals pro-
duced by the current, without explaining the nature of those
signals, or the particular means by which they are produced,
because all the circumstances attending their transmission from
station to station, which have been explained, are quite indepen-
dent of the particular character of the signals, and the way of
producing them. We shall hereafter explain the character of the
signals which are used, and the instruments by which they are
produced.

From all that has been stated meanwhile, it may be inferred
generally that by the commutating apparatus which has been
described above, or by any of the endless variety of equivalent
contrivances which telegraphic inventors have proposed, any of the
following effects may be produced by an agent at any station, at
which a current arrives : — 1 . Such a current may be made to pass
through the alarum, and give notice to the agent of its arrival.

2. It may be made to pass through the instrument and give signals.

3. It may be made to pass the station and continue its course
along the line withoiit affecting any part of the telegraphic appa-
ratus at the station. 4. If it pass through the alarum, or through
the instrument, it may be turned into the earth, and so be prevented
from going further along the line. 5. If it pass through the
alarum or through the instrument, it may after leaving them be
directed along the line, so as to continue its course to the other
stations below or above that at which it is supposed to arrive.

127. In some forms of telegraph, the system of signs transmitted
to a distant station depends entirely upon the current being alter-
nately suspended and transmitted for longer and shorter intervals,
and this succession of long and short intervals, variously combined
like the notes in music, is converted into a sort of telegraphic
language, which by practice is expressed and understood by the

186

KEY COMMUTATOR.

agent with as much facility and promptitude as ordinary written
or spoken language.

128. In such forms of telegraph, the alternate suspension and
transmission of the current is produced by a commutator, which
has the form of the key of a pianoforte and is played upon in a
very similar manner by the agent who transmits the dispatch.

One of the forms of these keys and the mechanism connected
with it, is represented in fig. 48. It is fixed upon a wooden block

Fig. 4S.

B .

B B. The key plays upon a centre E. To the lower side of the
longer arm (E D) is attached a projecting piece of metal v, called
the HAiiitEE, under which is a fixed piece of metal of correspond-
ing form and magnitude called the AXVIL.

The action of the key upon the current is the same precisely as
that already described (117) which is produced by the alternately
removing and restoring the hand to the contact piece in fig. 47.
The hammer in the present case represents the hand, and the anvil
the contact piece. One of the line-wires TO, is attached to the
anvil, and the «other n to the metallic support E of the hammer
and key. When the hammer is in contact with the anvil, the
current passes, and when it is raised from that contact, the current
is suspended.

The button D is faced with ivory to be pressed down by the
finger, and the screw d passing through the short arm of the key
is pressed upon the block x by the reaction of the spring r, when,
the key is not pressed down by the finger on D. The hammer vt
and anvil q are both faced with platinum to prevent oxydation,
which would obstruct that complete metallic contact which is
necessary to ensure the transmission of the current.

An expert manipulator can work the key D with as much
celerity and correctness as can a performer on the pianoforte and
can express in that way in telegraphic language any dispatch
which is placed in manuscript before him, so as to transmit it to any
distant station. This will be explained more fully hereafter.
"When no dispatch is being transmitted from the station at which

187

THE ELECTRIC TELEGRAPH.

the key is placed, it is necessary to leave a free passage for the
current along the line-wires m n. To effect this, the screw <7,
which passes through the short arm of the key, is turned so as to
raise the short arm, and consequently lower the arm E D until the
hammer v is brought into permanent contact with the anvil q.
When that takes place, the metallic continuity between m and n
will be established, and the current will flow without interruption
on the line-wire. Whenever it is desired to transmit a dispatch,
the screw d is turned so as to lower the arm d, and to raise E D,
and thus to raise the hammer from its contact with the anvil.
The key is then ready for the transmission of the dispatch in the
manner already described.

129. In some telegraphic apparatus it is necessary to make the
intervals of transmission and suspension of the current absolutely
equal in duration, and to succeed each other with chronometric
regularity. There are many expedients by which this can be
accomplished, of which the following is an example.

A metallic wheel put in connection with clock-work, so as to

Fig. 49.

receive a regular motion of rotation, has its edge divided into
equal parts by pieces of ivory, or some other non-conductor inlaid
upon it, as represented in fig. 49, where m represents the metal,
and i the ivory. A metallic spring r' connected with one end of the
conducting wire w', presses constantly upon its edge ; and another
r connected with the other end of the wire w, presses constantly
on the metallic axle of the wheel which is otherwise insulated.

Now, if the wheel be supposed to have an uniform motion of
revolution, the alternate divisions of ivory and metal on its edge
will pass in succession under the spring r', while the spring r will
be in constant metallic contact with the axis. If a current flows on
the wire w, it will be transmitted by the spring r to the axle, and
188

WHEEL COMMUTATORS.

thence by the metal of the wheel to r7, when r* is in contact with
any of the metallic parts m of the edge of the wheel, hut will be
^u^pended while it is in contact with the ivory parts i of the edge.
If the wheel, being impelled by clock-work, be moved at such
a rate that each of the divisions marked m and i shall move tinder
the spring in one second, the current will be transmitted and sus-
pended also during intervals of one second. It will in fact be sub-
ject to a regulated pulsation, the rate of which will be controlled and
determined by the horological mechanism which impels the wheel.

130. In some cases, the motion to be imparted to the wheel is
not either regular or continuous. In such cases, it may be moved
either directly by hand, or by a strap, or even by clock-work,
which is subject to a check which will suspend it at certain
positions of the wheel. In all these cases the pulsations of the
current in number, length, and continuance, are governed by
the motion imparted to the wheel.

131. As the suspension and transmission of the current are
instantaneous upon the breach and re-establishment of the metallic
contact of the spring ij and the wheel, there is no practical limit, to
the rapidity which can be given to its pulsations. The wheel may be
turned, for example, so that 500 divisions of its edge may pass under
the spring r' in a second, in which case there would be 250 intervals
of transmission, and 250 intervals of suspension in a second.

It might perhaps be imagined that in so short an interval of
time the current could not be stopped or established along the
entire length of the conducting wire. It has however been shown
that even with the longest continuous wires, practically used in
telegraphs, the ten-thousandth part of a second is more than
enough either to establish or stop the current.

132. The intervals of the suspension of the current may be
produced by a common toothed- wheel,

as represented in fig. 50, without ivory
or other inlaid non-conducting matter.
In this case, a piece of wedge-shaped
metal connected with the up line wire
is attached to the under side of a
wooden lever, while the axle of the
wheel is kept in constant metallic con-
nection with the down wire. TVhen
a tooth of the wheel comes against the
metal attached to the lever, metallic
contact is established, but when the
metal falls between the teeth, and the c<
surface of the wooden lever rests on one of them, and the metallic
contact being broken, the current is suspended.

189

THE ELECTRIC TELEGKAPH.

It is evident that during each revolution of the wheel there will
be as many pulsations of the current as there are teeth, and since
the rotation of the wheel may be as rapid as may be desired, and
the teeth as numerous, there is no practical limit to the possible
rapidity of these pulsations.

133. Another contrivance, by which pulsations are imparted to
the current, consists of a metallic wheel around the face of which
a sinuous groove is cut, in which a pin, projecting from the arm
of a metallic lever is inserted, so that when the wheel is turned
upon its axis, the pin attached to the lever receives from the
sinuosities of the groove a motion alternately right and left, which
is imparted to the other arm of the lever. This latter arm plays
between two metallic stops, one of which is connected with the wire
w, along which the current flows. When the arm of the lever
comes in contact with it, the current is transmitted on the lever
to the sinuous groove of the wheel, and from thence to the line-
wire w'. When the lever oscillates to the other side, the contact
with the wire w is broken, and the current is interrupted.

This will be more clearly understood by reference to the fig. 51,
where A B is the wheel, c c c the sinuous groove, G o H the lever

playing on the axis o. From
G, a short projecting piece,
G G', passes in front of the
wheel across the groove, and
from this piece a pin projects,
which enters the groove. The
arm H plays between two
stops, P and r', provided with
springs to ensure the contact
with the lever. The stop P
is connected with the con-
ducting wire w, and the groove
c is connected with the wire
w'. "When the wheel is turned,
the pin at G' is driven by the
sinuosities of the groove alter •
nately right and left, by which
a corresponding motion is imparted to the arm H of the lever, so
that its end is driven alternately against the stops P and P'.
When it is thrown against P it is in metallic connection with the
wire w. When it is thrown against P' that connection is broken.
Now, if a current flow along P, it will pass to the lever when H
falls against P, and will pass by the lever and the groove c c to the
wire w'. When the arm n is thrown against r', the contact with
p being broken, the current is suspended. Thus, as the lever is
190

ALARUM BY SHORT CIRCUIT.

made to oscillate between p and P*, by the motion of the wheel and
the action of the sinuous groove, the current will be alternately
transmitted and suspended, and will, in fine, receive a succession
of pulsations corresponding exactly with the sinuosities of the
groove. Thus, if there be sixty undulations of the groove in the
circumference of the wheel, the current will receive sixty pulsa-
tions in one revolution of the wheel, and if the wheel revolve at
the rate of sixty revolutions per minute, the current will have 3600
pulsations per minute.

134. An expedient has been sometimes adopted in telegraphic
apparatus for diverting the electric current from its direction,
which differs in principle from the commutator, and which
depends on the tendency of the current to follow the shortest and
widest route open to it between one point and another.

Let w, fig. 52, be the line-wire, B the bell-apparatus, and T
the telegraphic instrument. The line-wire is bent upwards in
the direction m to the

bell B, and then down- lg' °"

wards, and by m' and
"W to the telegraph T.
The current would, ac-
cording to this arrange-
ment, first pass by the
wire m to the bell #,
which it would ring,
and then by the wire
m' W to the telegraph T.
If the dispatch were
then transmitted, the
current constantly pass- ^ ^

ing through B during its \y

transmission, the bell
would be constantly
ringing, which would be inconvenient as well as unnecessary.

This is prevented, and the current transmitted directly to T,
without passing through B, by the following very simple expedient.

A thick piece of metal, a &, turns on an axis c, so that when it
is placed in the horizontal position, the ends a and b are brought
into close contact with the conducting wire at e and /. The
current, on arriving at e divides itself into two parts, one going
by a b to/, and thence to T, and the other as before, by m, through
the bell. But as a b is much shorter and thicker than the wire
m m\ the greater part of the current will go by a &, and the part
which passes along m m' will be too inconsiderable to exercise the
force necessary to ring the bell.

191

THE ELECTRIC TELEGRAPH.

The agent, therefore, at the station, receiving the dispatch,
being warned by the bell that the agent at the station s is going
to send a dispatch, turns the piece a b into the horizontal position,
and the bell ceases to ring, the telegraph x receiving the dispatch.

135. The manner in which the pulsations oi- the current are
produced, controlled, and regulated, by the operator at the station
s" being understood by these examples and illustrations, it will
next be necessary to show how they are made to produce signals
at the station to which the dispatch is transmitted, by which the
operator or observer there can be enabled to understand and
interpret the communication.

The effects of the current which have been found most conve-
nient for this purpose are —

1st. Its power to deflect a magnetic needle from its position of
rest, and to throw it into another direction.

2nd. Its power to impart temporary magnetism to soft iron,
this magnetism suddenly deserting the iron when the current is
suspended.

3rd. Its power to produce the chemical decomposition of certain
substances.

136. All forms of electric telegraph depending on one or other
of these properties of the current, it is indispensably necessary to
understand them before the reader can hope to comprehend the
mode of operation of these wonderful instruments.

If a wire be extended over and under a compass-needle which
directs itself to the magnetic north and south, parallel to the
needle, and as close to it as it can be placed without actually
touching it, as represented in fig. 53, the needle will remain
undisturbed in its position. Let the ends p and n of the wire be
then attached to the poles of a vol-
taic battery, so that a current of a
certain intensity shall be transmitted
upon it. The moment the current is
established upon the wire, the mag-
netic needle a b will be thrown out
of its usual direction, and instead of
pointing north and south, it will
point east and west.
If the direction of the current upon the wire be reversed, the
direction of the deflexion of the needle will be reversed.

Fig. 53.

192

Fig. 72.— FBENCH STATE TELEGRAPH.

THE ELECTRIC TELEGRAPH.

CHAPTEE VI.

137. Relation of the deflection to the direction of the current. — 138.
Galvanometer or multiplier. — 139. Method of covering the wire. —
140. Method of mounting the needle. — 141. Method of transmitting
signals by the galvanometer. — 142. How the current may produce
a temporary magnet. — 143. Electro-magnet constructed by Pouillet.
— 144. Electro-magnets formed by two straight bars. — 145. They
acquire and lose their magnetism instantaneously.— 146. Magnetic
pulsations as rapid as those of the current. — 147. How they are
rendered visible and counted. — 148. Extraordinary celerity of the
oscillations thus produced. — 149. They produce musical sounds by
which the rate of vibration may be estimated. — 150. How the vibra-
tions may impart motion to clock-work. — 151. Their action on an
escapement. — 152. How the movement of one clock may be trans-
mitted by the current to another. — 153. How an electro-magnet may
produce written characters on paper at a distant station. — 154. How
the motion of the hand upon a dial at one station can produce a like
motion of a hand upon a dial at a distant station. — 155, How an
agent at one station can ring an alarum at another station. — 156. Or
may discharge a gun or cannon there. — 157. Power of the bell or other
signal not dependent on the force of the current. — 158. Mechanism of
telegraphic alarum. — 159. Various alarums in telegraphic offices. —
160. Magneto-electricity. — 161. Method of producing a momentary
magneto-electric current. — 162. Application of an electro-magnet to
produce it.

LABDNER'S MGSEUM OF SCIENCE. o 193

No. 39.

THE ELECTRIC TELEGRAPH.

137. To explain the manner in which the deflection of the
needle depends on the direction of the current, let us suppose
the needle to be placed on an horizontal axis o, fig. 54, so as to
Fig 54. play in a vertical plane, and to be

maintained in the vertical direction
when not affected by the current, by
giving a slight preponderance to the
arm on which the south pole of the
needle is placed. By this arrangement
the needle, when undisturbed, will rest
in the vertical position, the north pole
IT being directed upwards, and the
south pole s being directed downwards.
Now if the current which is before
the needle be directed downwards and
that which is behind it upwards, the
north pole IT will be deflected to the
right, and consequently the south pole s to the left, as represented
in the figure. But if the direction of the current be reversed so
that before the needle, it shall be directed upwards and behind
it downwards, the north pole N will be deflected to the left and
the south pole s to the right.

If the intensity of the current be great, and the preponderance
given to the lower arm of the needle small, the deflective force of
the current will be sufficient to throw the needle completely at
right angles to its position of rest, that is, to give it the horizontal
direction ; but it is important to observe, that no greater intensity
of the current can affect it further. The north pole, for example,
cannot be deflected downwards, or the south pole upwards. In
fine, the needle cannot be more affected by any increase of force
of the current after it has once been thrown into the horizontal
direction.

If the intensity of the current be insufficient to throw the needle
into the horizontal direction, it will nevertheless take a position
intermediate between that and the vertical direction at which it
will rest. Its deflection from the vertical will be more and more
considerable as the current is more intense, and certain mathe-
matical conditions have been discovered by which the relative
intensity of the current may be determined by the amount of
the deflection of the needle which it produces.

138. It is evident that the sensibility of the needle will be so
much the greater as the preponderance of the arm s is diminished
and the intensity of the current increased. An expedient has,
however, been ingeniously contrived, by which the most feeble
current can be made to affect the needle. This is accomplished by
194

GALVANOMETEK.

winding the wire which carries the current several times round
the needle, each coil being still parallel to the needle. By this
contrivance, each successive coil of the wire produces a separate
effect upon the needle, and if there he fifty such coils passing suc-
cessively before and behind the needle, each portion of the wire
thus carrying the current producing an independent deflecting
force, there will be a total deflecting force an hundred times greater
than that which a single portion of the wire, passing once over or
under the needle would produce.

In this manner the deflecting power of the most feeble current
may be so multiplied as to produce upon the needle as powerful an
effect as would be produced by a current of great intensity.

An apparatus consisting of wire thus coiled round a magnetic
needle is called a ITTJLTIPLIEE, inasmuch as it multiplies the
deflecting power of the needle. It is also called a EEOSCOPE, or
BEOMETEE,* and sometimes a GALVANOSCOPE, or GALVAXOMETEE,
inasmuch as it indicates the presence, and by certain arrange-
ments, measures the intensity of a galvanic or voltaic current.

139. When the conducting wire is thus coiled round a needle,
it is necessary that it should be covered or coated by some substance
which is a non-conductor of electricity, since otherwise the coils
being necessarily in contact one with another, the current, instead
of following the continuous thread of wire, would pass from coil to
coil. In such cases, therefore, the wire is wrapped with silk or
cotton, which being a non-conductor, confines the current within
it just as water would be included in a pipe.

140. As the wire coiled in the manner above-described, and the
frame which carries it, would prevent the play of the needle from
being easily and conveniently observed, the needle included within
the frame is fixed upon the axis which supports it, so that the
axis turns with it. This axis passes through the side of the frame,
on which the wire is coiled, and upon the end of it which projects
beyond the frame a hand is fixed, so as to be parallel to the needle,
the play of which will necessarily correspond with that of the
needle. This hand plays upon a sort of dial, by which its devia-
tions to the right or to the left, from its position of rest are
indicated.

This will be more clearly understood by reference to fig. 55
(p. 196), which represents a section of the mounting of the needle,
the coil of wire and their appendages, made by a vertical plane
through the axis of the needle. The needle within the coil is
represented at a b, in its position of rest. The axis of the needle

* From two Greek words, peos (reos) a current, and nerpov (metron) a
measure.

0 2 195

THE ELECTRIC TELEGRAPH.

Fig. 55.

passing through the frame supporting the coil, and through the
dial plate, supports in front of the dial the hand a' &', which is
fixed upon the axis in a position parallel to
the needle a b, so that it must play before the
dial in a manner corresponding exactly with
the play of the needle a b within the coil.

141. In order to govern the play of the
needle, it is necessary that the agent at the
station from which the signal is transmitted
should have the power, 1st. To suspend and
transmit the current at the receiving station ;
and 2nd. To change its direction upon the
conducting wire. The former is necessary, to
enable him to bring at all times the needle to
its position of rest ; and the latter, to deflect
it to the right or to the left, according to the
exigencies of the telegraphic communications.
The general principle on which these changes
in the flow and direction of the current are
effected, has been already explained (111). It is easy to imagine,
that by very simple mechanism the movement of a lever or arm
may make or break the contact of the conducting wires, so as to
transmit or suspend the current at pleasure. Also by a simple
motion of such an arm the hands, A and A", fig. 48, or any equivalent
pieces, may be moved from p to N and from N to P, so as to reverse
the current upon the wire to which the arm A' is directed.

If then an agent at the station, s", for example, be provided with
any means of suspending or reversing the current which passes
along the wire, between s and s", he can at will bring a magnetic
needle, mounted at s, to its position of rest, that is, to the vertical
position, by suspending the current or deflect it to the right, by
causing the current to flow in one direction on the conducting
wire, or to the left, by reversing the direction of the current.
The particular manner in which these several operations sub-
serve to telegraphic purposes will be pre-
sently explained.

142. To explain the manner in which the
electric current can impart temporary mag-
netism to soft iron, let us suppose a copper
wire wrapped with silk, to prevent the me-
tallic contact of contiguous convolutions, to
be coiled round a rod of soft iron, bent into
the form of a horse-shoe, as represented in
fig. 56, care being taken, that in carrying
the wire from one arm to the other, the

Fig. 56.

ELECTRO-MAGNETS.

Fig. 57.

direction of the convolutions shall be the same as if the coils had
been continued round the bend.

So long as no electric current passes along the convolutions of
the wire the horse-shoe will be free from magnetism. But if the
ends of the wire, marked + and — , be put in connection with the
poles of a voltaic battery, so that a current flow round its convo-
lutions, the horse-shoe will instantly become a magnet, and will
be so much the more powerful as the current is more intense, and
the coils more multiplied.

If an armature loaded with a weight be presented to the ends
of the horse-shoe while the current passes on the wire, it will
adhere to them, and the weight, if not too great, will be sup-
ported.

143. In 1830 an electro-magnet of extraordinary power was
constructed under the superintendence of M. Pouillet, at Paris.
This apparatus, represented in tig. 57, consists of two horse-shoes,
the legs of which are presented to

each other, the bends being turned
in contrary directions. The superior
horse-shoe is fixed in the frame of the
apparatus, the inferior being attached
to a cross-piece which slides in ver-
tical grooves formed in the sides of
the frame. To this cross-piece a dish
or plateau is suspended in which
weights are placed, by the effect of
which the attraction which unites the
two horse-shoes is at length overcome.
Each of the horse-shoes is wrapped
with 10,000 feet of covered wire, and
they are so arranged that the poles

of contrary names shall be in contact. With a current of
moderate intensity the apparatus is capable of supporting a weight
of several tons.

144. It is found more convenient generally to construct
electro-magnets of two straight bars of soft iron, united at one
end by a straight bar transverse to them, and attached to them
by screws, so that the form of the magnet ceases to be that of
a horse-shoe, the end at which the legs are united being not
curved but square. The conductor of the heliacal current is
usually a copper wire of extreme tenuity.

145. In whatever form these magnets are constructed, the
circumstance which in their telegraphic use is of most importance
to notice, is that if proper conditions be observed in their pre-
paration, their acquisition of the magnetic virtue upon the

197

THE ELECTRIC TELEGRAPH.

establishment of the current, and their loss of it upon the suspen-
sion of the current, are, for all practical purposes, instantaneous.
The moment the extremities of the wire coiled round the horse-
shoe are put into connection with the poles of the battery the
horse-shoe becomes a magnet, and the moment the connection with
the battery is broken it loses the magnetic virtue.

146. It has been already shown, that by means of very simple
expedients, the current may be interrupted hundreds or even
thousands of times in a second, being fully re-established in the
intervals. The acquisition and loss of magnetism by the horse-
shoe accompany these pulsations with the most perfect and
absolute simultaneity. If the pulsations of the current be pro-
duced, at the rate of a thousand per second, the alternate presence
and absence of the magnetic virtue in the horse-shoe will equally
be produced at the rate of a thousand per second. Nor are these
effects in any way modified by the distance of the place of inter-
ruption of the current from the magnet. Thus, pulsations of the
current may be produced by an operator in London, and the
simultaneous pulsations of the magnetism may take place at
Vienna, provided only that the two places are connected by a con-
tinuous series of conducting wires.

147. It remains to show how these rapid pulsations of the mag-
netism of the bar can be rendered sensible, and how they may
even be estimated and counted.

Let two straight rods of soft iron be surrounded by a succession
of convolutions of covered wire, such as has been already de-
scribed, and let the ends, m, m', fig. 58, of these rods be connected
Fi 5g by a straight bar of soft iron, attached

to them by screws and nuts. Let the
wire, a b} proceeding from a distant
station, s, be put in metallic connection
with the extremity of the wire coiled
upon the rod, m, and let the wire, a' b',
connected with the extremity of the
last convolution of the wire on the rod,
m', be put in metallic connection with
the earth. If a current flow along a b,
it will therefore circulate round the rods,
m and m', and will pass to the earth by
the wire, a' b'. So long as this current
flows, the rods will be magnetic, and
they will lose their magnetism in the
intervals of its suspension.
Let g h be a light iron bar, supported on a pivot, at o, on which
it is capable of playing, so that its arm, o g, may move freely to
198

ELECTKO-MAGXETIC PULSATIONS.

the right or left. Let t if be two stops, placed a small distance to
the right and left of its extremity, g, so as to limit the range of
its play. Let s be a spring attached to the extremity, A, by
which that extremity will be constantly drawn to the left, and
therefore the opposite extremity, g, thrown to the right against
the stop, t. When the current is suspended, and the rods, m m',
divested of magnetism, the lever yielding to the action of the
spring, s, the end, <?, will rest against the stop, t. But when the
current passes on the wire, the rods, m m', becoming magnetic,
will attract the arm, o g, of the lever, and this attraction
exceeding the force of the spring, the arm, og, will be drawn
towards the electro-magnet, until it encounters the stop, t', against
which it will rest so long as the current continues to flow. But
the moment the current is suspended, the bars, m m', suddenly
losing their magnetism, the lever, o g, is abandoned to the action
of the spring, and it is again thrown back upon the stop, t, where
it rests until the current is re-established.

Let us suppose that an agent at the station, s, to which the
wire, a b, extends, and which may be at any distance, 500 miles
for example, from s", is supplied with any of the means which
have been explained, by which he can at will control the pulsa-
tions of the current. When he causes the current to flow, he
imparts magnetism to the bars, m m', and throws the lever, o g,
against the stop, if . When he suspends the current he deprives
the bars, m m', of their magnetism, and leaves the lever, o g, to
the action of the spring, s, by which it is thrown against the
stop, t.

It appears, therefore, that with each pulsation which the current
receives from the agent at s, the lever, o g, at s", 500 miles distant
from him, will perform a vibration between the stops, t and t .
As the transmission and suspension of the current, and also the
acquisition and loss of the magnetic power, by the rods, m m', are
both instantaneous, there is no practical limit to the velocity of
the pulsations of the current and those of the magnetism alternately
acquired and lost by the rods, m m1. The oscillations of the lever,
o g, produced by these pulsations are limited, however, by the
weight of the lever, the force of the spring, and the distance
between the stops, t and f . The greater the weight of the lever,
the force of the spring, and the distance between the stops, the
slower will be the motion of the lever from t to f, produced by a
current of given intensity. The greater the weight of the lever,
and the distance between the stops, and the less the force of the
spring, the slower will be the motion from t' to t.

The stop, tf , is so placed as to prevent the absolute contact of
the arm of the lever with the electro-magnet, but to allow it to

199

THE ELECTRIC TELEGRAPH.

approach the latter very closely. Absolute contact is to be
avoided, because it is found that in that case the arm adheres to
the magnet with a certain force after the current ceases to flow,
but so long as absolute contact is prevented, it is immediately
brought back by the spring, s, when the current is suspended.

148. It is evident, therefore, that the limit of the possible
celerity of vibration to be imparted to the lever, 'o g, by the pulsa-
tions of the current will depend on the nice adjustment of the
weight and play of the lever, and the force of the spring, s.

The velocity of oscillation, however, which can in this way be
imparted to the lever, is such as can scarcely be credited with-
out actually witnessing its effects. When that velocity does not
exceed a certain limit the oscillations may be registered and
counted, by causing the lever to give motion to the anchor of an
escapement, connected with a train of wheel- work, by which a
hand or index, moving on a graduated dial, is governed. But
these oscillations are susceptible of velocities so great that it
would be difficult to apply this expedient for counting them. M.
Gustave Froment, of Paris, suggested and applied to this purpose
with complete success, a method of ascertaining the velocity
depending on the laws which govern the vibrations of musical
strings.

149. It is well known that the pitch of any musical note is the
consequence of the rate of vibration of the string by which it is
produced, and that the more rapid the vibration the higher the
note will be in the musical scale, and the slower the vibration the
lower it will be. Thus the string of a pianoforte which produces

the bass note "- — t±— vibrates 132 times in a second, that
which produces the note — = vibrates 66 times in a second,

and that which produces the note BJ — : vibrates 264

t) ^&^

times per second.

On a seven octave pianoforte the highest note in the treble is

three octaves above ph— nr— , and the lowest note in the bass is

four octaves below it. The number of complete vibrations corre-
sponding to the former must be 3520 ; and the number of vibra-
tions per second corresponding to the latter is 27§.

If, therefore, the lever, o gy have any rate of vibration more
rapid than 27| vibrations per second, and less rapid than 3520 per
200

PULSATIONS MEASURED BY MUSICAL SOUNDS.

second, it will produce by its motion some definite musical sound,
and if the note formed upon a pianoforte, which is in unison with
it, be found, the rate of vibration of the string producing that note,
will be the same as that of the lever.

When it is stated that the vibrations imparted by the pulsations
of the current to levers, mounted in the manner here described, have
produced musical notes nearly two octaves higher than the highest
note on a seven octave piano, tuned to concert pitch, it may be
conceived in how rapid a manner the transmission and suspension
of the electric current, the acquisition and loss of magnetism in
the soft iron rods, and the consequent oscillation of the lever, upon
which these rods act, take place. The string which produces the
highest note, on such a piano, vibrates 3520 times per second. A
string which would produce a note an octave higher would vibrate
7040 times per second, and one which would produce a note two
octaves higher would vibrate 14080 times per second.

It may, therefore, be stated, that by the marvellously subtle
action of the electric current, the motion of a pendulum is produced,
by which a single second of time is divided into from twelve to
fourteen thousand equal parts !

150. It has been already shown how the motion of clock-
work may be applied to control and regulate the pulsations of the
electric current. We shall now show how, on the other hand, the
pulsations of the current may be made to govern the motion of
wheel-work. This expedient must be regarded with the more
interest inasmuch as it has been applied with the greatest effect
in several of the varieties of electric telegraph, which have been
proposed or brought into operation.

151. If we suppose the lever g A, fig. 58, to be put into connection
with the anchor of the escapement wheel of a system of clock-work,
it will be easy to see how that clock-work can be regulated by the
pulsations of the electric current.

In fig. 59 (p. 202), w w7 is the escapement wheel which is con-
stantly impelled by the force of a descending weight or mainspring
in the direction of the arrows. The anchor A B c, of the escapement,
is connected with an axis D, by the straight rod B D. This rod B B
may be either the vibrating arm of a lever, such as g h, fig. 58,
kept in oscillation by the current acting on an electro-magnet, or
it may be connected with such a lever in any convenient manner,
so as to oscillate simultaneously with it, and to have the extent of
play necessary for the action of the pallets A and c of the anchor
on the teeth of the escapement wheel.

When the anchor is not in a state of oscillation, a tooth of the
wheel will rest upon one of its pallets, and the wheel and clock-
work connected with it will be stopped. When the anchor moves

201

THE ELECTRIC TELEGRAPH.

Fig. 59.
D

from left to right, the tooth of the wheel, which was previously
stopped by the upper surface n' of the pallet c, is allowed to escape,

and in obedience to the
power of the spring or
weight, which moves
the clock-work, it ad-
vances towards m'.
Meanwhile the pallet A
enters the space be-
tween two teeth of the
wheel, one of which
coming against its lower
surface, it stops its
motion. "When the an-
chor moves back from
right to left, the pallet
c comes under the next
tooth of the wheel. In
this manner every move-
ment of the anchor to
Jc the right lets a tooth,
which was stopped by
the pallet c, advance,
and afterwards the pal-
let A stops the advance
of another tooth, while
every movement to the
left lets the tooth
stopped by A advance,
and afterwards the
pallet c stops the next tooth which advances on that side.

Thus each complete oscillation of the anchor, consisting of a
motion to the right and a motion to the left, lets one tooth of the
escapement wheel, and no more, pass.

Now if we suppose the pulsations of the current to impart to
the anchor by the intervention of the electro-magnet and its
appendages a motion of vibration, a tooth of the escapement
wheel, and no more than one tooth, will pass the anchor for each
pulsation of the current. If the current be suspended the move-
ment of the escapement wheel and the clock-work connected with
it will be also suspended, and when the pulsation of the current
recommences, the oscillations of the anchor, and consequently the
motion of the escapement wheel, and the clock-work connected
with it, will also recommence.

152. If the pulsations of the current be regulated (as they may
202

PULSATIONS PRODUCE WRITTEN CHARACTERS.

be according to what has been already explained (129), by the
pendulum of a clock at any station, the motion of the anchor of the
escapement established at any other station to which the current is
transmitted, will be synchronous with that of the pendulum of the
clock which governs the pulsations of the current, and thus a
regular motion may be imparted by one clock to another, provided
that between them there be established a conductor, and the pen-
dulum of the one clock regulates the pulsations of the current,
which govern the movement of the anchor of the escapement of
the other.

153. If the extremity of the lever, og, fig. 58, carry a pencil,
which presses upon paper, when the lever is drawn towards the
electro-magnet, and if at the same time the paper is moved under
the pencil with an uniform motion, a line will be traced upon the
paper by the pencil, the length of which will be proportionate to
that of the interval during which the lever off is held in contact
with the stop P. Now as the agent at s can regulate this interval
at will, by controlling the flow of the electric current, making
that current act for a short interval if he desire to make a short
line upon the paper, for a long interval if he desire to make a
long line, and for an instant if he desire to make merely a dot, it
will be understood how he can at will mark a sheet of paper at s",
500 miles distant, with any desired succession of lines of various
lengths or of dots, and how he may combine these in any way he
may find suitable to his purpose.

We have here supposed the pencil attached to the end of the lever
to be alternately pressed against the paper, and withdrawn from it
by the motion of the lever. If, however, the paper be so placed
that the lever shall oscillate parallel to it, the pencil presented
to the paper will remain permanently in contact with it, and will
trace upon the paper a line alternately right and left, whose
length will be equal to the play of the end g of the lever, to which
the pencil is attached. If while this takes place the paper be
moved under the pencil in a direction at right angles to the line
of its play, the pencil will trace upon the paper a zigzag line, the
form of which will depend on the relation between the motion of
the paper and that of the pencil. When the current is in this
case suspended, the paper being moved under the pencil at rest,
a straight line will be traced upon it.

Thus the paper will be marked either with a zigzag line,
or a straight line according as the current is transmitted or
suspended.

If the current be alternately transmitted and suspended during
intervals of unequal length, at the will of the agent, at s, the
paper at s" will be marked by a line alternately zigzag and

203

THE ELECTRIC TELEGRAPH.

straight, the length of the zigzag and straight parts being varied
at the will of the operator at s.

How these subserve to telegraphic purposes will be presently
more fully explained.

154. In the same manner, if a toothed wheel, moved by the
agent at s, produce a pulsation of the current by the passage of
each successive tooth, these pulsations will produce simultaneous
oscillations of the lever og, at the station s", and if these oscilla-
tions act upon the anchor of an escapement wheel attached to
clock-work at s", that wheel will be advanced in its revolution,
tooth for tooth, with the wheel at s, and if each of these wheels
govern the motions of hands upon dial plates, like the hands of a
clock, the hand of the dial at s" will have the same motion exactly
as the hand on the dial at s, so that if at the commencement of
the motion both hands point to the same figure or letter of the
dial, they will continue, moving together, to point always to the
same figures or letters.

Thus if the operator at s desire to direct the hand on the dial at
s", to the hour of 3 or 5, he will only have to turn the hand upon
the dial, at his own station, to the one or the other of these hours.

It will presently also be apparent how important this is in the
art of electro-telegraphy.

155. If the lever og, fig. 58, be connected with the tongue of
an alarum- bell, so that when og is put into vibration the bell will
ring, and will continue to ring so long as the vibration is con-
tinued, it is evident that the operator at s can, at will, ring a bell
at s", by producing pulsations of the current in any of the ways
already described.

An operator at s" may in like manner ring a bell at s.

By this mutual power of ringing bells, each operator can call
the attention of the other, when he is about to transmit a dis-
patch, and the other by ringing in answer can signify that he is
prepared to receive the dispatch, as already stated.

156. If the lever og were in connection with the lock or other
mechanism, by which the powder charging a cannon is fired, the
operator at T could at will discharge a cannon at E, no matter
what may be the distance of E from T.

157. It will be observed that when a bell is rung, or any similar
signal produced at the station s", by means of an electric current
transmitted from a distant station, s, it is not directly the force of
the current which acts upon the object by which the signal is
made. The current is only indirectly engaged, producing the
result by liberating the mechanism which makes the signal and
leaving the force which moves it free to act. Thus in the most
usual case of a bell, it is acted upon while it rings, not by the

204

ELECTRO-MAGNETIC ALARUM.

Fig. 60.

current, but by the force of a mainspring or descending weight,
transmitted to the hammer or tongue in the same manner exactly
as that in which the force of a mainspring or weight of a clock is
transmitted to the striking apparatus. The current does nothing
more than disengage a catch by which the motion of the wheel-
work acted on by the mainspring or weight, is arrested. The
catch once disengaged, the action of the current on the bell ceases,
and the ringing is continued by the action of the mainspring or
weight, and it may in like manner be stopped by the current
again throwing the catch between the teeth of one of the wheels.

It will, therefore, be apparent that since the force which
impels the bell is independent of the current, a bell of any desired
magnitude may be acted upon by a hammer of any desired weight,
without requiring any more force from the current than that
which is sufficient to enable the electro-magnet to disengage the
catch by which the mechanism of the bell is arrested.

158. Although the bell mechanism used for telegraphs differs in
nothing which is essential from that of a common alarum clock, it
may not be without interest to show one of the varieties of
mechanism in practical use.

In fig. 60 is given a view of
the bell mechanism, as used on
the telegraphic line of the South-
Eastern Railway Company.*

A is the electro-magnet.

B its armature.

B e a lever attached at the
upper end to the armature, and
having at the lower end a catch,
e, which when the armature is not
attracted towards the magnet is
pressed by a spring, /.

d a wheel having a tooth in
which the catch e is engaged by
the pressure of the spring/, when
the armature B is not attracted
towards the magnet, but which is
liberated from the catch e, when
the armature B is drawn towards
the magnet.

a a cylindrical box containing a strong mainspring, by which
the train of wheelwork is kept in motion so long as the catch e is
not engaged in the tooth of the wheel d.

Elect. Tel. Manip., p. 23,

205

THE ELECTEIC TELEGRAPH.

The actual contact of the armature B with the poles of the
electro-magnet is prevented by two small ivory knobs screwed into
the surface which is presented to the magnet. The play of the
armature B is so limited that the catch e shall be just disengaged
from the tooth of the wheel d, when the ivory knobs come into
contact with the poles of the magnet.

When the wheel- work is liberated by the magnet withdrawing
the catch e from the wheel d, the mainspring in the cylindrical
box a causes the toothed wheel attached to the box to revolve.
This wheel drives a pinion on the axle of the wheel 6 ; the wheel
b drives a pinion on the axle of the wheel c ; the teeth of the
wheel c are engaged with those of a pinion on the wheel d.
The movement of the train is stopped, when the catch e falls
under the tooth of the wheel d. The wheel i, which is engaged
in the anchor of the escapement g, is fixed upon the axle of
the wheel c, turns with the latter, and thus gives an oscil-
lating motion to the anchor, which is imparted to the hammer h
of the bell D. The bell is therefore acted upon by the hammer so
long as the magnet A keeps the catch e from falling under the tooth
of the wheel d.

159. Since the magnitude, loudness or pitch of the bell is
independent of the force of the current, the telegraphic offices are
provided with various bells for special purposes.

Sometimes a special wire is appropriated to the bell which is
acted upon by a special current.

In other cases the regular current intended to work the tele-
graph is diverted to the bell apparatus by the commutator. In
other cases again, the object is accomplished by the expedient
explained in (134), which is known as the short circuit.

160. Having explained the form and construction of electro-
magnets, we are prepared to show the manner in which an electric
current may be produced by the mere action of magnets without
any intervention of a voltaic battery.

The electricity thus produced has been called MAGNETO-

ELECTEICITY.

161. Let a silk or cotton covered wire be coiled heliacally on a
roller or bobbin having a hollow core of sufficient magnitude to
allow a cylindrical bar to be passed into it. Let the covered wire
be coiled constantly in the same direction, beginning from A B,
(fig. 61), and terminating at c D. Let the extremities mn of this
wire be joined to those of a wire m o n of any required length,
stretched to any required distance. Now let the north pole
N of a magnet s N be suddenly passed into the core of the

206

MAGXETO-ELECTRIC CURRENTS.

bobbin. An electric current will then be transmitted on the wire
m o «, the presence of which may be rendered manifest by a
galvanometer. This current, however, will be only momentary,
being manifested only at the moment the pole of the magnet

Fig. 61.

enters the core of
the bobbin. It
ceases immedi-
ately after that
entrance.

Xow if the
magnetic bar
after entering be
as suddenly

withdrawn, another current will be
produced upon the wire m o n, which
will also be only momentary, but its
direction on the wire will be con-
trary to that produced by the en-
trance of the magnetic pole.

Thus if upon the entrance of the
pole jr a current is produced, running
in the direction m o n, the with-
drawal of the pole x will produce a
current running from n o m.

If the south pole s be passed into
the core and withdrawn, momentary
currents will in like manner be pro-
duced, but they will have contrary
directions.

If the wire m o terminated at o,
no matter what may be the distance
of o from m, were put at o in me-
tallic communication with the earth,
or with a plate or other mass of
metal buried in the earth, and if the
extremity n of the wire of the coil
were put in metallic connection with
the earth in the same manner at n,
the transmission of the instantaneous
.currents would take place exactly in
the same manner as above described,
because in that case the earth would
play the part of a conductor between the end of the wire m o at o,
and the end of the coil wire n.

But if the metallic continuity either of the wire m o n, in case it

207

THE ELECTRIC TELEGRAPH.

extended from m to n, or of mo if it were as described above in
connection with, the earth at o, were anywhere broken, no current
would be produced by the entrance or withdrawal of the magnet.
It is therefore essential to the production of these phenomena that
the extremities m and n of the coil wire shall be in electric com-
munication with each other, by being united either with a
continuous metallic connection, or by means of the earth in the
manner already described.

The property in virtue of which soft iron acquires magnetic
properties, when the poles of a permanent magnet are brought
into proximity with it, supplies a very convenient method of
exhibiting the play of the phenomena of momentary currents above
described.

162. Let SON (fig. 62), be a powerful permanent horse-shoe
magnet, having its poles s, N, presented to and in close proximity
with a similar horse- shoe a b of soft iron,
wrapped with convolutions of covered wire
in the manner already described. Let the
extremities m and n of the coil be sup-
posed to be placed in connection with two
wires, which may be extended to any dis-
tances, and whose extremities are in me-
\n tallic communication with the earth in the
manner already explained.

When the poles s and N are brought into
proximity with the ends a and b of the
horse-shoe a b, the latter will, by the
inductive action of the magnet s o N, ac-
quire magnetic polarity, the end a, near the south pole s, having
northern, and the end b, near the north pole N, having southern
polarity. This magnetic polarity, however, of a b will only con-
tinue so long as the poles s and sr of the permanent magnet are
kept near to a and b. If they be removed, that instant the
polarity of a b will cease. If the poles be reversed, N being pre-
sented to a, and s to 6, then a will acquire south, and b north
polarity.

It appears, therefore, that by presenting the poles of the magnet
N o s to the horse-shoe the same effect is produced as if the poles
of a magnet were suddenly passed into the axis of the coil, and by
withdrawing the poles sr and s from a and &, the same effect is
produced on the coil as if the poles of the magnet which had been
passed along the axis were suddenly withdrawn.

208

LONDOX, August, 1854.

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