WALTON AND MABERLY,

UPPER' GaWER STREET & IVY LANE.
Price Eighteenpence.

i

5HS5E5ESE5ESH55

MAtV

EDITED BY

DIONYSIUS LARDNER, D.C.L.,

formerly Professor of Natural Philosophy and Astronomy in University College .London.

ILLUSTRATED BY ENGRAVINGS ON WOOD.
VOL. VI.

LONDON:
WALTON AND MABERLY,

UPPER GOWER STREET, AND IVY LANE, PATERNOSTER ROW.
1855.

•LOAN STACK

LONDON :
BRADBURY AND EVANS, PRINTERS, WHITEFr.IAF.S.

L 3
V.fr

CONTENTS.

COMMON THINGS— CLOCKS AND WATCHES.

PAGE

CHAP. I. — 1. General want of time measurers. — 2. No natural
measures for short intervals. — 3. Approximative expedient by
shadows. — 4. Sun-dials. — 5. Differently constructed for different
places. — 6. Earliest sun-dials. — 7. Clepsydra, or water-clock. —
8. Hour-glass. — 9. Mercurial time-gauge. — 10. Clocks — their
chief parts. — 11. Regulating power of the pendulum. — 12. 'Uni-
form rate of vibration. — 13. Analysis of a vibration. — 14.
Experimental verification of isochronism. — 15. Moving power
sustains the vibration. — 16. Vibration not dependent on weight
of pendulum. — 17. Time of vibration varies with the length. —
18. Analysis of motion of pendulous mass. — 19. How the pen-
dulum governs the hands. — 20. Produces intermitting motion. —
21. Pendulum's motion maintained by moving power

CHAP. II. — 22. Action of pendulum on escapement wheel. — 23. Rate
of motion of hands produced by tooth and pinion work. —
24. Method of making pinions. — 25. Mutual action of toothed
wheels. — 26. Wheel and pinion. — 27. Bevelled and crown
wheels. — 28. Weight applied as a moving power. — 29. Why
hands not turned back when clock is wound up. — 30. Main-
spring.— 31. Its power variable. — 32. The fusee. — 33. Balance-
wheel. — 34. Its vibrations uniform. — 35. General explanation
of a watch. — 36. Of a clock moved by a weight. — 37. Method
of regulating the rate 17

CHAP. III.— 38. Method of regulating a balance-wheel.— 39. Recoil
escapement. — 40. Cylindrical escapement. — 41. Duplex. —
42. Lever. — 43. Detached. — 44. Maintaining power of a clock
moved by a weight. — 45. Of a watch moved by a main-
spring.— 46. Weight of mainspring and pendulum and balance-
wheel variously combined. — 47. Watches and chronometers. —
48. Marine chronometers. — 49. Stationary chronometers. — 50.
Striking apparatus. 33

380

i\r CONTENTS.

MICROSCOPIC DRAWING AND ENGRAVING.

PAGE

CHAP. I. — 1. Beautiful precision of the minute structure of natural
objects.— 2. Cornea of a fly's eye. — 3. Number of eyes of diffe-
rent insects. — 4. Astonishing precision of artificial objects. — 5.
Demand for such objects by Microscopists. — 6. Classes of suck
artificial objects. — 7. Microscopic scales. — 8. Method of engraving
them. — 9. Measurement of microscopic objects with them. — 10.
Their minuteness. — 11. Scales of Mr. Froment. — 12. Rectangular
scales. — 13. Micrometric threads. — 14. Necessity for microscopic
tests. — 15. Test-objects. — 16. Telescopic tests ; double stars. —
17. Nebulae and stellar-clusters. — 18. Effects of different tele-
scopes upon them : telescopes of Herschel and Lord Rosse. — 19.
Remarkable nebulae described by Herschel. — 20. Differently seen
by Lord Rosse. — 21. Microscopic tests. — 22. Improved powers
of microscope. — 23. The Lepisma-Saccharina. — 24. ThePodura,
or Spring-tail 49

CHAP. II. — 25. Natural tests not invariable. — 26. Natural tests
imperfect standards. — 27. Nobert's test-plates. — 28. The degree
of closeness of their lines. — 29. Their use. — 30. Apparent error
respecting them. — 31. Froment's microscopic engraving. — 32.
Method of executing it. — 33. Various methods of microscopic
drawing. — 34. Drawings by squares. — 35. Dr. Goring's drawings.
• — 36. Structure and metamorphosis of insects. — 37. The day-fly.
— 38, The larva of this insect. — 39. Its organs of respiration. —
40. Its general structure. — 41. Its mobility. — 42. State of chry-
salis.— 43. The perfect insect. — 44. The production and deposi-
tion of its eggs, and its death. — 45. Death may be delayed by
postponing the laying of the eggs. — 46. They take no food. — 47.
Their countless numbers ; their bodies used as manure . . 65

CHAP. III.— 48. The beetle.— 49. Its larva.— 50. Drawing of it in
its natural size. — 51. Dr. Goring's magnified drawing. — 52.
Production of the beetle from the egg. — 53. The young larva.
— 54. Its voracity and manner of seizing its prey. — 55. De-
scription of its organs. — 56. Its chrysalis. — 57. Water-beetle.
— 58. Gnat.— 59. Dr. Goring's method of drawing.— 60. Draw-
ing by the camera-lucida. — 61. Section of the human skin ;
sweating-gland and duct. — 62. The itch insect. — 63. Method of
obtaining it . . . . . . . . • . -81

CHAP. IV.— 64. Structure of the itch insect.— 65. Its habits.—
66. The mange insect. — 67. Its form and structure. — 68. Defects
incidental to drawing with the camera. — 69. Microscopic photo-
graphs.— 70. Microscopic daguerreotypes by Messrs. Donne and
Foucault.— 71. Description of the blood.— 72. Red and white
corpuscles. — 73. Daguerreotype of a drop of blood magnified. —
74. Magnitude of the corpuscles.— 75. Cause of the redness of

CONTENTS.

PAGE

blood. — 76. Corpuscles of inferior animals. — 77. White globules.
— 78. White grains. — 79. White globules converted into red
corpuscles. — 80. Red corpuscles dissolved. — 81. Circulation of
the blood. — 82. Method of showing it in the tongue of a frog.
— 83. The arteries distinguishable from the veins. — 84. The
vascular system of the tongue. — 85. Mucous glands. — 86. Milk ;
its constitution. — 87. Magnified view of a drop of milk. —
88. The butter globules. — 89. Their number variable. — 90.
Analysis of the milk of different animals. — 91. Richness of
woman's milk. — 92. Analogy of milk to blood. — 93. Import-
ance of the quality of milk. — 94. Its richness ascertained. —
95. Quevenne's hydrometer applied to milk. — 96. Its fallacy.
— 97. Donne's lactoscope. — 98. Objections to it answered. —
99. Frauds practised by milk vendors. — 100. Fore-milk and
after-milk. — 101. Self-engraved photographic pictures. . .97

THE LOCOMOTIVE.

CHAP. I. — 1. Familiar to every eye. — 2. Its mechanism not generally
understood. — 3. Object of this Treatise. — 4. Two modes of pro-
pelling wheel carriages. — 5. How locomotive is propelled. —
6. Action of piston-rod on wheels. — 7. Dead points. — 8. Un-
equal action. — 9. How remedied. — 10. Connection of piston-
rods with wheels. — 11. Wheels fixed on their axles. — 12. Form
of locomotive. — 13. Driving-wheels. — 14. Coupled wheels. —
15. Consumption of steam. — 16. Evaporating power of boiler
determines efficacy of engine. — 17. Fire-box. — 18. Tubes through
boiler. — 19. Fuel.— 20. Blast-pipe. — 21. Tender.— 22. Plans
and sections, with their description . t . . .113

CHAP. II. — 23. Speed. — 24. Locomotive stock. — 25. What record of
the performance and condition of an engine should be kept. —
26. Cause of renewals of English locomotives. — 27. Average
mileage of engines. — 28. Locomotive requires rest. — 29. Expense
of cleaning and lighting. — 30. Reserve engines. — 31. Bank
engines.— 32. Time they are kept standing. — 33. Economy of
fuel. — 34. Register of consumption. — 35. Small amount of useful
service obtained. — 36. On Belgian lines. — 37. On other Con-
tinental lines. — 38. On London and North Western line. —
39. Comparisons between lines not fairly instituted. — 40. Legi-
timate test of comparison. — 41. Amount of locomotive stock
required.— 42. Gross receipts of European Railways in 1850. —
43. Mileage of the same. — 44. Great increase since. — 45. Enor-
mous consumption of coal. — 46. Mileage of passengers and
goods 129

vi CONTENTS.

THE THERMOMETER.

PAGE

Heat.— 2. Sensible heat. — 3. Latent heat. — 4. Contraction and
dilatation. — 5. Liquefaction and solidification. — 6. Vaporisation
and condensation. — 7. Incandescence. — 8. Combustion. — 9.
Temperature. — 10. Conduction. — 11. Radiation. — 12. Some
bodies are pervious to heat. — 13. Some reflect heat. — 14. Means
of measuring the degrees of heat. — 15. Mercurial thermometer.
— 16. Preparatidh of mercury. — 17. Selection of tube. — 18.
Formation of bulb. — 19. How the tube is filled.— 20. Scale
applied.— 21. Graduation of scale.— 22. Zero point.— 23. Stan-
dard points. — 24. Freezing and boiling temperatures universally
adopted. — 25. Fahrenheit's scale. — 26. Centigrade. — 27. Reau-
mur's.— 28. Increase of volume of mercury. — 29. Uniformity of
its dilatation. — 30. Standard thermometer. — 31. Range of scale.
— 32. Why mercury is employed in thermometers. — 33. Self-
registering thermometers. — 34. Alcohol thermometers. — 35. Air
thermometer. — 36. Differential thermometer . . . .145

THE NEW PLANETS.

Discovery of these planets. — 2. The old planets. — 3. Numerical
law of their distances. — 4. A missing planet. — 5. Conjecture of
Professor Bode. — 6. Discovery of Ceres. — 7- Of Pallas. — 8.
Theory of Dr. Olbers — a broken planet. — 9. Discovery of Juno.
— 10. Of Vesta.— 11. Rapid discovery of the others. — 12. Table
of the group. — 13. Circumstances corroborating the theory of
Dr. Olbers. — 14. Amateur astronomers. — 15. Minute bulk of
these planets. — 16. Corroboratory of Dr. Olbers' theory. — 17.
Force of gravity upon them 161

LE VERRIER AND ADAMS' PLANET.

1. Surprise excited by the discovery. — 2. How a body may be dis-
covered without seeing it. — 3. Generalisation of the principle.
— 4. Its application to the case of Neptune. — 5. Condition of
the solar system before the discovery. — 6. Observed disturbances
of Uranus. — 7. Great regularity of these effects. — 8. How they
would be produced by a more distant planet. — 9. Calculations
of Le Verrier and Adams. — 10. Elements of the sought planet
according to these geometers. — 11. Its actual discovery. — 12.
Its corrected elements. — 13. Discrepancies between the actual
and predicted elements explained. — 14. Comparison of the effects
of the real and predicted planets. — 15. The discovery not to be
ascribed to chance. — 16. The period of Neptune computed. — 17.
Computation of his distance. — 18. Its prodigious orbital motion.
— 19. Illustrated by a railway train. — 20. Its magnitude. — 21.
Its satellite. — 22. Its weight.— 23. Its bulk.— 24. The sun's
light and heat upon it. — 25. The sun's apparent diameter seen
from it. — 26. Its suspected ring 171

CONTENTS. yii

MAGNITUDE AND MINUTENESS.

1. Kelative magnitude. — 2. Manifestations of Divine wisdom. —
3. Smallness of great mountains compared with the bulk of the
earth. — 4. Of the earth compared with Jupiter and Saturn. —
5. With the Sun.— 6. With other celestial objects.— 7. Minute
particles of which all bodies are composed. — 8. Solid, liquid,
and gaseous states — how produced. — 9. Mechanical subdivision.
— 10. Pulverised marble. — 11. Inequalities of polished surfaces.
— 12. Particles of gold on touchstone. — 13. Filaments of glass. —
14. Micrometer wires. — 15. Gold leaf. — 16. Gilt silver threads
for embroidery. — 17. Soap bubbles. — 18. Insects' wings. — 19.
Filaments of wool, silk, and fur. — 20. Red Particles in the
blood. — 21. Animalcules. — 22. Spider's web. — 23. Minute sub-
division of a grain of salt. — 24. Of sulphate of copper. —
25. Of musk. — 26. Of strychnine. — 27. Of ammoniacal hypo-
sulphite.— 28. Of sugar. — 29. Is matter infinitely divisible ? —
30. Crystallisation of salt. — 31. Ultimate atoms. — 32. Natural
crystals. — 33. Plane of cleavage. — 34. Determinate figure of
ultimate atoms. — 35. Principles of mechanical science indepen-
dent of this hypothesis. — 36. Matter not destructible. — 37. By
combustion. — 38. By evaporation. — 39. By destructive distil-
lation.— 40. Nor by any other process 193

Fig. 17.

COMMON THINGS.

CLOCKS AND WATCHES.

CHAPTEE I.

1. General want of time measurers. — 2. No natural measures for short
intervals. — 3. Approximative expedient by shadows. — 4. Sun-dials.
— 5. Differently constructed for different places. — 6. Earliest sun-
dials.— 7. Clepsydra, or water-clock. — 8. Hour-glass. — 9. Mercurial
time-gauge. — 10. Clocks — their chief parts. — 11. Regulating power
of the pendulum. — 12. Uniform rate of vibration. — 13. Analysis of a
vibration. — 14. Experimental verification of isochronism. — 15. Moving
power sustains the vibration. — 16. Vibration not dependent on weight
of pendulum. — 17. Time of vibration varies with the length. —
18. Analysis of motion of pendulous mass. — 19. How the pendulum
governs the hands. — 20. Produces intermitting motion. — 21. Pen-
dulum's motion maintained by moving power.

1. AFTER the supply of the absolute necessaries of physical
existence — food, clothing, and lodging — one of the first wants of a
society, emerging from barbarism, is the means of measuring and
registering time. In civilised society, all contracts for labour,
and for all kinds of service, are based upon time. Even in the
cases of the highest public functionaries, and where the service
rendered is purely social and intellectual, still it is regulated,
limited, and compensated with relation to time. Time measurers

LARDNER'S MUSEUM OF SCIENCE. B 1

No. 66.

COMMON THINGS— CLOCKS AND WATCHES.

or chronometers were therefore among the earliest mechanical and
physical inventions.

2. Although nature has supplied visible signs to measure and
mark the larger chronometric units, such as days, months, and
years, she has not furnished any corresponding measures of the lesser
units of hours, minutes* and seconds. There are no visible marks
on the firmament by passing from one to another of which the
sun can note the hours, still less are there any signs for minutes
or seconds. These subdivisions are therefore merely artificial and
conventional, and to measure and mark them, artificial motions
must be contrived.

3. Rough approximations were first made to the chief divisions
of the day, by observing the apparent motion of the sun from
rising to setting. Thus the direction of the meridian, or of the
south, being once known, and marked by some fixed and visible
object, the time of noon was known by observing when the sun
had this direction. The hours before and after noon were roughly
estimated by the position of the sun between noon and the times
of its rising and setting. Greater precision was given to this
method, by erecting a wand or gnomon, the shadow of which
would fall upon a level surface, in a direction always opposite to
that of the sun. Thus, after sunrise, the shadow would be inclined
towards the west, the sun being then towards the east. From the
moment of sunrise until noon, the shadow would move continually
nearer and nearer to the direction of the north, and at noon it
would have exactly that direction. From noon to sunset the
shadow would be more and more inclined towards the east.

It is evident, however, that such a dial would not afford uniform
indications at all seasons of the year, so that the hour-lines of the
shadow determined in spring, for example, would not show the
same hours in winter as in summer. Without much astronomical
knowledge, it is easy to be convinced of this. At the equinoxes,
the sun rises and sets at six o'clock, and at the east and west
points precisely ; and, therefore, at these seasons, the six o'clock
hour-lines of such a dial would be for the morning due west, and
for the evening due east. But on the first day of summer (21st
June), the sun rises and sets at points of the horizon very much
north of the east and west points, and at six o'clock in the forenoon
and afternoon its bearing is north of the east and west points.

4. A dial so constructed at any given place would be useless
as a time indicator. To render it useful, it would be necessary
that the shadow of the style should fall in the same directions at
the same hours at all seasons of the year. Now, to attain this
object, the style must be not vertical, but must be directed to the
celestial pole. It is easy to comprehend that in that case a plane

2

SUN-DIALS.

passing through the style and the sun would always be carried
raund the style with an uniform motion by the diurnal motion of
the sun, and that at all seasons this plane would at the same hours
have the same position.

It is for this reason that the gnomon of sun-dials is placed at
such an inclination with the plate of the dial, that when the dial
is properly set the gnomon will be directed to the north pole of
the heavens, and being so placed, its shadow will fall upon the
same lines of the dial at the same hours, whatever be the season
of the year.

5. It is evident, therefore, that dials must be differently con-
structed for places which have different latitudes. We have shown
in a former Tract * that the elevation of the celestial pole is equal
to the latitude of the place, and consequently the inclination of
the gnomon of a sun-dial must be also equal to the latitude of
the place where the dial is intended to be set. It follows, there-
fore, that a dial constructed for London would not be suitable for
York, Newcastle, or Edinburgh.

The position of the plate of the dial upon which the shadow of
the gnomon is projected is quite unimportant. All that is really
important is the direction of the gnomon, which must always be
that of the celestial pole, whatever be the position of the plate of
the dial. Thus the plate of the dial may be either horizontal,
vertical, or oblique. Its position will depend upon the place
where it is to be erected. If it be in an open space, as in a garden
or field, having a clear exposure on all sides, it will be generally
most convenient to make it horizontal ; and, hence, in such cases,
it is usual to fix it upon the top of a column of three or four feet
high, so that it may be easily observed by a person of ordinary
height standing near it. Sometimes it is convenient to place it
upon the wall of a building, such as a church. A wall with a
southern exposure is in that case the most convenient; but to
indicate the hours of the early morning in the spring and
summer, an eastern exposure would be required, and to in-
dicate those of the late evening a western exposure would be
necessary.

Where these vertical dials are erected, it is therefore frequently
the practice to establish them at the same time on different walls
of the same building.

Whatever be the position of the plate of the dial, the position
of the hour-lines upon it is a matter of mere technical calculation,
for which the formula and principles of spherical trigonometry are
necessary, but which is not attended with any difficulty.

* Vol. i. page 102.

B 2 3

COMMON THINGS — CLOCKS AND WATCHES.

It must, however, be observed, that generally the hour-lines
are inclined to each other at unequal angles, as may be seen by
inspecting any ordinary sun-dial. There is ^one, and one only,
position which could be assigned to the plate of the dial, such
that the hour-lines would make equal angles with each other.
That position would be at right angles to the gnomon, and a dial
so constructed would be suitable to any place, whatever be its
latitude. All that would be necessary would be to set it so that
the gnomon would be directed to the celestial pole. The sun,
however, would shine upon the upper or north side of it during
the spring and summer, and on the lower or south side during the
autumn and winter. It would, therefore, be necessary that it
should be marked on both sides with hour-lines, and that a
gnomon should be fixed on both sides.

6. The name dial is derived from the Latin word dies, a day,
and the invention and use of the instrument as a time indicator is
very ancient. According to Herodotus, the invention came to
Greece from Chalctaa. The first dial recorded in history is the
hemisphere of Berosus, who is supposed to have lived 540 B.C.

7. The first attempts to measure time by motions artificially
produced, consisted in arrangements, by which a fluid was let fall
in a continuous stream through a small aperture in the pipe of a
funnel, the time being measured by the quantity of the fluid
discharged. The CLEPSYDEA, or water-clock, of the ancients, was
constructed upon this principle. This and the sun-dial were the
only instruments contrived or used by the ancients for the
measurement of time.

Clepsydras were contrived by the Egyptians, and were in
common use under the reign of the Ptolemys. In Home,
sun-dials were used in summer and clepsydras in winter. These
instruments, though subject to very obvious defects, were, never-
theless, when skilfully used, susceptible of considerable accuracy,
as may be easily conceived, when it is stated, that before the
invention of clocks and watches, they were the only chronometric
instruments used by astronomers. The chief sources of their
irregularities were the unequal celerity with which the fluid is
discharged, owing to its varying depth in the funnel and its
change of temperature.

8. The common hour-glass comes under this class of chronometric
instruments, but is the most imperfect of them. Nevertheless, for
certain purposes, it is even now, advanced as we are in the application
of science to the arts, still found the most convenient chronometer.
The process of ascertaining a ship's rate of sailing or steaming
by means of the log affords ari example of its use. One man holds
the reel from which the line runs off, while another holds the

4

CLEPSYDEA — SAND-GLASS.

sand-glass, and gives the signal when the sand has run out.
The number of knots run off from the reel is then the number of
miles per hour in the rate of the vessel. The intervals between
the knots, the quantity of sand in the glass, and the aperture
through which it falls, are so adapted to each other as to give this
result.

9. Notwithstanding the great perfection to which the art of
constructing chronometers has attained, an apparatus was not long
since proposed by the late Captain Kater for the measurement of
very small intervals of time, fractions of a second, for example,
which is a modification of the clepsydra. A quantity of pure and
clean mercury is poured into a funnel with a small aperture at its
apex, so that a stream of the quicksilver shall fall through it.
The flow is rendered uniform, by keeping the mercury in the
funnel at a constant level. The apparatus is intended in scientific
researches to note the exact duration of phenomena, and it is
so managed, that the stream issuing from the funnel, is turned
over a small receiver at the instant the phenomenon to be
observed commences, and is turned away from it the instant the
phenomenon ceases. The mercury discharged into the receiver is
then accurately weighed, and the number of grains, and parts
of a grain it contains, being divided by the number of grains
which would be discharged in a second, the number of seconds,
and the parts of a second, which elapsed during the continuance
of the phenomenon is found.

10. For the purposes of civil life, as well as for the more
precise objects of scientific research, all these contrivances have
been superseded by clocks and watches, which are now so
universal as to constitute a necessary article of furniture in the
most humble dwellings, and a necessary appendage of the person
in all civilised countries.

All varieties of this most useful mechanical contrivance include
five essential parts.

1. A moving power.

2. An indicator, by whose uniform motion time is measured.

3. An accurately divided scale, upon which the indicator moves
and by which its motion is measured.

4. Mechanism, by which the motion proceeding from the
moving power is imparted to the indicator.

5. A regulator, which renders the motion imparted to the
indicator uniform, and which fixes its celerity at the required rate.

Thus, for example, in a common clock, the moving power is the
weight suspended by cords over a pulley fixed upon the axle of a
wheel, to which the weight in descending imparts a motion of
rotation. The indicator is the hand. The scale is the dial plate

5

COMMON THINGS — CLOCKS AND WATCHES.

upon which the hours, minutes, and sometimes the seconds,
are marked by equal divisions, over which the point of the hand
moves. The mechanism is a train of wheelwork, so constructed
that the rato of rotation of the last wheel upon the axle of which
the hand is fixed, shall have a certain proportion to the rate of
rotation of the first wheel, upon the axle of which the weight is
suspended. And if, as is generally the case, there be two or
three hands, then the wheel-work is so constructed, that while
one of the hands makes one revolution, another shall make twelve
revolutions, and the third shall make sixty revolutions during a
single revolution of the latter, and therefore seven hundred and
twenty during a single revolution of the former.

If no other appendage were provided, the weight would,
in such an apparatus, descend with a continually increasing
velocity, and would therefore impart to the hands a motion of
rotation more and more rapid, which would not consequently
serve as a measure of time. This defect is removed by the
addition of a pendulum, combined with a wheel upon which it
acts called the escapement. It is the property of the pendulum
that its oscillations are necessarily made always in equal times,
and its connection with the escapement-wheel is such, that one
tooth of that wheel, and no more, is allowed to pass the upper
part of the pendulum during each oscillation right and left. But
this escapement-wheel itself forms part of the train of wheel-
work by which the first wheel, moved by the descending weight,
is connected with the wheels which move the hands, and con-
sequently, by regulating and rendering uniform the motion of this
escapement- wheel^ the pendulum necessarily regulates and renders
uniform the motion of the entire apparatus.

The instrument thus arranged, therefore, imparts an uniform
motion of rotation to each of the hands, but this is not enough to
render it a convenient time measurer. It is necessary that the
motion of the hands should have some definite and simple relation
to the natural and conventional division of time into days, hours,
minutes, and seconds. For this purpose it is required not only
that the hands should move uniformly, but that the first, or
slowest of them, should make two complete revolutions in a day,
or a single revolution in twelve hours ; and, as a necessary con-
sequence of this, that the second should make a single revolution
in an hour, and the third in a minute.

11. From what has been stated, it will be apparent that the
actual rate of motion imparted to the hands will be determined by
the rate of oscillation of the pendulum. It has been shown that
for each oscillation, right and left, of the pendulum, one tooth of
the escapement- wheel passes, and if the escapement-wheel have

THE PENDULUM.

thirty teeth, and if "the pendulum take one second to make a
single swing, it will allow the escapement-wheel to make a
complete revolution while it makes thirty swings from right to
left, and thirty from left to right, that is, in sixty seconds, or one
minute ; so that, if the axis of the third hand were in this case
fixed upon the axle of the escapement- wheel, that hand would
make one complete revolution in a minute, and consequently the
second would make one complete revolution in one hour, and the
third in twelve hours. The required conditions would therefore
be in this case fulfilled.

To render this explanation of the regulating property of the
pendulum complete, it will be sufficient to show — 1st, that the
time of vibration must be always rigorously the same with the same
pendulum ; 2nd, that this time can be made shorter or longer by
varying the length of the pendulum, so that a pendulum can
always be constructed which will vibrate in one second, or in half
a second, or, in short, in any desired time ; and 3rd, that the
connection of the pendulum with the escapement-wheel can be so
constructed, that the motion of the latter shall be governed by
the vibrations of the former, in the manner already described.

A pendulum consists of a heavy mass attached to a rod, the
upper extremity of which rests upon a point of support in such a
manner as to have as little friction as possible. Such an in-
strument will remain at rest when its centre of gravity is in the
vertical line immediately under the point of suspension or support.
But if the centre of gravity be drawn from this position on either
side, and then disengaged, the instrument will swing horizontally
from the one side to the other of the position in which it would
remain at rest, the centre of gravity describing alternately a
circular arc on the one side or the other of its position of rest.
If there were neither friction nor atmospheric resistance, this
motion of vibration or oscillation on either side of the position of
equilibrium would continue for ever ; but in consequence of the
combined effects of these resistances, the distances to which the
pendulum swings on the one side and on the other are continually
diminished, until, after the lapse of an interval, more or less
protracted, it comes to rest.

12. It is related that Galileo, when a youth, happening to
walk through the aisles of a church in Pisa, observed a chandelier
suspended from the roof, whose position had been accidentally
disturbed, and which was consequently in a state of oscillation.
The young philosopher, contemplating the motion, was struck
with the fact, that although the range of its vibration was
continually diminished as it approached a state of rest, the times
of the vibration were sensibly equal, the motion becoming slower

7

COMMON THINGS— CLOCKS AND WATCHES.

as the range of the oscillations became more limited. This led
him to infer that property of the pendulum expressed by the
word isochronism, in virtue of which the vibrations, whether
in longer or shorter arcs, are performed in the same time.

Although, however, as we shall presently show, pendulums
possess this property Vhen the arcs of vibration are very small,
they do not continue to manifest it when the range of vibration
becomes more considerable.

13. To simplify the exposition of the important theory of the
pendulum, it will be convenient, in the first instance, to consider
it as composed of a heavy mass of small magnitude, suspended by
a wire or a string, the weight of which may be neglected. Thus,
let us suppose a small ball of lead suspended by a fine silken
string, the length of which is incomparably greater than the
diameter of the leaden ball. Such an arrangement is called the
simple pendulum.

Let s, fig. 1, be the point of suspension; let s B be the fine
silken thread by which the ball B is suspended, and the
weight of which, in the present case,
is neglected. Let B be the position of
the ball when in the vertical under the
point of suspension s. In that posi-
tion the ball would remain at rest;
but if we suppose the ball drawn aside
to the position A, it will, if disengaged,
fall down the arc A B, of which the
centre is s, and the radius the length
of the string. Arriving at B, it will
have acquired a certain velocity, which,
in virtue of its inertia, it will have a
tendency to retain, and with this velo-
city it will commence to move through
the arc B A'. Supposing neither the
resistance of the atmosphere nor friction to act, the ball will rise
through an arc B A' equal to B A ; but it will lose the velocity which
it had acquired at B ; for it is evident that it will take the same
space, and the same time, to destroy the velocity which has been
acquired, as to produce it. Thus, the velocity at B, being acquired
in falling through the arc A B, will be destroyed in rising
through the equal arc B A'.

Having arrived at A', the ball, being brought to rest, will
again fall from A' to B, and at B will have again acquired the
same velocity which it had obtained in falling from A to B, but
in the contrary direction ; and in the same manner it may be
explained that this velocity will carry it from B to A. Having
8

ISOCHRONISM.

arrived at A, the ball, being again brought to rest, will fall once
more from A to B, and so the motion will be continued alternately
between A and A'.

The motion of the pendulum from A to A', or from A' to A, is
called an oscillation, and its motion between either of those
points and B is called a semi-oscillation, the motion from B to A
or from B to A' being called the ascending semi-oscillation, and
the motion from A or A' to B, the descending semi-oscillation.

The time which elapses during the motion of the ball between
A and A' is called the time of one oscillation.

It is evident, from what has been stated, that the time of
moving from either of the extremities A, A', of the arc of oscillation
to the point B, is half the time of an oscillation.

If, instead of falling from the point A, the ball had fallen from
the point c, intermediate between A and B, it would have then
oscillated between c and c' ; two points equally distant from B,
and the arc of oscillation would have been c c', more limited
than A A'.

But in commencing its motion from c, the declivity of the
arc down which it falls towards B would be evidently less than
the declivity at A ; consequently the force which would acce-
lerate it, commencing its motion at c, would be less than that
which would accelerate it, commencing its motion at A.
The ball, therefore, commencing its motion at A, would be
more rapidly accelerated than when it commences its motion
at c.

The result of this is, that, although the arc A B may be twice
as long as the arc c B, the time which the ball takes to fall from
A to B will not be sensibly different from the time it takes to
fall from c to B, provided that the arc of oscillation A B A' is not
considerable.

It was at first supposed, as we have just stated, that, whether
the oscillations were longer or shorter, the times would be
absolutely the same. Accurately speaking, however, this is not
the case : but if the total extent of the oscillation A A' do not
exceed 5° or 6°, then the time of oscillation in it may be con-
sidered, practically, the same as in the lesser arcs.

14. This important principle may be easily experimentally veri-
fied. Let two small leaden balls be suspended from the same point
of support, but one being in advance of the other, so that in oscil-
lating the two balls shall not strike each other. This being done,
let one of the balls be drawn from its point of rest through an
angle less than 3°, and let it be disengaged. It will oscillate
as described above. Let the other ball be now drawn from
its point of rest through a much less angle, and let it be so

9

COMMON THINGS — CLOCKS AND WATCHES.

disengaged that it shall commence its oscillation at the same
moment with the commencement of one of the oscillations of the
other ball.

Let it, in short, be so managed, that when the one ball is at
A, the other shall be at c ; and that both shall commence their
descending motion towards B at the same moment. It will be
then found that their oscillations will be synchronous for a con-
siderable length of time, that is to say, the balls will arrive at A'
and c', respectively, at the same instant; and returning, will
simultaneously arrive at A and c respectively.

If, in this case, the oscillation of the ball A were made through
an arc, even as great as 10°, that is to say, 5° each side of the
vertical, the oscillation of the ball c being made through an arc
of 2°, it would be found that 10001 oscillations of the latter
would be equal to 10000 oscillations of the former, so that the
actual difference between their times of oscillation would not
exceed the ten thousandth part of such time.

15. In the practical application of the pendulum, however,
this departure from absolute isochronism, small as it is, becomes
unimportant ; for a power is always provided, by which the loss
of motion which would be produced by friction and atmospheric
resistance is repaired, and the magnitude of the oscillations is
maintained uniform, as we shall presently show.

16. It might be expected that the time of oscillation of different
pendulums would depend, more or less, upon the weight of the
matter composing them, and that a heavy body would oscillate
more rapidly than a lighter one. Both theory and experience,
however, prove the result to be otherwise. The force of gravity
which causes the pendulum to oscillate acts separately on all the
particles composing its mass; and if the mass be doubled, the
effect of this force upon it is also doubled; and, in short, in
whatever proportion the mass of the pendulum be increased or
diminished, the action of the force of gravity upon it will be
increased or diminished in exactly the same proportion, and con-
sequently the velocity imparted by gravity to the pendulous mass
at each instant will be the same.

It is easy to verify this by experiment. Let different balls of
small magnitude, of metal, ivory, and other materials, be sus-
pended by light silken strings of the same length, and made to
oscillate ; their oscillations will be found to be equal.

17. If pendulums of different lengths have similar arcs of
oscillation, the times of oscillation of those which are shorter will
be less than the times of oscillation of those which are longer. Let
a, b, c, d, and e, fig. 2, be five small leaden balls, suspended
by light silken strings to the point of suspension s, and let all

10

KATE OF PENDULUM.

of them be supposed to form pendulums, having the same angle
of oscillation. The arc of oscillation of the ball a will be a a"",
that of Swill be I W", that
of c, c c"", and so on. In
commencing to fall from
the points #, 5, c, J, e
towards the vertical line,
these five balls are equally
accelerated, inasmuch as
the circular arcs down
which they fall are all
equally inclined at this
point to the vertical line.
The same will be true if
we take them at any cor-
responding points, such as
a', b', c', d', e'. It may there-
fore be concluded, that
throughout the entire range
of oscillation of each of
these five pendulums, they
will be impelled by equal accelerating forces.

Now it is shown by the principles of mechanics, that when bodies
are impelled by the same or equal accelerating forces, the spaces
through which they move are proportional to the squares of the
times of their motion ; therefore it follows, that the lengths of
these arcs of oscillation are proportional to the squares of the times.
But the lengths of these arcs are evidently in the same proportion
as the lengths of the pendulums, that is to say, the arc a a"" is
to 1 1"" as s a is to s b, and the arc b b"" is to c c"" as s b is
to s c, and so on.

It follows, therefore, that the squares of the times of oscillation
of pendulums are as their lengths, or, what is the same, the times
of oscillation are as the square roots of their lengths. This
principle is easily verified experimentally.

Let three small leaden balls be suspended vertically under each
other by means of loops of silken thread, as represented in fig. 3,
and in such a manner that they can all oscillate in the same
plane at right angles to the plane of the diagram, the suspending
loops not interfering with each other.

Let the loops be so adjusted that the distance of the ball 1
below the line M N shall be 1 foot, the distance of the ball 4,
4 feet, and the distance of the ball 9, 9 feet.

Let the ball 9 be put in a state of oscillation through small
arcs, and let the ball 4 be then drawn from its vertical position,

11

COMMON THINGS — CLOCKS AND WATCHES.

and disengaged so as to commence one of its oscillations with an
oscillation of the ball 9 ; and in the same manner let the ball
1 be started simultaneously with one of the
Fi£ 3 oscillations of the ball 9.

— ft will be found that two oscillations of
the one-foot pendulum are made in exactly
the same time as a single oscillation of the
four-foot pendulum; consequently, the
time of each oscillation of the latter will be
double that of the former, while its length
is fourfold that of the former.

In the same manner, while the one-foot
pendulum makes three oscillations, the
nine-foot pendulum will make one, and,
consequently, the time of oscillation of the
latter will be three times that of the
former, while its length is nine times that
of the former,

By this principle, the length of a pendulum which would
oscillate in any proposed time, or the time of oscillation of a
pendulum of any proposed length can be ascertained, provided
we know the length of a pendulum which oscillates in any
given time.

18. We have hitherto supposed that the pendulous body is a
heavy mass of indefinitely small magnitude, suspended by a wire
or string having no weight. These are conditions which cannot
be fulfilled in practice. Every real pendulous body has a defi-
nite magnitude, its component parts being at different distances
from the point of suspension ; the rod which sustains it is of con-
siderable weight, and all the points of this rod, as well as those of
the pendulous mass itself, are at different distances from the point
of suspension. In estimating, therefore, the effect of pendulums,
it is necessary to take into account this circumstance.

Let us suppose a, 6, c, d, e, f, g (fig. 4), to be as many small
heavy balls connected by independent strings, the weight of
which may be neglected, with a point of suspension s, and let
these seven balls be supposed to vibrate between the positions
s M and s M'. Now if these balls were totally independent of
each other, and connected with the point of suspension by inde-
pendent strings, they would all vibrate in different times, those
whicb are nearer the point s vibrating more rapidly than those
which are more distant from it. If, therefore, they be all dis-
engaged at the same moment from the line s M, those which are
nearest to s will get the start of those which are more distant,
and at any intermediate position between the extremes of their
12

CENTRE OF OSCILLATION.

vibration they will assume the positions a', b', c', d', e',f, g'. That
which is nearest to the point B, and which is the shortest pen-
dulum, will be foremost, since it has the most rapid vibration.
The next in length, b', will follow it, and so on ; the most remote
from s being the longest pendulum, g' being the last in order.

Now if, instead of supposing these seven balls to be suspended
by independent strings, we imagine them to be fixed upon the
same wire, so as to be rendered incapable of having any inde-
pendent motion, and compelled to keep in the same straight line ;
then it is evident, that while the whole series vibrates with a
common motion, those which are nearest to the point of suspension
will have a tendency to accelerate the motion of those which are
more distant, while those which are more distant will have a
tendency to retard the motion of those which are nearer.

These effects will produce a mutual compensation ; b and c will
vibrate slower than they would if they were moving freely, while
e and/ wiU evidently move more rapidly than if they were moving

13

COMMON THINGS — CLOCKS AND WATCHES.

freely. Among the series, there will he found a certain point,
which will separate those which are moving slower than their
natural rate, from those which are moving faster than their
natural rate ; and a ball placed at this point would vibrate exactly
as it would do if no other balls were placed either above or below
it. Such a ball would, as it were, be the centre which would
divide those which are accelerated from those which are re-
tarded.

Such a point has, therefore, been denominated the centre of
osoillation.

It is evident then, that a pendulous mass, of magnitude
more or less considerable, will vibrate in the same time as it
would do if the entire mass were concentrated at its centre
of oscillation, and formed there a material point of insensible
magnitude.

By the length of a pendulum, no matter what be its form,
is always to be understood the distance of its centre of oscillation
from its point of suspension.

It will be seen from what has been explained above, that
by varying the distance of the centre of gravity of the pen-
dulum from the point of suspension, the centre of oscillation,
and therefore the virtual length of the pendulum, and con-
sequently its time of vibration, may be varied. The instru-
ment may therefore be so adjusted, that the time of its vibration
shall be a second, or any fraction of a second, that may be
desired.

19. Supposing, then, the pendulum to be so adjusted, that it
shall make its vibrations at any required rate, one per second for
example, let us see how the motion of the indicating hands is
governed by such vibrations.

Upon the axis on which the pendulum oscillates is fixed a piece
of metal in the form of an anchor, such as D B A c (fig. 5), so that
this piece shall swing alternately right and left with the pendulum.
Two short pieces, m and m', called pallets, project inwards at
right angles to it from its extremities A and c.

The form and dimensions of the anchor ABC are accommodated
to those of the escapement- wheel, w w, which is part of the
clockwork, and which, in common with the other wheels forming
the train, is moved in the direction indicated by the arrow by
the weight or main-spring. "When the anchor swings to the right
the pallet m enters between two teeth of the wheel, the lower of
which coming against it, the motion of the wheel is for the
moment arrested. When it swings to the left, the pallet m is
withdrawn from between the teeth, and the wheel is allowed to
move, but only for a moment, for the other pallet m' enters
14

ESCAPEMENT.

Fig 5.

between two teeth at the other side, the upper of which coming
against it the motion of the wheel is again arrested.

The wheel, therefore,
is thus made to revolve
on its axis, E, not with
a continuous motion, as
would be the case if it
were impelled by the
weight or mainspring,
without the interference
of any obstacle, but
with an intermitting
motion. It moves by
starts, being stopped
alternately by one pallet
or the other coming in
the way of its teeth.

When the pendulum,
and therefore the an-
chor, is at the extreme
right of its play, the
pallet, m, having en-J
tered between two teeth,
a tooth rests against its
lower side, the wheel is
arrested, and the pallet,
m', is quite disengaged
from, and clear of, the
teeth of the wheel.
When in swinging to
the left the arm D B becomes vertical, the tooth of the wheel on the
left has just escaped from the pallet, m, and the wheel being
liberated, has just commenced to be moved* by the force of the
weight or mainspring. But at the same moment the pallet, m',
enters between the teeth of the wheel on the right, and when the
anchor has arrived at the extreme left of its play, the tooth of the
wheel, which is above the pallet, m', will have fallen upon it, so
that the motion will again be arrested.

Thus it appears, that during the first half of the swing from
right to left, the motion of the wheel is arrested by the pallet, m,
and during the remaining half of the swing the wheel moves, but
is arrested the moment the swing is completed.

In like manner it may be shown, that during the first half
of the swing from left to right, the motion of the wheel is
arrested by the pallet, w', that it is liberated and moves during

15

COMMON THINGS — CLOCKS AND WATCHES.

the latter half swing, and is again arrested when the swing is
completed.

20. The motion which is imparted to the hands upon the dial
necessarily corresponds with this intermitting motion of the
escapement-wheel. If the clock be provided with a seconds-
hand, the circumference of the dial being divided into sixty equal
parts by dots, the point of the seconds-hand moves from dot to dot
during the second half of each swing of the pendulum, having
rested upon the dot during the first half swing.

The whole train of wheel-work being affected with the same
intermitting motion, the minute and hour hands must move, like
the second hand, by intervals, being alternately moved and stopped
for half a second. This intermission, however, is not so observable
in them as in the seconds-hand, owing to their comparatively slow
motion. Thus, the minute-hand moving sixty times slower than
the seconds-hand, moves during each half swing of the pendulum
through only the sixtieth part of the space between the dots, and
the hour-hand moving twelve times slower than the minute-hand
moves in each half swing of the pendulum, through the 360th part
of the space between the dots. It is easy, therefore, to comprehend
how changes of position so minute are not perceptible.

21. If the pendulum vibrated upon its axis of suspension uncon-
nected with the clockwork, the range of its oscillation would be
gradually diminished by the combined effects of the friction upon
its axis and the resistance of the air, and this range thus becoming
less and less, the oscillation would at length cease altogether, and
the pendulum would come to rest. Now this not being the case
when the pendulum is in connection with the wheelwork, but on
the contrary, its oscillations having always the same range, it is
evident that it must receive from the escapement- wheel some force
of lateral impulsion, by which the loss of force caused by friction
and the resistance of the air is repaired.

It is easy to show how the effect is produced. It has been
shown that during the first half of each swing, a tooth of the
escapement-wheel rests upon one or other pallet of the anchor.
The pallet re-acts upon it with a certain force, arresting the motion
of the wheelwork, and receives from it a corresponding pressure.
This pressure has a tendency to accelerate the motion of the pen-
dulum, and this continues until the tooth slips off, and is liberated
from the pallet. It is this force which repairs the loss of motion
sustained by the pendulum by friction and atmospheric resistance.

Thus we see, that while on the one hand the pendulum regu-
lates and equalises the motion imparted to the wheelwork by the
weight or mainspring, its own range is equalised by the reaction
of the weight or mainspring upon it.
16

Fig 13.

W

COMMON THINGS.

CLOCKS AND WATCHES.

CHAPTEE II.

22. Action of pendulum on escapement wheel. — 23. Rate of motion of hands
produced by tooth and pinion work. — 24. Method of making pinions.
— 25. Mutual action of toothed wheels. — 26. Wheel and pinion. —
27. Bevelled and crown wheels. — 28. Weight applied as a moving
power. — 29. Why hands not turned back when clock is wound up.
—30. Mainspring.— 31. Its power variable.— 32. The fusee.— 33.

LARDNER'S MUSEUM OF SCIENCE. c 17

No. 70.

COMMON THINGS — CLOCKS AND WATCHES.

Balance-wheel. — 34. Its vibrations uniform. — 35. General explana-
tion of a watch. — 36. Of a clock moved by a weight. — 37. Method
of regulating the rate.

22. IP the action of the anchor of the pendulum upon the
escapement- wheel be attentively considered, it will be perceived
that one tooth only of the escapement passes the anchor for each
double vibration made by the pendulum. Thus, if we suppose
that when the pendulum is at the extreme left of its range, the
right-hand pallet is between the teeth m' and n't the tooth »' will
escape from the pallet c when the pendulum, swinging from left
to right, comes to the vertical position, which is the middle of its
swing. While it rises to the extreme right of its range, the tooth
n' advances to the place which m' previously occupied, and at the
same time the tooth m advances to the place which n previously
occupied ; but, at the same time, the pallet A, carried to the right,
enters between m and the succeeding tooth, and arrests the further
progress of the wheel. When the pendulum then swings to the
left, the wheel continues to be arrested until it arrives at the
middle of its swing, when the tooth below m escapes from the
pallet A, but at the same moment the pallet c enters below the
tooth which is above n', and receiving it at the end of the swing,
stops the motion of the wheel. Thus it appears,, that tooth after
tooth, in regular succession, falls upon the pallet c upon the arrival
of the pendulum at the extreme left of its play after each double
oscillation.

If the pendulum be so constructed that it shall vibrate in a
second, and that it be desired that the escapement-wheel shall
make a complete revolution in a minute, that is during sixty
vibrations of the pendulum, the wheel must have thirty teeth.
In that case, one tooth passing the anchor during each double
oscillation from right to left, and back from left to right, thirty
teeth, that is the whole circumference of the wheel, will pass the
anchor in thirty double oscillations, or in sixty single swings of the
pendulum, the time of each swing being one second.

23. The manner in which different rates of revolution can be
imparted to the different hands of a clock or watch, by tooth
and pinion work, is easily rendered intelligible.

The wheels commonly used in watch and clockwork are formed
from thin sheets of metal, usually brass, which are cut into
circular plates of suitable magnitude, upon the edges of which
the teeth are formed. The edges of the wheels thus serrated are
brought together, the teeth of each being inserted between those
of the other, so that if one be made to revolve upon its axle, its
teeth pressing upon those of the other, will impart a motion of
revolution to the other.
18

WHEELS AND PINIONS.

When a large wheel works in the teeth of a much smaller one,
which is a very frequent case in all species of wheelwork, the
smaller wheel is called for distinction a PINION, and its teeth are
called LEAVES.

24. The method of manufacturing the pinions and smaller
wheels used in watch and clockwork is very ingenious. A rod of
wire, the diameter of which a little exceeds that of the wheel or
pinion to be made, is drawn through an aperture cut in a steel plate,
having the exact form and magnitude of the wheel or pinion to be
formed. After being forced through this aperture by the ordinary
process of wire-drawing, it is converted into a fluted wire, the
ridges of the fluting corresponding exactly in form and magnitude
to the edge of the aperture, and therefore to the teeth or leaves of
the pinion or wheel.

This fluted wire, called pinion wire, is then cut by a cutter,
adapted to the purpose, into thin slices, at right angles to its length.
Each slice is a perfect wheel, or pinion ; and it is evident that all
of them must be absolutely identical in form and magnitude.

Such a wire-drawing plate, with apertures of different forms and
sizes, is represented in fig. 6.

Fig. 6.

*.* *

Fig. 7.

25. Two wheels of unequal magnitude, working one in the
other, are represented in fig. 7. It will be easily perceived, that
in this case their motions must be in
contrary directions. Thus, if the
wheel A move in the direction of the
hand of a watch, the wheel B must
move in the contrary direction.

Also, the rate at which they revolve
on their axles will be in the inverse
proportion of the number of their

teeth. Thus, if the wheel B have fifty teeth, while the wheel A
has only ten, it is evident that one revolution of B must be
accompanied by five revolutions of A, since an equal number of
teeth of each wheel must necessarily pass the point of contact c
in the same time.

Now, in clock and watchwork, one of the objects to be attained
is to cause certain wheels to revolve in a given numerical pro-
portion to others. Thus, that upon the axis of which the seconds
c 2 19

COMMON THINGS — CLOCKS AND WATCHES.

hand is fixed must make sixty revolutions, while that upon which
the minute hand is fixed makes one. This would, therefore, be
accomplished if the two wheels worked one in the other, the one
haying ten teeth and the other six hundred. But it is not
necessary or convenient that the two wheels should thus be
immediately in connection. Two or more wheels or pinions may
be interposed between them, so that their relative velocities of
rotation may result from the combined relations of the numbers
of teeth or leaves in all the intermediate wheels and pinions.

26. A wheel working in a pinion is represented in fig. 8. When
a very slow motion of rotation is to be converted into one many
times faster, or vice versa, this expedient is usually adopted.

A wheel and pinion are often fixed upon the same axis at
more or less distance asunder. The pinion in this case may
drive or be driven by a smaller wheel at a distance from the first,
which is often convenient in clockwork and other machinery.

Thus, in fig. 17, the wheel c drives the pinion d which is fixed
upon the axle of D, and drives it. The wheel D drives the pinion
e, which drives the wheel E on the same axle^and the wheel E
drives the pinion/, which drives the wheel
F, and so on. In this way combinations
of wheels and pinions may be arranged
so as to modify in any desired manner the
rate of rotation, and to transfer the rota-
tion from axle to axle according to any
proposed conditions.

27. In all these cases the axles round
which the motion of rotation is produced
are parallel one to another. In many cases, as well in clockwork
as in other machinery, it is required to produce a motion of

Fig. 10.

Fig. 8.

rotation round an axis at right angles to that upon which the
motion already obtained is produced.

This is very simply and beautifully effected by either of two
expedients, one of which is called BEVELLED, and the other CKOWN
wheels.
20

CLOCK WEIGHT.

Fig. II.1

The manner in which the object is attained by bevelled wheels
will be evident by inspecting fig. 9. The teeth in this case are
formed upon a surface inclined to the axis at an angle of 45°, and
the two axles make with each other consequently an angle of 90°.

In the crown wheel A, fig. 10, the teeth are raised upon the
edge parallel to the axis, and work in the teeth or leaves of a
wheel or pinion B, whose axle is at right angles to that of A.

In clockwork, the crown wheel is the expedient used for this
purpose, bevelled wheels being generally preferred in larger and
heavier applications of wheelwork.

28. It has been already
stated that the moving
power applied to clock or
watchwork is either a
weight or a mainspring.

If a weight be the mov-
ing power, it is suspended
to a cord which is coiled
upon a drum fixed upon
an horizontal axis, the first $
wheel of the train which \
gives motion to the hands
being fixed on the same
axis, so that it shall turn
when the drum turns.

Such an arrangement is
represented in fig. 11, where
A B is the drum, c D the
wheel attached to it and
moved by it, w the weight
which is the moving power
suspended to the cord E,
which is coiled upon the
drum A B. The end, r, of
the axis of the drum pro-
jecting beyond it, is made
square, so as to receive a
key made to fit it, by which
it is turned, so as to coil
the cord upon the axis,
when it has been uncoiled by the descending motion of the weight.

* This, and most of the succeeding diagrams have been copied from the
excellent work "Cours Elementaire de Mecanique," par Charles Delaunay
— Victor Masson — Paris, 1854, with the permission of the author and
publisher.

21

COMMON THINGS — BLOCKS AND WATCHES.

The direction: in wHch the wheel c D is turned by the force of
the descending weight is indicated by the arrow, and in that
direction it will continue to turn so long as the weight acts upon
the coil of the cord upon the drum. But so soon as the cord,
by the continued descent of the weight, shall have been dis-
charged from the drum, the rotation imparted to CD must cease.
It is then that the key must be applied to the square end, p, of
the axis of the drum, and turned continually in the direction
contrary to that in which the weight would turn the drum in
descending.

29. It will no doubt be perceived by the attentive reader, that,
in this case, the hands of the clock would be always turned back-
wards while the clock is being wound up, unless some special
provision were made against such an effect ; for it is evident, that
if the wheel c D, when turned by the descent of the weight w, in
the direction of the arrow, give a progressive motion to the hands,
the motion imparted to CD, by the ascent of the weight w, while
the clock is being wound up, must necessarily impart to the
hands a motion in the contrary direction, that is a backward
motion.

In all clocks this is prevented by an expedient called a ratchet
wheel and catch, the one being attached to the barrel A B, and
the other to the face of the wheel c D, the effect of which is to
allow the barrel A B, to be turned while the clock is being wound
up in the direction contrary to that indicated by the arrow with'
out turning the wheel c D ; but when the barrel A B is turned
by the descent of the weight w, in the direction of the arrow, the
catch acting in the teeth of the ratchet-wheel, the motion of A B is
imparted by the action of the catch on the ratchet-wheel to the
wheel c D, and by it to the hands.

Fie. 12.

The form and mode of application of the ratchet-wheel will be
presently more clearly explained.

30. The moving power of a weight can only be applied to time-
22

MAINSPRING.

pieces where the space necessary for the play of the weight in its
descent and ascent can be conveniently obtained. This condition
is obviously incompatible with the circumstances attending pocket-
watohes, all portable and moveable timepieces, chimney, table,
and console clocks, and in general all timepieces constructed on
a small scale.

The moving power applied to these universally is a mainspring,
which is a ribbon of highly tempered steel bent into a spiral form,
as represented in fig. 12. At one end, A, an eye is provided, by
which that extremity may be attached either to a fixed point or to
the side of the barrel to which the spring is intended to impart
motion. In the centre of the spiral an arbor, or axle, is intro-
duced, to which the inner extremity of the spring is attached.
Supposing the extremity A to be attached to a fixed point, let
the arbor B (fig. 13), be turned in the direction indicated by
the arrow. The spring will then be coiled closer and closer round
the arbor A B, while its exterior coils will be separated one from
another by wider and wider spaces.

Fig. 13.

After the spring has been thus coiled up by turning the arbor,
it will have a tendency to uncoil itself and recover its former
state, and if the arbor B be abandoned to its action and be free to
revolve, it will receive from the reaction of the spring a motion of
revolution contrary in direction to that which was given to the
arbor in coiling up the spring, and such motion would be imparted
to a wheel fixed upon the axle, and might from it be transmitted
to the hands in the same manner as if the arbor-wheel received
its motion from the power of a weight.

31. But between such a moving force and that of a weight
there is an obvious difference. The tension of the cord by which
the weight is suspended, and consequently its effect in giving
revolution to the barrel upon which the cord is coiled, is always

23

COMMON THINGS CLOCKS AND WATCHES.

the same until the clock altogether goes down. The moving
force of the spring, on the contrary, is subject to a continual
decrease of intensity. At first, when completely coiled up, its
intensity is greatest, but as it turns the arbor B it becomes
gfadually relaxed, and its intensity is continually less and less.
It exerts, therefore, a continually decreasing power upon the
wheel fixed upon the arbor, and therefore upon the hands to
which the motion is transmitted.

32. As a varying power would be incompatible with that
uniformity and regularity which are the most essential and
characteristic conditions of all forms of clockwork, such a spring
would be quite unsuitable if some expedient were not found by
which its variation could be equalised.

This has been accordingly accomplished, by a very beautiful me-
chanical contrivance, consisting of the combination of a flexible chain
and a conical barrel arranged to receive its coils, called a FUSEE.

Fig. 14.

This arrangement is represented in fig. 14. The mainspring is
attached by its inner extremity to the fixed arbor A, and by its
outside end at E, to a barrel B, which is capable of being turned
round the fixed axis A. A jointed chain is attached by one
extremity to the barrel at E, and being coiled several times round
it, is extended in the direction c, to the lowest groove of the
fusee E, to which its other end, e, is attached. This fusee is a
conical-shaped barrel, upon which a spiral groove is formed,
continued from the base to the summit to receive the chain. The
base is a toothed wheel, by which the motion imparted by the
mainspring and chain to the fusee is transmitted to the hands
through the wheelwork. The fusee is fixed upon an arbor, D G,
the lower end of which, projecting outside the case containing the
works, is formed square to receive a key made to fit it by which
the clock or watch is wound up.
24

FUSEE.

The action of the spring transmitted by the barrel to the chain,
and by the chain to the fusee, has a tendency to impart to the
fusee a motion of rotation in the direction of the arrows. The
fusee is connected with the wheel, w, by means of a ratchet-wheel
and catch similar to that described in the case in which the
moving power is a weight, by means of which the fusee F
imparts rotation to the wheel when it turns in the direction of the
arrows, but does not move it when turned in the opposite
direction.

These arrangements being understood, let us suppose the key
applied upon the square-end G of the arbor D G of the fusee,
and let it be turned round in the direction contrary to that
indicated by the arrows. The fusee will then be turned, but will
,not carry the wheel w with it ; the chain c will give to the barrel
B a motion of revolution contrary to the direction of the arrows,
the chain will be gradually uncoiled from the barrel B, and will
be coiled upon the spiral groove of the fusee, winding itself from
groove to groove, ascending on the spiral until the entire length
of the chain has been uncoiled from the barrel B, and coiled upon
,the fusee F, as represented in fig. 15.

During this process, the external extremity of the mainspring,
attached to the barrel at E, is carried round with the barrel, while
the internal extremity is fixed to the arbor A, which does not
turn with the barrel. By this means the spring is more and more
closely coiled round the arbor A, until the entire chain has been
discharged from the barrel to the fusee, when the spring will be
coiled into the form represented in fig. 15, and in this state the
intensity of its force of recoil, and the consequent tension of the
chain c, extended from the barrel B to the fusee E, is greatest.

Fig. 15.

The clock being thus wound up and left to the action of the
spring, the tension of the chain c, directed from the fusee to the

25

COMMON THINGS — CLOCKS AND WATCHES.

spiral, will make the fusee revolve in the direction indicated by
the arrows. This tension at the commencement acts upon the-
highest and smallest groove of the fusee. As the chain is
gradually discharged from the fusee to the barrel, the tension is
gradually decreased by reason of the relaxation of the spring, and
at the same time the cSain acts upon a larger and larger groove of
the fusee. In this way the tension of the chain is continually
decreased, and the radius of the groove on which it acts is con-
tinually increased, until the entire action has passed from the
fusee to the barrel, and the clock goes down.

Now the power of the chain to impart a motion of revolution
to the fusee depends on two conditions ; first the force of its
tension, and secondly the leverage by which this tension acts
upon the fusee. This leverage is in fact the semi-diameter of the
groove, upon which the chain is coiled at the point where it
passes from the fusee to the barrel. Without much mechanical
knowledge it will be easy to perceive that it requires less force to
turn a wheel or barrel if the force be applied at a great distance
from the axle than if it be applied at a small distance from it.
Upon this principle generalised, it follows that the power of the
tension of the chain to impart revolution to the fusee is augmented
in exactly the same proportion as the magnitude of the groove on
which it acts is increased.

The form given to the fusee is such that as the chain is gra-
dually discharged from it, the diameter of the groove on which
it acts increases in exactly the same proportion as that in which
the tension of the chain decreases. It follows, therefore, that the
power of the chain upon the fusee gains exactly as much by the
increase of its leverage as it loses by the decrease of its tension,
and consequently it remains invariable.

Complete compensation is therefore obtained by this beautiful
and simple expedient, and a variable force is thus made to produce
an invariable effect. It may be useful to state that this is only a
particular application of a mechanical principle of great generality.
In all cases whatever, the varying energy of a moving power may
be equalised by interposing between it and the object to be moved
some mechanism, by which the leverage, whether simple or com-
plex, through which its force is transmitted, shall vary in the
exact inverse proportion of the variation of the power, — increasing
as the intensity of the power is decreased, and decreasing as the
intensity of the power is increased.

33. Whatever be the moving power,- whether it be a weight or

mainspring, it would, if not controlled and regulated, impart to the

hands a motion more or less accelerated, and therefore unsuitable

to the measurement of time, which requires a motion rigorously

26

BALANCE-WHEEL.

uniform. It is on that account that the moving power must be
controlled and governed by some expedient, by which it shall be
rendered uniform.

How the combination of a pendulum and escapement-wheel
accomplishes this has been already explained. But this expedient
requires that the timepiece to which it is applied shall be sta-
tionary ; the slightest disturbance of its position would derange
the mutual action of the pendulum and the escapement- wheel, and
would either stop the movement, or permanently derange the
mechanism. It is evident that a pendulum is not only inap-
plicable to all forms of pocket timepiece, but that it cannot even
be used for marine purposes, the disturbances incidental to which
would be quite incompatible with the regularity of its action.

The expedient which has been substituted for it with complete
success in all such cases is the balance-wheel.

This is a wheel, like a small fly-wheel, having a heavy rim con-
nected with the centre by three or more light arms, as shown at
ABC, in fig. 16. Under, and parallel to it, is placed a spring
resembling in form the mainspring, but much finer and lighter,
and having much less force.

This spring is formed of ex- Fis- 16-

tremely fine and highly tem-
pered steel wire, so fine that
it is sometimes called a hair-
spring. One extremity of this
spring is attached to the
axis of the balance wheel, and
the other to any convenient
fixed point in the watch. The spring is so constructed that when
at rest it has a certain spiral form, to which it has a tendency to
return when drawn from it on the one side or the other. If we
suppose it, therefore, to be drawn aside from this position of rest
and disengaged, it will return to it, but on arriving at it, having
acquired by the elasticity a certain velocity, it will swing past it
to the other side, to a distance nearly as far from its position
of rest as that to which it had been originally drawn on
the other side. It will then swing back, and will thus oscillate
on the one side and the other of the position of rest, in
the same manner exactly as that in which a pendulum swings
on the one side or the other of the vertical line which is its
position of rest.

34. The balance-wheel thus connected with a spiral spring,
like the pendulum, is isochronous, that is, it performs all vibra-
tions— long and short — in the same time. It will be recollected
that this property of the pendulum depends on the fact that the

27

COMMON THINGS — CLOCKS AND WATCHES.

wider is the range of its vibrations the more intense is the force
with which it descends to the vertical direction, and consequently
wide vibrations are performed in as short a time as more contracted
ones. Now the vibrations of the balance-wheel are subject to like
conditions. The witer the range of its vibrations, the more in-
tense is the force with which the recoil of this spring carries it back
to its position of rest, and consequently it swings through these
wide vibrations in the same time as through more contracted ones,
in which the force of the spring is proportionally less intense.

The oscillation of the balance-wheel regulates the motion of
watchwork in the same manner by means of an escapement- wheel,
as that in which the pendulum regulates the motion of clock-
work. The pallets and the escapement- wheel are, however, very
variously formed in different watches.

35. Having thus explained generally the powers by which
clocks and watches are moved and regulated, it now remains to
show how the necessary motions are conveyed to the hands by
suitable combinations of wheels and pinions.

In fig. 17 (p. 1), are represented the works of a common watch,
moved by a mainspring A, and regulated by a balance-wheel H ;
the wheels and pinions, however, being changed in their relative
positions, and the fusee being omitted, so as to show more visibly
the connections and mutual dependency of the many parts. The
external extremity of the mainspring is attached to the base, o,
of a column of the frame. Its internal extremity is attached to
the lower end of an axle, of which the square end, T, at the top
enters a hole in the dial-plate into which the key is inserted when
the watch is to be wound up. The ratchet-wheel B is fixed
upon this axis so as to turn with it, but the other wheel c under
the ratchet-wheel is not fixed upon it, the axis being free to turn
in the hole in the centre of c, through which it passes. A catch
n o is attached by a pin on which it plays to the face of the
wheel c, and its point o is pressed against the teeth of the
ratchet-wheel B, by a spring provided for that purpose. When
the key is applied upon the end T, and turned in the direc-
tion in which the hands move, the ratchet-wheel is turned
with it, and the point o of the catch — pressed constantly
against the teeth while it turns — falls from tooth to tooth with
an audible click, and thus produces the peculiar sound, with which
every ear is familiar, while the watch is being wound up. During
this process the wheel c does not turn with the axle, which only
passes through the hole in its centre without being fixed upon it,
but the mainspring, A, being attached to the axle is coiled more
and more closely round it, and re-acts against the fixed point o
with greater and greater force.
28

MECHANISM OF A WATCH.

If the fusee, which is omitted in this figure, were introduced,
it would occupy the place of the spring, and would be turned by
the axle imparting a like revolution to the axis of the spring by
means of the chain.

When the watch is wound up, the re -action of the spring,
rendered uniform in its force by the fusee, imparts a motion of
revolution to the ratchet-wheel B, in the direction of the arrow.
By this motion the tooth of the ratchet-wheel in which the point
o of the catch is engaged, presses against the catch so as to carry
it round with it in the direction of the arrow ; but the catch being
attached to the face of the wheel c, at n, this wheel is carried
round also in the same direction, and with a common motion.

The teeth of the wheel c act in those of the pinion d, which
is fixed upon the axle d D. Upon the same axle is fixed the
wheel D, so that the wheel D and the pinion d receive a com-
mon motion of revolution from the wheel c.

The wheel D, in precisely the same manner, imparts a common
motion of revolution to the pinion e, and the wheel E ; and the
wheel E imparts a common motion of revolution to the pinion f
and the wheel F.

This last wheel F is of the form called a crown-wheel, and
acts upon the pinion </, imparting to it, and to the escapement
wheel G, a common motion of revolution. This escapement-
wheel is acted upon and controlled by the pallets or other con-
trivances attached to the axis of the balance-wheel H, so as to
regulate its motion by the oscillations of that wheel in the same
manner as the escapement- wheel of a clock is regulated by the
anchor of the pendulum.

It may be asked why so long a series of wheels and pinions are
interposed between the mainspring and the balance-wheel? and
why the first pinion d may not act directly upon the escapement-
wheel ? The object attained by the multiplication of the wheels
and pinions is to cause the mainspring, by acting through a small
space, to produce a considerable number of revolutions of the
escapement- wheel, for without that the spring would be speedily
relaxed, and the watch would require more frequent winding up.
Thus by the arrangement here shown, while the mainspring
causes the wheel c to revolve once, it causes the pinion d and
the wheel D to revolve as many times as the number of teeth
in c is greater than the number in d. Thus if there are ten
times as many teeth in c as in d, one revolution of c will produce
ten of d and i>. In like manner if D have ten times as many
teeth as e, one revolution of D will produce ten of e and E, and
so on. In this way it is evident that one revolution of the first
wheel c, which is on the axis of the fusee, can be made by the

29

COMMON THINGS CLOCKS AND WATCHES.

mutual adaptation of the intermediate wheels and pinions, to
impart as many revolutions as may be desired to the escapement-
wheel G.

The wheels which govern the motion of the hands are those
which appear in the figure between the watch face and the frame
XT. The relative power of the mainspring aud balance-wheel
must be so regulated that the wheel D shall make one revolution
in an hour. The axis upon which this wheel is fixed passing
through the centre of the dial, carries the minute hand, which
therefore revolves with it, making one complete revolution on the
dial in an hour.

Upon this axle of the minute hand is fixed a pinion k, which
drives the wheel /, on the axle of which is fixed the pinion m,
which drives a wheel p, through the centre of which the axle
of the minute hand passes without being fixed upon it. Upon the
axle of the minute hand a small tube is placed, within which
it can turn. Upon this tube the hour hand, as well as the
wheel p, is fixed. The pinion k, therefore, fixed upon the axis of
the minute hand, imparts motion to the hour hand by the inter-
vention of the wheel /, the pinion »i, and the wheel p. Since the
hour hand must make one revolution while the minute hand makes
twelve, it is necessary that the relative numbers of the teeth of
these intermediate wheels shall be such as to produce that
relation between the motions of the hands. An unlimited variety
of combinations would accomplish this, one of the most usual
being the following : —

Pinion it 8 teeth.

Wheel I 24 „

Pinion m . . . . 8 ,,
Wheels 32 „

By this arrangement^ will make eight revolutions, while m and
7 make thirty- two ; or, what is the same, p will make one revo-
lution, while m and I make four. In like manner, / will make
eight revolutions, while k, and therefore the minute hand, makes
twenty-four ; or, what is the same, I will make four revolutions,
while k and the minute hand make twelve. It follows, therefore,
that />, and therefore the hour hand, makes one revolution, while
k, and therefore the minute hand, makes twelve, which is the
necessary proportion.

In this case there is no seconds hand : but, if there were, its
motion would be regulated in like manner by additional wheels
and pinions.

36. The manner in which the moving power of a weight, and
the regulating power of a pendulum are applied in a clock to
SO

MOVEMENT OF HANDS.

produce the motion of the hands, does not differ in any important
respect from the arrangement explained above. Nevertheless, it
may be satisfactory to show the details of the mechanism. The
train of wheels connecting the weight with the anchor of the pen-
dulum is shown in fig. 18 (p. 17).

A side view of the mechanism, showing the wheels which more
immediately govern the motion of the hands, and also the pen-
dulum, with its appendages, is given in fig. 19 (p. 33).

The weight w acts by a cord on a barrel, as already explained.
This barrel and the ratchet-wheel, with its catch, are mounted
upon the axis of the great wheel c, and are behind it, as repre-
sented in fig. 18, their form and position being shown by the
white lines. The catch is attached to the wheel c by the screw n,
and its point o acts on the teeth of the ratchet-wheel, which is
attached to the barrel on which the rope is coiled. The spring
which presses the catch against the teeth of the ratchet is also
shown. When the clock is wound up by the key applied to the
square end T (fig. 19) of the axis of the barrel, the barrel is turned
in the direction opposite to that indicated by the arrows, and the
catch falls from tooth to tooth of the ratchet-wheel, making the
clicking noise which attends the process of winding up. When
the clock has been wound up, the weight acting on the barrel
presses the tooth of the ratchet-wheel against the catch, and
thereby carries round with it the wheel c. This wheel transmits
the motion to the escapement wheel G, fig. 17, through the series
of wheels and pinions, d, D, e, E, /, F, and g, in the same
manner exactly as has been already described (35) ; and the
pendulum, by means of the anchor NN, regulates the motion in
the manner described in 19.

The wheels which more immediately govern and regulate the
motion of the hands are those which appear in fig. 19 in front of
the plate XY.

The pendulum consists of a heavy disc of metal, seen edgeways
at v in fig. 19, attached to the end of a metal rod, RK, represented
broken, to bring it within the limits of the figure. This rod is
suspended by various means, but often, as in the figure, by two
elastic ribbons of steel, ss, which permit its swing right and left.
It passes between the prongs of a fork tr, by which a rod rr is
terminated, so that this rod swings right and left with the pen-
dulum. Upon the axis of this rod, and over the escapement
wheel G, is fixed the anchor N of the escapement.

37. Whether the movement be regulated by a pendulum or a
balance wheel, it is necessary to provide some means of adjustment
by which the rate of vibration may be increased or diminished
at pleasure within certain limits, for although in its original

31

COMMON THINGS — CLOCKS AND WATCHES.

construction the regulator may be made so as to oscillate nearly
at the required rate, it cannot be made to do so exactly. Besides,
even though it should vibrate exactly at the required rate, it will
be subject, from time to time, to lose that degree of precision, and
to vibrate too fast or too slowly from the operation of various
disturbing causes.

It has been already shown, that the rate of vibration of the
pendulum is rendered more or less rapid by transferring the centre
of gravity nearer to, or farther from, the point of suspension.
Upon this principle, therefore, the adjustment of the rate of
vibration depends. The heavy disc v, fig. 19, is made to slide
upon the rod RE, and can be moved upon it, upwards or down-
wards, by a fine screw attached to it, which works in a thread cut
in the rod. In this manner the centre of gravity of the disc v
may be transferred nearer to the suspension ss, so as to shorten
the time of its vibrations, or removed farther from ss, so as
to lengthen the time. If the clock is found to lose or go too
slowly, it is screwed up, and if it gain or go too fast, it is screwed
down.

In chimney and table time-pieces, the pendulum is regulated in
a different manner. It is usually suspended upon a loop of silken
thread, which can be drawn up or let down through a certain
limited space, by means of a rod, upon which one end of the
thread which forms the loop is coiled. This rod, passing through
the dial-plate, has a square end, upon which a key can be applied,
by turning which in the one direction or the other, the loop is
drawn up or let down.

38

Fig. 19.

COMMON THINGS.

CLOCKS AND WATCHES.

CHAPTER III.

Method of regulating a balance-wheel. — 39. Recoil
escapement. —40. Cylindrical escapement. — 41 .
Duplex.— 42. Lever.— 43. Detached.— 44. Main-
taining power of a clock moved by a weight.— 45. Of a watch
moved by a mainspring.— 46. Weight or mainspring and pendulum
LAUDNER'S MUSEUM OP SCIENCE. D 33

No. 74.

COMMON THINGS — CLOCKS AND WATCHES.

and balance-wheel variously combined. — 47. Watches and chrono-
meters.— 48. Marine chronometers. — 49. Stationary chronometers. —
50. Striking apparatus.

38. THE rate of oscillation of the balance-wheel cannot in the
same manner be so easily regulated by modifying its form ; but,
on the other hand, while the force which moves the pendulum,
being that of gravity, is beyond our control, that which moves
the balance-wheel being the force of the spiral spring, is at our
absolute disposition. It is accordingly by modifying this spring
that we are enabled to regulate the time of oscillation of this
regulator.

One of the most common expedients by which this is accom-
plished is represented in fig. 20.

Near the fixed point G, at the external extremity of the spiral,
is placed a small bar E, near the end, F, of which is a notch, or
o hole, through which the

wire of the spiral passes.
This arrests the action of
the spiral, so that the
only part of it which
oscillates is that which is
included between F and
its internal extremity.
In a word, the point F is
the virtual external ex-
tremity of the spiral. Now
this point F can be moved
in the one direction or
the other, so as to increase
or diminish the virtual

length of the spiral at pleasure, by means of the toothed arc AB
and the pinion c, which latter is turned by the index D. If
the index D be turned to the left, the bar E, and the point F,
is moved towards G, and the length of the spiral is increased. If
it be turned to the right, the point F is moved from G, and the
length of the spiral is diminished.

In this manner the rate of vibration of the balance-wheel may
be adjusted by varying at will the vertical length of the spiral-
spring.

39. The precision of the movement of all forms of timepieces
depends in a great degree on the mechanism of the escapement, and
accordingly much mechanical skill and ingenuity have been
directed to its improvement, and several varieties of form have
been adopted and applied.

The recoil escapement, represented in fig. 17, consists of two
34

CYLINDRICAL ESCAPEMENT.

pallets, which project from the axis of the balance-wheel at right
angles with each other, one of which acts at the top, and the
other at the bottom of the escapement- wheel G, the axis of which
is horizontal and the wheel vertical. These pallets, as the
balance-wheel oscillates, engage alternately in the teeth of the
escapement-wheel exactly in the same manner as do the pallets of
the anchor of the escapement attached to the pendulum already
described. This form of escapement was long the only one used,
and is still continued in the more ordinary sorts of watches.

It has, however, been superseded, in watches and chronometers
where greater precision is required, by others of more improved
construction.

40; In pocket watches, where great flatness is required, the
cylindrical escapement is used, in which the axis of the balance-
wheel, instead of having pallets attached to it, is formed into a
semicylinder, having a sort of notch in it, as represented on an
enlarged scale in fig. 21. The semicylinder a 6, is cut away at c,
through about half its height. The axis A B, fig. 22, of the
escapement- wheel is vertical, and the teeth raised at right angles

Fig 21.

Fig. 22.

to its plane, and therefore parallel to its axis, have the peculiar
form represented in the figure. As the balance-wheel oscillates
on the one side and the other, the semicylinder upon its axis

p 2 35

COMMON THINGS — CLOCKS AND WATCHES.

interposes itself alternately "between the teeth of the escapement-
wheel, stopping them and letting them escape in the usual way.
The manner in which the action takes place will be more clearly
understood by the figures 23 and 24, in which a view in plan
upon an enlarged scale is given of the position of the semicylinder

Fig 23

and the teeth of the escapement-wheel after each successive
oscillation.

In fig. 23, the balance-wheel swinging from right to left,
throws the convex side A D of the semicylinder before the tooth c
of the escapement-wheel, and thus for the moment arrests it,
while the side A E of the. semicylinder has turned out of the way
of the preceding tooth and has let it pass. The balance -wheel

Fig. 24.

then swings from left to right, and the convex side A D of the
semicylinder slides against the point of the tooth c. When the
edge D of the semicylinder passes the point of the tooth, the latter
in slipping over it gives to it a slight impulse, which restores to
36

DUPLEX ESCAPEMENT.

the balance-wheel the small quantity of force which it lost by the
previous reaction of the tooth upon its convex surface.

The side A E of the semicylinder is now thrown before the
tooth c, the point of which having advanced through a space
equal to the diameter of the semicylinder, is thrown against the
concave surface of A E, as shown in fig. 24.

The balance-wheel now swinging again from right to left, the
point of the tooth c slides upon the concave surface of the semi-
cylinder A E, until the edge E comes to it. The tooth then slips
over the inclined face of E, and in doing so gives the semicylinder
and consequently the balance-wheel another slight impulse,
restoring to it the force of which it deprived it while previously
sliding upon its concave -side.

The explanation here given of the action of this form of escapement
is well calculated to render the conditions which all escapements
should fulfil intelligible. These arrangements are primarily
directed to the regulation of the movement of the wheel- work, so
as to secure its uniformity. This will obviously be accomplished
provided that the escapement, whatever be its form, lets a tooth
of the wheel pass for each oscillation of the balance-wheel. But
owing to the friction of the axis of the balance-wheel, and of the
pallets on the teeth of the escapement- wheel, and the resistance
of the air, the range of its oscillations would be gradually
diminished, so that at last it would not be sufficient to allow the
successive passage of the teeth of the escapement- wheel, and the
watch would stop unless some adequate means are provided by
which the balance-wheel shall receive from the mainspring
through the escapement-wheel as much force as it thus loses,
All escapements accomplish this by the peculiar forms given to
the edges of the pallets and the teeth of the escapement- wheel.
In the present case, the object is attained by making the edge D
round and the edge E inclined, and by giving to the teeth the
form shown in the figure.

This form of escapement supplies a sufficiently good regulating
power for the best sorts of pocket watches, and is attended with
the advantages of allowing the works to be compressed within a
very small thickness. It is the form most commonly used in the
French and Swiss watches.

41. The form of escapement used in the best English made
watches consists of an escapement-wheel, which partakes at once
of the double characters of a spur and crown-wheel, and is hence
called the duplex escapement.

The spur teeth, A, B, c, &c. (fig. 25), are similar in their form
and arrangement to those of the cylindrical escapement described
above. The crown teeth, a, b, c, &c., project from the face of

37

COMMON THINGS — CLOCKS AND WATCHES.

the wheel, and have a position intermediate between the spur
teeth. Upon the axle of the balance-wheel just above the plane
of the escapement- wheel is fixed a claw pallet called the impulse
Fig 25. pallet, which by

the combination
of the oscillations
of the balance and
the progressive
motion of the es-
capement - wheel
falls successively
between the

crown -teeth of the
latter, receiving
from their reac-
tion as they escape
from it, the restoring action which maintains the range of the
oscillations of the balance-wheel.

Under the pallet and in the plane of the spur teeth is placed a
small roller usually formed of ruby or other hard stone, having a
notch on one side of it, into which the spur teeth successively fall.
After any crown tooth, a for example passes the pallet, the corre-
sponding spur tooth A falls into the notch of the roller, and this
alternate action continues so long as the watch goes. It will be
perceived therefore that the pallet and roller in the duplex
escapement play the same part as the two edges of the semicylinder
in the cylindrical escapement, and as the two pallets in the
common recoil escapement (fig. 17).

The chief advantage claimed for this system is that there is but

one pallet, and that the action
does not require as perfect
execution of the teeth of the
escapement - wheel as other
arrangements.

42. The lever escapement
is much used for English
pocket watches. A lever A B
(fig. 26), with a notch at one
end, is attached to the
anchor c. A pin at a, on a
disc D, on the verge or arbor
of the balance, enters this
notch at each vibration, and first moves the dead part of the
pallet off" the tooth of the scape-wheel E, and then receives an
impulse, which restores the force it has lost, leaving another tooth
33

LEVER AND DETACHED ESCAPEMENTS.

engaged in the opposite pallet. As the lever is detached from the
balance, except for an instant at the middle of each vibration,
the amount of friction is very small. Another advantage of this
movement is, that it is but little liable to derangement, and
when it is injured, is easily and cheaply repaired, while the
duplex and cylindrical escapements are expensive to make, and
can only be mended by such skilful workmen as are not often
found, except in the metropolis or large towns.

43. In the class of portable timepieces used for the purposes
of navigation, where the greatest attainable regularity of motion
is required, an arrangement is adopted called the detached
escapement. This system is represented in fig. 27.

Upon the arbor of the balance-wheel is attached a disc, in which
there is a notch i. A smaller disc, G, is also attached to it, from
which a small pin projects. By the oscillations of the balance-
wheel the notch i and the pin oscillate alternately right and left.

A fine flexible spring, A, attached to a fixed block, B, carries upon
it a projecting piece, c. To the block D is attached another fine
spring E, which extends to the edge of the small disc G. The
projecting piece c, is so placed that when the spring A is not
raised, it encounters a tooth of the scapewheel, but when slightly
raised it allows the tooth to pass. The spring E rests in a small
fork behind the extremity of A, and presented downwards.

Now, let us suppose the balance-wheel to swing from left to
right. The pin, projecting from the small disc G, coming against
the end of the spring E, raises it ; and this spring acting in the
fork behind it raises the spring A, and therefore lifts the piece c,
and liberates the tooth which that piece previously obstructed.
The scape-wheel therefore advances, but before the next tooth
comes to the place occupied by the former one, the balance swings

89

COMMON THINGS — CLOCKS AND WATCHES.

back from right to left. The spring E no longer supported by
the fork at the end of A, readily lets the pin pass, and the piece c
returning to its former position, comes in the way of the suc-
ceeding tooth and stops it.

At the moment that tffe balance is about to commence its swing
from left to right, and when the piece c is about to liberate the
tooth which rests against it, another tooth behind it rests against
the side of the notch i in the disc G, and when the escapement-
wheel is liberated, and the swing of the balance from left to right
is commencing, this tooth, pressing on the side of the notch z,
gives it and the balance-wheel an impulse which is sufficient to
restore to it all the force which it lost in the previous oscillation.
Except at this moment the balance-wheel in this form of escape-
ment is entirely free from all action of the mainspring.

44. While a clock or watch is being wound up, the weight or
mainspring no longer presses upon the catch nor upon the ratchet-
wheel, through which the motion is imparted to the wheel work.
The motion of the hands is therefore suspended during the time
occupied in winding up, consequently if the watch or clock keep
regular time while it goes, it must lose just so much time as may
be employed in the process of winding it up. Although this, in
common clocks and watches, does not produce any sensible effect,
the errors incidental to their rates of going generally exceeding it,
yet in clocks used in observatories and in chronometers used for the
purposes of navigation, where the greatest degree of regularity is
required, provisions are made by which the motion of the clock or
watch is continued notwithstanding the process of winding up.

Such expedients are called the MAINTAINING POWEB.

One of the most simple arrangements by which this is accom-
plished in clocks moved by a weight is shown in fig. 28. The
weight P, which is the moving power, is connected with another
much smaller weight p, by means of an endless cord which
passes over the grooves of a series of pullies, A, B, c, and D, of
which A and B are moveable, and c and D fixed. The force
with which p descends is the excess of its weight above that of p.

The pulley c, being prevented from revolving by the catch E
during the descent of the weight P, and the cord being prevented
from sliding upon its groove by the effects of its friction and
adhesion, the parts b a and c d, which descend from the pulley
C to the pulleys A and B, may be regarded as being virtually
attached to fixed points at b and c, so that they cannot descend.
This being the case, the weight P, descending by its prepon-
derance over p, and consequently the weight p being drawn up,
the part of the cord c d must pass over the pulley B, the part
e f over the pulley D, and the part g h over the pulley A. In this
40

MAINTAINING POWER OF A CLOCK.

way the parts b a and g h will be gradually lengthened as the
weight P descends at the expense of the parts c d and / e, which
will be shortened to an equal extent, so Fig. 23.

that the weight p will be raised through
the same space as that through which the
weight P is lowered. During this process
the wheel D is kept in constant revolution,
and the first wheel of the train of clock-
work being fixed on its axle, a motion is
imparted by it through that train to the
hands.

"When it is desired to wind up the clock,
the hand is applied to the cord c d, which
is drawn downwards, so that the fixed
pulley revolves, the catch E dropping from
tooth to tooth until the weight P has been
raised to the highest, and the weight p has
fallen to the lowest point. The parts g h
and f e of the cord not being at all affected
by this, the pulley D continues to turn as
before by the effect of the preponderance
of p, which acts as powerfully while it
ascends as it did when it descended.

It appears, therefore, that, by this ar-
rangement, the motion of the works and of
the hands is not suspended during the pro-
cess of winding up.

45. If the works of a watch be impelled
by the force of a mainspring without a fusee, in the manner
represented in fig. 17, it is evident that the movement must be
suspended during the process of winding up, because the ratchet-
wheel B, by which the force of the spring is transmitted to the
works, is then relieved from the action of the catch n o. This
defect may, however, in such case be removed by a very simple
expedient. Instead of connecting the external extremity of the
mainspring with a fixed point, let it be attached to the inside of a
barrel surrounding it, and let the wheel c be attached to this
barrel. In that case, when the axle of the ratchet-wheel is
turned in winding up, and the ratchet-wheel, therefore, relieved
from the action of the catch, the wheel c will be acted upon by
the barrel, which will itself be impelled by the reaction of the
external extremity of the spring which is attached to it, the
winding up being effected only by the internal extremity.

This is the arrangement generally adopted in chimney and table
time-pieces, as constructed in France and Switzerland, and also in

41

COMMON THINGS — CLOCKS AND WATCHES.

flat watches, in all of which the adoption of the cylindrical escape-
ment (fig. 22) enables the constructor to dispense with the fusee.

It will, of course, he understood, that in such arrangements,
while the wheel c is attached to the barrel, and by it to the
external extremity of ^he mainspring, the ratchet-wheel B is
attached to the axle T B (fig. 17), and by it to the internal
extremity of the mainspring.

When a fusee is used, the ratchet-wheel being fixed upon its
axis, and not on that of the barrel containing the mainspring,
this method of obtaining a maintaining power is not applicable.
In such cases, the object is attained by two ratchet-wheels upon
the axle of the fusee, having their teeth and catches turned in
opposite directions, one of them being impelled by a provisional
spring, which only comes into play when the action of the main-
spring is suspended during the process of winding up.

The fusee, with its appendages, as commonly constructed,
without a maintaining power, is drawn in fig. 29, the grooved
cone, with the ratchet-wheel attached to its base, being raised
Fi 29 from the cavity in the

toothed wheel c D, in which
it is deposited, to show the
arrangement more clearly,
and in the edge of which
the catch n is placed, so
that it shall fall into the
teeth of the ratchet-wheel.

When the watch is being
wound up, the chain passing
from the barrel to the
grooves of the fusee, the
teeth of the ratchet-wheel,
D A B, pass freely round the
cavity, the catch n falling
from tooth to tooth, and producing the clicking noise already
noticed. But when the watch is going, the tension of the chain
draws the fusee and the ratchet-wheel attached to it round in
the contrary direction, and, pressing the teeth of the ratchet-wheel
against the catch n, carries round the wheel c D, which gives
motion to all the other wheels, and through them to the hands.
Now, it will be evident, that when the watch is being wound up,
and the catch n relieved from the pressure of the teeth of the
ratchet-wheel, no motion will be imparted to c D, and consequently
the movement of the entire works will be suspended.

The modification by which a maintaining power is obtained
by the combination of two contrary ratchet-wheels, is shown in
42

MAINTAINING POWER OF A WATCH.

fig. 30, where c D is the first wheel of the train from which the
Avatch receives its motion. • The ratchet-wheel A is fixed upon
the base of the fusee, so as to
move with it. The catch,
m, which is pressed by a
spring into the teeth of this
ratchet-wheel, is attached to
the second ratchet-wheel B,
so that when A is carried
round by the chain acting
on the fusee, it must carry
the wheel B round with it
in the direction of the ar-
row/. The wheel B is con-
nected with the wheel c D by
a semicircular spring a b c,
which is attached to the wheel c D at c, and to the wheel B at a.
The catch, n, which falls into the teeth of the ratchet-wheel B,
is attached to a fixed point on the bed of the watch.

While the watch is going, the wheel B, driven by the fusee,
draws after it the spring a be, bending it round to a certain
extent, and this spring acting at c, on the wheel c D, draws it
round in the direction of the arrow/. Now, let us suppose that
the watch is being wound up. The ratchet-wheel A, being
turned by the key in the direction of the arrow r, the catch m
falls from tooth to tooth, and the force it before received from the
ratchet-wheel A is suspended. But the spring a b c has been
drawn from its form of equilibrium, to a certain small extent, in
drawing round after it the wheel c D, as already stated, and it has
still a tendency to draw that wheel after it, so as to recover its
form of equilibrium. In doing this, it will continue to act upon
the wheel c D, and to carry it round while the action of the fusee
upon it is suspended during the process of being wound up. The
spring a b c is so constructed as to act thus for an interval more
than is necessary to wind up the watch.

46. From what has been explained, it will be observed, that
timepieces in general are constructed with one or other of two
moving powers, a descending weight, or a mainspring, and with
one or other of two regulators, a pendulum or a balance-wheel.
These expedients are variously adopted and variously combined,
according to the position and circumstances in which the time-
piece is used, and t.he purpose to which it is appropriated.

A descending weight as a moving power, combined with a pen-
dulum as a regulator, supply the best chronometrical conditions.
But the weight can only be used where a sufficient vertical space
• 43

COMMON THINGS— CLOCKS AND WATCHES.

can be commanded for its ascent and descent, and neither it nor
the pendulum is applicable except to timepieces which rest in a
fixed and stable position.

In the case of timepieces whose position is fixed, but where
the vertical space for the play of the weight cannot be conveniently
obtained, the mainspring is applied as a moving power, combined
with the pendulum as a regulator. Chimney and table clocks
present examples of this arrangement. The height being limited,
it is necessary also in these cases to apply short pendulums. The
length of a pendulum which vibrates seconds being about 39
inches, such pendulums can only be used where considerable height
can be commanded.

It has been shown, that the lengths of pendulums are in the
proportions of the squares of the times of their vibration. It
follows, therefore, that the length of a pendulum which would
vibrate in half a second, will be one-fourth the length of one
which vibrates. in a second, and since the latter is 39 inches, the
former must be 9| inches. Such a pendulum can therefore be
conveniently enough applied to a chimney or a table clock high
enough to leave about ten. inches for its play.

The pendulum is so good a regulator, and the anchor-escape-
ment renders it so independent of the variation of the moving
power, that in timepieces where it is combined with a main-
spring a fusee is found to be unnecessary. In such cases, there-
fore, the axis of the first wheel is placed in the centre of the
mainspring, as represented in fig. 17.

47. The cylindrical escapement, shown in fig. 22, is nearly as
independent of the variation of the moving power as the pendulum,
and therefore in common watches, where this escapement is used,
the fusee is dispensed with.

In the class of timepieces called chronometers, used for the
purposes of navigation, and in general for all purposes where the
greatest attainable perfection is required in a portable timepiece,
all the expedients to insure regularity are united, and accordingly
the detached escapement is combined with fusee and mainspring.

Besides the expedients above mentioned, for insuring unifor-
mity of rate, provisions are made in the most perfect chronometers
to prevent the variations of rate which would arise from the
expansion and contraction of the metal composing the balance-
wheel by the variation of temperature. These expedients are very
various ; but in general they consist of contrivances by which the
expansion, of the rim of the wheel causes a part of it so to bend,
as to throw a heavier part nearer to the centre, to compensate for
the increased distance of another part produced by its general
enlargement.
-44

MARINE CHRONOMETER.

48. Marine chronometers are usually suspended in a box on
gimbals, like those which support the ship's compass. The
balance-wheel usually vibrates in half seconds, being a much
slower rate than that of common watches. They are of immense
utility in navigation, and especially in long voyages. See Tract
on " Latitudes and Longitudes," Museum, vol. i. p. 97.

49. In observatories where stationary timepieces can be used,
the clock moved by weights and regulated by a pendulum is
invariably adopted. The pendulum, in such cases, is always
so constructed that its rate of vibration shall not be affected by
variations of temperature. This is accomplished usually by con-
structing it of two different kinds of metal, which are differently
affected by heat, one being more expansible than the other. They
are so arranged that the expansion of one shall elevate the centre
of gravity, while that of the other lowers it, and the two effects
are made to compensate each other, so that, however the tempera-
ture may change, the rate of vibration will remain the same.

50. In clocks adapted for domestic and public use, it is found
desirable that they should give notice of the time, not only to the
eye, but to the ear ; and for that purpose a bell is attached to
them, which tolls at given intervals, the number of strokes being
equal to that of the units in the number expressing the hour.
This appendage is called the STUIKING TRAIN".

The striking train, though connected with that which moves
the hands, is quite independent of it, having its own moving and
regulating power, and its own system of wheels by which the
effect of the moving power is submitted to the regulator, and
transmitted to the tongue of the bell.

Unlike the train which moves the hands, the striking train is
not in continual motion. Its motion is always suspended, except
at the particular moment at which the clock strikes. The mecha-
nism partakes of the character of an alarum, being stopped by a
certain catch until the hands point to some certain hour, and then
being set free by the withdrawal of the catch. It remains free,
however, only so long as is necessary for the tongue or hammer to
make the necessary number of strokes upon the bell, after which the,
catch again engages itself in the striking mechanism, and stops it.

Some clocks only strike the hour. Others mark the half hours,
and others the quarters, by a single stroke.

The general principle of the striking mechanism will be rendered
intelligible by fig. 31, which represents it in the case of a common
clock moved by a weight.

The weight suspended from the cord E moves the train in the
same manner as in the case of the train which moves the hands.
The motion of the first wheel, c, is transmitted to the last wheel, I,

45

: COMMON THINGS — CLOCKS AND WATCHES.

which corresponds to the escapement-wheel by the intermediate
wheels and pinions, /, r, g, G, h, H, and t. The wheel r drives

Fig. 31.

the pinion k, upon the axle of which is fixed the regulator K.
This regulator is a fly, a side view of which, upon a larger
scale, is shown in fig. 32.

The pinion, which is made to revolve by the wheel w, gives
a motion of rotation to the fly A A' B'B, which consists of a thin
rectangular plate of metal, along the centre of which the pro-
longation M L of the axle of the pinion is attached. The flat
surfaces of the fly, revolving more or less rapidly, strike against
46

STRIKING APPARATUS.

the air, which resists them with a force which increases in the
proportion of the square of the velocity of the rotation. Thus,
if the velocity of rotation be in-
creased in a two-fold ratio, the ""
resistance to AA' B'B is increased
in a four- fold ratio ; if the rota-
tion be increased in a three-fold
ratio, the resistance is increased
in a nine-fold ratio, and so on.
It is evident, therefore, that by
this very rapid increase, the re-
sistance to the motion of the train
must soon become equal to the
descending force of the weight,
and then the motion will become
uniform ; for if it were to increase, the resistance would exceed
the force of the weight, and would slacken the rate of motion ;
and if it were to decrease, the resistance being less than the force
of the weight, the latter would accelerate the motion. In either
case the motion would immediately be rendered uniform.

Projecting from the face of the wheel H (fig. 31) there is a small
pin which rests upon the end m of a lever m n, which turns upon
the centre n. The lever m n when in this position stops the
motion of the striking train. Behind the same lever m n, and
projecting from it, there is another piece, which in the position
represented in the figure rests in a notch of the wheel o p, lying
behind the striking train, and indicated in the figure by dotted
lines. Around the edge of this wheel there is a series of similar
notches at unequal distances, determined in the manner which we
shall presently explain.

Upon the face of the wheel G, at equal distances one from
another surrounding it, a series of pins project, which, as the
wheel turns, successively encounter a lever 6, which plays^upon a
centre a. Upon the same centre a is fixed the handle a a' of the
hammer A by which the bell v is struck. A spring fixed upon
the same centre a causes the lever b to rest in the position repre-
sented in the figure, and to return to that position if raised
from it. The hammer handle a a' is made either elastic itself or
is provided with a like spring.

When the wheel G is made to revolve at a uniform rate by the
weight E, regulated by the fly K, the pins projecting from the face
of the wheel G encounter successively the lever &, and raising it,
throw back the handle a a' of the hammer which is in connection
with the lever b. After the pin has passed the lever b the latter
is brought back with a jerk by the action of the spring, and the

COMMON THINGS — CLOCKS AND WATCHES.

hammer A receiving the same jerk strikes upon the bell v and
instantly recoils from it ; and if the wheel o continues to revolve,
one pin after another upon it will encounter the lever 6, and the
hammer A will make a stroke upon the bell each time that a pin
passes the lever.

The wheel H is so constructed that it will make one revolution
in the interval between two successive strokes of the bell, or
what is the same, in the interval between the moments at which
two successive pins pass the lever b.

In the train which moves the hands, an expedient is provided
by which each time that the minute hand passes twelve upon the
dial, the lever m n is thrown back from the position which it has
in fig. 31, and the top m being withdrawn from under the pin
upon the wheel JET, that wheel and the entire striking train is
liberated and set in motion. At the same time the piece is taken
out of the notch in which it rested on the wheel o pt and that
wheel, in common with the other parts of the striking train, is put
in motion.

For every complete revolution that the wheel H makes, the
hammer A makes a stroke upon the bell, and the motion of H and
of the entire striking train will continue until the end m of the
lever m n again conies under the pin projecting from the face
of n. During the motion, the lever m n is kept back by the
edge of the wheel op acting against the piece projecting from the
lever m n. But when the wheel o p has turned so as to bring the
next notch to the projecting piece, it will be thrown into the notch,
and the end m of the lever m n coming under the pin projecting
from the wheel H, the motion of the train will be suspended.

Now, it will be evident from what has been stated, that when
the lever m n is thrown back by the works, it is kept back by the
edge of the wheel o p acting against the projecting piece, and so
long as it is thus kept back, the striking train continues to move
and the hammer continues to strike the bell. But the duration
of this motion will depend on the space between the notches on
the wheel o p, since it is while that space upon the edge passes
under the projecting piece on m n that the end m of the lever
m n is kept back so as to be out of the way of the pin projecting
from the wheel H. These spaces between the notches are there-
fore so proportioned, one to another, that the lever m n at each
hour is held back a sufficient time for the hammer to make upon
the bell the number of strokes denoting the hour and no more.

The arrangement for striking half-hours and quarters is based
upon similar principles.

48

I I

Fig. 37. — VIEW OF THE MANGE INSECT OF THE HORSE, MAGNIFIED 150 TIMES IN ITS
LINEAR AND THEREFORE 22500 TIMES IN ITS SUPERFICIAL DIMENSIONS.

MICROSCOPIC DRAWING & ENGRAVING.

CHAPTEE I.

1. Beautiful precision of the minute structure of natural objects. — 2.
Cornea of a fly's eye. — 3. Number of eyes of different insects. —
4. Astonishing precision of artificial objects. — 5. Demand for sucli
objects by Microscopists. — 6. Classes of such, artificial objects. — 7.
Microscopic scales. — 8. Method of engraving them. — 9. Measurement
of microscopic objects with them. — 10. Their minuteness. — 11. Scales

LARDNER'S MUSEUM OF SCIENCE. B 49

No. 67.

MICROSCOPIC DRAWING AND ENGRAVING.

of Mr. Froment. — 12. Rectangular scales. — 13. Micrometric threads.
— 14. Necessity for microscopic tests. — 15. Test-objects. — 16. Tele-
scopic tests ; double stars. — 17. Nebulae and stellar-clusters. — 18.
Effects of different telescopes upon them : telescopes of Herschel and
Lord Rosse. — 19. Remarkable nebulae described by Herschel. — 20.
Differently seen by Lord Rosse. — -21. Microscopic tests. — 22. Im-
proved powers of microscope. — 23. The Lepisrna-Saccharina. — 24.
The Podura, or Spring-tail.

1. No person can witness without the highest degree of admi-
ration the spectacle presented by certain parts of the structure of
the more minute members of the animal kingdom, when viewpd
with a powerful microscope. The absolute geometrical precision
and extreme beauty of design shown in such objects, are truly
remarkable. We will not say, that such perfection of workman-
ship discovered in these minute objects, which must have for ever
escaped the human eye without the intervention of scientific aid,
ought to excite surprise, because no result, however perfect, of
infinite power combined with infinite skill should raise that senti-
ment. Nevertheless, it must be admitted, as a matter of fact,
that the contemplation of such objects is generally attended with
a sense of wonder, approaching to awe, a striking proof how few
they are that have sufficiently familiarised their minds with the
ideas of omnipotence and omniscience.

2. Innumerable examples of the perfect precision of structure,
adaptation and design, combined with a minuteness, which not
only far surpasses the limits of the senses, but severely taxes the
imagination, are presented in the organisation of natural objects.
The membrane, which in the eyes of certain species of insects cor-
responds to the cornea of the human eye, presents an example of
this, A very exact notion of this membrane, as it exists in the
eye of the common house-fly, may be obtained by stretching a piece
of bobbin-net over the surface of a billiard-ball : the ball with its
reticulated hexagonal coating will then be a very precise model of
part of the eye of the insect, upon a prodigiously magnified
scale.

We have given in fig. 1 an engraving of this membrane, taken
from a microscopic drawing, magnified 100 times in its linear,
and therefore 10000 times in its superficial dimensions.

3. Each hexagon, as shown in the figure, is the cornea of a
separate eye, having behind it the proper optical apparatus to pro-
duce the sense of vision. But it is more particularly to the mi-
nuteness of these beautifully precise hexagonal eyes, that I desire
at present to direct attention. That minuteness will be most strik-
ingly manifested by stating the number of these eyes with which
different classes of insects are provided. According to the obser-
vations of various eminent naturalists, such as Swammerdam,

50

INSECTS' EYES.

Leuwenhoeck, Barter, Reaumur, Lyonnet, Paget, Miiller, Strauss,

Duges, Kirby, &c., the following are the number of eyes iu certain
species : —

Number of eyes. Number of eyes.

The Ant and the Zenos

The Sphinx . . 1300

The common Fly . . 4000

The Silkworm . . 6236

The Cockchaffer . 8820

50 I The Cosus Lipniperda

The Dragon Fly .
The Butterriy
The Mordella

]]300
12544
17355
25088

4. But if the perfection found in the most minute workmanship
of nature excite our admiration, how much more must we admire
and wonder at the approaches which have been made to a similar
degree of precision and perfection by the comparatively feeble and
imperfect agency of the human hand. "We propose in the present
article to call the attention of our readers to some striking exam-
ples of such skill and address, with which the general public is
not already familiar.

5. The improvements which have been made within the last
quarter of a century, in the construction of microscopes, has
created a demand for a class of drawings and engravings of a
degree of minuteness approaching to that of the objects to
which the researches of observers have been addressed. This

E 2 51

MICROSCOPIC DRAWING AND ENGRAVING.

demand of Science upon Art has been adequately and admirably
responded to.

6. Mechanism has been invented, by which minute tracings are
made by a diamond point on the surface of glass ; such tracings
being adapted to serve three distinct purposes : — 1st. As standard
measures of microscopic objects by superposition on them, just as
ordinary lengths and breadths are determined by the application
of the standard measure of yards, feet, and inches ; 2ndly, To
serve as tests of the degree of excellence attained in the con-
struction of microscopes, and as means of comparing the relative
excellence of different microscopes, by observing the degrees of
distinctness with which they enable the observer to see such
minute tracings ; and, 3rdly, to serve for the production of micro-
scopic engravings on its proper scale of any desired design.

This last process cannot be said to have been applied hitherto
to any useful purpose other than the exhibition of an artistic
tour deforce, being, so far as relates to its means of execution, by
far more difficult and ingenious than either of the former.

7. Microscopic objects are measured by divided scales of known
dimensions ; their lengths and breadths being ascertained by the
number of divisions of the scales on which they are placed, in-
cluded between their limits or within their contour. Such scales,
like larger measures, vary with the magnitude of the objects to
which they are to be applied, but, even when largest in their divi-
sions, are still very minute. They are generally traced upon small
oblong slips of glass, the divisions being marked by fine parallel
lines, every fifth division being a little longer than the intermediate
ones, and every tenth still longer, as is shown on a greatly mag-
nified scale in fig. 2.

Fig 2.

8. The slip of glass upon which the scale is engraved is usually
set in a brass framing, in which it is capable of sliding longitudi-
nally, being pressed forwards in one direction by a fine screw, and
in the other direction by the action of springs.

The diamond point by which the divisions are traced, is urged
upon the glass, with a regulated pressure, so as to make traces so
52

MIC110METRIC SCALES.

even and uniform that no irregularity in their edges is discover •

able by any microscopic power to which they are submitted. In

the process of tracing the divisions, the point is moved over the

glass, the latter being fixed, or the

glass moved under the point by means

of a very fine screw, called a micrometer

screw, the magnitude of the thread of

which is exactly known. The head

of this screw is a metallic disc, fig. 3 ;

the circumference of which is divided

into from 200 to 400 equal parts, or

even into a still greater number.

Let us suppose, then, the screw to be
so fine that there are 50 threads to an
inch, and the circumference of its head
is divided into 100 parts ; one revolu-
tion of the head will therefore move the
screw and the diamond point upon which it acts through the one-
fiftieth part of an inch. But if a fixed index be directed to the
circumference of the head, so that the motion of the head through
one division can be observed, such motion will move the diamond
point through the 1- 5000th of an inch.

The cutter, after tracing each division, is raised from the glass,
while the diamond point is pushed forward by the screw to the posi-
tion necessary to engrave the next division of the scale, and proper
mechanism limits the motion of the screw, so as to regulate the
relative lengths of the divisions of the scale in the manner already
explained.

9. A scale thus engraved, being viewed with a microscope whose
magnifying power is proportionate to its minuteness, the divisions
are rendered as distinctly visible as those of an ordinary rule are
to the naked eye, and if the object to be measured be laid upon the
glass its dimensions may be ascertained, as those of an object of
ordinary size would be by a common rule.

10. These scales vary in the magnitude of their divisions, ac-
cording to the magnitude of the objects which they are intended
to measure. On those which have the largest divisions, an inch
is divided into 500 parts ; scales, however, are furnished by the
opticians for microscopes in which an inch is divided into 2500 parts.

1 1 . However minute such scales may seem, they are by no means
the most minute that have been executed. Mr. Froment, whose
apparatus for the division of astronomical instruments is well
known, has supplied me with a scale in which a millimetre is di-
vided into 1000 equal parts. Each division of this scale is,
therefore, only the 1 -25000th part of an inch.

MICROSCOPIC DRAWING AND ENGRAVING.

12. Scales are sometimes engraved so as to indicate at once the
dimensions of an object in length and breadth, by lines dividing

Fig. 4.

the glass in directions at right angles one to the other, as shown
in fig. 4, upon a greatly magnified scale.

13. The dimensions of a minute object are sometimes ascer-
tained by a somewhat different
expedient.

Let two lines, a a' and b b',
fig. 5, intersecting at right
angles, be engraved upon a slip
of glass, which can be inserted
into the tube of a microscope, as
shown in figures 6 and 7, through
an opening in the side, which
can be closed when such measure-
ment is not required. These
engraved lines, when the micro-
scope is properly adjusted, will
be seen like two fine threads pro-
jected on the object, as shown in fig. 5.

Arrangements are made by which, while the object is'fixed,
54

USE OF TESTS.

the glass upon which the lines a a' and b b' are engraved, can be
moved by a fine micrometer screw until the line b b' shall pass

Fig. 7.

successively through the two extremities of the object, or the same
purpose will be served, if, while the glass remains at rest, the
stage which supports the object be similarly moved.

The number of threads of the screw to an inch being known, the
number of revolutions and parts of revolutions of the screw neces-
sary to make the line pass from one extremity to another, will
.give the length of the object, and a like process will determine
its breadth.

In the application of such scales to microscopic measurements,
various practical precautions and expedients are necessary, which
will be fully explained in our Tract on the Microscope.

14. Independently of being provided with means such as have
been described above, for ascertaining the dimensions of objects,
the advanced state of science renders it indispensable that the
observer should possess means of testing the power of his instru-
ment ; without such means, he can never be sure that the appear
ance of the object, as presented by his microscope, corresponds
with its real structure, or that important details of that structure
may not escape his observation. A more striking example of
this cannot be presented than one which was given by the late
Dr. Goring, who showed that a particle of the dust taken from
the wing of a certain species of butterfly, called the Morpho
Menelaus, exhibited the seven different appearances shown in
fig. 8 ; when viewed with the same microscope, the aperture of
the object-glass and, consequently, the brightness of the image
only being varied. It will be seen that details of structure are
rendered apparent in G, where the aperture is greatest, which are
very imperfectly shown in F, and not at all in those in which
the aperture was still more limited.

55

Fig. 8.

MICKOSCOl'lC DRAWING AND ENGRAVING.

If, therefore, the observer were only supplied with a micro-
scope, such as would have shown the object as exhibited at D,
he would evidently have formed a very
incorrect notion of its structure ; and it is
accordingly found, that every improve-
ment which has taken place has disclosed
to us a new order of natural facts.

In order, therefore, to put the observer
in a position to ascertain how far he can
rely upon the indications of his instrument,
it is necessary to supply him with some
objects of known structure, whose details
the instrument ought to make visible if
it have the power which it claims.

15. Such objects, which have proved to
be eminently useful in microscopic re-
searches, and highly conducive to the
progress of science, are called TEST-
OBJECTS.

16. In the case of the telescope applied
to astronomical researches, similar tests of
efficiency are found in countless numbers in
the heavens. Double, triple, and multiple
stars are the most obvious examples of
these. Such objects, as is well known,
appear when viewed with the Luked eye,
or even with ordinary telescopes, as single
stars; but when instruments of superior
power are directed to them they are
HESOLVED, as it is called, and seen as what
in fact they are, two or more minute stellar
points in such close proximity, that the
space between them is too small to affect
the eye in a sensible manner, unless when
magnified by artificial means.

17. Xebula3 supply another order of
telescopic test-objects. These appear, even
when viewed with telescopes of consider-
able power, as small patches of whitish,
cloudy light, of gi eater or less magnitude,
a character from which they have received
their name.

Such an object is represented, for example, in fig. 9.
When, however, a telescope of higher power is directed upon
the same oi jeet, it \\ill assume such an appearance as is shown

TELESCOPIC TESTS — NEBULA.

Fig,

in fig. 10, a faint and rather indistinct indication of minute stars

being perceptible ; but when a still higher power is brought to

bear upon it, the object will be

seen as what it really is, a

dense mass consisting of countless

numbers of separate stars, as

shown in fig. 11.

18. Different nebulae require
telescopes of different powers, and
many have never been yet re-
solved, even by the greatest
powers that scientific art has yet
produced. In proportion, how-
ever, as the telescopic power has
been increased, more and more
of these objects have been re-
solved. A remarkable illustration
of this state of progressive discovery is supplied in the case of a
well-known nebula, first observed and drawn by Sir John
Herschel, as seen in a twenty-foot reflector. Sir John

Fig. 10.

Fig. 11.

describes it as an object shaped like a dumb-bell, double-headed
shot, or hour-glass ; the elliptic outline being filled up by a more
feeble and nebulous light, as shown in fig. 12, copied from the
drawing of Sir John Herschel.

Such was the form and character assigned to this object until
Lord Rosse had constructed larger and more powerful instruments,
and when he directed upon it a twenty-seven foot reflector witli
three feet aperture, it assumed the appearance shown in fig. 13y
where a faint indication of stars can be seen ; subsequently r

57

MICROSCOPIC DKAWIKG AKD ENGRAV1KG.

liowever, when he examined the same object \\ith his great fifty-
three foot telescope, having six feet aperture, it assumed the
appearance shown in fig. 14.

19. Another very remarkable example of the change of appear-

ance produced in one of these wonderful objects, is presented in
the case of a nebula first observed by Sir Win. Herschel, and

Fig. 13.

described by nim as a bright round uebula, surrounded by a halo or
glory, and attended by a much _ smaller companion. Sir John

58

TELESCOPIC TESTS — NEBULA.

Herscliel observed the same object, and discovered in. it a very
remarkable feature, which the telescope of his father had failed
to disclose. This object, as drawn by Sir John Herschel, is shown
in fig. 15. The separation in what Sir William Herschel called a

Fig. 14.

halo or glory, and what Sir John Herschel calls a ring, was
the remarkable character which Sir John discovered. Sir John
conjectured, from the general appearance of the object,
that the central round nebula is a globular mass of stars, too
distant to admit of being resolved by his telescope, and that
what his father called a glory, is an annular mass of stars
surrounding the former and split in the direction of its plane,
so as to produce the appearance shown in the upper part of the
figure.

Sir John conjectured that such stellar masses might have some
analogy to the mass of stars which forms the milky way, and of
which our sun is an individual unit.

20. How completely these speculations, ingenious as they were,
were scattered to the winds, by bringing to bear on the same
object a higher telescopic power, will be apparent by inspecting

59

MICROSCOPIC DRAWING AND ENGRAVING.

fig. 16, in which the same object is shown as it was afterwards
seen with the great telescope of Lord Ilosse.

Lord Rosse thinks that the brilliant can volutions of the spiral
shown in his telescope,0 are identical with the split or divided part

of the ring ns seen by Sir John Herschel, and he lurtner observes,
that with each increase of optical power, the structure of this
object becomes more complicated and more unlike anything which
could be supposed to result from any form of dynamical law of
which we find a counter-part in our own system.

Before dismissing this very interesting subject of telescopic
tests, we shall indicate one other, scarcely less remarkable. In
fig. 17, is shown a small annular nebula, of a slightly oval form,
observed and drawn by Sir John Herschel ; the dark space in the
centre of the ring he described to be filled with nebulous light,
and that the edges were not sharply cut off, but were ill-defined,
and exhibited a curdled and confused appearance, like that of a
star seen with a telescope out of focus.
60

MICROSCOPIC TESTS.

The same object as seen with the more powerful telescope of
Lord Ilosse, is shown in fig. 18.

It is evident from this that very little more increase of optical

Fig. 16.

Fig. 17.

power would resolve this extraordinary object into an annuler
mass of stars.

21. Seeing then that the stupendous works of creation, existing
in regions of space at measureless dis-
tances from the earth, have supplied such
an unlimited variety of telescopic test-
objects, it was natural to seek in other
parts of creation where the more minute
workmanship of nature has play for a
corresponding series of microscopic test-
objects. At the moment when that great
and rapid improvement in microscopes
was commencing, which was so powerfully
promoted by the scientific and practical
skill of the late Dr. Goring and Mr.
Andrew Pritchard, it was found that
various minute parts of the structure of certain species of insects
•could be rendered distinctly visible only by instruments possessing
•certain degrees of optical efficiency.

Dr. Goring, accordingly, selected a certain number of these
objects, which he arranged in a graduated series, according to the
microscopic powers required to render distinctly visible the details
of their structure. These objects consisted chiefly of minute
scales, detached from the bodies and wings of certain species of

61

MICROSCOPIC DRAWING AND ENGRAVING.

insects ; the striae and dots upon which could be seen with more

or less distinctness, according to the excellence of the instrument.

It was to these that the name test-

Fig. 18. i - , <> j T -i

objects was first applied.

22. As the microscope has been
improved in its power from year to-
year, these test-objects have in-
creased in number ; new details of
structure being developed by every
increase of power and efficiency in
the instrument. A certain list of
such objects has been agreed upon
by general consent, and prepared for
sale by the makers, consisting of
hairs, scales, and feathers of insects ;
as, however, it is not my present
purpose to enter into any explana-
tion on the subject of microscopic
tests, except so far as may be neces-
sary to elucidate one of the uses of
microscopic engraving, it will be
sufficient here to give a few examples of these test-objects.

23. There is a little insect, vulgarly called the silt'cr-Jlsh, or the
silver-lady, of which the proper entomological name is the Lepisma-
Saccharina ; it is usually found in damp and mouldy cupboards,
and in old wood- work, such as window-frames. The silvery lustre
from which it takes its vulgar name, proceeds from a coating of
scale-armour, with which its entire body is invested. These scales,
when detached from the insect, and examined with a microscope,
present a beautiful striated appearance ; their magnitude varies;
one, whose length is the 1 14th, and width the 170th part of an inch,
is shown in fig. 19, as it appears in a good microscope, magnified
400 times in its linear, and therefore 160000 times in its super-
ficial dimensions.

The scale, as here shown, is divided along the middle of its
breadth, by a sort of geometrical axis, on either side of which the
structure is perfectly similar. A regular series of striated lines
diverge from this axis, at an angle of about 45°, intersected by
another series, very nearly parallel to the axis.

The divergent strire are very slightly curved; the concavity
being presented downwards, and the longitudinal ones ought to
appear with a microscope to stand out in bold relief, like the
ribs seen on Certain shells ; they are more closely arranged as they
approach the lower part of the scale, and become more prominent
as they are more separated in proceeding upwards.
62

LEPISMA AND PODUKA.

Although the Lepisma is usually ranked among the test-objects-
it must be observed that it is one of the lowest order, an instrument

Fig. 19.

of the most moderate efficiency never failing to render the stria>
tolerably distinct.

24. The Podura, or common Spring tail, is a little insect, gene-
rally found in great numbers in damp cellars, where they may be
seen, running and skipping about upon the walls. Mr. Pritchard
recommends the following method of collecting them : Sprinkle a
little oat-meal or flour upon a piece of blackened paper, and place

MICROSCOPIC DRAWING AND ENGRAVING.

Pig. 20.

it near their haunts ; the meal serving the purpose of a bait, they
will soon collect upon it; the paper may then be removed, and
being placed in a basin, should be
brought into the light, when the in-
sects will immediately jump from the
paper into the basin : they should
then be cautiously handled, and
placed either in glass tubes or boxes
with camphor, to preserve them from
other insects.

These insects, like the Lepisma,
are covered with an armour of scales,
which, when submitted to the micro-
scope, are found to be beautifully
striated ; one of them is shown in
tig. 20, magnified 550 times in its
linear, and, consequently, 302500
times in its superficial dimensions.
The real length of this scale was
the 260th, and its extreme breadth
the 700th, part of an inch.

Smaller, and still more finely
marked, scales of the same insect
are shown in fig. 21 ; the length
of the greater being the 250th, and

its breadth the 500th, of an inch ; and the length of the lesser the
700th, and its breadth the 1375th, of an inch.

These objects require much greater microscopic power to render
visible their minute and beautiful tracery, than such as would suf-
fice for the scale of the Lepisma, when submitted to the highest
practicable magnifying powers ; they are found to be marked by
countless numbers of delicate cuneiform markings, which are seen
to stand out in manifest relief from the general ground of [the
scale.

Fig. 39. — VIIJW OF THE BLOOD-VESSELS AND OTHER PARTS IX A PORTION OF THE UPPER
SURFACE OF THE TONGUE OF A FROG, THE REAL MAGNITUDE OF THE SURFACE
DELINEATED BEING A CIRCLE THE 120TH OF AN INCH IN DIAMETER. DAGUERREO-
TYPED BY MESSRS. DONNJ3 AND FOUCAULT.

MICROSCOPIC DRAWING & ENGRAVING.

CHAPTER II.

25. Natural tests not invariable. — 26. Natural tests imperfect standards.
— 27. Nobert's test-plates. — 28. The degree of closeness of their lines.
— 29. Their use. — 30. Apparent error respecting them. — 31. Fro-
ment's microscopic engraving. — 32. Method of executing it. — 33.
Various methods of microscopic drawing. — 34. Drawings by squares.
— 35. Dr. Goring' s drawings. — 36. Structure and metamorphosis of
insects.— 37. The day-fly.— 38. The larva of this insect.— 39. Its
organs of respiration. — 40. Its general structure. — 41. Its mobility. —
42. State of chrysalis. — 43. The perfect insect. — 44. The production
and deposition of its eggs, and its death. — 45. Death may be delayed
by postponing the laying of the eggs. — 46. They take no food. — 47.
Their countless numbers ; their bodies used as manure.

LARDNER'S MUSEUM OF SCIENCE.
No. 69.

65

MICROSCOPIC DRAWING AND ENGRAVING.

25. ALTHOUGH these, and numerous other objects selected from
the minute parts of the animal kingdom, have heen proposed, and
generally adopted, as microscopic tests ; they are subject to the
obvious objection, that,»when considered as standards, they are
wanting in permanence and identity. Not only do the scales
Fig 21 taken from different individuals of the

^^^^^^^^^^^^^H same species differ in the fineness and
delicacy of their tracery, but striking
differences are found between scale and
scale, taken from the body of the same
individual insect. Thus, for example, the
scales shown in fig. 21, and that shown in
fig. 20, were taken from the same Podura,
yet fig. 21 requires a much more efficient
instrument to develop its tracery than
fig. 20.

In fig. 22 is exhibited a scale of the
same Lepisma from which that represented
in fig. 19 was taken ; and which has been
drawn with 4;he same magnifying power.
The tracings upon this are evidently much
^^^^^^^^^^^™ more minute than those on fig. 19, and
are consequently shown with much less distinctness. It appears,

Fig. 22.

therefore, that these two scales, taken from the same individual
insect constitute different microscopic standards.
60

NOBERT'S TEST PLATES.

26. The erroneous estimates of the relative efficiency and power
of different microscopic instruments which would result from the
use of such test-objects, are obvious. A microscopist in London,
observing the tracery of the scale of a Podura, and another at
New York observing another scale of the same insect, the former
failing to see its striae, which would be visible to the latter, it
could not at all be safely inferred, that the instrument of the one
was inferior in efficiency and power to that of the other ; and it
might even happen, that, the instrument which failed to show the
stria) in London, was, nevertheless, superior to that which ren-
dered them distinctly visible in New York. The result of such a
comparison would entirely depend upon the structure of the two
scales adopted as tests, which might differ within very wide limits.

Independently of this uncertainty attending the application of
such tests, there is another not less serious objection to them ;
they hold out a temptation to microscope makers who supply them
with the instruments they sell, to select such only as are most
easily rendered visible ; and although it be true that this is an
expedient to which the most respectable class of makers would not
resort, it is nevertheless true that the inferior makers do so, and
thereby do injustice to those who are above such practices.

Natural objects, therefore, do not supply such permanent and
unalterable tests for the microscope as the double stars, stellar
clusters, and nebulae do for the telescope ; and this circumstance
has directed the attention of the higher class of artists, to the pro-
duction of artificial test-objects which shall have determinate and
certain qualities, and which, like manufactured articles, may be
reproduced with such absolute identity as to supply standards of
comparison that can be applied in different places, and at different
times, to different instruments, so as to give results which will
admit of comparison.

27. The production of micrometer scales, by Mr. Froment, the
divisions of which are separated by intervals so small as the
25000th of an inch, has been already mentioned.

Now the lines marking such divisions being in closer proximity
than those of the tracings upon certain test-objects, it will be
evident that artificial test- objects might be made by means similar
to those by which such scales have been executed, and there can
be little doubt that the great artistic skill which has succeeded in
producing traces, separated by the small interval above named,
could be pushed further, so as to produce striated surfaces, which
would serve all the purposes of test-objects.

Mr. Nobert, of Griefswall, in Prussia, has taken up this problem
of test-objects, and, without attempting, as it would appear, to
engrave micrometric scales, which would require intervals of some

p 2 67

MICROSCOPIC DRAWING AND ENGRAVING.

exact aliquot part of a standard unit of length, has, nevertheless,
produced bands engraved by a diamond point on slips of glass,
consisting of a greater or less number of parallel lines, separated
by intervals of surprising fninuteness.

Some remarkable specimens of the production of this eminent
artist were presented at the Great Exhibition in Hyde Park, in
1851. They consisted of ten bands, each composed of a certain
number of parallel lines ; those in each band being closer together
than those in the preceding one. In the .following table, we have
given in the second column the number of lines which would fill
the breadth of an inch in each succeeding band in one of these
specimens.

11265

J. .

II

Ill ....

13142
15332

IV

17873

V
VI

20853
24300

VIT. . . .
VIII
IX

28433
33153
38613

X.

, 49910

Thus it appears that, in this specimen, the closeness of the ruled
bands varied from 11000 to 50000 to the inch.

These bands are ruled on glass in parallel directions, being sepa-
rated band from band, by comparatively wide intervals, so that,
if sufficiently magnified, they present such an appearance as is
shown in fig. 24. The highest band being that in which the lines
are most separated, and the lowest that in which they are closest.
It is very difficult to convey a correct idea of the real appearance
of this system of engraved bands before it is magnified ; let us
suppose, however, that fig. 23 represents the real magnitude of the
slip of glass upon which the engrav-
jng is mac[ej and that the white
circle in the centre is the part of the
glass across which the series of ten
bands, shown in a magnified form
in fig. 24, are drawn. The entire
space occupied by all the ten bands
will then be less in width than the black line which is drawn
across the white circle in fig. 23. It must not be imagined that the
white circle in fig. 23 represents that shown in fig. 24, the latter cor-
responds with a minute circular space in the centre of fig. 23, not
much greater in diameter than the breadth of the black line.

28. Yarious other test-plates have been engraved, and put in
circulation by Mr. Nobert ; I subjoin the analysis of one consisting
68

CLOSENESS OP LINES.

Fig. 24.

of 15 bands, which has been examined and calculated by Mr. De
La Rue.

Series.

Number
of lines.

Distance in relation to
the English inch.

Number of lines in
an Eng'ish inch.

I

7

0-00008880

11261

2

8

0*00007548

13248

3

9

0*00006482

15427

4,

10

0-00005506

18162

5

ii

0*00004884

20475

6

'3

0-00004262

23463

7

15

0*00003552

28153

8

17

0-00003108

3^175

9

»9

0*00002664

37537

10

21

0*00002442

40950

ii

23

0*00002220

45°45

12

24

0-00002113

47326

13

26

0*00001998

50050

*4

27

0*00001891

52882

TC

2"

0-00001776

56306 :

MICROSCOPIC DRAWING AND ENGRAVING.

I am informed by Mr. De La Eue, that bands engraved upon
other plates, were observed and computed by himself, Mr. Lister,
and Mr. Nobert, and the results now before me, are in such
accordance as to leave no* doubt of their general accuracy, the
discrepancy being so trifling as to be explained by the small errors
inevitable in such observations.

It will be evident that microscopes, having different degrees
of power and efficiency, would be necessary to render the lines
composing the successive bands of such a series distinctly visible ;
to determine what power would be required for each band, it is
not at all necessary to have recourse to any microscopic observa-
tions; the question simply is, what is the degree of closeness
of the lines, that the naked eye can barely distinguish as
separate ; this will, of course, be somewhat different for different
eyes.

29. The use of these ^test-plates in determining the power and
efficiency of microscopes, will be easily understood ; instruments
of low powers, such, for example, as from 100 to 200, will only
make the wider bands, such as A B and c, fig. 24, distinctly
visible, the closer ones, E F G, will be barely visible as dark bands,
but the lines composing them will not be seen, and the closest of
the series, n I K, will not be seen at all. In proportion as the
power and efficiency of the microscope is increased, more and
more of the bands will be visible as distinct series of lines.

Mr. Nobert supplies test-plates, engraved with bands of diffe-
rent degrees of closeness, according to the power of the instruments
to which they are to be applied.

30. In the Report of the Juries of the Great Exhibition of 1851,
page 268, it is stated, that to see the bands of a test-plate of 10
bands, such as that described above, a linear magnifying power of
100 is necessary for the wider bands, such as I and II, but that to
distinguish those of the closest band, such as x, a magnifying
power of 2000 is necessary.

I think it is apparent that this statement is erroneous, being
evidently incompatible with the relative closeness of the lines of
the several bands. Thus, for example, while there are 11265
lines of the first band to an inch, there are 49910 lines of the
tenth band to an inch. Those of the latter are, therefore, only
4£ times closer than those of the former ; and it is evident, that
if these bands be viewed with two microscopes, one having a mag-
nifying power 4 1 times greater than that of the other, with
proportional defining and illuminating powers, the lines com-
posing them will appear equally separated ; and since it is
admitted in the report, that a power of 100 will render the lines of
the first band visible, as it evidently will do, it will follow that
70

NOBERT'S TEST PLATES.

a power of 450 will render the lines of the tenth band equally
visible ; indeed, it is not necessary at all to have recourse to the
microscope to ascertain the effect which a given magnifying power
ought to produce upon a band of a given degree of closeness, since
it is evident that the effect must be merely to make the lines com-
posing the bands more widely separated than they are in the exact
proportion of the magnifying power. Thus, if the lines composing
a band, separated by intervals of the 10000th part of an inch, be
viewed with the magnifying power of 100, they will appear as
those of a band separated by intervals of the 100th of an inch ; and
if it be viewed with a magnifying power of 1000, it will appear as
if the lines were separated by the 10th of an inch, and so on.

Now, let us apply this obvious principle to the case given in the
report of the Juries ; a magnifying power of 100 directed upon the
first band, would make the lines appear as if they were separated
by intervals of the 112th part of an inch; those of the second
band would appear separated by intervals of the 131st part of an
inch, and those of the third by the 153rd part of an inch. Now,
all these would, as admitted in the report, be distinctly seen as
separate lines, by eyes of average power. But let us see what
effect a magnifying power of 2000 would produce upon the closest
of the bands.

Since it would render the apparent intervals between line and
line 2000 times greater than they are, those between the lines of
the tenth band, would be the 25th; those of the ninth, the 19th;
and those of the eighth, the 17th part of an inch.

Although it must be quite evident that such intervals are much
greater than is necessary to enable any eye whatever that can see
at all, to perceive the lines distinctly separated, the reader will
be enabled better to appreciate the point by referring to the
numbers which we have placed on the right of fig. 24, which
express severally the number of lines to an inch in each of the
bands composing that figure ; thus, the lines of the bands B and c
are separated by intervals of the 48th part of an inch ; and it
follows, therefore, that a magnifying power directed upon the band
x of the test-plate, mentioned in the report of the Juries, would,
if viewed by a power of 2000, show the lines separated by intervals
twice as great, or equal to those of every other line in the bands
B and c, fig. 24.

For these reasons, it appears to me that a mistake has been
committed in the report of the Juries in this point, and I have
thought it the more desirable to call attention to it, inasmuch
as the statement has been reproduced in several recent works
upon the microscope.

It is easy to show what would be the degree of closeness of the

MICROSCOPIC DRAWING AND ENGRAVING.

lines composing a band, which a power of 2000 would barely
render visible to average eyes. Assuming that such eyes could
see distinctly without microscopic aid the lines of a band consisting
of 150 to an inch, it is evident that a power of 2000 would render
equally visible those of a band, the lines of which would be 300000
to an inch. I am not aware that Mr. Nobert, or, any other artist,
has ever produced such lines, and consequently doubt the existence
of any such artificial test for a power of 2000.

31. I now come to notice a sort of microscopic engraving, which,
though it is at once the most curious and difficult, has not, so far
as I am informed, had as yet any directly useful application.
Regarded, however, as an example of mechanical ingenuity and
skill, and as an artistic tour de force of the highest order, it is
full of interest.

However much we may admire the production of the micrometric
scales and microscopic test-plates described above, there is nothing
in them to excite surprise, save the precision which is combined
with such extreme minuteness. To draw a series of parallel lines
of regulated length and uniform intervals, is a problem, to the
solution of which it is easy to conceive that finely constructed
mechanism can be adapted ; but when it is proposed to delineate
objects and characters, in which no such regularity prevails, and, in
tracing which, the point of the graving tool must pursue a course
determined by conditions, which obviously cannot be represented
by any kind of mechanism, and to accom-
plish which it must be guided, directly or
indirectly, by the hand, a problem of quite
another, and far more difficult order, is
presented: such, however, is the curious
and complicated problem for which Mr.
Froment, already named, has found . a
solution.

This eminent artist has succeeded in
producing manuscripts and drawings, en-
graved upon glass, on a scale of minuteness
in no degree less surprising, though far
more difficult of execution than the test-
plates of Mr. Nobert.

To enable the reader more easily to
appreciate these wonderful productions, we
have given in fig. 25 the forms and magni-
tudes of five small circular spaces, A, B, c, D,
E, the diameters of which are severally the 6th, 12th, 30th, 70th,
and 160th of an inch.

Mr. Froment wrote for me, in less than five minutes, within a

FEOMENTS MICROSCOPIC WRITING.

circle of glass, the 40th of an inch in diameter, less, therefore, by
one third than the small white spot c, fig. 25 ; the sentence which,
when magnified in its linear, 120, and in its superficial dimen-
sions, 14400 times, presented the appearance shown in fig. 26.

On the occasion of the Great Exhibition in 1S51, the characters
and figures shown in fig. 27 were engraved by Mr. Froment,
within a circular space equal to that shown at c in fig. 25.

32. As the method by which these marvellous effects are pro-
duced is not yet patented or made public, we are not at liberty to
explain its details ; but it may be stated generally to consist of a
mechanism by which the point of the graver or style is guided by
a system, of levers, which are capable of imparting to it three
motions in right lines which are reciprocally perpendicular, two
of them being parallel, and the third at right angles to the surface
on which' the characters or design are written or engraved. The
combination of the motions in the direction of the axis parallel
to the surface on which the characters are engraved or written,

73

MICROSCOPIC DRAWING AND ENGRAVING.

determines the form of the characters, and the motion in the direc-
tion of the axis at right angles to that surface determines the depth
of the incision, if it be engraving, or the thickness of the stroke, if
it be writing.

33. Having thus explained the principal results of the art of
microscopic engraving, it remains to offer some notice of the not

Ffc. 27.

APPEARANCE AS SEEN IN THE FIELD OF THE MICROSCOPE, THE OUTER CIRCLE BEING
ONLY THE 30TH OF AN INCH IN DIAMETER.

less interesting methods of delineating microscopic objects, or trans-
ferring to paper, metals, or wood fac-similes of the appearances
presented in the microscope: The methods of accomplishing this
have varied with the varying resources presented to art, by the
progress of the sciences.

34. The first attempts at delineation of this kind were made by
dividing the field of the microscope into a system of squares, by
74

DAY FLY.

means of micrometer threads or wires extended transversely to
each other across the field of view, as shown in fig. 4. By this
means, the field of view was, as it were, mapped out in squares,
like lines of latitude and longitude, upon which the magnified
images of the objects to be delineated were seen projected. The
draftsman having previously prepared on paper a corresponding
system of lines, transversely intersecting each other at distances,
one from another, determined by the scale of the intended drawing,
he proceeded to trace the outlines of the objects, guided by the
correspondence between the system of squares upon his paper, and
the system of squares seen in the microscope. The outlines being
then obtained, which could always be most conveniently done with
a low magnifying power, which would include at once within the
field the entire object, or objects, to be drawn, the minute details
of form and structure, were filled up within the outlines by
viewing the parts of the object successively with much higher
powers.

Neither this method, nor any other, depending on mere mecha-
nical experience, would admit of being applied to the delineation
of living objects, which are liable constantly to shift their positions
and change their attitudes. To delineate these, the microscopist
must also be an artist, and one of rather a high order ; happily,
the combination of the two qualities was not unfrequently found,
and many beautiful representations, on a magnified scale, of the
minuter members of the creation, have been supplied by the
researches and talents of microscopic observers.

35. We shall select from these one or two admirable examples
supplied by the late Dr. Goring ; and it will not be unacceptable
to the reader, if we accompany them with a brief account of the
objects they represent.

36. For those who have not devoted attention to the history of
the insect world, it may be well here to premise, that these little
creatures are generally produced from eggs, and that, unlike all
other members of the animal kingdom, they pass during their life
through three stages of existence, in which their forms, habits,
nourishment, and dwellings, differ one from another, for the same
individual insect, as widely as do those of a crocodile and a
peacock.

37. There is a certain little insect of the class of flies, called a
day-fly, because the duration of its life, from the moment it
attains the third and perfect stage of its existence never exceeds
a day.

This insect deposits its eggs in water, well knowing, as it would
seem, that its young, when hatched, are destined to be aquatic
animals, although it is itself one of the gayest animals of the air.

75

MICROSCOPIC DRAWING AND ENGRAVING.

In due time, generally towards the decline of summer, the young,
breaking the shell, issues from the egg in the form proper to the
. 9g first of the ^hree stages of its existence, in which it
is called a larva ; its length, when full grown, in this
state, is about half an inch, and it is represented in
its proper magnitude in fig. 28. It is represented
magnified in its linear dimensions 6| times ; and,
therefore, in its superficial dimensions, 42 times, in
fig. 29.*

38. As the larva increases in size, the serpentine
vessels attached to its sides become more apparent, and
the tail assumes that rich feathered appearance which, in con-
junction with the paddles projecting from its sides, constitute ono
of its most beautiful features.

The body of the insect when young, being very pellucid, its inter-
nal organisation may be very clearly seen with the microscope by
light transmitted through it. The peristaltic motion of the intestines ;
the circulation of blood, and the pulsations of the dorsal vessel,
which in these creatures supplies the place of a heart, can be
observed with the greatest facility. As it grows, it assumes a
variety of colours, losing much of its transparency, when it is a
few months old ; at which time, the period approaches at which it
is destined to pass into the second stage of its existence. The
eyes, as will be seen in the figure, are large, protuberant, and
curiously reticulated; they are of a citron colour. The body
exhibits a beautiful play of various tints, finally assuming a rich
brown colour, with various shadings.

39. It must be here observed, that the important function of
respiration is performed in a very different manner, by different
animals ; the breathing apparatus being always admirably adapted
to the element which they inhabit. The higher class of animals
respire through the mouth and nose. Fishes take air through
their gills, and insects through orifices provided for the purpose,
either in the hinder extremity of their bodies, or along their sides.
From these openings, the air passes through, and inflates vessels
called tracheaB, which extend along their sides ; in these it en-
counters the blood, on which it produces effects similar to those
produced in the superior animals. These vessels appear in the
figure running along each side of the body, and throwing out
numerous ramifications which traverse the several leaf-shaped
paddles projecting from the body.

The orifices by which air is supplied to the tracheae for respira-

* This figure and the succeeding ones, drawn by Dr. Goring, have been
copied with the permission of Mr. Pritchard from the microscopic
illustrations.
76

MAGNIFIED VIEW OF THE LARVA OF THE DAV-FLV. DRAWN BY DK. GORIKO.

77

MICROSCOPIC DRAWING AND ENGRAVING.

ticm, are situated in the membraneous paddles, or swimmers, pro- '
jecting on either side of the body ; they imbibe the air from the
circumambient fluid which passes from them into the trachea.

Ramifications of the tracheae extend along the legs, the antennae,
which diverge from the head, and along the three-forked tail ;
small oblong corpuscles of blood may be seen passing rapidly
around the tracheae with every pulsation of the dorsal vessel.
This vessel, says Mr. Bowerbank, extends nearly along the whole
length of the body, and is of great comparative magnitude ; it is
furnished at regular intervals with double valves, one pair for
each section of the body.

A portion of this vessel, with its valves, is represented as seen
under a higher magnifying power in fig. 30.

The action of these valves is a most interesting and beautiful
spectacle. While in the greatest state of collapse the point of the

lower valve is seen closely compressed within the upper one. At
the commencement of the expansion of the artery, the blood is seen
flowing in from the lateral apertures, as shown by the arrows in
the figure, and at the same time the stream in the artery com-
mences its ascent ; when it has nearly attained its greatest state
of expansion, the sides of the lower valve are forced upwards by
the increasing flow of the blood from the section below the valve,
the lateral openings are closed, and the main current of the blood
forces its way through the two valves.

40. The three-pronged tail is beautifully fringed with bunches
of fine hair, as shown in the figure. As the time approaches at
which the insect is destined to pass into its next stage of existence,
the central prong of the tail becomes more transparent, and as-
sumes the appearance of a jointed tube or sheath ; the two external
prongs, at the same time, exhibit within them parts which are des-
tined to become the tail of the insect in the third stage of its life.

The rapidity with which this creature moves is truly surprising ;
besides its six legs, it is furnished with the six double paddles at-
tached diagonally to the serpentine vessels on each side of its
78

THE PEKFECT INSECT.

body, and with, its tail, all of which, it employs for rowing, balanc-
ing, and guiding itself in the water, the tail playing the part of
the rudder.

41. Such is the mobility of these members, that even when the
creature is in repose, all the paddles are in rapid motion ; the
steering prong of the tail alone being at rest.

Independent of its faculty of locomotion by means of its legs,
paddles, and tail, it possesses a power of leaping and springing in
the water, by bending its body backwards, and then suddenly
straightening it ; by this movement it raises itself to the surface
with great celerity.

42. During the second stage of the life of this insect, called the
state of chrysalis, it retains the faculty of swimming ; its motions
are altogether subservient to its will, and it leaps with great ala-
crity. As the epoch, however, approaches at which it is to pass
into the third and most perfect state, in which it receives the name
of day-fly, some parts of it assume a metallic lustre, just as if
the thin casing in which it is wrapped like a mummy, were partly
filled with mercury ; this casing is so thin and translucent, that
every part of the body of the perfect insect, which is soon about
to emerge from it, is plainly enough visible through it. The me-
tallic appearance, 'just mentioned, is supposed to arise from the
evolution of a small quantity of gas from the body of the insect
in the change which it is undergoing ; this gas, by insinuating
itself between the case of the chrysalis and the body of the insect,
helps to detach the former from the latter, and thus facilitates
the natural process by which the insect emerges from its prison.
The envelope of the chrysalis is adapted to the form and members
of the insect, just as a glove is to the hand, so that after the insect
has escaped from it, this envelope will exhibit with great precision
its shape and proportion?.

43. When the creature has divested itself of its envelope, it
remains apparently inert for a few minutes on some neighbouring

Fig. 31.

plant, where it carefully cleanses its wings, and divests them of
the last pellicle of the sheath in which they had been inserted ;
it then assumes the beautiful form, and exercises the functions

79

MICROSCOPIC DRAWING AND ENGRAVING.

which appertain to it in the perfect state, and becomes the day-fly
shown in fig. 31.

44. It now rises upon its wings into its new element, the air,
where it joins tens of thousands of its fellows, who have almost
simultaneously undergone a similar transformation. In the fine
afternoons of summer and autumn, swarms of these creatures may
be seen hovering in the air, all of them having emerged the same
day from the state of chrysalis. Each female in these nights seeks
its mate ; which having chosen, they retire together to the leaves
of some neighbouring plants. Immediately after their conjugal
union, their proceedings are such as would be prompted by the
tenderest parental solicitude for their future offspring, which,
however, they are never destined to behold. Conscious, apparently,
that their young must inhabit a very different element from that
in which their short existence passes, they fly off in quest of water,
in which, when found, the provident mother deposits her eggs,
collected in a little packet in which they can float ; the parents
then abandon them to the warmth of the atmosphere, by which
they are subsequently hatched, and having thus performed the
last and most important duty of their life, that of increasing and
multiplying their species, drop dead, the whole period of the exist-
ence of this gay insect being limited to a few hours of a summer
afternoon.

45. So imperious is the will of nature in enforcing her laws,
that if by artificial interference, the insect after emerging from
the envelope of the chrysalis be prevented from joining its fellows
and kept in solitude, its life will be prolonged far beyond its natural
term, as if it lived only for the performance of the duty prescribed
to it by its Maker. Dr. Goring ascertained this fact by catching
a day-fly just emerged from the chrysalis, which he imprisoned for
several days, during which it continued to live ; he observed that
in such cases the insect did not seem at all enfeebled, even when
thus confined for a week, so that upon being liberated it flew
briskly away, found its mate, produced and provided for its eggs,
and immediately died.

46. It is remarkable that these little creatures, during their
ephemeral existence, take no food ; the only function they
exercise being that of propagation.

47. It appears, that in some localities, these flies prevail in such
countless numbers that their bodies are found after death covering
the ground to a considerable depth, and they are collected in cart
loads by the agriculturists, who use them for the purpose of
manure.

SO

Fig. 38. — VIEW OF A THIN DISC OF HUMAN BLOOD, PRESSED BETWEEN TWO PLATES OF
GLASS, THE REAL DIAMETER OF THE PART SHOWN BEING THE 120TH OF AN INCH,
DAUUERREOTYPED BY MESSRS. DONNlJ AND FOUCAULT.

MICROSCOPIC DRAWING & ENGRAVING.

CHAPTER III.

48. The beetle. — 49. Its larva. — 50. Drawing of it in its natural size. —
51. Dr. Goring's magnified drawing. — 52. Production of the beetle
from the egg. — 53. The young larva. — 54. Its voracity and manner
of seizing its prey. — 55. Description of its organs. — 56. Its chrysalis.
—57. Water-beetle.— 58. Gnat.— 59. Dr. Goring's method of
drawing. — 60. Drawing by the camera-lucida. — 61. Section of the
human skin ; sweating-gland and duct. — 62. The itch insect. — 63.
Method of obtaining it.

48. ANOTHEK of the tribe of insects, of whose larva Dr. Goring
has left a beautiful drawing, is the beetle, shown in fig. 32.

49. The larva of this insect, like the former, is an inhabitant of
the water. It is remarkable for its ferocious and savage disposition,

LARDNER'S MUSEUM OF SCIENCE. o ,81 .

No. 71.

MICROSCOPIC DRAWING AND ENGRAVING.

and for the various organs supplied to it by nature for the gratifi-
cation of its ravenous propensities. It may be truly affirmed
at no similar creature is provided
with weapons of destruction so power-
fid, so numerous, and so perfectly
adapted to their end ; it is on this
account, that the insect, in this first
state of its existence, has been vulgarly
called the "water-devil." Its length,,
when full grown, is about an inch and.
a half, and the strength, courage, and
ferocity with which it attacks small
fish and other aquatic animals larger
than itself, are truly surprising.

50. The representation of this crea-
ture, in its natural size, when young, and before it has reached
its full growth, is given in fig. 33.

Fig 33 5** The magnified representation of it given in fig. 34,,
has been engraved from Dr. Goring' s drawing.

52. In the first months of Spring, small nests con-
taining the eggs of these insects, may be seen floating
among the weeds, in stagnant pools ; they are formed
like balls, of a dusky-white colour, and silky texture ;
they are attached to the roots or stalks of weeds at the
bottom of the water by a thin stem of the same material
as the nest, but stronger and more dense. Thus placed, they
remain during the winter preserved from the effects of cold, even
when the surface of the water is frozen over ; since by a natural
thermal law the temperature increases in going downwards.*

Early in spring, the stem or thread by which they are attached to
the weeds, is broken by the winds, and the nest being detached and
lighter, bulk for bulk, than the water, rises by its buoyancy to the
surface, where being exposed to the warmth of the sun as the season
advances, the eggs are hatched. The larva, however, after breaking
the shell, is still confined in the bag-shaped nest ; it accomplishes
its liberation by gnawing a hole in it, from which escaping, it dives
immediately to the bottom, eagerly devouring all the small aquatic
insects that fall in its way. If, however, it should happen that
there is a short supply of this food, the voracity of these creatures
is such, that they fall upon and devour each other.

53. "When the larva is very young, measuring not above a quarter
of an inch in length, it is sufficiently translucent to enable an
observer to see its internal structure with the microscope, by light

* See Tract on ''Terrestrial Heat," also Handbook of Natural Philosophy,,
"Heat."

THE WATER DEVIL.

83

MICROSCOPIC DRAWING AND ENGRAVING.

transmitted through it. The colour of the head is then a strong
Indian yellow, with darker shadings of a bright chesnut. The
eyes are a brilliant carmine ; its covering of hairs is more sparse
than when it arrives at maturity ; its swimmers or paddles are
shorter, and its head bears a greater proportion to its body.

54. The manner in which it deals with its prey, shows extra-
ordinary intelligence ; many of the creatures upon which it feeds,
being crustaceous, are invested on the head and back with a shell-
armour, being unprotected on the belly and lower part of the
body ; when they attract the notice of the larva, the latter accom-
plishes its object by swimming under its intended victim; when
sufficiently near, turning its head upwards, it seizes its prey,
between its jointed antennae, A A, fig. 34 ; having thus secured it,
it stabs it in the belly with its sharp mandibles, B B, so as to disable
it, it then rises to the surface of the water, and holding its victim
above the surface, so as to prevent it from struggling, shakes it,
as a dog would a rat.

Its next operation is to pierce it with a weapon represented at D,
which issues from a horny sheath ; this instrument, when not
in use, is withdrawn into the sheath. As shown in the figure, it
is protruded from the sheath to about three-fourths of its length.
This curious weapon consists of a piercer and sucker, the one
giving the wound and the other drawing the blood or other juices.
When from the nature of the part attacked, this weapon fails of
its purpose, the victim is seized between the serrated hooks of a
pair of forceps, c c, by which it is torn to pieces, and the juices
more easily approached by the sucker, D.

55. When supplied with abundant food, this creature arrives at
its full growth in three or four months, and is then nearly opaque
and covered with hair. When caught and kept several days
without food, its ferocity is greatly increased, so that it will
attack insects much larger than itself, if supplied to it, and will
even devour other individuals of its own species. Its prudence
and intelligence, however, are displayed by studiously avoiding
those with whom a contest would be dangerous to it, such for
example as the water-scorpion.

The eyes are compound, but of a very peculiar formation, con-
sisting of seven oval pupils, arranged like leaves on each side
of a stem, as shown at E E ; the entire head and chest are curiously
marked with lines and spots.

There are three pair of legs, the fore legs F F, the hind legs H H,
and the middle legs G G ; each leg terminates in a sharp claw. Pro-
jecting from each side of the body are seven swimmers or paddles,
similar in their position and arrangement, though not in their struc-
ture, to those of the larva of the day-fly already described; they are
84

THE WATER DEVIL.

here covered with hairs, and in the specimen from which the
drawing has been made, a vast number of minute bell- shaped
animalcules were attached to them, which will be recognised in
the figure.

The abdomen is united to the chest or thorax a little above the
first pair of swimmers, and extends to the commencement of the
bifurcated tail ; along the sides of the abdomen are extended the
two tracheso or air-vessels, which as already explained perform
the functions of lungs ; they are in this case of a light blue
colour, and throw out numerous branches at various intervals in
their course. These tracheae consist of curiously formed fibres,
winding round them like the twisted filaments of a rope, as may
be seen in the figure. These vessels are usually distended by the
air which inflates them ; their diameter in a full-grown larva is
about the sixteenth of an inch.

Dr. Goring states that when these membranes are submitted to
examination with the microscope in the usual way, they exhibit
the most beautiful specimen of line-work that it is possible to
imagine. The filaments of the upper and under sides, intersecting
each other at different angles/'produce an effect which could not
be surpassed by the finest and most beautiful engine-turning.

The orifices by which respiration is performed are at its tail,
and each time that it makes an inspiration, it is obliged to ascend
to the surface, above which it projects its tail, through the
apertures of which it draws in air, until the entile tracheae have
been inflated ; thus provided, it sinks again into its proper
element, and according as the air thus inspired has changed its
character by contact with the blood, and has therefore been
rendered unfit for the support of life, it is expelled from the
same orifices in the tail at which it entered, and may be seen
rising in bubbles to the surface.

Dr. Goring observes that a comparison of the organs of respira-
tion of this insect with those of a caterpillar, affords a beautiful
example of the adaptation of their organisation to the elements
in which they live. In the case of the caterpillar, every part
being constantly exposed to the atmosphere, mouths or orifices
tor inhaling the air are arranged along both sides of the body ;
while in the aquatic larva, this system could not be made available
without compelling the creature to elevate its entire body out of
the water, each time it makes an inspiration. The necessity for
this is superseded by placing the breathing-mouths in the tail.

While admitting the admirable fitness of this arrangement in
the two classes of insects, it must not be forgotten, that in the
case of the larva of the day-fly, also an aquatic insect,^ formerly
mentioned, the breathing-mouths, according to Dr. Goring's

MICROSCOPIC DRAWING AND ENGRAVING.

description, are placed in the membraneous paddles along its sides,
and the air is imbibed from the surrounding fluid.

56. After this creature h§s remained for a considerable time in
the state of larva, and when it appears to become conscious that
the epoch of its passage into the second stage of its existence, that
of chrysalis, is approaching, it issues from the water and proceeds
to excavate for itself a hole in the ground, in which it undergoes
the metamorphosis by which it passes into the state of a chrysalis,
in which it remains for some days, after which it emerges a per-
fect beetle.

The female bears on each side of the hinder extremity of her
body a spinning apparatus, which she uses to make the bag in
which her eggs are deposited, and which has been already
described.

57. Dr. Goring has also left a drawing of another species of
dytiscus, called the water -beetle.

This insect resembles, in the manner of its propagation and its
habits, that which has been above described. It is carnivorous,
and of a ferocious and cruel character. If it is placed in a vessel
with other aquatic insects, it soon devours them.

A magnified view of it is shown in fig. 35 ; the insect, in its real
size, being represented in the lower figure. The drawing from which
this engraving was taken, was made immediately after it had cast
its first skin, a moment at which its internal organisation is more
distinctly visible than at any other period of its existence, by
reason of the thinness and transparency of its newly-developed
vessels. Its anatomical structure is more delicate and beautiful
than that of any other larva of the order of coleoptera, and,
although its weapons of attack appear less formidable than those
of the water-devil and some other species, the remarkable manner
in which its internal functions are rendered visible more than
compensate for this, when the insect is regarded merely as a
microscopic object.

It is armed with a pair of curved mandibles, which move
horizontally, and are long enough to cross each other when
closed. They are of a fine nut colour, becoming darker towards
the points, which are hard and sharp. With these the insect
seizes its prey, and bringing it towards its mouth, sucks its blood
after having first pierced it. This it delights to do without
killing its victim, unless it is constrained to do so, by the superior
strength of the latter. If it seizes the larva of the gnat, or any
other tender insect, it brings different parts of its body to its
mouth, devouring it piecemeal, except the skin, which it rejects.
If «its prey is a strong animal, protected by an external shell, it
seizes it, and holds it for some time at rest, until its victim
86

WATER-BEETLE.

becomes completely exhausted ; or, having wounded it in several
places, it turns it upon its back and sucks its juices.

MICROSCOPIC DRAWING AND ENGRAVING.

These larvae swim -with great agility, the hind legs acting
together in concert like those of a frog ; the antennae being at
the same time erected, an,d the palpi concealed. The voracity of
this creature is not directed alone to aquatic insects, but proves
often very destructive to young fish in fish-ponds. Mr. Anderson,
the curator of the Chelsea Botanic Gardens, informs Mr. West-
wood, that he suffered much from these insects attacking young
gold and silver fish, eating their dorsal and pectoral fins.
Dr. Burmeister also mentions, that a specimen which he kept,
devoured two frogs in the space of forty hours, and, nevertheless,
when he dissected it shortly afterwards, it was found to have
entirely digested them. They are very fearless in their attacks,
seizing insects much larger than themselves. They employ their
fore-legs as claws in seizing their prey.

A specimen which Esper kept in water alive for three years and
a half, feeding it with raw beef, is recorded by Clairville to-
have destroyed a specimen, twice its own size, of the large
hydruspicius, piercing it with its jaws, at the junction of the head
and thorax, its only vulnerable point. Dr. Esper observed that
his specimen sucked the blood of the bits of meat with which he
furnished it, and that the residue of them appeared like small
white masses floating on the water.

According to Esper and Erichson, they are, however, able to
fast for many weeks, and even months, provided they are kept in
water, but die, if withdrawn from it, in a few days. They are
observed to ascend frequently to the surface to obtain air for
respiration, where they may be observed in sunny weather resting
with the extremity of their body protruded above the water, and
their legs extended at right angles.

They may be often seen in a calm summer evening issuing from
the water and creeping up the stalks of rushes, from which, after
a little time, they take flight, rising into the air perpendicularly
until they are out of sight. Their descent is also perpendicular,
dropping with considerable force into the water. It would also
appear that it is by the reflection of the light from the surface of
the water, that they are informed of a proper place for their
descent, Mr. Westwood having several times seen them fall with
violence upon glazed garden-frames, which they had evidently
mistaken for water.

They are to be found in all seasons of the year, but more fre-
quently towards the autumn. During the winter some remain in
the water, or bury themselves in the mud, in a torpid state ; others
retain their agility, and may be seen coming to take air in
places where the ice is broken. Mr. Westwood has seen them even
swimming about in the water under the ice on which he was skating.
88

WATER-BEETLE.

The female deposits her eggs about the beginning of spring,
each laying consisting of from forty to fifty eggs of a long and
cylindrical form, which are deposited in the water at random, the
larvse being hatched in the course of a fortnight.

The larva of the dytiscus marginalis is very active, and casts
its skin, for the first time, when four or five days old. The second
moulting takes place after an equal interval, and as the insect
continues to grow, it casts its skin at intervals of about ten days.
The hide which it throws off may often be observed floating on
the water, with the mandibles, tail, and its appendages attached.
These Iarva3 are of a dark ochre, or dirty brown colour, with the
body long and subcylindric, more slender at each extremity, but
especially towards the tail. The body consists of eleven seg-
ments, exclusive of the head. The first nine segments are some-
what scaly above, but fleshy beneath. The first segment is longer
and narrower than the following. The sixth, seventh, and eighth,
are larger than the others, which are of nearly equal size, and the
two terminal joints are long and conical ; the apex being slightly
truncated and scaly, with the sides fringed with hairs, whereby
the insect is enabled to swim along in the water, the action of
these joints being the same as that of an oar used in sculling a
boat.

The terminal segment of the tails is provided with a pair of
long and slender pilose appendages, whereby the insect is enabled
to suspend itself at the surface of the water, which, as Swam-
merdam says, flows from them on every side, and thus the
suspension is effected. These appendages are tubular, and com-
municate with the air-vessels which run along the sides of the
body, which is moreover furnished with a series of spiracular
points, as shown in the figure. The head is large, rounded, and
depressed, and united to the first segment of the body by a short
neck, with five or six small elevated tubercles representing the
eyes. There are two slender antennae, shown at a a in the
fig. 35, having a length nearly equal to the diameter of the head,
inserted in front of the eyes, and composed of seven joints. The
mouth is remarkably constructed, being destitute of the ordinary
aperture, so that the insect may be, and, indeed, has been,
described as wanting a mouth.

The mandibles, which appear" in the figure projecting from the
front of the head, are hollow, having a longitudinal slit near the
extremity, so as to enable the creature to suck through them the
juices of its prey, as a liquid is sucked through a straw or a quill,
the juices thus running down the mandibles into the mouth.

The legs of the insect are long, slender, and ciliated on the
inside, serving as oars when swimming quickly. The body,

89

MICROSCOPIC DRAWING AND ENGRAVING.

generally straight, curves itself in the shape of the letter S when
the creature seizes its prey. During the summer the larva is said
to attain its full size jn about fifteen days, when it quits the
water and creeps into the neighbouring earth, where it forms with
considerable skill a round cell, in which, in about five days, it
changes to a pupa of a whitish colour, with two obtuse points at
the extremity of the body. In about a fortnight or three weeks it
issues as a perfect beetle. If, however, the change to the pupa
state take place in the autumn, the creature does not pass into the
form of a perfect insect until the following spring.

The beetle is at first soft and yellowish, but soon hardens and
assumes a darker colour. It is not, however, until the end of
eight days, that it has acquired its proper consistency.*

Dr. Goring, in describing the specimen from which the drawing
was taken, says that the three first segments of the body, com-
mencing from the neck, contain a bundle of nerves, terminating
with three loops, which are very perceptible in the young larva,
being of a colour more brilliant than the other parts of the body.
They are shown in the figure like a bundle of strings or cords,
extending from the centre of the head to the extremity of the
third joint of the body.

The two large trachea?, commencing from the head, attain
their greatest development about the third joint of the body.
They follow the sides of the body to a point near its extremity,
where they coalesce and terminate. These air-tubes, in their
passage along the body, throw out numerous ramifications, which
are shown in the figure. These tracheae are four in number, two
interior and two exterior. The interior ones commence at the
ganglion, which terminates at the third joint of the body, and
they disappear at the third joint from the tail. In the last joint
Trat one is situated the organ of pulsation.

58. Dr. Goring has also left two very beautiful engravings of
the larva and the pupa of the gnat, taken from a specimen of the
species called tipula crystallina of De Geer, the chironomus
plumicornis of Fabricius, and the corethra plumicornis of
Stephens. I have reproduced these beautiful objects from Dr.
Ooring's engravings, the larva being represented in fig. 1, the
pupa in fig. 2, and a plan, or bird's-eye view of the larva, in its
natural size, in fig. 3.

The gnat, of which these are the previous forms, is represented
in fig. 36, the drawing having been taken while the creature was
in the act of laying the cluster of eggs figured on the right side.
The short line between the figures gives the real length of the

* Westwood on "Insects," vol, i., p. 95.
90

STRAW-COLOURED GNAT.

MICROSCOPIC DRAWING AND ENGRAVING.

body of the insect. The length of the eggs varies from the 40th to
the 50th of an inch.

In the larva (fig.»l) the obvious and curious parts are the
kidney-shaped bodies, b and rf, two of which are situated near the

Fig. 30.

head, and the other two in the third division from the lower
extremity. The first pair are inclined towards each other, while
the others lie in parallel planes, as represented in the plan, or
bird's-eye view, drawn of the natural size in fig. 3. ^ Physiologists
have not ascertained what may be the functions, performed by
these singular organs : it is worthy of remark, however, that a
similar structure is observable in the tadpole, and figured in
Sir Everard Home's Lectures on Comparative Anatomy. The other
parts of its structure, which appear equally singular and curious,
are a number of globules, a, which are situated near the first
pair of bodies, b. These globules have a slight oscillatory motion
in different directions, and, like the reniform bodies, seem to
have a metallic lustre, but are not opaque. From the exquisite
polish of these globules, they reflect the forms of surrounding
objects, as window-bars, &c., which are indicated in the drawing
by small squares, resembling the images formed by convex
mirrors.

When the larva, as shown of the full size in fig. 3, is examined
from above, it exhibits the position and decussation of the various
muscles lying along the back, which are observed to cross at the
joints, and at points situate midway between them.

The alimentary canal appears to contain some particles of a
pinkish coloured matter : but every part of the object, as seen
beneath the microscope, is so accurately noted in the drawing, that
a more minute description must be deemed superfluous.

If the insect have a sufficient supply of food, it only continues
for a few weeks in the larva state, when it rapidly changes to the
pupa, shown in the drawing (fig. 2). When it is desirable to
92

STKAW-COLOURED GNAT.

preserve it for the microscope, this change may be retarded by
keeping it in clear spring or river water. The former seldom offers
sustenance to animalcules, and, therefore, effects this object, which
is often very desirable, on account of the scarcity of this species.

The transformation of this animal from the larva to the pupa is
one of the most singular and wonderful changes that can be con-
ceived ; and, under the microscope, .presents to the admirer of
nature a most curious and interesting spectacle. Although the
whole operation be under the immediate inspection of the observer,
yet so complete is the change, that its former organisation can
scarcely be recognised in its new state of existence.

If we now compare the different parts of the larva with the.
pupa, we remark a very striking change in the tail, which, in the
previous state of being, was composed of twenty-two beautifully
plumed branches, while, in the latter, it is converted into two
fine membranous tissues, ramified with numerous vessels. This
change appears the more remarkable, as not the slightest resem-
blance can be discovered between them, nor are the vestiges of the
former tail readily found in the water. The partial disappearance
of the shell-like or reniform bodies is another curious circumstance.
The lower two, it may be conjectured, go to form the new tail ;
for, if the number of joints be counted from the head, the new tail
will be found appended to that joint which was nearest to them in
the larva state, as referred to by the dotted line d, connecting
figs. 1 and 2. The two small horns, c c, which form the white-
plumed antennas of this species of gnat, when in its perfect state,
are discernible in the larva, folded up under the skin near the
head at c, in fig. 1. The alimentary canal appears nearly to
vanish in the pupa, as in that state there is no necessity for it,
the insect then entirely abstaining from food; while, near this
canal, the two intertwined vessels, seen in the larva, have now
become more distinct, and are supplied with several anastomosing
branches.

During the latter part of the day on which the drawing (fig. 2)
was taken, the rudiments of the legs of the perfect insect might
be seen, folded within that part which appears to be the head of
the pupa, and several of the globules had vanished, those remaining
longest that were situated near the head. It may be necessary to
observe, that the head of the pupa floats just under the surface of
the water ; and the insect, in this state, is nearly upright in that
fluid, while the larva swims with its body in a horizontal position,
or rests on its belly or sides, at the bottom of the pond or vessel
in which it is kept, the fringed tail being downwards.

The colour of the larva when young is a faint and scarcely
perceptible yellow ; but as it approaches the change, it assumes a

93

MICROSCOPIC DRAWING AND ENGRAVING.

richer and deeper colouring, and all its internal parts acquire
their definite forms and tints, as exhibited in the drawing.

A curious circumstance attends the observation of this insect ;
so rapid is its locomotion, that it torments the eye while attempting
to delineate it, presenting alternately bits head and tail to the
observer. This it effects by bending itself laterally into a circular
form, and suddenly whisking round in the opposite direction to
that in which it had just bent itself.

Many species of this genus of insects are, in their perfect state,
possessed of a sheathed proboscis, containing instruments with
which they are enabled to pierce the skin of men and cattle,
injecting at the same time an acrimonious fluid into the wound.
The species we are now describing, however, has not been
examined minutely enough to determine the form of these organs.
It is of a light straw colour, and has two beautiful antennee, or
feelers.

The wings also of this gnat are of a delicate straw colour, and
make very beautiful objects when mounted under thin glass in
sliders. Some species have wings marginated, and covered with
fine scales. These, as well as the feathers on the edges, are good
objects for the microscope, and exhibit five or six longitudinal
lines on each, which are so strongly marked as to be seen with
any kind of light, and do not require superior penetration in the
instrument to show them.

These insects generate while hovering in the air, and the female
lays her eggs in the water, selecting an unfrequented spot, where
she may deposit them free from danger. This is probably the
cause why this larva is discovered with so much difficulty ; the
collector being seldom able to procure it two seasons consecutively
in the same place.

59. The method of executing these drawings, practised by
Dr. Goring, differed in nothing from that by which an artist
makes a portrait, the eye guiding the pencil, and the accuracy of
the resemblance depending altogether upon the skill of the artist.

60. Dr. Goring considered that in such cases the great security
for precision offered by the camera-lucida, was not available,
owing to the constant mobility of the object delineated; this
objection, however, is only applicable to living objects, and
that admirable instrument is accordingly used to a great extent
in the production of microscopic drawings. As we shall describe
it in a future Tract, and explain its mode of application
to the microscope, it will not be necessary here to give that
exposition. It will be sufficient to observe that a practised
draughtsman is capable of giving, not only the general outline,
but most of the less minute details of a microscopic object, by a

THE ITCH INSECT.

process precisely similar to, and susceptible of, as much accuracy
as that by which a drawing is reproduced on tracing paper. It
must be observed, however, that in the finishing touches, and the
most minute details, the pencil of the draughtsman must after
all be guided by his artistic skill. To what extent this is true, is
proved by the fact, tkat two drawings of the same object, viewed
in the same microscope, and' made
with the same camera, by artists
of different skill, will be different.
, We shall here, as in the former
case, present the reader with some
examples of microscopic drawings
made by the aid of the camera.

61. In fig. 41 is a magnified
section of the human skin, cut in-
wards at right angles to its surface,
to the depth of about the sixth of an
inch. The following is the succes-
sion of organised parts included
within that depth : — a the sudori-
ferous gland ; b c the sudoriferous
duct, leading to the surface of the
skin ; d the subcutaneous cellular
and adipose tissue ; e the derma or
true skin ; f the papillae ; y mucous
tissue or interior epidermis ; h the
epidermis or superficial skin.

62. It is now admitted, though
the fact was long doubted, that the
malady called the itch in the human
body, and that called the mange in
the horse, are produced by an insect
hatched under the cuticle of the
skin ; the insect which produces the
itch, called the acarus-scabiei, is
represented, highly magnified, in

fig. 42. To extract this insect, the operator must, says Mr.
Q,uekett, examine carefully the parts surrounding each pustule,
and he will generally find, in the early stage of the disease, a
red spot or line communicating with it ; this part, and not the
pustule, must be probed with a pointed instrument, and the
insect, if present, turned out of its lurking-place. The operator
must not be disappointed by repeated failures, as in the best
marked cases, it is often difficult to detect the haunts of the
creature.

95

FIG. 41.— MAGNIFIED SECTION OK
THE HUMAN SKIN, SHOWING
THE PERSPIRATORY GLAND, WITH
ITS DUCT, DRAWN WITH A CA-
MERA BY DR. MANDL.

MICROSCOPIC DRAWING AND ENGRAVING.

63. That the itch is occasioned by such an insect is by no
means a modern doctrine. Kirby mentions a Moorish physician,
who, in the twelfth century, affirmed that the malady was pro-
duced by little mites or lice that creep under the skin of the
hands, legs, and feet, producing pustules full of matter ; he
quotes also " Joubert," another ancient physician, who describes

Fig. 42. — VILW Of THE ITCH INSECT, DRAWN WITH A CAMERA
BY DR. MANDL, MAGNIFIED 120 TIMES IN ITS LINEAR, AND
THEREFORE 14400 TIMES IN ITS SUPERFICIAL DIMENSIONS.

the itch insects under the name of " sirones," and says they are
always concealed beneath the epidermis, under which they creep
like moles, gnawing it, and producing a most troublesome itching.
It was supposed by some that they were identical with lice ; but
Dr. Adams showed that this could not be the case, since they live
under the cuticle ; he speaks of them as living in burrows which
they have excavated in the skin, near a lake of water, from which
if they be extracted with a needle, and put upon the nail, they
show in the sun their red heads and the feet with which they
walk ; they have been extracted and delineated with the aid of
the microscope by many modern observers. The individual
delineated in fig. 42, was drawn by my friend Dr. Mandl, well
known for his great work on microscopic anatomy.

Fig. 40. — THIN DISC OF COW'S MILK, THE 120TH OF AK INCH IN DIAMETER, MAGNIFIED
400 TIMES IN ITS LINEAR, AND 160000 TIMES IN ITS SUPERFICIAL DIMENSIONS.

MICROSCOPIC DRAWING & ENGRAVING.

CHAPTEE IV.

64. Structure of the itch insect. — 65. Its habits. — 66. The mange insect.
— 67. Its form and structure. — 68. Defects incidental to drawing
with the camera. — 69. Microscopic photographs. — 70. Microscopic
daguerreotypes % Messrs. Donne and Foucault. — 71. Description of
the blood. — 72. Red and white corpuscles. — 73. Daguerreotype of
a drop of blood magnified. — 74. Magnitude of the corpuscles. — 75.
Cause of the redness of blood. — 76. Corpuscles of inferior animals.
— 77. White globules. — 78. White grains. — 79. White globules con-
verted into red corpuscles. — 80. Red corpuscles dissolved. — 81.
Circulation of the blood.— 82. Method of showing it in the tongue
of a frog. — 83. The arteries distinguishable from the veins. — 84. The
vascular system of the tongue. — 85. Mucous glands. — 86. Milk ; its

LARDNER'S MUSEUM OF SCIENCE. H 97

MICROSCOPIC DRAWING AND ENGRAVING.

constitution. — 87. Magnified view of a drop-of milk. — 88. The butter
globules. — 89. Their number variable. — 90. Analysis of the milk of
different animals. — 91. Richness of woman's milk. — 92. Analogy of
milk to blood. — 93. Jmportance of the quality of milk. — 94. Its
richness ascertained. — 95. Quevenne's hydrometer applied to milk.
— 96. Its fallacy. — 97. Donne's lactoscope. — 98. Objections to it
answered. — 99. Frauds practised by milk vendors. — 100. Fore-milk
and after-milk. — 101. Self-engraved photographic pictures.

64. DR. BONONIO, having directed his researches to the itch
insect, found that it was very nimble in its motions, covered with
short hairs, and furnished with a formidable head, from which a
pair of strong mandibles projected.

• At the extremities of its four pairs of legs, there are feet of
remarkable form, each of which is provided with a sucker, by
means of which he inferred that it sucks or draws its way under
the skin, having first excavated a space for itself with its man-
dibles. The insects form their nests there, deposit their eggs, and
multiply rapidly.

65. More recently, Dr. Bourguignon has studied the habits of
this insect by means of a microscope specially adapted to the
purpose, and has confirmed the discoveries of Bononio. He found
that the insect fastens itself in the furrows of the skin by means
of the suckers of its feet, aided by small bristles, being likewise
covered with similar bristles in various parts of its body, by which
it fixes itself more firmly, while it works its way with its man-
dibles ; it is not furnished with eyes, but in a moment of danger
it quickly draws in its head and feet, this motion and that of its
gait resembling those of a tortoise. It usually lays sixteen eggs,
which it deposits, ranged in pairs, in the furrows under the
skin, where they are hatched in about ten days.*

66. The insect which produces or accompanies the mange in
horses, and which is called the acants-exulcerans, is represented
in fig. 37, p. 49, magnified in its linear dimensions one hundred
and fifty times.

67. This animalcule is larger and more easily obtained than
the former ; it is found under the whitish scales which are de-
tached from the skin of the horse, and if several individuals be
taken, they will be found to be in different states of development,
having four pair of legs when full grown ; the two foremost pairs
are terminated in a strong and sharp claw, and their general form
is like that of the legs of a flea, consisting of five joints or
segments.

The head consists of nothing but a mouth, in which the organs
of mastication are seen, consisting of a pair of very fine and sharp

* Bourguignon, quoted by " Hogg '' on the Microscope, p. 318.
98

MICROSCOPIC DAGUERREOTYPES.

mandibles terminated by two teeth, the form of the entire organ
being that of a pincers. The skin, which is of a tough leathery
texture, is elegantly marked by sinuous and parallel tracings,
bearing some resemblance to engine-turning. Wrinkles are in
some places seen upon it, as if it were divided into separate
segments, united edge to edge, like the bones composing the
human skull ; upon the legs, the skin is finely granulated and
not striated, as upon the body ; several long hairs issuing from the
legs are seen in the figure.

68. Although the general fidelity of microscgpic drawings made
with a camera may be relied upon, yet, as has been already
observed, the more minute details are executed by the artist in
the same manner as that in which a portrait-painter produces his
effects, and in whatever degree the artistic skill of the draughts-
man may be manifested in such parts of the drawing, the rigorous
fidelity demanded by science, even in the minutest arts, cannot be
claimed for them.

69. Under these circumstances, other means, ensuring more
rigorous accuracy, and rendering the drawing independent
altogether of those impulses which imagination and taste never fail
to impart to the pencil even of the most. conscientious artist, have
been eagerly sought by naturalists, and have been happily sup-
plied by photography. The magnified image of the object under
examination, produced by a solar microscope, is received upon a
prepared daguerreotype-plate, or a leaf of photographic paper, and
there the optical image delineates itself with the most unerring
fidelity and rigorous accuracj7".

70. This felicitous application of the photographic art, to the
promotion of natural science, after some experimental essays,
more or less successful, was first carried out, so as to be available
for the practical purposes of science, by Dr. Donne", assisted by
M. Leon Foucault, in 1845. In that year Dr. Donne* published
an atlas to illustrate his course on microscopic anatomy and
physiology, which had appeared in the previous year, consisting
of twenty plates, on each of which were four microscopic engrav-
ings, made from daguerreotype plates which had been produced
in the manner above described. I avail myself gladly of the
kind permission of the authors of this work, and of Mr.
Bailliere, its publisher, to reproduce four of these engravings upon
the scale on which they are given by the authors.

71. The blood of animals is not, as it seems at first view to be,
a homogeneous liquid holding in complete solution certain sub-
stances, and destitute of all solid and concrete matter ; if it were
so, we could not follow its course through the vessels in which it
moves, as we do so easily and distinctly with the microscope.

H 2 99

MICROSCOPIC DRAWING AND ENGRAVING.

The motion of an homogeneous liquid in tubes completely filled
with it could not be made sensible to the sight ; but on the other
hand, that of a liquid containing solid particles suspended in it,
continually entering into Collision with and displacing each other,
would be perfectly visible.

The blood therefore contains certain solid particles floating in
and circulating with it, to which moreover are due several of its
most important properties ; these particles exist in countless num-
bers, and of minuteness so extreme, that a single drop of blood,
no larger than might be suspended from the point of a needle,
contains myriads of them Until recently, observers recognised
only one species of the corpuscles, such being the only ones per-
ceivable by the ordinary methods of observation, and being
incomparably more numerous than tho others, which, besides
being more rare, are generally hidden by the former, which com-
pletely fill the field of the microscope.

72. These sanguineous corpuscles are distinguished by regular
and constant forms, by a complex composition and a determinate
structure. They possess a real organisation, and pass through a
regular succession of phases, having a beginning, a development,
and an end.

They consist of three species : first, red corpuscles ; secondly,
white globules ; and thirdly, white granular particles, much
smaller, to which observers have applied the name " globulines."

73. Nothing can be more simple or more facile than the method
of observing the first class of these corpuscles. Take a sharp
needle and prick with it slightly the end of the finger, so as to
draw the smallest drop of blood ; having previously rendered a
small slip of glass perfectly clean and dry, touch it with the
blood, a small portion of which will adhere to it, and upon this
lay a thin film of glass, such as are prepared by the opticians for
microscopic use, so as to flatten between the two glasses the small
drop of blood. Let the glass thus carrying the blood be placed
under a microscope having a magnifying power of about 400 ; a
multitude of the red corpuscles will then be immediately visible,
distributed irregularly over the field of view of the instrument.

Fig. 38, p. 81, has been reproduced from one of Dr. Donne's
engravings ; it represents a thin disc of human blood, having a
diameter equal to the 120th part of an English inch, included
between the two glasses.

The red corpuscles alone are here visible ; their form is that of
flat discs a little concave in the middle, swelling upwards towards
the edges, which are slightly rounded. Some of them, such as
a a a, are presented with their flat sides to the line of sight, so
as to show very distinctly their form ; others, such as b b, are
100

DROP OF BLOOD.

seen edgeways, and others at all degrees of obliquity ; some are
scattered separately, but others are grouped together in piles,
with their edges presented to the eye, having the appearance of
rouleaux of coin lying on their sides on a table, the faces of the
coins being more or less inclined to the surface of the table.

The flat disc-shape form of the corpuscles was not recognised by
the earlier observers, who took them to be red spherules. The
cause of this error was not any defect of their observation, but
arose from their having previously washed the blood with water,
being ignorant that the immediate effect of the contact of water
with human blood is to change the form of the flat corpuscles into
that of little globes.

74. The magnitude of these corpuscles, since the recent im-
provements of the microscope, has been very exactly measured.
Their diameters are found to vary from the 3125th to the 3000th
of an inch : this small variation being due to their different states
of development, as will be presently explained.

75. The blood consists of a transparent, limpid, and colourless
fluid, in which the solid particles already mentioned float, and
the redness of which arises altogether from the colour of the
corpuscles here described. A person, who may observe for the first
time these corpuscles with the microscope, is generally surprised
and disappointed to find that they are not red, but rather of a
yellowish colour, having a very faint reddish tint. This circum-
stance, however, is an optical effect of a very general class, which
has been explained more than once in our Tracts. When any
coloured medium is submitted to the eye, the depth of its tint
will always be diminished with the thickness of the medium,
which may be reduced to such a degree of tenuity as to render
its peculiar colour altogether imperceptible. "We mentioned
formerly, as an example of this, the case of coloured wine, such as
sherry, viewed through a tapering Champagne glass. At the
upper part, where the eye looks through a greater thickness of
the liquid, the peculiar gold colour is strongly pronounced ; but
in going downwards to the point of the cone, the colour becomes
paler and paler, and at the very point is scarcely perceptible. It
is the same with the red corpuscles of the blood. "When they are
seen singly through their very minute thickness, they appear of
the faintest reddish yellow ; seen in rouleaux edgeways, they are
redder ; but it is only when amassed together, in a stratum of
blood of some thickness, that they impart to the liquid the red
colour so characteristic of the blood.

76. The disc-shaped form which thus characterises human
blood, is common to all species of animals which suckle their
young, with the single exception, so far as is known at present,

101

MICROSCOPIC DRAWING AND ENGRAVING.

of the camel species. It appears, from some recent observations
of Dr. Mandl, that the blood of this species presents an anomalous
exception, the red corpuscles being elliptical in their form, but
still flat and concave at their sides.

In comparing the red corpuscles of the blood of different species
of mammalia, or suckling animals, one with another, they are
found to vary in their diameters, being greater or less in different
species, but the variation in each species being confined within
narrow limits, as in man-

The corpuscles of the blood of birds, fishes, and reptiles, are all
like those of the exceptional case of the camel, oval discs of
various magnitudes, somewhat concave in their centres, like the
blood of mammalia.

77. The discovery of the white globules is entirely due to recent
observers, and particularly to Professor Miiller, Dr. Mandl, and
Dr. Donne.

The white globules have nothing in common with the red
corpuscles, either as to colour, form, or composition. Unlike the
latter, they are spherical, their contour is slightly fringed, and
not well defined like that of the red corpuscles ; their surface is
granulated, and their diameter is a little greater, varying from
the 2500th to the 3000th of an inch. They appear to consist of
a thin vesicle, or envelope, the interior of which is filled with
solid granulated matter, consisting usually of three or four grains,
while the red corpuscles are filled with an homogeneous and
semi-fluid matter in the case of mammalia, and a single solid
kernel in the case of other vertebrated animals.

The white globules also have chemical properties totally
different from those of the red corpuscles.

78. In fine, the third class of solid particles which float in the
blood cannot be properly denominated globules, being only very
minute granulations, which are continually supplied by the chyle
to the sanguineous fluid ; they appear in the microscope as minute
roundish grains, isolated, or irregularly agglomerated, and having"
a diameter not exceeding the 8000th of an inch: they have,
however, a physiological importance of the first order, since they
are the primary elements of the blood, and therefore of all the
Other organised parts of the body.

79. It appears to follow from the observations, researches,
experiments, and reasoning "of Dr. Donne, that these granular
particles form themselves into the white globules by grouping
themselves together, and investing themselves with an albuminous
envelope. By a subsequent process, the white globules are con-
verted gradually into the red corpuscles, the place where this
change is produced being supposed by Dr. Donne to be the spleen.

102

CIRCULATION OF THE BLOOD.

80. In fine, the red corpuscles, after having been fully developed
in the circulation, are dissolved, and being converted into the
fibrinous fluid, pass into the other parts of the organisation, so as
to form the different organs of the system.

81. Next to the constitution of the blood, no subject con-
nected with it is more interesting and important than its circula-
tion, and we know no spectacle presented by any of the scientific
artifices, by which the secret operations of nature are disclosed
to our view, which excites more astonishment and admiration
than the circulation of the blood, as rendered visible with the
microscope.

82. Let any one imagine an animal organ, full of every variety
of blood-vessels of the most complex structure, into the composi-
tion of which enter every form of organ : arteries, veins, capillaries,
muscles, nerves, glands, and membranes : representing in short a
microcosm of the whole animal organisation ; and let us suppose this
brought within the field of the microscope, so as to display, before
the wondering view of the observer, all the complicated motions
and operations of which it is the theatre. Such a spectacle is
presented by the tongue of the frog, an object first submitted to
this species of experiment by Dr. Donne, at the suggestion of a
young Englishman, a Mr., since Dr., Waller, who was in at-
tendance upon his course. The method of accomplishing this,
with some modifications, as described in the Physiological Journal,
is as follows: — "A piece of cork, from two to three inches in
breadth, and six to eight inches in length, is to be procured, in
which is to be bored, a hole of about half an inch in diameter
midway between the sides, and about an inch and a half to two
inches from one of its ends. In this part the piece of cork should
be of double thickness, which is effected by joining, by means of
marine glue, a small piece of cork upon the first piece. Upon
this is laid the frog, previously enveloped in a linen band, or fixed
to the cork by pins thrust through the four extremities, so as to
prevent any great movements of its body or its feet ; it is placed
upon the back, the end of the nose abutting on the border of the
hole. The tongue, the free end of which is directed backwards, is
then to be drawn out of the mouth gently with a forceps, and
slightly stretched and elongated until it reaches a little beyond
the opposite edge of the hole, where it is to be fastened by two
pins ; the sides are to be fastened over the hole in a similar way.
In this state, the tongue presents the appearance of a semi-trans-
parent membrane, which permits us to see through its substance ;
and when placed between the light and the object-glass of the
microscope, offers one of the most beautiful and marvellous
spectacles which can possibly be witnessed. It will be found most

103

MICROSCOPIC DKAWING AND ENGRAVING.

convenient to view it, first, with a simple magnifying-glass, having
a power of 1 5 to 20, so as to obtain a general view of the vessels
and of the circulation ; e^en with this small power the observer will
be filled with astonishment at the magnificence of the spectacle,
especially if a strong light is thrown upon the lower side of the
tongue. To imagine a geographical map to become suddenly
animated, by their proper motions being imparted to all the
rivers delineated upon it, with their tributaries and aflluents,
from their fountains to their embouchures, would afford a most
imperfect idea of this object, in which is rendered plainly visible,
not only the motion of the blood through the great arterial trunks,
and thence through all their branches and ramifications to the
capillaries, but also its complicated vorticular motions in the
glands, its return through the smaller ramifications of the veins to
the larger trunk veins, and its departure thence en route for the
heart. Such is the astonishing spectacle, circumscribed within a
circle having the diameter of the 120th of an inch, magnified,
however, 400 times in its linear, and therefore 160000 times in its
superficial dimensions, which has been daguerreotyped by Messrs.
Donne and Foucault, and which is reproduced on the same scale
in fig. 39, p. 65.

83. The arteries are distinguishable from the veins very readily,
by observing the direction in which the blood flows, its velocity,
and their comparative calibre. In the arteries the blood flows
from the trunk to the branches, its course is marked by the
arrows in fig. 39, where t is a trunk-artery entering near the
lowest point of the field of view ; the arrows show the course of
the blood passing into the principal branches, 1, 2, and 3, from
which it flows into all the smaller arterial ramifications. The
course of the blood in the veins, on the contrary, is from the
branches to the trunk, from whence it finds its way back to the
heart. The arteries, moreover, are of less calibre than the veins,
and consequently the blood flows in them with greater velocity.
The greater arteries are accompanied by a greyish flexible cord,
which can be perceived, but not without some attention ; it passes
along the sides of the artery : this cord is only a nerve.

As the ramifications of the arteries are multiplied they are
diminished in calibre, and merge at length in the capillaries, from
which they are scarcely distinguishable, the latter being equally
indistinguishable from the smaller veins. As these conduits of
the blood diminish in diameter, the red corpuscles at length so
completely fill them, that they can only move in them one by one,
and they can be thus seen following one another at perceptible
intervals. If the microscope be directed to that part of the edge
of the tongue, which is within the limits of the hole made in the
104

MICROSCOPIC VIEW OF MILK.

cork, the blood can be traced in its course to the extreme arteries,
and thence from the smaller to the larger veins on its return to
the heart.

84. The vascular system of the tongue appears traced upon a
greyish semi-transparent brown, on which a multitude of fine
fibres, v v, are seen extended in different directions ; these
existing at different depths within the thickness of the tongue,
appear superposed and interlaced ; these fibres belong to the
muscle of the organ, and their characteristic action is rendered
evident in the microscope, by their alternate contraction and
extension. A number of greyish spots, somewhat round in their
outline and a little more opaque than the neighbouring parts,
appear scattered through the tongue ; these spots belong to the
mucous-membrane, and are in fact parts of the glands in which
saliva is secreted. They are the theatres of a surprisingly
complicated and active blood-motion. The sanguine fluid enters
them at one side, generally by a single small artery, rarely by
two, and following the course of this artery, it pursues a nodu-
lated path, resembling the form of a bow of ribbon, or the
figure 8, and issues from them at a point opposite to that it entered.
The organ of which we speak, says Dr. Donne, having a certain
thickness, we cannot always see at once the entrance and departure
of the blood, the point of its departure being often in a plane
inferior or superior to that of its entrance, and the two points
not being, therefore, at the same time in focus. But in any case,
nothing can be more curious or more profoundly interesting than
the vortices of rapid circulation, thus exhibited, in a space so
circumscribed and within the limits of an organ, which is evidently
one of secretion.

85. These greyish spots in short, in which the circulation proves
to be so active, are nothing but the mucous-follicles of the tongue,
the little glands in which is secreted the viscous humour which
coats in such abundance the tongue of the frog, and we accord-
ingly find that if it be wiped off, it will be almost immediately
reproduced.

86. The milk of mammalia being the first nourishment taken
by their young, and their only nourishment until a certain epoch
of their growth, it might naturally be expected that that fluid
would have a olose analogy to the blood. The examination of
milk accordingly, whether with the microscope or by means of
chemical analysis, proves such an anticipation to be well-founded.
If a small drop of milk be laid upon a clean slip of glass, and
covered by a thin film of glass, so that a thin stratum of the
fluid shall be included between them, it is found on submitting it
to the microscope, in the same manner as has already been described

105

MICROSCOPIC DRAWING AND ENGRAVING.

in the case of the blood, that very similar appearances are pre-
sented, A multitude of minute pearly spherules with the most
perfect outline, reflecting light brilliantly from their centre and
varying in magnitude from the 12500th to the 3000th part of an
inch in diameter, and even larger still, are seen floating in the fluid.
The general magnitude and number of these globules vary
much, not only in the case of one species of animal compared with
another, but with different individuals of the same species, and
even with the same individual under different circumstances.

87. In fig. 40, p. 97, we have given the appearance presented by a
thin disc, the 120th of an inch in diameter, of common cow's
milk magnified 400 times in its linear, and therefore 160000 times
in its superficial dimensions, engraved from a daguerreotype by
MM. Donne and Foucault.

88. It appears from the researches of physiologists on this
subject that the pearl-like globules, which thus float in such
multitudes in milk are the constituents out of which butter is
formed. The serous fluid in which they float is composed of the
constituent out of which cheese is formed, combined with another
substance called sugar-of-milk, and water, the last constituting
from 80 to 90 per cent, of the whole, so that, in fine, milk in
general may be regarded as water holding in solution the sub-
stances called sugar-of-milk and caseine, the name given to the
cheesy principle, with the globules of butter already described
floating in it.

89. The proportion in which these constituents enter into the
composition of milk varies, the richness always depending on the
proportion of globules of butter contained in it.

90. The following is an analysis of the milk of the woman,
the cow, the goat, and the ass, according to Meggenhofen, Yan-
Stiptrian, Liuscius, Bonpt, and Peligot : —

Woman. Cow. Goat. Ass.

Butter . . . .8-97 2-68 4-56 1-29

Sugar of Milk . . . 1'20 5*68 912 6'29

Cheesy matter . . . 1'93 8 '95 4 '38 1'95

Water 87 '90 .82-69 81 '94 90-47

100-00 100-00 100-00 100-00

91. From this and similar analyses it appears that woman's
milk is by far the richest of the mammalia, containing generally
little short of 10 per cent, of butter, while the milk of other
species contains no more than from 1 to 4 per cent, of that
principle.

It must, however, be observed that these are average proportions,
106

CONSTITUTION OF MILK.

and that the richness of the milk differs considerably in different
individuals. It is found that in all cases the milk is sufficiently
rich in the cheesy principle, the constituent in which it fails
being the butter, which is the most important in respect to-
nutriment.

The butter globules of woman's milk, though much greater in
quantity, as appears above, than those in the milk of inferior
animals, appear from the observations of Dr. Donne to be
smaller in magnitude. We have given in fig. 43, the appearance

Fig. 43. — THIN DISC OF WOMAN'S MIJ^K, THE 120TH OF AN INCH IN DIAMETER, MAGNIFIED*

400 TIMES IN ITS LINEAR, AND 160000 TIMES IN ITS SUPERFICIAL DIMENSIONS.

of a disc of ordinary woman's milk, magnified similarly to fig. 40.
The difference between the magnitude of the globules is apparent.
92. The analogy of milk to blood manifested in a manner so
striking by the microscope, was still farther investigated in a
series of highly interesting experiments made by Dr. Donne". .

107

MICROSCOPIC DRAWING AND ENGRAVING.

That eminent physiologist transfused milk into the blood vessels
of various animals, with all the precautions necessary to prevent
the admission of air. • It was found • generally that the vital
functions of the animal, were neither interrupted nor disturbed ;
the milk mingled with the blood and circulated with it through
the system, its presence being detected in all the vessels. But the
most interesting and important result of these researches, was,
that the butter globules of the milk were found to assimilate
themselves to, and play the same part with, the white globules of
the blood, and like them were gradually converted into red cor-
puscles, and it appeared that the place where this change was
elaborated was, as in the case of the white corpuscles of the
blood, the spleen.

These researches and their results, however, being recent and
novel, must be received with that caution which is always neces-
sary in physical researches, until they are repeated and like results
reproduced by other observers.

93. The question of the quality of milk in respect to its
richness, has high sanitary and economic importance, and yet it
is one which hitherto does not appear to have received the atten-
tion which it merits. We hear on all hands the adulteration of
milk complained of, and the frauds of the milkman reprehended ;
but we seldom hear of any practical methods applied for the pur-
pose of detecting and checking this abuse. It will perhaps not
be out of place here, to say a few words in illustration of this
question.

94. The richness of milk, as has been just observed, depends on
the proportion of butter globules which it contains ; these globules
being lighter, bulk for bulk, than the liquid in which they float,
have a tendency to rise to the surface, and when milk is allowed
to stand still they do rise to the surface, where, mixed with a
certain portion of the cheesy principle and sugar-of-milk, they
form cream. Now it follows, that being thus lighter, bulk for
bulk, than the fluid in which they float, they have a tendency,
when mixed with that fluid, as they are when the milk is in its
natural state, to render the milk lighter, and the larger the pro-
portion is in which these butter globules are mixed with the milk,
the lighter will be the milk. It was therefore inferred, that the
lightness of the milk might be taken as a test of its richness, and
M. Quevenne invented a species of hydrometer, which he pro-
posed to apply to test the richness of milk, in the same manner
as the ordinary hydrometer is applied to test the strength of
spirits. But the indications of this instrument, ingenious as it is,
are fallacious.

95. Let- us suppose that the fraudulent milkman allowing the
108

ADULTERATION OF MILK — LACTOSCOPE. '

milk he proposes to sell, to stand until the richer portion forms
a creamy stratum at its surface, then skims off this stratum
which he sells at a high price, as cream. The remainder and
impoverished portion of the milk is then undoubtedly heavier
than before it was deprived of the cream, and its poverty would
be detected by Quevenne's hydrometer : but the crafty milkman,
aware of this, has the adroitness, not only to correct the too great
weight of the fluid, but to do so to his own increased profit. He
knows that the addition of water will diminish the specific
gravity of his skimmed milk, and he accordingly mixes with it
just so much of that cheap liquid as will reduce its weight to that
of milk of the proper richness.

96. This manoeuvre is attended also with another deceptive
effect ; it is found that the mixture of water with milk facilitates
the disengagement of cream, and expedites its collection at the
surface. Whatever creamy particles, therefore, may remain in
the milk thus impoverished and adulterated, will rise quickly to
the surface, and collecting there, will deceive the consumer, pro-
ducing the impression that the milk on which cream so quickly
collects, must necessarily be rich.

The great importance of discovering such an easy and practi-
cable test of the quality of an element so important to the
sanitary condition of the people, as milk, ought, one should have
supposed, to stimulate scientific men to such an invention. The
frauds practised so extensively by the vendors of milk on great
public establishments, such as hospitals and schools, are notorious.
An eminent medical practitioner says, that in conversing with one
of the great milk contractors of the public establishments in
Paris, during a season in which forage had risen to a very high
price, the milkman observed frankly, and with a smile, "in
common seasons, we do put a little water to the milk, but at pre-
sent we are obliged to put milk to the water."

97. Dr. Donne has invented an instrument to ascertain the
richness of milk, which he calls a lactoscope, which was presented
to the Academy of Sciences, and favourably reported upon by a
committee consisting of MM. Thenard, Chevreul, Boussingault,
Regnault et S6guier, who experimented with it and verified its
results. This instrument is based upon the fact, that while the
butter globules, which float in milk, are opaque, the liquid which
surrounds them is nearly transparent. It follows from this, that
the transparency of milk will diminish as its richness increases,
and vice versd.

The lactoscope consists of two plates of glass, set parallel to
each other, so as to form a cell in the end of a tube, like an
opera-glass, the cell being at the wide end of the tube. A screw-

109

MICROSCOPIC DRAWING AND ENGRAVING.

adjustment is provided, by which the distance between the
plates of glass may be varied within certain limits, so that by
turning the screw in one way, the plates may be brought into
absolute contact, and By turning it the other way, they may be
separated by any desired interval. Over this cell, is provided a
small cup, with a hole in its bottom, by means of which the cell
may be filled with milk. Let us now suppose this cup to be filled
with the milk to be tested, the screw having been previously
turned until the plates of glass composing the cell are in contact.
The milk in that case, will not pass between them, but will
remain in the cup. Let the observer, applying his eye to the
small end of the instrument, look through the cell at the flame of
a candle, placed at about three feet distance from it, and let him at
the same time slowly turn the screw, so as to let the milk flow
into the cell ; at first the candle will be seen dimly through the
milk, but when the plates have been separated by the screw to a
•certain distance, the flame will be no longer visible, being inter-
cepted by the multitude of butter globules in the milk.

Now it will be found, as may be expected from what has been
explained, that the poorer the milk is, the greater will be the dis-
tance to which the glasses must be separated in order to intercept
the flame, and the richer it is, on the other hand, the less will be
the distance which will suffice to produce that effect,

These instruments are made and sold by the Paris opticians.

98'. It may be objected that the certainty of this instrument
•depends upon the fact that the milk is impoverished either by
skimming it or by mixing it with water, but that if it be adul-
terated by any substance which will promote its opacity, the
indications of the instrument must fail. The answer to this
objection is, that such a mode of adulteration is impracticable ;
the substance used for such a fraudulent purpose must in the first
place be one, which, when mixed with the milk, will not sensibly
alter its conspicuous and well-known properties, such as its
•colour, taste, odour, and general consistency. It must, moreover,
be soluble in the milk, and not merely mixed with it, since if so,
it would either sink to the bottom, forming a sediment, or rise to
the top, as oil would in water, and in either case, would be
immediately detected. It must also be such as will not be
disengaged by heat, and thereby be betrayed in boiling the milk :
in fine, it must obviously be a substance cheaper than milk, and
the process of combination must be so simple as to be inexpensive
and to admit of a certain secrecy ; now it is quite apparent, that
there k one substance only which will fulfil all these conditions,
^nd tnat substance is water.

99. The frauds practised by the vendors of milk do not always
110

FEAUDS OP MILK SELLERS.

oonsist in adulteration ; we have already mentioned the case of
skimming the milk, and selling the richer and poorer portions at
different prices ; this cannot be characterised as fraud, so long as
the difference of quality is admitted, but yet it has the effect of
fraud upon the consumer of the skimmed portion, for the milk
he obtains is precisely the same in quality as he would obtain
if the milkman instead of skimming the milk had left it in its
natural state, but watered it, so as to reduce it to the poverty of
skimmed milk.

100. There is another expedient, commonly enough practised,
which is attended with similar effects, when the milk is allowed
to accumulate in the breasts or dugs of the animal until they
become filled and distended, the first portion drawn from them will
be poor, and the milk will become richer and richer until the
vessels are emptied. This physiological fact is quite familiar to
•dairymen, who divide the milking of the cow into two parts,
the fore-milk and the after-milk; the latter being sometimes called
strippinys. Now this richer portion of the milk is often reserved
for cream, the fore-milk only being sold to the consumer. In
accordance with the same principles it will be easily understood,
that the more frequently the animal is milked, the more uniformly
rich will be the fluid.

All the circumstances here explained, and the tests provided,
to ascertain the qnality of the milk of inferior animals, are
•equally applicable to human milk. Wet-nurses differ one from
another evidently enough in the abundance of their milk, and this
is a point which, accordingly, is never overlooked in the selection of
nurses. The quality of the milk, however, being much less obvious,
is rarely attended to. Yet it is even more important than the
mere question of quantity. The physical researches of some of the
French physiologists have shown that cases frequently occur in
which there is a superabundance of milk ; and where, though the
woman presents the aspect of health and vigour, the milk is poor
in butter, the globules being small either in magnitude or number,
or both ; they are sometimes observed to be ill-formed, to float in a
liquid of little density, and sometimes to be mixed with corpuscles
of mucus and of a granular substance. These are characters incom-
patible with the healthiness of the milk, yet they are such as can
only be detected by the microscope." Nevertheless, it is rare indeed
that the medical practitioner ever thinks of instituting such
inquiries, much less of resorting to the microscope or any other
lactoscopic test.

101. We have now indicated, so far as we are informed, all the
methods by which the representations of microscopic objects are
obtained, and of these that which gives the strongest guarantee of

111

MICROSCOPIC DRAWING AND ENGRAVING.

accuracy and fidelity is the photographic method. It must, however,
be observed, that even in this method, as it was practised in the
production of the Microscopic Atlas of Messrs. Donne and Foucault,
there is still a possible source of inaccuracy remaining, the engraver
having to reproduce the photographic picture upon his plate, and
for the fidelity of this process, there is no other guarantee than the
general accuracy of the engraver's art.

Measures are, however, now being taken, with a fair prospect of
success, by which an optical picture being projected upon a plate,
will engrave itself — an approach to this has indeed been made ;
the photographic picture being projected upon a surface of wood,
properly prepared and being there delineated by its own light, as
it would be on a daguerreotype plate. The engraver after this has
nothing to do but to follow the lines of the picture with his
graving tool.

Attempts, however, are being made to cause the light itself to
engrave the plate, and I have seen microscopic pictures of the
blood corpuscles thus self engraved, which, if not completely satis-
factory as works of art, have been sufficient to impress me with
the conviction, that we are not far from the attainment of a
measure of such high scientific importance as that of making
natural objects engrave themselves.

112

LONDON ENTRANCfi TO XilE LONDON AND NOliTii- WESTERN RAILUOAD.

THE LOCOMOTIVE.

CHAPTEE I.

1. Familiar to every eye. — 2. Its mechanism not generally understood. —
3. Object of this Treatise. — 4. Two modes of propelling wheel car-
riages.— 5. How locomotive is propelled. — 6. Action of piston-rod
on wheels. — 7. Dead points. — 8. Unequal action. — 9. How remedied.
— 10. Connection of piston-rods with wheels. — 11. Wheels fixed on
their axles. — 12. Form of locomotive. — 13. Driving-wheels. — 14.
Coupled wheels. — 15. Consumption of steam. — 16. Evaporating
power of boiler determines efficacy of engine. — 17. Fire-box. — 18.
Tubes through boiler.— 19. Fuel.— 20. Blast-pipe.— 21. Tender.—
22. Plans and sections, with their description.

1. ALTHOUGH it be the variety of the steam-engine, whose in-
vention is the most recent in date, the locomotive is the form of
the machine which is most familiar to the public in every country.
To behold the vast engines used for drainage, mining countries

LARDNER'S MUSEUM OF SCIENCE. i 113

No. 68.

THE LOCOMOTIVE.

must be visited ; to see those adapted to useful machinery, we must
go to the factories ; to view those applied to navigation, we must
descend into the holds o^ ships. The locomotive, however, needs
not be sought. It is patent and obtrusive. It addresses the
senses of hearing and seeing. The warning whistle and the
snorting chimney are familiar to every ear, and the flashing speed
of the engine, with its snake-like appendage of vehicles of tran-
sport, is familiar to every eye.

2. Of the countless multitudes in all civilised countries who
witness the extraordinary performances of the locomotive, and
participate in its use and enjoyment, few comprehend the source
of its power, or the principle of its action. They see it sweep
along with the speed of the hurricane, drawing after it carriages,
carrying hundreds of human beings, or hundreds of head of cattle,
or tons of goods, but the agency which accomplishes this miracle
is to them wrapt in mystery. Many desire to possess the key to
the enigma, to unlock the secret, but recoil from the labours
which the perusal and study of even the most .popular treatise on
the locomotive would require, a labour for which few have the
disposable time, and still fewer the qualifications depending on
preliminary knowledge and intellectual aptitude.

3. It is this nmltitude that we now desire to address, hoping
to offer, in a small compass, such a simple and clear account of the
variety of steam-engine referred to, as will be intelligible to all
persons, without more labour than all can conveniently devote
to it.

4. A moving power may be applied in two ways to propel a
vehicle supported OB wheels. It may be harnessed to it as horses
to a carriage, and may draw it on by traces, or it may be applied
to the wheels, so as to make them revolve. If the wheels be made
to revolve, they must either slip upon the road, or the vehicle
must advance. But if the weight upon them be considerable, and
the state of the road suitable, they will have such adhesion with
the road at the points where they rest upon it, that they will not in
general slip ; and if they do not, the vehicle which they support
must be propelled by each revolution of the wheels through a space
equal to the external circumference of their tires.

5. Now it is by this latter means that the power of steam is
applied to propel the locomotive. The steam pistons are connected
by iron rods, called connecting-rods, either with the spokes of the
wheels, at certain regulated distances from the axles, or with
arms, called cranks, formed on the axles between the wheels.
The force with which the pistons are alternately driven by the
steam from end to end of the cylinders, is conveyed by the con-
necting rods to the spokes or cranks, and it acts upon them in the

114

ACTION OF PISTON ON WHEELS.

Fig. 1.

same manner as the arm of a man acts upon a windlass, thus

imparting a continuous motion of revolution to the wheels.

6. To render this action of the piston on the wheels more appa-
rent, the piston-rod, the connecting-rod, and the spoke or crank,

are shown in fig. 1, in eight successive

positions assumed by them during

each revolution of the crank. The

direction in which the connecting-
rod acts upon the crank is indicated

by the arrow.

The joint p unites the connecting-
rod with the end of the piston-rod,

and the joint r unites it with the

end of the crank or spoke, the fixed

centre round which the crank or

spoke revolves being c.

While the piston makes a double

stroke from one end of the cylinder

to the other and back, the joint r

makes one complete revolution round

the centre c.

In the position shown in A, the

piston is at the end of the cylinder

most remote from the crank, and the

joint r is directly between the centre

c and the joint p.

In the position B, the joint r has
moved from that position, the piston
moving towards c, and the connect-
ing-rod and crank forming an obtuse
angle. The force of the steam im-
pelling the connecting-rod in the
direction shown by the arrow, acts at
an obtuse angle with the crank.

As the piston continues to move,
the angle formed by the connecting-
rod and crank becomes less and less,
until in the position shown in c the
angle becomes a right angle, and
then the whole force given to the
connecting-rod becomes effective.

In the position D, the angle formed
by the connecting rod and crank

becomes acute, and in the position E, the joint r assumes a posi-
tion in a direct line with c and p, and the piston has reached

i 2 115

THE LOCOMOTIVE.

the end of the cylinder nearest to c. After this the piston begins
to move from c towards the more remote end of the cylinder, and
the joint r assumes successively the positions shown in F, G, and
H, the crank making first an acute angle, then a right angle, and,
in fine, an obtuse angle with the connecting-rod, until the piston
has arrived at the more remote end of the cylinder, when the
points c, r, and p, receive the position shown in A.

7. It must be observed, that in the positions shown in A and E,
the connecting-rod being parallel to the crank, can have no power
to turn it; that in passing from the position A to the position c,.
the rod being less and less oblique to the crank, has a continually
increasing power to turn it, until at c, being at right angles
to it, it has full power upon it. After passing the position c, the
rod becoming more and more oblique to c, has less and less power
upon it, until arriving at the position E, it is parallel with it, and
loses all power over it.

The two positions shown in A and E, in which the piston is at
one end or the other of the cylinder, and in which the piston loses
all power to move the crank, are called the DEAD POINTS.

8. After passing the position E, when the piston, having changed
the direction of its motion begins to return to the other end of the
cylinder, the rod again forms an acute angle with the crank, and
acts upon it, but with disadvantage, as shown in F.

The angle formed by the rod and the crank increasing, becomes
at length a right angle, as in G, when the rod acts with full effect
on the crank.

After this, the angle between the rod and the crank becomes
obtuse, as in H, and the action is again disadvantageous, and
more and more so as the angle becomes more and more obtuse,
until at length the rod and crank return to the position repre-
sented in A.

Since the action of the piston upon the wheel is, therefore,
unequal, having its greatest efficiency at the points shown in c
and G, and ceasing altogether in the positions A and E, a single
piston would give to the engine an unequal progressive motion. It
would advance by starts, being impelled with most effect when
the piston has the positions c and G, and moving only in virtue of
the velocity already imparted to it when the piston is at the dead
points A and E. The motion would be alternately fast and slow,
according to the varying position of the connecting-rod and crank.

9. This inequality is effaced, and an uniform motion obtained
by using two cylinders driving different cranks or different wheels,
and so arranging them, that when either is at its dead points, the
other is in its positions of greatest efficiency. This is accomplished
simply by placing the two cranks at right angles to each other, or

116

CRANKED AXLE.

by connecting the rods with spokes at right angles to each other.
By such an arrangement, the combined effects of the two cranks
will be invariable, or nearly so, the effect of either increasing
exactly as that of the other decreases.

10. The cylinders are sometimes placed between and sometimes
outside the wheels.

If they are placed between one pair of wheels the axle of another
pair is formed with two cranks, placed at right p5<r „

angles to each, which are worked by the con-
necting-rods of the pistons.

Such a double-cranked axle is shown in
tig. 2, the cranks being seen in a position
oblique to the plane of the diagram. The
connecting-rods are understood to be attached
to the cranks at B, and the wheels, which are
to be driven, are keyed upon the extremity of
the axle at G.

When the cylinders are placed outside the
wheels, the connecting-rods are attached to
two spokes, one upon each of the wheels which
they are intended to drive, these two spokes
being in positions at right angles to each
other, and the wheels being keyed upon the
axles, so that bthe wheels and axles turn
together.

11. It may be stated generally that the
wheels of railway vehicles and engines do not
turn upon their axles like those of common
road carriages, but are always fixed upon the
axles, so that the wheel and axle turn toge-
ther, and, consequently, whether the force
of the connecting-rods act upon the spokes of
the wheels, or upon cranks formed upon the
axle, they will be equally efficient in impart-
ing rotation to the wheels and consequently
impelling the engine.

12. The locomotive engine is commonly sup-
ported on three pairs of wheels. In some cases
of small and light engines there are only two
pairs, and in others there are four pairs.

The general form and disposition of the parts of a locomotive
upon three pairs of wheels is shown in fig. 3. In this case the
two cylinders are placed immediately in front of the fore wheels
and under the chimney. The intermediate pair of wheels are
driven by the connecting-rods.

117

THE LOCOMOTIVE,

13. The pair of wheels to which revolution is imparted by the
piston-rod, through the intervention of the connecting-rods, are

Fig. 3.

called the DRIVING-WHEELS, since it is by their immediate action
that the engine draws the train which is attached to it. They
are generally of greater diameter than the supporting- wheels, in
order that the engine may be propelled through a greater space
by each stroke of the piston, since the space through which it
moves by each double stroke is equal to the circumference of
the driving-wheels.

The actual dimensions of such an engine as is represented, arc
indicated on the diagram.

In some engines of more recent construction the driving-wheels
are placed in the hindermost part of the engine, the cylinders

Fig. 4.

Diameter of piston f 1 * 4-'
Slro/ce 1?*'

being between the intermediate and foremost pairs of wheels, as
118

DIFFERENT FORMS OF LOCOMOTIVES.

represented in fig. 4. In these the driving-wheels are of greater
dimensions, and the engine is adapted to attain greater speed.

A lighter and less powerful class of locomotive, supported on
two pairs of wheels, is shown in fig. 5, the hinder pair being the
driving-wheels.

Fig. 5.

14. When locomotives are intended to draw very heavy loads
with less speed, as in the case of goods engines, the driving-
wheels have less dimensions, and, in order to give them a greater
hold upon the rails, it is usual to connect two pair of side wheels,
of exactly equal dimensions, so that the piston shall act at once on
both by means of the connecting-rods. The two pair of driving-
wheels thus connected are said to be COTTPLED, and the engine is

called a coupled-engine. Such an engine is shown in fig. 6,
where the hinder and intermediate pairs are coupled, the connect-

119

THE LOCOMOTIVE.

ing-rods being attached to the intermediate pair, and through
them acting also on the hinder pair.

15. It has been shown ^hat to give a revolution to the driving-
wheels, each of the pistons must move once backwards and for-
wards in the cylinder, and consequently the boiler must supply to
the cylinders four measures of steam. In this way, the consump-
tion of steam necessary for a given progressive speed of the car-
riage may be calculated. Thus, if the circumference of the
driving-wheels be thirty feet, four cylinders full of steam will be
consumed for each thirty feet through which the carriage
advances. It is apparent, therefore, that the ability of the engine
to move the load with any requisite speed is resolved into the
power of the boiler to produce steam of the requisite pressure at
this required rate.

Let it be supposed that it is desired to transport a certain load
at the rate of thirty miles an hour, which is at the rate of half a
mile, or 2640 feet per minute. Let the circumference of the
driving-wheels be twenty-six feet and four-tenths. These wheels
will revolve one hundred times in moving over 2640 feet, or half
a mile, that is to say, one hundred times per minute. But since
each revolution requires the boiler to supply four cylinders full of
steam, the consumption of steam per minute will be four hundred
times the contents of the cylinder.

16. The pressure of the steam will depend upon the resistance
of the load. By the common principles of mechanics, the power
acting upon the pistons necessary to balance a given resistance at
the circumference of the wheel can be easily calculated, and thus
the necessary pressure of the steam ascertained. In this manner
it can always be determined how much steam, of a given pressure,
the boiler must produce, in order to enable the engine to carry a
given load with any required speed.

The mechanism being properly constructed, it follows, there-
fore, that the efficacy of the engine must depend ultimately on the
evaporating power of the boiler.

In the case of the locomotive engine there are particular condi-
tions which limit the magnitude and weight of the machinery,
and create impediments and difficulties in the construction of the
machine, which are not encountered in stationary engines. As
the engine itself is transported, and travels with its load, it must
necessarily be subject to narrow limits as to weight and bulk.
It has to pass under bridges, and through tunnels, which circum-
stance not only limits its general magnitude, but almost deprives
it of the appendage of a chimney, so indispensable to the efficiency
of stationary steam-engines.

It follows that this limitation of weight and bulk can only be
120

EVAPORATING POWER — FURNACE.

rendered compatible with great power of evaporation by expe-
dients which shall produce, in a small furnace, an extremely
intense combustion, and which shall ensure the transmission to
the water completely, and immediately, of the heat developed in
such combustion.

17. The heat developed in the combustion of fuel in a furnace
is propagated in two ways. A part radiates from the vivid fuel
in the manner, and according to nearly the same laws which
govern the radiation of light. These rays of heat, diverging in
every direction from burning fuel, strike upon all the surfaces
which surround the furnace. Now, as it is essential that they
should be transmitted immediately to the water in the boiler, it
follows that the furnace ought to be surrounded on every side
with a portion of the boiler containing water ; in short, a hollow
casing of metal, filled with water, ought to surround the fire-
place. . By this expedient, the heat radiating from the fuel, strik-
ing upon the metal which forms the inner surface of such casing,
will enter the water, and become efficient in producing
evaporation.

Whatever then be the particular form given to the engine, the
furnace must be surrounded by such a casing. This casing is
called the FIRE-BOX. The bottom of it is occupied by a grate,
which should consist of bars sufficiently deep to prevent them
from being fused by the fuel which rests upon them, having
sufficient space between them to allow the air to enter so freely
as to sustain the combustion, but not such as to allow the unburnecl
fuel to fall through them.

18. The limited magnitude of locomotive boilers renders the
construction of the extensive flues used in stationary boilers
impracticable ; and accordingly, in the early engines, a great
waste of heat was occasioned, owing to the flame and heated air
being permitted to issue into the chimney before their tempera-
ture was sufficiently reduced by contact with the flues.

At length an admirable expedient was adopted which com-
pletely attained the desired end. The boiler was traversed by a
considerable number of small tubes of brass or copper, running
parallel to each other from end to end, the furnace being at one
end of the boiler, and the chimney at the other. The flame and
heated air which passed from the furnace had no other issue to
the chimney except through these tubes, It was thus driven, in
a multitude of threads, through the water. The magnitude and
number of the tubes was so regulated, that when the air arrived
at the chimney, it had given out as much of its heat as was prac-
ticable to the water.

The full importance of this expedient was not appreciated until

121

THE LOCOMOTIVE.

long after its first adoption. In the first instance, the tubes
traversing the boiler were small in number, and considerable in
diameter, but as theif effects were rendered more and more
evident by experience, their diameter was diminished and their
number increased, and at length it was not uncommon for the
boiler to be traversed by one hundred and fifty tubes of one inch
and a half in internal diameter.

The heat was thus, as it were, strained out of the air before the
latter was dismissed into the chimney.

These tubes were necessarily kept below the surface of the
water in the boiler, so that they were constantly washed by the
water, and the heat taken up from them was absorbed imme-
diately by the bubbles of steam generated at their surface, which
bubbles continually rose to the top of the boiler and collected in
the steam chamber.

It will be understood from these observations, that the evapo-
rating power of the locomotive boiler, is determined by the
quantity of surface exposed to the radiant heat in the fire-box
and the quantity of surface exposed to the action of the heated air
in the tubes. The expression of the quantity of this surface in
square feet is the usual test of the evaporating power of the boiler.

19. Much of the efficacy of these boilers depends on the quality
of the fuel. As the engines travel through districts of the
country more or less populous, the evolution of smoke is inad-
missible in consequence of the nuisance it would produce. It
was, therefore, resolved to use coke as fuel instead of coal.

Another advantage, however, attended the use of this fuel.
Coke being composed chiefly of carbon, to the exclusion of the
more volatile constituents of coal which produce flame in the com-
bustion, the chief part of the heat developed acts by radiation.
No flame issues from the furnace, and heated air only passes
through the tubes. It is more easy, therefore, to extract the
heat than would be the case if flame were developed. In short,
with this fuel, the portion of the heat developed in the furnace is
much greater than that which would be developed in the com-
bustion of coal. The surface of the fire-box becomes relatively
more efficient, and the flues less so than in stationary engines
where coal is used.

Independently, therefore, of the advantage of developing no
smoke, the coke is a form of fuel better adapted to the condition
of the lomocotive engine.

20. To sustain a rapid and intense combustion on a grate
necessarily small, a proportional force of draft is indispensable.
In stationary engines, as is well known, the draft in the furnace
is usually produced by a chimney of corresponding elevation ; but

122

BLAST PIPE — FEED PUMPS.

this being inadmissible tinder the conditions of the locomotive
engine, it is necessary to adopt some other expedient to produce
the necessary current of air through the tube. A blower, or
fanner, working in the funnel or in any other convenient position,
would answer the purpose ; but a much better expedient has been
adopted.

The steam, after driving the piston, is allowed to escape, but in
order to turn it to profitable account, instead of being dismissed
into the atmosphere, where it would produce a cloud of vapour
around the engine, it is conducted through ;a pipe to the base of
the funnel, where it is allowed to escape in a jet directly up the
chimney. In this manner a puff of waste steam escaping from the
cylinders as the pistons arrive at the one end or the other, is
. injected into the chimney, and a constant succession of these puffs
take place, four being made for every revolution of the driving-
wheels. These continual puffs of vapour maintain in the chimney
a constant current upwards, by which the air and gases of com-
bustion are drawn from the fire-box through the tubes.

The pipe by which these jets are directed up the chimney,
called the blast-pipe, serves the purpose of a most efficient
bellows.

Those who are not familiar with steam machinery will not find
it difficult to comprehend that a bellows would produce the same
effect on the fire if it acted in the chimney, or even at the top of
the chimney, as if it were applied at the grate bars, provided only
that the mouth of the chimney near the fire be closed by a door,
as it always is in steam-engines.

21. To keep the locomotive boiler supplied with water, and its
furnace with fuel, it is accompanied by a carriage called a tender,
which bears a supply of fuel, and a cistern of sufficient magnitude,
containing water.

This cistern is connected with the interior of the boiler by pipes
and force-pumps. The force-pumps are worked by the engine.
The engineer is supplied with a lever, by which he can suspend
the action of the pumps at pleasure ; so that, if he finds the boiler
becoming too full, he can, to use a technical phrase, " cut off the
feed." Gauges are provided, by which he can at all times ascer-
tain the quantity of water in the boiler, or, which is the same, the
position of its surface. He is accompanied by a stoker or fireman,
who from time to time opens the door of the fire-box and feeds the
furnace.

22. This general description of a locomotive and its accessories,
will be more clearly understood by the aid of diagrams, showing
the principal sections and plans of an engine and tender.

A series of drawings, showing in section and elevation various

123

PLANS AND SECTIONS OF ENGINE.

views of a loco-
motive engine on
three pairs of
wheels with its
tender, is given
in figs. 7, 8, 9, 10,
Il,12,13,andl4.

Fig. 7 is a
longitudinal ver-
tical section,
made by a plane
parallel to the
wheels, and pass-
ing through the
axis of the boiler
and the smoke-
funnel.

Fig. 8 is a
plane of the
working machi-
nery between the
wheels and be-
neath the boiler.

Fig. 9 is
transverse verti-
cal section made
by a plane pass-
ing through the
fire-box at right
angles to the
wheels.

Fig. 10 is a
similar trans-
verse section,
made by a plane
passing through
the smoke - box
and the axis
of the smoke-
funnel.

Fig. 11 is an
elevation of the
end of the engine
near the driver's
stage.

125

THE LOCOMOTIVE.
Fig. 12 is a similar elevation of the end next the smoke-funnel.

Fig. 0.

Fig. 13 is a longitudinal vertical section of the tender, by a
plane at right angles to the wheels, and midway between them.

Fig. 14 is a plan of the tender seen from above.

The same parts in the different drawings are generally indicated
by the same letters.
326

PLANS AND SECTIONS.

The principal parts will be recognised by the preceding general
description, and the following references : —

The steam cylinders

The steam pistons ....
The piston-rods . .
The connecting-rods ....
The cranks driven by them which in this case are
constructed on the axle of the driving-wheels
The driving-wheels ....

The supporting-wheels

The passages to allow the entrance and escape of

the steam to and from the cylinder .
The case containing the slide by which these

passages are opened and closed .
Two pair of eccentrics by which the slides are
moved, one governing the steam so as

move the engine forward, and the other so as
to move it backward
The rods by which these eccentrics act upon those

of the slides ...
The handle or lever by which the engine driver

throws one or other pair of eccentrics into

connexion with the slides
The steam -chest, where dry steam free from mixture

with aqueous spray is received from the boiler
The steam-pipe leading from this chest by which

steam flows to the slides and to the cylinder
The blast-pipe, by which steam, after entering the

piston, is discharged in puffs up the smoke-
funnel

The fire-box containing the burning coke .

The hollow metal casing surrounding it secured

by bolts and nuts, and filled with water
The grate bars forming the bottom of the fire-box
The fire door through which coke is put in from \

time to time to feed the furnace .
The tubes traversing the boiler longitudinally \

through which the hot gases of combustion f

and smoke pass from the fire-box to the

smoke-box . . . .
The smoke-box at the base of the funnel, receiving

the heated air from the tubes
The smoke-funnel over the smoke-box and blast-

pipe . .

The regulator, by which more or less steam

allowed to pass along the steam-pipe, and by

closing which the steam is altogether cut off f

from the cylinder *

The stage upon which the engine driver and stoker

stand .

•

dumber of
diagram.

Letters of
reference.

7,8

7,8
7,8

H
X
Y

B'

e

I

7, 8

C'

7, 8, 9
7, 8, 10,
11, 12

V
L, M

Df

8

m, n, o

36

8

U

*e
0

IS

8

E'E",
F'F"

36

8

e" J", f"

2r

bo

7

a'"

re

er

7,11

T

jh
er

7

SS

le

e-

7,10

P

.

7,9

G G

3d

7,8, 9

kJc

3X

"I

7,8,9
11

D

g

Iy

an f

hei

7, 9, 10

EE

ng

7, 8, 10

F

jt-

7, 10, 12

G

is)
byf
off(

7

h'

er

7,H

P'c"

' 127

THE LOCOMOTIVE.

Number of I Letters of

The water gauge, being a glass tube communi-
cating above and below with the interior of
the boiler, in which the water stands at the
same level as in the boiler . . . .

Gauge-cocks, which serve a like purpose, one
being below and the other above the proper
level of the water. If the water be below
the proper level, steam would issue from the
lower, and if above it, water would issue
from the upper cock .....

The feed-pump, being a force-pump worked by"")
the engine, by which water is forced into the I
boiler from time to time to replace that which f
is evaporated . . . . . . -.

The feed-pipe, leading from the feed-cistern on
the tender to the feed-pump

The levers by which the engine driver governs the
feed. These open or close the feed-pipe accord-
ing as they are turned one way or the other.
When the engine driver sees the level fall too
low in the water gauge or by the gauge-cocks,
he opens the feed-pipe by these cocks and
puts on the feed, and when it has risen to
the proper point he closes them. There are
usually two feed-pumps, with their appen-

The smoke-box door, opening on hinges at the top
by which that part of the engine may be
cleaned .......

The buffers, being circular cushions fixed upon the
ends of strong iron rods, which re-act against
spiral springs, to break the force in case of
collision .......

The heads of the cylinders, which are secured by
bolts and nuts, and can be taken off for the
purpose of cleansing the ash-pit

The feeding cistern on the tender

The feed-pipe proceeding from it . . . .

The coupling of the parts of the feed-pipe attached
to the engine and the tender

The coupling bar of the tender and engine . .

The coupling chain of tender and train

The buffers of the tender . ....

The lids of the feed-cistern ....

The handle of the brake upon the tender . .

The space for coke

diagram, referem

11 L

, 11

M

1 "3
I "

K'

7

K

11

f f

i 12

t

7, 12

TT'

12

\YW

13, 14
13

I"
P' Q"

13

P"

13

W"

13

Y"

13, 14

D"

14

N"

14

X"

14

B"

128

VIADUCT, NEAR WATFORD, LONDON AND NORTH-WESTERN RAIL-ROAD.

THE LOCOMOTIVE.

CHAPTER II.

23. Speed. — 24. Locomotive stock. — 25. What record of the performance
and condition of an engine should be kept. — 26. Cause of renewals of
English locomotives. — 27. Average mileage of engines. — 28. Locomo-
tive requires rest. — 29. Expense of cleaning and lighting. — 30. Keserve
engines. — 31. Bank engines. — 32. Time they are kept standing. —
33. Economy of fuel. — 34. Register of consumption. — 35. Small
amount of useful service obtained. — 36. On Belgian lines. — 37. On
other Continental lines. — 38. On London and North Western line. —
39. Comparisons between lines not fairly instituted. — 40. Legitimate
test of comparison. — 41. Amount of locomotive stock required. — 42.
Gross receipts of European Railways in 1850. — 43. Mileage of the
same. — 44. Great increase since. — 45. Enormous .consumption of
coal. — 46. Mileage of passengers and goods.

23. WHEN the extraordinary speed sometimes imparted to the
loads drawn hy locomotive engines on the English railways is
considered, it will not be uninteresting to explain what operations

LARDNER'S MUSEUM OF SCIENCE. K 129

No, 72.

THE LOCOMOTIVE.

the machinery of the engine must perform in order to accomplish
such effects.

Let us take the example, not uncommon, of a train of coaches

\

Fig, 10.

carried upon a railway, at a rate of sixty miles per hour. Assum-
ing, as in a former example, that the circumference of the driving
•wheel measures 26^ feet, these wheels, as already explained, will
revolve one hundred times in passing over half a mile, and there-
130

OPERATION OP ENGINE.

fore two hundred times in passing over a mile. The speed of sixty
miles an hour is that of a mile per minute. The driving wheels
will, therefore, revolve two hundred times per minute. But it

Ffc. 11.

w

has heen already explained that to produce one revolution of the
wheels each piston is moved once backwards and forwards in each
cylinder, and each cylinder must be twice filled with steam from

K2 131

THE LOCOMOTIVE.

the boiler, and that steam must be twice discharged from each
cylinder through the blast ppe. It follows, that to accomplish the
speed above mentioned, the boiler must supply to the cylinders

Fig. 12.

eigiit hundred measures of steam of the requisite pressure per
minute. The valves which admit this steam to each cylinder must
be opened four hundred times per minute, as must also both valves
132

NECESSARY EVAPORATION.

by which the steam is ejected. The puffs from the blast-pipe must
be made at the rate of eight hundred per minute.

If we assume that the contents of each cylinder is one cubic foot
and a quarter, then the boiler must supply to the cylinder per
minute 1000 cubic feet of steam. If this steam be assumed to
have a pressure of 50 Ibs. per square inch, then one cubic foot

of water evaporated will produce about 500 cubic feet of such
steam ; and consequently, to supply 1000 cubic feet of steam per
minute to the cylinders, the boiler must evaporate two cubic feet
of water per minute, or 120 cubic feet per hour. This is a rate of
evaporation which would correspond to a stationary boiler of a
nominal power of 120 horses.

133

THE LOCOMOTIVE.

24. When the magnitude of the capital invested in the locomo-
tive stock of a railway, jfhd the large proportion of the annual
revenue absorbed in maintaining it are considered, its economical
importance may be readily estimated.

The locomotive stock may be primarily resolved into two classes —
that which is employed in working the passenger traffic, and that
which is employed in drawing the goods trains.

The passenger engines are so constructed as to draw light loads
at great speed, the goods engines heavy loads at a low speed. In
the one, the driving-wheels are large, so as to carry the train
forward through a great space by each stroke of the piston ; in the
other, they are of more limited magnitude, in order to give the
moving power a greater leverage upon the load. In the one, they
134

LOCOMOTIVE REGISTER.

are single, rendering the engine light, so as to absorb less of the
moving power in propelling itself ; in the other, they are double
and coupled, and sometimes even tripled, so as to give a greater
purchase to the impelling power. In the one class of engine
steam of small density is consumed rapidly and in great volume ; in.
the other, steam of greater density is consumed at a slower rate.

These different mechanical requirements render it necessary, in
general, to provide a locomotive stock for the goods service, separate
from, and independent of, that provided for the passenger service.

25. In the locomotive department a register should be kept con-
taining a record of the past and current performances and condi-
tion of every engine in the service of the railway. Such a record
should contain the following particulars of the past services of each
engine : —

1st. The day and year it was put upon the road.

2nd. Its maker.

3rd. The diameter and stroke of its cylinders.

4th. The diameter and number of its driving-wheels.

5th. The number of times it was cleaned, lighted, and had
steam raised.

6th. The number of hours it was standing with steam raised.

7th. Its total mileage, from the commencement of its service to
the current date.

8th. The total quantity of fuel it had consumed.

9th. Original cost of engine.

10th. Total sum expended on its repairs.

And, with respect to its current service during the past year,
the following details should be given : —

1st. The number of times it was lighted, and had steam raised.

2nd. The number of hours it stood with steam raised.

3rd. Its mileage by months, and its total mileage.
, 4th. The quantity of fuel consumed in lighting and raising
steam.

5th. The quantity of fuel consumed in standing.

6th. The quantity of fuel consumed in working.

7th, A memorandum of any accident, or other notable circum-
stance, attending the performance of the engine.

Such a record as the above is neither impracticable nor unim-
portant. A register of this kind is kept by the administration of
the Belgian railways, and the principal results of it are published
annually, in a tabulated form, in the " Compte Rendu," or official
report of the service of the railways, delivered to the Chambers
by the Minister of Public Works every session. Such a table ex-
hibits a " coup d'ceil " of the condition and the past history of the
entire locomotive stock.

135

THE LOCOMOTIVE.

26. Iji the progress of the English railways, locomotives have
been, from time to time,^ast aside, and put, as it were, upon the
retired list ; but this has often arisen, not from the circumstance
of their being superannuated, but because the conditions of the
traffic had undergone such a change that the natural powers of
these engines were not suited to it. Immediately after the com-
mencement of the operation of the railway system, the traffic aug-
mented so rapidly as to exceed all the previsions of those who
constructed and organised the first railways. The weight and
strength of the rails were successively increased, as well as the
weight and magnitude of the trains, and the weight and power of
tine engines underwent a corresponding augmentation*

A regularly kept journal of the life of some of the oldest loco-
motives working on the English railways would be a record of
profound interest. Whether such a register exists, I am not
aware; but none such has, I believe, ever been published.

27. From a comparison of the total mileage of each class of the
locomotive stock with the number of engines in service, the average
mileage of each engine can be ascertained.

As an example of such a calculation, let us take the Belgian
railways for 1847.

The total number of engines in active service was 154, and their
total mileage was 2,366885 ; this divided by 154 gives 15369 as
the average annual mileage of each engine, the average daily
mileage being therefore 42 miles.

28. It may be asked, whether a locomotive engine, once lighted,
may not be worked almost indefinitely ?

It is known that many steam-engines used in the manufactures
and in mining are kept for several months together in unceasing
action night and day ; and the engines used in steam-ships are
often kept in incessant operation throughout a voyage of 3000
miles. Why therefore, it may be demanded, may not a locomo-
tive engine be worked for a much longer distance without inter-
ruption, and thus distribute the expense of lighting and cleaning
over a greater extent of mileage, and thereby diminish the cost
per mile ?

Although the mileage of the engine might be augmented much
beyond its present amount, it is nevertheless indispensable that it
should not exceed a certain practical limit. The locomotive engine,
an iron horse, requires intervals of repose as much as do the horses
of flesh, blood, and bones. It becomes fatigued, so to speak, with
its work, and its joints become relaxed by labour, its bolts loosened,
its rubbing surfaces heated, and often unequally expanded and
strained. Its grate-bars and fire-box become choked with clinkers,
its tubes become charged with coke; and were its labour continued
136

RESERVE ENGINES.

to a certain point, it would end in a total inability to move. The
durability of the engine, therefore, requires that its work should
be suspended before these causes of disability operate to an inju-
rious extent.

When its labour ceases, the engine-cleaners, who are, as it were,
its grooms, clean out its fireplace, scrape its grate-bars and the
internal surface of the fire-box, clean out its tubes, tighten all its
bolts and rivets, oil and grease all its moving parts, and, in a
word, put it again into working order.

29. The expense of cleaning an engine, and the cost of the fuel
consumed in lighting it and raising the steam, so as to prepare it
for propulsion, must necessarily be charged upon the mileage
which it performs ; and the cost of this mileage will therefore be
augmented in the inverse proportion of the ratio of the total
mileage of the engine to the number of times it has been cleaned
and lighted during the period of its service. It is therefore im-
portant, in the economy of the locomotive power, to ascertain with
precision the proportion which the mileage of the engines bears to
the number of times they have been cleaned and lighted.

Hence appears the importance of the record above mentioned,
of the number of times each engine has been lighted and cleaned.

To determine the average number of miles run by each engine
after such cleaning and lighting, it is only necessary to divide the
total mileage of the locomotive stock, or of each class of it, by the
total number of engines lighted ; the quotient will give the distance
run by each engine lighted.

In the practical working of the locomotive stock, it inevitably
happens that engines, after they have been lighted, had their
steam raised and prepared for starting, have to stand, keeping
their steam up more or less time, waiting for trains which they are
to draw ; and thus an expense is incurred, not directly productive,
for fuel and wages.

30. But, besides this, the service of the road requires that, at
certain stations, engines shall be kept waiting with their steam up
ready for work, for the mere purpose of providing for the contin-
gencies of the active service of the road. Thus, if an accident
occur to a train, by which the engine that draws it is disabled,
notice is sent forward by the electric telegraph, by signals or other-
wise, to the next engine station, summoning an engine to proceed
to the spot to take on the train. If an engine were not prepared
for such a contingency, with its steam up, the road would be ob-
structed for a considerable length of time by the train thus acci-
dentally brought to a stand.

The engines thus kept prepared for accidents are called Reserve
Engines.

187

THE LOCOMOTIVE.

31. Another cause wliicli renders it necessary at certain points
of the line to keep engines waiting with their steam up, is the
existence of exceptional gradients.

Thus, if a railway be generally laid out with gradients of about
15 feet a mile, but at a particular point a natural elevation of the
ground, or other cause, renders the construction of a gradient
rising at the rate of 60 feet a mile necessary, then the engines
which are adapted to the general character of the line become in-
sufficient for such exceptional gradient ; and, in such case, the
expedient resorted to is to keep one or more powerful engines con-
stantly waiting with their steam up at the foot of the incline, for
the purpose of aiding in propelling the trains in their ascent.

These engines are denominated Assistant Engines or Bank
Engines. Their mode of operation is as follows. They wait near
the foot of the incline in a siding provided for the purpose ; and
when a train arrives and begins to ascend, the assistant engine
follows it, and, pushing from behind, aids the regular engine in
front in propelling it up the plane. When it arrives at the summit,
the assistant engine drops off, and, descending the plane, returns
to its station.

32. It appeared from calculations, based on the preceding
principles, which I made some years since, that on the Belgian
lines the average distance run by each engine lighted was 78
miles, and on some of the French lines 76 miles. It also appeared
that each engine lighted was kept seven and a half hours standing
with steam up, including, of course, the reserve engines. Thus,
it follows, that for every ten miles over which an engine works,
it is kept an hour standing.

33. The fuel consumed in working a railway may be classed
under three heads : —

1st. That which is consumed in lighting the engines and raising
their steam, to prepare them for work.

2nd. That which is consumed while the engines stand with
their steam up, waiting for the trains they are intended to draw,
or standing in reserve, prepared for the contingency of accidents
on the line.

3rd. That which is consumed in drawing the trains.

"When the engine has stopped work, its fire-box is cleared, pre-
paratory to the engine being cleaned. A certain portion of coke,
more or less, according to the state of the fire-box at the moment
the engine is stopped, is collected in this way half consumed.
This coke is to a certain extent available to aid in lighting the
engine when next started. The small coke which has been
rejected as unfit for the working engine is mixed, in a greater or
less proportion, by the engineer with the large coke used for
138

ECONOMY OF FUEL.

raising the steam, for in this process the draft is not so strong as
to carry this small coke injuriously through the tubes. The small
coke is also used, mixed in a certain proportion with the large
coke, for keeping the steam up in the reserve engines.

The quantity of coke consumed in drawing a train will depend
upon the magnitude and weight of the train, and the speed with
which it is moved. The greater the resistance which it has to
overcome, the greater will be the consumption of fuel in a given
distance. The resistance increases in a high ratio with the
speed. Now as the speed of passenger trains is usually greater
than that of goods trains, the consumption of fuel, so far as it is
affected by the speed, will be greater in the former than in the
latter ; but, on the other hand, goods trains consisting of a much
greater number of vehicles and of a greater gross weight than pas-
senger trains, the resistance due to the load is greater in the latter
case than in the former.

On the Belgian railways the economy of fuel is very strictly
attended to. Rules are established by which a certain weight of
coke is allowed to the engineer for the different purposes.

For lighting and raising the steam, 280 kilogrammes, equal to

618 Ibs., of coke are allowed.
For each passenger coach drawn, f of a kilogramme per kilometre,

equal to 2 '6 4 Ibs. per mile, are allowed.
For each loaded goods waggon, f of a kilogramme per kilometre,

equal to 2 '35 Ibs. per mile, are allowed.
Two empty waggons are accounted as equal to a loaded one, and

24 kilogrammes per kilometre, equal to 8*82 Ibs. per mile,

are allowed for an engine without a load.
Ten kilogrammes, equal to 22 Ibs., per hour are allowed for

keeping up the steam while an engine is standing.

These quantities are, however, understood to be average major
limits which ought not to be exceeded. To stimulate the engi-
neers and their superintendents to the observance of a due economy
of fuel, premiums are awarded, in proportion to the extent of the
saving effected upon these allowances ; 5s. Qd. a ton is allowed to
the engineer for every ton of coke by which his actual consump-
tion falls short of these limits, and a further premium of one-
fourth of this amount is allowed to the superintendents of the
locomotive department.

34. In the locomotive department, a register should be kept of
the fuel consumed, distinguishing such consumption under the
three heads of standing, lighting, and working, together with
which should be noted the hours standing, the engines lighted,
and the mileage worked. There is nothing impracticable or
difficult in the maintenance of such a register in every well-
organised establishment, and such a one is regularly kept in the

THE LOCOMOTIVE.

administration of tjje Belgian railways. It appears from these
records, that the following was the fuel consumed for these pur-
poses respectively on the Belgian railways during the years
1846 and 1847:—

1

1846.

1847.

1 Number of hours standing

204124

214610

Number of Ibs. of coke consumed in standing

4, 5°3°77

5,306573

Average number of Ibs. consumed per hour .

22'O

247

Number of engines lighted

27452

30676

Total number of Ibs. consumed in lighting .

16,828505

18,605263

Average number of Ibs. consumed per engine

lighted

613*0

606-5

Total mileage worked ....

2,027014

2,366885

Total number of Ibs. of coke consumed in

working

60,698538

71,500965

Average number of Ibs. consumed per mile

worked

3O'O

3°'°

Average consumption per mile, including coke

consumed in lighting and standing .

40-5

40-3

It may then be stated in round numbers, that 600 Ihs. of fuel
are consumed in lighting an engine, and raising the steam, and
that every engine lighted travels, on an average, as "worked upon
the Belgian lines, 70 miles.

The fuel consumed in lighting adds, therefore, 8| Ibs. per mile
to the working consumption, which latter heing 30 Ibs., the pro-
portion consumed in lighting is 28 per cent. The fuel consumed
in standing with steam up, either as an engine of reserve or other-
wise, adds 1§ per cent, more to the working consumption per
mile, the total amount of which may be taken in round numbers
at 40 Ihs., as these railways are worked.

35. One of the most striking results of the calculations which I
have made of the performance of locomotive engines as well in
England as on the continent, is the small amount of useful service
obtained from them.

36. It appears that in each run an engine, on the Belgian lines, at
the most improved epoch of the service yet reported, did not quite
average 78 miles, and that even this was performed only four
days in seven. Thus the average daily work of an engine would
appear to be only 44 miles.

But it also appears, that for 74 miles run the engine is kept, on
an average, 7£ hours standing. This being reduced to a daily
average, leads to the conclusion, that the daily service of the
engines consisted in 44 miles run and 4 hours standing with the
steam up.

But as the average speed on the Belgian railway is about 20
140

MILEAGE OF ENGINES.

miles an hour, the run of 44 miles would occupy more than
two hours,

The daily service of an engine, therefore, expressed in time,
would be about 2 hours working and 4 waiting with steam up.

37. These inferences are so striking, that we naturally turn else-
where to inquire how far the results of other railways vary from
or corroborate them.

I accordingly made like calculations upon the statistical reports
of most of the continental railways, and found that the average
daily mileage of the engines is under 33 miles, being therefore
inferior to the useful service of the Belgian engines.

38. The data supplied by the English railways are so scanty,
and in general so vague, as to afford no adequate means of general
comparison with the results above given. In the case of the Lon-
don and North- Western lines however, a more detailed account
was published, which, "considering the great extent and traffic of
that system of railways, is entitled to much attention.

The traffic of these lines was worked, during the twelve months
ending June 30, 1849, by 457 locomotive engines, the total
mileage of which was as follows : —

Mileage.

Passenger engines . . . . 4,649556
Goods engines 2,882674

Total . 7,532230

Hence the average daily run of each engine was 45 miles.

These results, obtained from services so various and numerous,
leave no doubt that the average daily service of each locomotive
engine is much less than would have been expected. If the
average speed on the North- Western lines be taken at 28 miles
an hour, we shall obtain the singular and somewhat unexpected
conclusion, that the engines, taken one with another, are each
worked with traffic little more than one hour and a half a day.

By a return which I obtained from the North- Western Com-
pany, I found that, in the twelve months ending June 30, 1849,
they had in active employment an average number of 275 engine-
drivers, and an equal number of firemen. Now it has already
been stated, that during the same period the. number of engines
employed was 457 ; there were thus 10 engine drivers and fire-
men for every 16 engines.

By dividing the total annual mileage of the engines by the total
number of engine-drivers and firemen employed, we shall find the
total annual distance driven by each ; and dividing this by 365,
we shall obtain the average daily work of each engine-driver and
fireman, expressed in distance. This distance, divided by the

141

THE LOCOMOTIVE.

average speed in miles per hour, will give the daily work on the
road in time. The flowing are the details of this for the lines
worked by the North- Western Company : — •

Total mileage of engines . . . .7, 532230
Number of engine drivers and firemen . . 275

Annual distance worked per head . . 27390 miles
Daily distance worked per head . . . 75 ,,

Time daily on the road (at the average speed

• of 28 miles per hour) .... 2| hours

If it be assumed that the engines, one with another, work on
alternate days, the actual distance run in each trip by each
engine on the system of lines worked by the North- Western Com-
pany will be 90 miles ; which in time, at 28 miles an hour, would
he 3^ hours.

It appears, therefore, that the locomotive power is worked to
greater advantage on these than on the continental lines generally.
We have seen that the average distance run by each engine lighted
on the Belgian lines was about 78 miles.

39. It has been customary, in some of the reports presented to
the railway companies, to institute comparisons between one line
of railway and another, founded upon the relation between the
locomotive stock and the length of the line.

Now such a mode of comparison can afford no legitimate conse-
quence of the least importance, either in a financial or mechanical
point of view. The quantity of locomotive power does not in any
manner depend on the length of the railway. The locomotive
power is used to draw the traffic, and for no other purpose. Its
quantity, therefore, will depend on the quantity of the traffic,
and the average distance to which it is carried, or, in other words,
on the mileage of the goods and passengers.

Two railways having the same traffic mileage will require the
same locomotive stock, be their length equal or unequal. If a
million of tons of goods require to be annually transported an
average distance of 500 miles, and ten millions of passengers
also require to be annually transported 300 miles, it is manifest,
that the same locomotive power will be requisite to execute the
traffic, whether the railway on which it is carried be 400 miles or
800 miles in length.

If the object be to compare the merits of the management of
the locomotive power, then the test of comparison should be the
quantity of work executed by a given quantity of this power ; and
the quantity of work must be decided by the useful mileage of
the engines, and not by the length of the line.

Nevertheless, we find railway authorities in high repute
announcing, that to stock a line requires so many engines per
142

LOCOMOTIVE STOCK.

mile. To such a statement there can be no objection, provided
it be made with the understanding that it applies to railways-
only which have a certain understood amount of average traffic.

But it is clear that, with every variation of the traffic upon the
proposed railway, there must be a corresponding and proportional
variation in the necessary amount of locomotive stock.

40. A legitimate mode of comparing the merits of the manage-
ment of the locomotive department will be found in the estimate
of the average daily mileage of the engines.

It is evident, that if we find on one railway — for example, the
North-Western, — the engines performing a daily mileage of 45
miles, while on another — the North of France, we find them per-
forming a daily service under 30 miles, that the locomotive stock
in the one case was more profitably managed than the other in
the ratio of 2 to 3, it being understood that other things are similar.
But even in this comparison it would be necessary that the length
and weight of the trains should be taken into account ; for if it
prove that the weight of the train drawn 30 miles is greater than
the weight of the train drawn 45 miles in the proportion of 3 to
2, then the useful labour of the engines will, after all, be the
same. In short, the test, and the only test, of the useful effect of
the locomotive power is the actual mileage (including in that term
the quantity) of the traffic which it executes in a given time.

41. The conditions which determine the amount of the loco-
motive stock necessary to work any given railway form a very
important subject of inquiry in railway economy; but it is a subject
upon which we as yet possess but scanty and unsatisfactory data.
As has been already stated, railway authorities have, with more
rashness than skill, given a sort of rough estimate of it at so much
per mile. This must, however, be regarded as utterly unworthy
of attention, for the very intelligible reasons already explained.

The amount of locomotive stock depends exclusively on the
mileage of the traffic. The question is thus reduced to the determi-
nation of the number of engines necessary to work a given mileage.

If we assume the results of the working of the North-Western
lines as a general modulus, it would follow, that to find the
quantity of stock necessary for working a given daily mileage,
it will be sufficient to divide this mileage by 45 ; the quotient
will express the requisite number of locomotive engines.

42. From calculations based upon authentic statistical returns
which were published in a series of articles, written by me for the
"Times," in 1851, it appeared, that in the year 1850, the gross
receipts of all the European railways then in operation, amounted
to 23,309000/., of which 12,755000^., or about the half, was
collected on the railways of the United Kingdom.

143

THE LOCOMOTIVE.

Of this amount about 60 per cent has been expended on per-
sonal locomotion, and«40 per cent on the transport of goods of
every denomination.

43. The movement of the locomotive engines in executing this
traffic has been as follows : —

Miles run by engines.

United Kingdom 40,162000

Germanic States 23,572000

'France 10,041000

Belgium . . 4,540000

Total distance travelled by locomotive engines

in 1850 .... . . 78,315000

44. Since the date of these calculations, the amount of railway
locomotion, as well in the United Kingdom as throughout
Europe generally, has undergone a great increase. Thus, in the
half year ending 30th June, 1852, the gross receipts of the rail-
ways in the United Kingdom amounted to 7,19555U.

The mileage, or aggregate distance travelled by the locomotive
engine, has increased in a proportion still greater than the in-
crease of the gross receipts. Thus, while in 1850, the total
annual mileage of the engines on the railways of the United
Kingdom was about forty millions, in the first six months of 1852
it was twenty-eight and a half millions, being at the rate of
fifty-seven millions in the year.

It may now (1854) be assumed that the aggregate annual
mileage of the locomotive engines on all the European railways is
not less than an hundred and twenty millions of miles !

45. In the performance of this work, the total quantity of coal
consumed is two millions and three quarters of tons.

46. This movement is shared between passengers and goods as
follows : —

Distance travelled by passenger trains . . 72,000000
„ ,, goods „ . . . 48,000000

Since each passenger train transported on an average 70 pas-
sengers, and each goods train 60 tons, it follows that the total loco-
motion of persons within the year was equivalent to 5040,000000
persons carried one mile, and the transport of goods to
2880,000000 tons transported one mile.

The number of locomotive engines employed in executing this
movement was about 7500, of which 3700 were employed on the
British railways, and about 5000 were constructed in England.

144

Fig 5.

F g. 6.

METHOD OP DETERMINING THE BOILING POINT.

THE THERMOMETER.

1. Heat. — 2. Sensible heat— 3. Latent heat. — 4. Contraction and dilatation.

— 5. Liquefaction and solidification. — 6. Vaporisation and Condensa-
tion. — 7. Incandescence. — 8. Combustion. — 9. Temperature. — 10.
Conduction. — 11. Radiation. — 12. Some bodies are pervious to heat. —
13. Some reflect heat. — 14. Means of measuring the degrees of heat,

— 15. Mercurial thermometer. — 16. Preparation of mercury. — 17.
Selection of tube. — 18. Formation of bulb. — 19. How the tube is
filled.— 20. Scale applied.— 21. Graduation of scale.— 22. Zero
point. — 23. Standard points. — 24. Freezing and boiling temperatures
\miversally adopted. — 25. Fahrenheit's scale. — 26. Centigrade. — 27.
Reaumur's. — 28. Increase of volume of mercury. — 29. Uniformity of
its dilatation. — 30. Standard thermometer. — 31. Range of scale. —
32. Why mercury is employed in thermometers. — 33. Self- registering
thermometers. — 34. Alcohol thermometers. — 35. Air thermometer.

— 36. Differential thermometer.

1. HEAT is one of the physical agencies upon which the well-
being of organised nature in general, and of the human race in
particular, is most essentially dependent. The instruments,
therefore, which have been contrived for indicating and measuring
its quantity and degrees have great interest and importance,

LARDNER'S MUSEUM OF SCIENCE. L 145

No. 75.

THE THERMOMETER.

not only in physical science, but in the arts and in domestic
economy.

2. But to comprehend clearly the principle and application of
these instruments, it is first necessary to obtain some acquaintance
with the principal effects of heat, upon which their indications
depend, and the degrees of which they are applied to measure.

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

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

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

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

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

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

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

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

6. If heat be imparted in sufficient quantity to a body in the
liquid state, it will pass into the state of vapour. Thus, water
being heated sufficiently, will pass into the form of steam. This
change is called vaporisation. .

146

EFFECTS OF HEAT.

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

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

7. Heat, when imparted to bodies in a certain quantity, will in
some cases render them luminous.

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

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

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

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

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

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

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

The phenomena of combustion and properties of combustibles
have been fully explained in our Tract on •* Fire."

9. The degree of sensible heat by which a body is affected,
is called its temperature, and the instruments by which the
temperature of bodies is indicated and measured are called
thermometers and pyrometers ; the latter term being applied to
those which are adapted to the measurement of the higher order
of temperatures.

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

L 2 147

THE THERMOMETER.

10. When heat is communicated to any part of a body, the
temperature of that part 1s momentarily raised above the general
temperature of the body. This excessive heat, however, is
gradually transmitted from particle to particle throughout the
entire volume, .until it becomes uniformly diffused, and the
temperature of the body becomes equalised.

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

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

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

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

12. Certain bodies are pervious to the rays of heat, just as glass
and other transparent media are pervious to the rays of light.
They are called diathermanous bodies. Thus, atmospheric air and
gaseous bodies in general are diathermanous.

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

Bodies are diathermanous in different degrees.

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

13. The surfaces of bodies also reflect heat in different
148

EFFECTS OF HEAT.

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

14. Of all the various effects of heat, that which is best adapted
to indicate and measure temperature is dilatation and
contraction. The same body always has the same

volume at the same temperature, and always suffers
the same change of volume with the same change of
temperature.

Since the volume and change of volume admit of
the most exact measurement and of the most precise
numerical expression, they become the means of sub-
mitting the degrees of warmth and cold, or, which is
the same, the degrees of temperature, to arithmetical
measure and expression.

Although all bodies whatever are susceptible of
dilatation and contraction by change of temperature,
they are not equally convenient for thermoscopic
agents.

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

15. The mercurial thermometer consists of a capil-
lary * tube of glass, (fig. 1), at one end of which a
thin spherical or cylindrical bulb is blown, the bulb
and a part of the tube being filled with mercury.

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

It is found that the dilatability of mercury is greater than the

* So called from its bore being so small as not to exceed the diameter of
a hair, the Latin word CAPILLA signifying a hair.

149

THE THERMOMETER.

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

The space through which the mercury will rise in the tube by
a given increase of temperature will be greater or less according
to the proportion which the tube bears to the capacity of the
bulb. The smaller that proportion, the greater will be the
elevation of the column produced by a given increase of tem-
perature ; for a given increase of temperature will produce a
definite increase of volume in the mercury, and this increase
of volume will fill a greater space in the tube in proportion to the
smallness of the bore compared with the capacity of the bulb.

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

For this purpose it is necessary, in the first instance, that the
mercury with which the tube is filled shall be perfectly pure and
homogeneous. This object is attained by the same means as have
been already explained in the case of the barometer.*

17. In the selection of the tube it is necessary that it be
capillary, that is to say, a tube having an extremely small bore,
and that the bore should be of uniform magnitude throughout its.
entire length.

The smallness of the bore is essential to the sensibility of the
instrument, as already explained ; and its uniformity is necessary
in order that the same change of volume of the mercury should
correspond to the same length of the column in every part of
the tube.

The uniformity of the bore of the tube may be tested by letting
into it a small drop of mercury, sufficient to fill about a third of
an inch of the tube. Let this be made to fall gradually through
the entire length of the tube, stopping its motion at intervals, and

* See our Tract on "The Barometer."
150

FILLING THE TUBE.

let the space it occupies at different parts of the tube be measured.
If this space be everywhere the same, the bore is uniform ; if not,
the tube must be rejected.

18. The bulb, whether spherical or cylindrical, can be formed
upon the end of the tube by the ordinary process of glassblowing.
The sensibility of the thermometer requires that the capacity of
the bulb should bear a large proportion to the calibre of the tube.
If, however, the capacity of the bulb be considerable, the quantity
of mercury it contains may be so great that it will not be affected
by the temperature of the surrounding medium with sufficient
promptitude.

A cylindrical bulb of the same capacity will be more readily
affected by the temperature of the surrounding medium than a
spherical bulb, since it will expose a greater surface.

The glass of which the bulb is formed should be as thin as is
compatible with the necessary strength, in order that the heat may
pass more freely from the external medium to the mercury.

19. The tube to be filled is represented in fig. 2, where B A c is
a tube, and c D a reservoir formed at the

top for the purpose of filling it, which is
to be afterwards detached. Let the tube
be first dried by holding it over the flame
of a spirit-lamp, so as to evaporate and
expel all moisture which maybe attached
to the inner surface of the glass. To fill
it, let a quantity of purified mercury be
poured into the reservoir c D. This will
not fall through the bore, being prevented
by the air included in the reservoir A B
and in the tube. To expel this, and cause
the mercury to take its place, let the tubo
be placed in an inclined position over a
charcoal fire or the flame of a spirit-lamp,
so that the air shall be heated. When
heated it will expand, force itself in
bubbles through the mercury in c D, and
escape into the atmosphere. This will
continue until all the air in the bulb A B
and in the tube A c has been expelled.
The pressure of the atmosphere acting on
the mercury in c D will then force it
through the tube into the bulb A B, which,
as well as the entire length of the tube,
it will ultimately fill. If a sufficient quantity of mercury be
supplied to the reservoir c D, the bulb A B, the tube A c, and a

151

THE THERMOMETER.

part of the reservoir c D, will be filled with mercury after all the
air has been expelled. "

When this has been accomplished, let the tube be removed from
the source of heat, and allowed gradually to cool. A file applied
at c, where the top of the tube is joined to the superior reservoir,
detaches that reservoir from the tube, which remains with the
bulb A B completely filled with mercury.

In this state the instrument would give no indication of change
of temperature, no space being left for exhibiting the play of the
mercury by dilatation and contraction.

To obtain space for this, let the bulb A B be exposed to a tem-
perature higher than any which the instrument is intended to
indicate. The mercury dilating will then overflow, and will con-
tinue to overflow until the mercury acquires the extreme
temperature to which it is exposed.

A jet of flame being now directed by a blow-pipe (fig. 3), on

the end c, it will
be hermetically *
sealed; after which,
'^ being allowed to
cool, the mercurial
column will subside,
the space in the tube
above it being a
vacuum, since the
air is expelled. The
column will continue to subside until the mercury assumes that
state which corresponds to the temperature of the air surrounding
the instrument.

20. The variation of the height of the mercurial column in such
a tube will in all cases correspond with the changes of tempera-
ture incidental to the surrounding medium ; but, in order that it
may supply a numerical expression and measure of such changes,
a scale must be attached to the tube, by which the variations of
the column may be indicated, and the divisions or units of such
scale must correspond to some known change of temperature. It
is evident that such a scale, like all other standards for the

* An opening of a tube or vessel is said to be hermetically closed or
sealed when the material of the tube or vessel itself is fused around it, and
the edges when thus soft brought together so as to close the opening, being
then allowed to harden by cold as sealing-wax does. The term <4 hermeti-
cally " means chemically, the science of alchemy which preceded chemistry
being supposed to have been invented by Hermes Trismegistus. So that
"hermetically sealed or closed" means to be sealed or closed in the manner
adopted in chemical vessels.
162

STANDARD POINTS.

arithmetical measure of physical effects, must be to some extent
arbitrary. We accordingly find different scales and different
thermometric units prevailing in different countries, and even
in the same country at different times.

21. Whatever thermometric unit be adopted, it is necessary
that two standard temperatures be selected, to which the mercury
can be reduced at the times and places where thermometers may
be required to be constructed or verified. The instrument being
exposed to these two temperatures, the points at which the mer-
curial column stands are marked upon the scale. The space upon
the scale between these points is then divided into a certain
number of equal parts, which are called degrees, the degree
being the thermometric unit. The same divisions are then con-
tinued upon the scale above the higher and below the lower
standard point, and such divisions may be continued indefinitely.
The scale is then complete.

In this process, the number of equal parts into which the space
between the standard points is divided, is altogether arbitrary.

22. It now remains to number the scale ; and, for this purpose,
a zero point must be selected. If there existed a minor limit to
temperature, a temperature below which no body could possibly
fall, then such a temperature would supply a natural thermometric
zero, and the scale might be numbered upwards from it.

In that case, although the thermometric unit would still remain
arbitrary, the zero of the scale would not be so. But no such
natural thermometric zero exists.

There is no natural limit either to the increase or diminution of
temperature. The zero, therefore, of the thermometric scale, like
the thermometric scale itself, must be arbitrary.

23. Thermal phenomena present great varieties of standard
temperatures, by which thermometric scales may be established,
and which may serve equally as terms of temperature for the pur-
pose of distinguishing the indications of different thermometers
constructed at different times and places. Thus, the temperatures
at which all solid bodies fuse, and those at which all liquids con-
geal, are fixed. For different bodies these are different, but
always the same for the same body. In like manner, the tem-
peratures at which all liquids boil under a given pressure are
invariable for the same liquids, though different for different
liquids. The temperature of the blood in the human species
presents another example of a fixed temperature.

24. Now, any two of these various temperatures naturally fixed
might be taken as the thermometric standards, the choice being
altogether arbitrary. Thus, it appears that the arithmetical
division of the scale, and consequently the thermometric unit, the

153

THE THERMOMETER.

Fig. 4.

position of its zero, a^d, in fine, the standard temperatures by
which alone the indication of different thermometers can be ren-
dered comparable, are severally arbitrary. Unanimity, never-
theless, has prevailed in the selection of standard temperatures.
The temperature at which ice melts, and that at which distilled
water boils, when the barometer stands at 29-8 inches, have
been adopted in all countries as the two temperatures with refer-
ence to which thermometric scales are constructed.

The bulb and tube, as already described, being filled with pure
mercury, and a blank scale being attached to the tube, the instru-
ment is immersed successively in melting ice and boiling water,
and the points at which the mercurial column stands in each case
are marked upon the scale. The former is called the FREEZING-
POINT, and the latter the BOILING-POINT.

The apparatus by which the freezing point is determined is
shown in fig. 4. The thermometer is
immersed nearly to the level of the
mercury in a vessel of pounded ice,
which being in a state of fusion, the
water proceeding from it discharged
through a funnel in the bottom is re-
ceived in a vessel placed under it.

The apparatus for determining the
boiling point is shown in fig. 5, where
D is the boiler, placed over a charcoal
furnace, the whole being shown in sec-
tion in fig. 6, p. 145. From the top of
the boiler a tube proceeds, open at the
top, which is enveloped in another
larger one, A, closed at the top, and
soldered at the bottom to the top of the
boiler. In the external tube A, there
are three openings, in one of which, m,
the tube of the thermometer T is in-
serted. In another, a siphon mercurial
gauge G H, and in the third a discharge
pipe c B, is inserted. When the water

boils the steam rises, surrounding the bulb and tube, and
descending between the two tubes, issues from the discharge pipe
B. If the steam be generated too rapidly in the boiler, it will
press on the mercury in the gauge, which will then stand at a
higher level, w, in the ascending than in the descending leg.
The pressure of the steam will be in that case greater than that of
the atmosphere, and the force of the furnace must be moderated
until the levels of the mercury in the two legs of the siphon-
154

DIFFERENT SCALES.

coincide. In that case the pressure of the stearn will be exactly
equal to that of the atmosphere.

25. The same unanimity has not prevailed either as respects
the unit or the thermometric zero. In England, Holland, some
of the German States, and in North America, the interval between
the freezing and boiling points is divided into 180 equal parts,
each part representing the thermometric unit. The scale is
continued by equal divisions above the boiling and below the
freezing points.

The zero is placed at the thirty-second division below the freez-
ing point ; so that, on this scale, the freezing point is 32°, and the
boiling point 32°+lSOD=212°.

This scale is known as Fahrenheit's, and was adopted about
1724.

The reason for fixing the zero of the scale at 32° below the
freezing point is, that that point indicated a temperature which
was at that time believed to be the natural zero of temperature,
or the greatest degree of cold that could exist, being the most
intense cold which had been observed in Iceland.

We shall see hereafter that much lower temperatures, natural
and artificial, have been since observed.

The division of the interval between the freezing and boiling1
points into 180 equal parts was founded upon some inexact suppo-
sition connected with the dilatation of mercury.

.The divisions of this scale are continued in the same manner
below zero, such divisions being considered negative, and expressed
by the negative sign prefixed to them. Thus, + 32° signifies 32°
above zero, but — 32° signifies 32° below zero.

26. In France, Sweden, and some other parts of Europe, the
Centigrade scale prevails.

In this scale the interval between the freezing and boiling points
is divided into 100 equal parts, and the zero is placed at the
freezing point.

27. In some countries the scale of Reaumur is used, in which the
interval between the freezing and boiling points is divided into
eighty equal parts, the zero being placed at the freezing point.

28. It has been ascertained by experiment, that mercury, when
raised from 32° to 212°, suffers an increment of volume amounting
to 2-11 Iths of its volume at 32°. Thus, 111 cubic inches of mer-
cury at 32° will, if raised to 212°, become 113 cubic inches.
From this may be deduced the increment of volume which mer-
cury receives for each degree of temperature. For, since the
increase of volume corresponding to an elevation of 180° is T£T of
its volume at 32°, we shall find the increment of volume corre-
sponding to one degree by dividing TfT by 180, or, what is the

155

THE THERMOMETER.

same, by dividing ,4^. by 90, which gives ^y^. For each degree
of temperature by wftich the mercury is raised, it will therefore
receive an increment of volume amounting to the 9990th part of
its volume at 32°, and it follows, that the weight of mercury which
fills the portion, of a thermometric tube representing one degree
of temperature, will be the 9990th part of the total weight con-
tained in the bulb and tube.

29. In adopting the dilatation of mercury as a measure of
temperature, it is assumed that equal dilatations of this fluid are
produced by equal increments of heat. Now, although it is
certain that to raise a given quantity of mercury from the freez-
ing to the boiling point will always require the same quantity of
heat, it does not follow that equal increments of volume will
correspond to equal increments of heat throughout the whole
extent of the thermometric scale. Thus, although the same
quantity of heat must always be imparted to the mercury contained
in the tube to raise it from 32° to 212°, it may happen that more
or less heat may be required to raise it from 32° to 42°, than from
202° to 212°. In other words, the dilatation produced by equal
increments of heat, in differents parts of the scale, might be
variable. Experiments conducted, however, under all the con-
ditions necessary to ensure accurate results, have proved that
mercury is uniformly dilated between the freezing and boiling
points, or that equal increments of heat imparted to it produce
equal increments of volume.

30. A thermometer having once been carefully graduated may
be used as a standard instrument for graduating other ther-
mometers, just as good chronometers once accurately set are used
as regulators for other time-pieces. To graduate a thermometer
by means of such a standard, it is only necessary to expose the
two instruments to the same varying temperatures, and to mark
upon the blank scale of that which is to be graduated two points
corresponding to any two temperatures shown by the standard
thermometer, and then to divide the scale accordingly.

Thus, for example, if the two instruments be immersed in
warm water and the column of the standard thermometer be
observed to indicate the temperature of 150°, let the point at
which the mercury stands in the other thermometer be marked
150 upon its scale.

Let the two instruments be then immersed in cold water and
let us suppose that the standard thermometer indicates 50°. Let
the point at which the instrument to be graduated stands be then
marked. Let the intervals of the scale between these two points,
thus corresponding to the temperatures of 50° and 150°, be
divided into one hundred equal parts ; each part will be a degree

156

STANDARD THERMOMETER.

in the scale, which may be continued by like divisions above 150°
and below 50°.

31. The range of the scale of thermometers is determined by the
purpose to which they are to be applied. Thus, thermometers
intended to indicate the temperature of dwelling-houses need not
range above or below the extreme temperatures of the air, and
the scale does not usually extend much below the freezing point
nor above 100°; and thus the sensitiveness of the instrument may
be increased, since a considerable length of the tube may represent
a limited range of the scale.

32. Mercury possesses several thermal qualities which render
it a convenient fluid for common thermometers. It is highly
sensitive to change of temperature, dilating with promptitude by
the same increments of heat with great regularity and through
a considerable range of temperature. It will be shown hereafter
that a smaller quantity of heat produces in it a greater dilata-
tion than in most other liquids. It freezes at a very low and
boils at a very high temperature. At the temperatures which are
not near these extreme limits, it expands and contracts with
considerable uniformity.

The freezing point of mercury being — 40°, or 40° below zero,
and its boiling point + 600°, such a thermometer will have
correct indications through a very large range of temperature.

33. It is sometimes needed, in the absence of an observer, to
ascertain the variations which may have taken place in a ther-
mometer. Instruments called self- registering thermometers have
been contrived, which partially serve this purpose by indicating,
not the variations of the mercurial column, but the limits of its
play within a given time. This is accomplished by floating
indices placed on the mercury within the tube, which are so
adapted that one is capable of being raised with the column, but
not depressed, and the other of being depressed, but not raised.
The consequence is, that one of these indices will remain at the
highest, and the other at the lowest point which the mercurial
column may have attained in the interval, and thus register the
highest point and lowest point of its range.

One of the most common and useful forms of self-registering
thermometer is that of Rutherford, shown in fig. 7, which consists
of two tubes, attached in a horizontal position to a plate of glass,
being bent at right angles near the bulbs ; one, A, containing
mercury and the other, B, alcohol. In the tube of the former
there is a small piece of iron wire, which moves in it freely, being
pushed along by the mercury as it expands. When the tube is placed
in the vertical position the wire falls back upon the mercury.

The other tube contains a small piece of coloured glass, having

157

THE THERMOMETER.

a knob at each end, which allows the alcohol to pass it freely
from right to left. Hut when the alcohol contracts and moves

towards the bulb, it carries with it the glass index, which conse-
quently remains in the position given to it when exposed to the
lowest temperature.

The instrument, therefore, after the lapse of any time, indi-
cates the highest and lowest temperatures to which it has been
exposed. A small magnet is sometimes attached, to aid in bring-
ing the wire gently into contact again with the mercury, and in
cheap instruments, especially in England, the scale is engraved
on a slab of wood instead of a plate of glass.

A maximum and minimum thermometer has lately been intro-
duced by Messrs. JSTegretti and Zambra, which is a modification
of the above. Having introduced into the tube a little rod of
glass, the tube is softened with the blow-pipe, and slightly bent
where the glass rod stands, so that it becomes fixed in the tube,
leaving nevertheless sufficient space around it for the mercury to
pass. Supposing, then, the instrument to be suspended with the
tube horizontal, and exposed to an increasing temperature, the
mercury passes the bend ; but when the temperature falls, the mer-
cury which has just passed will not return. The extremity of the
column will therefore indicate the highest temperature to which
the instrument has been exposed. This instrument is represented
in fig. 8.

34. Alcohol is frequently used as a thermoscopic liquid. It has
the advantage of being applicable to a range of temperature
below the freezing point of mercury ; no degree of cold yet ob-
served in nature or attained by artificial processes having frozen
it. It is usually coloured so as to render the column easily
observable in the tube.

35. Atmospheric air is a good thermoscopic fluid. It has the
158

DIFFERENTIAL THERMOMETERS.

advantage over liquids in retaining its gaseous state at all tem-
peratures, and in the perfect uniformity of its dilatation and

Fig. 8.

Co'

10 0' 12,0

Fig.

o

contraction. It is also highly sensitive, indicating changes of
temperature with great promptitude. Since, however, it is not
visible, its expansion and contraction must be rendered
observable by expedients which interfere with and
render complicated its indications.

The air thermometer of Drebbel, or according to some
of Sanctorius, is represented in fig. 9. A glass tube,
A B, open at one end, and having a large thin bulb
c at the other, is placed with its open end in a coloured
liquid, so that the air contained in the tube shall have
a less pressure than the atmosphere. A column of the
liquid will therefore be sustained in the tube A B,
the weight of which will represent the difference
between the pressure of the external air and the air
inclosed in the tube.

If the bulb c be exposed to a varying temperature, the air
included in it will expand and contract, and will cause the column
of coloured liquid in the tube A B to rise and fall,
thereby indicating the changes of temperature.

Another form of air thermometer is represented in
fig. 10. The air included fills half the capacity of the
bulb c, and its expansion and contraction cause the
coloured liquid to rise or fall in the tube A B.

36. Of all forms of air thermometer, that which
has proved of greatest use in physical enquiries is the
c differential thermometer represented in figs. 11, 12.
This consists of two glass bulbs, A and B, 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 con-
tained in the bulbs and tube, separated into two parts by the

159

Fig. 10.

THE THERMOMETER.

liquid. The instrument is so adjusted that, when the drop of
liquid is at the middle oT the horizontal tube, the air in the bulbs

Fig. 11.

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 temperatures, the liquid will be driven from

Fig. 12.

that side at which the temperature is greatest, and the extent of
its departure from the zero or middle is indicated by the scale.

By these instruments changes of temperature, not exceeding
the 6000th part of a degree, are rendered sensible.

160

MR. BISHOP'S OBSEEVATORY, REGENT'S PARK, MEMORABLE BY THE DISCOVERY
THERE OP ELEVEN PLANETS.

THE NEW PLANETS.

1. — Discovery of these planets. — 2. The old planets. — 3. Numerical law
of their distances. — 4. A missing planet. — 5. Conjecture of Professor
Bode.— 6. Discovery of Ceres.— 7. Of Pallas. — 8. Theory of Dr.
Olbers — a broken planet. — 9. Discovery of Juno. — 10. Of Vesta. —
11. Rapid discovery of the others. — IV. Table of the group.
— 13. Circumstances corroborating the theory of Dr. Olbers. —
14. Amateur astronomers. — 15. Minute bulk of these planets. —
16. Corroboratory of Dr. Olbers' theory. — 17. Force of gravity upon
them.

1. WITHOUT being astronomers, every one who reads the
newspapers must be familiar with the fact, that within the last
few years a multitude of small planets has been discovered,
which, notwithstanding the vigilance and sagacity of observers,
in various parts of Europe, had hitherto escaped notice. As the
circumstances attending and preceding this extraordinary mass
of astronomical discovery are novel and interesting, we propose at
present to bring them before our readers.
LARDNER'S MUSEUM OP SCIENCE. M 161

No. 76.

THE NEW PLANETS.

2. Almost every one who knows anything beyond the limits of
the most ordinary education*, is aware that the solar system, as it
was known until the last hundred years, consisted of six planets,
which, proceeding outwards from the sun, received the mytholo-
gical names of Mercury, Venus, the Earth orTellus, Mars, Jupiter,
and Saturn. It is now about three-quarters of a century since the
late Sir William Herschel added one to this number, by the dis-
covery of the planet since called Uranus, revolving outside the
orbit of Saturn.

3. On comparing the successive distances of these several
planets from the sun, it was observed by Kepler, that a remark-
able numerical harmony prevailed among them. Thus, if we
begin from the nearest planet to the sun, Mercury, and measure
the intervals between planet and planet proceeding outwards, it
will be found that each successive interval is almost exactly
double the one before, subject, nevertheless, to a striking excep-
tion in the case of the interval between Mars and Jupiter.

4. Although this remarkable arithmetical harmony was not
fulfilled with that numerical precision which characterises some
other astronomical laws, there was, nevertheless, so striking an
approximation to it as to produce a strong impression, that it
must be founded upon some physical cause, and not merely acci-
dental. The near approximation to its exact fulfilment, supplied
grounds for a very reasonable conjecture, that a planet was
wanting in the system, whose position between Mars and Jupiter
would be such as to fill the vacant place in the progression of
distances.

To show how strong the analogy was in favour of such a sup-
position, we have placed in the following table the succession of
calculated distances from Mercury's orbit, which will exactly
fulfil it, in juxtaposition with the actual distances of the planets,
the earth's distance from the sun being the unit.

Calculated distance
from Mercury.

Actual distance
from Mercury.

Venus
Earth .
Mars
Absent planet
Jupiter
Saturn
Uranus .

0-3362
0-6724
I'3448
2-6896

5'3792
10-7584.
21-5168

0-3362
0-6129
1-1366

4-8157
9-1517
187953

By comparing these numbers, it will be apparent, that although
the succession of distances does not correspond precisely with a t
162

DISCOVERY OP CERES AND PALLAS.

numerical series in duple progression, there is nevertheless a cer-
tain approach to such a series, and at all events a glaring breach
of continuity between Mars and Jupiter.

5. Towards the close of the last century, Professor Bode, of
Berlin, revived this question of a deficient planet, and gave the
numerical progression which indicated its absence in the form in
which it has just been stated ; and an association of astronomers
was formed under the auspices of the celebrated Baron de Zach,
of Gotha, to organise and prosecute a course of observation,
with the special purpose of searching for the supposed undis-
covered member of the solar system. The very remarkable
results which have followed this measure, the consequences
of which have not even yet been fully developed, will presently
be apparent.

6. On the first day of the present century, Professor Piazzi
observing in the fine serene sky of Palermo, noticed a small star
of about the 7th or 8th magnitude which was not registered in
the catalogues. On the night of the 2nd Jan. again observing it, he
found that its position relative to the surrounding stars was sen-
sibly changed. The object appearing to be invested with a nebu-
lous haze, he took it at first for a comet, and announced it as such
to the scientific world. Its orbit being, however, computed by
Professor Gauss, of Gottingen, it was found to have a period of
1652 days, and a mean distance from the sun expressed by 2*735,
that of the earth being 1.

By comparing this distance with that given in the preceding
table at which a planet was presumed to be absent, it will be seen
that the object thus discovered filled the place with striking arith-
metical precision.

Piazzi gave to this new member of the system the name
CERES.

7. Soon after the discovery of Ceres, the planet passing into
conjunction ceased to be visible. In searching for it after emerg-
ing from the sun's rays in March, 1802, Dr. Olbers noticed on the
28th a small star in the constellation of Virgo, at a place which
he had examined in the two preceding months, and where he
knew that no such object was then apparent. It appeared as a
star of the seventh magnitude, the smallest which is visible
without a telescope. In the course of a few hours he found
its position visibly changed in relation to the surrounding stars.
In fine, the object proved to be another planet, bearing a
striking analogy to Ceres, and what was then totally unprece-
dented in the system, moving in an orbit at very nearly the same
mean distance from the sun, and having, therefore, nearly the
same period.

M 2 163

THE NEW PLANETS.

Dr. Olbers called this planet PALLAS.

8. This circumstance, combined with the exceptional minute-
ness of these two planets, suggested to Olbers the startling, and
then, as it must have appeared, extravagantly improbable hypo-
thesis, that a single planet of the ordinary magnitude existed
formerly at the distance indicated by Bode's analogy,— that it
was broken into small fragments either by internal explosion from
some cause analogous to volcanic action, or by collision with a
comet, — that Ceres and Pallas were two of its fragments, and in
fine, that it was very likely that many other fragments, smaller
still, were revolving in similar orbits, many of which might
reward the labour of future observers who might direct their
attention to these regions of the firmament.

In support of this curious conjecture, it was urged that in the
case of such a catastrophe as was involved in the supposition, the
fragments, according to the established laws of physics, would
necessarily continue to revolve in orbits, not differing much in
their mean distances from that of the original planet ; that the
obliquities of the orbits to each other and to that of the original
planet might be subject to a wider limit ; that the eccentricities
might also have exceptional magnitudes ; and, finally, that such
bodies might be expected to have magnitudes so indefinitely
minute as to be out of all analogy or comparison, not only with
the other primary planets, but even with the smallest of the
secondary ones.

Ceres and Pallas were both so small as to elude all attempts
to estimate their diameters, real or apparent. They appeared
like stellar points with no appreciable disk, but surrounded with
a nebulous haziness, which would have rendered very uncertain
any measurement of an object so minute. Sir W. Herschel
thought that Pallas did not exceed 75 miles in diameter. Others
have admitted that it might measure a few hundred miles. Ceres
is still smaller.

The obliquity of the orbit of Ceres to the plane of the ecliptic
is above 10^°, and that of Pallas more than 34|°. Both planets,
therefore, when most remote from the ecliptic pass far beyond the
limits of the zodiac, and differ in obliquity from each other by
a quantity far exceeding the entire inclination of any of the older
planets.

It was further observed by Dr. Olbers, that at a point near the
descending node of Pallas, the orbits of the two planets very nearly
coincided.

Thus it appeared that all the conditions which rendered these
bodies exceptional, and in which they differed from the other
members of the solar system, were precisely those .which were
164

DISCOVERY OF JUNO AND VESTA.

consistent with the hypothesis of their origin advanced by
Dr. Gibers.

9. A year and a half elapsed before any further discovery was
produced to favour this hypothesis. Meanwhile, observers did
not relax their zeal and their labours, and on Sept. 1, 1804, at
ten o'clock, P.M., Professor Harding, of Lilienthal, discovered
another minute planet, which observation soon proved to agree
in all its essential conditions with the hypothesis of Olbers,
having a mean distance very nearly equal to those of Ceres
and Pallas, an exceptional obliquity of 13°, and a considerable
eccentricity.

This planet was named Juxo.

Juno has the appearance of a star of the 8th magnitude, and a
reddish colour. It was discovered with a very ordinary telescope,
of 30 inches focal length and 2 inches aperture.

10. On the 29th of March, 1807, Dr. Olbers discovered another
planet, under circumstances precisely similar to those already
related in the cases of the former discoveries. The name VESTA
was given to this planet, which, in its minute magnitude, and the
character of its orbit, was analogous to Ceres, Pallas, and Juno.

Yesta is the brightest, and, apparently, the largest of all this
group of planets ; and, when in opposition, may be sometimes
distinguished by good and practised eyes without a telescope.
Observers differ in their impressions of the colour of this
planet. Harding and other German observers consider her to
be reddish ; others contend that she is perfectly white. Mr. Hind
says that he has repeatedly examined her under various powers, and
always received the impression of a pale yellowish cast in her light.

11. The labours of the observers of the beginning of the century
having been now prosecuted for some years without further results,
were discontinued ; and it is probable that but for the admirable
charts of the stars which have been since published, no other
members of this remarkable group of planets would have been
discovered. These, however, containing all the stars up to the
9th or 10th magnitude, included within a zone of the firmament
30° in width, extending to 15° on each side of the celestial equator,
supplied so important and obvious an instrument of research, that
the subject was again resumed, with a better prospect of successful
results. It was only necessary for the observer, map in hand, to
examine, degree by degree, the zone within which such bodies are
known to move, and to compare, star by star, the heavens with
the map. When a star is observed which is not marked on the
map, it is watched from hour to hour, and from night to night.
If it do not change its position, it must be inferred that it has been
omitted in the construction of the map, and it is marked upon it

165

THE NEW PLANETS.

in its proper place. If ty change its position, it must be inferred
to be a planet, and its orbit is soon calculated from its observed
changes of position.

By these means M. Hencke, an amateur observer of Driesen in
Prussia, discovered, on the 8th December, 1845, another of the
small planets, which has been named ASTRJEA.

This discovery was the signal for an extraordinary start. It
had so happened that within some years several private observa-
tories had been established, and a most respectable, intelligent, and
weakhy body of amateurs and volunteers has been added to the
regular professional astronomical corps. The result of this is, that
within a few years a most unexpected number of planets has been
discovered, all occupying nearly the same place in the system ;
thus, three were discovered in 1847, one in 1848, one in 1849,
three in 1850, two in 1851, eight in 1852, four in 1853, and six in
1854, and one on the 6th April, 1855, — making the total number
discovered to the date of writing these lines (1st May, 1855)
thirty-four.

12. A tabular statement of the elements of these planets was
published in the " Annuaire du Bureau des Longitudes" at
Paris for the present year, 1855, by M. Le Terrier and his
assistants. Recently, however, a much more complete table has
been published by Mr. Bishop, whose observatory in the Regent's
Park has been signalised by the discovery of eleven of these thirty-
four bodies. Desiring to give as wide circulation as possible to
this mass of interesting astronomical data, I would refer the reader
to Mr. Bishop's table, from which I have extracted the one
annexed to this notice.

To facilitate such researches, Mr. Bishop and his assistants
commenced in the winter of 1846-7 the preparation of a series of
charts, including all stars to those of the eleventh magnitude,
within 3° of the ecliptic. " At the present moment," says Mr.
Bishop, writing in March, 1855, " fourteen maps are finished,
engraved, and published to assist other observers in their search
for new planetary bodies, and it is hoped to place the others
before the public with no great delay." It was in the prepara-
tion of these charts, aided by those of Berlin, that ten planets
were discovered at Mr. Bishop's observatory by Mr. Hind, and
the eleventh more recently by Mr. Marth.

Mr. Bishop remarks, that during the preparation of his maps
several other planets were seen, but lost again through the long-
continuance of unfavourable weather, or owing to the object not
having been missed at a sufficiently early period after it was
entered upon the map.

Too much credit cannot be given to various astronomers,
166

ZODIACAL STELLAR CHARTS.

amateur as well as professional, for the spirit and perseverance
with which they have undertaken the preparation of these
Zodiacal Stellar Charts. Mr. Cooper of Sligo, and his assistant
Mr. Graham, are understood to be thus occupied. They have
already published three volumes containing the approximate posi-
tions of more than 45000 stars. Professor De Gasparis, of Naples,
and Mr. Chacornac, of Paris, are similarly engaged.

In further illustration of the table annexed to this notice, Mr.
Bishop adds the following observations : —

The fourth column contains the estimated magnitude or degree of bright-
ness of each planet at the time of discovery. It would appear that the
four which attain the highest degree of brilliancy are Vesta (often visible
without a telescope), Pallas, Iris, and Flora.

The fifth column gives the mean longitude for noon, Greenwich time,
on the 1st of January, 1855, reckoned from the equinox of that date.

In the sixth is found the longitude of the perihelion, or nearest point of
approach of each planet to the sun, as viewed from that luminary.

The seventh contains the position of the ascending node, or the point in
the ecliptic where the planet passes from south to north latitude, as viewed
from the sun.

The eighth shows the inclination of each orbit to the ecliptic, or the
angle between the planes of the paths of the earth and planet. It will be
remarked that Pallas, Euphrosyne, and Phocea, have the largest inclina-
tions, while Massilia and Themis exhibit the least ; or, in other words,
revolve nearly in the ecliptic.

The ninth column expresses the amount of excentricity or deviation
from the circle. It varies from 0*075 in the case of Amphitrite to 0'346
in that of Polyhymnia.

The tenth gives the mean daily sidereal motion, or the space through
which each planet would move in one day, if it described a circle round
the sun with its average velocity. The numbers in this column multiplied
by the periods expressed in days will, therefore, be equal to the circum-
ference, or 360°.

The eleventh shows the mean distances from the sun, or the semi-axes
major of the orbits, expressed in units of the earth's average distance
from that body, and carried to two places of decimals. Flora has the
least, and, according to the table, Euphrosyne the greatest ; though the
recent date of this planet's discovery, and consequent comparatively short
•extent of observation, leaves us in a little uncertainty whether its mean
distance will ultimately be found to exceed that of Hygeia or Thernis.

The twelfth shows the length of the sidereal revolution in days. The
periods vary from 1193 days, that of Flora, to 2048 days, which is that
of Euphrosyne ; the difference amounting to 855 days, or 2^ years.

I have annexed to the table the thirty-fourth and thirty-fifth
planets discovered by Mr. Chacornac and M. Luther since Mr.
Bishop's table was printed. The elements of the last of these
objects, however, have not yet been determined.

13. In their exceptional minuteness of volume, their mean
distances from the sun, and the very variable obliquities and
•eccentricities of their orbits, they all resemble the first four dis-

167

THE NEW PLANETS.

covered in the beginning of the century*
ami are therefore in complete accordance
with the conditions mentioned in the cu-
rious hypothesis of Olbers above stated.

The planet discovered by M. Gasparis,
on the 17th of March, 1852, was observed
by that astronomer at the Naples Obser-
vatory, on the 17th, 19th, and 20th March.
It appeared as a star of the 10th or llth
magnitude. The observations were pub-
lished in the " Comptes Rendus," of the
Academy of Sciences, Paris, tome xxxiv.
p. 532.

The planet discovered by M. Luther was
observed by that astronomer at Bilk, near
Dusseldorf, on the 17th April, and again
by M. Argelander, on the 22d April, at
Bonn. The observations were published
in the "Comptes llendus " of the Paris
Academy, tome xxxiv. p. 647.

14. Dr. Olbers was a practitioner in
medicine, Messrs. Hencke, Luther, and
Goldschmidt amateur observers, Mr. Hind
lias been engaged in the private observa-
tory of Mr. Bishop, in the Regent's Park,
and Mr. Graham in that of Mr. Cooper, at
Markree, in the county of Sligo, in Ireland.
It appears, therefore, that of these twenty-
three members of the solar system the
scientific world owes no less than fourteen
to amateur astronomers, and observatories
erected and maintained by private indi-
viduals, totally unconnected with any na-
tional or public establishments, and receiv-
ing no aid or support from the state. Mr,
Hind has obtained for himself the honour-
able distinction which must attach to the
discoverer of ten of these bodies. Five are
due to M. de Gasparis, assistant-astronomer
at the Royal Observatory at Naples.

M. Hermann Goldschmidt is an historical
painter, a native of Frankfort-on-the-
Maine, but resident for the last eighteen
years in Paris. He discovered the planet
with a small ordinary telescope, placed in
168

TOTAL NUMBER DISCOVERED.

the balcony of his apartment, No. 12, Rue de Seine, in the
Faubourg St. Germain.

15. By inspecting the above table, it will be seen that these thirty-
three planets move within a region of the solar system comprised
between 2 '2 and 3-2 times the mean distance of the earth. Their
magnitudes are too minute to be ascertained with any degree of
precision and certainty by any means of measurement hitherto
discovered, and it may be inferred, with great probability, that
they do not in general exceed 100 miles, that is, the 80th
part of the diameter of the earth. Assuming, then, such to
be their mean dimensions, and considering that the bulk of globes
is in the proportion of the cubes of their diameters, it would
follow, that, to make a globe as large as the earth, it would be
necessary that 512000 such planets as these • should be rolled
into one.

16. It will not fail to be observed, what great probability this
extreme minuteness of bulk, combined with the circumstance of
their being all so nearly at the same distance from the sun, gives
to the hypothesis of Dr. Olbers.

To show the relative position of this group of planets and those
of the larger members of the system, we have represented in fig. 1,
in their proper proportions, the successive distances of the planets
from the sun, the place of these new planets being indicated by
the band of parallel circles drawn in close proximity.

Being distinguished from the other planets of the system by so
many singular circumstances, some astronomers denominated
these bodies Asteroids; we think, however, that, for reasons that
must be obvious, the name Planetoids would be preferable.

17. From the minuteness of their masses, the force of gravity
on the surface of these bodies must be very inconsiderable ; and
this would account for a circumstance which has been observed
on some of them, namely, that their atmospheres are relatively
much more extensive than those of the larger planets, since the
same mass of air, feebly attracted, would dilate into a volume
comparatively enormous. Muscular power would be more effica-
cious on them in the same proportion ; thus, a man might spring
upwards through sixty or eighty perpendicular feet, and return
to the ground, sustaining no greater shock than would be felt
upon the earth in descending from the height of two or three
feet. " On such planets," observes Herschel, "giants might
exist, and those enormous animals which on earth require the
buoyant power of water to counteract their weight."

169

THE NEW PLANETS.

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170

Fig. 4.

LE VERRIER AND ADAMS' PLANET.

1. — Surprise excited by the discovery. — 2. How a body may be discovered
without seeing it. — 3. Generalisation of the principle. — 4. Its appli-
cation to the case of Neptune. — 5. Condition of the solar system
before the discovery. — 6. Observed disturbances of Uranus. — 7. Great
regularity of these effects. — 8. How they would be produced by a
more distant planet. — 9. Calculations of Le Verrier and Adams. —
10. Elements of the sought planet according to these geometers.
— 11. Its actual discovery. — 12. Its corrected elements. — 13. Dis-
crepancies between the actual and predicted elements explained.
— 14. Comparison of the effects of the real and predicted planets. —
15. The discovery not to be ascribed to chance. — 16. The period ot
Neptune computed. — 17. Computation of his distance. — 18. Its pro-
digious orbital motion. — 19. Illustrated by a railway train. — 20. Its
magnitude. — 21. Its satellite. — 22. Its weight. — 23. Its bulk. — 24.
The sun's light and heat upon it. — 25. The sun's apparent diameter
seen from it. — 26. Its suspected ring.

1. THE universal astonishment which was excited some years
ago by the announcement that certain astronomers, whose names

171

LE YERKIER AND ADAMS* PLANET.

till then were but littlejmown in the scientific world, and not at all
to the general public, had discovered the existence of a new
planet, without ever having seen it themselves, and without its
having been seen by any one else, will not be soon forgotten.

2. Nevertheless, a little reflection will show that there was not so
much cause for surprise in such a discovery, as there might at first
appear to be ; the only cause of the surprise must depend upon the
supposition, that the existence of such a body could only be ascer-
tained by the immediate evidence of the eye directed upon it ; but
surely cases without number will suggest themselves to every
one, in which not only the existence of bodies, but their haunts,
are ascertained otherwise than by seeing them. The sports-
man goes forth, attended by his hounds, in pursuit of the fox ; the
existence of the game is ascertained by the scent of the hounds,
without seeing it, and possibly at a long distance from the place
where it lies ; by following closely the scent which it has left upon
its track, its place of concealment is soon attained, and the game
is started.

3. If we generalise the principles suggested by this familiar
illustration, we shall find that it amounts to this, that the exis-
tence of a body, and the place at which it is to be found, can be
ascertained with as much certainty and precision, by closely
observing the peculiar effects which that body produces upon
other bodies upon which it acts, and by tracing these effects,
as if we actually saw the body we are in quest of. It is the
peculiar nature of the fox to leave upon the ground on which
he treads an odour which characterises him. The organs of the
hound are so constituted as to be highly susceptible of being
affected by this odour, and a sufficient number of these animals
being started over the ground, they are trained to seek for the
scented track, and when found to follow it. The game is thus
discovered, not by the sense of sight, but by the effects which
it has produced upon other bodies, which themselves affect a
different sense.

4. Now let us suppose it possible, that a planet moving through
the universe, which was never seen by any observer, should pro-
duce upon other planets, which are seen and observed, certain
effects ; that these effects can be seen and ascertained by astrono-
mers, and that the said astronomers can infer from the general
principles of their peculiar science, that these effects are such as
could only be produced by a planetary body, moving at a given
time in a given direction ; such effects would, in that case, prove
the existence of a planet, even though it were never seen. What
the scent is to the hound, these effects are to the not less sagacious
instincts of the astronomer.

172

PERTU11BATION EXPLAINED.

Such, then were in fact the means by which the discovery of the
planet, since called Neptune, was made; a discovery which was
incontestably one of the most signal triumphs ever attained by
mathematical science, and which marked an era that must be for
ever memorable in the history of physical investigation.

If the planets were subject only to the attraction of the sun,
they would revolve in exact ellipses, of which the sun would be
the common focus ; but being also subject to the attraction of
each other, which, though incomparably more feeble than that
of the presiding central mass, produces sensible and measurable
effects, consequent deviations from these elliptic paths, called
PERTURBATIONS, take place. The masses and relative motions of
the planets being known, these disturbances can be ascertained
with such, accuracy, that the position of any known planet at any
epoch, past or future, can be determined with the most surprising
degree of precision.

If, therefore, it should be found, that the motion which a
planet is observed to have is not in accordance with that which
it ought to have, subject to the central attraction of the sun,
and the disturbing actions of the surrounding planets, it
must be inferred that some other disturbing attraction acts
upon it, proceeding from an undiscovered cause, and, in this
case, a problem novel in its form and data, and beset with diffi-
culties which might well appear insuperable, is presented to
the physical astronomer. If the solution of the problem, to
determine the disturbances produced upon the orbit of a planet
by another planet, whose mass and motions are known, be re-
garded as a stupendous achievement in physical and mathe-
matical science, how much more formidable must not the converse
question be regarded, in which the disturbances are given to
find the planet.

Such was, nevertheless, the problem of which the discovery of
Neptune has been the astonishing solution.

Although no exposition of the actual process by which this great
intellectual achievement has been effected, could be comprehended
without the possession of an amount of mathematical knowledge
far exceeding that which is expected from the readers of works
much less elementary than the present, we may not be altogether
unsuccessful in attempting to illustrate the principle on which an
investigation, attended with so surprising a result, has been
based, and even the method upon which it has been conducted ;
so as to strip the proceeding of much of that incomprehensible
character, which, in the view of the great mass of those who con-
sider it, without being able to follow the steps of the actual
investigation, is generally attached to it, and to show at least

173

LE VERRIER AND ADAMS PLANET.

Fit? 1.

the spirit of the reasoning by which the
solution of the problem has been accom-
plished.

For this purpose, it will be necessary,
first, to explain the nature and character
of those disturbances which were observed
and which could not be ascribed to the
attraction of any of the known planets ;
and, secondly, to show in what manner an
undiscovered planet, revolving outside the
known limits of the solar system, could
produce such effects.

5. At the epoch of this celebrated dis-
covery, the solar system was supposed to
consist of the principal planets, Mercury,
Venus, the Earth, Mars, Jupiter, Saturn, and
Uranus, revolving round the sun, in the order
in which we have given their names, and at
distances bearing to each other the propor-
tion which is represented with tolerable
exactness in fig. 1. Between Mars and
Jupiter a group of very minute bodies,
called planetoids or asteroids, had been
discovered, occupying the place of a planet,
which had been supposed to be wanting in
the system. Since the discovery which now
engages us, the number of these planetoids
discovered has been greatly increased, its
amount being at the time we write (1st
February, 1855,) not less than 33.

If the reader will cany in his eye the
plan of the solar system thus exhibited, he
will find the following observations and
reasoning not difficult to comprehend.

6. The planet Uranus, revolving at the
extreme limits of the solar system, was the
object in which were observed those dis-
turbances which, not being the effects of
the action of any of the known planets,
raised the question of the possible ex-
istence of another planet exterior to it,
which might produce them.

After the discovery of that planet by Sir
W. Herschel, in 1781, its motions, being
regularly observed, supplied the data by ,

174

PERTURBATION OF URANUS.

which, its elliptic orbit was calculated, and the disturbances pro-
duced upon it by the masses of Jupiter and Saturn ascertained,
the other planets of the system, by reason of their remoteness,
and the comparative minuteness of their masses, not producing
any sensible effects. Tables founded on these results were
computed, and ephemerides constructed, in which the places at
which the planet ought to be found from day to day for the future
were duly registered.

The same kind of calculations which enabled the astronomer
thus to predict the future places of the planet, would, as is
evident, equally enable him to ascertain the places which had
been occupied by the planet in times past. By thus examining,
retrospectively, the apparent course of the planet over the firma-
ment, and comparing its computed places at particular epochs
with those of stars which had been observed, and which had
subsequently disappeared, it was ascertained that several of these
stars had in fact been Uranus itself, whose planetary character
had not been recognised from its appearance, owing to the imper-
fection of the telescopes then in use ; nor from its apparent motion,
owing to the observations not having been sufficiently continuous
and multiplied.

In this way it was ascertained, that Uranus had been observed,
and its position recorded as a fixed star, six times by Flamstead :
viz., once in 1690, once in 1712, and four times in 1715; — once
by Bradley in 1753, once by Mayer in 1756, and twelve times by
Lemonnier between 1750 and 1771.

Now, although the observed positions of these objects, combined
with their subsequent disappearance, left no doubt whatever of
their identity with the planet, their observed places deviated
sensibly from the places which the planet ought to have had,
according to the computations founded upon its motions after
its discovery in 1781. If these deviations could have been
shown to be irregular and governed by no law, they would be
ascribed to errors of observation. If, on the other hand, they
were found to follow a regular course of increase and decrease
in determinate directions, they would be ascribed to the agency
of some undiscovered disturbing cause, whose action at the
epochs of the ancient observations was different from its action at
more recent periods.

The ancient observations were, however, too limited in number
and too discontinuous to demonstrate in a satisfactory manner
the irregularity or the regularity of the deviation. Nevertheless,
the circumstance raised much doubt and misgiving in the mind
of Bouvard, by whom the tables of Uranus, based upon the
modern observations, were constructed ; and he stated that he

175

LE VERRIER AND ADAMS' PLANET.

would leave to futurity the decision of the question, whether these
deviations were due to errors of observation, or to an undiscovered
disturbing agent. We shall presently he enabled to appreciate
the sagacity of this reserve.

7. The motions of the planet continued to be assiduously
observed, and were found to be in accordance with the tables for
about fourteen years from the date of the discovery of the planet.
About the year 1795, a slight discordance between the tabular
and observed places began to be manifested, the latter being a
little in advance of the former, so that the observed longitude L
of the planet was greater than the tabular longitude L'. After
this, from year to year, the advance of the observed upon the
tabular place increased, so that the excess L — L' of the observed
above the tabular longitude was continually augmented. This
increase of L — L' continued until 1822, when it became stationary,
and afterwards began to decrease. This decrease continued until
about 1830-31, when the deviation L — L' disappeared, and the
tabular and observed longitudes again agreed. This accordance,
however, did not long prevail. The planet soon began to fall
behind its tabular place, so that its observed longitude L, which
before 1831 was greater than the tabular longitude L', was now
less ; and the distance I/ — L of the observed behind the tabular
place increased from year to year, and still increases.

It appears, therefore, that in the deviations of the planet from
its computed place, there was nothing irregular and nothing com-
patible with the supposition of any cause depending on the
accidental errors of observation. The deviation, on the contrary,
increased gradually in a certain direction to a certain point ; and
having attained a maximum, then began to decrease, which
decrease still continues.

The phenomena must, therefore, be ascribed to the regular
agency of some undiscovered disturbing cause.

8. It is not difficult to demonstrate that deviations from
its computed place, such as those described above, would
be produced by a planet revolving in an orbit having the
same or nearly the same plane as that of Uranus, which
would be in heliocentric conjunction with that planet at the
epoch at which its advance beyond its computed place attained
its maximum.

Let A B c D E F, fig. 2, represent the arc of the orbit of Uranus
described by the planet during the manifestation of the perturba-
tions. Let N N' represent the orbit of the supposed undiscovered
planet in the same plane with the orbit of Uranus. Let a, b, c,
d, e, and / be the positions of the latter when Uranus is at the
points A, B, c, D, E, and F. It is therefore supposed, that Uranus
176

PERTURBATION OF URANUS.

when at D is in heliocentric conjunction with the supposed planet,
the latter being then at d.

The directions of the orbital motions of the two planets are
indicated by the arrows beside their paths ; and the directions of

Pig. 2.

the disturbing forces * exercised by the supposed planet on Uranus
are indicated by the arrows beside the lines joining that planet
with Uranus.

Now, it will be quite evident, that the attraction exerted by
the supposed planet at a on Uranus at A tends to accelerate
the latter. In like manner, the forces exerted by the supposed
planet at b and c upon Uranus at B and c tend to accelerate
it. But as Uranus approaches to D, the direction of the dis-
turbing force, being less and less inclined to that of the orbital
motion, has a less and less accelerating influence, and on
arriving at D, the disturbing force being in the direction D d
at right angles to the orbital motion, all accelerating influence
ceases.

After passing D the disturbing force is inclined against the
motion, and instead of accelerating retards it; and as Uranus
takes successively the positions E, P, &c., it is more and more
inclined, and its retarding influence more and more increased, as
will be evident if the directions of the retarding force and the
orbital motion, as indicated by the arrows, be observed.

* To simplify the explanation, the effect of the attraction of Uranus on
the sun is omitted in this illustration. In the chapter on Perturbations in
my "Handbook on Astronomy," the method of determining the exact
direction of the disturbing force is explained.

LARDNER'S MUSEUM OF SCIENCE. N 177

No. 77.

LE VEREIER AND ADAMS* PLANET.

It is then apparent, that from A to D the disturbing force,
accelerating the orbital motion, will transfer Uranus to a position
in advance of that which it would otherwise have occupied ; and
after passing D, the disturbing force retarding the planet's motion
will continually reduce this advance, until it bring back the
planet to the place it would have occupied had no disturbing force
acted; after which, the retardation being still continued, the
planet will fall behind the place it would have had if no disturb-
ing force had acted upon it.

Now it is evident that these are precisely the kind of dis-
turbing forces which act upon Uranus ; and it may, therefore,
be inferred that the deviations of that planet from its com-
puted place are the physical indications of the presence of
a planet exterior to it, moving in an orbit whose plane either
coincides with that of its own orbit, or is inclined to it at a
very small angle, and whose mass and distance are such as to
give to its attraction the degree of intensity necessary to pro-
duce the alternate acceleration and retardo^'on which have been
observed.

Since, however, the intensity of the disturbing force depends
conjointly on the quantity of the disturbing mass and its distance,
it is easy to perceive that the same disturbance may arise from
different masses, provided that their distances are so varied as to
compensate for their different weights or quantities of matter. A
double mass at a fourfold distance will exert precisely the same
attraction. The question, therefore, under this point of view,
belongs to the class of indeterminate problems, and admits of an
infinite number of solutions. In other words, an unlimited
variety of different planets may be assigned, exterior to the sys-
tem which would cause disturbances observed in the motion of
Uranus, so nearly similar to those observed, as to be distinguishable
from them only by observations more extended and elaborate than
any to which that planet could possibly have been submitted since
its discovery.

9. The idea of taking these departures of the observed from the
computed place of Uranus, as the data for the solution of the
problem to ascertain the position and motion of the planet which
could cause such deviations, occurred, nearly at the same time,
to two astronomers, neither of whom at that time had attained
either the age or the scientific standing which would have raised
the expectations of achieving the most astonishing discovery of
modern times.

H. Le Verrier, in Paris, and Mr. J. C. Adams, Fellow and
Assistant Tutor of St. John's College, Cambridge, engaged in the
investigation, each without the knowledge of what the other was
178

CALCULATIONS OF THE DISCOVERERS.

doing, and believing that he stood alone in his adventurous and,
as would then have appeared, hopeless attempt. Nevertheless,
both not only solved the problem, but did so with a completeness
that filled the world with astonishment and admiration, in which
none more ardently shared than those who, from their own
attainments, were best qualified to appreciate the difficulties of
the question.

The question, as has been observed, belonged to the class of
indeterminate problems. An infinite number of different planets
might be assigned which would be equally capable of producing
the observed disturbances. The solution, therefore, might be
theoretically correct, but practically unsuccessful. To strip the
question as far as possible of this character, certain conditions
were assumed, the existence of which might be regarded as in the
highest degree probable. Thus it was assumed that the disturb-
ing planet's orbit was in or nearly in the plane of that of Uranus,
and therefore in that of the ecliptic ; that its motion in this orbit
was in the same direction as that of all the other planets of the
system, that is, according to the order of the signs ; that the orbit
was an ellipse of very small eccentricity ; and, in fine, that its
mean distance from the sun was, in accordance with the general
progression of distances noticed by Bode, nearly double the
mean distance of Uranus. This last condition, combined with
the harmonic law, gave the inquirer the advantage of the
knowledge of the period, and therefore of the mean heliocentric
motion.

Assuming all these conditions as provisional data, the problem
was reduced to the determination, at least as a first approxima-
tion, of the mass of the planet and its place in its orbit at a given
epoch, such as would be capable of producing the observed
alternate acceleration and retardation of Uranus.

The determination of the heliocentric * place of the planet at a
given epoch would have been materially facilitated if the exact
time at which the amount of the advance (L — I/) of the observed
upon the tabular place of the planet had attained its maximum
were known ; but this, unfortunately, did not admit of being
ascertained with the necessary precision. When a varying
quantity attains its maximum state, and, after increasing, begins
to diminish, it is stationary for a short interval ; and it is always
a matter of difficulty, and often of much uncertainty, to determine
the exact moment at which the increase ceases and the decrease
commences. Although, therefore, the heliocentric place of the

* That is, the place in which, the planet would appear to be, if the
observer were at the centre of the system, where the sun is.

N 2 179

LE YERRIER AND ADAMS PLANET.

disturbing planet could Jae nearly assigned about 1822, it could
not be determined with the desired precision.

Assuming, however, as nearly as was practicable, the longitude
of Uranus at the moment of heliocentric conjunction * with the
disturbing planet, this, combined with the mean motion of the
sought planet, inferred from its period, would give a rough
approximation to its place for any given time.

10. Rough approximations were not, however, what MM. Le
Yerrier and Adams sought. They aimed at more exact results ;
and, after investigations involving all the resources and ex-
hausting all the vast powers of analysis, these eminent
geometers arrived at the following elements of the undiscovered
planet : —

Le Vcrrier.

Adams.

Epoch of the elements

1 Jan. 1847.

1 Jan. 1846.

Mean longitude at the epoch . .

318° 47''4

323° 2'

Mean distance of planet from sun

36-1539

37-2474

Eccentricity of the orbit . . .

0-107610

0-120615

Longitude of perihelion

284° 45'-8

299° 11'

Mass (sun = 1)

0-00010727

0-00015003

11. On the 23rd September, 1846, Dr. Galle, one of the astrono-
mers of the Royal Observatory at Berlin, received a letter from
M. Le Yerrier, announcing to him the principal results of his
calculations, informing him that the longitude of the sought
planet must then be 326°, and requesting him to look for it.
Dr. Galle, assisted by Professor Encke, accordingly did "look for
it," and found it that very night. It appeared as a star of the
8th magnitude, having the longitude of 326° 52', and consequently
only 52' from the place assigned by M. Le Yerrier. The calcula-
tions of Mr. Adams, reduced to the same date, gave for its place
329° 19', being 2° 27' from the place where it was actually
found.

To illustrate the relative proximity of these remarkable predic-
tions to the actual observed place, let the arc of the ecliptic,
from long. 323° to long. 330°, be represented in fig. 3. The
place assigned by M. Le Yerrier for the sought planet is indi-

* Two objects are said to be in heliocentric conjunction, when they are
so placed that they would be seen in the same direction by an observer
looking at them from the sun.
180

NEPTUNE DLSCOYEKED.

cated by the small circle at L, that assigned by Mr. Adams by the

small circle at A, and the place at which it was

actually found by the dot at N. The distances

of L and A from N may be appreciated by the

circle which is 'described around the dot N,

and which represents the apparent disk of the

moon.

; The distance of the observed place of the planet

from the place predicted by M. Le Yerrier was

less than two diameters, and from that predicted

by Mr. Adams less than five diameters of the

lunar disc.

12. In obtaining the elements given above, Mr.
Adams based his calculations on the observations
of Uranus made up to 1840, while the calcula-
tions of M. Le Yerrier were founded on observa-
tions continued to 1845. On subsequently taking
into computation the five years ending 1845, Mr.
Adams concluded that the mean distance of the
sought planet would be more exactly taken at
33-33.

After the planet had been actually discovered,
and observations of sufficient continuance were
made upon it, the following proved to be its more
exact elements : —

Epoch of the elements
Mean longitude at the epoch
Mean distance from sun
Eccentricity of orbit
Longitude of perihelion
Longitude of ascending node
Inclination of orbit .
Periodic time
Mean annual motion .

Greenwich.

Uan.l847,M. Noon.
328° 32' 44" -2.

30-0367.

0-00871946.

47° 12' 6" -50.

130° 4' 20" -81.

1° 46' 58" -97.

164-6181 years.

2°-18688.

13. Now it will not fail to strike every one who devotes the
least attention to this interesting question, that considerable
discrepancies exist, not only between the elements presented in
the two proposed solutions of this problem, but between the actual
elements of the discovered planet and both of these solutions.

181

LE VERRIER AND ADAMS PLANET.

There were not wanting, some who, viewing these discordances,
did not hesitate to declare that the discovery of the planet was
the result of chance, and not, as was claimed, of mathematical
reasoning, since, in fact, the planet discovered was not identical
with either of the two planets predicted.

To draw such a conclusion from such premises, however, betrays
a total misapprehension of the nature and conditions of the
problem. If the problem had been determinate, and, conse-
quently, one which admits of but one solution, then it must have
been inferred, either that some error had been committed in the
calculations which caused the discordance between the observed
and computed elements, or that the discovered planet was not
that which was sought, and which was the physical cause of the
observed disturbances of Uranus. But the problem, as has been
already explained, being more or less indeterminate, admits of
more than one, — nay, of an indefinite number of different solu-
tions, so that many different planets might be assigned which
would equally produce the disturbances which had been observed;
and this being so, the discordance between the two sets of pre-
dicted elements, and between both of them and the actual elements,
are nothing more than might have been anticipated, and which,
except by a chance, against which the probabilities were millions
to one, were, in fact, inevitable.

So far as depended on reasoning, the prediction was verified ;
so far as depended on chance it failed. Two planets were
assigned, both of which lay within the limits which fulfilled the
conditions of the problem. Both, however, differed from the
true planet in particulars which did not affect the conditions of
the problem. All three were circumscribed within those limits,
and subject to such conditions as would make them produce
those deviations or disturbances which were observed in the
motions of Uranus, and which formed the immediate subject of
the problem.

14. It may be satisfactory to render this still more clear, by
exhibiting in immediate juxtaposition the motions of the hypo-
thetical planets of MM. Le Verrier and Adams and the planet
actually discovered, so as to make it apparent that any one of the
three, under the supposed conditions, would produce the observed
disturbances. We have accordingly attempted this in fig. 4,
where the orbits of Uranus, of Neptune, and of the planets
assigned by MM. Le Yerrier and Adams are laid down, with the
positions of the planets respectively in them for every fifth year,
from 1800 to 1845 inclusively. This plan is, of course, only
roughly made ; but it is sufficiently exact for the purposes of the
present illustration. The places of Uranus are marked by Q»
182

DISCREPANCIES EXPLAINED.

those of Neptune by Q, those of M. Le Terrier's planet by 0,
and those of Mr. Adams' planet by ®.

It will be observed that the distances of the two planets assigned
by MM. Le Verrier and Adams, as laid down in the diagram,
differ less from the distance of the planet Neptune than the
mean distances given in their elements differ from the mean dis-
tance of Neptune. This is explained by the eccentricities of the
orbit, which, in the elements of both astronomers, are consider-
able, being nearly an eighth in one and a ninth in the other,
and by the positions of the supposed planets in their respective
orbits.

If the masses of the three planets were equal, it is clear that
the attraction with which Le Terrier's planet would act upon
Uranus, would be less than that of the true planet, and that of
Adams' planet still more so, each being less in the same ratio as
the square of its distance from Uranus is greater than that of
Neptune. But if the planets are so adjusted that what is lost by
distance is gained by the greater masses, this will be equalised,
and the supposed planet will exert the same disturbing force as the
actual planet, so far as relates to the effects of variation of dis-
tance. It is true that, throughout the arcs of the orbits over which
the observations extend, the distances of the three planets in simul-
taneous positions are not everywhere in exactly the same ratio, while
their masses must necessarily be so ; and, therefore, the relative
masses, which would produce perfect compensation in one position,
would not do so in others. This cause of discrepancy would ope-
rate, however, under the actual conditions of the problem, in a
degree altogether inconsiderable, if not insensible.

But another cause of difference in the disturbing action of the
real and supposed planets would arise from the fact, that the
directions of the disturbing forces of all the three planets are
different, as will be apparent on inspecting the figure in which
the degree of divergence of these forces at each position of the
planets is indicated ; but it will be also apparent, that this diver-
gence is so very inconsiderable that its effect must be quite insen-
sible in all positions in which Uranus can be seriously affected.
Thus, from 1800 to 1815, the divergence is very small. It
increases from 1815 to 1835; but it is precisely here, near the
epoch of heliocentric conjunction, which took place in 1822,
that all the three planets cease to have any direct effect in
accelerating the motion of Uranus. When the latter planet
passes this point sufficiently to be sensibly retarded by the dis-
turbing action, as is the case after 1835, the divergence again
becomes inconsiderable.

From these considerations it will therefore be understood, that

183

LE TERRIER AND ADAMS7 PLANET.

the disturbances of the motion of Uranus, so far as these were
ascertained by observation, would be produced without sensible
difference, either by the actual planet which has been discovered,
or by either of the planets assigned by MM. Le Terrier and
Adams, or even by an indefinite number of others which might
be assigned, either within the path of Neptune, or between it and
that of Adams' planet, or, in fine, beyond the latter — within certain
assignable limits.

15. That the planets assigned by MM. Le Terrier and Adams
are not identical with the planet to the discovery of which their
researches have conducted practical observers is, therefore, true ;
but it is also true that, if they or either of them had been iden-
tical with it, such excessive amount of agreement would have
been purely accidental, and not at all the result of the sagacity
of the mathematician. All that human sagacity could do with
the data presented by observation was done. Among an indefinite
number of possible planets capable of producing the disturbing
action, two were assigned, both of which were, for all the purposes
of the inquiry, so nearly coincident with the real planet as inevit-
ably and immediately to lead to its discovery.

16. It might appear from considering merely the enormous dis-
tance of this planet from the earth, that the problem to ascertain
the rate of its motion, and the time it takes to make a complete
revolution round the sun, would be attended with great diffi-
culty; nothing, on the contrary, can be more easy or simple.
By observing the place of the planet with precision on any given
night, — say, for example, on the 1st January, 1853, — and again
on the 1st January, 1854, it will be found to have moved through
2-187° ; we infer, therefore, that this is the rate of its annual
motion; and this inference would be verified by repeating the
same observation on the 1st of January, 1855, and, in a word, on
the same night in each succeeding year.

Having thus ascertained that Neptune moves round the sun at
the rate of 2-187° per annum, the question is : how long he will
take to make a complete revolution — that is 360° — round the sun ;
and this, it is clear, is a question in the simple Rule of Three,
that, can be solved by any school-boy, and is thus stated —

2-187° : 360° :: 1 year : 36° = 164-6 years.

Thus it appears that this planet will make a complete revolution
round the sun in about 164 years and 7 months, and although
not more than a few years have elapsed since the date of its dis-
covery, we are just as certain, that it will complete its revolution
in that interval as our posterity will be, who will witness the
completion of its period, in the year of our Lord 2011.
184

DISTANCE OF NEPTUNE.

17. There is a remarkable astronomical law Fis- 5-
which was discovered, as a matter of fact, by

Kepler, and shown by Newton to be a necessary
consequence of the principle of universal gravi-
tation, called the harmonic law; according to
this celebrated law, the successive distances of
the planets from the sun, have a certain fixed
relation to their times of revolutions, shortly
called their periodic times, by means of which
their relative distances can be easily computed,
when their periodic times are known. This
celebrated law is expressed as follows : —

The squares of the numbers zvhich express the
periodic times of any two planets, are in the
same proportion as the cubes of the numbers
which express their distances from the sun.

This rule reduces the problem to determine
the distance of Neptune from the sun to a ques-
tion in the simple Rule of Three.

The periodic time of the earth being a year,
will be expressed by 1, and that of Neptune will
be, as already shown, 164*6 ; now the squares of
these numbers are 1 and 27093. To find the
cube of Neptune's distance, is therefore a Rule
of Three question stated as follow : —
1 : 27093 : : 1 : 27093.
Therefore this number 27093 is in fact the cube
of Neptune's distance from the sun, the earth's
distance from the sun being expressed by 1.
To find Neptune's distance, therefore, we have
only to find the number whose cube is 27093, and
by the ordinary processes of arithmetic, that
number is found to be 30-034.

"We may, therefore, state in round numbers,
that Neptune is 30 times farther from the sun
than the earth. But the distance of the earth
from the sun being, in round numbers, 100 mil-
lions of miles ; it follows that the distance of
Neptune from the sun is, in round numbers, about
3000 millions of miles. Greater numerical pre-
cision than this has been attained by the com-
putations of astronomers, but the purpose of our
numerous readers will be best served at present
by adhering to these round numbers.

18. To convey some notion of the prodigious

185

LE VERRIER AND ADAMS' PLANET.

scale upon which the orbital motion of this planet takes place, we
have represented in tig. 5, the orhit of the earth, E, E', E", E"',
the distance of E from s, the sun, being 100 millions of miles ;
s N will then be upon the same scale, the distance of Neptune from
the sun.

Although it is easy by this expedient to convey a sufficiently
exact notion of the relative distances of these planets from the
sun, it is by no means so easy to acquire any adequate idea of
their actual distances, or what is the same, of the scale of the
solar system.

To obtain, even in the case of magnitudes infinitely less than
these, any just notions, it is necessary to compare them, and, as
it were, to measure them by some standard of magnitude, with
which we have a practical familiarity. Let us see then, whether
by such an expedient we can obtain some notion, however faint,
of the scale of the solar system, at the extreme limit of which
Neptune moves.

19. Every one is at this time familiar enough, with the motion
of a railway train having a given speed, say, for example, 30
miles an hour ; we know that in such a train, moving with that
speed, stoppages included, we can go from London to Liverpool
in 7 hours ; in what time, let us ask, could we be transported in
such a train from the sun to the earth ? The distance, as already
stated, is 100 millions of miles ; if this be divided by 30 we shall
find the number of hours which such a journey would take, this
number would therefore be 3,333333 hours. If this be divided
successively by 24 and by 365| we shall find the number of days
and of years in such a journey ; the result of such a calculation
in round numbers will show that such a train will take 380 years
to move from the sun to the earth.

But Neptune being, as we have seen, 30 times more distant
than the earth from the sun, it would take the same train an
interval 30 times longer to move to that planet; we therefore
arrive at the astounding conclusion that a railway -train moving
constantly without stoppage would take 114000 years to move from
the sun to Neptune, that is to the extreme limit of the solar system.

The circumference of a circle, whose diameter is 6000, is 18849 ;
now since the diameter of Neptune's orbit is 6000 millions of
miles, its circumference is 18849 millions of miles, and round this
circumference the planet moves in 164'6 years, and it therefore
moves at the rate of 114,500000 miles per year, or 313500 miles
per day, or 13000 miles an hour.

Such is the colossal scale on which the movements of the system
are conducted.

20. It will doubtless be asked, whether the magnitude of this
186

MAGNITUDE OF NEPTUNE.

body have any proportion to such prodigious distances and
motions ? or whether, indeed, its magnitude at such a distance
as 3000 millions of miles, can be at all ascertained ? Difficult,
nevertheless, as such a problem may seem, it is, on the con-
trary, among the most easy and simple which are presented to the
astronomer.

When a powerful astronomical telescope is directed to a planet,
the object which to the naked eye appears as a mere stellar point of
light, is seen with a circular disc like that of the moon, but in
general much smaller. The visual angle of the moon's disc is
1800"; now it is found that the visual angle of the disc of Neptune is
only 2 '8", and, therefore, is very nearly 643 times less than the
disc of the moon ; but the distance of Neptune is 30 times greater
than that of the sun, and the distance of the sun is 400 times
greater than that of the moon. Therefore the distance of Neptune
is 12000 times greater than that of the moon, consequently it will
follow, that if the moon were removed to Neptune's distance, its
visual angle would be 12000 times less than it is ; but from what
has been just stated it appears that the visual angle of Neptune
is only 643 times less than that of the moon. It follows, there-
fore, that the actual diameter of Neptune must be greater than
the actual diameter of the moon, in the proportion of 12000 to
643, or 19 to 1 very nearly. But since we know the diameter of
the moon to be a little more than 2000 miles, it follows that the
actual diameter of Neptune will be about 38000 miles.

This is a rough method of calculation which we have adopted
to render the point familiar to those who are not accustomed to
the more exact methods of astronomical calculations.

How little the result nevertheless varies from the truth, will
be perceived when we state, that, according to the most exact
observations and calculations of astronomers, the actual diameter
of Neptune is 37500 miles.

21. A satellite of this planet was discovered by Mr. Lassell in
October, 1846, and was afterwards observed by other astronomers
both in Europe and the United States. The first observations
then made raised some suspicions as to the presence of another
satellite as well as of a ring analogous to that of Saturn.
Notwithstanding the numerous observers, and the powerful instru-
ments which have been directed to the planet since the date of
these observations, nothing has been detected which has had any
tendency to confirm these suspicions.

The existence of the satellite first seen by Mr. Lassell has, how-
ever, not only been fully established, but its motion, and the
elements of its orbit, have been ascertained, first by the observa-
tions of M. 0. Struve in September and December, 1847, and later,

187

LE TERRIER AND ADAMS* PLANET.

and more fully, by thtJse of his late relative M. Auguste Struve,
in 1848-9. ^

Prom these observations it appears, that the distance of the satel-
lite from the planet at its greatest elongation subtends an angle of
18" at the sun ; and since the diameter of the planet subtends an
angle of 2 "-8 at the same distance, it follows, therefore, that the
distance of the satellite from the centre of the planet is equal to
thirteen semidiameters of the latter.

The mean daily angular motion of the satellite round the centre
of the planet is, according to the observations of Struve, 610%2625,
and, consequently, the period of the satellite is —
Sfirt

or 5d 21h l«8m, a result which is subject to an error not exceeding
5 minutes.

If the semidiameter of the planet be 18750 miles, the actual
distance of the satellite is

18750 X 12 = 225000 miles,

being a little less than the distance of the moon from the earth's
centre.

22. If it excite surprise that the dimensions of a globe so
enormously distant from the earth as that of Neptune should be
so exactly and so easily measured, it will not create less astonish-
ment when we affirm that the mass of matter in that globe can be,
and has been weighed, and not only weighed, but weighed with
as much or even more precision than that which is attained by
the chemist in the operations conducted upon the small masses of
matter under his hands.

What then, it will naturally enough be asked, can be the form
and structure of the balance, by which an operation so wonderful
can be performed ?

Let us see whether we cannot explain this.

If a mass of matter attached to the extremity of a string,
the other extremity of which is attached to a fixed point,
be whirled round in a circle, of which that fixed point is the
centre, the string will be, as every one knows, stretched with
a certain force, and that this force will be greater and greater
as the velocity with which the body is whirled is increased.
Now the moon whirls round the earth with just such a circular
motion, and if it were connected by a string with the centre of
the earth, that string would be stretched with a force depending
upon the velocity of the moon's motion ; but since no such string
exists, something else must exist which will exercise the same
force upon the moon as the string would, and that something is
the earth's attraction.
188

MOON OF NEPTUNE.

It is proved by theory, and verified by experiment, that the
force with which the string connecting such a body with the
centre would be stretched, would increase in the same proportion
as the square of the velocity of the revolving body increases, other
things being the same. If, therefore, the moon's velocity in
whirling round the earth were twice what it is, the force with
which it would react against the earth's attraction, would be four
times greater than it is, and as the earth's attraction would still
be the same, the moon, in that case, would escape from her orbit,
and would depart to a greater distance from the earth. If, on the
other hand, the moon moved with half its present velocity, the
force with which it would stretch the string would be four times
less than it is, and being then less than the earth's attraction upon
it, the moon would fall towards the earth to a much less distance.
But since the moon neither departs to greater distances nor
approaches to less distances, it follows that the attraction of the
•earth upon it is neither more nor less than that with which a string
would be stretched which would connect the moon with the centre
of the earth.

Now we have seen by what has been explained, that Neptune,
as well as the earth, has a moon, and moreover, that this moon
whirls round Neptune at a distance a little less than that at which
our moon moves round the earth. To simplify the question, let
us suppose for a moment that these distances are equal. If then
Neptune's moon had the same velocity as ours, a string connecting
it with Neptune would be stretched with the same force as that
with which a string would be stretched connecting the moon with
the earth ; and since the attraction of the two planets on their
respective moons is represented by the tension of such string, it
would follow, in that case, that the two planets would exert equal
attractions on moons revolving at equal distances from them. But
since these attractions depend only on the quantities of matter in
the two planets, or what is the same on their weights, it would,
in that case, follow, that the weight of Neptune would be equal
to that of the earth.

But Neptune's moon, instead of revolving in the same time as
ours, revolves as it appears, by what has been explained, in 5-8763
days. Now we have just explained that the force with which the
^whirling body would stretch a string increases, other things being
the same, in the proportion of the square of its velocity, and
since our moon takes 27-322 days to make a complete revolution,
while that of Neptune makes a revolution in 5-876 days, the
velocity of the latter will be greater than that of the former in
the proportion of 5876 to 27322 ; and consequently the forces
with which they will react upon the planetary attractions which

189

LE VERRIER AND ADAMS' PLANET.

hold them in their orbits will be proportional to the squares of
these numbers. But the squares of these numbers, if computed,
will be found to be in the proportion of 2 1| to 1 very nearly. It
would follow, therefore, that the weight of Neptune is 21| times
that of the earth.

But it must not be forgotten that in this calculation we have
supposed that the distance of the satellite from Neptune is equal
to the distance of the moon from the earth, but in fact the dis-
tance of Neptune's satellite is less than that of the moon, in the
proportion of 225 to 238, and, therefore, the estimate of the mass
of Neptune, computed as above, upon the supposition of the exact
equality of the two distances, must be reduced in the same pro-
portion, which would make Neptune's mass 20 times that of the
earth.

This, as in the former case, is a very rough method of calcula-
tion, adopted to render familiar a problem, which, in its more
exact details, would be much too difficult for any but professed
astronomers perfectly to understand. By more exact methods it
appears that the weight of Neptune is about 19 times that of the
earth.

23. The relative bulks, or volumes, of globes being in the pro-
portion of the cubes of their diameters, and the diameter of
Neptune being 37500 miles, while that of the earth is about 7900
miles, it follows that the bulk of Neptune is about 107 times
greater than that of the earth ; or that 107 globes like the earth,
being rolled into one, would form a planet equal to Neptune.

24. Since the brightness of the sun's light, and the warmth
produced by its heat, decrease in the same proportion as the super-
ficial magnitude of his disc decreases, and since the diameter of
that disc decreases in the same proportion as the distance of the
observer from the sun increases, it follows that the superficial
magnitude of the sun's disc, and therefore the brightness of the
light of day, and the warmth of the solar rays, will be less at
Neptune than they are at the earth, in the same proportion
in which the square of Neptune's distance from the sun is greater
than the square of the earth's distance ; and since Neptune is
30 times more distant than the earth, it follows that the brightness
of day and the sun's warmth at Neptune are 900 times less than
at the earth,

25. The apparent diameter of the sun, as seen from Neptune,
being 30 times less than from the earth, is,

The sun, therefore, appears of the same magnitude as Venus
seen as a morning or evening star.
190

SOLAR LIGHT AND HEAT.

The relative apparent magnitudes are exhibited in fig. 6, at
E and IST.

It would, however, be a great mistake to infer that the light of
the sun at Neptune approaches in any degree to the faintness of
that of Yenus at the earth. If Yenus, when that planet appears
as a morning or evening star, with the apparent diameter of 60",
had a full disc (instead of one halved or nearly so, like the moon
at the quarters), and if the actual intensity of light on its surface
were equal to that on the surface of the sun, the light of the

Fig. 6.

planet would be exactly that of the sun' at Neptune. But the
intensity of the light which falls on Yenus is less than the inten-
sity of the light on the sun's surface in the ratio of the square of
Yenus' distance to that of the sun's semidiameter, upon the
supposition that the light is propagated according to the same law
as if it issued from the sun's centre ; that is, as the square of 37
millions to the square of half a million nearly, or as 37* : |, that
is, as 5476 to 1. If, therefore, the surface of Yenue reflected
(which it does not) all the light incident upon it, its apparent
light at the earth (considering that little more than half its
illuminated surface is seen) is about 11000 times less than the
light of the sun at Neptune.

Small, therefore, as is the apparent magnitude of the sun at
Neptune, the intensity of its daylight is probably not less than
that which would be produced by about 20000 stars shining at
once in the firmament, each being equal in splendour to Yenus
when that planet is brightest.

In addition to these considerations, it must not be forgotten
that all such estimates of the comparative efficiency of the illu-

191

LE TERRIER AND ADAMS* PLANET.

urinating and heating pojver of the sun are based upon the supposi-
tion that his light is received under like physical conditions ; and
that many conceivable modifications in the physical state of the
body or medium on or into which the light falls, and in the
structure of the visual organs which it affects, may render light
of an extremely feeble intensity as efficient as much stronger light
is found to be under other conditions.

26. Messrs. Lassell and Challis have at times imagined that
indications of some such appendage as a ring, seen nearly edge-
wise, were perceptible upon the disc of Neptune. These conjec-
tures have not yet received any confirmation. When the
declination of the planet shall have so far increased as to present
the ring, if such an appendage be really attached to the planet, at
a less oblique angle to the visual ray, the question will probably
be decided.

102

Fig. 3,

Fig. 4.

Fig. 5.

Figs. 1, 2.— TELESCOPIC VIEW OF STELLAR CLUSTERS, INCLUDING MANY MILLIONS OF

SUNS REDUCED BY DISTANCE TO NEBULOUS SPOTS.
3. — MAGNIFIED VIEW OF THE ROTIFER ANIMALCULE.

Figs. 4, 5. — MAGNIFIED VIEW OF FOSSIL ANIMALCULES so MINUTE THAT 187 MIL-
LIONS OF THEM WOULD NOT WEIGH MORE THAN A GRAIN.

MAGNITUDE AND MINUTENESS.

1. Relative magnitude. — 2. Manifestations of Divine wisdom. — 3. Small-
ness of great mountains compared with the bulk of the earth. — 4. Of
the earth compared with Jupiter and Saturn. — 5. With the Sun. —
6. With other celestial objects. — 7. Minute particles of which all
LARDNER'S MUSEUM OP SCIENCE, o 193

No. 78.

MAGNITUDE AND MINUTENESS.

bodies are composed* — 8. Solid, liquid, and gaseous states — how pro-
duced.— 9. Mechanical subdivision. — 10. Pulverised marble. — 11.
Inequalities of polished surfaces. — 12. Particles of gold on touch-
stone.— 13. Filaments of glass. — 14. Micrometer wires. — 15. Gold
leaf. — 16. Gilt silver threads for embroidery. — 17. Soap bubbles. —
18. Insects' wings. — 19. Filaments of wool, silk, and fur. — 20. Red
Particles in the blood.— 21. Animalcules.— 22. Spider's web.— 23.
Minute subdivision of a grain of salt. — 24. Of sulphate of copper. —
25. Of musk. — 26. Of strychnine. — 27. Of ammoniacal hyposulphite.
— 28. Of sugar. — 29. Is matter infinitely divisible ?— 30. Crystallisa-
tion of salt. — 31. Ultimate atoms. — 32. Natural crystals. — 33. Plane
of cleavage. — 34. Determinate figure of ultimate atoms. — 35. Prin-
ciples of mechanical science independent of this hypothesis. — 36.
Matter not destructible. — 37. By combustion. — 38. By evaporation. —
39. By destructive distillation. — 40. Nor by any other process.

1. ALL our conceptions of material objects are relative. Great
and small, long and short, big and little, and such like, are words
which severally have tacit reference to some standards which
habit, and the things among which we live, and by which we are
surrounded, have established in our thoughts. "Whenever objects
are presented to the senses or raised in the imagination, departing
in any extraordinary degree from these familiar and habitual
standards, emotions of surprise, astonishment, wondei, admira-
tion, ridicule, pity, or contempt, according to varying circum-
stances, are excited. How susceptible we are of such feelings,
and how peculiar is the enjoyment produced by their excitement,
will be understood when it is recollected with what skill Swift has
played upon them in his fiction of Gulliver, and the unbounded
pleasure derived by young minds from tales of giants, dwarfs, and
fairies.

2. The contemplation and study of the natural world, aided by
the lights of science, disclose to us objects which soon emancipate
the mind from the narrow limits imposed upon it by all those
familiar and habitual standards of magnitude, and show us creative
power working with equal sublimity, perfection, and wisdom, upon
masses compared with which the most enormous objects around
us, the most stupendous mountains, nay, the entire globe of our
earth itself, dwindle into insignificant atoms ; and, on the other
hand, upon objects so minute as to be rendered perceptible to the
senses only by extraordinary expedients supplied by the resources
of science, such as the microscope. In both extremes of creation
are found the same character and manifestations of infinite power,
wisdom,, and skill, compared with which, the greatest attainable
by the most exalted human intellect are mere foolishness ; benevo-
lence of purpose, of which there appears neither end, limit, nor
cessation; and grandeur of -design, compared with which all*

194

MAGNITUDE OF SUN. AND PLANETS.

speculations of philosophy, and all visions of poetry, are puerile
and ridiculous.

3. We make excursions into Wales or the Scottish Highlands
to enjoy the sublime spectacles of Snowdou and Ben Nevis, or to
the Alps, to contemplate the stupendous masses of Mont Blanc and
Mont Rosa, or to the Andes, or the Himalaya, to behold the still
more enormous peaks of Chimborazo or Kunchinginga.

Now, the height of the most lofty summit of the highest of
these peaks does not attain to six miles. But astronomers have
demonstrated that the earth is a globe eight thousand miles in
diameter, so that the height of the most lofty mountain is less than
the 1300th part of the diameter.

Let us consider how such mountains should be regarded com-
paratively with such a globe.

Take a common terrestrial globe, for example, 24 inches in
diameter. It is evident that, compared with the earth itself, 3
inches on such a globe would represent 1000 miles, and conse-
quently 18 thousandths or the 55th part of an inch would repre-
sent six miles. A mountain six miles high would, therefore, be
represented upon the surface of such a globe by a particle of dust,
whose diameter would not exceed the 55th part of an inch.

If the base of a mountain six miles high measured 1000 square
miles, and the form of the mountain were nearly pyramidal, its
solid dimensions would amount to 2000 cubic miles. Now it will be
found by the most simple calculations of arithmetic and geometry
that a globe 8000 miles in diameter must consist of above 250000
millions of cubic miles. It follows, therefore, that the bulk of the
earth must be more than 125 million times greater than the bulk
of such a mountain.

4. The discoveries of astronomers, however, have taught us,
that stupendous as the earth is when compared to such standards
of magnitude, it is small when compared with other globes which
in company with it revolve round the sun, and which like it.
according to probabilities which amount to moral certainty, are
also inhabited worlds ; and that, compared with the sun itself, to
say nothing of still more enormous bodies which have been dis-
covered, it shrinks to a mere point.

Thus the bulk of the planet Saturn is nearly 900 times, and that
of Jupiter nearly 1400 times that of the earth. Yet these, com-
paratively stupendous as they are, appear to be the theatres of the
same physical phenomena, and to play the same part in the crea-
tion as the earth.*

5. When we turn our view to the sun we encounter another

* See our Tract on "The Planets."

o 2 10.-

MAGNITUDE AND MINUTENESS.

order of magnitude. • Astronomers have shown that that great
central mass has a bulk which is nearly 1,400000 times greater
than that of the earth,* or, in other words, that enormous as the
globe of the earth is, compared with any standard of magnitude
which falls under the immediate observation of the senses, it would
be necessary to roll 1,400000 such globes into one to make a globe
equal to the sun.

6. Nor do we stop even here. Suns occupying positions in the
universe so distant, that to our vision, even when aided by the
most powerful telescopes, they appear only as luminous points,
have been shown to be many times larger than ours. Comets
have been observed and measured, the tails of which have a bulk
hundreds of times greater than that of the sun. Clusters con-
sisting of countless thousands of suns are brought by the telescope
within our observation which exceed the magnitude, not of the
sun only, but of a sun which would fill the entire solar system in
a proportion to which it is impossible even to approximate.

Two of these clusters of suns which are reduced by distance to
nebulous spots are shown in figs. 1 and 2, page 193.

Thus as astronomy has advanced, it has enabled us to ascend in
the scale of the sublime from magnitude to magnitude, each suc-
cessive discovery reducing all former standards to comparative
minuteness, until the understanding and the imagination are con-
founded by the stupendous spectacle which the material world
presents, and lost in that immensity which is the theatre of the
creative and beneficent power of the Most High.

7. If our astonishment and admiration are excited by the vast
scale of the stellar universe, they are not less awakened by the
wonders disclosed when a minute analysis of bodies brings under
our view the wonderful structure of their component parts, and the
extraordinary manifestation of power and purpose in the organ-
isation of things which would elude the senses unaided by the
microscope.

The materials of bodies, even the most massive and ponderous,
are infinitely minute, but, minute as they are, their particles or
molecules are often formed with the most delicately exact
geometrical precision. The separation of these particles, and the
discovery of their forms and properties, are among the most
marvellous results of scientific research.

8. Material substances are always found in one or other of three
states, the solid, the liquid, and the gaseous or vaporous.

Stones, woods, and metals are obvious examples of the solid
state, water of the liquid, and air and steam of the gaseous or
vaporous state.

* See our Tract on "The Sun."
196

UNLIMITED DIVISIBILITY.

Solids, generally, by means of heat applied in sufficient quantity
and under fit conditions, maybe made to pass into the liquid state,
the process being called fusion or liquefaction, and all liquids may
by like means be made to pass into the gaseous or vaporous state,
the process being called vaporisation.

In like manner gases and vapours generally may, by the abstrac-
tion of heat, be made to pass into the liquid state, the process being
called condensation, and liquids in like manner may be made to
pass into the solid state, the process being called congelation or
solidification.

In producing these changes upon particular substances, there
have been practical difficulties which have pi evented the success
of the operation, but all analogy supports the conclusion that the
principle is general.

These changes, produced by the supply and abstraction of heat,
have furnished some of the most efficacious means of determining
the nature and properties of the minute component parts of bodies.

9. Bodies may, however, without other physical agency than
mere mechanical subdivision, be reduced to particles of surprising
minuteness.

As this quality of unlimited divisibility involves conditions of
the most profound interest, as well in the sciences as in the arts,
we shall offer here several examples in illustration of it.

10. The most solid bodies are capable of unlimited comminu-
tion, by a variety of mechanical processes, such as cutting, filing,
pounding, grinding, &c. If a mass of marble be reduced to
a fine powder by the process of grinding, and this powder be
then purified by careful washing, its particles, if examined by a
powerful microscope, will be found to consist of blocks having
rhomboidal forms, and angles as perfect and as accurate as the finest
specimens of calcareous spars. These rhomboids, minute as they
are, may be again broken and pulverized, and the particles into
which they are divided will still be rhomboids of the same form
and possessing the same character. The particles of such powder
being submitted to the most powerful microscopic instruments, and
the process of pulverization being pushed to the utmost practical
limit, it is still found that the same forms are reproduced.

11. The polish of which the surfaces of certain bodies, such as
steel, the diamond and other precious stones, are susceptible, is an
evidence at once of the limited sensibility of our organs, and the
unlimited divisibility of matter. This polish is produced, as is
well known, by the friction of emery powder or diamond dust, and
consequently each individual grain of such powder or dust must
leave a little trench or trace upon the surface submitted to such
friction. It is evident, therefore, that after this process has been

197

MAGNITUDE AND MINUTENESS.

completed, the surface, which presents to the senses such brilliant
polish, and apparently infinite smoothness, is in reality covered
with protuberances and indentations, the height and depth of
which cannot be less than the diameter of the particles of powder
by which the polish has been produced.

12. In the detection of matter in a state of extreme comminution,
the sense of sight is infinitely more delicate than that of touch.
If we rub a piece of gold upon a touchstone, we plainly see the
particles of matter which are left upon the surface of the stone.
The touch, however, cannot detect them.

13. In the preceding examples the comminution, however great,
cannot be easily submitted to actual measurement. Certain pro-
cesses, however, in the arts enable us to obtain exact numerical
estimates of a minute divisibility, which without them might appear
incredible. If a 'thin tube of glass, being held before the name of
a blow-pipe until the glass be softened and acquire a white heat,
be drawn end from end, a thread of glass may be obtained so fine
that its diameter will not exceed the two-thousandth part of an
inch. This filament of glass will have all the fineness and almost
all the flexibility of silk, and yet a bore proportional to that which
passed through the original tube will still pass through its centre.
The presence of this bore may be rendered manifest by passing a
fluid through it.

It has been conjectured that if a filament of this degree of
fineness could be obtained of a material that would retain
sufficient inflexibility, it might be made to penetrate the
flesh without producing pain or injury, inasmuch as its mag-
nitude would be so much less than the pores of the integu-
ments.

14. In the application of the telescope to astr nomical purposes,
the distance between objects which are present at one and the
same time within the field of view of the instrument, is measured
by fine threads which are extended parallel to each other across
the field of view, and which may be moved towards and from
each other until they are made to pass through the objects between
which we desire to measure the distance. An experiment, then,
which determines the distance between these threads measures
the distance between the objects.

But these threads, being placed before the eye-glass of the
telescope, and therefore necessarily magnified in the same manner
as the objects themselves, would, unless such filaments were of an
extreme degree of tenuity, appear in the field of view like great
broad bands, and would conceal many of the objects which it
might be necessary to observe. It was therefore necessary to
resort to the use of filaments of extraordinary minuteness for this*
198

METALLIC THREADS — SOAP BUBBLE.

purpose. The threads of the web of the spider were used, with
more or less success ; but the late Dr. "Wollaston invented a
beautiful expedient by which metallic threads of any degree of
fineness might be obtained.

Let us suppose a piece of platinum wire, the one-hundredth
of an inch in diameter, a fineness easily obtainable by the process
of wire-drawing, to be extended along the axis of a cylindrical
mould, the one-fifth of an inch in diameter, the wire being thus
the twentieth part of the diameter of the mould. Let the mould
be then filled with silver in a state of fusion. When this is cold
we shall have a cylinder of silver, having in its axis a thread of
platinum the twentieth part of its diameter.

This compound cylinder is then submitted to the common pro-
cess of wire-drawing, during which the platinum in its centre is
drawn with the silver, the proportion of their diameters being
still maintained. When the wire is drawn to the greatest degree
of fineness practicable, a piece of it is plunged in nitric acid, by
which the surrounding silver is dissolved, and the platinum wire
remains uncovered.

By this process Dr. Wollaston obtained platinum wire so fine,
that thirty thousand pieces, placed side by side in, contact, would
not cover more than an inch.

It would take one hundred and fifty pieces of this wire bound
together to form a thread as thick as a filament of raw silk.

Although platinum is the heaviest of the known bodies, a mile
of this wire would not weigh more than a grain.

Seven ounces of such wire would . extend from London to New.
York.

15. Gold is subdivided into parts of inconceivable minuteness
by the gold beater. A pile of leaf gold, an inch high, would
contain 280000 leaves. The thickness of each leaf would there-
fore be the 280000th part of an inch. Yet such leaves, used for
gilding, not only produce a perfect coating of gold, but protect
the article they cover from the action of external agents that might
otherwise tarnish it.

16. In the manufacture of gold embroidery, threads of silver
gilt are used. These threads- are produced by flattening very
finely drawn gilt wire. The gold which coats an inch of such a
thread weighs no more than the eight millionth part of an ounce.
Yet this inch may be divided into 100 parts, each of which will
be visible without a microscope. In this way the eight hundred
millionth part of an ounce of gold is rendered visible. But if
a microscope magnifying 500 times, be used, a portion of gold,
500 times less, that is the four hundred thousand millionth part
of an ounce will become visible !

199

MAGNITUDE AND MINUTENESS.

17. The optical investigations of Newton disclosed some aston-
ishing examples of the^ninute divisibility of matter.

A soap-bubble, as it floats in the light of the sun reflects to the
eye an endless variety of the most gorgeous tints of colour.
Newton showed, that to each of these tints corresponds a certain
thickness of the substance forming the bubble ; in fact, he showed
in general, that all transparent substances, when reduced to a
certain degree of tenuity, would reflect these colours.

Near the highest point of the bubble, just before it bursts, is
always observed a spot which reflects no colour and appears black.
Newton showed that the thickness of the bubble at this black
point was the 2,500000th patt of an inch! Now, as the bubble
at this point possesses the properties of water as essentially as
does the Atlantic Ocean, it follows, that the ultimate molecules
forming water must have less dimensions than this thickness.

18. The same optical experiments were extended to the organic
world, and it was shown, that the wings of insects which reflect
beautiful tints resembling mother-of-pearl owe that quality to
their extreme tenuity.

Some of these are so thin that 50000 placed one upon the
other would not form a heap of more than a quarter of an inch in
height !

19. The natural filaments of wool, silk, and fur afford striking
examples of the minute divisibility of organised matter. The
following numbers show how many filaments of each of the
annexed substances placed in contact, side by side, would be
necessary to cover an inch : —

Coarse wool 500

Fine Merino wool 1250

Silk 2500

The hairs of the finest furs, such as beaver and ermine, hold
a place between the filaments of Merino and silk, and the wools
in general have a fineness between that of Merino and coarse
wool.

All these objects are sensible to the touch.

It will be remembered that they are compound textures, having
a particular structure, each containing very different elements,
which are prepared by the processes of nutrition and secretion.

20. Microscopic observations have shown that blood is not as it
appears to the naked eye an uniformly red liquid, but that it is a
clear transparent colourless liquid, in which float countless numbers
of thin, flat, red particles of a round or oval shape. The diameter
of these red particles in the human blood, is the 3500th part of
an inch. In certain species of animals it is much smaller, and

200

FOSSIL ANIMALCULES.

measures only the 12000th of an inch. It follows from these
dimensions that in a drop of human blood which would remain
suspended from the point of a fine needle, there must be about
3,000000 of discs, and' in a like drop of the blood of the musk-
deer, there would be about 120,000000 ; yet these corpuscles are
rendered not only distinctly visible to the senses by the aid of
the microscope, but their forms and dimensions are rendered
apparent.

21. But these globules, small as they are, are exceeded in
minuteness by innumerable creatures, whose existence the micros-
cope has disclosed, and whose entire bodies are inferior in magni-
tude to the globules of blood.

Microscopic research has disclosed the existence of animals, a
million of which do not exceed the bulk of a grain of sand, and
yet each of these is composed of members as admirably suited to
their mode of life as those of the largest species. Their motions
display all the phenomena of vitality, sense, and instinct. In the
liquids which they inhabit they are observed to move with the
most surprising speed and agility; nor are their motions and
actions blind and fortuitous, but evidently governed by choice
and directed to an end. They use food and drink, by which they
are nourished, and must, therefore, be supplied with a digestive
apparatus. They exhibit a muscular power far exceeding in
strength and flexibility, relatively speaking, the larger species.
They are susceptible of the same appetites, and obnoxious to the
same passions, as the superior animals, and, though differing in
degree, the satisfaction of these desires is attended with the same
results as in our own species.

Spallanzani observes that certain animalcules devour others so
voraciously that they fatten and become indolent and sluggish by
over-feeding. After a meal of this kind, if they be confined in
distilled water so as to be deprived of all food, their condition
becomes reduced, they regain their spirit and activity, and once
more amuse themselves in pursuit of the more minute animals
which are supplied to them. These they swallow without depriving
them of life, as by the aid of the microscope, the smaller, thus
devoured, has been observed moving within the body of the
greater.

An animalcule called a Rotifer is represented magnified in an
enormous proportion in fig. 3, page 193. This creature has the
appearance of throwing out before it two toothed wheels, which,
being moved with prodigious velocity, produce whirlpools in the
fluid in which it moves, into which other still smaller animalcules
are drawn. This apparent apparatus of helical wheels, like those
which propel the recently constructed steam-vessels, is supposed

201

MAGNITUDE AND MINUTENESS.

to be in reality the effect of certain ciliated organs attached to
the head of the animal, to which it imparts a rapid conical
motion. It appears, that it has the power of drawing in these
appendages, and when it does so, it changes its form from the
oblong shape represented in the figure, to that of a roundish
globule.

This creature possesses another property still more astonishing :
when withdrawn from the liquid element which is his proper
habitation, it is reduced to a grain of dust, so minute as to be
visible only by the microscope. In this state it can be kept for
long intervals of time, apparently deprived of all life. When,
however, it is again immersed in water, it recovers all its original
force, and resumes its habits. The most eminent observers have
affirmed, that they have submitted the same individual rotifer,
several times successively, to these alternations of life and
temporary death.

The microscopic researches of Ehrenberg have disclosed most
surprising examples of the minuteness of which organised matter
is susceptible. He has shown that many species of infusoria
exist which are so small that millions of them collected into one
mass would not exceed the bulk of a grain of sand, and a thousand
might swim side by side through the eye of a needle.

The shells of these creatures are found to exist fossilised in the
strata of the earth in quantities so great as almost to exceed the
limits of credibility.

By microscopic measurement it has been ascertained that
in the slate found at Bilin, in Bohemia, which consists almost
entirely of these shells, a cubic inch contains 41000,000000; and
as a cubic inch weighs 220 grains, it follows that one hundred
and eighty six millions of these shells must go to a grain,
each of which would consequently weigh the 186,000000th part
of a grain.

. All these phenomena lead to the conclusion that these creatures
must be supplied with an organisation corresponding in beauty
with those of the larger species.

In figs. 4 and 5, page 1 93, are represented some of the fossil
animalcules found in the tripoli of Bilin, magnified in a great
proportion.

22. A thread of spider's web, four miles long, weighs little
more than a grain. Every one is familiar with the fact that the
spider spins a thread by which its own weight hangs. It has been
ascertained that this thread consists of 6000 filaments !

23. One of the most obvious means of producing a high degree
of subdivision is by dissolving in a large measure of water a
small portion of the substance to be divided.

202

SUBDIVISION BY SOLUTION.

If a grain of salt be dissolved in 1000 grains of distilled water,
each grain of the water will contain the 1000th part of the grain
of salt ; and if a grain of this water be mixed with 1000 grains
of distilled water, the 1000th part of a grain of salt which it
holds in solution will be uniformly diffused through the latter, so
that each grain of the latter solution will contain the 1,000000th
part of a grain of salt. The presence of the salt in this second
solution can be detected by certain chemical tests.

It is evident that this process may be continued to a still greater
extent.

24. A grain of sulphate of copper, dissolved in a gallon of
water, will impart to the whole mass of the liquid a plainly per-
ceptible tinge of blue; and a grain of carmine will give its
peculiar red to the same quantity of water. It follows, therefore,
that a minute drop of such water will contain such a proportion
of either of these substances as the drop bears to the gallon.

25. The sense of smelling, although it does not inform us of
the mechanical qualities of minute masses of matter, determines,
nevertheless, their presence : thus, it is known that a grain of
musk will impregnate the atmosphere of a room with its odour
for a quarter of a century, or more, without suffering any consi-
derable loss in its weight.

Every particle of the atmosphere which produces the sense
of the odour must contain a certain quantity of the musk.

26. The sense of taste, like that of smelling, may determine
the presence of matter, without manifesting, by direct evidence,
anything concerning its mechanical qualities.

A portion of strychnine, so minute as to be scarcely perceptible
to the sight, dissolved in a pint of water, will render every drop
of the water bitter. Now, it is evident that in this case, the
strychnine being uniformly diffused through the water, the
minute portion of it above mentioned is subdivided into as many
parts as there are drops of water in a pint.

27. In like manner, a single grain of the salt of silver, called
ammoniacal hyposulphite, will impart a flavour of sweetness to a
gallon of water. Now, a gallon of water will weigh about seventy
thousand grains ; and as the flavour of the salt is perceptible in
each grain of the water, it follows that one grain of this salt is
thus divided into seventy thousand equal parts.

28. A small lump of sugar, dissolved in a cup of tea measuring
half a pint, will sweeten the whole perceptibly. In this half-pint
of tea there are thirty-one thousand drops. Each drop, therefore,
must contain the thirty-one thousandth part of the sugar dis-
solved, and each such drop is perceptibly sweet. But if the point
of a needle be inserted in one of these drops, and withdrawn from

203

MAGNITUDE AND MINUTENESS.

it, a film of moisture wiH remain upon it, and the drop will not be
visibly diminished. Yet this film of moisture will still be sweet,
and will, therefore, contain a fraction of the 31000th part of the
lump of sugar, too minute to admit of numerical estimation.

29. It may be asked, whether we are then to conclude, from
these various facts, that matter is infinitely divisible, and that
there are no original constituent atoms of determinate magnitude
and figure, at which all subdivision must cease. Such an infer-
ence, however, would be unwarranted, even if we had no other
means of deciding the question except those of direct observation,
as we should thus impose those limits on the operations of nature
which she has imposed upon our powers of observing them.

Although we are unable, by direct observation, to perceive the
existence of molecules, or material atoms of determinate figure,
yet there are many observable phenomena which render their
existence in the highest degree probable, if not positively
certain.

30. The most remarkable of such phenomena are observed in
the crystallization of salts.

"When salt is dissolved in distilled water, as in the preceding
example, the mixture presents the appearance of a transparent
liquid like water itself, the salt altogether disappearing from sight
and touch. The presence of the salt in the water, however, can
be established by weighing the solution, which will be found to
exceed the original weight of the water by the exact amount of
the weight of the salt dissolved.

Now, if this solution be heated to a sufficient temperature, the
water will gradually evaporate ; but this process of evaporation
not affecting the salt, the remaining water will still contain the
same quantity of salt in solution, and it will consequently
become, by degrees, a stronger and stronger saline solution, the
water bearing, consequently, a less and less proportion to the salt.
The water will at length be diminished, by evaporation, to that
point, that a sufficient quantity does not remain to hold in solu-
tion the entire quantity of salt contained in it. "When this has
taken place, each particle of water which is evaporated leaving
behind it the salt which it held in solution, and this salt not
being capable of being dissolved by the water which remains, it
will float in such water in its solid and natural state, undissolved,
just as particles of dust, or other matter not soluble in the water,
would do. But the saline particles which thus remain floating in
the liquid undissolved, will not collect in irregular solid pieces,
but will exhibit themselves in regular figures, terminated by
plane surfaces, always forming regular angles, these figures being
invariably the same for the same species of salt, but different for
204

CRYSTALLISATION — ULTIMATE MOLECULES.

different species. There are several circumstances attending the
formation of these crystals which merit attention.

If one of these be detached from the others, and the gradual
progress of its. formation be submitted to observation, it will be
found to grow large, always preserving its original figure. Now,
since its increase must be produced by the continual accession of
saline molecules, disengaged by the water evaporated, it follows
that these molecules, or atoms, must have such a shape, that, by
attaching themselves successively to the crystal, they will main-
tain the regularity of its bounding planes, and preserve the angles
which these planes form with each other unvaried.

In fact, they must be so shaped, that the structure of the
crystal they form may be built up by their regular aggregation
into the form which it assumes.

If one of these crystals be taken from the liquid during the
process of its formation, and be broken, so as to destroy the regu-
larity of its form, and then restored to the liquid, it will be
observed soon to recover its regular form, the atoms of salt,
successively dismissed by the evaporating water, filling up the
irregular cavities produced by the fracture.

31. Two consequences obviously follow from this phenomenon.
First. That the atoms of the salt dismissed by the water

evaporated have such a form, as enables them, by combination,
to give to the crystals the shape which they exhibit ; and,

Secondly. That the atoms which are successively attached to
the crystals in the process of formation, attach themselves in a
particular position, to explain which it is necessary to suppose
that corresponding sides of the crystals have attractions for each
other, so that the atoms of salt not only attach themselves to the
sides of the crystals, but place themselves there in a particular
position. In a word, w.e must suppose that the walls of the crystal
are built with these atoms in the same manner, and with the same
regularity, as the walls of a building are formed with bricks.

All these, and many similar details of the process of crystalliza-
tion, are, therefore, very evident indications of a determined figure
in the ultimate atoms of the substances which are crystallized.

32. But besides these substances thus reduced by art to the
form of crystals, there are large classes of bodies which naturally
exist in this state.

33. There are certain planes called planes of cleavage, in the
direction of which natural crystals are easily divided. In sub-
stances of the same kind, these planes have always the same rela-
tive position ; but they differ in different substances.

The surfaces of the planes of cleavage are not always observable
before Hhe crystals are divided; but when the crystals are

205

MAGNITUDE AND MINUTENESS.

divided, these surfaces^exhibit an intense polish which no effort
of art can equal.

We must conclude, therefore, that these planes of cleavage are
parallel to the sides of the constituent atoms of the crystals, and
their directions therefore form so many conditions for the deter-
mination of the shape of these atoms.

This shape being once determined, it is not difficult to assign
all the various ways in which they may be arranged, so as to
produce regular figures ; and we accordingly find that regular
figures thus indicated by mathematical reasoning correspond with
the forms assumed by the crystals of the same substances.

34. It follows, therefore, from these effects, and the reasoning
established upon them, that the substances which are susceptible
of crystallization consist of ultimate atoms of different figure.
Now, all solid bodies whatever are included in this class, for they
have severally been found in, or are reducible to a crystallized form.
Liquids crystallize in freezing : several of the gases have been
already reduced to the liquid and solid forms, and analysis justifies
the conclusion that all are capable of being reduced to this form.

Hence it appears reasonable to presume that all bodies whatever
are composed of ultimate atoms, having determinate shape and
magnitude ; that the different qualities with which we find dif-
ferent bodies endued, depend upon the shape and magnitude of
these atoms ; that these atoms cannot be disturbed or changed so
long as the body to which they belong is not decomposed into
other elements, as we find the qualities which depend on them
unchangeably the same under all the influences to which they
have been submitted.

"We must conclude also that these atoms are so minute in their
magnitudes that they cannot be observed by any means which
human art has yet contrived, but nevertheless that such magni-
tudes still have limits.

35. It is necessary, however, to observe that notwithstanding
the strong analogies which support these conclusions as to the
ultimate constitution of material substances, the principles of
mechanical science are quite independent of them, and do not
rest upon any hypothesis concerning such atomic constitution, and
therefore the truth of these principles would not be in any wise
disturbed even though it should be established that matter is in
the most literal sense infinitely divisible, and is not formed of
ultimate atoms.

The basis of mechanical science is observed facts ; and since the
reasoning upon these observed facts is demonstrative, the conclu-
sions, when rightly deduced, have the same degree of certainty as
the facts from which they are inferred.
206

COMBUSTION — DESTRUCTIVE DISTIL L ATION.

36. The extreme division to which bodies are subjected in many
natural and artificial processes, and especially when exposed to
the application of heat or fire, has naturally suggested to minds
not habituated to the rigid process of scientific reasoning, the idea
that bodies are destructible. The ancients, instead of the modern
practice of inhumation, disposed of the bodies of their dead by
burning them, upon the supposition that their component parts
were by such operation destroyed.

The more exact reasoning of modern philosophy, however,
teaches us that a power to destroy matter would be as inconceiv-
able in a finite agent as a power to create it.

It is certain that the quantity of matter which exists upon and
in the earth has never been diminished by the annihilation of a
single atom.

Matter is in fact indestructible by any agency short of divine
power. It may be asked, then, what becomes of the matter com-
posing a body Avhich, being subjected to the action of fire, gradu-
ally and completely disappears. The answer is, that in this, as
well as in all other cases of the apparent destruction of matter,
nothing takes place except its subdivision and the change of its
form and position.

37. When a body is subjected to the action of heat, its elements
are decomposed, and its constituent particles separated, many of
them combine with other particles of matter, and form new sub-
stances possessing other qualities. Thus, when coal or other fuel
is burned, the carbon enters into combination with one of the
constituents of the atmosphere called oxygen, and forms a gaseous
substance called carbonic acid, which rises into and mixes with
the atmosphere. Another element, hydrogen, combines with the
same constituent of the atmosphere and forms vapor, which also
disperses in the atmosphere.*

Sulphur, which is also occasionally present in fuel, combines
with the same constituent of the air, forming a gas called sulphu-
reous acid, which also escapes into the atmosphere. Thus the
entire matter of the fuel, with the exception of a small portion of
incombustible matter which falls into the ash-pit, is dispersed in
the air, and no destruction or annihilation takes place.

That no portion of the matter of the fuel is destroyed or anni-
hilated .can be established by the incontrovertible experimental
proofs of the chemist, for by the expedients of his science
all the products of the combustion which have been just men-
tioned can be preserved and weighed. The oxygen which has
entered into combination with each element of the fuel can be

* See our Tract on " Fire."

207

MAGNITUDE AND MINUTENESS.

reproduced, as well as tfie constituents of the fuel itself, the latter
of which being weighed, as well as the incombustible ash, the
weight of the whole is found to be precisely equal to the weight of
the fuel which was burned and apparently destroyed.

38. Liquids when subjected to heat are converted into vapor,
and this vapor disperses in the atmosphere, so that the liquid
seems to be boiled away ; but if the vapor be preserved, as it may
be in a separate vessel, and exposed to cold, it will return to the
liquid form, and its weight and measure will be found to be pre-
cisely the same as that of the liquid evaporated.

39. There is a process in chemistry which is called destructive
distillation. The term is objectionable, because it implies a de-
struction where no destruction takes place. If a piece of wood,
being previously weighed, be placed in a close retort and submitted
to what is called destructive distillation, it will be found that
water, a certain acid, and several gases will issue from it, all of
which may be preserved, and mere charcoal will remain in the
retort at the end of the process. If the water, acid, and gases
which thus escape be weighed with the charcoal, the weight of the
whole will be found to be precisely equal to that of the wood which
was subjected to destructive distillation.

40. Thus various forms of matter may be fused, evaporated, or
submitted to combustion ; animals and vegetables may die, orga-
nised bodies may be dissolved and decomposed, but in all cases
their elementary and constituent parts maintain their existence.
The remains of our own bodies after death are deposited in the
grave, and enter into innumerable combinations with the mate-
rials of the soil, with the vegetation which covers it, and the air
which circulates above it.

Consequently, these parts enter into an infinite series of other
combinations, forming parts of other organised bodies, animal and
vegetable, and which, after having discharged their functions,
are thrown off again, mixing with the soil, the air, or organised
matter, and once more running through the round of physical
combinations.

The constituent atoms of matter are thus constantly performing
a circle of duties in the economy of nature with infinitely more
certainty and regularity than is observed in the most disciplined
army or in the best regulated manufactory.

203

LONDON, May, 1855.

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