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FRAGMENTS OE SCIENCE

FOR

UNSCIENTIFIC PEOPLE:

A SERIES OF DETACHED ESSAYS, LECTURES,
AND REVIEWS.

BY

JOHN TYNDALL, LL. D., F. R. S.,

AUTHOR OF "HEAT AS A "™"* IF rnrtir" "T— rrrrn ON SOUND," ETC., ETC.

NEwTORK :

D. APPLETON AND COMPANY,

549 & 551 BROADWAY.

1871.

PKEFAOE.

MY MOTIVE in writing these papers was mainly that
which prompted the publication of my Koyal Institu
tion lectures ; a desire, namely, to extend sympathy for
science beyond the limits of the scientific public.

The fulfilment of this desire has caused a tempo
rary and sometimes reluctant deflection of thought
from the line of original research. But considering
the result aimed at, and in part I trust achieved, I do
not regret the price paid for it.

I have carefully looked over all the articles here
printed, added a little, omitted a little — in fact, tried
as far as my time permitted to render the work pre
sentable. Most of the essays are of a purely scien
tific character, and from those which are not, I have
endeavored, without veiling my convictions, to exclude
every word that could cause needless irritation.

From America the impulse came which induced me
to gather these " Fragments " together, and to my
friends in the United States I dedicate them.

JOHN TYNDALL.

CLUB : March, 1871.

CONTENTS.

I. — THE CONSTITUTION OP NATURE, .... 7

II. — THOUGHTS ON PRAYER AND NATURAL LAW, . . 33

III. — MIRACLES AND SPECIAL PROVIDENCES, . . , . 43

IV. — MATTER AND FORCE, . . . . . 71

V. — AN ADDRESS TO STUDENTS, . . . . .95

VI. — SCOPE AND LIMIT OF SCIENTIFIC MATERIALISM, . 107

.'VII. — SCIENTIFIC USE OF THE IMAGINATION, . . .125

VIII.— ON RADIATION, . . . . .167

A IX. — ON RADIANT HEAT IN RELATION TO THE COLOR AND CHEMI
CAL CONSTITUTION OF BODIES, . . .211
X. — ON CHEMICAL RAYS AND THE STRUCTURE AND LIGHT OF

THE SKY, . . . . . . 235

XI. — DUST AND DISEASE, ..... 275

ADDITION TO " DUST AND DISEASE," . . . 323

XII.: — LIFE AND LETTERS OF FARADAY, . . . 329

XIII. — AN ELEMENTARY LECTURE ON MAGNETISM, . . 353

XIV. — SHORTER ARTICLES:

SLATES, ...... 377

DEATH BY LIGHTNING, .... 397

SCIENCE AND SPIRITS, .... 402

VITALITY, . . . . . .410

ADDITIONAL REMARKS ON MIRACLES, . . 418

I.

THE CONSTITUTION OF NATURE.

" .. AN ESSAY.
\FortnigJitly Review, vol. iii. p. 129.]

" The gentle Mother of all
Showed me the lore of colors and of sounds ;
The innumerable tenements of beauty ;
The miracle of generative force ;
Far-reaching concords of Astronomy
Felt in the plants and in the punctual birds ;
Mainly, the linked purpose of the whole ;
And, chiefest prize, found I true liberty —
The home of homed plain-dealing Nature gave/'

RALPH WALDO ESIERSOX.

I.

THE CONSTITUTION OF NATURE.

WE cannot think of space as finite, for wherever in
imagination we erect a boundary we are compelled to think
of space as existing beyond that boundary. Thus by the
incessant dissolution of limits we arrive at a more or less
adequate idea of the infinity of space. But though com
pelled to think of space as unbounded, there is no mental
necessity to compel us to think of it either as filled or as
empty ; whether it is filled or empty must be decided by
experiment and observation. That it is not entirely void,
the starry heavens declare ; but the question still remains,
Are the stars themselves hung in vacua? Are the vast
regions which surround them, and across which their light
is propagated, absolutely empty ? A century ago the
answer to this question would be, " No, for particles of
light are incessantly shot through space." The reply of
modern science is also negative, but on a somewhat differ
ent ground. It has the best possible reasons for rejecting
the idea of luminiferous particles ; but, in support of the
conclusion that the celestial spaces are occupied by matter,
it is able to offer proofs almost as cogent as those which
can be adduced for the existence of an atmosphere round
the earth. Men's minds, indeed, rose to a conception of
the celestial and universal atmosphere through the study
of the terrestrial and local one. From the phenomena of
sound as displayed in the air, they ascended to the phe-

10 FRAGMENTS OF SCIENCE.

nomena of light as displayed in the ether / which is the
name given to the interstellar medium.

The notion of this medium must not be considered as
a vague or fanciful conception on the part of scientific men.
Of its reality most of them are as convinced as they are of
the existence of the sun and moon. The luminiferous ether
has definite mechanical properties. It is almost infinitely
more attenuated than any known gas, but its properties are
those of a solid rather than of a gas. It resembles jelly
rather than air. A body thus constituted may have its
boundaries ; but, although the ether may not be coexten
sive with space, we at all events know that it extends as
far as the most distant visible stars. In fact, it is the ve
hicle of their light, and without it they could not be seen.
This all-pervading substance takes up their molecular tre
mors, and conveys them with inconceivable rapidity to our or
gans of vision. It is the transported shiver of bodies count
less millions of miles distant, which translates itself in human
consciousness into the splendor of the firmament at night.

If the ether have a boundary, masses of ponderable
matter might be conceived to exist beyond it, but they
could emit no light. Beyond the ether dark suns might
burn ; there, under proper conditions, combustion might be
carried on ; fuel might consume unseen, and metals be
heated to fusion in invisible fires. A body, moreover, once
heated there, would continue forever heated ; a sun or
planet, once molten, would continue forever molten. For,
the loss of heat being simply the abstraction of molecular
motion by the ether, where this medium is absent no cool
ing could occur. A sentient being, on approaching a heated
body in this region, would be conscious of no augmentation
of temperature. The gradations of warmth dependent on
the laws of radiation would not exist, and actual contact
would first reveal the heat of an extra ethereal sun.

Imagine a paddle-wheel placed in water and caused to

THE CONSTITUTION OF NATURE. H

rotate. From it, as a centre, waves would issue in all
directions, and a wader, as he approached the place of dis
turbance, would be met by stronger and stronger waves.
This gradual augmentation of the impressions made upon
the wader's body is exactly analogous to the augmentation
of light when wre approach a luminous source. In the one
case, however, the coarse common nerves of the body suf
fice ; for the other we must have the finer optic nerve. But
suppose the water withdrawn; the action at a distance
would then cease, and, as far as the sense of touch is con
cerned, the wader would be first rendered conscious of the
motion of the wheel by the actual blow of the paddles.
The transference of motion from the paddles to the water
is mechanically similar to the transference of molecular
motion from the heated body to the ether ; and the propa
gation of waves through the liquid is mechanically similar
to the propagation of light and radiant heat.

As far as our knowledge of space extends, we are to
conceive it as the holder of the luminiferous ether, through
which are interspersed, at enormous distances apart, the
ponderous nuclei of the stars. Associated with the star
that most concerns us we have a group of dark planetary
masses revolving at various distances round it, each again
rotating on its own axis ; and, finally, associated with some
of these planets we have dark bodies of minor note — the
moons. Whether the other fixed stars have similar plane
tary companions or not is to us a matter of pure conjecture,
which may or may not enter into our conception of the
universe. But, probably, every thoughtful person believes,
with regard to those distant suns, that there is in space
something besides our system on which they shine.

Having thus obtained a general view of the present
condition of space, and of the bodies contained in it, we
may inquire whether things were so created at the begin
ning. Was space furnished at once, 'by the fiat of Omnipo-

FRAGMENTS OF mi-M K

1, with these burning orbs? To this question the mail
of science, if he confine himself within his own limits, will
give no answer, though it must be remarked that in the
formation of an opinion he has better materials to guide
him than anybody else. He can clearly show, however,
that the present state of things may be derivative. He
can even assign reasons which render probable its deriva
tive origin — that it was not originally what it now is. At
all events, he can prove that out of common non-luminous
matter this whole pomp of stars might have been evolved.

The law of gravitation enunciated by Newton is, that
every particle of matter in the universe attracts every other
particle with a force which diminishes as the square of the
distance increases. Thus the sun and the earth mutually
pull each other ; thus the earth and the moon are kept in
company ; the force which holds every respective pair of
masses together being the integrated force of their com
ponent parts. Under the operation of this force, a stone
falls to the ground and is warmed by the shock ; under its
operation meteors plunge into our atmosphere and rise to
incandescence. Showers of such doubtless fall incessant ly
upon the sun. Acted on by this force, were it stopped in
its orbit to-morrow, the earth would rush toward, and finally
combine with, the sun. Heat would also be developed by
this collision, and Mayer, Helmholtz, and Thomson, have
calculated its amount. It would equal that produced by
the combustion of more than five thousand worlds of solid
coal, all this heat being generated at the instant of collision.
In the attraction of gravity, therefore, acting upon non-
luminous matter, we have a source of heat more powerful
than could be derived from any terrestrial combustion. And
were the matter of the universe cast in cold detached frag
ments into space, and there abandoned to the mutual gravi
tation of its own parts, the collision of the fragments would
in the end produce tin* fnvs of the stars.

THE CONSTITUTION OF NATURE. 13

The action of gravity upon matter originally cold may,
in fact, be the origin of all light and heat, and the proxi
mate source of such other powers as are generated by
light and heat. But we have now to inquire what is the
light and what is the heat thus produced ? This question
has already been answered in a general way. Both light
and heat are modes of motion. Two planets clash and
come to rest; their motion, considered as masses, is de
stroyed, but it is really continued as a motion of their
ultimate particles. It is this motion, taken up by the
ether, and propagated through it with a velocity of one
hundred and eighty-five thousand miles a second, that comes
to us as the light and heat of suns and stars. The atoms
of a hot body swing with inconceivable rapidity, but this
power of vibration necessarily implies the operation of
forces between the atoms themselves. It reveals to us
that, while they are held together by one force, they are
kept asunder by another, their position at any moment de
pending on the equilibrium of attraction and repulsion. The
atoms are virtually connected by elastic springs, which op
pose at the same time their approach and their retreat, but
which tolerate the vibration called heat. When two bod
ies drawn together by the force of gravity strike each other,
the intensity of the ultimate vibration, or, in other words,
the amount of heat generated, is proportional to the vis
viva destroyed by the collision. The molecular motion
once set up is instantly shared with the ether, and diffused
by it throughout space.

We on the earth's surface live night and day in the
midst of ethereal commotion. The medium is never still.
The cloud-canopy above us may be thick enough to shut
out the light of the stars, but this canopy is itself a warm
body, which radiates its motion through the ether. The
earth also is warm, and sends its heat-pulses incessantly
forth. It is the waste of its molecular motion in space

14 FRAGMENTS OF SCIENCE.

that chills the earth upon a clear night ; it is the return
of its motion from the clouds which prevents the earth's
temperature on a cloudy night from falling so low. To the
conception of space being filled, we must therefore add
the conception of its being in a state of incessant tremor.
The sources of vibration are the ponderable masses of the
universe. Let us take a sample of these and examine it in
detail. When we look to our planet we find it to be an
aggregate of solids, liquids, and gases. When we look at
any one of these, we generally find it composed of still
more elementary parts. We learn, for example, that the
water of our rivers is formed by the union, in definite pro
portions, of two gases, oxygen and hydrogen. We know
how to bring these constituents together, and to cause them
to form water : we also know how to analyze the water,
and recover from it its two constituents. So, likewise, as
regards the solid proportions of the earth. Our chalk-hills,
for example, are formed by a combination of carbon, oxy
gen, and calcium. These are elements the union of which,
in definite proportions, has resulted in the formation of
chalk. The flints within the chalk we know to be a com
pound of oxygen and silicium, called silica; and our or
dinary clay is, for the most part, formed by the union of
silicium, oxygen, and the well-known light metal, alumin
ium. By far the greater portion of the earth's crust is
compounded of the elementary substances mentioned in
these few lines.

The principle of gravitation has been already described
Bfl an attraction which every particle of matter, however
small, has for every other particle. With gravity there is
no selection; no particular atoms choose, by preference,
oilier particular atoms as objects of attraction ; the attrac
tion of gravitation is proportional to the quantity of the
attracting matter, regardless of its (jualiiy. But in the
molecular world which we have now entered matters are

THE CONSTITUTION OF NATURE. 15

otherwise arranged. Here we have atoms between which
a strong attraction is exercised, and also atoms between
which a weak attraction is exercised. One atom can jostle
another out of its place in virtue of a superior force of at
traction. But though the amount of force exerted varies
thus from atom to atom, it is still an attraction of the same
mechanical quality, if I may use the term, as that of grav
ity itself. Its intensity might be measured in the same
way, namely, by the amount of motion which it can impart
in a certain time. Thus the attraction of gravity at the
earth's surface is expressed by the number thirty-two, be
cause, when acting freely on a body for a second of time,
it imparts to the body a velocity of thirty-two feet a second.
In like manner the mutual attraction of oxygen and hydro
gen might be measured by the velocity imparted to the
atoms in their rushing together. Of course such a unit of
time as a second is not here to be thought of, the whole
interval required by the atoms to cross the minute spaces
which separate them not amounting probably to more than
an inconceivably small fraction of a second.

It has been stated that when a body falls to the earth
it is warmed by the shock. Here we have what we may
call a mechanical combination of the earth and the body.
Suffer the falling body and the earth to dwindle in imagi
nation to the size of atoms, and for the attraction of grav
ity substitute that of chemical affinity, which is the name
given to the molecular attraction, we have then what is
called a chemical combination. The effect of the union in
this case also is the development of heat, and from the
amount of heat generated we can infer the intensity of the
atomic pull. Measured by ordinary mechanical standards,
this is enormous. Mix eight pounds of oxygen with one
of hydrogen, and pass a spark through the mixture ; the
gases instantly combine, their atoms rushing over the little
distances between them. Take a weight of forty-seven

10 LGMENTS ol-'

thousand pounds to mi elevation of one thousand feet above
i he earth's surface, and let it fall; the energy with which
it would strike the earth would not exceed that of the, eight
pounds of oxygen atoms as they dash against one pound
of hydrogen atoms to form water.

It is sometimes stated that the force of gravity is dis-
tinir lushed from all other forces by the fact of its resisting
ron version into any other. Chemical affinity, it is said,
can be converted into heat and light, and these again into
magnetism and electricity. But gravity refuses to be so
converted ; it is a force which maintains itself under all
circumstances, and is not capable of disappearing to give
p!a«-e to another. If by this is meant that a particle of
matter can never be deprived of its weight, the assertion
is correct ; but the law which affirms the convertibility of
natural forces was never meant, in the minds of those who
understood it, to affirm that such a conversion as that here
implied occurs in any case whatever. As regards converti-
bility into heat, gravity and chemical affinity stand on pre
cisely the same footing. The attraction in the one case is
as indestructible as in the other. Nobody affirms that
when a stone rests upon the surface of the earth the mutual
attraction of the earth and stone is abolished; nobody
means to affirm that the mutual attraction ol oxygen for
hvdrogcn ceases after the atoms have combined to form
water. What is meant in the case of chemical affinity is,
that the pull of that affinity, acting through a certain space,
imparts a motion of translation of the one atom toward the
other. This motion of translation is not heat, nor is the
force that produces it heat. But when the atoms strike and
recoil, the motion of translation is converted into a motion
of vibration, and this latter motion is heat. But the vibra
tion, SO far from causing llir extinction of the original ai-
traction, is in part carried on by that a itruct i HL The atoms
recoil in virtue of the elastic force which opposes actual

THE CONSTITUTION OF NATURE. 17

contact, and in the recoil they are driven too far back. The
original attraction then triumphs over the force of recoil,
and urges the atoms once more together. Thus, like a pen
dulum, they oscillate, until their motion is imparted to the
surrounding ether ; or, in other words, until their heat be
comes radiant heat.

In this sense, and in this sense only, is chemical affinity
converted into heat. There is, first of all, the attraction
between the atoms ; there is, secondly, space between them.
Across this space the attraction urges them. They collide,
they recoil, they oscillate. There is a change in the form
of the motion, but there is no real loss. It is so with the
attraction of gravity. To produce motion here, space must
also intervene between the attracting bodies : when they
strike motion is apparently destroyed, but in reality there
is no destruction. Their atoms are suddenly urged together
by the shock ; by their own perfect elasticity these atoms
recoil ; and thus is set up the molecular oscillation which
announces itself to the nerves as heat.

It was formerly universally supposed that by the colli
sion of unelastic bodies force was destroyed. Men saw, for
example, when two spheres of clay, or painter's putty, or
lead, were urged together, that the motion possessed by
the masses prior to impact was more or less annihilated.
They believed in an absolute destruction of the force of
impact. Until recent times, indeed, no difficulty was ex
perienced in believing this, whereas, at present, the ideas
of force and its destruction refuse to be united in most
philosophic minds. In the collision of elastic bodies, on the
contrary, it was observed that the motion with which they
clashed together was in great part restored by the resiliency
of the masses, the more perfect the elasticity the more com
plete being the restitution. This led to the idea of perfectly
elastic bodies — bodies competent to restore by their recoil
the whole of the motion which they possessed before impact.

18 1 RAGMENTS OF SCIENCE.

Hence the idea of the conservation of force, as opposed
to the destruction of force, which was supposed to occur
when inelastic bodies met in collision.

We now know that the principle of conservation holds
equally good with elastic and unelastic bodies. Perfectly
elastic bodies develop no heat on collision. They retain
their motion afterward, though its direction may be changed ;
and it is only wThen sensible motion is, in w7hole or in part,
destroyed that heat is generated. This always occurs in
unelastic collision, the heat developed being the exact
equivalent of the motion extinguished. This heat virtually
declares that the property of elasticity, denied to the masses,
exists among their atoms, and by their recoil and oscillation
the principle of conservation is vindicated.

But ambiguity in the use of the term " force " has been
for some time more and more creeping upon us. We called
the attraction of gravity a force without any reference to
motion. A body resting on a shelf is as much pulled by
gravity as when after having been pushed off the shelf it
falls toward the earth. We applied the term force also to
that molecular attraction which we called chemical affinity.
When, however, we spoke of the conservation of force in
the case of elastic collision, we meant neither a pull nor a
push, which, as just indicated, might be exerted upon inert
matter, but we meant the moving force, if I may use the
term, of the colliding masses.

What I have called moving force has a definite me
chanical measure in the amount of work that it can perform.
The simplest form of work is the raising of a weight. A
man walking up-hill or up-stairs with a pound weight in
his hand, to an elevation say of sixteen feet, performs a cer
tain amount of work over and above the lifting of his own
body. If he ascend to a height of thirty-two feet, he does
twii-e the work; if to a height of forty-eight feet, he does
ihn-p times the work; if to sixty-four feet, he does four

THE CONSTITUTION OF NATURE. 19

times the work, and so on. If, moreover, he carries up two
pounds instead of one, other things being equal, he does
twice the work ; if three, four, or five pounds, he does three,
four, or five times the work. In fact, it is plain that the
work performed depends on two factors, the weight raised
and the height to which it is raised. It is expressed by the
product of these two factors.

But a body may be caused to reach a certain elevation
in opposition to the force of gravity, without being actually
carried up to the elevation. If a hodman, for example,
wished to land a brick at an elevation of sixteen feet above
the place where he stands, he would probably pitch it up to
the bricklayer. He would thus impart, by a sudden effort,
a velocity to the brick sufficient to raise it to the required
height; the work accomplished by that effort being pre
cisely the same as if he had slowly carried up the brick.
The initial velocity which must be imparted in the case here
assumed, is well known. To reach a height of sixteen feet,
the brick must quit the man's hand with a velocity of
thirty-two feet a second. It is needless to say that a body
starting with any velocity, would, if wholly unopposed or
unaided, continue to move forever with the same velocity.
But when, in the case before us, the body is thrown upward,
it moves in opposition to gravity, which incessantly retards
its motion, and finally brings it to rest at an elevation of
sixteen feet. If not here caught by the bricklayer, it would
return to the hodman with an accelerated motion, and
reach his hand with the precise velocity it possessed on
quitting it.

Supposing the man competent to impart to the brick, at
starting, a speed of sixty-four feet a second, or twice its
former speed, would the amount of work performed in this
effort be only twice what it was in the first instance ? No ;
it would be four times that quantity. A body starting with
twice the velocity of another, will rise to four times the

20 FRAGMENTS OF SCIENCE.

height; in like manner, a threefold velocity will give a
ninefold elevation, a fourfold velocity will give a sixteen-
fold elevation, and so on. The height attained, then, or the
work done, is not proportional to the velocity, but to the
square of the velocity. As before, the work is also pro
portional to the weight elevated. Hence the work which
any moving masses whatever arc competent to perform, .by
the motion which they at any moment possess, is jointly
proportional to the weight and the square of the velocity.
Here, then, we have a second measure of work, in which we
simply translate the idea of height into its equivalent idea
of motion.

In mechanics, the product of the mass of a moving body
into the square of its velocity, expresses what is called the
vis viva, or living force. It is also sometimes called the
" mechanical effect." If, for example, we point a cannon
upward, and start a ball with twice the velocity imparted
by a second cannon, the ball will rise to four times the
height. The speedier ball, if directed against a target, will
also do four times the execution. Hence the importance
of imparting a high velocity to projectiles in war. Having
thus cleared our way to a perfectly clear conception of the
vis viva of moving masses, we are prepared for the an
nouncement that the heat generated by the collision of a
falling body against the earth is proportional to the vis
viva annihilated. In point of fact it is not an annihilation
at all, but a transference of vis viva from the mass, to its
ultimate particles. This, as we now learn, is proportional
to the square of the velocity. In the case, therefore, of two
cannon-balls of equal weight, if one strike a target with
twice the velocity of the other, it will generate four times
the heat ; if with three times the velocity, it will generate
nine times the heat, and so on.

Mr. Joule lias shown that in falling from a height of 772
feet, a body will generate an amount of heat sufficient to

THE CONSTITUTION OF NATURE. 21

raise its own weight of water one degree Fahrenheit in
temperature. "We have here the mechanical equivalent of
heat. Now, a body falling from a height of 772 feet, has,
upon striking the earth, a velocity of 223 feet a second ;
and if this velocity were imparted to a body, by any other
means, the quantity of heat generated by the stoppage of
its motion would be that stated above. Six times that ve
locity, or 1,338 feet, would not be an inordinate one for a
cannon-ball as it quits the gun ; but if animated by six
times the velocity, thirty-six times the heat will be gener
ated by the stoppage of its motion. Hence a cannon-ball
moving with a velocity of 1,338 feet a second, would, by
collision, generate an amount of heat competent to raise its
own weight of water 36 degrees Fahrenheit in tempera
ture. If composed of iron, and if all the heat generated
were concentrated in the ball itself, its temperature would
be raised about 360 degrees Fahrenheit ; because one de
gree in the case of water is equivalent to about ten de
grees in the case of iron. In artillery practice the heat
generated is usually concentrated upon the front of the
bolt, and on the portion of the target first struck. By this
concentration the heat developed may become sufficiently
intense to raise the dust of the metal to incandescence, a
flash of light often accompanying collision with the target.

Let us now fix our attention for a moment on the gun
powder which urges the cannon-ball. This is composed of
combustible matter, which if burnt in the open air would
yield a certain amount of heat. It will not yield this
amount if it performs the work of urging a ball. The heat
then generated by the gunpowder will fall short of that
produced in the open air, by an amount equivalent to the
vis viva of the ball ; and this exact amount is restored by
the ball on its collision with the target. In this perfect
way are heat and mechanical motion connected.

Broadly enunciated, the principle of the conservation

22 FRAGMENTS OF SCIENCE.

of force asserts that the quantity of force in the universe is
as unalterable as the quantity of matter ; that it is alike
impossible to create force and to annihilate it. But in
what sense are we to understand this assertion ? It would
be manifestly inapplicable to the force of gravity as New
ton defined it ; for this is a force varying inversely as the
square of the distance, and to affirm the constancy of a
varying force would be self-contradictory. Yet, when the
question is properly understood, gravity forms no exception
to the law of conservation. Following the method pur
sued by Helmholtz, I will here attempt an elementary ex
position of this law, which, though destined in its applica
tions to produce momentous changes in human thought, is
not difficult of comprehension.

For the sake of simplicity we will consider a particle of
matter, which we may call F, to be perfectly fixed, and a
second movable particle, IX, placed at a distance from F.
We will assume that these two particles attract each other
according to the Newtonian law. At a certain distance the
attraction is of a certain definite amount, which might be
determined by means of a spring-balance. At half this dis
tance the attraction would be augmented four times ; at a
third of the distance it would be augmented nine times ; at
one-fourth of the distance sixteen times, and so on. In
every case the attraction might be measured by determin
ing, with the spring-balance, the amount of tension which
is just sufficient to prevent D from moving toward F.
Thus far we have nothing whatever to do with motion ; wo
deal with statics, not with dynamics. AVe simply take into
account the distance of D from ^", and the pull exerted by
gravity at that distance.

It is customary in mechanics to represent the magni
tude of a force by a line of a certain length, a force of
double magnitude being represented by a line of double
Length, and BO OD. Placing then the particle I) at a dis-

THE CONSTITUTION OF NATURE. 23

tance from F, we can in imagination draw a straight line
from D to F, and at D erect a perpendicular to this line,
which shall represent the amount of the attraction exerted
on D in this position. If D be at a very great distance
from F the attraction will be very small, and the perpendic
ular consequently very short. Let us now suppose that at
every point in the line joining F and D a perpendicular is
erected proportional in length to the attraction exerted at
that point ; we should thus obtain an infinite number of
perpendiculars of gradually increasing length as D ap
proaches F. Uniting the ends of all these perpendiculars,
we should obtain a curve, and between this curve and the
straight line joining F and D we should have an area con
taining all the perpendiculars placed side by side. Each
one of this infinite series of perpendiculars representing an
attraction, or tension as it is sometimes called, the area just
referred to represents the total effort capable of being ex
erted by the tensions upon the particle D, during its pas
sage from its first position up to F.

Up to the present point we have been dealing with ten
sions, and not with motion. Thus far vis viva has been
entirely foreign to our contemplation of D and F. Let us
now suppose D placed at a practically infinite distance from
F ; here the pull of gravity would be nothing, and the per
pendicular representing it would dwindle to a point. In
this position the sum of the tensions capable of being ex
erted on D would be a maximum. Let D now begin to
move in obedience to the attraction exerted upon it. Mo
tion being once set up, the idea of vis viva arises. In
moving toward F the particle D consumes, as it were, the
tensions. Let us fix our attention on D at any point of the
path over which it is moving. Between that point and F
there is a quantity of unused tensions ; beyond that point
the tensions have been all consumed, but we have in their
place an equivalent quantity of vis viva. After D has

24 FRAGMENTS OF SCIENCE.

passed any point, the tension previously in store at that
point disappears, but not without having added, during the
infinitely small duration of its action, a due amount of
motion to that previously possessed by D. The nearer D
approaches to F, the smaller is the sum of the tensions re
maining, but the greater is the living force ; the farther D
is from F, the greater is the sum of the unconsumed ten
sions, and the less is the living force. Now the principle
of conservation affirms not the constancy of the value of the
tensions of gravity, nor yet the constancy of the vis viva,
taken separately, but the absolute constancy of the value
of the sum of both. At the beginning the vis viva was
zero and the tension area was a maximum ; close to F the
vis viva is a maximum, while the tension area is zero. At
every other point the work-producing power of the particle
D consists in part of vis viva and in part of tensions.

If gravity, instead of being attraction, were repulsion,
when the particles are in contact, the sum of the tensions
between two material particles D and F would be a maxi
mum, and the vis viva zero. K D, in obedience to the
repulsion, moved away from F, vis viva would be gener
ated ; and the farther D retreated from F the greater
would be its vis viva, and the less the amount of tension
still available for producing motion. Taking repulsion into
account as well as attraction, the principle of the conserva
tion of force affirms that the mechanical value of the ten
sions and vires vivce of the material universe is a constant
quantity. The universe, in short, possesses two kinds of
property which are mutually convertible, at an unvarying
rali'. The diminution of either carries with it the enhance
ment of the other, the total value of the property remain
ing urn-hanged.

The considerations that \ve have here applied to gravity
applv equally to chemical affinity. In a mixture of oxygen
and hydrogen the atoms exist apart, but by the application

THE CONSTITUTION OF NATURE. 25

of proper means they may be caused to rush together
across the space that separates them. While this space
exists, and as long as the atoms have not begun to move
toward each other, we have tensions and nothing else.
During their motion toward each other the tensions, as in
the case of gravity, are converted into vis viva. After
they clash we have still vis viva, but in another form. It
was translation, it is vibration. It was molecular transfer,
it is heat. The same considerations apply to a mixture of
hydrogen and chlorine. When these gases are mingled in
the dark they remain separate, but if a sunbeam fall upon
the mixture the atoms rush together with detonation.
Here also we have tension converted into molecular trans
lation, and molecular translation into heat and sound.

It is possible to reverse these processes, to unlock the
embrace of the atoms and replace them in their first posi
tions. But to accomplish this as much heat would be re
quired as was generated by their union. Such reversals
occur daily and hourly in Nature. By the solar waves, the
oxygen of water is divorced from its hydrogen in the leaves
of plants. As molecular vis viva the waves disappear, but
in so doing they reendow the atoms of oxygen and hydro
gen with tension. The atoms are thus enabled to recom-
bine, and when they do so they restore the precise amount
of heat consumed in their separation. The same remarks
apply to the compound of carbon and oxygen, called car
bonic acid, which is exhaled from our lungs, produced by
our fires, and found sparingly diffused everywhere through
out the air. In the leaves of plants the sunbeams also
wrench these atoms asunder, and sacrifice themselves in the
act ; but when the plants are burnt the amount of heat
consumed in their production is restored.

This, then, is the rhythmic play of Nature as regards
her forces. Throughout all her regions she oscillates from
tension to vis viva, from vis viva to tension. We have
2

20 FRAGMENTS OF SCIENCE.

the same play in the planetary system. The earth's orbit
is an ellipse, one of the foci of which is occupied by the
sun. Imagine the earth at the most distant part of the
orbit. Her motion, and consequently her vis viva, is then
a minimum. The planet rounds the curve, and begins to
approach the sun. In front it has a store of tensions,
\\ -li irh is gradually consumed, an equivalent amount of vis
i'ira being generated. When nearest to the sun the mo-
lion, and consequently the vis viva, is a maximum. But
here the available tensions have been used up. The earth
rounds this portion of the curve and retreats from the sun.
Tensions are now stored up, but vis viva is lost, to be again
restored at the expense of the complementary force on the
opposite side of the curve. Thus beats the heart of the
universe, but without increase or diminution of its total
stock of force.

I have thus far tried to steer clear amid confusion by
fixing the mind of the reader upon things rather than upon
names. But good names are essential; and here, as yet,
we are not provided with such. We have had the force of
gravity and living force — two utterly distinct things. We
have had pulls and tensions; and we might have had the
force of heat, the force of light, the force of magnetism, or
the force of electricity — all of which terms have1 been em
ployed more or less loosely by writers on physics. This
confusion is happily avoided by the introduction of the
term " energy," embracing under it both tension and ria
viva. Energy is possessed by bodies already in motion ;
it is then actual, and we agree to call it actual or <7y/^/,/,/,-
< in /y/y. It is our old vis viva. On the other hand, energy
is possible to bodies not in motion, but which, in virtue of
attraction or repulsion, possess a power of motion which
would realize itself if all hinderanees were removed.
Looking, for example, at gravity, a body on the earth's
surface in a position from which it cannot fall to a lower

THE CONSTITUTION OF NATURE. 27

one possesses no energy. It has neither motion nor power
of motion. But the same body suspended at a height
above the earth has a power of motion though it may not
have exercised it. Energy is possible to such a body, and
we agree to call this potential energy. It embraces our old
tensions. We, moreover, speak of the conservation of en
ergy instead of the conservation of force ; and say that the
sum of the potential and dynamic energies of the material
universe is a constant quantity.

A body cast upward consumes the actual energy of
projection, and lays up potential energy. When it reaches
its utmost height all its actual energy is consumed, its
potential energy being then a maximum. When it re
turns, there is a reconversion of the potential into the
actual. A pendulum at the limit of its swing possesses
potential energy ; at the lowest point of its arc its energy
is all actual. A patch of snow resting on a mountain-slope
has potential energy ; loosened, and shooting down as an
avalanche, it possesses dynamic energy. The pine-trees
growing on the Alps have potential energy ; but rushing
down the Holzrinne of the wood-cutters they possess actual
energy. The same is true of the mountains themselves.
As long as ihe rocks which compose them can fall to a
lower level, they possess potential energy, which is con
verted into actual when the frost ruptures their cohesion
and hands them over to the action of gravity. The hammer
of the great bell of Westminster, when raised before strik
ing, possesses potential energy ; when it falls, the energy
becomes dynamic ; and after the stroke, we have the
rhythmic play of potential and dynamic in the vibrations
of the bell. The same holds good for the molecular oscilla
tions of a heated body. An atom is pressed against its
neighbor, and recoils. But the ultimate amplitude of the
recoil is soon attained, the motion of the atom in that
direction is checked, and for an instant its energy is all

23 FRAGMENTS OF SCIENCE.

potential. It is then drawn toward "its neighbor with
accelerated speed, thus, by attraction, converting its poten
tial into dynamic energy. Its motion in this direction is
also finally checked, and, for an instant, again its energy is
all potential. It again retreats, converting, by repulsion,
its potential into dynamic energy, till the latter attains a
maximum, after which it is again changed into potential
energy. Thus, what is true of the earth, as she swings to
:ui(l fro in her yearly journey round the sun, is also true of
her minutest atom. We have wrheels within wheels, and
rhvlhm within rhythm.

When a body is heated, a change of molecular arrange
ment always occurs, and to produce this change heat is
consumed. Hence, a portion only of the heat communi
cated to the body remains as dynamic energy. Looking
back on some of the statements made at the beginning of
this article, now that our knowledge is more extensive, we
see the necessity of qualifying them. When, for example,
two bodies clash, heat is generate*! ; but the heat, or molec
ular dynamic energy, developed at the moment of collision,
is not the equivalent of the sensible dynamic energy de
stroyed. The true equivalent is this heat, plus the potential
energy conferred upon the molecules by the placing of
greater distances between them. This molecular potential
energy is afterward, on the cooling of the body, converted
into heat.

Wherever two atoms capable of uniting together by
their mutual attractions exist separately, they form a store
of potential energy. Thus our woods, forests, and coal
fields on the one hand, and our atmospheric oxvuvn on the
other, constitute a vast store of energy of this kind — vast,
but far from infinite. We have, besides our coal-fields,
bodies in the metallic condition more or less sparsely dis
tributed in the earth's crust. These bodies can be oxidized,
and liemv are, so far as they g«>, stores of potent ial energy.

THE CONSTITUTION OF NATURE. 29

But the attractions of the great mass of the earth's crust
are already satisfied, and from them no further energy can
possibly be obtained. Ages ago the elementary constitu
ents of our rocks clashed together and produced the motion
of heat, which was taken up by the ether and carried away
through stellar space. It is lost forever as far as we are
concerned. In those ages the hot conflict of carbon,
oxygen, and calcium, produced the chalk and limestone
hills which are now cold ; and from this carbon, oxygen,
and calcium, no further energy can be derived. And so it
is with almost all the other constituents of the earth's
crust. They took their present form in obedience to mo
lecular force ; they turned their potential energy into dy
namic, and gave it to the universe ages before man
appeared upon this planet. For him a residue of potential
energy remains, vast truly in relation to the life and wants
of an individual, but exceedingly minute in comparison
with the earth's primitive store.

To sum up. The whole stock of energy or working-
power in the world consists of attractions, repulsions, and
motions. If the attractions and repulsions are so circum
stanced as to be able to produce motion, they are sources
of working-power, but not otherwise. As stated a moment
ago, the attraction exerted between the earth and a body
at a distance from the earth's surface is a source of working-
power ; because the body can be moved by the attraction,
and in falling to the earth can perform work. "When it
rests upon the earth's surface it is not a source of power or
energy, because it can fall no farther. But though it has
ceased to be a source of energy, the attraction of gravity still
acts as deforce, which holds the earth and weight together.

The same remarks apply to attracting atoms and mole
cules. As long as distance separates them, they can move
across it in obedience to the attraction, and the motion
thus produced may, by proper appliances, be caused to

30 FRAGMENTS OF SCIENCE.

perform mechanical work. When, for example, two atoms
of hydrogen unite with one of oxygen, to form water, the
atoms are first drawn toward each other — they move, they
clash, and then, by virtue of their resiliency, they recoil and
quiver. To this quivering motion we give the name of
heat. Now this atomic vibration is merely the redistribu
tion of the motion produced by the chemical affinity ; and
this is the only sense in which chemical affinity can be said
to be converted into heat. We must not imagine the
chemical attraction destroyed, or converted into any thing
else. For the atoms when mutually clasped to form a
molecule of water, are held together by the very attraction
which first drew them toward each other. That which has
really been expended is the putt exerted through the space by
which the distance between the atoms has been diminished.

If this be understood it will be at once seen that gravity
may in this sense be said to be convertible into heat ; that
it is in reality no more an outstanding and inconvertible
agent, as it is sometimes stated to be, than chemical affin
ity. By the exertion of a certain pull through a certain
space a body is caused to clash with a certain definite
velocity against the earth. Heat is thereby developed,
and this is the only sense in which gravity can be said to
be converted into heat. In no case is the force which pro
duces the motion annihilated or changed into any thing
else. The mutual attraction of the earth and weight exists
when they are in contact as when they were separate ;
but the ability of that attraction to employ itself in the
production of motion does not exist.

The transformation, in this case, is easily followed by
the mind's eye. First, the weight as a whole is set in
motion by the attraction of gravity. This motion of the
mass is arrested by collision with the earth, being broken up
into molecular tremors, to which we give the name of heat,

And when we reverse the process, ami employ those

THE CONSTITUTION OF NATURE. 31

tremors of heat to raise a weight, as is done through the
intermediation of an elastic fluid in the steam-engine, a
certain definite portion of the molecular motion is de
stroyed in raising the weight. In this sense, and this sense
only, can the heat be said to be converted into gravity, or,
more correctly, into potential energy of gravity. It is not
that the destruction of the heat has created any new
attraction, but simply that the old attraction has now a
power conferred upon it, of exerting a certain definite pull
in the interval between the starting-point of the falling
weight and its collision with the earth.

When, therefore, writers on the conservation of energy
speak of tensions being " consumed " and " generated,"
they do not mean thereby that old attractions have been an
nihilated, and new ones brought into existence, but that,
in the one case, the power of the attraction to produce
motion has been diminished by the shortening of the dis
tance between the attracting bodies, and that in the other
case the power of producing motion has been augmented
by the increase of the distance. These remarks apply to
all bodies, whether they be sensible masses or molecules.

Of the inner quality that enables matter to attract
matter we know nothing; and the law of conservation
makes no statement regarding that quality. It takes the
facts of attraction as they stand, and affirms only the con
stancy of working-power. That power may exist in the
form of MOTION ; or it may exist in the form of FOKCE, with
distance to act through. The former is dynamic energy,
the latter is potential energy, the constancy of the sum of
both being affirmed by the law of conservation. The con
vertibility of natural forces consists solely in transforma
tions of dynamic into potential, and of potential into dy
namic energy, which are incessantly going on. In no other
sense has the convertibility of force, at present, any scien
tific meaning.

II.

THOUGHTS ON PRAYER AND NATURAL
LAW.

AN EXTRACT.
[Mountaineering in 1801, p. 33.]

'Aber im stillon Geniach cniwirft bcdcutcndc Zirkd

Sinnend der Weise.

Folgt durch die Luftc dcm Klang, folgt durch den Aether dem Strahl,

Sucht das vertraute Geset/ iu des Zu falls grausenden Wundern,

Sucht den ruhendcn Pol iu dor Ersdieinungen Fluelit."

ScniLLER.

II.

PRAYER AND NATURAL LAW.

THE aspects of Nature are more varied and impressive
in Alpine regions than elsewhere. The mountains in their
setting of deep-blue sky ; the glow of firmament and peaks
at sunrise and sunset ; the formation and distribution of
clouds ; the descent of rain, hail, and snow ; the stealthy
slide of glaciers and the rush of avalanches and rivers ;
the fury of storms ; thunder and lightning, with their
occasional accompaniment of blazing woods — all these
things tend to excite the feelings and to bewilder the mind.
In this ent-anglement of phenomena it seems hopeless to
seek for law or orderly connection. And before the
thought of law dawned upon the human mind men natu
rally referred these inexplicable effects to personal agency.
The savage saw in the fall of a cataract the leap of a spirit,
and the echoed thunder-peal was to him the hammer-clang
of an exasperated god. Propitiation of these terrible
powers was the consequence, and sacrifice was offered to
the demons of earth and air.

But observation tends to chasten the emotions and to
check those structural efforts of the intellect which have
emotion for their base. One by one natural phenomena
have been associated with their proximate causes; and
the idea of direct personal volition mixing itself in the
economy of Nature is retreating more and more. Many of
us fear this tendency ; our faith and feelings are dear to us,

36 FRAGMENTS OF SCIENCE.

and we look with suspicion and dislike on any philosophy,
the apparent tendency of which is to dry up the soul.
Probably every change from ancient savagery to our present
enlightenment excited, in a greater or less degree, a fear
of this kind. But the fact is, that we have not yet deter
mined whether the form under which they now appear in
the world is necessary to the life and warmth of religious
feeling. We may err in linking the imperishable with the
transitory, and confound the living plant with the decaying
r pole to which it clings. My object, however, at present is
not to argue, but to mark a tendency. We have ceased to
propitiate the powers of Nature — ceased even to pray for
things in manifest contradiction to natural laws. In Prot
estant countries, at least, I think it is conceded that the
age of miracles is past.

The general question of miracles is at present in able
and accomplished hands ; and were it not so, my polemical
acquirements are so limited, that I should not presume to
enter upon a discussion of this subject on its entire merits.
But there is one little outlying point, which attaches itself
to this question, on which a student of science, without
quitting the ground which strictly belongs to him, may
offer a remark.

At the aubergc near the foot of the Rhone glacier, I
met, in the summer of 1858, an athletic young priest, who,
after a solid breakfast, including a bottle of wine, informed
me that he had come up to " bless the mountains." This
was the annual custom of the place. Year by year the
Highest was entreated, by official intercessors, to make
such meteorological arrangements as should insure food
and shelter for the flocks and herds of the Valaisians. A
diversion of the Rhone, or a deepening of the river's bed,
would have been of incalculable benefit to the inhabitants
of the valley at the time I now mention. But the priest
would have shrunk from the idea of asking the Omnipo-

PRAYER AND NATURAL LAW. 37

tent to open a new channel for the river, or to cause a
portion of it to flow over the Grimsel Pass, and down the
vale of Oberhasli to Brientz. This he would have deemed
a miracle, and he did not come to ask the Creator to per
form miracles, but to do something which he manifestly
thought lay quite within the bounds of the natural and
non-miraculous. A Protestant gentleman, who was present
at the time, smiled at this recital. He had no faith in the
priest's blessing, still he deemed his prayer different in
kind from a request to open a new river-cut, or to cause
the water to flow up-hill.

In a similar manner we Protestants smile at the honest
Tyrolese priest, who, when he feared the bursting of a
glacier-dam, offered the sacrifice of the mass upon the ice
as a means of averting the calamity. That poor man did
not expect to convert the ice into adamant, or to strengthen
its texture so as to enable it to withstand the pressure of
the water ; nor did he expect that his sacrifice would cause
the stream to roll back upon its source and relieve him, by
a miracle, of its presence. But beyond the boundaries of
his knowledge lay a region where rain was generated, he
knew not how. He was not so presumptuous as to expect
a miracle, but he firmly believed that in yonder cloud-land
matters could be so arranged, without trespass on the
miraculous, that the stream which threatened him and his
flock should be caused to shrink within its proper bounds.

Both these priests fashioned that which they did not
understand to their respective wants and wishes. In their ,
case imagination wrought, unconditioned by a knowledge
of laws. A similar state of mind was long prevalent
among mechanicians ; many of whom, and some of them
extremely skilful ones, were occupied a century ago with
the question of a perpetual motion. They aimed at con
structing a machine which should execute work without
the expenditure of power ; and many of them went mad

38 FRAGMENTS OF SCIEM K.

in the pursuit of this object. The faith in such a consum
mation, involving as it did immense personal interest to
the inventor, was extremely exciting, and every attempt to
destroy this faith was met by bitter resentment on the
part of those who held it. Gradually, however, as men
became more and more acquainted with the true functions
of machinery, the dream dissolved. The hope of getting
work out of mere mechanical combinations disappeared;
but still there remained for the speculator a cloud-land
denser than that which filled the imagination of the Tyrol-
ese priest, and out of which he still hoped to evolve per
petual motion. There was the mystic store of clicmic
force, which nobody understood; there were heat and
light, electricity and magnetism, all competent to produce
mechanical motions.1 Here, then, is the mine in which
v we must seek our gem. A modified and more refined form
of the ancient faith revived ; and, for aught I know, a rem
nant of sanguine designers may at the present moment be
engaged on the problem which like-minded men in former
years left unsolved.

And why should a perpetual motion, even under modern
conditions, be impossible ? The answer to this question is
the statement of that great generalization of modern sci
ence, which is known under the name of the Conservation
of Energy. This principle asserts that no power can make
its appearance in Nature without an equivalent expenditure
of some other power ; that natural agents are so related to
each other as to be mutually convertible, but that no new
agency is created. Light runs into heat ; heat into elec
tricity ; electricity into magnetism ; magnetism into me
chanical force ; and mechanical force again into light and
heat. The Proteus changes, but he is ever the same ; and
his changes in Nature, supposing no miracle to supervene,
are the expression, not of spontaneity, but of physical neces-
1 Sec Ilclmholtz— " Wcclipclwirkung dcr Naturkrafte."

PRAYER AND NATURAL LAW. 39

sity. A perpetual motion, then, is deemed impossible, be
cause it demands the creation of force, whereas the principle
of Conservation is, no creation but infinite conversion.

It is an old remark that the law which moulds a tear
also rounds a planet. In the application of law in Nature
the terms great and small are unknown. Thus the principle
referred to teaches us that the Italian wind gliding over
the crest of the Matterhorn is as firmly ruled as the earth
in its orbital revolution round the sun ; and that the fall of
its vapor into clouds is exactly as much a matter of neces
sity as the return of the seasons. The dispersion, there
fore, of the slightest mist by the special volition of the
Eternal, would be as much a miracle as the rolling of the
Rhone over the Grimsel precipices and down Haslithal to
Brientz.

It seems to me quite beyond the present power of
science, to demonstrate that the Tyrolese priest, or his
colleague of the Rhone valley, asked for an " impossibility "
in praying for good weather ; but science can demonstrate
the incompleteness of the knowledge of Nature which
limited their prayers to this narrow ground ; and she may
lessen the number of instances in which we " ask amiss,"
by showing that we sometimes pray for the performance
of a miracle when we do not intend it. She does assert,
for example, that, without a disturbance of natural law,
quite as serious as the stoppage of an eclipse, or the rolling
of the St. Lawrence up the Falls of Niagara, no act of
humiliation, individual or national, could call one shower
from heaven, or deflect toward us a single beam of the sun.

Those, therefore, who believe that the miraculous is still
active in Nature, may, with perfect consistency, join in our
periodic prayers for fair weather and for rain : while those
who hold that the age of miracles is past, will refuse to
join in such petitions. And if these latter wish to fall back
upon such a justification, they may fairly urge that the

40 FRAGMENTS OF SCIENCE.

latest conclusions of science arc in perfect accordance with
the doctrine of the Master Himself, which manifestly was
that the distribution of natural phenomena is not affected
by moral or religious causes. " He maketh His sun to rise
on the evil and on the good, and sendeth rain on the just
and on the unjust." Granting "the power of Free-will in
man," so strongly claimed by Professor Mansel in his ad
mirable defence of the belief in miracles, and assuming the
efficacy of free prayer to produce changes in external
Nature, it necessarily follows that natural laws are more or
less at the mercy of man's volition, and no conclusion
founded on the assumed permanence of those laws would
be worthy of confidence.

It is a wholesome sign for England that she numbers
among her clergy men wise enough to understand all this,
and courageous enough to act up to their knowledge.
Such men do service to the public character by encourag
ing a manly and intelligent conflict with the causes of
disease and scarcity, instead of a delusive reliance on
supernatural aid. But they have also a value beyond this
local and temporary one. They prepare the public rnind
for changes which, though inevitable, could hardly, without
such preparation, be wrought without violence. Iron is
strong ; still, water in crystallizing will shiver an iron
envelope, and the more unyielding the metal is, the worse
for its safety. There are men among us who would encom
pass philosophic speculation by a rigid envelope, hoping-
thereby to restrain it, but in reality giving it explosive
force. If we want an illustration of this we have only to
look at modern Rome. In England, thanks to men of the
stamp to which I have alluded, scope is gradually given to
thought for changes of aggregation, and the envelope
slowly alters its form in accordance witli the necessities o/
the time.

THE proximate origin of the foregoing slight article, and probably the
remoter origin of the next following one, was this : Some years ago, a
day of prayer and humiliation, on account of a bad harvest, was ap
pointed by the proper religious authorities ; but certain clergymen of the
Church of England, doubting the wisdom of the demonstration, declined
to join in the services of the day. For this act of nonconformity they
were severely censured by some of their brethren. Rightly or wrongly,
my sympathies were on the side of these men ; and, to lend them a help
ing hand in their struggle against odds, I inserted the foregoing chapter
in the little book mentioned on the title-page. Some time subsequently
I received from a gentleman of great weight and distinction in the scien
tific world, and, I believe, of perfect orthodoxy in the religious one, a
note directing my attention to an exceedingly thoughtful article on
Prayer and Cholera in the Pall Mall Gazette. My eminent correspondent
deemed the article a fair answer to the remarks made by me in 1861.
I also was struck by the temper and ability of the article, but I could
not deem its arguments satisfactory, and, in a short note to the editor of
the Pall Mall Gazette, I ventured to state so much. This letter elicited
some very able replies, and a second leading article was also devoted to
the subject. In answer to all, I risked the publication of a second letter,
and soon afterward, by an extremely courteous note from the editor, the
discussion was closed.

Though thus stopped locally, the discussion flowed in other directions.
Sermons were preached, essays were published, articles were written,
while a copious correspondence occupied the pages of some of the re
ligious newspapers. It gave me sincere pleasure to notice that the dis
cussion, save in a few cases where natural coarseness had the upper
hand, was conducted with a minimum of vituperation. The severity
shown was hardly more than sufficient to demonstrate earnestness, while
gentlemanly feeling was too predominant to permit that earnestness to
contract itself to bigotry or to clothe itself in abuse. It was probably
the memory of this discussion which caused another excellent friend of
mine to recommend to my perusal the exceedingly able work which in
the next article I have endeavored to review.

III.
MIRACLES AND SPECIAL PROVIDENCES.

A REVIEW.

[Fortnightly Review, New Scries, vol. i., p. 645.]

" Mr. Mozley's book belongs to that class of writing of which Butler
jiiay lie taken as the type. It is strong, genuine argument about difficult
matters, fairly tracing what is difficult, fairly trying to grapple, not with
what appears the gist and strong point of a question, but with what really
at bottom is the knot of it. It is a book the reasoning of which may not
satisfy every one. . . . But we think it is a book for people who wish to
see a great subject handled on a scale which befits it, and with a percep
tion of its real elements. It is a book which will have attractions for
those who like to see a powerful mind applying itself, without shrinking
or holding back, without trick, or reserve, or show of any kind, as a
wrestler closes body to body with his antagonist, to the strength of an
adverse and powerful argument." — The Times, Tuesday, June 5, 1866.

" We should add, that the faults of the work are wholly on the surface
and in the arrangement ; that the matter is as solid and as logical as that
of any book within recent memory, and that it abounds in striking pas
sages, of which we have scarcely been able even to give a sample. No
future arguer against miracles cau afford to pass it over." — Saturday Rc-
riw, Sqrtcmbcr 15, 1866.

III.

MIRACLES AND SPECIAL PROVIDENCES.

IT is my privilege to enjoy the friendship of a select
number of religious men, with whom I converse frankly
upon theological subjects, expressing without disguise the
notions and opinions I entertain regarding their tenets, and
hearing in return these notions and opinions subjected to
criticism. I have thus far found them liberal and loving
men, patient in hearing, tolerant in reply, who know how
to reconcile the duties of courtesy with the earnestness of
debate. From one of these, nearly a year ago, I received
a note, recommending strongly to my attention the volume
of " Bampton Lectures " for 1865, in which the question of
miracles is treated by Mr. Mozley. Previous to receiving
this note, I had in part made the acquaintance of the work,
through the able and elaborate review of it which had ap
peared in the Times. The combined effect of the letter
and the review was to make the book the companion of
my summer tour in the Alps. There, during the wet and
snowy days which were only too prevalent last year, and
during the days of rest interpolated between days of toil,
I made myself more thoroughly conversant with Mr. Moz-
ley's volume. I found it clear and strong — an intellectual
tonic, as bracing and pleasant to my mind as the keen air
of the mountains was to my body. From time to time I
jotted down my thoughts regarding it, intending afterward,
if time permitted, to work them up into a coherent whole.

4G l-KACMKNTS OF SCIKNCK.

Other duties, however, interfered Avitli the carrying1 out of
this intention, and what I wrote last summer I now pub
lish, not hoping within any reasonable time to be able to
render my defence of scientific method more complete.

Mr. Mozley refers at the outset of his task to the move
ment against miracles which of late years has taken place,
and which determined his choice of a subject. He acquits
modern science of having had any great share in the pro
duction of this movement. The objection against miracles,
he says, does not arise from any minute knowledge of the
laws of Nature, but simply because they are opposed to
that plain and obvious order of Nature which everybody
sees. The present movement is, he thinks, to be as"cribe< 1 1 « >
the greater earnestness and penetration of the present age.
Formerly miracles were accepted without question, because
without reflection; but the exercise of what Mr. Mozley
calls the historic imagination is a characteristic of our own
time. Men are now accustomed to place before themselves
vivid images of historic facts, and when a miracle rises to
view, they halt before the astounding occurrence, and real
izing it with the same clearness as if it were now passing
before their eyes, they ask themselves, " Can this have
taken place ? " In some instances the effort to answer this
question has led to a disbelief in miracles, in others to a
strengthening of belief. The end and aim of Mr. Mozley's
lectures is to show that the strengthening of belief is the
logical result which ought to follow from the examination
of the facts.

Attempts have been made by religious men to bring
>cripture miracles within the scope of the order of
Nature, but all such attempts are rejected by Mr. Mo/ley
as utterly futile and wide of the mark. Regarding mira
cles as a necessary accompaniment of a revelation, their
evidential value in his eyes depends entirely upon their
deviation from the order of Nature. Thin deviating, they

MIRACLES AND SPECIAL PROVIDENCES. 47

suggest and illustrate to him a power higher than JNature,
a " personal will ; " and they commend the person in whom
this power is vested as a messenger from on high. With
out these credentials such a messenger would have no right
to demand belief, even though his assertion regarding his
divine mission were backed by a holy life. Nor is it by
miracles alone that the order of Nature is, or may be, dis
turbed. The material universe is also the arena of " spe
cial providences." Under these two heads Mr. Mozley dis
turbs the total preternatural. One form of the preternatural
may shade into the other, as one color passes into another
in the rainbow ; but while the line which divides the spe
cially providential from the miraculous cannot be sharply
drawn, their distinction broadly expressed is this, that
while a special providence can only excite surmise more
or less probable, it is " the nature of a miracle to give
proof, as distinguished from mere surmise of divine de-
sign." m

Mr. Mozley adduces various illustrations of what he re
gards to be special providences as distinguished from mira
cles. " The death of Arius," he says, " was not miraculous,
because the coincidence of the death of a heresiarch taking
place when it was peculiarly advantageous to the orthodox
faith .... was not such as to compel the inference of ex
traordinary Divine agency ; but it was a special providence,
because it carried a reasonable appearance of it. The mir
acle of the Thundering Legion was a special providence,
but not a miracle, for the same reason, because the coinci
dence of an instantaneous fall of rain in answer to prayer
carried some appearance, but not proof, of preternatural
agency." The eminent lecturer's remarks on this head
brought to my recollection certain narratives published in
Methodist magazines, which I used to read with avidity
when a boy. The title of these chapters, if I remember
right, was " The Providence of God asserted," and in them

48 FRAGMENTS <>r .-en;

the most extraordinary and exciting escapes from peril were
recounted and ascribed to prayer, while equally wonderful
instances of calamity were adduced as illustrations of Di
vine retribution. In such magazines, or elsewhere, I found
recorded the case of the celebrated Samuel Hick, which, as
it illustrates a whole class of special providences, approach-
in. ir in conclusiveness to miracles, is worthy of mention here.
It is related of this holy man — and I, for one, have no doubt
of his holiness — that flour was lacking to make the sacra
mental bread. Grain was present, and a windmill was
present, but there was no wind to grind the corn. With
faith, undoubting Samuel Hick prayed to the Lord of the
winds: the sails turned, the corn was ground, after which
the wind ceased. According to the canon of the Bampton
Lecturer, this, though carrying a strong appearance of an
immediate exertion of Divine energy, lacks by a hair's-
breadth the quality of a miracle. For the wind uu<jht have
arisen, and miyht have ceased, in the ordinary course of
Nature. Hence the occurrence did not " compel the infer
ence of extraordinary Divine agency." In like manner Mr.
Mozley considers that " the appearance of the cross to
Constantino was a miracle, or a special providence, ac
cording to which account of it we adopt. As only a mete
oric appearance in the shape of a cross it gave some token
of preternatural agency, but not full evidence."

In the Catholic canton of Switzerland where I now
write, and still more among the pious Tyrolese, the moun
tains are dotted with shrines, containing offerings of all
kinds, in acknowledgment of special mercies — legs, feet,
arms, and hands of gold, silver, brass, and wood, according
•rldly possessions enabled the grateful heart to cxj.iv-s
ii> indebtedness. Most of these oil' e made to the

to Mary. They are recognitions of "special provi
dences," wrought through the instrumentality of the Mother
of God. Mr. M"zl''y's belief, that of the Methodic i.-hron-

MIRACLES AXD SPECIAL PROVIDENCES. 49

icier, and that of the Tyrolese peasant, are substantially the
same. Each of them assumes that Nature, instead of flow
ing ever onward in the uninterrupted rhythm of cause and
effect, is mediately ruled by the free human will. As re
gards direct action upon natural phenomena, man's will is
confessedly powerless, but it is the trigger which, by its
own free action, liberates the Divine power. In this sense,
and to this extent, man, of course, commands Nature.

Did the existence of this belief depend solely upon the
material benefits derived from it, it could not, in my opinion,
last a decade. As a purely objective fact we should soon
see that the distribution of natural phenomena is unaffected
by the merits or the demerits of man ; that the law of gravi
tation crushes the simple worshippers of Ottery St. Mary,
while singing their hymns, just as surely as if they were
engaged in a midnight brawl. The hold of this belief upon
the human mind is not due to outward verification, but to
the inner warmth, force, and elevation with which it is com
monly associated. It is plain, however, that these feelings
may exist under the most various forms. They are not
limited to Church of England Protestantism — they are not
even limited to Christianity. Though less refined, they are
certainly not less strong, in the heart of the Methodist and
the Tyrolese than in the heart of Mr. Mozley. Indeed, those
feelings belong to the primal powers of man's nature. A
" skeptic " may have them. They find vent in the battle-
cry of the Moslem. They take hue and form in the hunting-
grounds of the red Indian ; and raise all of them, as they
raise the Christian, upon a wave of victory, above the ter
rors of the grave.

The character, then, of a miracle, as distinguished from
a special providence, is that the former furnishes proof,
while in the case of the latter we have only surmise,
solve the element of doubt, and the alleged fact passes from
the one class of the preternatural into the other. In other
3

50 FRAGMENTS OF SCIENCE.

words, if a special providence could be proved to be a spe
cial providence, it would cease to be a special providence
and become a miracle. There is not the least cloudiness
about Mr. Mozley's meaning here. A special providence is
a doubtful miracle. Why, then, not use the correct phra
seology ? The term employed conveys no negative sug
gestion, whereas the negation of certainty is the peculiar
characteristic of the thing intended to be expressed. There
is an apparent unwillingness on the part of Mr. Mozley to
call a special providence what his own definition makes it
to be. Instead of speaking of it as a doubtful miracle, he
calls it " an invisible miracle." He speaks of the point of
contact of supernatural power with the chain of causation
being so high up as to be wholly, or in part, out of sight,
whereas the essence of a special providence is the uncer
tainty whether there is any contact at all, either high or
low. By the use of an incorrect term, however, a grave
danger is avoided. For the idea of doubt, if kept system
atically before the mind, would soon be fatal to the special
providence as a means of edification. The term employed,
on the contrary, invites and encourages the trust which is
necessary to supplement the evidence.

This inner trust, though at first rejected by Mr. Mozley
in favor of external proof, is subsequently called upon to
do momentous duty with regard to miracles. Whenever
the evidence of the miraculous seems incommensurate with
the fact which it has to establish, or rather when the fact
is so amazing that hardly any evidence is sufficient to estab
lish it, Mr. Mozley invokes "the affections." They must
urge the reason to accept the conclusion from which unaided
it recoils. The affections and emotions are eminently the
court of appeal in matters of real religion, which is an affair
of the heart, but they are not, I submit, the court in which
to weigh allegations regarding the credibility of physical
foots. These must be judged by the dry light of the intel-

MIRACLES AND SPECIAL PROVIDENCES. 51

lect alone, appeals to the affections being reserved for cases
where moral elevation, and not historic conviction, is the
aim. It is, moreover, because the result, in the case under
consideration, is deemed desirable that the affections are
called upon to back it. If undesirable, they would, with
equal right, be called upon to act the other way. Even to
the disciplined scientific mind this would be a dangerous
doctrine. A favorite theory — the desire to establish or
avoid a certain result — can so warp the mind as to destroy
its power of estimating facts. I have known men to work
for years under a fascination of this kind, unable to extri
cate themselves from its fatal influence. They had certain
data, but not, as it happened, enough. By a process exactly
analogous to that invoked by Mr. Mozley they supplemented
the data, and went wrong. From that hour their intellects
were so blinded to the perception of adverse phenomena
that they never reached truth. If, then, to the disciplined
scientific mind, this incongruous mixture of proof and trust
be fraught with danger, what must it be to the indiscrimi
nate audience which Mr. Mozley addresses ? In calling
upon this agency he acts the part of Frankenstein. It is
the monster thus evoked that we see stalking abroad, in
the so-called spiritualistic phenomena of the present day.
Again, I say, where the aim is to elevate the mind, to
quicken the moral sense, to kindle the fire of religion in the
soul, let the affections by all means be invoked ; but they
must not be permitted to color our reports, or to influence
our acceptance of reports of occurrences in external Nature.
Testimony as to natural facts is usually worthless when
wrapped in this atmosphere of the affections, the most
earnest subjective truth being thus rendered perfectly com
patible with the most astounding objective error.

There are questions in judging of which the affections
or sympathies are often our best guides, the estimation of
moral goodness being one of these. But at this precise

52 FRAGMENTS OF SCIENCE.

point, where they are really of use, Mr. Mozley excludes
the affections, and demands a miracle as a certificate of
character. He will not accept any other evidence of the
perfect goodness of Christ. " No outward life or conduct,"
he says, " however irreproachable, could prove His perfect
sinlessness, because goodness depends upon the inward
motive, and the perfection of the inward motive is not
proved by the outward act." But surely the miracle is an
outward act, and to pass from it to the inner motive im
poses a greater strain upon logic than that involved in our
ordinary methods of estimating men. There is, at least,
moral congruity between the outward goodness and the
inner life, but there is no such congruity between the mira
cle and the life within. The test of moral goodness laid
down by Mr. Mozley is not the test of John, who says, " He
that doeth righteousness is righteous ; " nor is it the test
of Jesus — " By their fruits ye shall know them ; do men
gather grapes of thorns, or figs of thistles ? " But it is the
test of another : " If thou be the Son of God, command that
these stones be made bread." For my own part, I prefer
the attitude of Fichte to that of Mr. Mozley. " The Jesus
of John," says this noble and mighty thinker, " knows no
other God than the True God, in whom we all are, and live,
and may be blessed, and out of whom there is only Death
and Nothingness. And he appeals, and rightly appeals, in
support of this truth, not to reasoning, but to the inward
practical sense of truth in man, not even knowing any other
proof than this inward testimony, ' If any man will do the
will of Him who sent me, he shall know of the doctrine
whether it be of God." '

Accepting Mr. Mozley's test, with which alone I am now
dealing, it is evident that, in the demonstration of moral
goodness, the quantity of the miraculous comes into play.
Had Christ, for example, limited Himself to the conversion
of water into wine, He would have fallen short of the per-

MIRACLES AND SPECIAL PROVIDENCES. 53

formancc of Jannes and Jambres, for it is a smaller thing to
convert one liquid into another than to convert a dead rod
into a living serpent. But Jannes and Jambres, we are in
formed, were not good. Hence, if Mr. Mozley's test be a
true one, a point must exist, on the one side, of which
miraculous power demonstrates goodness, while on the other
side it does not. How is this " point of contrary flexure "
to be determined ? It must lie somewhere between the
magicians and Moses, for within this space the power passed
from the diabolical to the Divine. But how to mark the
point of passage — how, out of a purely quantitative differ
ence in the visible manifestation of power we are to infer a
total inversion of quality — it is extremely difficult to see.
Moses, we are informed, produced a large reptile, Jannes
and Jambres produced a small one. I do not possess the
intellectual faculty which would enable me to infer from
those data either the goodness of the one or the badness of
the other ; and in the highest recorded manifestations of the
miraculous I am equally at a loss. Let us not play fast and
loose with the miraculous ; either it is a demonstration of
goodness in all cases or in none. If Mr. Mozley accepts
Christ's goodness as transcendent, because He did such
works as no other man did, he ought, logically speaking, to
accept the works of those who, in His name, had cast out
devils, as demonstrating a proportionate goodness on their
part. But it is people of this class who are consigned to
everlasting fire prepared for the devil and his angels. Such
zeal as that of Mr. Mozley for miracles tends, I fear, to eat
his religion up. The logical threatens to stifle the spiritual.
The truly religious soul needs no miraculous proof of the
goodness of Christ. The words addressed to Matthew at
the receipt of custom required no miracle to produce obedi
ence. It was by no stroke of the supernatural that Jesus
caused those sent to seize Him to go backward and fall to
the ground. It was the sublime and holy effluence from

54 FRAGMENTS OF SCIENCE.

within, which needed no prodigy to commend it to the rev
erence even of his foes.

As regards the function of miracles in the founding of a
religion, Mr. Mozley institutes a comparison between the
religion of Christ and that of Mahomet, and he derides the
latter as " irrational " because it does not profess to adduce
miracles in proof of its supernatural origin. But the re
ligion of Mahomet, notwithstanding this drawback, has
thriven in the world, and at one time it held sway over
larger populations than Christianity itself. The spread and
influence of Christianity are, however, brought forward bv
Mr. Mozley as " a permanent, enormous, and incalculable
practical result" of Christian miracles; and he actually
makes use of this result to strengthen his plea for the mirac
ulous. His logical warrant for this proceeding is not clear.
It is the method of science, when a phenomenon presents
itself, to the production of which several elements may con
tribute, to exclude them one by one, so as to arrive at
length at the truly effective cause. Heat, for example, is
associated with a phenomenon ; we exclude heat, but the
phenomenon remains : hence, heat is not its cause. Mag
netism is associated with a phenomenon ; we exclude mag
netism, but the phenomenon remains : hence, magnetism is
not its cause. Thus, also, when we seek the cause of the
diffusion of a religion — whether it be due to miracles or to
the spiritual force of its founders — we exclude the miracles,
and, finding the result unchanged, we infer that miracles
are not the effective cause. This important experiment
Mahometanism has made for us. It has lived and spread
without miracles ; and to assert, in the face of this, that
Christianity has spread because of miracles, is not more op
posed to the spirit of science than to the common-sense of
mankind.

The incongruity of inferring moral goodness from mirac
ulous power has been dwelt upon above ; in another par-

MIRACLES AND SPECIAL PROVIDENCES. 55

ticular also the strain put upon miracles by Mr. Mozley is,
I think, more than they can bear. In consistency with his
principles, it is difficult to see how he is to draw from the
miracles of Christ any certain conclusion as to His Divine
nature. He dwells very forcibly on what he calls " the argu
ment from experience," in the demolition of which he takes
evident delight. He destroys the argument, and repeats it
for the mere pleasure of again and again knocking the
breath out of it. Experience, he urges, can only deal with
the past ; and the moment we attempt to project experience
a hair's breadth beyond the point it has at any moment
reached, we are condemned by reason. It appears to me
that, when he infers from Christ's miracles a divine and
altogether superhuman energy, Mr. Mozley places himself
precisely under this condemnation. For what is his logical
ground for concluding that the miracles of the New Testa
ment illustrate Divine power ? May they not be the result
of expanded human power ? A miracle he defines as some
thing impossible to man. But how does he know that the
miracles of the New Testament are impossible to man ?
Seek as he may, he has absolutely no reason to adduce save
this — that man has never hitherto accomplished such things.
But does the fact that man has never raised the dead prove
that he can never raise the dead ? " Assuredly not," must
be Mr. Mozley's reply ; " for this would be pushing experi
ence beyond the limit it has now reached — which I pro
nounce unlawful." Then a period may come when man
will be able to raise the dead. If this be conceded — and I
do not see how Mr. Mozley can avoid the concession — it
destroys the necessity of inferring Christ's divinity from his
miracles. He, it may be contended, antedated the humanity
of the future ; as a mighty tidal-wave leaves high upon the
beach a mark which by-and-by becomes the general level
of the ocean. Turn the matter as you will, no other warrant
will be found for the all-important conclusion that Christ's

56 FRAGMENTS OF SCIENCE.

miracles demonstrate Divine power, than an argument
which has been stigmatized by Mr. Mozley as " a rope of
sand " — the argument from experience.

The learned Hampton Lecturer would be in this posi
tion even if he had seen with his own eyes every miracle
recorded in the New Testament. But he has not seen these
miracles ; and his intellectual plight is, therefore, worse.
He accepts these miracles on testimony. Why does he be
lieve that testimony ? How does he know that it is not
delusion ; how is he sure that it is not even falsehood ?
He will answer that the writing bears the marks of sobriety
and truth ; and that, in many cases, the bearers of this mes
sage to mankind sealed it with their blood. Granted with
all my heart; but whence the value of all this? Is it not
solely derived from the fact that men, as ice know them, do
not sacrifice their lives in the attestation of that which they
know to be untrue ? Does not the entire value of the tes
timony of the apostles depend ultimately upon our expe
rience of human nature ? It appears, therefore, that those
who alleged to have seen the miracles based their inferences
from what they saw on the argument from experience ; and
that Mr. Mozley bases his belief in their testimony on the
same argument. The weakness of his conclusion is aug
mented by this double insertion of a principle of belief to
which he flatly denies rationality. His reasoning, in fact,
cuts two ways — if it destroys our trust in the order of Na-
turo, it far more effectually abolishes the basis on which
Mr. Mozley seeks to found the Christian religion.

Over this argument from experience, which, at bottom,
is hi A argument, Mr. Mozley rides rough-shod. There is a
dash of scorn in the energy with which he tramples on it.
Probably some previous writer had made too much of it,
and thus invited his powerful assault. Finding the diffi
culty of belief in miracles to arise from their being in con
tradiction to the order of Nature, he set himself to examine

MIRACLES AND SPECIAL PROVIDENCES. 57

the grounds of our belief in that order. With a vigor of
logic rarely equalled, and with a confidence in its conclu
sions never surpassed, he disposes of this belief in a manner
calculated to startle those who, without due examination,
had come to the conclusion that the order of Nature was
secure.

What we mean, he says, by our belief in the order of
Nature, is the belief that the future will be like the past.
There is not, according to Mr. Mozley, the slightest rational
basis for this belief.

" That any cause in Nature is more permanent than its existing and
known effects, extending further, and about to produce other and more
instances besides what it has produced already, we have no evidence.
Let us imagine," he continues, " the occurrence of a particular physical
phenomenon for the first time. Upon that single occurrence we should
have but the very faintest expectation of another. If it did occur again,
once or twice, so far from counting on another occurrence, a cessation
would occur as the most natural event to us. But let it continue one
hundred times, and we should find no hesitation in inviting persons from
a distance to see it ; and if it occurred every day for years, its occur
rence would be a certainty to us, its cessation a marvel. . . . What
ground of reason can we assign for an expectation that any part of the
course of Nature will be the next moment what it has been up to this
moment, i. e., for our belief in the uniformity of Nature ? None. No
demonstrative reason can be given, for the contrary to the recurrence of
a fact of Nature is no contradiction. No probable reason can be given,
for all probable reasoning respecting the course of Nature is founded upon
this presumption of likeness, and, therefore, cannot be the foundation
of it. No reason can be given for this belief. It is without a reason.
It rests upon no rational grounds, and can be traced to no rational prin
ciple."

" Every thing," Mr. Mozley, however, adds, " depends
upon this belief, every provision we make for the future,
every safeguard and caution we employ against it, all cal
culation, all adjustment of means to ends supposes this be
lief ; and yet this belief has no more producible reason for
it than a speculation of fancy. ... It is necessary, all-im-

58 FRAGMENTS OF SCIENCE.

portant for the purposes of life, but solely practical, and
possesses no intellectual character. . . . The proper func
tion," continues Mr. Mozley, " of the inductive principle,
the argument from experience, the belief in the order of
Nature — by whatever phrase we designate the same instinct
— is to operate as a practical basis for the affairs of life and
the carrying on of human society." To sum up, the belief
in the order of Nature is general, but it is " an unintelligent
impulse, of which we can give no rational account." It is
inserted in our constitution solely to induce us to till our
fields, to raise our winter fuel, and thus to meet the future
on the perfectly gratuitous supposition that that future will
be like the past.

" Thus, step by step," says Mr. Mozley, with the empha
sis of a man who feels his position to be a strong one, " has
philosophy loosened the connection of the order of Nature
with the ground of reason, befriending in exact proportion
as it has done this the principle of miracles." For " this
belief, not having itself a foundation in reason, the ground
is gone upon which it could be maintained that miracles,
as opposed to the order of Nature, are opposed to reason."
When we regard this belief in connection with science, " in
which connection it receives a more imposing name, and is
called the inductive principle," the result is the same.
" The inductive principle is only this unreasoning impulse
applied to a scientifically ascertained fact. . . . Science has
led up to the fact, but there it stops, and for convert ing
this fact into a law a totally unscientific principle comes
into play, the same as that which generalizes the common
est observation of Nature."

The eloquent pleader of the cause of miracles passes
over without a word the results of scientific investigation
as proving any thing rational regarding the principles or
methods by which such results have been achieved. Here,
as before, he declines the t?st, " By their fruits shall ye

MIRACLES AND SPECIAL PROVIDENCES. 59

know them." Perhaps the best way of proceeding will be
to give one or two examples of the mode in which men of
science apply the unintelligent impulse with which Mr.
Mozley credits them, and which shall show by illustration
the surreptitious character of the method by which they
climb from the region of facts to that of laws.

It was known before the sixteenth century that, the end
of an open tube being dipped into water, on drawing an
air-tight piston up the tube the water follows the piston,
and this fact had been turned to account in the construction
of the common pump. The effect was explained at the
time by the maxim, " Nature abhors a vacuum." It was
not known that there was any limit to the height to which
the water would ascend, until, on one occasion, the garden
ers of Florence, while attempting to raise the water a very
great elevation, found that the column ceased at a height
of thirty-two feet. Beyond this all the skill of the pump-
maker could not get it to rise. The fact was brought to
the notice of Galileo, and he, soured by a world which had
not treated his science over-kindly, is said to have twitted
the philosophy of the time by remarking that Nature evi
dently abhorred a vacuum only to a height of thirty-two
feet. But Galileo did not solve the problem. It was taken
up by his pupil Torricelli, who pondered it, and while he
did so various thoughts regarding it arose in his mind. It
occurred to him that the water might be forced up in the
tube by a pressure applied to'the surface of the water out
side. But where, under the actual circumstances, was such
a pressure to be found? After much reflection, it flashed
upon Torricelli that the atmosphere might possibly exert
the pressure ; that the impalpable air might possess weight,
and that a column of water thirty-two feet high might be
of the exact weight necessary to hold the pressure of the
atmosphere in equilibrium.

There is much in this process of pondering and its

60 FRAGMENTS OF SCIENCE.

results which it is impossible to analyze. It is by a kind of
inspiration that we rise from the wise and sedulous con
templation of facts to the principles on which they depend.
The mind is, as it were, a photographic plate, which is
gradually cleansed by the effort to think rightly, and which
when so cleansed, and not before, receives impressions from
the light of truth. This passage from facts to principles is
called induction, which in its highest form is inspiration ;
but, to make it sure, the inward sight must be shown
to be in accordance with outward fact. To prove or dis
prove the induction, we must resort to deduction and ex
periment.

Torricelli reasoned thus : If a column of water thirty-
two feet high holds the pressure of the atmosphere in
equilibrium, a shorter column of a heavier liquid ought to
do the same. Now, mercury is thirteen times heavier than
water; hence, if my induction be correct, the atmosphere
ought to be able to sustain only thirty inches of mercury.
Here, then, is a deduction which can be immediately sub
mitted to experiment. Torricelli took a glass tube a yard
or so in length, closed at one end and open at the other,
and filling it with mercury, he stopped the open end with
his thumb, and inverted it in a basin filled with the liquid
metal. One can imagine the feeling with which Torricelli
removed his thumb, and the delight he experienced when
he found that his thought had forestalled a fact never before
revealed to human eyes. The column sank, but ceased to
sink at a height of thirty inches, leaving the Torricellian
vacuum overhead. From that hour the theory of the pump
was established.

The celebrated i Pascal followed Torricelli with a still
further deduction. He reasoned thus : If the mercurial
column be supported by the atmosphere, the higher we
ascend in the air the lower the column ought to sink, for
the less will be the weight of the air overhead. He ascend-

MIRACLES AND SPECIAL PROVIDENCES. 61

ed the Puy de Dome, carrying with him a barometric
column, and found that as he ascended the mountain the
column sank, and that as he descended the column rose.

Between the time here referred to and the present,
millions of experiments have been made upon this subject.
Every village pump is an apparatus for such experiments.
In thousands of instances, moreover, pumps have refused
to work ; but on examination it has infallibly been found
that the well was dry, that the pump required priming, or
that some other defect in the apparatus accounted for the
anomalous action. In every case of the kind the skill of
the pump-maker has been found to be the true remedy. In
no case has the pressure of the atmosphere ceased ; con
stancy, as regards the lifting of pump-water, has been
hitherto the demonstrated rule of Nature. So also as regards
Pascal's experiment. His experience has been the universal
experience ever since. Men have climbed mountains, and
gone up in balloons ; but no deviation from Pascal's result
has ever been observed. Barometers, like pumps, have
refused to act; but instead of indicating any suspension of
the operations of Nature, or any interference on the part of
its Author with atmospheric pressure, examination has in
every instance fixed the anomaly upon the instruments
themselves. It is this welding, then, of rigid logic to veri
fying fact that Mr. Mozley refers to an " unreasoning im
pulse."

Let us now briefly consider the case of Newton. Before
his time men had occupied themselves with the problem of
the solar system. Kepler had deduced, from a vast mass
of observations, the general expressions of planetary motion
known as " Kepler's laws." It had been observed that a
magnet attracts iron ; and by one of those flashes of inspi
ration which reveal to the human mind the vast in the
minute, the general in the particular, it occurred to Kepler,
that the force by which bodies fall to the earth might also

62 FRAGMENTS OF SC

be an attraction. Newton pondered all these things. He
had a great power of pondering. He could look into the
darkest subject until it became entirely luminous. How
this light arises we cannot explain ; but, as a matter of
fact, it does arise. Let me remark here, that this power of
pondering facts is one with which the ancients could be
but imperfectly acquainted. They found the uncontrolled
exercise of the imagination too pleasant to expend much
time in gathering and brooding over facts. Hence it is that
when those whose education has been derived from the
ancients speak of " the reason of man," they are apt to
omit from their conception of reason one of its greatest
powers. "Well, Newton slowly marshalled his thoughts, or
rather they came to him while he "intended his mind,"
rising one after another like a series of intellectual births
out of chaos. He made this idea of attraction his own.
But to apply the idea to the solar system, it was necessary
to know the magnitude of the attraction and the law of its
variation with the distance. His conceptions first of all
passed from the action of the earth as a whole, to that of
its constituents particles, the integration of which composes
the whole. And persistent thought brought more and
more clearly out the final divination, that every particle of
matter attracts every other particle by a force which varies
inversely as the square of the distance between the par
ticles. This is Newton's celebrated law of inverse squares.
Here we have the flower and outcome of his induction ; and
how to verify it, or to disprove it, was the next question.
The first step of Newton in this direction was to prove,
mathematically, that if this law of attraction be the true
one ; if the earth be constituted of particles which obey
this law ; then the action of a sphere equal to the earth in
size on a body outside of it, is the same as that which
would be exerted if the whole mass of the sphere were
contracted to a point at its centre. Practically speaking,

MIRACLES AND SPECIAL PROVIDENCES. 03

then, the centre of the earth is the point from which
distances must be measured to bodies attracted by the
earth. This was the first-fruit of his deduction.

From experiments executed before his time, Newton
knew the amount of the earth's attraction at the earth's sur
face, or at a distance of 4,000 miles from its centre. His
object now was to measure the attraction at a greater dis
tance, and thus to determine the law of its diminution.
But how was he to find a body at a sufficient distance ?
He had no balloon, and even if had, he knew that any height
which he could attain would be too small to enable him to
solve his problem. WTiat did he do ? He fixed his thoughts
upon the moon — a body at a distance of 240,000 miles, or
sixty times the earth's radius from the earth's centre. He
virtually weighed the moon, and found that weight to be
3-gVo^h of what it would be at the earth's surface. This is
exactly what his theory required. I will not dwell here upon
the pause of Newton after his first calculations, or speak of
his self-denial in withholding them, because they did not
quite agree with the observations then at his command.
Newton's action in this matter is the normal action of the
scientific mind. If it were otherwise — if scientific men were
riot accustomed to demand verification — if they were satis
fied with the imperfect while the perfect is attainable, their
science, instead of being, as it is, a fortress of adamant,
would be a house of clay, ill-fitted to bear the bufferings of
the theologic storms to which it has been from time to time,
and is at present exposed.

Thus, we see, that Newton, like Torricelli, first pondered
his facts, illuminated them with persistent thought, and
finally divined the character of the force of gravitation. But
having thus travelled inward to the principle, he had to re
verse his steps, carry the principle outward, and justify it
by demonstrating its fitness to external Nature. This he
did by determining the attraction of the earth and moon.

64 FRAGMENTS OF SCIENCE.

And here, in passing, I would notice a point which is
well worthy of attention. Kepler had deduced his laws
from observation. As far back as those observations ex
tended, the planetary motions had obeyed these laws ; and,
neither Kepler nor Newton entertained a doubt as to their
continuing to obey them. Year after year, as the ages
rolled, they believed that those laws would continue to
illustrate themselves in the heavens. But this was not suf
ficient. The scientific mind can find no repose in the mere
registration of sequence in Nature. The further question
intrudes itself with resistless might : whence conies the se
quence ? What is it that binds the consequent with its an-
^tecedent in Nature ? The truly scientific intellect never can
attain rest until it reaches the forces by which the observed
succession is produced. It was thus with Torricelli ; it was
thus with Newton ; it is thus preeminently with the real
scientific man of to-day. In common with the most igno
rant, he shares the belief that spring will succeed winter,
that summer will succeed spring, that autumn will succeed
summer, and that winter will succeed autumn. But he
knows still further — and this knowledge is essential to his
intellectual repose — that this succession, besides being per
manent, is, under the circumstances, necessary ; that the
gravitating force exerted between the sun, and a revolving
sphere with an axis inclined to the plane of its orbit, tmint
produce the observed succession of the seasons. Not until
this relation between forces and phenomena has been es
tablished is the law of reason rendered concentric with the
law of Nature, and not until this is effected does the mind
of the scientific philosopher rest in peace.

The expectation of likeness, then, in the procession of
phenomena is not that on which the scientific mind founds
its belief in the order of Nature. If the force be permanent
the phenomena are necessary, whether they resemble or do
not resemble any thing that has gone before. Hence, in

MIRACLES AND SPECIAL PROVIDENCES. 65

judging of the order of Nature, our inquiries eventually
relate to the permanence of force. From Galileo to Newton,
from Newton to our own time, eager eyes have been scan
ning the heavens, and clear heads have been pondering the
phenomena of the solar system. The same eyes and minds
have been also observing, experimenting, and reflecting on
the action of gravity at the surface of the earth. Nothing
has occurred to indicate that the operation of the law has
for a moment been suspended ; nothing has ever intimated
that Nature has been crossed by spontaneous action, or
that a state of things at any time existed which could not
be rigorously deduced from the preceding state. Given the
distribution of matter and the forces in operation in the
time of Galileo, the competent mathematician of that day
could predict what is now occurring in our own. We cal
culate eclipses before they have occurred, and find them
true to the second. We determine the dates of those that
have occurred in the early times of history, and find calcu
lations and history at peace. Anomalies and perturba
tions in the planets have been over and over again observed,
but these, instead of demonstrating any inconstancy on the
part of natural law, have invariably been reduced to conse
quences of that law. Instead of referring the perturba
tions of Uranus to any interference on the part of the
Author of Nature with the law of gravitation, the question
which the astronomer proposed to himself was, " How, in
accordance with this law, can the perturbation be pro
duced ? " Guided by a principle, he was enabled to fix the
point of space in which, if a mass of matter were placed,
the observed perturbations would follow. We know the
result. The practical astronomer turned his telescope tow
ard the region which the intellect of the theoretic astrono
mer had already explored, and the planet now named
Neptune was found in its predicted place. A very re
spectable outcome, it will be admitted, of an impulse which

66 FRAGMENTS OF SCIENCE.

" rests upon no rational grounds, and can be traced to no
rational principle ; " which possesses " no intellectual char
acter ; " which " philosophy " has uprooted from " the
ground of reason," and fixed in that " large irrational de
partment " discovered for it by Mr. Mozley, in the hitherto
unexplored wildernesses of the human mind.

The proper function of the inductive principle, or the
belief in the order of Nature, says Mr. Mozley, is " to act
as a practical basis for the affairs of life, and the carrying
on of human society." But what, it may be asked, has the
planet Neptune, or the belts of Jupiter, or the whiteness
about the poles of Mars, to do with the affairs of society ?
How is society affected by the fact that the sun's atmos
phere contains sodium, or that the nebula of Orion contains
hydrogen gas ? Nineteen-twentieths of the force employed
in the exercise of the inductive principle, wThich, reiterates
Mr. Mozley, is " purely practical," have been expended upon
subjects as unpractical as these. What practical interest
has society in the fact that the spots on the sun have a
decennial period, and that when a magnet is closely
watched for half a century, it is found to perform small
motions which synchronize with the appearance and disap
pearance of the solar spots ? And yet, I doubt not, Sir
Edward Sabine would deem a life of intellectual toil amply
rewarded by being privileged to solve, at its close, these
infinitesimal motions.

The inductive principle is founded in man's desire to
know — a desire arising from his position among phenom
ena which are reducible to order by his intellect. The
material universe is the complement of the intellect, and
without the study of its laws reason would never have
awoke to its higher forms of self-consciousness at all. It
is the non-ego, through and by which the ego is endowed
with self-discernment. We hold it to be an exercise of
reason to explore the meaning of a universe to which we

MIRACLES AND SPECIAL PROVIDENCES. 67

stand in this relation, and the work we have accomplished
is the proper commentary on the methods we have pursued.
Before these methods were adopted the unbridled imagi
nation roamed through Nature, putting in the place of
law the figments of superstitious dread. For thousands of
years witchcraft, and magic, and miracles, and special provi
dences, and Mr. Mozley's " distinctive reason of man," had
the world to themselves. They made worse than nothing
of it — worse, I say, because they let and hindered those
who might have made something of it. Hence it is that
during a single lifetime of this era of " unintelligent im
pulse," the progress in natural knowledge is all but infinite
as compared with that of the ages which preceded ours.

The believers in magic and miracles of a couple of
centuries ago had all the strength of Mr. Mozley's present
logic on their side. They had done for themselves what
he rejoices in having so effectually done for us — cleared the
ground of the belief in the order of Nature, and declared
magic, miracles, and witchcraft, to be matters for ordinary
evidence to decide. "The principle of miracles" thus
" befriended " had free scope, and we know the result.
Lacking that rock-barrier of natural knowledge which we,
laymen of England, now possess, keen jurists and cultivated
men were hurried on to deeds, the bare recital of which
makes the blood run cold. Skilled in all the rules of human
evidence, and versed in all the arts of cross-examination,
these men, nevertheless, went systematically astray, and
committed the deadliest wrongs against humanity. And
why ? Because they could not put Nature into the witness-
box, and question her ; of her voiceless " testimony " they
knew nothing. In all cases between man and man, their
judgment was to be relied on ; but in all cases between
man and Nature they were blind leaders of the blind.1

1 " In 1664 two women were hung in Suffolk, under a sentence of Sir
Matthew Hale, who took the opportunity of declaring that the reality of

68 FRAGMENTS OF SCIENCE.

Mr. Mozley concedes that it would be no great result
for miracles to be accepted by the ignorant and superstitious,
" because it is easy to satisfy those who do not inquire."
But he does consider it " a great result " that they have
been accepted by the educated. In what sense educated ?
Like those statesmen, jurists, and church dignitaries whose
education was unable to save them from the frightful errors
glanced at above? Not even in this sense; for the great
mass of Mr. Mozley's educated people had no legal training,
and must have been absolutely defenceless against delusions
which could set even that training at naught. Like nine-
tenths of our clergy at the present day, they were versed in
the literature of Greece, Rome, and Judea ; but as regards
a knowledge of Nature, which is here the one thing needful,
they were " noble savages," and nothing more. In the
case of miracles, then, it behooves us to understand the
weight of the negative, before we assign a value to the
positive ; to comprehend the protest of Nature before we
attempt to measure, with it, the assertions of men. We
have only to open our eyes to see what honest, and even
intellectual, men and women are capable of in the way of
evidence in this nineteenth century of the Christian era,
and in latitude fifty-two degrees north. The experience
thus gained ought, I imagine, to influence our opinion
regarding the testimony of people inhabiting a sunnier
clime, with a richer imagination, and without a particle of
that restraint which the discoveries of physical science have
imposed upon mankind.

witchcraft was unquestionable ; ' for first, the Scriptures had affirmed eo
much ; and secondly, the wisdom of all nations had provided laws against
such persons, which is an argument of their confidence of such a crime.'
Sir Thomas Browne, who was a great physician as well as a great writer,
was called as a witness, and swore ' that he was clearly of opinion that
the persons were bewitched.' " — Lccky's History of Rationalism, vol. i.
p. 120.

MIRACLES AND SPECIAL PROVIDENCES. 69

Having thus submitted Mr. Mozley's views to the ex
amination which they challenged at the hands of a student
of the order of Nature, I am unwilling to quit his book
without expressing my high admiration and respect for his
ability. His failure, as I consider it to be, must, I think,
await all attempts, however able, to deal with the material
universe by logic and imagination, unaided by experiment
and observation. With regard to the style of the book, I
willingly subscribe to the description with which the Times
winds up its able and appreciative review. " It is marked
throughout with the most serious and earnest conviction,
but is without a single word from first to last of asperity or
insinuation against opponents, and this not from any de
ficiency of feeling as to the importance of the issue, but
from a deliberate and resolutely maintained self-control,
and from an overruling, ever-present sense of the duty, on
themes like these, of a more than judicial calmness." 1

[ To the argument regarding the quantity of the mirac
ulous, introduced at page 52, Mr. Mozley has done me the
honor of publishing a reply in the seventh volume of the
Contemporary Jteview. — J. T., 1871.]

1 See Appendix at the eud of the book.

IV.
MATTER AND FORCE.

A LECTURE TO THE WORKING-MEN OF DUNDEE.
September 5, 1867.

" Ilcard are the voices,
Heard are the sages,
The worlds and the ages,
4 Choose well, your choice is
Brief and yet endless.

" ' Here eyes do regard you
In eternity's stillness ;
Here is all fulness
Ye brave to reward you,
Work and despair not.' "

GOKTHK.

IY.

MATTER AND FORCE.

IT is the custom of the Professors in the Royal School
of Mines in London to give courses of evening lectures
every year to working-men. Each course is duly adver
tised, and at a certain hour the working-men assemble to
purchase tickets for the course. The lecture-room holds
six hundred people, and tickets to this amount are disposed
of as quickly as they can be handed to those who apply for
them. So desirous are the working-men of London to
attend these lectures, that the persons who fail to obtain
tickets always bear a large proportion to those who suc
ceed. Indeed, if the lecture-room could hold two thousand
instead of six hundred, I do not doubt that every one of its
benches would be occupied on these occasions. It is,
moreover, worthy of remark that the lectures are but rarely
of a character which could help the working-man in his
daily pursuits. The knowledge acquired is hardly ever of
a nature which admits of being turned into money. It is a
pure desire for knowledge, as a thing good in itself, and
without regard to its practical application, which animates
these men. They wish to know more of the wonderful
universe around them ; their minds desire this knowledge
as naturally as their bodies desire food and drink, and to
satisfy this intellectual want they come to the School of
Mines.

It is also my privilege to lecture to another audience in
4

71 FRACMHNTS OF SHKNCE.

London, composed in part of the aristocracy of rank,
while the audience just referred to is composed wholly of
the aristocracy of labor. As regards attention and cour
tesy to the lecturer, neither of these audiences has any
thing to learn of the other ; neither can claim superiority
over the other. I do not, however, think that it would
/ be quite correct to take those persons who flock to the
School of Mines as average samples of their class ; they
are probably picked men — the aristocracy of labor, as I have
just called them. At all events, their conduct demonstrates
that the essential qualities of a gentleman are confined
to no class, and they have often raised in my mind the
wisli that the gentlemen of all classes, artisans as well as
lords, could, by some process of selection, be sifted from
the general mass of the community, and caused to know
each other better.

When pressed some months ago by the Council of the
British Association to give an evening lecture to the work
ing-men of Dundee, my experience of the working-men of
London naturally rose to my mind ; and, though heavily
weighted with other duties, I could not bring myself to de
cline the request of the Council. Hitherto, the evening
discourses of the Association have been delivered before
its members and associates alone. But after the meeting
at Nottingham, last year, where the working-men, at their
own request, were addressed by our late President, Mr.
Grove, and by my excellent friend Professor Huxley, the
idea rose of incorporating with all subsequent meetings of
the Association an address to the working-men of the town
in which the meeting is held. A resolution to that effect
was sent to the Committee of Recommendations ; the com
mittee supported the resolution ; the Council of the Asso
ciation ratified the decision of the committee; :ind lu>re f
am to carry out to the best of my ability their united
wishes.

MATTER AND FORCE. 75

Whether it be a consequence of long-continued develop
ment, or an endowment conferred once for all on man at
his creation, we find him here gifted with a mind, curious is
to know the causes of things, and surrounded by objects
which excite its questionings, and raise the desire for an
explanation. It is related of a young prince of one of the
Pacific Islands, that when he first saw himself in a looking-
glass, he ran round the glass to see who was standing at
the back. And thus it is with the general human intellect,
as regards the phenomena of the external world. It wishes
to get behind and learn the causes and connections of these fc
phenomena. What is the sun, what is the earth, what
should we see if we came to the edge of the earth and
looked over? What is the meaning of thunder and light
ning, of hail, rain, storm, and snow ? Such questions pre
sented themselves to early men, and by-and-by it was dis
covered, that this desire for knowledge was not implanted
in vain. After many trials it became evident that man's
capacities were, so to speak, the complement of Nature's -
facts, and that, within certain limits, the secret of the uni
verse was open to the human understanding. It was found
that the mind of man had the power of penetrating far be
yond the boundaries of his five senses ; that the things
which are seen in the material world depend for their action
upon things unseen ; in short, that besides the phenomena
which address the senses, there are laws and principles and
processes which do not address the senses at all, but which
must be, and can be, spiritually discerned.

There are two things which form, so to say, the sub
stance of all scientific thought. The entire play of the
scientific intellect is confined to the combination and res
olution of the ideas of matter and force. Newton, it is
said, saw an apple fall. To the common mind this pre
sented no difficulty and excited no question. Not so with
Newton. He observed the fact ; but one side of his great

76 FRAGMENTS OF SCIENCE.

intellectual nature was left unsatisfied by the mere act of
observation. He sought after the principle which ruled
the fact. Whether this anecdote be true or not, it illus
trates how the ordinary operations of Nature, which most
people take for granted as perfectly plain and simple, are ^
often those which most puzzle the scientific man. To the
conception of the matter of the apple, Newton added that
of the force that moved it. The falling of the apple was
due to an attraction exerted mutually between it and the
earth. He applied the idea of this force to suns, and plan
ets, and moons, and showed that all their motions were
necessary consequences of this attraction.

Newton, you know, was preceded by a grand fellow
named John Kepler — a true working-man — who, by analyz
ing the astronomical observations of his master, Tycho
Brahe, had actually found that the planets moved as they are
now known to move. As a matter of fact, Kepler knew as
much about the motion of the planets as Newton did ; in
fact, Kepler taught Newton and the world generally the
facts of planetary motion. But this was not enough. The
question arose — Why should the facts be so ? This was
the great question for Newton, and it was the solution of
this question which renders his name and fame immortal.
He proved that the planetary motions were what observa
tion made them to be, because every particle of matter in
the solar system attracts every other particle by a force
which varies as the inverse square of the distance between
the particles. He showed that the moon fell toward the
earth, and that the planets fell toward the sun, through the
operation of the same force that pulls an apple from its
tree. This all-pervading force, \vhich forms the sojder of
the material universe, and the conception of which was
necessary to Newton's intellectual peace, is called the force ^
of gravitation.

All force may be ultimately reduced to a push or a pull in

^ MATTER AND FORCE. 77

a straight line ;'but its manifestations are various, and some
times so complex as entirely to disguise its elementary con
stituents. Its different manifestations have received differ
ent names. Here, for example, is a magnet freely suspended.
I bring the end of a second magnet near one of the ends
of the suspended one — attraction is the consequence. I re
verse the position of one of the magnets — repulsion follows.
This display of power is called magnetic force. In the
case of gravitation we have a simple attraction, in the case
of magnetism attraction and repulsion always go together.
Thus magnetism is a double force, or, as it is usually called,
a polar force. I present a bit of common iron to the magnet,
the iron itself becomes a temporary magnet, and it now
possesses the power of attracting other iron. And if sev
eral pieces of iron be presented at the same time, not only
will the magnet act on them, but they will also act upon
each other.

This leads me to j&if experiment which will give you
some idea of how bodies arrange themselves under the
operation of a polar force. Underneath this plate of glass
is placed a small magnet, and by an optical arrangement
comprising a powerful lamp, a magnified image of the mag
net is now cast upon the screen before you. I scatter iron
filings over the glass. You already notice a certain arrange
ment of the particles of iron. Their free action is, how
ever, hampered by friction. I therefore tap the glass,
liberate the particles, which, as I tap, arrange themselves in
these beautiful curves. This experiment is intended to
make clear to you how a definite arrangement of particles
— a kind of incipient structure — may result from the oper
ation of a polar force. We shall by-and-by see far more
wonderful exhibitions of the same structural action when
we come to deal with the force of crystallization.

The magnetic force has here acted upon particles of
matter visible to the eye. But, as already stated, there are

78 FRAGMENTS OF SCIENCE.

numerous processes in Nature which entirely elude the eye
of the body, and must be figured by the eye of the miiul.
The processes of chemistry are examples of these. Long
thinking and experimenting on the materials which compose
our world have led philosophers to conclude that matter is
composed of atoms from which, whether separate or in com-
bination, the whole material world is built up. The air we
breathe, for example, is mainly a mixture of the atoms of
two distinct substances, called oxygen and nitrogen. The
water we drink is also composed of two distinct substances,
called oxygen and hydrogen. But it differs from the air in
this particular, that in water the oxygen and hydrogen are
not mechanically mixed, but chemically combined. In fact,
the atoms of oxygen and those of hydrogen exert enormous
attractions on each other, so that when brought into sufficient
proximity they rush together with an almost incredible
force to form a chemical compound. But powerful as is the
force with which these atoms lock themselves together, we
have the means of tearing them asunder, and the agent by
which we accomplish this may here receive a few moments'
attention.

Into a vessel containing acidulated water I dip these
two strips of metal, the one being zinc and the other plati
num, not permitting them to touch each other in the liquid.
I now connect the two upper ends of the strips by a piece
of copper wire. The wire is apparently unchanged, but it
is not so in reality. It is now the channel of what, for
want of a better name, we call an electric current — a power
generated and maintained by the chemical action going on
in the vessel of acidulated water. What the inner change
of the wire is we do not know, but we do know that a change
has occurred, by the external effects produced by the wire.
Let me show you one or two of these effects. And here it
is convenient to operate with greater power than can be ob
tained from a single small pan: of strips of metal, and a

MATTER AND FORCE. 79

single vessel of acidulated water. Before you is a series of
ten vessels, each with its pair of metals, and I wish to get
the added force of all ten. This arrangement is called a
voltaic battery. I take a piece of copper wire in my hand,
and plunge it among these iron filings ; they refuse to cling
to it ; the wire has no power over the filings. J now em
ploy the self-same wire to connect the two ends of the bat
tery, and subject it to the same test. The iron filings now
crowd round the wire and cling to it. This is one of the
effects of the electric current now traversing the wire. I
interrupt the current, and the filings immediately fall ; the
power of attraction continues only so long as the wire con
nects the two ends of the battery.

Here is a piece of similar wire, overspun with cotton, to
prevent the contact of its various parts. It is formed into
a coil, which at present has no power over these iron nails ;
but I now make the coil part of the wire which connects
the two ends of the voltaic battery. No visible change has
occurred in the coil, but it is no longer what it was. By
the attractive force with which it has become suddenly en
dowed, it now empties this tool-box of its nails. I twist a
covered copper wire round this common poker. At present
the poker is powerless over these iron nails ; but when we
connect with the wire surrounding the poker the two ends
of the voltaic battery, the poker is instantly transformed
into a strong magnet. Here, again, are two flat spirals sus
pended facing each other. They are about six inches
apart. By turning this handle in a certain direction a cur
rent is sent through both spirals. When this is done they
clash suddenly together, being drawn together by their mu
tual attraction. By turning the handle in another direction,
I reverse what is called the direction of the current in one
of the spirals, and now they fly asunder, being driven apart
by their mutual repulsion. All these effects are due to the
power which we name an electric current, and which we

80 FRAGMENTS OF SCIENCE.

figure as flowing through the wire when the voltaic circuit
is complete.

I have said that no visible change occurs in the wire
when the current passes through it. Still a change over
and above what you have seen really does take place. Lay
hold of those spirals, and you will find them warm. Let
me exalt this warmth so as to render it visible to you. In
front of the table is a thin platinum wire six feet long. On
sending a current from a battery of fifty pairs of plates
through this wire it glows, as you see, vividly red. I shorten
the wire ; more electricity now flows through it, and its
light becomes more intense. It is now bright yellow ; and
now it is a dazzling white. This light is so strong that
though the wrire is not much thicker than a bristle, it ap
pears to those on the nearest benches as thick as a quill ;
Avliile to those at a distance it appears as thick as a man's
finger. This effect, which we call irradiation, is always pro
duced by a very strong light. It is this same electric cur
rent that furnished us with the powerful light employed in
one of our first experiments. The lamp then made use of
is provided with these coke rods ; and when the electric
current passes between them we obtain a light almost as
brilliant as that of the sun.

And now let us return to the point at which the elec
tric current was introduced — the point, namely, where the
tearing asunder of the locked atoms of a chemical com
pound was spoken of. The agent by which we effect this
is also the electric current; and I hope to make its action
visible to you all. Into this small cell, containing water,
dip two thin wires. By means of a solar microscope and
the powerful light of our electric lamp, a magnified image
of this cell is thrown upon the screen before you. You
see plainly the images of the wires. And now I send
from a second small battery which rests upon this table an
electric current from wire to wire. Bubbles of gas rise

MATTER AND FORCE. 81

immediately from each of them, and these are the two
gases of which the water is composed. The ox}^gen is
always liberated on the one wire, the hj-drogen on the
other. The two gases may be collected separately ; in
fact, they have been thus collected in these jars. A lighted
taper* placed in one jar inflames the gas, which proves it to
be hydrogen ; a burning ember of wood placed in the
other jar instantly bursts into vivid combustion, which
proves the gas in the jar to be oxygen. I place upon my
hand a soap-bubble filled with a mixture of both gases in
the exact proportions in which they exist in water. Apply
ing a taper to the bubble, a loud explosion is heard. The
gases have rushed together with detonation, but without
injury to my hand, and the water from which they were
extracted is the result of the reunion.

I wish you to see with the utmost possible clearness
what has here taken place,- First, then, you are to re
member that to form water the proportions by weight of
oxygen and hydrogen are as eight to one. Eight ounces
of oxygen, for example, unite with one of hydrogen to
form nine ounces of water. But if, instead of comparing
weights, we compare volumes, two volumes of hydrogen
unite with one of oxygen to form water. Now, these vol
umes, and not the weights, express the proportions in
which the atoms of hydrogen unite with those of oxygen.
In the act of combination two atoms of hydrogen combine
with one of oxygen to form what we call the molecule of
water. Every such molecule is a group of three atoms,
two of which are hydrogen and one oxygen.

One consequence of the rushing together of the atoms
is the development of heat. What is this heat ? How
are we to figure it before our minds ? I do not despair of
being able to give you a tolerably distinct answer to this '
question. Here are two ivory balls suspended from the
same point of support by two short strings. I draw them

82 FRAGMENTS OF SCIEXCF,

thus apart and then liberate them. They clash together,
but, by virtue of their elasticity, they quickly recoil from
each other, and a sharp vibratory rattle succeeds their col
lision. This experiment will enable you to figure to your
mind a pair of clashing atoms. We have, in the first place,
a motion of the one atom toward the other — a motion of
translation, as it is usually called. But when the atoms
come sufficiently near each other, elastic repulsion sets in,
the motion of translation is stopped and converted into a
motion of vibration. To this vibratory motion we give the
name of heat. Thus, three things are to be kept before
the mind — first, the atoms themselves ; secondly, the force
with which they attract each other ; and thirdly, the mo
tion consequent upon the exertion of that force. This mo
tion must be figured first as a motion of translation, and
then as a motion of vibration ; and it is not until the mo
tion reaches the vibratory stage that we give it the name
of heat. It is this motion imparted to the nerves that pro
duces the sensation of heat.

It would be useless to attempt a more detailed descrip
tion of this molecular motion. After the atoms have
been thrown into this state of agitation, very complicated
motions must ensue from their incessant collision. There
must be a wild whirling about among the molecules. For
some time after the act of combination this action is so
violent as to prevent the molecules from coming together.
The water is maintained for a time in a state of vapor.
But as the vapor cools, or in other words loses its mo
tion, the water molecules coalesce to form a liquid. Ami
now we are approaching a new and wonderful display of
force. No one who had only seen water in its vaporous or
liquid form could imagine the existence of the forces now
to be referred to ; for as long as the substance remains in
a lii|iii(l or vaporous condition, the play of these forces is
altogether masked and hidden. But let the heat be gradu-

MATTER AND FORCE. 83

ally withdrawn, the antagonist to their union being re
moved, the molecules prepare for new arrangements and
combinations. Like the particles of iron in our magnetic
experiment, the water molecules are endowed with attractive
and repulsive poles, and they arrange themselves together
in accordance with these attractions and repulsions. Solid
crystals of water are thus formed, to which we give the fa
miliar name of ice. To the eye of science these ice-crystals
are as precious as the diamond — as purely formed, as deli
cately built. Where no disturbing causes intervene, there
is no disorder in this crystalline architecture. By their own
constructive power molecule builds itself on to molecule
with a precision far greater than that attainable by the
hands of man. We are apt to overlook the wonderful when
it becomes common. Imagine the bricks and stones of
this town of Dundee endowed with locomotive power. Im
agine them attracting and repelling each other, and arrang
ing themselves in consequence of these attractions and re
pulsions to form streets and houses and Kinnaird Halls ;
would not that be wonderful ? Hardly less wonderful is
the play of force by which the molecules of water build
themselves into the sheets of crystal which every winter
roof your ponds and lakes.

If I could show you the actual progress of this molecu
lar architecture, its beauty would delight and astonish you.
A reversal of the process may be actually shown. The
molecules of a piece of ice may be taken asunder before
your eyes, and from the manner in which they separate, you
may to some extent infer the manner in which they aggre
gate. When a beam is sent from our electric lamp through
a plate of glass, a portion of the beam is intercepted, and
the glass is warmed by the portion thus retained within it.
When the beam is sent through a plate of ice, a portion
of the beam is also absorbed ; but instead of warming the
ice, the intercepted heat melts it internally. It is to the

84 FRAGMENTS OF SCIENCE.

delicate, silent action of this beam within the ice that I
now wish to direct your attention. Upon the screen is
thrown a magnified image of the slab of ice : the light of
the beam passes freely through the ice without melting it,
and enables us to form the image, but the heat of the
beam is in great part intercepted by the ice, and that heat
no\v applies itself to the work of internal liquefaction.
Observe those stars breaking out over the white surface,
and expanding in size as the action of the beam continues.
These stars are liquefied ice, and each of them, you ob
serve, has six rays. They still more closely resemble
flowers, each of six petals. Under the action of the heat
the molecules of the ice fall asunder, so as to leave be
hind them these exquisite forms. We have here the pro
cess of crystallization reversed. In this fashion, and in
strict accordance with this hexangular type every ice mole
cule takes its place upon our ponds and lakes during the
frosts of winter. To use the language of an American
poet, " the atoms march in tune," moving to the music of
law, which thus renders the commonest substance in Na
ture a miracle of beauty.

It is the function of science, not as some think to divest L-
this universe of its wonder and its mystery, but, as in the
case here before us, to point out the wonder and the
mystery of common things. Those fern-like forms, which
on a frosty morning overspread your window-panes, illus
trate the action of the same force. Breathe upon such a
pane before the fires are lighted, and reduce the solid crys
talline film to the liquid condition, then watch its subse
quent appearance. You will see it all the better if you
look at it through a common magnifying-glass. After you
have ceased breathing, the film, abandoned to the action of
its own forces, appears for a moment to be alive. Lines of
motion run through it ; molecule closes with molecule, until
finally the whole film passes from the state of liquidity,

MATTER AND FORCE. 85

through this state of motion, to its final crystalline re
pose.

i ' I can show you something similar. Over a piece of
perfectly clean glass I pour a little water in which a crystal
has been dissolved. A film of the solution clings to the
glass, and this film will now be caused to crystallize before
your eyes. By means of a microscope and a lamp, an image
of the plate of glass is thrown upon the screen. The beam
of the lamp, besides illuminating the glass, also heats it ;
evaporation sets in, and, at a certain moment, when the
solution has become supersaturated, splendid branches of
crystals shoot out over the screen. A dozen square feet of
surface are now covered by those beautiful forms. With
another solution we obtain crystalline spears, feathered
right and left by other spears. From distant nuclei in
the middle of the field of view the spears shoot with magical
rapidity in all directions. The film of water on a window-
pane on a frosty morning exhibits effects quite as wonderful
as these. Latent in this formless solution, latent in every
drop of water, lies this marvellous structural power, which
only requires the withdrawal of opposing forces to bring it
into action.

Our next experiment on crystallization you will probably
consider more startling even than these. The clear liquid
now held up before you is a solution of nitrate of silver — a
compound of silver and nitric acid. When an electric cur
rent is sent through this liquid the silver is severed from
the acid, as the hydrogen was separated from the oxygen
in a former experiment ; and I would ask you to observe
how the metal behaves when its molecules are thus succes
sively set free. The image of the cell, and of the two wires
which dip into the liquid of the cell, are now clearly shown
upon the screen. Let us close the circuit, and send the
current through the liquid. From one of the wires a beau
tiful silver tree commences immediately to sprout. Branches

86 FRAGMENTS OF SCIENCE.

of the metal are thrown out, and umbrageous foliage loads
the branches. You have here a growth apparently as won
derful as that of any vegetable perfected in a minute before
your eyes. Substituting for the nitrate of silver acetate of
lead, which is a compound of lead and acetic acid, the
electric current severs the lead from the acid, and there you
see the metal slowly branching into these exquisite metallic
ferns, the fronds of which, as they become too heavy, break
from their roots and fall to the bottom of the cell.

These experiments show that the common matter of our
earth — " brute matter," as Dr. Young pleases to call it —
when its atoms and molecules are permitted to bring then-
forces into free play, arranges itself, under the operation of
these forces, into forms which rival in beauty those of the
vegetable world. And what is the vegetable world itself
but the result of the complex play of these molecular forces ?
Here, as elsewhere throughout Nature, if matter moves, it
is force that moves it ; and if a certain structure, vegetable
or mineral, is produced, it is through the operation of the
forces exerted between the atoms and molecules. These
atoms and molecules resemble little magnets with mutually
attractive and mutually repellant poles. The attracting
poles unite, the repellant poles retreat, and vegetable as
well as mineral forms are the final expression of this com
plicated molecular action.

In the formation of our lead and silver trees, we needed
an agent to wrest the lead and the silver from the acids
with which they were combined. A similar agent is re
quired in the vegetable world. The solid matter of which
our lead and silver trees were formed was, in the first in
stance, disguised in a transparent liquid ; the solid matter
of which our woods and forests are composed is also, for
the most part, disguised in a transparent gas, which is
mixed in small quantities with the air of our atmosphere.
This gas is formed by the union of carbon and oxygen, and

MATTER AND FORCE. 87

is called carbonic acid gas. Two atoms of oxygen and one
of carbon unite to form the molecule of carbonic acid which,
as I have said, is the material from which wood and vege
table tissues are mainly derived. The carbonic acid of the
air being subjected to an action somewhat analogous to
that of the electric current in the case of our lead and silver
solutions, has its carbon liberated and deposited as woody
fibre. The watery vapor of the air is subjected to similar
action ; its Irydrogen is liberated from its oxygen, and lies
doAvn side by side with the carbon in the tissues of the
tree. The oxygen in both cases is permitted to wander
away into the atmosphere. But what is it which thus tears
the carbon and the hydrogen from the strong embrace of
the oxygen ? What is it in Nature that plays the part of
the electric current in our experiments ? The rays of
sun. The leaves of the plants absorb both the carbonic
acid and the aqueous vapor of the air; these leaves an
swer to the cells in which our decompositions by the electric
current took place. In the leaves the solar rays decompose
both the carbonic acid and the water, permitting the oxygen
in both cases to escape into the air, and allowing the carbon
and the hydrogen to follow the bent of their own forces.
And just as the molecular attractions of the silver and the
lead found expression in the production of those beautiful
branching forms seen in our experiments, so do the molecular
attractions of the liberated carbon and hydrogen find ex
pression in the architecture of grasses, plants, and trees.

In the fall of a cataract and the rush of the wind we
have examples of mechanical power. In the combinations
of chemistry and in the formation of crystals and vegetables
we have examples of molecular power. But before pro
ceeding further I should like to make clear to you the
present condition of the surface of our globe wTith reference
to powTer generally. You have learned how the atoms of
oxygen and hydrogen rush together to form water. I have

88 FRAGMENTS OF SCIENCE.

not thought it necessary to dwell upon the mighty mechani
cal energy of their act of combination, but, in passing, I
would say that the clashing together of 1 Ib. of hydrogen
and 8 Ibs. of oxygen to form 9 Ibs. of aqueous vapor, is
greater than the clash of a weight of 1,000 tons falling
from a height of 20 feet against the earth. Now, in order
that the atoms of oxygen arid hydrogen should rise by their
mutual attractions to the velocity corresponding to this
enormous mechanical effect, a certain distance must exist
between the particles. It is in rushing over this that the
velocity is attained.

This idea of distance between the attracting atoms is of
the highest importance in our conception of the system of
the world. For the world may be divided into two kinds
of matter ; or rather the matter of the world may be classi
fied under two distinct heads — namely, of atoms and mole
cules which have already rushed together and thus satisfied
their mutual attractions, and of atoms and molecules which
have not yet rushed together, and whose mutual attractions
are, therefore, as yet unsatisfied. Now, as regards motive
power, the working of machinery, or the performance of
mechanical work generally, by means of the materials of
the earth's crust, we are entirely dependent on those atoms;
and molecules whose attractions are as yet unsatisfied. Those
attractions can produce motion, because sufficient distance
intervenes between the attracting molecules, and it is this
molecular motion that we utilize in our machines. Thus
we can get power out of oxygen and hydrogen by the ;i< -i
of their union, but once they are combined, and once the
motion consequent on their combination has been expended,
no further power can be got out of the mutual attraction
of oxygen and hydrogen. As dynamic agents they are
dead. If we examine the materials of which the earth's
crust is composed, we find them to consist for the most part
of substances whose atoms have already closed in chetnical

MATTER AND FORCE. 89

union — whose mutual attractions are satisfied. Granite,
for instance, is a widely-diffused substance, but granite
consists, in great part, of silicon, oxygen, potassium, cal
cium, and aluminum, the atoms of which substances met
long ago in chemical combination, and are therefore dead.
Limestone is also a widely-diffused substance. It is com
posed of carbon, oxygen, and a metal called calcium. But
the atoms of those substances closed long ago in chemical
union, and are therefore dead. And in this way we might
go over the whole of the materials of the earth's crust, and
satisfy ourselves that though they were sources of power in
ages past, and long before any being appeared on the
surface of the earth capable of turning their power to
account, they are sources of power no longer. And here
we might halt for a moment to remark on that tendency, ^
so prevalent in the world, to regard every thing as made for
human use. Those who entertain this notion hold, I think,
an overweening opinion of their own importance in the
system of Nature. Flowers bloomed before men saw them,
and the quantity of power wasted before man could utilize \,
it is all but infinite compared with what now remains to be
applied. The healthy attitude of mind with reference to
this subject is that of the poet, who, when asked whence
came the rhodora, replied :

" Why thou wert there, 0 rival of the rose !

I never thought to ask, I never knew,
But in my simple ignorance supposed

The self-same power that brought me there brought you." 1

A few exceptions to this general state of union of the
particles of the earth's crust — all-important to us, but trivial
in comparison to the total store of which they are the resi
due — still remain. They constitute our main sources of
motive power. By far the most important of these are our

1 Emerson.

90 l-'IIACMKNTS OF SCIENCE.

beds of coal, composed chiefly of carbon, which has not yet
closed in chemical union with oxygen. Distance still inter
venes between the atoms of carbon and those of oxygen,
across which the atoms may be impelled by their mutual
attractions, and we can do nothing more than utilize the
motion produced by this attraction. Once the carbon and
the oxygen have rushed together, so as to form carbonic
acid, their mutual attractions are satisfied, and, while they
continue in this condition, as dynamic agents they are dead.
A pound of coal produces by its combination with oxygen
an amount of heat which, if mechanically applied, would
raise a weight of 100 Ibs. to a height of twenty miles above
the earth's surface. Conversely, 100 Ibs. falling from a
height of twenty miles, and striking against the earth,
would generate an amount of heat equal to that devel
oped by the combustion of a pound of coal. Wherever
work is done by heat, heat disappears. A gun which fires
a ball is less heated than one which fires blank cartridge.
The quantity of heat communicated to the boiler of a
working steam-engine is greater than that which could be
obtained from the recondensation of the steam after it had
done its work ; and the amount of work performed is the
exact equivalent of the amount of heat missing. We dig
annually nearly 100 millions of tons of coal from our pits.
The amount of mechanical force represented by this quantity
of coal seems perfectly fabulous. The combustion of a
single pound of coal, supposing it to take place in a minute,
would be equivalent to the work of 300 horses; and if we
suppose 120 millions of horses working day and night with
unimpaired strength, for a year, their united energies would
enable them to perform an amount of work just equivalent
to the heat to be derived from the annual produce of our
coal-fields. Our woods and forests are also sources of
mechanical energy, because they also have the power of
uniting with the atmospheric oxygen, and the molecular

MATTER AND FORCE. 91

motion produced in the act of union may be turned to
mechanical account. Passing from dead matter to living ^
matter, we find that the source of motive power here re
ferred to is also the source of muscular power. A horse
can perform work, and so can a man, but this work is at
bottom the molecular work of the elements of the food and
the oxygen of the air. We inhale this vital gas, and bring
it into sufficiently close proximity with the carbon and the
hydrogen of the food. They unite in obedience to their
mutual attractions, and their motion toward each other,
properly turned to account by the wronderful mechanism of
the body, becomes muscular motion.

One fundamental thought pervades all these statements : /
there is one-tap root from which they all spring. This is
the ancient maxim that out of nothing nothing comes ; that
neither in the organic world nor in the inorganic is power
produced without the expenditure of other power; that
neither in the plant nor in the animal is there a creation of
force or motion. Trees grow, and so do men and horses ;^
and here we have new power incessantly introduced upon
the earth. But its source, as I have already stated, is the
sun. For he it is who separates the carbon from the oxy
gen of the carbonic acid, and thus enables them to recom-
bine. Whether they recombine in the furnace of the
steam-engine or in the animal body, the origin of the power
they produce is the same. In this sense we are all " souls
of fire and children of the sun." But, as remarked by
Helmholtz, we must be content to share our celestial
pedigree with the meanest living things. The frog, and
the toad, and those terrible creatures, the monkey and {/
the gorilla, draw their power from the same source as
man. .

Some estimable persons, here present, very possibly
shrink from accepting these statements ; they may be
frightened by their apparent tendency toward what is called

92 FRAGMENTS OF SCIENCE.

materialism — a word which, to many minds, expresses some
thing very dreadful. But it ought to be known and avowed
that the physical philosopher, as such, must be a pure ma
terialist. His inquiries deal with matter and force, and
with them alone. The action which he has to investigate
is necessary action ; not spontaneous action — the transfor
mation, not the creation, of matter and force. And what
ever be the forms which matter and force may assume,
whether in the organic world or in the inorganic, whether
in the coal-beds and forests of the earth, or in the brains
and muscles of men, the physical philosopher will make
good his right to investigate them. It is perfectly vain to
attempt to stop inquiry as to the actual and possible actions
of matter and force. Depend upon it, if a chemist by
bringing the proper materials together, in a retort or
crucible, could make a baby, he would do it. There is no
law, moral or physical, forbidding him to do it — his in
quiries in this direction are limited solely by his own ca
pacity and the laws of matter and force. At the present
moment there are, no doubt, persons experimenting on
the possibility of producing what we call life out of in
organic materials. Let them pursue their studies in peace ;
it is only by such trials that they will learn the limits of
their powers.

But while I thus make the largest demand for freedom
of investigation — while I as a man of science feel a natural
pride in scientific achievement, wrhile I regard science as the
most powerful instrument of intellectual culture, as well as
the most powerful ministrant to the material wants of men ;
if you ask me whether science has solved, or is likely in our
day to solve, the problem of this universe, I must shake my
head in doubt. You remember the first Napoleon's ques
tion, when the savans who accompanied him to Egypt dis
cussed in his presence the origin of the universe, and sol VIM!
it to their own apparent satisfaction. He looked aloft to

MATTER AND FORCE. 93

the starry heavens, and said, " It is all very well, gentle
men ; but who made all these ? " That question still re
mains unanswered, and science makes no attempt to answer
it. As far as I can see, there is no quality in the human
intellect which is fit to be applied to the solution of the
problem. It entirely transcends us. The mind of man may
be compared to a musical instrument with a certain range
of notes, beyond which in both directions we have an
infinitude of silence. The phenomena of matter and force
lie within our intellectual range, and as far as they reach
we will at all hazards push our inquiries. But behind, and
above, and around all, the real mystery of this universe lies
unsolved, and, as far as we are concerned, is incapable of
solution. Fashion this mystery as you will, with that I
have nothing to do. But be careful that your conception
of it be not an unworthy one. Invest that conception with
your highest and holiest thought, but be careful of pre
tending to know more about it than is given to man to
know. Be careful, above all things, of professing to see in
the phenomena of the material world the evidences of Di
vine pleasure or displeasure. Doubt those who would
deduce from the fall of the tower of Siloam the anger of the
Lord against those who were crushed. Doubt those equally
who pretend to see in cholera, cattle-plague, and bad har
vests, evidences of Divine" anger. Doubt those spiritual
guides who in Scotland have lately propounded the mon
strous theory that the depreciation of railway scrip is a con
sequence of railway travelling on a Sunday. Let them not,
as far as you are concerned, label and libel the system of
Nature with their ignorant hypotheses. Well might the
mightiest of living Scotchmen, that hero of the intellect
who might have been a hero in the field, that strong and
earnest soul who has made every soul of like nature in
these islands his debtor — looking from the solitudes of
thought into this highest of questions, well, I say, might

94 FRAGMENTS OF SCIENCE.

your noble old Carlyle scornfully retort on such interpreters
of the ways of God to men :

The Builder of this universe was wise,

He formed all souls, all systems, planets, particles ;

The plan he formed his worlds and ^Eons by,

Y*"us — Heavens ! — was thy small nine-and-thirty articles !

V.

ADDRESS TO THE STUDENTS OF UNIVER-
, SITY COLLEGE, LONDON,

ON THE DISTRIBUTION OF PHIZES IN THE FACULTY OF AliTS.

Session 1868-'69.

" Self-reverence, self-knowledge, self-control,
These three alone lead life to sovereign power,
Yet not for power (power of herself
Would come uncalled for), but to live by law,
Acting the law we live by without fear ;
And, because right is right, to follow right
Were wisdom in the scorn of consequence."

TENNYSON.

Y.

AN ADDRESS TO STUDENTS.

THERE is an idea regarding the nature of man which
modern philosophy has sought, and is still seeking, to raise
into clearness, the idea, namely, of secular growth. Man
is not a thing of yesterday ; nor do I imagine that the
slightest controversial tinge is imported into this address
when I say that he is not a thing of 6,000 years ago.
Whether he came originally from stocks or stones, from
nebulous gas or solar fire, I know not ; if he had any such
origin the process of his transformation is as inscrutable to
you and to me as that of the grand old legend, according
to which " the Lord God formed man of the dust of the
ground, and breathed into his nostrils the breath of life ;
and man became a living soul." But, however obscure
man's origin may be, his growth is not to be denied. Here
a little and there a little added through the ages have
slowly transformed him from what he Avas into what he is.
The doctrine has been held that the mind of the child is like
a sheet of white paper, on which by education we can write
what characters we please. This doctrine assuredly needs
qualification and correction. In physics, when an external
force is applied to a body with a view of affecting its inner
texture, if we wish to predict the result, we must know
whether the external force conspires with or opposes the
internal forces of the body itself; and in bringing the influ
ence of education to bear upon the new-born man his inner
5

98 FRAGMENTS OF SCIENCE.

powers must be also taken into account. He comes to us
as a bundle of inherited capacities and tendencies, labelled
" from the indefinite past to the indefinite future ; " and he
makes his transit from the one to the other through the
education of the present time. The object of that educa
tion is, or ought to be, to provide wise exercise for his ca
pacities, wise direction for his tendencies, and through this
exercise and this direction to furnish his mind with such
knowledge as may contribute to the usefulness, the beauty,
and the nobleness of his life.

How is this discipline to be secured, tin's knowledge im
parted ? Two rival methods now solicit attention — the one
organized and equipped, the labor of centuries having been
expended in bringing it to its present state of perfection ;
the other, more or less chaotic, but becoming daily less so,
and giving signs of enormous power, both as a source of
knowledge and as a means of discipline. These two
methods are the classical and the scientific method. I wish
they were not rivals ; it is only bigotry and short-sighted
ness that make them so ; for assuredly it is possible to give
both of them fair play. Though hardly authorized to ex
press any opinion whatever upon the subject, I nevertheless
hold the opinion that the proper study of a language is an
intellectual discipline of the highest kind. If I except dis
cussions on the comparative merits of popery and Protes
tantism, English grammar was the most important discipline
of my boyhood. The piercing through the involved and
inverted sentences of "Paradise Lost;" the linking of the
verb to its often distant nominative, of the relative to its
distant antecedent, of the agent to the object of the transi
tive verb, of the preposition to the noun or pronoun which
it governed — the study of variations in mood and tense, the
transformations often necessary to bring out the true gram-
mat ical structure of a sentence — all this was to my young
mind n discipline of the highest value, and, indeed, a source

AN ADDRESS TO STUDENTS. 99

of unflagging delight. How I rejoiced when I found a
great author tripping, and was fairly able to pin him to a
corner from which there was no escape ! As I speak, some
of the sentences which exercised me when a boy rise to my
recollection. "He that hath ears to hear let him hear."
That was one of them, where the " He " is left, as it were,
floating in mid air without any verb to support it. I speak
thus of English because it was of real value to me. I do
not speak of other languages because their educational value
for me was almost insensible. But, knowing the value of
English so well, I should be the last to deny, or even to
doubt, the high discipline involved in the proper study of
Latin and Greek.

That study, moreover, has other merits and recommen
dations which have been already slightly touched upon.
It is organized and systematized by long-continued use.
It is an instrument wielded • by some of the best intellects
of the country in the education of youth ; and it can point
to results in the achievements of our foremost men. What,\
then, has science to offer which is in the least degree likely ,
to compete with such a system ? I cannot better reply
than by recurring to the grand old story from which I have /
already quoted. Speaking of the world and all that therein
is, of the sky and the stars around it, the ancient writer
says, " And God saw all that he had made, and behold it
was very good." It is the body of things thus described
which science offers to the study of man. There is a very
renowned argument much prized and much quoted by
theologians, in which the universe is compared to a watch.
Let us deal practically with this comparison. Supposing a
watchmaker, having completed his instrument, to be so
satisfied with his work as to call it very good, what would
you understand him to mean ? You would not suppose
that he referred to the dial-plate in front and the chasing
of the case behind, so much as to the wheels and pinions,

100 FRAGMENTS OF SCIEXCK.

the springs and jewelled pivots of the works within, those
qualities and powers, in short, which enable the watch to
perform accurately its work as a keeper of time. With re
gard to the knowledge of such a watch he would be a mere
ignoramus who would content himself with outward inspec
tion. I do not wish to say one severe word here to-dav,
but I fear that many of those who are very loud in their
praise of the works of the Lord know them only in this out-
xfeide and superficial way. It is the inner works of the uni
verse which science reverently uncovers ; it is the study of
these that she recommends as a discipline worthy of all
acceptation.

The ultimate problem of physics is to reduce matter by
analysis to its lowest condition of divisibility, and force to
its simplest manifestations, and then by synthesis to con
struct from these elements the world as it stands. We are
still a long way from the final solution of this problem ;
and when the solution comes, it will be one more of spir
itual insight than of actual observation. But though we
are still a long way from this complete intellectual mastery
of Nature, we have conquered vast regions of it, have
learned their polities and the play of their powers. We
live upon a ball of matter eight thousand miles in diameter,
s \vathed by an atmosphere of unknown height. This ball
has been molten by heat, chilled to a solid, and sculptured
by water ; it is made up of substances possessing distinctive
properties and modes of action, properties which have an
immediate bearing upon the continuance of man in health,
and on his recovery from disease, on which moreover de
pend all the arts of industrial life. These properties and
modes of action offer problems to the intellect, some profit
able to the child, and others sufficient to tax the highr-t
powers of the philosopher. Our native sphere turns on its
axis and revolves in space. It is one of a band which do
the same. It is illuminated by a sun which, though nearly

AN ADDRESS TO STUDENTS. 101

a hundred nlillions of miles distant, can be brought virtually
into our closets and there subjected to examination. It ^
has its winds and clouds, its rain and frost, its light, heat,
sound, electricity, and magnetism. And it has its vast
kingdoms of animals and vegetables. To a most amazing
extent the human mind has conquered these things, and
revealed the logic which runs through them. Were they
facts only, without logical relationship, science might, as a
means of discipline, suffer in comparison with language.
But the whole body of phenomena is instinct with law ;
the facts are hung on principles, and the value of physical
science as a means of discipline consists in the motion of
the intellect, both inductively and deductively, along the
lines of law marked out by phenomena. As regards that
discipline to which I have already referred as derivable
from the study of languages — that, and more, are involved
in the study of physical science. Indeed, I believe it would
be possible so to limit and arrange the study of a portion
of physics as to render the mental exercise involved in it
almost qualitatively the same as that involved in the un
ravelling of a language.

I have thus far limited myself to the purely intellectual
side of this question. But man is not all intellect. If he
were so, science would, I believe, be his proper nutriment.
But he feels as well as thinks ; he is receptive of the sub
lime and the beautiful as well as of the true. Indeed, I be
lieve that even the intellectual action of a complete man is,
consciously or unconsciously, sustained by an under-current
of the emotions. It is vain, I think, to attempt to separate
moral and emotional nature from intellectual nature. Let
a man but observe himself, and he* will, if I mistake not,
find that in nine cases out of ten, moral or immoral consid
erations, as the case may be, are the motive force which
pushes his intellect into action. The reading of the works
of two men, neither of them imbued with the spirit of

102 FRAGMENTS OF SCIENCE.

modern science, neither of them, indeed, friendly to that
spirit, has placed me here to-day. These men are the Eng
lish Carlyle and the American Emerson. I must ever re
member with gratitude that through three long, cold Ger
man winters Carlyle placed me in my tub, even when ice
was on its surface, at five o'clock every morning ; not
slavishly, but cheerfully, meeting each day's studies with a
resolute will, determined whether victor or vanquished not
to shrink from difficulty. I never should have gone through
Analytical Geometry and the Calculus had it not been for
those men. I never should have become a physical inves
tigator, and hence without them I should not have been
here to-day. They told me what I ought to do in a way
that caused me to do it, and all my consequent intellectual
action is to be traced to this purely moral source. To Car
lyle and Emerson I ought to add Fichte, the greatest rep
resentative of pure idealism. These three unscientific men
made me a practical scientific worker. They called out,
" Act ! " I hearkened to the summons, taking the liberty,
however, of determining for myself the direction which
effort was to take.

And I may now cry, " Act ! " but the potency of action
must be yours. I may pull the trigger, but if the gun be
not charged there is no result. "NVe arc creators in the
intellectual world as little as in the physical. We may
remove obstacles, and render latent capacities active, but
we cannot suddenly change the nature of man. The " new
birth " itself implies the preexistence of the new character
which requires not to be created but brought forth. You
cannot by any amount of missionary labor suddenly trans
form the savage into the civilized Christian. The improve
ment of man is secular — not the work of an hour or of a
day. But though indubitably bound by our organizations,
no man knows what the potentialities of any human mind
may be, which require only release to be brought into ac-

AN ADDRESS TO STUDENTS. 103

tion. Let me illustrate this point. There are in the min
eral world certain crystals, certain forms, for instance, of
fluor-spar, which have lain darkly in the earth for ages, but
which nevertheless have a potency of light locked up within
them. In their case the potential has never become actual— -
the light is in fact held back by a molecular detent. When
these crystals are warmed, the detent is lifted, and an out
flow of light immediately begins. I know not how many
of you may be in the condition of this fluor-spar. For aught
I know, every one of you may be in this condition, requiring
but the proper agent to be applied — the proper word to be
spoken — to remove a detent, and to render you conscious
of light within yourselves and sources of light to others.

The circle of human nature, then, is not complete with
out the arc of feeling and emotion. The lilies of the field
have a value for us beyond their botanical ones — a certain
lightening of the heart accompanies the declaration that,^
" Solomon in all his glory was not arrayed like one of these."
The sound of the village bell which comes mellowed from
the valley to the traveller upon the hill, has a value beyond
its acoustical one. The setting sun when it mantles with
the bloom of roses the alpine snows, has a value beyond its
optical one. The starry heavens, as you know, had for Im-
manuel Kant a value beyond their astronomical one. Round
about the intellect sweeps the horizon of emotions from
which all our noblest impulses are derived. I think it very
desirable to keep this horizon open ; not to permit either
priest or philosopher to draw down his shutters between
you and it. And here the dead languages, which are sure
to be beaten by science in the purely intellectual fight, have
an irresistible claim. They supplement the work of science
by exalting and refining the aesthetic faculty, and must on
this account be cherished by all who desire to see human
culture complete. There must be a reason for the fascina
tion which these languages have so long exercised upon

104 FRAGMENTS OF SCIENCE.

the most powerful and elevated minds — a fascination which
will probably continue for men of Greek and Rom£n mould
to the end of time.

In connection with this question of the emotions one
very obvious danger besets many of the more earnest spirits
of our day — the danger of haste in endeavoring to give the
feelings repose. We are distracted by systems of theology
and philosophy which -were taught to us when young, and
which now excite in us a hunger and a thirst for knowledge
not proved to be attainable. There are periods when the
judgment ought to remain in suspense, the data on which
a decision might be based being absent. This discipline
of suspending the judgment is a common one in science,
but not so common as it ought to be elsewhere. I walked
down Regent Street some time ago with a man of great
gifts and acquirements, discussing with him various theo
logical questions. I could not accept his views of the origin
and destiny of the universe, nor was I prepared to enun
ciate any definite views of my own. He turned to me at
length and said, " You surely must have a theory of the
universe." That I should in one way or another have solved
this mystery of mysteries seemed to my friend a matter of
course. " I have not even a theory of magnetism," was my
reply. We ought to learn to wait, and pause before closing
with the advances of those expounders of the ways of God
to men, who offer us intellectual peace at the modest cost
of intellectual life.

The teachers of the world ought to be its best men, and
for the present at all events such men must learn self-trust.
They must learn more and more to do without external aid ;
save such aid as comes from the contemplation of a uni
verse, which, though it baffles the intellect, can elevate the
heart. But they must learn to feel the mystery of that
universe without attcMnpting to give it a rigid form, per
sonal or otherwise. By the fulness and freshness of their

AN ADDRESS TO STUDENTS. 1Q5

own lives and utterances they must awaken life in others/
The position of science is already assured, but I think the \
poet also will have a great part to play in the future of the
world. To him it is given for a long time to come to fill
those shores which the recession of the theologic tide has
left exposed ; to him, when he rightly understands his mis
sion, and does not flinch from the tonic discipline which it
assuredly demands, we have a right to look for that height
ening and brightening of life which so many of us need.
He ought to be the interpreter of that power which as

" Jehovah, Jove, or Lord,"

has hitherto filled and strengthened the human heart.

Let me utter one practical word in conclusion — take
care of your health. There have been men who by wise
attention to this point might have risen to any eminence —
might have made great discoveries, written great poems,
commanded armies, or ruled states, but who by unwise
neglect of this point have come to nothing. Imagine Her
cules as oarsman in a rotten boat ; what can he do there
but by the very force of his stroke expedite the ruin of his
craft. Take care then of the timbers of your boat, and
avoid all practices likely to introduce either wet or dry rot
among them. And this is not to be accomplished by desul
tory or intermittent efforts of the will, but by the formation
of habits. The will no doubt has sometimes to put forth
its strength in order to strangle or crush the special tempta
tion. But the formation of right habits is essential to your
permanent security. They diminish your chance of falling
when assailed, and they augment your chance of recovery
when overthrown.

VI.

SCOPE AND LIMIT OF SCIENTIFIC
MATERIALISM.

AN ADDRESS.

DELIVERED IN THE MATHEMATICAL AND PHYSICAL SECTION OF
THE BRITISH ASSOCIATION IN NORWICH.

August 19, 1868.

"As I proceeded I found my philosopher altogether forsaking mind
or iinv other principle of order, and having recourse to air and ether, and
water, and other eccentricities. I might compare him to a person who
bcLran by maintaining generally that mind is the cause of the actions of
Socrates, but who, when he endeavored to explain the cause of my several
actions in detail, went on to show that I sit here because my body is
made up of bones and muscles ; and the bones he would say are hard
mid have ligaments which divide them, and the muscles are elastic, and
they cover the bones, which have also a covering or environment of flesh
and skin which contains them ; and as the bones are lifted at their joints
by the contraction or relaxation of the muscles, I am able to bend my
limbs, and this is why I am sitting here in a curved posture ; that is
what lie would say, and he would have a similar explanation of my talk
ing to you, which he would attribute to sound, and air, and hearing, and
he would assign ten thousand other causes of the same sort, forgetting to
mention the true cause, which is that the Athenians have thought fit to
condemn me, and accordingly I have thought it better and more right to
remain here and undergo my sentence ; for I am inclined to think that
tliese muscles and bones of mine would have gone off to Megara or
UnMitia — by the dog of Egypt they would, if they had been guided by
their own idea of what was best, and if I had not chosen as the better and
nobler part, instead of playing truant and running away, to undergo any
punishment which the State inflicts." — PLATO, JowctCs Translation.

:

VI.

SCIENTIFIC MATERIALISM.

THE CELEBRATED FiCHTE, in his lectures on the "Vo
cation of the Scholar," insisted on a culture which should
not be one-sided, but all-sided. The scholar's intellect
was to expand spherically and not in a single direction
only. In one direction, however, Fichte required that
the scholar should apply himself directly to Nature, be
come a creator of knowledge, and thus repay by original
labors of his own the immense debt he owed to the
labors of others. It was these which enabled him to sup
plement the knowledge derived from his own researches,
so as to render his culture rounded and not one-sided.

As regards science Fichte's idea is to some extent
illustrated by the constitution and the labors of the British
Association. We have a body of men engaged in the
pursuit of Natural Knowledge, but variously engaged.
While sympathizing with each of its departments, and
supplementing his culture by knowledge drawn from all
of them, each student among us selects one subject for the
exercise of his own original faculty — one line along which
he may carry the light of his private intelligence a little
way into the darkness by which all knowledge is sur
rounded. Thus, the geologist deals with the rocks ; the
biologist with the conditions and phenomena of life ; the
astronomer with stellar masses and motions ; the mathe
matician with the relations of space and number; the

\J

110 FRAGMENTS OF SCIENCE.

chemist pursues bis atoms, while the physical investigator
has his own large field in optical, thermal, electrical,
acoustical, and other phenomena. The British Associa
tion then, as a whole, faces physical Nature on all sides
and pushes knowledge centrifugally outward, the sum of
its labors constituting what Fichte might call the sphere of
natural knowledge. In the meetings of the Association it
is found necessary to resolve this sphere into its component
parts, which take concrete form under the respective letters
of our Sections.

This is the Mathematical and Physical Section. Mathe
matics and physics have been long accustomed to coalesce.
For, no matter how subtle a natural phenomenon may be,
whether we observe it in the region of sense, or follow it
into that of imagination, it is in the long-run reducible to
mechanical laws. But the mechanical data once guessed
or given, mathematics become all-powerful as an instru
ment of deduction. The command of geometry over the
relations of space, the far-reaching power which organized
symbolic reasoning confers, are potent both as means of
physical discovery, and of reaping the entire fruits of dis
covery. Indeed, without mathematics, expressed or im
plied, our knowledge of physical science would be friable
in the extreme.

Side by side with the mathematical method we have
the method of experiment. Here, from a starting-point
furnished by his own researches, or those of others, the in
vestigator proceeds by combining intuition and verification.
He ponders the knowledge he possesses and tries to push
it further, he guesses and checks his guess, he conjectures
and confirms or explodes his conjecture. These guesses
and conjectures are by no means leaps in the dark ; for
knowledge once gained casts a faint light beyond its own
immediate boundaries. There is no discovery so limited
as not to illuminate something beyond itself. The force

SCIENTIFIC MATERIALISM. m

of intellectual penetration into this penumbral region which
surrounds actual knowledge is not, as some seem to think,
dependent upon method, but upon the genius of the in
vestigator. There is, however, no genius so gifted as not
to need control and verification. The profoundest minds
know best that Nature's ways are not at all times their
ways, and that the brightest flashes in the world of
thought are incomplete until they have been proved to
have their counterparts in the world of fact. Thus ihe
vocation of the true experimentalist may be defined as
the continued exercise of spiritual insight, and its inces
sant correction and realization. His experiments consti
tute a body, of which his purified intuitions are, as it were,
the soul.

Partly through methematical and partly through ex
perimental research, physical science has of late years as
sumed a momentous position in the world. Both in a
material and in an intellectual point of view it has pro
duced, and it is destined to produce, immense changes —
vast social ameliorations, and vast alterations in the popu
lar conception of the origin, rule, and governance of natural
things. By science, in the physical world, miracles are
wrought, while philosophy is forsaking its ancient meta
physical channels and pursuing others which have been
opened or indicated by scientific research. This must be
come more and more the case as philosophical writers
become more deeply imbued with the methods of science,
better acquainted with the facts which scientific men have
won, and with the great theories which they have elaborated.

If you look at the face of a watch, you see the hour
and minute hands, and possibly also a second-hand, moving
over the graduated dial. Why do these hands move ? and
why are their relative motions such as they are observed
to be ? These questions cannot be answered without open-
in"" ilio watch, mastering its various parts, and ascertaining

112 FRAGMENTS OF SCIENCE.

their relationship to each other. When this is done, we
find that the observed motion of the hands follows of ne
cessity from the inner mechanism of the watch, when acted
upon by the force invested in the spring.

The motion of the hands may be called a phenomenon
of art, but the case is similar with the phenomena of Nature.
These also have their inner mechanism, and their store of
force to set that mechanism going. The ultimate problem
of physical science is to reveal this mechanism, to discern
this store, and to show that from the combined action of
both the phenomena of which they constitute the basis
must of necessity flow.

I thought an attempt to give you even a brief and
sketchy illustration of the manner in wrhich scientific think
ers regard this problem would not be uninteresting to you
on the present occasion ; more especially as it will give me
occasion to say a word or two on the tendencies and limits
of modern science ; to point out the region which men of
science claim as their own, and where it is mere waste of
lime to oppose their advance, and also to define, if possible,
the bourne between this and that other region to which
the questionings and yearnings of the scientific intellect
are directed in vain.

But here your tolerance will be needed. It was the
American Emerson, I think, who said that it is hardly pos
sible to state any truth strongly without apparent injustice
to some other truth. Truth is often of a dual character,
taking the form of a magnet with two poles ; and many of
the differences which agitate the thinking part of mankind
are to be traced to the exclusiveness with which partisan
reasoners dwell upon one-half of the duality in forgetfulness
of the other. The proper course appears to be to state
both halves strongly, and allow each its fair share in the
formation of the resultant conviction. But this waiting for
the statement of the two sides of a questM--.! implies pa-

SCIENTIFIC MATERIALISM. 113

tience. It implies a resolution to suppress indignation if
the statement of the one-half should clash with our convic
tions, and to repress equally undue elation if the half-state
ment should happen to chime in with our views. It implies
a determination to wait calmly for the statement of the
whole, before we pronounce judgment in the form of either
acquiescence or dissent.

This premised, and, I trust, accepted, let us enter upon
our task. There have been writers who affirmed that the
pyramids of Egypt were the productions of Nature ; and in
his early youth Alexander von Humboldt wrote a learned
essay with the express object of refuting this notion. We
now regard the pyramids as the work of men's hands, aided
probably by machinery of which no record remains. We
picture to ourselves the swarming workers toiling at those
vast erections, lifting the inert stones, and, guided by the
volition, the skill, and possibly at times by the whip of the
architect, placing them in their proper positions. The
blocks in this case were moved and posited by a power
external to themselves, and the final form of the pyramid
expressed the thought of its human builder.

Let us pass from this illustration of constructive power
to another of a different kind. When a solution of common
salt is slowly evaporated, the water which holds the salt
in solution diappears, but the salt itself remains behind. At
a certain stage of concentration the salt can no longer retain
the liquid form ; its particles, or molecules, as they are
called, begin to deposit themselves as minute solids, so
minute, indeed, as to defy all microscopic power. As evapo
ration continues solidification goes on, and we finally obtain,
through the clustering together of innumerable molecules,
a finite crystalline mass of a definite form. What is this
form ? It sometimes seems a mimicry of the architecture
of Egypt. We have little pyramids built by the salt,
terrace above terrace from base to apex, forming a series of

114 FRAGMENTS OF SCIENCE.

steps resembling those up which the Egyptian traveller is
dragged by his guides. The human mind is as little dis
posed to look unquestioning at these pyramidal salt-crys
tals as to look at the pyramids of Egypt without inquiring
whence they came. How, then, are those salt-pyramids
built up ?

Guided by analogy, you may, if you like, suppose that
swarming among the constituent molecules of the salt,
there is an invisible population, controlled and coerced by
some invisible master, and placing the atomic blocks in
their positions. This, however, is not the scientific idea,
nor do I think your good sense will accept it as a likely
one. The scientific idea is that the molecules act upon each
other without the intervention of slave labor ; that they
attract each other and repel each other at certain definite
1 mints, or poles, and in certain definite directions ; and that
the pyramidal form is the result of this play of attraction
and repulsion. While, then, the blocks of Egypt were laid
down by a power external to themselves, these molecular
blocks of salt are self-posited, being fixed in their places by
the forces with wThich they act upon each other.

I take common salt as an illustration because it is so
familiar to us all ; but any other crystalline substance would
answer my purpose equally well. Everywhere, in fact,
throughout inorganic Nature, we have this formative power,
as Fichte would call it — this structural energy ready to
come into play, and build the ultimate particles of matter
into definite shapes. The ice of our winters and of our
polar regions is its handywork, and so equally are the
quartz, felspar, and mica of our rocks. \ Our chalk-beds are
for the most part composed of minute shells, which are also
the product of structural energy ; but, behind the shell, as
a whole, lies a more remote and subtle formative act. These
shells are built up of little crystals of calc-spar, and to form
these crystals the structural force had to deal with the

SCIENTIFIC MATERIALISM. 115

intangible molecules of carbonate of lime. This tendency
on the part of matter to organize itself, to grow into shape,
to assume definite forms in obedience to the definite action
of force, is, as I have said, all-pervading. It is in the
ground on which you tread, in the water you drink, in the
air you breathe. Incipient life, as it were, manifests itself
throughout the whole of what we call inorganic Nature.

The forms of the minerals resulting from this play of
polar forces are various, and exhibit different degrees of
complexity. Men of science avail themselves of all possible
means of exploring their molecular architecture. For this
purpose they employ in turn as agents of exploration, light,
heat, magnetism, electricity, and sound. Polarized light is
especially useful and powerful here. A beam of such light,
when sent in among the molecules of a crystal, is acted on
by them, and from this action we infer with more or less of
clearness the manner in which the molecules are arranged.
That differences, for example, exist between the inner
structure of rock-salt and crystallized sugar or sugar-candy,
is thus strikingly revealed. These actions often display
themselves in chromatic phenomena of great splendor, the
play of molecular force being so regulated as to remove
some of the colored constituents of white light, and to leave
others with increased intensity behind.

And now let us pass from what we are accustomed to
regard as a dead mineral to a living grain of corn. When
it is examined by polarized light, chromatic phenomena
similar to those noticed in crystals are observed. And
why ? Because the architecture of the grain resembles the
architecture of the crystal. In .the grain also the molecules
are set in definite positions, and in accordance with their
arrangement they act upon the light. But what has built
together the molecules of the corn ? I have already said
regarding crystalline architecture that you may, if you
please, consider the atoms and molecules to be placed in

116 FRAGMENTS OF SCIENCE.

position by a power external to themselves. The same
hypothesis is open to you now. But if in the case of crys
tals you have rejected this notion of an external architect,
I think you are bound to reject it now, and to conclude
that the molecules of the corn are self-posited by the forces
with which they act upon each other. It would be poor
philosophy to invoke an external agent in the one case and
to reject it in the other.

Instead of cutting our grain of corn into slices and sub
jecting it to the action of polarized light, let us place it in
the earth and subject it to a certain degree of warmth. In
other words, let the molecules, both of the corn and of the
surrounding earth, be kept in that state of agitation which
we call warmth. Under these circumstances, the grain and
the substances which surround it interact, and a definite
molecular architecture is the result. A bud is formed ; this
bud rqaches the surface, where it is exposed to the sun's
rays, which are also to be regarded as a kind of vibratory
motion. And as the motion of common heat with \vhich
the grain and the substances surrounding it were first
endowed, enabled the grain and these substances to exer
cise their attractions and repulsions, and thus to coalesce
in definite forms, so the specific motion of the sun's rays
now enables the green bud to feed upon the carbonic acid
and the aqueous vapor of the air. The bud appropriates
those constituents of both for which it has an elective
attraction, and permits the other constituent to resume its
place in the air. Thus the architecture is carried on.
Forces are active at the root, forces are active in the blade,
the matter of the earth and the matter of the atmosphere
are drawTi toward the root and blade, and the plant aug
ments in size. We have in succession the bud, the stalk,
the ear, the full corn in the ear; the cycle of molecular
action being completed by the production of grains similar
to that with which the process began.

SCIENTIFIC MATERIALISM. 117

Now there is nothing in this process which necessarily
eludes the conceptive or imagining power of the purely
human mind. An intellect the same in kind as our own
would, if only sufficiently expanded, be able to follow the
whole process from beginning to end. It would sec every
molecule placed in its position by the specific attractions
and repulsions exerted between it and other molecules, the
whole process and its consummation being an instance of
the play of molecular force. Given the grain and its envi
ronment, the purely human intellect might, if sufficiently
expanded, trace out a priori every step of the process of
growth, and by the application of purely mechanical prin
ciples demonstrate that the cycle must end, as it is seen to
end, in the reproduction of forms like that with which it
began. A similar necessity rules here to that which rules
the planets in their circuits round the sun.

You will notice that I am stating my truth strongly, as
at the beginning we agreed it should be stated. But I
must go still further, and affirm that in the eye of science
the animal body is just as much the product of molecular
force as the stalk and ear of corn, or as the crystal of salt
or sugar. Many of the parts of the body are obviously
mechanical. Take the human heart, for example, with its
system of valves, or take the exquisite mechanism of the
eye or hand. Animal heat, moreover, is the same in kind
as the heat of a fire, being produced by the same chemical
process. Animal motion, too, is as directly derived from
the food of the animal, as the motion of Trevethyck's walk
ing-engine from the fuel in its furnace. As regards matter,
the animal body creates nothing ; as regards force, it creates
nothing. Which of you by taking thought can add one
cubit to his stature ? All that has been said, then, regard
ing the plant may be restated with regard to the animal.
Every particle that enters into the composition of a muscle,
a nerve, or a bone, has been placed in its position by mo-

118 FRAGMENTS OF SCIENCE.

lecular force. And unless the existence of law in these
matters be denied, and the element of caprice introduced,
we must conclude that, given the relation of any molecule
of the body to its environment, its position in the body
might be determined mathematically. Our difficulty is not
with the quality of the problem, but with its complexity •
and this difficulty might be met by the simple expansion
of the faculties which we now possess. Given this expan
sion, with the necessary molecular data, and the chick
might be deduced as rigorously and as logically from the
egg as the existence of Neptune from the disturbances of
Uranus, or as conical refraction from the undulatory theory
L of light.

You see I am not mincing matters, but avowing nakedly
what many scientific thinkers more or less distinctly be
lieve. The formation of a crystal, a plant, or an animal, is
in their eyes a purely mechanical problem, which differs
from the problems of ordinary mechanics in the smallness
of the masses and the complexity of the processes involved.
Here you have one half of our dual truth ; let us now glance
ut the other half. Associated with this wonderful mechan
ism of the animal body we have phenomena no less certain
than those of physics, but between which and the mechan
ism we discern no necessary connection. A man, for ex
ample, can say, I feel, I think, I love ; but how does
consciousness infuse itself into the problem ? The human
brain is said to be the organ of thought and feeling j when
we are hurt the brain feels it, when we ponder it is the
brain tluit thinks, when our passions or affections are ex
cited it is through the instrumentality of the brain. Let us
endeavor to be a little more precise here. I hardly imagine
there exists a profound scientific thinker, who has reflected

I upon the subject, unwilling to admit the extreme proba
bility of the hypothesis that, for every fact of consciousness,
whether in the domain of sense, of thought, or of emotion,

SCIENTIFIC MATERIALISM. 119

a definite molecular condition of motion or structure is set
up in the brain ; or who would be disposed even to deny
that if the motion or structure be induced by internal
causes instead of external, the effect on consciousness will
be the same ? Let any nerve, for example, be thrown by
morbid action into the precise state of motion which would
be communicated to it by the pulses of a heated body,
surely that nerve will declare itself hot — the mind will
accept the subjective intimation exactly as if it were ob
jective. The retina may be excited by purely mechanical
means. A blow on the eye causes a luminous flash, and
the mere pressure of the finger on the external ball pro
duces a star of light, which Newton compared to the circles
on a peacock's tail. Disease makes people see visions and
dream dreams ; but, in all such cases, could we examine
the organs implicated, we should, on philosophical grounds,
expect to find them in that precise molecular condition
which the real objects, if present, would superinduce.

The relation of physics to consciousness being thus
invariable, it follows that, given the state of the brain, the
corresponding thought or feeling might be inferred; or
given the thought or feeling, the corresponding state of the
brain might be inferred. But how inferred ? It would be
at bottom not a case of logical inference at all, but of
empirical association. You may reply that many of the
inferences of science are of this character ; the inference,
for example, that an electric current of a given direction
will deflect a magnetic needle in a definite way ; but the
cases differ in this, that the passage from the current to the
needle, if not demonstrable, is thinkable, and that we enter
tain no doubt as to the final mechanical solution of the
problem. But the passage from the physics of the brain
to the corresponding facts of consciousness is unthinkable.
Granted that a definite thought, and a definite molecular 7
action in the brain occur simultaneously ; we do not possess

120 FRAGMENTS OF SCIEXCE.

the intellectual organ, nor apparently any rudiment of the
organ, which would enable us to pass, by a process of rea
soning, from the one to the other. They appear together,
but we do not know why. Were our minds and senses so
expanded, strengthened, and illuminated as to enable us to
see and feel the very molecules of the brain ; were we
capable of following all their motions, all their groupings,
all their electric discharges, if such there be ; and were we
intimately acquainted with the corresponding states of
thought and feeling, we should be as far as ever from the
solution of the problem, " How are these physical processes
connected jwith the facts of consciousness ? " The chasm
between the two classes of phenomena would still remain
intellectually impassable. Let the consciousness of love,
for example, be associated with a right-handed spiral
motion of the molecules of the brain, and the consciousness
of hate with a left-handed spiral motion. We should then
know when we love that the motion is in one direction,
and when we hate that the motion is in the other ; but the
" WHY ? " would remain as unanswerable as before. '

In affirming that the growth of the body is mechanical,
find that thought, as exercised by us, has its correlative in
the physics of the brain, I think the position of the " Ma
terialist" is stated, as far as that position is a tenable
one. I think the materialist will be able finally to main
tain this position against all attacks ; but I do not think,
in the present condition of the human mind, that he can
pass beyond this position. I do not think he is entitled
to say that his molecular groupings and his molecular
motions erplain every thing. In reality, they explain
nothing. The utmost he can affirm is the association of
two classes of phenomena, of whose real bond of union
he is in absolute ignorance. The problem of the con
nection of body and soul is as insoluble in its modern
form as it was in the prescientific ages. Phosphorus is

SCIENTIFIC MATERIALISM. 121

known to enter into the composition of the human brain,
and a trenchant German writer has exclaimed, --^-Qhne
Phe^phoiykeitt-XS^daiike-." That may or may not be the
case ; but even if we knew it to be the case, the knowledge
would not lighten our darkness. On both sides of the zone
here assigned to the materialist he is equally helpless. If
you ask him whence is this " Matter " of which we have
been discoursing, who or what divided it into molecules,
who or what impressed upon them this necessity of running
into organic forms, he has no answer. Science is mute in
reply to these questions. But if the materialist is con
founded and science rendered dumb, who else is prepared .
with a solution ? To whom has this arm of the Lord been ^
revealed ? Let us lower our heads and acknowledge our
ignorance, priest and philosopher, one and all.

Perhaps the mystery may resolve itself into knowledge
tit some future day. The process of things upon this earth
has been one of amelioration. It is a long way from the
Iguanodon and his contemporaries to the President and
members of the British Association. And whether we re
gard the improvement from the scientific or from the theo
logical point of view, as the result of progressive develop
ment, or as the result of successive exhibitions of creative
energy, neither view entitles us to assume that man's present
faculties end the series — that the process of amelioration
stops at him. A time may therefore come wrhen this ultra-
scientific region by which we are now enfolded may offer it
self to terrestrial, if not to human investigation. Two-thirds
of the rays emitted by the sun fail to arouse in the eye the
sense of vision. The rays exist, but the visual organ requi
site for their translation into light does not exist. And so
from this region of darkness and mystery which surrounds
us, rays may now be darting which require but the develop
ment of the proper intellectual organs to translate them
into knowledge as far surpassing ours as ours surpasses
G

122 FRAGMENTS OF SCIENCE.

that of the wallowing reptiles which once held possession
gf this planet. Meanwhile the mystery is not without its
uses. It certainly may be made a power in the human soul ;
but it is a power which has feeling, not knowledge, for its
base. It may be, and will be, and I hope is, turned to
account, both in studying and strengthening the intellect,
and in rescuing man from that littleness to which, in the
struggle for existence, or for precedence in the world, he
is continually prone.

Musings on the Matterhorn,. Jidy 27, 1868.

" HACKED and hurt by time, the aspect of the mountain from its
higher crags saddened me. Hitherto the impression it made was that of
savage strength ; here we had inexorable decay. But this notion of decay
implied a reference to a period when the Matterhorn was in the full
strength of mountainhood. Thought naturally ran back to its remoter
origin and sculpture. Nor did thought halt there, but wandered on
through molten worlds to that nebulous haze which philosophers have
regarded, and with good reason, as the proximate source of all material
things. I tried to look at this universal cloud, containing within itself the
prediction of all that has since occurred ; I tried to imagine it as the seat
of those forces whose action was to issue in solar and stellar systems,
and all that they involve. Did that formless fog contain potentially the
sadness with which I regarded the Matterhorn ? Did the thougM which
now ran back to it simply return to its primeval home ? If so, had we
not better recast our definitions of matter and force ; for if life and
thought be the very flower of both, any definition which omits life and
thought must be inadequate, if not untrue. Are questions like these
warranted ? Why not ? If the final goal of man has not been yet
attained ; if his development has not been yet arrested, who can say that
such yearnings and questionings are not necessary to the opening of a
finer vision, to the budding and the growth of diviner powers ? When I
look at the heavens and the earth, at my own body, at my strength and
weakness of mind, even at these ponderings, and ask myself, is there no
being or thing in the universe that knows more about these matters than
I do ; what is my answer ? Supposing our theologic schemes of crea
tion, condemnation, and redemption, to be dissipated ; and the warmth
of denial which they excite, and which, as a motive force, can match the
warmth of affirmation dissipated at the same time ; would the undeflected
human mind return to the meridian of absolute neutrality as regards these
ultra-physical questions ? Is such a position one of stable equilibrium ?
The channels of thought being already formed, such are the questions
without replies, which could run athwart consciousness during a ten-
minutes, halt upon the weathered point of the Matterhorn."

VII.

ON THE

SCIENTIFIC USE OF THE IMAGINATION,

A DISCOURSE.

DELIVERED BEFOEE THE BEITISII ASSOCIATION AT LITEEPOOL.

September 16, 1870.

If thou wouldst know the mystic song

Chanted when the sphere was young,

Aloft, abroad, the paean swells,

() wise man, hear'st thou half it tells ?

To the open ear it sings

The early genesis of things ;

Of tendency through endless ages

Of star-dust and star-pilgrimages,

Of rounded worlds, of space and tune,

Of the old floods' subsiding slime,

Of chemic matter, force and form,

Of poles and powers, cold, wet, and warm.

The rushing metamorphosis

Dissolving all that fixture is,

Melts things that be to things that seem,

And solid Nature to a dream."

EMERSON.

" Was war' ein Gott dcr nur von aussen sticssc
Im Kreis das All am Finger laufeu liesse !
Him ziemt's, die Welt im Innern zu bewegen,
Natur in Sicb, Sich in Natur zu hegen."

GOETHE.

SCIENTIFIC USE OF THE IMAGINATION.

" Lastly, physical investigation more than any thing besides liclps to teach
us tJie actual value and rigid use of the Imagination — of that wondrous
faculty, which, left to ramble uncontrolled, leads us astray into a wilderness of
perplexities and errors, a land of mists and shadows ; but which properly con
trolled by experience and reflection, becomes the noblest attribute of man : the
source of poetic genius, the instrument of discovery in Science, without the aid
of which Neicton would never have invented fluxions, nor Davy have decom
posed the earths and alkalies, nor would Columbus have found another Con
tinent.1'1 — Address to the Royal Society by its President, Sir Benjamin
Brodie, November 30, 1859.

I CARRIED with me to the Alps this year the heavy
burden of this evening's work. In the way of new inves
tigation I had nothing complete enough to be brought
before you ; so all that remained to me was to fall back
upon such residues as I could find in the depths of con
sciousness, and out of them to spin the fibre and weave the
wreb of this discourse. Save from memory I had no direct
aid upon the mountains ; but to spur up the emotions, on
which so much depends, as well as to nourish indirectly the
intellect and will, I took with me two volumes of poetry,
Goethe's " Farbenlehre," and the work on " Logic " recently
published by Mr. Alexander Bain.1 The spur, I am sorry
to say, was no match for the integument of dulness it had

1 One of my critics remarks, that he does not see the wit of calling
Goethe's " Farbenlehre" and Bain's " Logic," " two volumes of poetry."
Nor do I.

128 FKAGMEXTS OF SCIENCE.

to pierce. In Goethe, so glorious otherwise, I chiefly
noticed the self-inflicted hurts of genius, as it broke itself
in vain against the philosophy of Newton. For a time,
Mr. Bain became my principal companion. I found him
learned and practical, shining generally with a dry light,
but exhibiting at times a flush of emotional strength, which
proved that even logicians share the common fire of hu
manity. He interested me most when he became the
mirror of my own condition. Neither intellectually nor
socially is it good for man to be alone, and the griefs of
thought are more patiently borne when we find that they
have been experienced by another. From certain passages
in his book I could infer that Mr. Bain was no stranger to
such sorrows. Take this passage as an illustration. Speak
ing of the ebb of intellectual force, which we all from time
to time experience, Mr. Bain says, " The uncertainty where
to look for the next opening of discovery brings the pain of
conflict and the debility of indecision." These words have
in them the true ring of personal experience. The action
of the investigator is periodic. He grapples with a subject
of inquiry, wrestles with it, overcomes it, exhausts, it may
be, both himself and it for the time being. He breathes a
space, and then renews the struggle in another field. Now
this period of halting between two investigations is not
always one of pure repose. It is often a period of doubt
and discomfort, of gloom and ennui. "The uncertainly
where to look for the next opening of discovery brings the
pain of conflict and the debility of indecision." Such was
my precise condition in the Alps this year ; in a score of
words Mr. Bain has here sketched my mental diagnosis ;
and it wras under these evil circumstances that I had to
equip myself for the hour and the ordeal that are now
come.

Gladly, however, as I should have seen this duly in
other hands, I could by no means shrink from it. Uisluy-

SCIENTIFIC USE OF THE IMAGINATION. 129

alty would have been worse than failure. In some fashion
or other — feebly or strongly, meanly or manfully, on the
higher levels of thought, or on the flats of commonplace —
the task had to be accomplished. I looked in various direc
tions for help and furtherance ; but without me for a time
I saw only " antres vast," and within me "deserts idle."
case resembled that of a sick doctor who had forgotten
his art and sorely needed the prescription of a friend. Mr.
Bain wrote one for me. He said, " Your present knowl
edge must forge the links of connection between what has
been already achieved and what is now required." ] In
these words he admonished me to review the past and re
cover from it the broken ends of former investigations. I
tried to do so. Previous to going to Switzerland I had
been thinking much of light and heat, of magnetism and
electricity, of organic germs, atoms, molecules, spontaneous
generation, comets, and skies. With one or another of
these I now sought to reform an alliance, and finally suc
ceeded in establishing a kind of cohesion between Thought
and Light. The wish grew within me to trace, and to en
able you to trace, some of the more occult operations of
this agent. I wished, if possible, to take you behind the
drop-scene of the senses, and to show you the hidden mech
anism of optical action. For I take it to be well worth
the while of the scientific teacher to take some pains, and
even great pains, to make those whom he addresses copart
ners of his thoughts. To clear his own mind in the first place
of all haze and vagueness, and then to project into lan
guage which shall leave no mistake as to his meaning —
which shall leave even his errors naked — the definite ideas
he has shaped. A great deal is, I think, possible to scien
tific exposition conducted in this way. It is possible, I
believe, even before an audience like the present, to un
cover to some extent the unseen things of Nature; and

1 Induction, p. 422.

130 FRAGMENTS OF SCIENCE.

thus to give not only to professed students, but to others
with the necessary bias, industry, and capacity, an intelli
gent interest in the operations of science. Time and labor
are necessary to this result, but science is the gainer from
the public sympathy thus created.

How, then, are those hidden things to be revealed ?
How, for example, are we to lay hold of the physical basis
of light, since, like that of life itself, it lies entirely without
the domain of the senses ? Philosophers may be right in
affirming that we cannot transcend experience ; but we can
at all events carry it a long way from its origin. We can also
magnify, diminish, qualify, and combine experiences, so as to
render them fit for purposes entirely new. We are gifted
with the power of imagination — combining what the Ger
mans call Anschauungsgabe and Einbildungskraft — and by
this power we can lighten the darkness which surrounds the
world of the senses. There are tories even in science who
regard imagination as a faculty to be feared and avoided
rather than employed. They had observed its action in
weak vessels, and were unduly impressed by its disasters.
But they might with equal justice point to exploded boil
ers as an argument against the use of steam. Bounded and
conditioned by cooperant Reason, imagination becomes the
mightiest instrument of the physical discoverer. Newton's
passage from a falling apple to a falling moon was, at the
outset, a leap of the imagination. When William Thom
son tries to place the ultimate particles of matter between
his compass-points, and to apply to them a scale of milli
metres, he is powerfully aided by this faculty. And in
much that has been recently said about protoplasm and
life, we have the outgoings of the imagination guided and
controlled by the known analogies of science. In fact,
without this power, our knowledge of Nature would be a
mere tabulation of coexistences and sequences. We should
still believe in the succession of day and night, of summer

SCIENTIFIC USE OF THE IMAGINATION. 131

and winter ; but the soul of Force would be dislodged from
our universe ; causal relations would disappear, and with
them that science which is now binding the parts of Nature
to an organic whole.

/ I should like to illustrate by a few simple instances the
use that scientific men have already made of this power of
imagination, and to indicate afterward some of the further
uses that they are likely to make of it. Let us begin with
the rudimentary experiences. Observe the falling of heavy
rain-drops into a tranquil pond. Each drop as it strikes the
water becomes a centre of disturbance, from which a series
of ring-ripples expand outwards. Gravity and inertia are
the agents by which this wave-motion is produced, and a
rough experiment will suffice to show that the rate of
propagation does not amount to a foot a second. A series
of slight mechanical shocks is experienced by a body
plunged in the water as the wavelets reach it in succes
sion. But a finer motion is at the same time set up and
propagated. If the head and ears be immersed in the wa
ter, as in an experiment of Franklin's, the shock of the
drop is communicated to the auditory nerve — the tick of
the drop is heard. Now this sonorous impulse is propa
gated, not at the rate of a foot a second, but at the rate of
forty-seven hundred feet a second. In this case it is not
the gravity, but the elasticity of the water that is the ur
ging force. Every liquid particle pushed against its neigh
bor delivers up its motion with extreme rapidity, and the
pulse is propagated as a thrill. The incompressibility of
water, as illustrated by the famous Florentine experiment,
is a measure of its elasticity, and to the possession of this
property in so high a degree the rapid transmission of a
sound-pulse through water is to be ascribed.

But water, as youiknow, is not necessary to the conduc
tion of sound ; air is its most common vehicle. And you
know that when the air possesses the particular density

132 FRAGMENTS OF SCIENCE.

and elasticity corresponding to the temperature of freezing
water the velocity of sound in it is ten hundred and ninety
feet a second. It is almost exactly one-fourth of the ve
locity in water ; the reason being that though the greater
weight of the water tends to diminish the velocity, the
enormous molecular elasticity of the liquid far more than
atones for the disadvantage due to weight. By various
contrivances we can compel the vibrations of the air to
declare themselves ; we know the length and frequency of
sonorous waves, and we have also obtained great mastery
over the various methods by which the air is thrown into
vibration. We know the phenomena and laws of vibrating
rods, of organ-pipes, strings, membranes, plates, and bells.
We can abolish one sound by another. We know the
physical meaning of music and noise, of harmony and dis
cord. In short, as regards sounds we have a very clear
notion of the external physical processes which corre
spond to our sensations.

In these phenomena of sound we travel a very little
way from downright sensible experience. Still the imagi
nation is to some extent exercised. The bodily eye, for
example, cannot see the condensations and rarefactions of
the waves of sound. We construct them in thought, and
we believe as firmly in their existence as in that of the air
itself. But now our experience has to be carried into a
newr region, where a new use is to be made of it. Having
mastered the cause and mechanism of sound, we desire to
know the cause and mechanism of light. We wish to ex
tend our inquiries from the auditory nerve to the optic nerve.
There is in the human intellect a power of expansion-i— I
might almost call it a power of creation-p-which is brought
into play by the simple brooding upon facts. The legend
of the Spirit brooding over chaos may have originated in a
knowledge of this power. In the case now before us it has
manifested itself by transplanting into space, for the pur-

SCIENTIFIC USE OF THE IMAGINATION. 133

poses of light, an adequately modified form of the mechan
ism of sound. We know intimately whereon the velocity
of sound depends. When we lessen the density of a medium
and preserve its elasticity constant we augment the velocity.
When we heighten the elasticity and keep the density con
stant we also augment the velocity. A small density,
therefore, and a great elasticity, are the two things neces
sary to rapid propagation. Now light is known to move
with the astounding velocity of 185,000 miles a second.
How is such a velocity to be obtained? By boldly dif
fusing in space a medium of the requisite tenuity and
elasticity.

Let us make such a medium our starting-point, endow
ing it with one or two other necessary qualities ; let us
handle it in accordance with strict mechanical lawrs ; let us
give to every step of our deduction the surety of the syl
logism ; let us carry it thus forth from the world of imagi
nation into the world of sense, and see whether the final
outcrop of the deduction be not the very phenomena of
light which ordinary knowledge and skilled experiment re
veal. If in all the multiplied varieties of these phenomena,
including those of the most remote and entangled descrip
tion, this fundamental conception always brings us face to
face with the truth ; if no contradiction to our deductions
from it be found in external Nature, but on all sides agree
ment and verification ; if, moreover, as in the case of Coni
cal Refraction and in other cases, it has actually forced
upon our attention phenomena which no eye had previously
seen, and which no mind had previously imagined, such a
conception, which never disappoints us, but always lands
us on the solid shores of fact, must, we think, be something
more than a mere figment of the scientific fancy. In form
ing it that composite and creative unity in which reason
and imagination are together blent, has, we believe, led us
into a world not less real than that of the senses, and of

1.14 FRAGMENTS OF SCIENCE.

which the world of sense itself is the suggestion and justi
fication.

Fur be it from me, however, to wish to fix you immov
ably in this or in any other theoretic conception. With
all our belief of it, it will be well to keep the theory plastic
and capable of change. You may, moreover, urge that
although the phenomena occur as if the medium existed,
the absolute demonstration of its existence is still wanting.
Far be it from me to deny to this reasoning such validity
as it may fairly claim. Let us endeavor by means of anal
ogy to form a fair estimate of its force. You believe that
in society you are surrounded by reasonable beings like
yourself. You are perhaps as firmly convinced of this as
of any thing. What is your warrant for this conviction ?
Simply and solely this, your fellow-creatures behave as if
they were reasonable ; the hypothesis, for it is nothing
more, accounts for the facts. To take an eminent example :
you believe that our President is a reasonable being. Why ?
There is no known method of superposition by wThich any
one of us can apply himself intellectually to another so as
to demonstrate coincidence as regards the possession of
reason. If, therefore, you hold our President to be reason
able, it is because he behaves as if he were reasonable. As
in the case of the ether, beyond the " as if" you cannot go.
Nay I should not wonder if a close comparison of the data
on which both inferences rest, caused many respectable
persons to conclude that the ether had the best of it,

This universal medium, this light-ether as it is called, is
a vehicle, not an origin of wave-motion. It receives and
transmits, but it does not create. Whence does it dnive
the motions it conveys ? For the most part from luminous
bodies. By this motion of a luminous body I do not moan
its sensible motion, such as the flicker of a candle, or the
shooting out of red prominences from the limb of the sun.
I mean an intestine motion of the atoms or molecules of

SCIENTIFIC USE OF THE IMAGINATION. 135

the luminous body. But here a certain reserve is necessary.
Many chemists of the present day refuse to speak of atoms
and molecules as real things. Their caution leads them to
stop short of the clear, sharp, mechanically intelligible
atomic theory enunciated by Dalton, or any form of that
theory, and to make the doctrine of multiple proportions
their intellectual bourne. I respect the caution, though I
think it is here misplaced. The chemists who recoil from
these notions of atoms and molecules accept without hesita
tion the Undulatory Theory of Light. Like you and me,
they one and all believe in an ether and its light-producing
waves. Let us consider what this belief involves. Bring
your imaginations once more into play and figure a series
of sound-waves passing through air. Follow them up to
their origin, and what do you there find ? A definite, tan
gible, vibrating body. It may be the vocal chords of a
human being, it may be an organ-pipe, or it may be a
stretched string. Follow in the same manner a train of
ether-waves to their source ; remembering at the same time
that your ether is matter, dense, elastic, and capable of
motions subject to and determined by mechanical laws.
What then do you expect to find as the source of a series
of ether-waves ? Ask your imagination if it will accept a
vibrating multiple proportion — a numerical ratio in a state
of oscillation ? I do not think it will. You cannot crown
the edifice by this abstraction. The scientific imagination,
which is here authoritative, demands as the origin and cause
of a series of ether-waves a particle of vibrating matter
quite as definite, though it may be excessively minute, as
that which gives origin to a musical sound. Such a particle
we name an atom or a molecule. I think the seeking intel
lect when focussed so as to give definition without penum-
bral haze, is sure to realize this image at the last.

With a view of preserving thought continuous through
out this discourse, and of preventing either failure of knowl-

136 FRAGMENTS OF SCIENCE.

edge or of memory from causing any rent in our picture, I
here propose to run rapidly over a bit of ground which is
probably familiar to most of you, but which I am anxious to
make familiar to you all. The waves generated in the ether
by the swinging atoms of luminous bodies are of different
lengths and amplitudes. The amplitude is the width of
swing of the individual particles of the wave. In water-
waves it is the height of the crest above the trough, while
the length of the wave is the distance between two con
secutive crests. The aggregate of waves emitted by the sun
may be broadly divided into two classes : the one class com
petent, the other incompetent, to excite vision. But the
light-producing waves differ markedly among themselves
in size, form, and force. The length of the largest of these
waves is about twice that of the smallest, but the amplitude
of the largest is probably a hundred times that of the
smallest. Now the force or energy of the wave, which, ex
pressed with reference to sensation, means the intensity of
the light, is proportional to the square of the amplitude.
Hence the amplitude being one-hundred-fold, the energy of
the largest light-giving waves would be ten-thousand-fold
that of the smallest. This is not improbable. I use these
figures not with a view to numerical accuracy, but to give
you definite ideas of the differences that probably exist
among the light-giving waves. And if we take the whole
range of solar radiation into account — its non-visual as well
as its visual waves — I think it probable that the force or
eo<5rgy of the largest wave is a million times that of the
smallest.

Turned into their equivalents of sensation, the different
light-waves produce different colors. Red, for example, is
roduced by the largest waves, violet by the smallest, while
green is produced by a wave of intermediate length and
amplitude. On entering from air into more highly refract
ing substances, such as glass or water, or the sulphide of

SCIENTIFIC USE OF THE IMAGINATION. 137

carbon, all the waves are retarded, but the smallest ones
most. This furnishes a means of separating the different
classes of waves from each other ; in other words, of ana
lyzing the light. Sent through a refracting prism, the waves
of the sun are turned aside in different degrees from their
direct course, the red least, the violet most. They are vir
tually pulled asunder, and they paint upon a white screen
placed to receive them " the solar spectrum." Strictly
speaking, the spectrum embraces an infinity of colors, but
the limits of language and of our powers of distinction cause
it to be divided into seven segments :'\ red, orange, yellow,
green, blue, indigo, violet. These are the seven primary or
prismatic colors.

Separately, or mixed in various proportions, the solar
waves yield all the colors observed in nature and employed
in art. Collectively, they give us the impression of white
ness. Pure unsifted solar light is white ; and if all the
wave-constituents of such light be reduced in the same pro
portion the light, though diminished in intensity, will still
be white. The whiteness of Alpine snow with the sun
shining upon it, is barely tolerable to the eye. The same
snow under an overcast firmament is still white. Such a
firmament enfeebles the light by reflection, and when we lift
ourselves above a cloud-field — to an Alpine summit, for in
stance, or to the top of Snowdon — and see, in the proper
direction, the sun shining on the clouds, they appear daz-
zlingly white. Ordinary clouds, in fact, divide the solar
light impinging on them into two parts — a reflected part
and a transmitted part, in each of which the proportions of
wave-motion which produce the impression of whiteness
are sensibly preserved.

It will be understood that the conditions of whiteness
would fail if all the waves were diminished equally r, or by
the same absolute quantity. They must be reduced pro
portionately, instead of equally. If by the act of reflection

138 FRAGMENTS OF SCIENCE.

the waves of red light are split into exact halves, then, to
preserve the light white, the waves of yellow, orange, green,
and blue must also be split into exact halves. In short, the
reduction must take place, not by absolutely equal quanti
ties, but by equal fractional parts. In white light the pre
ponderance as regards energy of the latter over the smaller
waves must always be immense. Were the case otherwise,
the physiological correlative, blue, of the smaller waves
would have the upper hand in our sensations.

My wish to render our mental images complete, causes
me to dwell briefly upon these known points, and the
same wish will cause me to linger a little longer among
others. But here I am disturbed by my reflections. When
/I consider the effect of dinner upon the nervous system, and
the relation of that system to the intellectual powers I am
now invoking — when I remember that the universal expe
rience of mankind has fixed upon certain definite elements
of perfection in an after-dinner speech, and when I think
how conspicuous by their absence these elements are on the
present occasion, the thought is not comforting to a man
who wishes to stand well with his fellow-creatures in gen
eral, and with the members of the British Association in
particular. My condition might well resemble that of the
ether, which is scientifically defined as an assemblage of
vibrations. And the worst of it is, that unless you reverse
the general verdict regarding the effect of dinner, and prove
in your own persons that a uniform experience need not con
tinue uniform — which will be a great point gained for some
people — these tremors of mine are likely to become more
and more painful. But I call to mind the comforting words
of an inspired though uncanonical writer, who admonishes
us in the Apocrypha that fear is a bad counsellor. Let me
then cast him out, and let me trustfully assume that you
will one and all postpone that balmy sleep, of which dinner
might under the circumstances be regarded as the indis-

SCIENTIFIC USE OF THE IMAGINATION. 139

soluble antecedent, and that you will manfully and woman-
fully prolong your investigations of the ether and its waves
into regions which have been hitherto crossed by the
pioneers of science alone.

Not only are the waves of ether reflected by clouds,
by solids, and by liquids, but when they pass from light air
to dense, or from dense air to light, a portion of the wave-
motion is always reflected. Now our atmosphere changes
continually in density from top to bottom. It will help
our conceptions if we regard it as made up of a series of thin
concentric layers, or shells of air, each shell being of the
same density throughout, and a small and sudden change
of density occurring in passing from shell to shell. Light
would be reflected at the limiting surfaces of all these shells,
and their action would be practically the same as that of the
real atmosphere. And now I would ask your imagination
to picture this act of reflection. What must become of the
reflected light ? The atmospheric layers turn their convex
surfaces toward the sun ; they are so many convex mirrors
of feeble power, and you will immediately perceive that the
light regularly reflected from these surfaces cannot reach
the earth at all, but is dispersed in space.

But though the sun's light is not reflected in this fashion
from the aerial layers to the earth, there is indubitable evi
dence to show that the light of our firmament is reflected
light. Proofs of the most cogent description could be here
adduced ; but we need only consider that we receive light
at the same time from all parts of the hemisphere of heav
en. The light of the firmament comes to us across the di
rection of the solar rays, *uid even against the direction of
the solar rays ; and this lateral and opposing rush of wave-
motion can only be due to the rebound of the waves from
the air itself, or from something suspended in the air. It is
also evident that, unlike the action of clouds, the solar light
is not reflected by the sky in the proportions which produce

140 FRAGMENTS OF SCIENCE.

white. The sky is blue, which indicates a deficiency on part
of the larger waves. In accounting for the color of the sky,
the first question suggested by the analogy would undoubt
edly be, Is not the air blue ? The blueness of the air has
in fact been given as a solution of the blueness of the sky.
But reason, basing itself on observation, asks in reply, How,
if the air be blue, can the light of sunrise and sunset, which
travels through vast distances of air, be yellow, orange, or
even red ? The passage of white solar light through a blue
medium could by no possibility redden the light. The hy
pothesis of a blue air is therefore untenable. In fact, the
agent, whatever it is, which sends us the light of the sky,
exercises in so doing a dichroitic action. The light reflected
is blue, the light transmitted is orange or red. A marked
distinction is thus exhibited between the matter of the sky
and that of an ordinary cloud, which exercises no such di
chroitic action.

By the force of imagination and reason combined we
may penetrate this mystery also. The cloud takes no note
of size on the part of the waves of ether, but reflects them
all alike. It exercises no selective action. Now, the cause
of this may be that the cloud-particles are so large in com
parison with the size of the waves of ether as to reflect them
all indifferently. A broad cliff reflects an Atlantic roller as
easily as a ripple produced by a sea-bird's wing ; and in the
presence of large reflecting surfaces, the existing differences
of magnitude among the waves of ether may disappear.
But supposing the reflecting particles, instead of being very
large, to be very small, in comparison with the size of the
waves. In this case, instead of the wrhole wave being
fronted and in great part thrown back, a small portion only
is shivered off. The great mass of the wave passes over
such a particle without reflection. Scatter, then, a handful
of such minute foreign particles in our atmosphere, and set
imagination to watch their action upon the solar waves.

SCIENTIFIC USE OF THE IMAGINATION. 141

Waves of all sizes impinge upon the particles, and you see
at every collision a portion of the impinging wave struck
off. All the waves of the spectrum, from the extreme red
to the extreme violet, are thus acted upon. But in what
proportions will the waves be scattered ? A clear picture
will enable us to anticipate the experimental answer. Re
membering that the red waves are to the blue much in the
relation of billows to ripples, let us consider whether those
extremely small particles are competent to scatter all the
waves in the same proportion. If they be not — and a little
reflection will make it clear to you that they are not — the
production of color must be an incident of the scattering.
Largeness is a thing of relation ; and the smaller the wave,
the greater is the relative size of any particle on which the
wave impinges, and the greater also the ratio of the scat
tered portion to the total wave. A pebble placed in the
way of the ring-ripples produced by our heavy rain-drops
on a tranquil pond will throw back a large fraction of the
ripple incident upon it, while the fractional part of a larger
wave thrown back by the same pebble might be infinitesi
mal. Now we have already made it clear to our minds
that to preserve the solar light white, its constituent pro
portions must not be altered ; but in the act of division
performed by these very small particles we see that the
proportions are altered ; an undue fraction of the smaller
waves is scattered by the particles, and, as a consequence,
in the scattered light, blue will be the predominant color.
The other colors of the spectrum must, to some extent, be
associated with the blue. They are not absent but deficient.
We ought, in fact, to have them all, but in diminishing pro
portions, from the violet to the red.

We have here presented a case to the imagination, and,
assuming the undulatory theory to be a reality, we have, I
think, fairly reasoned our way to the conclusion that, were
particles, small in comparison to the size of the ether-waves3

142 FRAGMENTS OF SCIENCE.

sown in our atmosphere, the light scattered by those parti
cles would be exactly such as we observe in our azure skies.
When this light is analyzed, all the colors of the spectrum
are found ; but they are found in the proportions indicated
by our conclusion.

Let us now turn our attention to the light which passes
unscattered among the particles. How must it be finally
affected ? By its successive collisions with the particles,
the white light is more and more robbed of its shorter
waves ; it therefore loses more and more of its due propor
tion of blue. The result may be anticipated. The trans
mitted light, where short distances are involved, will appear
yellowish. But as the sun sinks toward the horizon the
atmospheric distances increase, and consequently the num
ber of the scattering particles. They abstract in succession
the violet, the indigo, the blue, and even disturb the pro
portions of green. The transmitted light under such cir
cumstances must pass from yellow through orange to red.
Tin's also is exactly what we find in Nature. Thus, while
the reflected light gives us at noon the deep azure of the
Alpine skies, the transmitted light gives us at sunset the
warm crimson of the Alpine snowrs. The phenomena cer
tainly occur as if our atmosphere were a medium rendered
slightly turbid by the mechanical suspension of exceedingly
small foreign particles.

/ Here, as before, we encounter our skeptical " as if" It-
is one of the parasites of science, ever at hand, and ready
to plant itself and sprout, if it can, on the weak points of
our philosophy. But a strong constitution defies the para
site, and in our case, as we question the phenomena, proba
bility grows like growing health, until in the end the malady
of doubt is completely extirpated. The first question that
naturally arises is, Can small particles be really proved to
act in the manner indicated ? No doubt of it. Each one
of you can submit the question to an experimental test.

SCIENTIFIC USE OF THE IMAGINATION. 143

Water will not dissolve resin, but spirit will; and when
spirit which holds resin in solution is dropped into water,
the resin immediately separates in solid particles, which
render the water milky. The coarseness of this precipitate
depends on the quantity of the dissolved resin. You can
cause it to separate in thick clots or in exceedingly fine
particles. Professor Briicke has given us the proportions
which produce particles particularly suited to our present
purpose. One gramme of clean mastic is dissolved in
eighty-seven grammes of absolute alcohol, and the trans
parent solution is allowed to drop into a beaker containing
clear water kept briskly stirred. An exceedingly fine
precipitate is thus formed, which declares its presence by
its action upon light. Placing a dark surface behind the
beaker, and permitting the light to fall into it from the top
or front, the medium is seen to be distinctly blue. It is not
perhaps so perfect a blue as I have seen on exceptional
days, this year, among the Alps, but it is a very fair sky-
blue. A trace of soap in water gives a tint of blue. Lon-
.fxion, and I fear Liverpool milk, makes an approximation to
the same color through the operation of the same cause ;
and Helmholtz has irreverently disclosed the fact that the
deepest blue eye is simply a turbid medium.

The action of turbid media upon light was illustrated
by Goethe, who, though unacquainted with the undula-
tory theory, was led by his experiments to regard the
firmament as an illuminated turbid medium with the dark
ness of space behind it. He describes glasses showing a
bright yellow by transmitted, and a beautiful blue by re
flected light. Professor Stokes, who was probably the first
to discern the real nature of the action of small particles
on the waves of ether, describes a glass of a similar kind.1

1 This glass, by reflected light, had a color " strongly resembling that
of a decoction of a horse-chestnut bark." Curiously enough, Goethe
refers to this very decoction : " Man nehme "einen Streifen frischer Rinde

144 FRAGMENTS OF SCIEXCE.

Capital specimens of such glass are to be found at Salviati's
iu St. James's Street. What artists call "chill" is no
doubt an effect of this description. Through the action of
minute particles, the browns of a picture often present the
appearance of the bloom of a plum. By rubbing the var
nish with a silk handkerchief optical continuity is estab
lished, and the chill disappears. Some years ago I wit
nessed Mr. Hirst experimenting at Zermatt on the turbid
water of the Visp, which was charged with the finely-divided
matter ground down by the glaciers. When kept still for
a day or so, the grosser matter sank, but the finer matter
remained suspended, and gave a distinctly blue tinge to
the water. The blueness of certain Alpine lakes has been
shown to be in part due to this cause. Professor Roscoe has
noticed several striking cases of a similar kind. In a very
remarkable paper the late Principal Forbes showed that
steam issuing from the safety-valve of a locomotive, when
favorably observed, exhibits at a certain stage of its con
densation the colors of the sky. It is blue by reflected
light, and orange or red by transmitted light. The same
effect, as pointed out by Goethe, is to some extent ex
hibited by peat-smoke. More than ten years ago I amused
myself at Killarney by observing on a calm day the straight
smoke-columns rising from the cabin chimneys. It was
easy to project the lower portion of a column against a
dark pine, and its upper portion against a bright cloud.
The smoke in the former case was blue, being seen mainly
by reflected light ; in the latter case it was reddish, being
seen mainly by transmitted light. Such smoke was not in
exactly the condition to give us the glow of the Alps,
but it was a step in this direction. Brlicke's fine pre
cipitate above referred to koks yellowish by transmitted

von der Rosskastanie, man stecke denselbcn in cin Glas Wasser, und in
der kiirzesten Zcit werden wir das vollkommenste Himmclblau entstrhen
srlu-n." — Goethe's JHr/r, 1>. xxi\'., p. 24.

SCIENTIFIC USE OF THE IMAGINATION. 145

light, but by duly strengthening the precipitate you may
render the white light of noon as ruby-colored as the sun
when seen through Liverpool smoke, or upon Alpine hori
zons. I do not, however, point to the gross smoke arising
from coal as an illustration of the action of small particles,
because such smoke soon absorbs and destroys the waves
of blue instead of sending them to the eyes of the observer.
These multifarious facts, and numberless others which
cannot now be referred to, are explained by reference to
the single principle, that where the scattering particles are
small in comparison to the size of the waves we have in
the reflected light a greater proportion of the smaller
waves, and in the transmitted light a greater proportion
of the larger waves, than existed in the original white
light. The physiological consequence is that in the one
light blue is predominant, and in the other light orange
or red. And now let us push our inquiries forward.
Our best microscopes can readily reveal objects not more
than -jo"oToth of an inch in diameter. This is less than
the length of a wave of red light. Indeed, a first-rate
microscope would enable us to discern objects not exceed
ing in diameter the length of the smallest waves of the
visible spectrum. By the microscope, therefore, we can
submit our particles to an experimental test. If they are
as large as the light-waves they will infallibly be seen :
and if they are not seen it is because they are smaller. I
placed in the hands of our President a bottle containing
Brticke's particles in greater number and coarseness than
those examined by Briicke himself. The liquid was a
milky blue, and Mr. Huxley applied to it his highest
microscopic power. He satisfied me at the time that had
particles of even I0o1o6oth of an inch in diameter existed
in the liquid they could not have escaped detection. But
no particles were seen. Under the microscope the turbid
liquid was not to be distinguished from distilled water.
7

146 KKA<,MI;NTS OF SCIENCK.

Brilcke, I may say, also found the particles to be of ultra-
microscopic magnitude.

But \ve have it in our power to imitate far more closely
than we have hitherto done the natural conditions of this
problem. We can generate in air, as many of you know,
artificial skies, and prove their perfect identity with the
natural one, as regards the exhibition of a number of
wholly unexpected phenomena. By a continuous process
of growth, moreover, we are able to connect sky-matter,
if I may use the term, with molecular matter on the one
side, and with molar matter, or matter in sensible masses,
on the other. In illustration of this, I will take an ex
periment described by M. Morren of Marseilles at the last
meeting of the British Association. Sulphur and oxygen
combine to form sulphurous acid gas. It is this choking
gas that is smelt when a sulphur-match is burnt in air.
Two atoms of oxygen and one of sulphur constitute the
molecule of sulphurous acid. Now it has been recently
shown in a great number of instances that waves of ether
issuing from a strong source, such as the sun or the
electric light, are competent to shake asunder the atoms
of gaseous molecules. A chemist would call this " decom
position" by light; but it behooves us, who are examin
ing the power and function of the imagination, to keep
constantly before us the physical images which underlie
our terms. Therefore, I say, sharply and definitely, that
the components of the molecules of sulphurous acid are
shaken asunder by the ether-waves. Enclosing the sub
stance in a suitable vessel, placing it in a dark room, and
sending through it a powerful beam of light, we at first
see nothing : the vessel containing the gas is as empty
as a vacuum. Soon, ho\yever, along the track of the
beam a beautiful sky-blue color is observed, which is
due to the liberated particles of sulphur. For a time
the blue grows more intense; it then becomes whitish;

SCIENTIFIC USE OF THE IMAGINATION. 147

and from a whitish blue it passes to a more or less perfect
white. If the action be continued long enough, we end
by filling the tube with a dense cloud of sulphur-particles,
which by the application of proper means may be rendered
visible.

Here, then, our ether-waves untie the bond of chemical
affinity, and liberate a body — sulphur — which at ordinary
temperatures is a solid, and which therefore soon becomes
an object of the senses. We have first of all the free
atoms of sulphur, which are both invisible and incompetent
to stir the retina sensibly with scattered light. But these
atoms gradually coalesce and form particles, which grow
larger by continual accretion, until after a minute or two
they appear as sky-matter. In this condition they are in
visible themselves, but competent to send an amount of
wave-motion to the retina sufficient to produce the fir-
mamental blue. The particles continue, or may be caused
to continue, in this condition for a considerable time,
during which no microscope can cope with them. But
they continually grow larger, and pass by insensible grada
tions into the state of cloud, when they can no longer elude
the armed eye. Thus without solution of continuity we
start with matter in the molecule, and end with matter in
the mass, sky-matter being the middle term of the series of
transformations.

Instead of sulphurous acid, we might choose from a
dozen other substances, and produce the same effect with
any of them. In the case of some — probably in the case
of all — it is possible to preserve matter in the skyey con
dition for fifteen or twenty minutes under the continual
operation of the light. During these fifteen or twenty
minutes the particles are constantly growing larger, with
out ever exceeding the size requisite to the production of
the celestial blue. Now, when two vessels are placed be
fore you, each containing sky-matter, it is possible to state

148 FRAGMENTS 0* SCIENCE.

with great distinctness which vessel contains the largest
particles. The retina is very sensitive to differences of
light, when, as here, the eye is in comparative darkness,
and when the quantities of wave-motion thrown against
the retina are small. The larger particles declare them
selves by the greater whiteness of their scattered light.
Call now to mind the observation, or effort at observation,
made by our President, when he failed to distinguish the
particles of mastic in Brlicke's medium, and when you have
done so follow me. I permitted a beam of light to act
upon a certain vapor. In two minutes the azure appeared,
but at the end of fifteen minutes it had not ceased to be
azure. After fifteen minutes, for example, its color, and
some other phenomena, pronounced it to be a blue of dis
tinctly smaller particles than those sought for in vain by
Mr. Huxley. These particles, as already stated, must have
been less than 100*06uth of an inch in diameter. And now
I want you to submit to your imagination the following
question: Here are particles which have been growing
continually for fifteen minutes, and at the end of that time
are demonstrably smaller than those which defied the mi
croscope of Mr. Huxley : what must have been the size of
these particles at the beginning of their growth? "What
notion can you form of the magnitude of such particles ?
The distances of stellar space give us simply a bewildering
sense of vastness without leaving any distinct impression
on the mind, and the magnitudes with which we have here
to do bewilder us equally in the opposite direction. We
are dealing with infinitesimals compared with which the
test objects of the microscope are literally immense.

From their perviousness to stellar light and other con
siderations, Sir John Herschel drew some startling conclu
sions regarding the density and weight of comets. You
know that these extraordinary and mysterious bodies some-
throw out tails 100,000,000 of miles in length, and

SCIENTIFIC USE OF THE IMAGINATION. 149

50,000 miles in diameter. The diameter of our earth is
8,000 miles. Both it and the sky, and a good portion of
space beyond the sky, would certainly be included in a
sphere 10,000 miles across. Let us fill a hollow sphere of
this diameter with cometary matter, and make it our unit
of measure. To produce a comet's tail of the size just men
tioned, about 300,000 such measures would have to be
emptied into space. Now, suppose the whole of this stuff
to be swept together and suitably compressed, what do you
suppose its volume would be ? Sir John Herschel would
probably tell you that the whole mass might be carted
away at a single effort by one of your dray-horses. In fact,
I do not know that he would require more than a small
fraction of a horse-power to remove the cometary dust.
After this you will hardly regard as monstrous a notion I
have sometimes entertained concerning the quantity of
matter in our sky. Suppose a shell to surround the earth
at a height above the surface which would place it beyond
the grosser matter that hangs in the lower regions of the
air — say at the height of the Matterhorn or Mont Blanc.
Outside this shell we have the deep-blue firmamerit. Let
the atmospheric space beyond the shell be swept clean, and
let the sky-matter be properly gathered up. What is its
probable amount ? I have sometimes thought that a lady's
portmanteau would contain it all. I have thought that
even a gentleman's portmanteau — possibly his snuff-box —
might take it in. And whether the actual sky be capable
of this amount of condensation or not, I entertain no doubt
that a sky quite as vast as ours, and as good in appearance,
could be formed from a quantity of matter which might be
held in the hollow of the hand.

Small in mass, the vastness in point of number of the
particles of our sky may be inferred from the continuity of
its light. It is not in broken patches, nor at scattered points
that the heavenly azure is revealed. To the observer on

150 FRAGMENTS OF SCIENTI-.

the summit of Mont Blanc the blue is as uniform and co
herent as if it formed the surface of the most close-grained
solid. A marble dome would not exhibit a stricter con
tinuity. And Mr. Glaisher will inform you that if our hy
pothetical shell were lifted to twice the height of Mont
Bkinc above the earth's surface, we should still have the
azure overhead. Everywhere through the atmosphere those
sky-particles are strewn. They fill the Alpine valleys,
spreading like a delicate gauze in front of the slopes of
pine. They sometimes so swathe the peaks with light as
to abolish their definition. This year I have seen the
"Weisshorn thus dissolved in opalescent air. By proper
instruments the glare thrown from the sky-particles against
the retina may be quenched, and then the mountain which
it obliterated starts into sudden definition. Its extinction
in front of a dark mountain resembles exactly the with
drawal of a veil. It is the light then taking possession of
the eye, and not the particles acting as opaque bodies, that
interferes with the definition. By day this light quenches
the stars ; even by moonlight it is able to exclude from
vision all stars between the fifth and the eleventh magni
tude. It may be likened to a noise, and the stellar radiance
I-) a whisper drowned by the noise.

What is th^ nature of the particles which shed this
light ? The celebrated De la Rive ascribes the haze of the
Alps in fine weather to floating organic germs. Now, the
possible existence of germs in such profusion has been held
up as an absurdity. It has been affirmed that they would
darken the air, and on the assumed impossibility of their
existence in the requisite numbers, without invasion of the
solar light, a powerful argument has been based by be
lievers in spontaneous generation. Similar arguments
have been used by the opponents of the germ theory of
epidemic disease, who have triumphantly challeged an ap
peal to the microscope and the chemist's balance to decide

SCIENTIFIC USE OF THE IMAGINATION. 151

the question. Such arguments are absolutely valueless.
Without committing myself in the least to De la Rive's
notion, without offering any objection here to the doctrine
of spontaneous generation, without expressing any adhe
rence to the germ theory of disease, I would simply draw
attention to the fact that in the atmosphere we have parti
cles which defy both the microscope and the balance, which
do not darken the air, and which exist, nevertheless, in
multitudes sufficient to reduce to insignificance the Israel-
itish hyperbole regarding the sands upon the sea-shore.

The varying judgments of men on these and other ques
tions may perhaps be, to some extent, accounted for by
that doctrine of relativity which plays so important a part
in philosophy. This doctrine affirms that the impressions
made upon us by any circumstance, or combination of cir
cumstances, depend upon our previous state. Two travellers
upon the same peak, the one having ascended to it from
the plain, the other having descended to it from a higher
elevation, will be differently affected by the scene around
them. To the one Nature is expanding, to the other it is
contracting, and feelings are sure to differ which have two
such different antecedent states. In our scientific judg
ments the law of relativity may also play an important part.
To two men, one educated in the school of the senses, who
has mainly occupied himself with observation, and the other
educated in the school of imagination as well, and exercised
in the conceptions of atoms and molecules, to which we
have so frequently referred, a bit of matter, say -^-o-J-^o"th of
of an inch in diameter, will present itself differently. The
one descends to it from his molar heights, the other climbs
to it from his molecular low-lands. To the one it appears
small, to the other large. So also as regards the apprecia
tion of the most minute forms of life revealed by the micro
scope. To one of these men they naturally appear conter
minous with the ultimate particles of matter, and he readily

I.-.J FIJACMKNTS OF SCIEXCK.

figures the molecules from which they directly spring; with
him there is but a step from the atom to the organism.
The other discerns numberless organic gradations between
both. Compared with his atoms, the smallest vibrios and
bacteria of the microscopic field are as behemoth and levia-
than. The law of relativity may to some extent explain
the different attitudes of these two men with regard to the
question of spontaneous generation. An amount of evi
dence which satisfies the one entirely fails to satisfy the
other ; and while to the one the last bold defence and start
ling expansion of the doctrine will appear perfectly conclu
sive, to the other it will present itself as imposing a profit
less labor of demolition on subsequent investigators.1

I trust, Mr. President, that you — whom untoward circum
stances have made a biologist, but who still keep alive your
sympathy with that class of inquiries which Nature intend
ed you to pursue and adorn — will excuse me to your breth
ren if I say that some of them seem to form an inadequate
estimate of the distance which separates the microscopic
from the molecular limit, and that, as a consequence, they
sometimes employ a phraseology which is calculated to mis
lead. When, for example, the contents of a cell are de
scribed as perfectly homogeneous, as absolutely structure
less, because the microscope fails to distinguish any struct
ure, then I think the microscope begins to play a mischiev
ous part. A little consideration will make it plain to all
of you that the microscope can have no voice in the real
question of germ-structure. Distilled water is more per-
fivily homogeneous than the contents of any possible or
ganic germ. What causes the liquid to cease contract inir
at 39° Fahrenheit, and to expand until it freezes ? It is a
Mnictural process of which the microscope can take no
note, nor is it likely to do so by any conceivable extension

1 A resolute scrutiny of the experiments, recently executed with
to this question, is sure to yield instructive results.

SCIENTIFIC USE OF THE IMAGINATION. 153

of its powers. Place this distilled water in the field of an
electro-magnet, and bring a microscope to bear upon it.
Will any change be observed when the magnet is excited ?
Absolutely none ; and still profound and complex changes
have occurred. First of all, the particles of water are ren
dered diamagnetically polar ; and secondly, in virtue of the
structure impressed upon it by the magnetic strain of its
molecules, the liquid twists a ray of light in a fashion per
fectly determinate both as to quantity and direction. It
would be immensely interesting to both you and me if one
whom I hoped to see here present,1 who has brought his
brilliant imagination to bear upon this subject, could make
us see as he sees the entangled molecular processes involved
in the rotation of the plane of polarization by magnetic
force. While dealing with this question, he lived in a world
of matter and of motion, to which the microscope has no
passport, and in which it can offer no aid. The cases in
which similar conditions hold are simply numberless. Have
the diamond, the amethyst, and the countless other crystals
formed in the laboratories of Nature and of man no struct
ure ? Assuredly they have ; but what can the microscope
make of it ? Nothing. It cannot be too distinctly borne
in mind that between the microscope limit and the true
molecular limit there is room for infinite permutations and
combinations. It is in this region that the poles of the
atoms are arranged, that tendency is given to their powers,
so that when these poles and powers have free action and
proper stimulus in a suitable environment, they determine
first the germ, and afterward the complete organism. This
first marshalling of the atoms on which all subsequent ac
tion depends baffles a keener power than that of the micro
scope. Through pure excess of complexity, and long be
fore observation can have any voice in the matter, the most
highly-trained intellect, the most refined and disciplined

1 Sir William Thomson

154 FRACMI:NTS OF SCIENCE.

imagination, retires in bewilderment from the contempla
tion of the problem. We are struck dumb by an astonish
ment which no microscope can relieve, doubting not only
the power of our instrument, but even whether we ourselves
possess the intellectual elements which will ever enable us
to grapple with the ultimate structural energies of Nature.
But the speculative faculty, of which imagination forms
so large a part, will nevertheless wander into regions where
the hope of certainty would seem to be entirely shut out.
A\V think that though the detailed analysis may be, and
may forever remain, beyond us, general notions may be at
tainable. At all events, it is plain that beyond the present
outposts of microscopic inquiry lies an immense field for
the exercise of the speculative power. It is only, however,
iho privileged spirits who know how to use their liberty
without abusing it, who are able to surround imagination
by the firm frontiers of reason, that are likely to work with
any profit here. But freedom to them is of such paramount
importance that, for the sake of securing it, a good deal of
wild ness on the part of weaker brethren may be overlooked.
In more senses than one Mr. Darwin has drawn heavily
upon the scientific tolerance of his age. He has drawn
heavily upon time in his development of species, and he has
drawn adventurously upon matter in his theory of pangen-
< sis. According to this theory, a germ already microscopic
is a world of minor germs. Not only is the organism as a
wlmle wrapped up in the germ, but every organ of the or
ganism has there its special seed. This, I say, is an adven
turous draft on the power of matter to divide itself and
distribute its forces. But, unless we arc perfectly sure thai
he is overstepping the bounds of reason, that he is unwit
tingly sinning against observed fact or demonstrated law —
for a mind like that of Darwin can never pin wittingly
against either fact or law — we ought, I think, to be cautious
in limiting his intellectual horizon. If there be the least

SCIENTIFIC USE OF THE IMAGINATION. 155

doubt in the matter, it ought to be given in favor of the
freedom of such a mind. To it a vast possibility is in it
self a dynamic power, though the possibility may never
be drawn upon. It gives me pleasure to think that the
facts and reasonings of this discourse tend rather toward
the justification of Mr. Darwin than toward his condemna
tion, that they tend rather to augment than to diminish the
cubic space demanded by this soaring speculator ; for they
seem to show the perfect competence of matter and force,
as regards divisibility and distribution, to bear the heaviest
strain that he has hitherto imposed upon them.

In the case of Mr. Darwin, observation, imagination, and
reason combined, have run back with wonderful sagacity
and success over a certain length of the line of biological
succession. Guided by analogy, in his " Origin of Species,"
he placed at the root of life a primordial germ, from which
he conceived the amazing richness and variety of the life
that now is upon the earth's surface might be deduced. If
this hypothesis were true, it would not be final. The hu
man imagination would infallibly look behind the germ,
and, however hopeless the attempt, would inquire into the
history of its genesis. In this dim twilight of conjecture
the searcher welcomes every gleam, and seeks to augment
his light by indirect incidences. He studies the methods
of Nature in the ages and the worlds within his reach, in
order to shape the course of speculation in the antecedent
ages and worlds. And though the certainty possessed by
experimental inquiry is here shut out, the imagination is
not left entirely without guidance. From the examination
of the solar system, Kant and Laplace came to the conclu
sion that its various bodies once formed parts of the same
imdislocated mass ; that matter in a nebulous form preceded
matter in a dense form ; that as the ages rolled away, heat
was wasted, condensation followed, planets were detached,
and that finally the chief portion of the fiery cloud reached,

156 FRAGMENTS OF SCIENCE.

by self-compression, the magnitude and density of our sun.
The earth itself oilers evidence of a fiery origin ; and in our
day the hypothesis of Kant and Laplace receives the inde
pendent countenance of spectrum analysis, which proves
the same substances to be common to the earth and sun.

Accepting some such view of the construction of our
system as probable, a desire immediately arises to connect
the present life of our planet with the past. We wish to
know something of our remotest ancestry. On its first de
tachment from the central mass, life, as we understand it,
could hardly have been present on the earth. How, then,
did it come there ? The thing to be encouraged here is
a reverent freedom — a freedom preceded by the hard disci
pline which checks licentiousness in speculation — while the
tiling- to be repressed, both in science and out of it, is dog
matism. And here I am in the hands of the meeting —
willing to end, but ready to go on. I have no right to in
trude upon you, unasked, the unformed notions which are
floating like clouds, or gathering to more solid consistency
in the modern speculative scientific mind. But if you wish
me to speak plainly, honestly, and undisputatiously, I am
willing to do so. On the present occasion —

" You arc ordained to call, and I to come."

Two views, then, offer themselves to us. Life was pres
ent potentially in matter when in the nebulous form, and
was unfolded from it by the way of natural development,
or it is a principle inserted into matter at a later date. With
regard to the question of time, the views of men have
changed remarkably in our day and general i< m ; and I
must say as regards courage also, and a manful willingness
to engage in open contest, with fair weapons, a great

•change has also occurred. The clergy of England — at all
events the clergy of London — have nerve enough to listen
to the strongest views which any one among us would care

SCIENTIFIC USE OF THE IMAGINATION. 157

to utter ; and they invite, if they do not challenge, men of
the most decided opinions to state and stand by those opin
ions in open court. Let the hardiest theory be stated only
in the language current among gentlemen, and they look it
in the face ; smiting the theory, if they do not like it, not
with theologicfulmination, but with honest secular strength.
With the country clergy I am told the case is different. It
is right that I should say this, because the clergy of Lon
don have more than once offered me the chance of meeting
them in open, honorable discussion.

Two or three years ago, in an ancient London College,
I listened to such a discussion at the end of a remarkable
lecture by a very remarkable man. Three or four hundred
clergymen were present at the lecture. The orator began
with the civilization of Egypt in the time of Joseph ;
pointing out that the very perfect organization of the
kingdom, and the possession of chariots, in one of which
Joseph rode, indicated a long antecedent period of civili
zation. He then passed on to the mud of the Nile, its
rate of augmentation, its present thickness, and the re
mains of human handiwork found therein ; thence to the
rocks which bound the Nile valley, and which teem with
organic remains. Thus in his own clear and admirable
way he caused the idea of the world's age to expand itself
indefinitely before the mind of his audience, and he con
trasted this with the age usually assigned to the world.
During his discourse he seemed to be swimming against
the stream ; he manifestly thought that he was opposing
a general conviction. He expected resistance ; so did I.
But it was all a mistake : there was no adverse current,
o opposing conviction, no resistance, merely here and
there a half-humorous, but unsuccessful attempt to entan
gle him in his talk. The meeting agreed with all that
had been said regarding the antiquity of the earth and of
its life. They had, indeed, known it all long ago, and

158 FRAGMENTS OF SCIENCE.

they good-humoredly rallied the lecturer for coming among
them with so stale a story. It was quite plain that this
large body of clergymen, who were, I should say, the finest
samples of their class, had entirely given up the ancient
Landmarks, and transported the conception of life's origin
to an indefinitely distant past.

^- This leads us to the gist of our present inquiry, which
is this : Does life belong to what we call matter, or is it an
independent principle inserted into matter at some suitable
epoch — say when the physical conditions became such as to
permit of the development of life ? Let us put the ques
tion with all the reverence due to a faith and culture in
which we all were cradled — a faith and culture, moreover,
which are the undeniable historic antecedents of our pres
ent enlightenment. I say, let us put the question rever
ently, but let us also put it clearly and definitely. There
are the strongest grounds for believing that during a cer
tain period of its history the earth was not, nor was it fit
to be, the theatre of life. Whether this was ever a nebu
lous period, or merely a molten period, does not much
matter ; and if we revert to the nebulous condition, it is
because the probabilities are really on its side. Our ques-
lion is this : Did creative energy pause until the nebulous
matter had condensed, until the earth had been detached,
until the solar fire had so far withdrawn from the earth's
/ vicinity as to permit a crust to gather round the planet ?

. Did it wait until the air was isolated, until the seas were
formed, until evaporation, condensation, and the descent of
rain had begun, until the eroding forces of the atmosphere
had weathered and decomposed the molten rocks so as to
form soils, until the sun's rays had become so tempered by
distance and by waste as to be chemically fit for the de
compositions necessary to vegetable life ? Having waited
through those ^Eons until the proper conditions had set in,
did it send the fiat forth, " Let Life be ! " ? These ques-

SCIENTIFIC USE OF THE IMAGINATION. 159

tions define a hypothesis not without its difficulties, but
the dignity of which was demonstrated by the nobleness
of the men whom it sustained.

Modern scientific thought is called upon to decide be
tween this hypothesis and another: and public thought
generally will afterward be called upon to do the same.
You may, however, rest secure in the belief that the hy
pothesis just sketched can never be stormed, and that it is
sure, if it yield at all, to yield to a prolonged siege. To
gain new territory modern argument requires more time
than modern arms, though both of them move with greater
rapidity than of yore. But however the convictions of indi
viduals here and there may be influenced, the process must
be slow and secular which commends the rival hypothesis
of Natural Evolution to the public mind. For what are the
core and essence of this hypothesis ? Strip it naked and
you stand face to face with the notion that not alone the
more ignoble forms of animalcular or animal life, not alone
the nobler forms of the horse and lion, not alone the exqui
site and wonderful mechanism of the human body, but that
the human mind itself — emotion, intellect, will, and all their
phenomena — were once latent in a fiery cloud. Surely
the mere statement of such a notion is more than a refu
tation. But the hypothesis would probably go even further
than this. Many who hold it would probably assent to the
position that at the present moment all our philosophy, all
our poetry, all our science, and all our art — Plato, Shake
speare, Newton, and Raphael — are potential in the fires of
the sun. We long to learn something of our origin. If
the Evolution hypothesis be correct, even this unsatisfied
yearning must have come to us across the ages which sepa
rate the unconscious primeval mist from the consciousness
of to-day. I do not think that any holder of the Evolution
hypothesis would say that I overstate it or overstrain it in
any way. I merely strip it of all vagueness, and bring

160 FRAGMENTS OF SCIENCE.

before you unclothed and unvarnished the notions by which
it must stand or fall.

Surely these notions represent an absurdity too mon
strous to be entertained by any sane mind. Let us, how
ever, give them fair play. Let us steady ourselves in front
of the hypothesis, and, dismissing all terror and excitement
from our minds, let us look firmly into it with the hard sharp
eye of intellect alone. Why are these notions absurd, and
why should sanity reject them ? The law of Relativity, of
which we have previously spoken, may find its application
here. These Evolution notions are absurd, monstrous, and
fit only for the intellectual gibbet, in relation to the ideas
concerning matter which were drilled into us wrhen young.
Spirit and matter have ever been presented to us in the
rudest contrast, the one as all-noble, the other as all-vile.
But is this correct ? Does it represent what our mightiest
spiritual teacher would call the Eternal Fact of the Uni
verse ? Upon the answer to this question all depends.
Supposing, instead of having the foregoing antithesis of
spirit and matter presented to our youthful minds, we had
been taught to regard them as equally worthy and equally
wonderful ; to consider them in fact as two opposite faces
of the self-same mystery. Supposing that in youth we had
been impregnated with the notion of the poet Goethe, in
stead of the notion of the poet Young, looking at matter,
not as brute matter, but as " the living garment of God ; "
do you not think that under these altered circumstances
the law of Relativity might have had an outcome different
from its present one ? Is it not probable that our repug
nance to the idea of primeval union between spirit and
matter might be considerably abated ? Without this total
revolution of the notions now prevalent, the Evolution hy
pothesis must stand condemned ; but in many profoun<lly
thoughtful minds such a revolution has already taken place.
They degrade neither member of the mysterious duality

SCIENTIFIC USE OF THE IMAGINATION. 161

referred to ; but they exalt one of them from its abasement,
and repeal the divorce hitherto existing between both. In
substance, if not in words, their position as regards the
relation of spirit and matter is : " What God hath joined
together let not man put asunder." And with regard to
the ages of forgetfulness which lie between the unconscious
life of the nebula and the conscious life of the earth, it is,
they would urge, but an extension of that forgetfulness
which preceded the birth of us all.

I have thus led you to the outer rim of speculative
science, for beyond the nebulas scientific thought has never
ventured hitherto, and have tried to state that which I con
sidered ought, in fairness, to be outspoken. I clo not think
this Evolution hypothesis is to be flouted away contempt-
"ously ; I do not think it is to be denounced as wicked. It
is to be brought before the bar of disciplined reason, and
there justified or condemned. Let us hearken to those who
wisely support it, and to those who wisely oppose it ; and
let us tolerate those, and they are many, who foolishly try
to do either of these things. The only thing out of place
in the discussion is dogmatism on either side. Fear not
the Evolution hypothesis. Steady yourselves in its presence
upon that faith in the ultimate triumph of truth which was
expressed by old Gamaliel when he said : " If it be of God,
ye cannot overthrow it ; if it be of man, it will come to
naught." Under the fierce light of scientific inquiry, this
hypothesis is sure to be dissipated if it possess not a core
of truth. Trust me, its existence as a hypothesis in the
mind is quite compatible with the simultaneous existence
of all those virtues to which the term Christian has been
applied. It does not solve — it does not profess to solve —
the ultimate mystery of this universe. It leaves in fact
that mystery untouched. For granting the nebula and its
potential life, the question, whence came they ? would still
remain to baffle and bewilder us. At bottom, the hypothe-

162 FRAGMENTS OF SCIENCE.

sis does nothing more than " transport the conception of
life's origin to an indefinitely distant past."

Those who hold the doctrine of Evolution are by no
means ignorant of the uncertainty of their data, and they
yield no more to it than a provisional assent. They regard
the nebular hypothesis as probable, and in the utter absence
of any evidence to prove the act illegal, they extend the
method of Nature from^the present into the past. Here the
observed uniformity of Nature is their only guide. Within
the long range of physical inquiry, they have never dis
cerned in Nature the insertion of caprice. Throughout
this range the laws of physical and intellectual continuity
have run side by side. Having thus determined the ele
ments of their curve in a world of observation and experi
ment, they prolong that curve into an antecedent world,
and accept as probable the unbroken sequence of develop
ment from the nebula to the present time. You never hear
the really philosophical defenders of the doctrine of Uni
formity speaking of impossibilities in Nature. They never
say, what they are constantly charged with saying, that it
is impossible for the Builder of the universe to alter His
work. Their business is not with the possible, but the
actual — not with a world which might be, but with a world
that is. This they explore with a courage not unmixed
with reverence, and according to methods which, like the
^quality of a tree, are tested by their fruits. They have but
_nne desire — to know the truth. They have but one fear —
lo believe a lie. And if they know the strength of science,
and rely upon it with unswerving trust, they also know the
limits beyond which science ceases to be strong. They best
know that questions offer themselves to thought which
science, as now prosecuted, has not even the tendency to
solve. They keep such questions open, and will not toler
ate any unnecessary limitation of the horizon of their souls.
They have as little fellowship with the atheist who says

SCIENTIFIC USE OF THE IMAGINATION. 163

there is no God, as with the theist who professes to know
the mind of God. "Two things," said Immanuel Kant,
" fill me with awe : the starry heavens and the sense of
moral responsibility in man." And in his hours of health
and strength and sanity, when the stroke of action has
ceased and the pause of reflection has set in, the scientific
investigator finds himself overshadowed by the same awe.
Breaking contact with the hampering details of earth, it
associates him with a power which gives fulness and tone
to his existence, but which he can neither analyze nor com
prehend.

A TRANSLATION

OF

GOETHE'S PROEMIUM TO " GOTT UND WELT.'

To Him who from eternity, self-stirred,
Himself hath made by His creative word !
To Him, Supreme, who causeth faith to be,
Trust, hope, love, power, and endless energy !
To Him, who, seek to name Him as we will,
UNKNOWN within Himself abideth still !

Strain ear and eye, till sight and sense be dim ;

Thou'lt find but faint similitudes of Him :

Yea, and thy spirit in her flight of flame

Still strives to gauge the symbol and the name :

Charmed and compelled thou climb'st from height to height,

And round thy path the world shines wondrous bright ;

Time, space, and size, and distance cease to be,

And every step is fresh infinity.

What were the God who sat outside to scan

The spheres that 'neath His finger circling ran ?

God dwells within, and moves the world and moulds,

Himself and Nature in one form enfolds :

Thus all that lives in Him, and breathes, and is,

Shall ne'er His puissance, ne'er His spirit miss.

The soul of man, too, is a universe ;

Whence follows it that race with race concurs

In framing all it knows of good and true

God ? — yea, its own God ; and, with homage due,

Surrenders to His sway both earth and heaven ;

]-V;irs Him, and loves, where place for love is given.

J. A. S.
Spectator, KptoiJxr 21, 1870.

VIII.
ON RADIATION.

THE "REDE" LECTURE.

DELIVERED IN THE SENATE-HOUSE BEFOKE THE UNIVERSITY OIP
CAMBRIDGE.

On Tuesday, May 16, 1865.

" Forsitan et rosea Sol alte lampade lucens,
Possideat multum caecis fervoribus ignem
Circum sc, qui sit fulgore notatus,
^Estifer ut tantum radiorum exaugcat ictum."

Lucretius^ v. 610.

" Perhaps too the sun as he shines aloft with rosy lamp has round
about him much fire with heats that are not visible, and thus the fire may
be marked by no radiance, so that fraught with heat it increases to such
a degree the stroke of the rays." — Jfonro's Translation.

My attention was drawn to this remarkable passage by the late ex
cellent and accomplished Sir Edmund Head, Bart.

VIII.
KADI ATI ON.

1. Visible and Invisible Radiation.

BETWEEN the mind of man and the outer world are in
terposed the nerves of the human body, which translate,
or enable the mind to translate, the impressions of that
world into facts of consciousness and thought.

Different nerves are suited to the perception of different
impressions. We do not see with the ear, nor hear with
the eye, nor are we rendered sensible of sound by the
nerves of the tongue. Out of the general assemblage of
physical actions, each nerve, or group of nerves, selects and
responds to those for the perception of which it is specially
organized.

The optic nerve passes from the brain to the back of
the eyeball and there spreads out, to form the retina, a web
of nerve filaments, on which the images of external objects
are projected by the optical portion of the eye. This nerve
is limited to the apprehension of the phenomena of radia
tion, and, notwithstanding its marvellous sensibility to
certain impressions of this class, it is singularly obtuse to
other impressions.

Nor does the optic nerve embrace the entire range even
of radiation. Some rays, when they reach it, are incom
petent to evoke its power, while others never reach it at
all, being absorbed by the humors of the eye. To all rays

1GS FRAGMENTS OF SCIENCE.

which, whether they reach the retina or not, fail to excite
vision, we give the name of invisible or obscure rays. All
non-luminous bodies emit such rays. There is no body in
Nature absolutely cold, and every body not absolutely cold
emits rays of heat. But to render radiant heat fit to affect
the optic nerve a certain temperature is necessary. A cool
poker thrust into a fire remains dark for a time, but when
its temperature has become equal to that of the surrounding
coals it glows like them. In like manner, if a current of
electricity of gradually increasing strength be sent through
a wire of the refractory metal platinum, the wire first be
comes sensibly warm to the touch ; for a time its heat aug
ments, still, however, remaining obscure ; at length we can
no longer touch the metal with impunity ; and at a certain
definite temperature it emits a feeble red light. As the
current augments in power the light augments in brilliancy,
until finally the wire appears of a dazzling white. The
light which it now emits is similar to that of the sun.

By means of a prism Sir Isaac Newton unravelled the
'texture of solar light, and by the same simple instrument
we can investigate the luminous changes of our platinum
wire. In passing through the prism all its rays (and they
are infinite in variety) are bent or refracted from their
straight course ; and as different rays are differently re
fracted by the prism, we are by it enabled to separate one
class of rays from another. By such prismatic analysis Dr.
Draper has shown that, when the platinum wire first begins
to glow, the light emitted is a pure red. As the glow
augments the red becomes more brilliant, but at the same
lime orange rays are added to the emission. Augmenting
Ihe temperature still further, yellow rays appear beside the
orange, after the yellow green rays are emitted, and after
the green come, in succession, blue, indigo and violet rays.
To display all these colors at the same time the platinum
wire must be white-hot : the impression of whiteness being

RADIATION. 169

in fact produced by the simultaneous action of all these
colors on the optic nerve.

In the experiment just described we began with a plat
inum wire at an ordinary temperature, and gradually
raised it to a white heat. At the beginning, and even
before the electric current had acted at all upon the wire,
it emitted invisible rays. For some time after the action
of the current had commenced, and even for a time after
-the wire had become intolerable to the touch, its radiation
was still invisible. The question now arises, what becomes
of these invisible rays when the visible ones make their
appearance ? It will be proved in the sequel that they
maintain themselves in the radiation ; that a ray once
emitted continues to be emitted when the temperature
is increased, and hence the emission from our platinum
wire, even when it has attained its maximum brilliancy,
consists of a mixture of visible and invisible rays. If,
instead of the platinum wire, the earth itself were raised to
incandescence, the obscure radiation which it now emits
would continue to be emitted. To reach incandescence the
planet would have to pass through all the stages of non-
luminous radiation, and the final emission would embrace
the rays of all these stages. There can hardly be a doubt
that from the sun itself, rays proceed similar in kind to
those which the dark earth pours nightly into space. In
fact, the various kinds of obscure rays emitted by all the
planets of our system are included in the present radiation
of the sun.

The great pioneer in this domain of science was Sir
William Herschel. Causing a beam of solar light to pass
through a prism he resolved it into its colored constituents ;
he formed what is technically called the solar spectrum.
Exposing thermometers to the successive colors he deter
mined their heating power, and found it to augment from
the violet or most refracted end, to the red or least refracted

170 FRAGMENTS OF SCIENCE.

end of the spectrum. But be did not stop here. Pushing
his thermometers into the dark space beyond the red he
found that, though the light had disappeared, the radiant
heat falling on the instruments was more intense than that
at any visible part of the spectrum. In fact, Sir William
Herschel showed, and his results have been verified by vari
ous philosophers since his time, that besides its luminous
rays, the sun pours forth a multitude of other rays more
powerfully calorific than the luminous ones, but entirely
unsuited to the purposes of vision.

At the less refrangible end of the solar spectrum, then,
the range of the sun's radiation is not limited by that of
the eye. The same statement applies to the more refran
gible end. Hitter discovered the extension of the spectrum
into the invisible region beyond the violet; and, in recent
times, this ultra-violet emission has had peculiar interest
conferred upon it by the admirable researches of Professor
Stokes. The complete spectrum of the sun consists, there
fore, of three distinct parts : first, of ultra-red rays of high
heating power, but unsuited to the purposes of vision ;
secondly, of luminous rays which display the succession of
colors, red, orange, yellow, green, blue, indigo, violet;
thirdly, of ultra-violet rays which, like the ultra-red ones,
are incompetent to excite vision, but which, unlike the
ultra-red rays, possess a very feeble heating power. In
consequence, however, of their chemical energy these ultra
violet rays arc of the utmost importance to the organic
world.

2. Orlfjbi and Character of Radiation. The Ether.

Whon we see a platinum wire raised gradually to a
white heat, and emitting in succession all the colors of the
spectrum, we are simply conscious of a series of changes in
the condition of our own eyes. We do not see the actions
in which these successive colors originate, but the mind

RADIATION. 171

irresistibly infers that the appearance of the colors corre
sponds to certain contemporaneous changes in the wire.
What is the nature of these changes ? In virtue of what
condition does the wire radiate at all? We must now
look from the wire as a whole to its constituent atoms.
Could we see those atoms, even before the electric current
has begun to act upon them, we should find them in a
state of vibration. In this vibration, indeed, consists such
warmth as the wire then possesses. Locke enunciated this
idea with great precision, and it seems placed beyond the
pale of doubt by the excellent quantitative researches of
Mr. Joule. " Heat," says Locke, " is a very brisk agitation
of the insensible parts of the object, which produce in us
that sensation from which we denominate the object hot :
so what in our sensation is heat in the object is nothing
but motion" When the electric current, still feeble, begins
to pass through the wire, its first act is to intensify the
vibrations already existing, by causing the atoms to swing
through wider ranges. Technically speaking, the ampli
tudes of the oscillations are increased. The current does
this, however, without altering the periods of the old vi
brations, or the times in which they were executed. But
besides intensifying the old vibrations the current gener
ates new and more rapid ones, and when a certain definite
rapidity has been attained the wire begins to glow. The
color first exhibited is red, which corresponds to the lowest
rate of vibration of which the eye is able to take cognizance.
By augmenting the strength of the electric current more
rapid vibrations are introduced, and orange rays appear.
A quicker rate of vibration produces yellow, a still quicker
green ; and by further augmenting the rapidity, we pass
through blue, indigo, and violet, to the extreme ultra-violet
rays.

Such are the changes which science recognizes in the
wire itself, as concurrent with the visual changes taking

172 FRAGMENTS OF SCIENCE.

place in the eye. But what connects the wire with this
organ ? By what means does it send such intelligence of
its varying condition to the optic nerve ? Heat being, as
defined by Locke, " a very brisk agitation of the insensible
parts of an object," it is readily conceivable that on touch-
Ing a heated body the agitation may communicate itself to
the adjacent nerves, and announce itself to them as light
or heat. But the optic nerve does not touch the hot plati
num, and hence the pertinence of the question, By what
agency are the vibrations of the wire transmitted to the
eye?

The answer to this question involves, perhaps, the most
important physical conception that the mind of man has
yet achieved : the conception of a medium filling space and
fitted mechanically for the transmission of the vibrations
of light and heat, as air is fitted for the transmission of
sound. This medium is called the luminiferous ether.
Every vibration of every atom of our platinum wire raises
in this ether a wave, which speeds through it at the rate
of 186,000 miles a second. The ether suffers no rupture
of continuity at the surface of the eye, the inter-molecular
spaces of the various humors are filled with it ; hence the
waves generated by the glowing platinum can cross these
humors and impinge on the optic nerve at the back of the
eye. Thus the sensation of light reduces itself to the com
munication of motion. Up to this point we deal with pure
mechanics ; but the subsequent translation of the shock of
the ethereal waves into consciousness eludes the analysis
of science. As an oar dipping into the Cam generates
systems of waves, which, speeding from the centre of dis
turbance, finally stir the sedges on the river's bank, so do
the vibrating atoms generate in the surrounding ether un
dulations, which finally stir the filaments of the retina.
The motion thus imparted is transmitted with measurable
and not very great velocity to the brain, where, by a pro-

KADIATION. 173

cess which science does not even tend to unravel, the tre
mor of the nervous matter is converted into the conscious
impression of light.

Darkness might then be defined as ether at rest ; light
as ether in motion. But in reality the ether is never at
rest, for in the absence of light-waves we have heat-waves
always speeding through it. In the spaces of the universe
both classes of undulations incessantly commingle. Here
the waves issuing from uncounted centres cross, coincide,
oppose, and pass through each other, without confusion or
ultimate extinction. The waves from the zenith do not
jostle out of existence those from the horizon, and every
star is seen across the entanglement of wave-motions pro
duced by all other stars. It is the ceaseless thrill which
those distant orbs collectively create in the ether, which
constitutes what we call the temperature of space. As the
air of a room accommodates itself to the requirements of an
orchestra, transmitting each vibration of every pipe and
string, so does the inter-stellar ether accommodate itself to
the requirements of light and heat. Its waves mingle in
space without disorder, each being endowed with an in
dividuality as indestructible as if it alone had disturbed the
universal repose.

All vagueness with regard to the use of the terms radia
tion and absorption will now disappear. Radiation is the
communication of vibratory motion to the ether, and when
a body is said to be chilled by radiation, as for example the
grass of a meadow on a starlight night, the meaning is, that
the molecules of the grass have lost a portion of their mo
tion, by imparting it to the medium in which they vibrate.
On the other hand, the waves of ether once generated may
so strike against the molecules of a body exposed to their
action as to yield up their motion to the latter ; and in this
transfer of the motion from the ether to the molecules con
sists the absorption of radiant heat. All the phenomena

17 i FRAGMENTS OF SCIENCE.

•

of heat are in this way reducible to interchanges of motion ;
and it is purely as the recipients or the donors of this mo
tion, that we ourselves become conscious of the action of
heat and cold.

3. The Atomic Theory in reference to the Ether.

The word " atoms " has been more than once employed
in this discourse. Chemists have taught us that all matter
is reducible to certain elementary forms to which they give
this name. These atoms are endowed with powers of
mutual attraction, and under suitable circumstances they
coalesce to form compounds. Thus oxygen and hydrogen
are elements when separate, or merely mixed, but they may
be made to combine so as to form molecules, each consisting
of two atoms of hydrogen and one of oxygen. In this con
dition they constitute water. So also chlorine and sodium
are elements, the former a pungent gas, the latter a soft
metal ; and they unite together to form chloride of sodium
or common salt. In the same way the element nitrogen
combines with hydrogen, in the proportion of one atom of
the former to three of the latter, to form ammonia or spirit
of hartshorn. Picturing in imagination the atoms of ele
mentary bodies as little spheres, the molecules of compound
bodies must be pictured as groups of such spheres. This is
the atomic theory as Dalton conceived it. Now, if this
theory have any foundation in fact, and if the theory of an
ether pervading space and constituting the vehicle of atomic
motion be founded in fact, we may assuredly expect the
vibrations of elementary bodies to be profoundly modified
by the act of combination. It is on the face of it almost
certain that both as regards radiation and absorption, that
is to say, both as regards the communication of motion to
the ether and the acceptance of motion from it, the deport
ment of the uncombined will be different from that of the
combined atoms.

RADIATION. 175

4. Absorption of Radiant Heat by Gases.

We have now to submit these considerations to the
only test by which they can be tried, namely, that of ex
periment. An experiment is well denned as a question put
to Nature ; but to avoid the risk of asking amiss we ought
to purify the question from all adjuncts which do not neces-
. sarily belong to it. Matter has been shown to be composed
of elementary constituents, by the compounding of which
all its varieties are produced. But besides the chemical
unions which they form, both elementary and compound
bodies can unite in another and less intimate way. By the
attraction of cohesion gases and vapors aggregate to liquids
and solids, without any change of their chemical nature.
We do not yet know how the transmission of radiant heat
may be affected by the entanglement due to cohesion, and
as our object now is to examine the influence of chemical
union alone, we shall render our experiments more pure by
liberating the atoms and molecules entirely from the bonds
of cohesion, and employing them in the gaseous or vapor
ous form.

Let us endeavor to obtain a perfectly clear mental image
of the problem now before us. Limiting in the first place
our inquiries to the phenomena of absorption, we have to
picture a succession of waves issuing from a radiant source
and passing through a gas ; some of them striking against
the gaseous molecules and yielding up their motion to
the latter ; others gliding round the molecules or passing
through the inter-molecular spaces without apparent hinder-
ance. The problem before us is to determine whether such
free molecules have any power whatever to stop the waves
of heat, and, if so, whether different molecules possess this
power in different degrees.

The source of waves which I shall choose for these

176 KK AC. MK NTS OF SCIENCE.

experiments is a plate of copper, against the back of which
a steady sheet of flame is permitted to play. On emerging
from the copper, the waves, in the first instance, pass
through a space devoid of air, and then enter a hollow
glass cylinder, three feet long and three inches wide. The
two ends of this cylinder are stopped by two plates of rock-
salt, this being the only solid substance which offers a
scarcely sensible obstacle to the passage of the calorific
waves. After passing through the tube, the radiant heat
falls upon the anterior face of a thermo-electric pile,1 which
instantly applies the heat to the generation of an electric
current. This current conducted round a magnetic needle
deflects it, and the magnitude of the deflection is a measure
of the heat falling upon the pile. This famous instrument,
and not an ordinary thermometer, is what we shall use in
these inquiries, but we shall use it in a somewhat novel
way. As long as the two opposite faces of the thermo
electric pile are kept at the same temperature, no matter
how high that may be, there is no current generated. The
current is a consequence of the difference of temperature
between the two opposite faces of the pile. Hence, if after
the anterior face has received the heat from our radiating
source, a second source, which we may call the compensat
ing source, be permitted to radiate against the posterior
face, this latter radiation will tend to neutralize the former.
When the neutralization is perfect, the magnetic needle
connected writh the pile is no longer deflected, but points to
the zero of the graduated circle over which it hangs.

And now let us suppose the glass tube, through which
pass the waves from the heated plate of copper, to be ex
hausted by an air-pump, the two sources of heat acting at
the same time on the two opposite faces of the pile. Per
fectly equal quantities of heat being imparted to the two

1 In the Appendix to the first chapter of " Heat as a Mode of Motion,''
the construction of the thermo-electric pile is fully explained.

RADIATION. 177

faces, the needle points to zero. Let any gas be now per
mitted to enter the exhausted tube ; if the molecules pos
sess any power of intercepting the calorific waves, the
equilibrium previously existing will be destroyed, the com
pensating source will triumph, and a deflection of the mag
netic needle will be the immediate consequence. From the
deflections thus produced by different gases, we can readily
deduce the relative amounts of wave-motion which their
molecules intercept.

In this way the substances mentioned in the following
table were examined, a small portion only of each being
admitted into, the glass tube. The quantity admitted was
just sufficient to depress a column of mercury associated
with the tube one inch ; in other words, the gases were
examined at a pressure of one-thirtieth of an atmosphere.
The numbers in the table express the relative amounts of
wave-motion absorbed by the respective gases, the quantity
intercepted by atmospheric air being taken as unity :

Radiation through Gases.

»-»•'««• <££&

Air , 1

Oxygen 1

Nitrogen 1

Hydrogen 1

Carbonic oxide 750

Carbonic acid 972

Hydrochloric acid 1,005

Nitric oxide 1,590

Nitrous oxide 1,860

Sulphide of hydrogen 2,100

Ammonia ". 5,460

Olefiant gas 6,030

Sulphurous acid 6,480

Every gas in this table is perfectly transparent to light,
that is to say, all waves within the limits of the visible

178 FRAGMENTS OF SCIENCE.

spectrum pass through it without obstruction ; but for the
waves of slower period, emanating from our heated plate
of copper, enormous differences of absorptive power are
manifested. These differences illustrate in the most unex
pected manner the influence of chemical combination. Thus
the elementary gases, oxygen, hydrogen, and nitrogen, and
the mixture atmospheric air, prove to be practical vacua to
the rays of heat ; for every ray, or, more strictly speaking,
for every unit of wave-motion, which any one of them is
competent to intercept, perfectly transparent ammonia in
tercepts 5,460 units, olefiant gas G,030 units, while sulphur
ous acid gas absorbs 6,480 units. What becomes of the
wave-motion thus intercepted ? It is applied to the heating
of the absorbing gas. Through air. oxygen, hydrogen, and
nitrogen, on the contrary, the waves of ether pass without
absorption, and these gases are not sensibly changed in
temperature by the most powerful calorific rays. The po
sition of nitrous oxide in the foregoing table is worthy of
particular notice. In this gas we have the same atoms, in
a state of chemical union, that exist uncombined in the
atmospheric air; but the absorption of the compound is
1,800 times that of air.

5. Formation of Invisible Foci.

This extraordinary deportment of the elementary gases
naturally directed attention to elementary bodies in another
state of aggregation. Some of Melloni's results now at
tained a new significance ; for this celebrated experimenter
had found crystals of the element sulphur to be highly per
vious to radiant heat ; he had also proved that lamp-black
and black glass (which owes its blackness to the element
carbon) were to considerable extent transparent to calorific
rays of low refrangibility. These facts, harmonizing so
strikingly with the deportment of the simple gases, sug-

RADIATION. 179

gested further inquiry. Sulphur dissolved in bisulphate of
carbon was found almost perfectly transparent. The dense
and deeply-colored element bromine was examined, and
found competent to cut off the light of our most brilliant
flames, while it transmitted the invisible calorific rays with
extreme freedom. Iodine, the companion-element of bro
mine, was next thought of, but it was found impracticable
to examine the substance in its usual solid condition. It
however dissolves freely in bisulphide of carbon. There is
no chemical union between the liquid and the iodine ; it is
simply a case of solution, in which the uncombined atoms
of the element can act upon the radiant heat. When per
mitted to do so, it was found that a layer of dissolved
iodine, sufficiently opaque to cut off the light of the mid
day sun, was almost absolutely transparent to the invisible
calorific rays.

By prismatic analysis Sir William Herschel separated
the luminous from the non-luminous rays of the sun, and
he also sought to render the obscure rays visible by con
centration. Intercepting the luminous portion of his spec
trum he brought, by a converging lens, the ultra-red rays
to a focus, but by this condensation he obtained no light.
The solution of iodine offers a means of filtering the solar
beam, or, failing it, the beam of the electric lamp, which
renders attainable far more powerful foci of invisible rays
than could possibly be obtained by the method of Sir Wil
liam Herschel. For to form his spectrum he was obliged
to operate upon solar light which had passed through
a narrow slit or through a small aperture, the amount of
the obscure heat being limited by this circumstance. But
with our opaque solution we may employ the entire surface
of the largest lens, and having thus converged the rays,
luminous and non-luminous, we can intercept the former by
the iodine, and do what we please with the latter. Ex
periments of this character, not only with the iodine solu-

180 FRAGMENTS OF SCIENCE.

tion, but also with black glass and layers of lamp-black,
were publicly performed at the Royal Institution in the
early part of 1862, and the effects at the foci of invisible
rays then obtained were such as had never been witnessed
previously.

In the experiments here referred to, glass lenses were
employed to concentrate the rays. But glass, though
highly transparent to the luminous, is in a high degree
opaque to the invisible heat-rays of the electric lamp, and
hence a large portion of those rays was intercepted by the
glass. The obvious remedy here is to employ rock-salt
lenses instead of glass ones, or to abandon the use of lenses
wholly, and to concentrate the rays by a metallic mirror.
Both of these improvements have been introduced, and, as
anticipated, the invisible foci have been thereby rendered
more intense. The mode of operating remains, however, the
same, in principle, as that made known in 1862. It was
then found that an instant's exposure of the face of the
thermo-electric pile to the focus of invisible rays, dashed
the needles of a coarse galvanometer violently aside. It is
now found that on substituting for the face of the thermo
electric pile a combustible body, the invisible rays are
competent to set that body on fire.

6. Visible and Invisible Rays of the Electric Light.

We have next to examine wrhat proportion the non
luminous rays of the electric light bear to the luminous
ones. This the opaque solution of iodine enables us to do
with an extremely close approximation to the truth. The
pure bisulphide of carbon, which is the solvent of the
iodine, is perfectly transparent to the luminous, and almost
perfectly transparent to the dark rays of the electric lamp.
Through the transparent bisulphide the total radiation of
the lamp may be considered to pass, while through the

KADIATION. 181

solution of iodine only the dark rays are transmitted.
Determining, then, by means of a thermo-electric pile, the
total radiation, and deducting from it the purely obscure,
we obtain the amount of the purely luminous emission.
Experiments, performed in this way, prove that if all the
visible rays of the electric light were converged to a focus
of dazzling brilliancy, its heat would only be one-ninth of
that produced at the unseen focus of the invisible rays.

Exposing his thermometers to the successive colors of
the solar spectrum, Sir William Herschel determined the
heating power of each, and also that of the region beyond
the extreme red. Then drawing a straight line to represent
the length of the spectrum, he erected, at various points,
perpendiculars to represent the calorific intensity existing
at those points. Uniting the ends of all his perpendiculars,
he obtained a curve which showed at a glance the manner
in which the heat was distributed in the solar spectrum.
Professor Mliller, of Freiburg, with improved instruments,
afterward made similar experiments, and constructed a
more accurate diagram of the same kind. We have now to
examine the distribution of heat in the spectrum of the
electric light ; and for this purpose we shall employ a par
ticular form of the thermo-electric pile, devised by Melloni.
Its face is a rectangle, which by means of movable side-
pieces can be rendered as narrow as desired. We can, for
example, have the face of the pile the tenth, the hundredth,
or even the thousandth of an inch in breadth. By means
of an endless screw, this linear thermo-electric pile may be
moved through the entire spectrum, from the violet to the
red, the amount of heat falling upon the pile at every point
of its march, being declared by a magnetic needle associated
with the pile.

When this instrument is brought up to the violet end of
the spectrum of the electric light, the heat is found to be
insensible. As the pile gradually moves from the violet

182 FRAGMENTS OF SCIENCE.

end toward the red, heat soon manifests itself, augmenting
as we approach the red. Of all the colors of the visible
spectrum the red possesses the highest heating power. On
pushing the pile into the dark region beyond the red, the
heat, instead of vanishing, rises suddenly and enormously
in intensity, until at some distance beyond the red it
attains a maximum. Moving the pile still forward, the
thermal power falls, somewhat more rapidly than it rose.
It then gradually shades away, but for a distance beyond
the red greater than the length of the whole visible spec
trum, signs of heat may be detected. Drawing a datum
line, and erecting along it perpendiculars, proportional in
length to the thermal intensity at the respective points, we
obtain the extraordinary curve, shown on the adjacent page,
which exhibits the distribution of heat in the spectrum of
the electric light. In the region of dark rays, beyond the
red, the curve shoots up to B, in a steep and massive peak
— a kind of Matterhorn of heat, which dwarfs the portion
of the diagram C D E, representing the luminous radiation.
Indeed, the idea forced upon the mind by this diagram is
that the light-rays are a mere insignificant appendage to
the heat-rays represented by the area A B C D, thrown in
as it were by Nature for the purposes of vision.

The diagram drawn by Professor Mliller to represent
the distribution of heat in the solar spectrum is not by any
means so striking as that just described, and the reason,
doubtless, is that prior to reaching the earth the solar rays
have to traverse our atmosphere. By the aqueous vapor
there diffused, the summit of the peak representing the
sun's invisible 'radiation is cut off. A similar lowering of
the mountain of invisible heat is observed when the rays
from the electric light are permitted to pass through a film
of water, which acts upon them as the atmospheric vapor
acts upon the rays of the sun.

184 FRAGMENTS OF SCIENCE.

7. Combustion by Invisible Hays.

The sun's invisible rays far transcend the visible ones
in heating power, so that if the alleged performances of
Archimedes during the siege of Syracuse had any founda
tion in fact, the dark solar rays would have been the phi
losopher's chief agents of combustion. On a small scale
we can readily produce with the purely invisible rays of
the electric light all that Archimedes is said to have per
formed with the sun's total radiation. Placing behind the
electric light a small concave mirror, the rays are converged,
the cone of reflected rays and their point of convergence
being rendered clearly visible by the dust always floating
in the air. Placing, between the luminous focus and the
source of rays, our solution of iodine, the light of the cone
is entirely cut away, but the intolerable heat experienced
when the hand is placed, even for a moment, at the dark
focus, shows that the calorific rays pass unimpeded through
the opaque solution.

Almost any thing that ordinary fire can effect may be
accomplished at the focus of invisible rays ; the air at the
focus remaining at the same time perfectly cold, on ac
count of its transparency to the heat-rays. An air-ther
mometer, with a hollow rock-salt bulb, would be unaffected
by the heat of the focus : there would be no expansion,
and in the open air there is no convection. The ether at
the focus, and not the air, is the substance in which the
heat is embodied. A block of wood, placed at the focus,
absorbs the heat, and dense volumes of smoke rise swiftly
upward, showing the manner in which the air itself would
rise, if the invisible rays were competent to heat it. At
the perfectly dark focus dry paper is instantly inflamed :
chips of wood are speedily burnt up : lead, tin, and zinc,
are fused : and disks of charred paper are raised to vivid
incandescence. It might be supposed that the obscure rays

RADIATION. 185

would show no preference for black over white ; but they
do show a preference, and, to obtain rapid combustion, the
body, if not already black, ought to be blackened. When
metals are to be burned, it is necessary to blacken or
otherwise tarnish them, so as to diminish their reflective
power. Blackened zinc-foil, when brought into the focus
of invisible rays, is instantly caused to blaze, and burns
with its peculiar purple flame. Magnesium wire flattened,
or tarnished magnesium ribbon, also bursts into splendid
combustion. Pieces of charcoal suspended in a receiver
full of oxygen are also set on fire : the dark rays after hav
ing passed through the receiver still possessing sufficient
power to ignite the charcoal, and thus initiate the attack
of the oxygen. If, instead of being plunged in oxygen,
the charcoal be suspended in vacua, it immediately glows
at the place where the focus falls.

8. Transmutation of Rays : l Calorescence.

Eminent experimenters were long occupied in demon
strating the substantial identity of light and radiant heat,
and we have now the means of offering a new and striking
proof of this identity. A concave mirror produces beyond
the object which it reflects an inverted and magnified image
of the object ; withdrawing, for example, our iodine solu
tion, an intensely luminous inverted image of the carbon
points of the electric light is formed at the focus of the
mirror employed in the foregoing experiments. When the
solution is interposed, and the light is cut away, what
becomes of this image ? It disappears from sight, but an
invisible thermograph remains, and it is only the peculiar
constitution of our eyes that disqualifies us from seeing
the picture formed by the calorific rays. Falling on
white paper, the image chars itself out : falling on black

1 I borrow this term from Professor Challis, " Philosophical Maga
zine," vol. xii., p. 521.

18G FRAGMENTS OF SCIENCE.

paper, two holes are pierced in it, corresponding to the
images of the two coal points : but falling on a thin plate
of carbon in vacuo, or upon a thin sheet of platinized plat
inum, either in vacuo or in air, radiant heat is converted
into light, and the image stamps itself in vivid incandes
cence upon both the carbon and the metal. Results similar to
those obtained with the electric light have also been obtained
with the invisible rays of the lime-light and of the sun.

Before a Cambridge audience it is hardly necessary to
refer to the excellent researches of Professor Stokes at
the opposite end of the spectrum. The above results con
stitute a kind of complement to his discoveries. Professor
Stokes named the phenomena which he has discovered and
investigated Fluorescence ; for the new phenomena here
described I have proposed the term Calorescence. He, by
the interposition of a proper medium, so lowered the re-
frangibility of the ultra-violet rays of the spectrum as to
render them visible ; and here, by the interposition of the
platinum-foil, the refrangibility of the ultra-red rays is so
exalted as to render them visible. Looking through a
prism at the incandescent image of the carbon points, the
light of the image is decomposed, and a complete spectrum
obtained. The invisible rays of the electric light, remoulded
by the atoms of the platinum, shine thus visibly forth ; ultra-
red rays being converted into red, orange, yellow, green,
blue, indigo, and ultra-violet ones. Could we, moreover,
raise the original source of rays to a sufficiently high tem
perature, we might not only obtain from the dark rays of
such a source a single incandescent image, but from the
dark rays of this image we might obtain a second one, from
the dark rays of the second a third, and so on — a series of
complete images and spectra being thus extracted from the
invisible emission of the primitive source.1

1 On investigating the calorescence produced by rays transmitted
through glasses of various colors, it was found that in the case of certain

RADIATION. 187

9. Deadness of the Optic Nerve to the Calorific Hays.

The layer of iodine used in the foregoing experiments
intercepted the light of the noonday sun. No trace of
light from the electric lamp was visible in the darkest
room, even when a white screen was placed at the focus of
the mirror employed to concentrate the light. It was
thought, however, that if the retina itself were brought
into the focus the sensation of light might be experienced.
The danger of this experiment was twofold. If the dark
rays were absorbed in a high degree by the humors of the
eye, the albumen of the humors might coagulate along the
line of the rays. If, on the contrary, no such high ab
sorption took place, the rays might reach the retina with a
force sufficient to destroy it. To test the likelihood of these
results, experiments were made on water and on a solution of
alum, and they showed it to be very improbable that in the
brief time requisite for an experiment any serious damage

specimens of blue glass, the platinum-foil glowed with, a pink or purplish
light. The effect was not subjective, and considerations of obvious in
terest are suggested by it. Different kinds of black glass differ notably
as to their power of transmitting radiant heat. In thin plates some de
scriptions tint the sun with a greenish hue : others make it appear a
glowing red without any trace of green. The latter are far more diather
mic than the former. In fact, carbon when perfectly dissolved, and in
corporated with a good white glass, is highly transparent to the calorific
rays, and by employing it as an absorbent, the phenomena of " calores-
cence " may be obtained, though in a less striking form than with the
iodine. The black glass chosen for thermometers, and intended to ab
sorb completely the solar heat, may entirely fail in this object, if the
glass in which the carbon is incorporated be colorless. To render the
bulb of a thermometer a perfect absorbent, the glass ought in the first
instance to be green. Soon after the discovery of fluorescence the late
Dr. William Allen Miller pointed to the lime-light as an illustration of
exalted refrangibility. Direct experiments have since entirely confirmed
the view expressed at page 210 of his work on " Chemistry," published
in 1855.

188 FRAGMENTS OF SCIEXCE.

could be done. The eye was therefore caused to approach
the dark focus, no defence, in the first instance, being pro
vided ; but the heat, acting upon the parts surrounding the
pupil, could not be borne. An aperture was, therefore,
pierced in a plate of metal, and the eye placed behind the
aperture, was caused to approach the point of convergence
of invisible rays. The focus was attained, first by the
pupil and afterward by the retina. Removing the eye, but
permitting the plate of metal to remain, a sheet of platinum-
foil was placed in the position occupied by the retina a mo
ment before. The platinum became red hot. No sensible
damage was done to the eye by this experiment ; no im
pression of light was produced; the optic nerve was not
even conscious of heat.

But the humors of the eye are known to be highly im
pervious to the invisible calorific rays, and the question
therefore arises, " Did the radiation in the foregoing experi
ment reach the retina at all ? " The answer is, that the
rays were in part transmitted to the retina, and in part ab
sorbed by the humors. Experiments on the eye of an ox
showed that the proportion of obscure rays which reached
the retina amounted to 18 per cent, of the total radiation ;
while the luminous emission from the electric light amounts
to no more than 10 per cent, of the same total. Were the
purely luminous rays of the electric lamp converged by our
mirror to a focus, there can be no doubt as to the fate of a
retina placed there. Its ruin would be inevitable ; and yet
this would be accomplished by an amount of wave-motion
but little more than half of that which the retina bears,
without exciting consciousness, at the focus of invisible
rays.

This subject will repay a moment's further attention.
At a common distance of a foot the visible radiation of the
electric light is 800 times the light of a candle. At the
same distance, the portion of the radiation of the electric

RADIATION. 189

light which reaches the retina but fails to excite vision, is
about 1,500 times the luminous radiation of the candle.1
But a candle on a clear night can readily be seen at a dis
tance of a mile, its light at this distance being less than
one 20,000,000th of its light at the distance of a foot.
Hence, to make the candle-light a mile off equal in power
to the non-luminous radiation received from the electric
light at a foot distance, its intensity would have to be mul
tiplied by 1,500 X 20,000,000, or by thirty thousand mill
ions. Thus the thirty thousand millionth part of the in
visible radiation from the electric light, received by the
retina at the distance of a foot, would, if slightly changed
in character, be amply sufficient to provoke vision. Nothing
could more forcibly illustrate that special relationship sup
posed by Melloni and others to subsist between the optic
nerve and the oscillating periods of luminous bodies. The
optic nerve responds, as it were, to the waves with which
it is in consonance, while it refuses to be excited by others
of almost infinitely greater energy, whose periods of recur
rence are not in unison with its own.

10. Persistence of Hays.

At an early part of this lecture it was affirmed that
when a platinum wire was gradually raised to a state of
high incandescence, new rays were constantly added,
while the intensity of the old ones was increased. Thus
in Dr. Draper's experiments the rise of temperature that
generated the orange, yellow, green, and blue rays, aug
mented the intensity of the red ones. What is true of the
red is true of every other ray of the spectrum, visible and
invisible. We cannot indeed see the augmentation of in-

1 It will be borne in mind that the heat which any ray, luminous or
non-luminous, is competent to generate is the true measure of the energy
of the ray.

190 ' FRAGMENTS OF SCIENCE.

tensity in the region beyond the red, but we can measure
it and express it numerically. With this view the following
experiment was performed. A spiral of platinum wire was
surrounded by a small glass globe to protect it from cur
rents of air ; through an orifice in the globe the rays could
pass from the spiral and fall afterward upon a thermo-elec
tric pile. Placing in front of the orifice an opaque solution
of iodine, the platinum was gradually raised from a low
dark heat to the fullest incandescence, with the following
results :

Appearance Energy of

of spiral. obscure radiation.

Dark 1

Dark, but hotter 3

Dark, but still hotter 5

Dark, but still hotter 10

Feeble red 19

Dull red 25

Red 37

Full red 62

Orange 89

Bright orange 144

Yellow 202

White 276

Intense white 440

Thus the augmentation of the electric current, which
raises the wire from its primitive dark condition to an in
tense white heat, exalts at the same time the energy of the
obscure radiation, until at the end it is fully four hundred
and forty times what it was at the beginning.

What has been here proved true of the totality of the
ultra-red rays is true for each of them singly. Placing our
linear thermo-electric pile in any part of the ultra-red spec
trum, it may be proved that a ray once emitted continues
to be emitted with increased energy as the temperature is
augmented. The platinum spiral so often referred to being

RADIATION. 191

raised to whiteness by an electric current, a brilliant spec
trum was formed from its light. A linear thermo-electric
pile was placed in the region of obscure rays beyond the
red, and by diminishing the current the spiral was reduced
to a low temperature. It was then caused to pass through
various degrees of darkness and incandescence, with the
following results :

Appearance Energy of

of spiral. obscure rays.

Dark 1

Dark 6

Faint red 10

Dullred 13

Red 18

Full red 27

Orange 60

Yellow 93

White 122

Here, as in the former case, the dark and bright radia
tions reached their maximum together; as the one aug
mented, the other augmented, until at last the energy of
the obscure rays of the particular refrangibility here chosen,
became one hundred and twenty-two times what it was at
first. To reach a white heat the wire has to pass through
all the stages of invisible radiation, and in its most brilliant
condition it embraces, in an intensified form, the rays of all
those stages.

And thus it is with all other kinds of matter, as far as
they have hitherto been examined. Coke, whether brought
to a white heat by the electric current, or by the oxyhydro-
gen jet, pours out invisible rays with augmented energy,
as its light is increased. The same is true of lime, bricks,
and other substances. It is true of all metals which are
capable of being heated to incandescence. It also holds
good for phosphorus burning in oxygen. Every gush of
dazzling light has associated with it a gush of invisible ra-

192 FRAGMENTS OF

diant heat, which far transcends the light in energy. This
condition of things applies to all bodies capable of being
raised to a white heat, either in the solid or the molten
condition. It would doubtless also apply to the luminous
fogs formed by the condensation of incandescent vapors.
In such cases when the curve representing the radiant en
ergy of the body is constructed, the obscure radiation tow
ers upward like a mountain, the luminous radiation resem
bling a mere spur at its base. From the very brightness
of the light of some of the fixed stars we may infer the
intensity of the dark radiation, which is the precursor and
inseparable associate of their luminous rays.

We thus find the luminous radiation appearing when
the radiant body has attained a certain temperature ; or,
in other words, when the vibrating atoms of the body have
attained a certain width of swring. In solid and molten
bodies a certain amplitude cannot be surpassed without
the introduction of periods of vibration, which provoke
the sense of vision. How are we to figure this ? If per
mitted to speculate, we might ask, Are not these more
rapid vibrations the progeny of the slower ? Is it not really
the mutual action of the atoms, when they swing through
very wide spaces, and thus encroach upon each other, that
causes them to tremble in quicker periods ? If so, what
ever be the agency by which the large swinging space is
obtained, we shall have light-giving vibrations associated
\vitli it. It matters not whether the large amplitudes be
produced by the strokes of a hammer, or by the blows of
the molecules of a non-luminous gas, such as the air at some
height above a gas-flame ; or by the shock of the ether-
particles when transmitting radiant heat. The result in
all cases will be incandescence. Thus, the invisible waves
of our filtered electric beam may be regarded as generating
synchronous vibrations among the atoms of the platinum
on which they impinge ; but once these vibrations have at-

RADIATION. 193

tained a certain amplitude, the mutual jostling of the atoms
produces quicker tremors, and the light-giving waves fol
low as the necessary product of the heat-giving ones.

11. Absorption of Radiant Heat by Vapors
and Odors.

We commenced the demonstrations brought forward in
this lecture by experiments on permanent gases, and we
have now to turn our attention to the vapors of volatile
liquids. Here, as in the case .of the gases, vast differences
have been proved to exist between various kinds of mole
cules, as regards their power of intercepting the calorific
waves. While some vapors allow the waves a compara
tively free passage, the minutest bubble of other vapors,
introduced into the tube already employed for gases, causes
a deflection of the magnetic needle. Assuming the ab
sorption effected by air at a pressure of one atmosphere to
be unity, the followng are the absorptions effected by a se
ries of vapors at a pressure of one-sixtieth of an atmos
phere :

Name of vapor. Absorption.

Bisulphide of cai'bon 4 "7

Iodide of methyl 115

Benzol 136

Amylene 321

Sulphuric ether 440

Formic ether , 548

Acetic ether G12

Bisulphide of carbon is the most transparent vapor in
this list ; and acetic ether the most opaque ; one-sixtieth
of an atmosphere of the former, however, produces forty-
seven times the effect of a whole atmosphere of air, while
one-sixtieth of an atmosphere of the latter produces six
hundred and twelve times the effect of a whole atmos
phere of air. Reducing dry air to the pressure of the acetic
9

194 FRAGMENTS OF SCIENCE.

ether here employed, and comparing them then together,
the quantity of wave-motion intercepted by the ether would
be many thousand times that intercepted by the air.

Any one of these vapors discharged into the free atmos
phere, in front of a body emitting obscure rays, intercepts
more or less of the radiation. A similar effect is produced
by perfumes diffused in the air, though their attenuation is
known to be almost infinite. Carrying, for example, a cur
rent of dry air over bibulous paper moistened by patchouli,
the scent taken up by the current absorbs 30 times the
quantity of heat intercepted by the air which carries it ;
and yet patchouli acts more feebly on radiant heat than
any other perfume yet examined. Here follow the results
obtained with various essential oils, the odor, in each case,
being carried by a current of dry air into the tube already
employed for gases and vapors :

Name of perfume. Absorption.

Patchouli 30

Sandal- wood 32

Geranium 33

Oil of cloves 34

Otto of roses 37

Bergamot 44

Neroli 47

Lavender 60

Lemon 65

Portugal 67

Thyme 68

Rosemary 74

Oil of laurel 80

Camomile-flowers 87

Cassia 109

Spikenard 355

Anisesccd 372

Thus the absorption by a tube full of dry air being 1,
that of the odor of patchouli diffused in it is 30, that of

RADIATION. 195

lavender 60, that of rosemary 74, while that of aniseseed
amounts to 372. It would be idle to speculate on the
quantities of matter concerned in these actions.

12. Aqueous Vapor in relation to the Terrestrial
Temperatures?

\Ve are now fully prepared for a result which, without
such preparation, might appear incredible. Water is, to
some extent, a volatile body, and our atmosphere, resting
as it does upon the surface of the ocean, receives from it a
continual supply of aqueous vapor. It would be an error
to confound clouds or fog or any visible mist with the va
por of water : this vapor is a perfectly impalpable gas, dif
fused, even on the clearest days, throughout the atmosphere.
Compared with the great body of the air, the aqueous vapor
it contains is of almost infinitesimal amount, 99|- out of
every 100 parts of the atmosphere being composed of oxy
gen and nitrogen. In the absence of experiment, we should
never think of ascribing to this scant and varying constitu
ent any important influence on terrestrial radiation ; and
yet its influence is far more potent than that of the great
body of the air. To say that on a day of average humidity
in England, the atmospheric vapor exerts 100 times the
action of the air itself, would certainly be an understate
ment of the fact. The peculiar qualities of this vapor, and
the circumstance that at ordinary temperatures it is very
near its point of condensation, render the results which it
yields in the apparatus already described, less than the
truth ; and I am not prepared to say that the absorption by
this substance is not 200 times that of the air in which it is
diffused. Comparing a single molecule of aqueous vapor
with an atom of either of the main constituents of our at
mosphere, I am not prepared to say how many thousand
times the action of the former exceeds that of the latter.
1 See Note at the end of this Lecture.

190 FRAGMENTS OF SCIENCE.

But it must be borne in mind that these large numbers
depend in part upon the extreme feebleness of the air ; the
power of aqueous vapor seems vast, because that of the air
with which it is compared is infinitesimal. Absolutely con
sidered, however, this substance, notwithstanding its small
specific gravity, exercises a very potent action. Probably
from 10 to 15 per cent, of the heat radiated from the earth
is absorbed within 10 feet of the earth's surface. This
must evidently be of the utmost consequence to the life of
the world. Imagine the superficial molecules of the earth
trembling writh the motion of heat, and imparting it to the
surrounding ether ; this motion would be carried rapidly
away, and lost forever to our planet, if the waves of ether
had nothing but the air to contend with in their outward
course. But the aqueous vapor takes up the motion of the
ethereal waves, and becomes thereby heated, thus wrapping
the earth like a warm garment, and protecting its surface
from the deadly chill which it would otherwise sustain.
Various philosophers have speculated on the influence of
an atmospheric envelope. De Saussure, Fourier, M. Pouil-
let and Mr. Hopkins have, one and all, enriched scientific
literature with contributions on this subject, but the con
siderations which these eminent men have applied to atmos
pheric air, have, if my experiments be correct, to be trans
ferred to the aqueous vapor.

The observations of meteorologists furnish important,
though hitherto unconscious evidence of the influence of
this agent. Wherever the air is dry we are liable to daily
extremes of temperature. By day, in such places, the sun's
heat reaches the earth unimpeded, and renders the maxi
mum high ; by night, on the other hand, the earth's heat
escapes unhindered into space, and renders the minimum
low. Hence the difference between the maximum and min
imum is greatest where the air is driest. In the plains
of India, on the heights of the Himalaya, in central Asia, in

RADIATION. 197

Australia — wherever drought reigns, we have the heat of
day forcibly contrasted with the chill of night. In the Sa
hara itself, when the sun's rays cease to impinge on the
burning soil, the temperature runs rapidly down to freezing,
because there is no vapor overhead to check the calorific
drain. And here another instance might be added to the
numbers already known, in which Nature tends as it were
to check her own excess. By nocturnal refrigeration, the
aqueous vapor of the air is condensed to water on the sur
face of the earth, and as only the superficial portions ra
diate, the act of condensation makes water the radiating
body. Now experiment proves that to the rays emitted by
water, aqueous vapor is especially opaque. Hence the very
act of condensation, consequent on terrestrial cooling, 'be
comes a safeguard to the earth, imparting to its radiation
that particular character which renders it most liable to be
prevented from escaping into space.

It might however be urged that, inasmuch as we derive
all our heat from the sun, the self-same covering which pro
tects the earth from chill must also shut out the solar ra
diation. This is partially true, but only partially ; the
sun's rays are different in quality from the earth's rays, and
it does not at all follow that the substance which absorbs
the one must necessarily absorb the other. Through a
layer of water, for example, one-tenth of an inch in thick
ness, the sun's rays are transmitted with comparative free
dom ; but through a layer half this thickness, as Melloni has
proved, no single ray from the warmed earth could pass.
In like manner, the sun's rays pass with comparative free
dom through the aqueous vapor of the air ; the absorbing
power of this substance being mainly exerted upon the heat
that endeavors to escape from the earth. In consequence
of this differential action upon solar and terrestrial heat,
the mean temperature of our planet is higher than is due to
its distance from the sun.

198 FRAGMENTS OF SCIENCE.

13. Liquids and their Vapors in relation to JRadiant
Heat.

The deportment here assigned to atmospheric vapor has
been established by direct experiments on air taken from
the streets and parks of London, from the downs of Epsom,
from the hills and sea-beach of the Isle of Wight, and also
by experiments on air in the first instance dried, and after
ward rendered artificially humid by pure distilled water.
It has also been established in the following way : Ten
volatile liquids were taken at random and the power of
these liquids, at a common thickness, to intercept the waves
of heat was carefully determined. The vapors of the liquids
were next taken, in quantities proportional to the quantities
of liquid, and the power of the vapors to intercept the waves
of heat was also determined. Commencing with the sub
stance which exerted the least absorptive power, and pro
ceeding upward to the most energetic, the following order
of absorption was observed :

Liquids. Vapors.

Bisulphide of carbon. Bisulphide of carbon.

Chloroform. Chloroform.

Iodide of methyl. Iodide of methyl.

Iodide of ethyl Iodide of ethyl.

Benzol. Benzol.

Amylenc. Amylene.

Sulphuric ether. Sulphuric ether.

Acetic ether. Acetic ether.

Formic ether. Formic ether.

Alcohol. Alcohol.
Water.

We here find the order of absorption in both cases to
be the same. We have liberated the molecules from the
bonds which trammel them more or less in a liquid condi
tion ; but this change in their state of aggregation does not

RADIATION. 199

change their relative powers of absorption. Nothing could
more clearly prove that the act of absorption depends upon
the individual molecule, which equally asserts its power in
the liquid and the gaseous state. We may assuredly con
clude from the above table that the position of a vapor is
determined by that of its liquid. Now, at the very foot of
the list of liquids stands water, signalizing itself above all
others by its enormous power of absorption. And from
this fact, even if no direct experiment on the vapor of water
had ever been made, we should be entitled to rank that
vapor as the most powerful absorber of radiant heat hitherto
discovered. It has been proved by experiment that a shell
of air two inches in thickness surrounding our planet, and
saturated with the vapor of sulphuric ether, would intercept
35 per cent, of the earth's radiation. And though the
quantity of aqueous vapor necessary to saturate air is
much less than the amount of sulphuric ether vapor which
it can sustain, it is still extremely probable that the esti
mate already made of the action of atmospheric vapor
within 10 feet of the earth's surface, is altogether under
the mark ; and that we are ^indebted to this wonderful sub
stance, to an extent not accurately determined, but certainly
far beyond what has hitherto been imagined, for the tem
perature now existing at the surface of the globe.

14. Reciprocity of Radiation and Absorption.

Throughout the reflections which have hitherto occupied
us, the image before the mind has been that of a radiant
source generating calorific waves, which, on passing among
the scattered molecules of a gas or vapor, were intercepted
by those molecules in various degrees. In all cases it was
the transference of motion from the ether to the compara
tively quiescent molecules of the gas or vapor. We have
now to change the form of our conception, and to figure

200 FRAGMENTS OF SCIENCE.

these molecules not as absorbers, but as radiators, not as
the recipients, but as the originators of wave motion. That
is to say, we must figure them vibrating and generating in
the surrounding ether undulations which speed through it
with the velocity of light. Our object now is to inquire
whether the act of chemical combination, which proves so
potent as regards the phenomena of absorption, does not
also manifest its power in the phenomena of radiation. For
the examination of this question it is necessary, in the first
place, to heat our gases and vapors to the same tempera
ture, and then examine their power of discharging the
motion thus imparted to them upon the ether in which
they swing.

A heated copper ball was placed above a ring gas-
burner possessing a great number of small apertures, the
burner being connected by a tube with vessels containing
the various gases to be examined. By gentle pressure the
gases were forced through the orifices of the burner against
the copper ball, where each of them, being heated, rose in
an ascending column. A thermo-electric pile, entirely
screened off from the hot ball, was exposed to the radiation
of the warm gas, and the deflection of a magnetic needle
connected with the pile declared the energy of the radia
tion.

By this mode of experiment it was proved that the self
same molecular arrangement which renders a gas a power
ful absorber, renders it in the same degree a powerful
radiator — that the atom or molecule which is competent to
intercept the calorific waves is in the same degree compe
tent to generate them. Thus, while the atoms of element
ary gases proved themselves unable to emit any sensible
amount of radiant heat, the molecules of compound gases
were shown to be capable of powerfully disturbing the sur
rounding ether. By special modes of experiment the same
was proved to hold good for the vapors of volatile liquids,

RADIATION. 201

the radiative power of every vapor being found proportional
to its absorptive power.

The method of experiment here pursued, though not of
the simplest character, is still within your grasp. When
air is permitted to rush into an exhausted tube, the tem
perature of the air is raised to a degree equivalent to the
vis viva extinguished.1 Such air is said to be dynamically
heated, and if pure, it shows itself incompetent to radiate,
even when a rock-salt window is provided for the passage
of its rays. But if instead of being empty the tube contain
a small quantity of vapor, then the warmed air will com
municate heat by contact to the vapor, which will be thus
enabled to radiate. Thus the molecules of the vapor con
vert into the radiant form the heat imparted dynamically
to the atoms of the air. By this process, which has been
called dynamic radiation, the radiative power of both vapors
and gases has been determined, and the reciprocity of their
radiation and absorption proved. a

In the excellent researches of Leslie, De la Provostaye
and Desains, and Balfour Stewart, the reciprocity of radia
tion and absorption as regards solid bodies has been vari
ously illustrated ; while the labors, theoretical and experi
mental, of Kirchhoff have given this subject a wonderful
expansion, and enriched it by applications of the highest
kind. To their results are now to be added the foregoing,
whereby gases and vapors which have been hitherto thought
inaccessible to experiments of this kind are proved to ex
hibit the duality of radiation and absorption, the influence
on both of chemical combination being exhibited in the
most decisive and extraordinary way.

1 See page 20 for a definition of vis viva.

2 When heated, air imparts its motion to another gas or vapor ; the
transference of heat is accompanied by a change of vibrating period. The
dynamic radiation of vapors is rendered possible by the transmutation of
vibrations.

202 FRAGMENTS OF SCIENCE.

15. Influence of Vibrating Period and Molecular Form.
Physical Analysis of the Human Breath.

In the foregoing experiments with gases and vapors we
have employed throughout invisible rays ; some of these
bodies are so impervious that in lengths of a few feet only
they intercept every ray as effectually as a layer of pitch
would do. The substances, however, which show themselves
thus opaque to radiant heat are perfectly transparent to
light. Now the rays of light differ from those of invisible
heat only in point of period, the former faih'ng to affect the
retina because their periods of recurrence are too slow.
Hence, in some way or other the transparency of our gases
and vapors depends upon the periods of the waves which
impinge upon them. What is the nature of this depend
ence ? The admirable researches of Kirchlioff help us to an
answer. The atoms and molecules of every gas have cer
tain definite rates of oscillation, and those waves of ether
are most copiously absorbed whose periods of recurrence
synchronize with the periods of the molecules among which
they pass. Thus, when we find the invisible rays absorbed
and the visible ones transmitted by a layer of gas, we con
clude that the oscillating periods of the gaseous molecules
coincide with those of the invisible, and not with those of
the visible spectrum.

It requires some discipline of the imagination to form a
clear picture of this process. Such a picture is, however,
possible, and ought to be obtained. When the waves of
ether impinge upon molecules whose periods of vibration
coincide with the recurrence of the undulations, the timed
strokes of the waves, the vibration of the molecules aug
ments, as a heavy pendulum is set in motion by well-timed
puffs of breath. Millions of millions of shocks are received
every second from the calorific waves, and it is not difficult

RADIATION. 203

to see that, as every wave arrives just in time to repeat tbe
action of its predecessor, the molecules must finally be
caused to swing through wider spaces than if the arrivals
were not so timed. In fact, it is not difficult to see that an
assemblage of molecules, operated upon by contending
waves, might remain practically quiescent, and this is act
ually the case when the waves of the visible spectrum pass
through a transparent gas or vapor. There is here no sen
sible transference of motion from the ether to the molecules ;
in other words, there is no sensible absorption of heat.

One striking example of the influence of period may here
be recorded. Carbonic-acid gas is one of the feeblest of
absorbers of the radiant heat emitted by solid sources. It
is, for example, to a great extent transparent to the rays
emitted by the heated copper-plate already referred to.
There are, however, certain rays, comparatively few in num
ber, emitted by the copper, to which the carbonic acid is
impervious ; and could. we obtain a source of heat emitting
such rays only, we should find carbonic acid more opaque to
the radiation from that source than any other gas. Such a
source is actually found in the flame of carbonic oxide,
where hot carbonic acid constitutes the main radiating body.
Of the T&JS emitted by our heated plate of copper, olefiant
gas absorbs ten times the quantity absorbed by carbonic
acid. Of the rays emitted by a carbonic-oxide flame, car
bonic acid absorbs twice as much as olefiant gas. This won
derful change in the power of the former as an absorber is
simply due to the fact that the periods of the hot and cold
carbonic acid are identical, and that the waves from the
flame freely transfer their motion to the molecules which
synchronize with them. Thus it is that the tenth of an at
mosphere of carbonic acid, enclosed in a tube four feet long,
absorbs 60 per cent, of the radiation from a carbonic-oxide
flame, while one-thirtieth of an atmosphere absorbs 48 per
cent, of the heat from the same origin.

204 FRAGMENTS OF SCIENCE.

In fact, the presence of the minutest quantity of car
bonic acid may be detected by its action on the rays from
the carbonic-oxide flame. Carrying, for example, the dried
human breath into a tube four feet long, the absorption
there effected by the carbonic acid of the breath amounts
to 50 per cent, of the entire radiation. Radiant heat may
indeed be employed as a means of determining practically
the amount of carbonic acid expired from the lungs. My
late assistant, Mr. Barrett, has made this determination.
The absorption produced by the breath freed from its moist
ure, but retaining its carbonic acid, was first determined.
Carbonic acid artificially prepared was then mixed with dry
air in such proportions that the action of the mixture upon
the rays of heat was the same as that of the dried breath.
The percentage of the former being known, immediately
gave that of the latter. The same breath analyzed chemi
cally by Dr. Frankland, and physically by Mr. Barrett, gave
the following results :

Percentage of Carbonic Acid in the Human Breath.

Chemical analysis. Physical analysis.

4.66 4.56

6.33 5.22

It is thus proved that in the quantity of ethereal motion
which it is competent to take up, we have a practical meas
ure of the carbonic acid of the breath, and hence of the
combustion going on in the human lungs.

Still this question of period, though of the utmost im
portance, is not competent to account for the whole of the
observed facts. The ether, as far as we know, accepts
vibrations of all periods with the same readiness. To it
the oscillations of an atom of oxygen are just as acceptable
as those of a molecule of olefiant gas ; that the vibrating
oxygen then stands so far below the oleliant gas in radiant

RADIATION. 205

power must be referred not to period, but to some other
peculiarity of the elementary gas. The atomic group which
constitutes the molecule of olefiant gas, produces many
thousand times the disturbance caused by the oxygen, be
cause the group is able to lay a vastly more powerful hold
upon the ether than the single atoms can. The cavities and
indentations of a molecule composed of spherical atoms
may be one cause of this augmented hold. Another, and
probably very potent one may be, that the ether itself, con
densed and entangled among the constituent atoms of a
compound, virtually increases the magnitude of the group,
and hence augments the disturbance. But whatever may
be the fate of these attempts to visualize the physics of the
process, it will still remain true that, to account for the
phenomena of radiation and absorption we must take into
consideration the shape, size, and complexity of the mole
cules by which the ether is disturbed.

16. Summary and Conclusion.

Let us now cast a momentary glance over the ground
that we have left behind. The general nature of light and
heat was first briefly described : the compounding of matter
from elementary atoms and the influence of the act of com
bination on radiation and absorption were considered and
experimentally illustrated. Through the transparent ele
mentary gases radiant heat was found to pass as through a
vacuum, while many of the compound gases presented
almost impassable obstacles to the calorific waves. This
deportment of the simple gases directed our attention to
other elementary bodies, the examination of which led to
the discovery that the element iodine, dissolved in bisul
phide of carbon, possesses the power of detaching, with
extraordinary sharpness, the light of the spectrum from its
heat, intercepting all luminous rays up to the extreme red,

206 FRAGMENTS OF SCIENCE.

and permitting the calorific rays beyond the red to pass
freely through it. This substance was then employed to
filter the beams of the electric light, and to form foci of .
invisible rays so intense as to produce almost all the effects
obtainable in an ordinary fire. Combustible bodies were
burnt and refractory ones were raised to a white heat by the
concentrated invisible rays. Thus, by exalting their rc-
frangibility, the invisible rays of the electric light were
rendered visible, and all the colors of the solar spectrum
were extracted from utter darkness. The extreme richness
of the electric light in invisible rays of low refrangibility
was demonstrated, one-ninth only of its radiation consisting
of luminous rays. The deadness of the optic nerve to those
invisible rays was proved, and experiments were then
added, to show that the bright and the dark rays of a
solid body raised gradually to intense incandescence, are
strengthened together ; intense dark heat being an inva
riable accompaniment of intense white heat. A sun could
not be formed, or a meteorite rendered luminous, on any
other condition. The light-giving rays, constituting only a
small fraction of the total radiation, their unspeakable im
portance to us is due to the fact that their periods are
attuned to the special requirements of the eye.

Among the vapors of volatile liquids vast differences
were also found to exist, as regards their powers of absorp
tion. We followed various molecules from a state of liquid
to a state of gas, and found in both states of aggregation,
the power of the individual molecules equally asserted.
The position of a vapor as an absorber of radiant heat was
shown to be determined by that of the liquid from which it
is derived. Reversing our conceptions, and regarding the
molecules of gases and vapors not as the recipients, but as
the originators of wave-motion; not as absorbers but as
radiators ; it was proved that the powers of absorption and
radiation went hand in hand, the self-same chemical act

RADIATION. 207

which rendered a body competent to intercept the waves
of ether, rendering it competent in the same degree to gen
erate them. Perfumes were next subjected to examination,
and notwithstanding their extraordinary tenuity, they were
found vastly superior, in point of absorptive power, to the
body of the air in which they were diffused. We were led
thus slowly up to the examination of the most widely
diffused and most important of all vapors — the aqueous
vapor of our atmosphere — and we found in it a potent
absorber of the purely calorific rays. The power of this
substance to influence climate, and its general influence
on the temperature of the earth, were then briefly dwelt
upon. A cobweb spread above a blossom is sufficient to
protect it jrom nightly chill ; and thus the aqueous vapor
of our air, attenuated as it is, checks the drain of terrestrial
heat, and saves the surface of our planet from the refriger
ation which would assuredly accrue, were no such sub
stance interposed between it and the voids of space. We
considered the influence of vibrating period and molecular
form on absorption and radiation, and finally deduced, from
its action upon radiant heat, the exact amount of carbonic
acid expired by the human lungs.

Thus in brief outline were placed before you some of
the results of recent inquiries in the domain of Radiation,
and my aim throughout has been to raise in your minds
distinct physical images of the various processes involved
in our researches. It is thought by some that natural
science has a deadening influence on the imagination, and
a doubt might fairly be raised as to the value of any study
which would necessarily have this effect. But the experi
ence of the last hour must, I think, have convinced you
that the study of natural science goes hand in hand with
the culture of the imagination. Throughout the greater
part of this discourse we have been sustained by this
faculty. We have been picturing atoms, and molecules,

208 FRAGMENTS OF SCIENCE.

and vibrations, and waves, which eye has never seen nor
ear heard, and which can only be discerned by the exercise
of imagination. This, in fact, is the faculty which enables
us to transcend the boundaries of sense, and connect the
phenomena of our visible world with those of an invisible
one. Without imagination we never could have risen to
the conceptions which have occupied us here to-day ; and
in proportion to your power of exercising this faculty aright,
and of associating definite mental images with the terms
employed, will be the pleasure and the profit which you
will derive from this lecture. The outward facts of Nature
are insufficient to satisfy the mind. We cannot be content
with knowing that the light and heat of the sun illuminate
and warm the world. We are led irresistibly to inquire
what is light, and what is heat ? and this question leads us
at once out of the region of sense into that of imagination.
Thus pondering, and questioning, and striving to sup
plement that which is felt and seen, but which is incom
plete, by something unfelt and unseen which is necessary
to its completeness, men of genius have in part discerned,
not only the nature of light and heat, but also, through
them, the general relationship of natural phenomena. The
working power of Nature is the power of actual or poten
tial motion, of which all its phenomena are but special
forms. This motion manifests itself in tangible and in in
tangible matter, being incessantly transferred from the one
to the other, and incessantly transformed by the change.
It is as real in the waves of the ether as in the waves of
the sea ; the latter, derived as they are from winds, which
in their turn are derived from the sun, being nothing more
than the heaped-up motion of the former. It is the calo
rific waves emitted by the sun which heat our air, produce
our winds, and hence agitate our ocean. And whether they
break in foam upon the shore, or rub silently against the
ocean's bed, or subside by the mutual friction of their own

RADIATION. 209

parts, the sea-waves, which cannot subside without pro
ducing heat, finally resolve themselves into waves of ether,
thus regenerating the motion from which their temporary
existence was derived. This connection is typical. Nature
is not an aggregate of independent parts, but an organic
whole. If you open a piano and sing into it, a certain
string will respond. Change the pitch of your voice ; the
first string ceases to vibrate, but another replies. Change
again the pitch ; the first two strings are silent, while an
other resounds. Now, in altering the pitch you simply
change the form of the motion communicated by your vocal
chords to the air, one string responding to one form, and
another to another. And thus is sentient man acted on by
Nature, the optic, the auditory, and other nerves of the
human body being so many strings differently tuned and
responsive to different forms of the universal power.

NOTE. — The statements regarding the action of aqueous vapor, made
in sections 12 and 13 of this Lecture, have been controverted by the late
Professor Magnus, of Berlin. I therefore wish the reader to hold in sus
pension his judgment of these two sections until new light can be thrown
upon the subject. This will soon be done.

IX.
OK RADIANT HEAT

IN RELATION TO THE COLOR AND CHEMICAL CONSTITUTION
OF BODIES.

A DISCOURSE.

DELIVERED IN THE KOYAL INSTITUTION OF GKEAT BEITAIN.

January 19, 1866.

" I took a number of little square pieces of broadcloth from a tailor's
pattern-card, of various colors. They were black, deep blue, lighter blue,
green, purple, red. yellow, white, and other colors, or shades of color. I
laid them all out upon the snow on a bright, sunshiny morning. In a few
hours (I cannot now be exact as to the time), the black, being warmed
most by the sun, was sunk so low as to be below the stroke of the sun's
rays ; the dark blue almost as low, the lighter blue not quite so much as
the dark, the other colors less as they were lighter. The white remained
on the surface of the snow, not having entered it at ah".

" What signifies philosophy that does not apply to some use ? May
we not learn from hence that black clothes are not so fit to wear in a hot,
sunny climate or season as white ones ; because in such clothes the body
is more heated by the sun when we walk abroad, and are at the same time
heated by the exercise, which double heat is apt to bring on putrid, dan
gerous fevers ? That soldiers and seamen, who must march and labor in
the sun, should, in the East or West Indies, have a uniform of white ?
That summer hats for men or women should be white, as repelling that
heat which gives headaches to so many, and to some the fatal stroke that
the French call coup dc sokil ? That the ladies' summer hats, however,
should be lined with black, as not reverberating on their faces those rays
which are reflected upward from the earth or water ? That the putting
of a white cap of paper or linen within the crown of a black hat, as most
do, will not keep out the heat, though it would if placed without ? That
fruit walls being blacked may receive so much heat from the sun in the
daytime as to continue warm in some degree through the night, and
thereby preserve the fruit from frosts, or forward its growth — with sun
dry other particulars of greater or less importance that will occur from
time to time to attentive minds ? "

BENJAMIN* FRANKLIN,
Letter to Miss Mary Stevenson.

IX.

ON RADIANT HEAT IN RELATION TO THE COLOR
AND CHEMICAL CONSTITUTION OF BODIES,

ONE of the most important functions of physical sci
ence, considered as a discipline of the mind, is to enable us by
means of the tangible processes of Nature to apprehend the
intangible. The tangible processes give direction to the
line of thought • but this once given, the length of the line
is not limited by the boundaries of the senses. Indeed, the
domain of the senses in Nature is almost infinitely small in
comparison with the vast region accessible to thought
which lies beyond them. From a few observations of a
comet, when it comes within the range of his telescope, an
astronomer can calculate its path in regions which no tele
scope can reach ; and in like manner, by means of data
furnished in the narrow world of the senses, we make our
selves at home in other and wider worlds, which can be
traversed by the intellect alone.

From the earliest ages the questions, " What is light ? "
and " What is heat ? " have occurred to the minds of men ;
but these questions never would have been answered had
they not been preceded by the question, " What is sound ? "
Amid the grosser phenomena of acoustics the mind was
first disciplined, conceptions being thus obtained from
direct observation, which were afterward applied to phe
nomena of a character far too subtle to be observed directly.
Sound we know to be due to vibratory motion. A vibrating

214 FRAGMENTS OF SCIEXCE.

tuning-fork, for example, moulds the air round it into un
dulations or waves, which speed away on all sides with a
certain measured velocity, impinge upon the drum of the
ear, shake the auditory nerve, and awake in the brain the
sensation of sound. When sufficiently near a sounding
body, we can feel the vibrations of the air. A deaf man,
for example, plunging his hand into a bell when it is
sounded, feels through the common nerves of his body those
tremors which, when imparted to the nerves of healthy ears,
are translated into sound. There are various ways of ren
dering those sonorous vibrations not only tangible but
visible; and it was not until numberless experiments of
this kind had been executed, that the scientific investigator
abandoned himself wholly, and without a shadow of uncer
tainty, to the conviction that what is sound within us is,
outside of us, a motion of the air.

But once having established this fact — once having
proved beyond all doubt that the sensation of sound is
produced by an agitation of the nerve of the ear, the
thought soon suggested itself that light might be due to
an agitation of the nerve of the eye. This was a great step
in advance of that ancient notion which regarded light as
something emitted by the eye, and not as any thing
imparted to it. But if light be produced by an agitation
of the optic nerve or retina, what is it that produces the
agitation ? Newton, you know, supposed minute particles
to be shot through the humors of the eye against the
retina, which hangs like a target at the back of the eye.
The impact of these particles against the target, Newton
believed to be the cause of light. But Newton's notion
has not held its ground, being entirely driven from the
field by the more wonderful and far more philosophical
notion that light, like sound, is a product of wave-motion.

The domain in which this motion of light is carried on
lies entirely beyond the reach of our senses. The \\

RADIANT HEAT AND ITS RELATIONS. 215

of light require a medium for their formation and propaga
tion, but we cannot see, or feel, or taste, or smell this
medium. How, then, has its existence been established ?
By showing that by the assumption of this wonderful
intangible ether all the phenomena of optics are accounted
for with a fulness and clearness and collusiveness which
leave no desire of the intellect unfulfilled. When the law
of gravitation first suggested itself to the mind of Newton,
what did he do ? He set himself to examine whether it
accounted for all the facts. He determined the courses of
the planets ; he calculated the rapidity of the moon's fall
toward the earth ; he considered the precession of the
equinoxes, the ebb and flow of the tides, and found all
explained by the law of gravitation. He therefore regarded
this law as established, and the verdict of science sub
sequently confirmed his conclusion. On similar, and, if
possible, on stronger grounds, we found our belief in the
existence of the universal ether. It explains facts far
more various and complicated than those on which New
ton based his law. If a single phenomenon could be
pointed out which the ether is proved incompetent to
explain, we should have to give it up ; but no such phe
nomenon has ever been pointed out. It is, therefore, at
least as certain that space is filled with a medium by
means of which suns and stars diffuse their radiant power,
as that it is traversed by that force which holds, not only
our planetary system, but the immeasurable heavens them
selves, in its grasp.

There is no more wonderful instance than this of the
production of a line of thought from the world of the senses
into the region of pure imagination. I mean by imagination
here, not that play of fancy which can give to " airy nothing
a local habitation and a name," but that power which
enables the mind to conceive realities which lie beyond the
range of the senses — to present to itself distinct physical

216 FRAGMENTS OF SCIENCE.

images of processes which, though mighty in the aggregate
beyond all conception, are so minute individually as to
elude all observation. It is the waves of air excited by
this tuning-fork which render its vibrations audible. It is
the waves of ether sent forth from those lamps overhead
which render them luminous to us ;laut so minute are these
waves, that it would take from 30,000 to 60,000 of them
placed end to end to cover a single inch. Their number,
however, compensates for their minuteness. Trillions of
them have entered your eyes and hit the retina at the back
of the eye in the time consumed in the utterance of the
shortest sentence of this discourse. This is the steadfast
result of modern research ; but we never could have reached
it without previous discipline. ("We never could have
measured the waves of light, nor even imagined them to
exist, had we not previously exercised ourselves among the
waves of sound. Sound and light are now mutually help
ful, the conceptions of each being expanded, strengthened,
and defined, by the conceptions of the other.

The ether which conveys the pulses of light and heat
not only fills the celestial spaces, bathing the sides of suns
and planets, but it also encircles the atoms of which these
suns and planets are composed. It is the motion of these
atoms, and not that of any sensible parts of bodies, that
the ether conveys ; it is this motion that constitutes the
objective cause of wrhat in our sensations are light and
/neat. An atom, then, sending its pulses through the infi-
V, nite ether, resembles a tuning-fork sending its pulses
through the air. Let us look for a moment at this thrilling
ether, and briefly consider its relation to the bodies whose
vibrations it conveys. Different bodies, when heated to the
same temperature, possess very different powers of agitat
ing the ether: some are good radiators, others are bad
radiators ; which means that some are so constituted as to
communicate their motion freely to the ether, producing

RADIANT HEAT AND ITS RELATIONS. 217

therein powerful undulations; while others are unable
thus to communicate their motion, but glide through the
ether without materially disturbing its repose. Recent
experiments have proved that elementary bodies, except
under certain anomalous conditions, belong to the class of
bad radiators. An atom vibrating in the ether resembles
this naked tuning-fork vibrating in the air. The amount
of motion communicated to the air by these thin prongs is
too small to evoke at any distance the sensation of sound.
But if we permit the atoms to combine chemically and
form molecules, the result in many cases is an enormous
change in the power of radiation. The amount of ethereal
disturbance produced by the combined atoms of a body
may be many thousand times that produced by its constitu
ent atoms when uncombined. The effect is roughly typi
fied by this tuning-fork when connected with its resonant
case. The fork and its case now swing as a compound
system, and the vibrations which were before inaudible, are
now the source of a musical sound so powerful that it
might be plainly heard by thousands at once. The fork
and its case combined may be roughly regarded as a good
radiator of sound.

The pitch of a musical note depends upon the rapidity
of its vibrations, or, in other words, on the length of its
waves. Now, the pitch of a note answers to the color of
light. Taking a slice of white light from the beam of an
electric lamp, I cause that light to pass through an arrange
ment of prisms. It is decomposed, and we have the effect
obtained by Newton, who first unrolled the solar beam into
the splendors of the solar spectrum. At one end of this
spectrum we have red light, at the other violet, and be
tween those extremes lie the other prismatic colors. As
we advance along the spectrum from the red to the violet,
the pitch of the light — if I may use the expression — height
ens, the sensation of violet being produced by a more rapid
10

218 FRAGMENTS OF SCIENCE.

succession of impulses than that which produces the im
pression of red. The vibrations of the violet are about
twice as rapid as those of the red ; in other words, the
range of the visible spectrum is about an octave.

There is no solution of continuity in this spectrum ;
one color changes into another by insensible gradations.
It is as if an infinite number of tuning-forks, of gradually
augmenting pitch, were vibrating at the same time. But
turning to another spectrum — that, namely, obtained from
the incandescent vapor of silver — you observe that it con
sists of two narrow and intensely luminous green bands.
Here it is as if two forks only, of slightly different pitch,
were vibrating. The length of the waves which produce
this first band is such that 47,460 of them, placed end to
end, would fill an inch. The waves which produce the
second band are a little shorter ; it would take of these
47,920 to fill an inch. In the case of the first band, the
number of impulses imparted in one second to every
eye which now sees it, is 577 millions of millions ; while
the number of impulses imparted in the same time by the
second band is GOO millions of millions. I now cast upon
the screen before you the beautiful stream of green light
from which these bands were derived. This luminous
stream is the incandescent vapor of silver. The rates of
vibration of the atoms of that vapor are as rigidly fixed as
those of two tuning-forks; and to whatever height the
temperature of the vapor may be raised, the rapidity of its
vibrations, and consequently its color, which wholly de
pends upon that rapidity, remains unchanged.

The vapor of water, as well as the vapor of silver, has
its definite periods of vibration, and these are such as to
disqualify the vapor, when acting freely as such, from
being raised to a white heat. The oxyhydrogen flame, for
example, consists of hot aqueous vapor. It is scarcely
visible in the air of this room, and it would be still leas

RADIANT HEAT AND ITS RELATIONS. 219

visible if we could burn the gas in a clean atmosphere.
But the atmosphere, even at the summit of Mont Blanc,
is dirty ; in London it is more than dirty ; and the burning
dirt gives to this flame the greater portion of its present
light. But the heat of the flame is enormous. Cast-iron
fuses at a temperature of 2,000° Fahr. A piece of platinum
is heated to vivid redness at a distance of two inches be
yond the visible termination of the flame. The vapor
which produces incandescence is here absolutely dark. In
the flame itself the platinum is raised to dazzling white
ness, and is finally pierced by the flame. When this flame
impinges on a piece of lime, we have the dazzling Drum-
mond light. But the light is here due to the fact that
when it impinges upon the solid body, the vibrations ex
cited in that body by the flame are of periods different from
its own.

Thus far we have fixed our attention on atoms and
molecules in a state of vibration, and surrounded by a
medium which accepts their vibrations, and transmits them
through space. But suppose the waves generated by one
system of molecules to impinge upon another system, how
will the waves be affected ? Will they be stopped, or will
they be permitted to pass ? Will they transfer their mo
tion to the molecules on which they impinge, or will they
glide round the molecules, through the intermolecular
spaces, and thus escape ?

The answer to this question depends upon a condition
which may be beautifully exemplified by an experiment on
sound. These two tuning-forks are tuned absolutely alike.
They vibrate with the same rapidity, and mounted thus
upon their resonant stands, you hear them loudly sounding
the same musical note. I stop one of the forks, and throw
the other into strong vibration. I now bring that other
near the silent fork, but not into contact with it. Allow
ing them to continue in this position for four or five seconds,

220 FRAGMENTS OF SCIENCE.

I stop the vibrating fork ; but the sound has not ceased.
The second fork has taken up the vibrations of its neigh
bor, and is now sounding in its turn. I dismount one of
the forks, and permit the other to remain upon its stand.
I throw the dismounted fork into strong vibration, but you
cannot hear it sound. Detached from its stand the amount
of motion which it can communicate to the air is too small
to make itself sensible to the ear at any distance. I now
bring the dismounted fork close to the mounted one, but
not into actual contact with it. Out of the silence rises a
mellow sound. "Whence comes it ? From the vibrations
which have been transferred from the dismounted fork to
the mounted one.

That motion should thus transfer itself through the air
it is necessary that the two forks should be in perfect unison.
If I place on one of the forks a morsel of wax not larger
than a pea, it is rendered thereby powerless to affect, or to
be affected by, the other. It is easy to understand this
experiment. The pulses of the one fork can affect the other,
because they are perfectly timed. A single pulse causes
the prong of the silent fork to vibrate through an infinitesi
mal space. But just as it has completed this small vibra
tion, another pulse is ready to strike it. Thus, the small
impulses add themselves together. In the five seconds
during which the forks were held near each other, the vi
brating fork sent 1,280 waves against its neighbor, and
those 1,280 shocks, all delivered at the proper moment, all,
as I have said, perfectly timed, have given such strength
to the vibrations of the mounted fork as to render them
audible to you all.

Let me give you one other curious illustration 'of the
influence of synchronism on musical vibrations. Here are
three small gas-flames inserted in three glass tubes of dif
ferent lengths. Each of these flames can be caused to emit
a musical note, the pitch of which is determined by the

RADIANT HEAT AND ITS RELATIONS. 221

length of the tube surrounding the flame. The shorter the
tube the higher is the pitch. The flames are now silent
within their respective tubes, but each of them can be
caused to respond to a proper note sounded anywhere in
this room. Here is an instrument called a siren, by which
a powerful musical note can be produced. Beginning with
a note of low pitch, and ascending gradually to a higher
one, I finally reach the note of the flame in the longest tube.
The moment it is reached, the flame bursts into song. But
the other flames are still silent within their tubes. I urge
the instrument on to higher notes ; the second flame has
now started, and the third alone remains. But a still higher
note starts it also. Thus, as the sound of the siren rises
gradually in pitch, it awakens every flame in passing, by
striking it with a series of waves whose periods of recur
rence are similar to its own.

Now the wave-motion from the siren is in part taken up
by the flame which synchronizes with the waves ; and had
these waves to impinge upon a multitude of flames, instead
of upon one flame only, the transference might be so great
as to absorb the whole of the original wave-motion. Q Let
us apply these facts to radiant heat. This blue flame~is
the flame of carbonic oxide ; this transparent gas is carbonic-
acid gas. In the blue flame we have carbonic acid intensely
heated ; or, in other words, in a state of intense vibration.
It thus resembles the sounding tuning-fork, while this cold
carbonic acid resembles the silent one. What is the con
sequence ? Through the synchronism of the hot and cold
gas transmission of motion through the gas is prevented ;
it is all transferred. The cold gas is intensely opaque to
the radiation from this particular flame, though highly
transparent to heat of every other land. We are here
manifestly dealing with that great principle which lies at
the basis of spectrum analysis, and which has enabled
scientific men to determine the substances of which the sun,

222^ FRAGMENTS OF SCIENCE.

the stars, and even the nebulae, are composed : the principle,
namely, that a body which is competent to emit any ray,
whether of heat or light, is competent in the same degree
to absorb that ray. The absorption depends on the syn
chronism which exists between the vibrations of the atoms
from which the rays, or more correctly the leaves , issue, and
those of the atoms against which they impinge.

To its incompetence to emit white light, aqueous vapor
adds incompetence to absorb white light. It cannot, for
example, absorb the luminous rays of the sun, though it
can absorb the non-luminous rays of the earth. This in
competence of aqueous vapor to absorb luminous rays is
shared by water and ice — in fact, by all really transparent
substances. Their transparency is due to their inability to
absorb luminous rays. The molecules of such substances
are in dissonance with the luminous waves, and hence such
waves pass through transparent substances without dis
turbing the molecular rest. A purely luminous beam, how
ever intense may be its heat, is sensibly incompetent to
melt the smallest particle of ice. We can, for example,
converge a powerful luminous beam upon a surface covered
with hoar-frost without melting a single spicula of the ice-
crystals. How then, it may be asked, are the snows of the
Alps swept away by the sunshine of summer ? I answer
they are not swept away by sunshine at all, but by solar
rays which have no sunshine whatever in them. The lumi
nous rays of the sun fall upon the snow-fields and arc flashed
in echoes from crystal to crystal, but they find next to no
lodgment within the crystals. They are hardly at all ab
sorbed, and hence they cannot produce fusion. But a body
of powerful dark rays is emitted by the sun, and it is these
rays that cause the glaciers to shrink and the snows to dis
appear ; it is they that fill the banks of the Arve and Ar-
veyron, and liberate from their frozen captivity the Rhone
and the Rhine.

RADIANT HEAT AND ITS RELATIONS. 223

Placing a concave silvered mirror behind the electric
light I converge its rays to a focus of dazzling brilliancy.
I place in the path of the rays, between the light and the
focus, a vessel of water, and now introduce at the focus a
piece of ice. The ice is not melted by the concentrated
beam which has passed through the water, though matches
are ignited at the focus and wood is set on fire. The pow
erful heat, then, of this luminous beam is incompetent to
melt the ice. I withdraw the cell of water ; the ice imme
diately liquefies, and you see the water trickling from it
in drops. I reintroduce the cell of water; the fusion is
arrested and the drops cease to fall. The transparent water
of the cell exerts no sensible absorption on the luminous
rays, still it withdraws something from the beam, which,
wyhen permitted to act, is competent to melt the ice. This
something is the dark radiation of the electric light. Again,
I place a slab of pure ice in front of the electric lamp ; send
a luminous beam first through our cell of water and then
through the ice. By means of a lens an image of the slab
is cast upon a white screen. The beam, sifted by the water,
has no power upon the ice. But observe what occurs when
the water is removed ; we have here a star and there a star,
each star resembling a flower of six petals, and growing
visibly larger before our eyes. As the leaves enlarge their
edges become serrated, but there is no deviation from the
six-rayed type. We have here, in fact, the crystallization
of the ice inverted by the invisible rays of the electric beam.
They take the molecules down in this wonderful way, and
reveal to us the exquisite atomic structure of the substance
with which Nature every winter roofs our ponds and lakes.

Numberless effects, apparently anomalous, might be ad
duced in illustration of the action of these lightless rays.
Here, for example, are two powders, both white, and undis-
tinguishable from each other by the eye. The luminous
rays of the lamp are unabsorbed by both powders — from

224 FRAGMENTS OF SCIENCE.

those rays they acquire no heat ; still one of the substances,
sugar, is heated so highly by the concentrated beam of the
electric lamp that it first smokes violently and then inflames,
while the other substance, salt, is barely warmed at the
focus. Here, again, are two perfectly transparent liquids
placed in a test-tube at the focus ; one of them boils in a
couple of seconds, while the other in a similar position is
hardly warmed. The boiling-point of the first liquid is 78°
C., which is speedily reached; that of the second liquid is
only 48° C., which is never reached at all. These anoma
lies are entirely due to the unseen element which mingles
with the luminous rays of the electric beam, and, indeed,
constitutes 90 per cent, of its calorific power.

I have here a substance by which these dark rays may
be detached from the total emission of the electric lamp.
This ray-filter is a black liquid — that is to say, black as
pitch to the luminous, but bright as a diamond to the non-
luminous radiation. It mercilessly cuts off the former, but
allows the latter free transmission. I bring these invisible
rays to a focus at a distance of several feet frcm the electric
lamp ; the dark rays form there an invisible image of the
source from which they issue. By proper means this in
visible image may be transformed into a visible one of "daz
zling brightness. I could, moreover, show you, if .time per
mitted, how out of those perfectly dark rays we might ex
tract, by a process of transmutation, all the colors of the
solar spectrum. I could also prove to you that those rays,
powerful as they are, and sufficient to fuse many metals,
may be permitted to enter the eye and to break upon the
retina without producing the least luminous impression.

The dark rays are now collected before you ; you see
nothing at their place of convergence ; with a proper ther
mometer it could be proved that even the air at the focus
is just as cold as the surrounding air. And mark the con
clusion to which this leads'. It proves the ether at the focus

RADIANT HEAT AND ITS RELATIONS. 225

to be practically detached from the air — that the most vio
lent ethereal motion may there exist without the least
aerial motion. But though you see it not, there is suffi
cient heat at that focus to set London on fire. The heat
there at the present, moment is competent to raise iron to a
temperature at which it throws off brilliant scintillations.
It can heat platinum to whiteness and almost fuse that re
fractory metal. It actually can fuse gold, silver, copper,
and aluminium. The moment, moreover, that wood is
placed at the focus it bursts into a blaze.

It has been already affirmed that whether as regards ra
diation or absorption the elementary atoms possess but little
power. This might be illustrated by a long array of facts ;
and one of the most singular of these is furnished by the
deportment of that extremely combustible substance, phos
phorus, when placed at this dark focus. It is impossible to
ignite there a fragment of amorphous phosphorus. But or
dinary phosphorus is a far quicker combustible, and its de
portment to radiant heat is still more impressive. It may
be exposed to the intense radiation of an ordinary fire with
out bursting into flame. It may also be exposed for twenty
or thirty seconds at an obscure focus of sufficient power to
raise platinum to a white heat, without ignition. Notwith
standing the energy of the ethereal waves here concentrated,
notwithstanding the extremely inflammable character of
the elementary body exposed to their action, the atoms of
that body refuse to partake of the motion of the waves, and
consequently cannot be powerfully affected by their heat.

The knowledge which we now possess will enable us to
analyze with profit a practical question. White dresses are
worn in summer because they are found to be cooler than
dark ones. The celebrated Benjamin Franklin made the fol
lowing experiment: He placed bits of cloth of various colors
upon snow, exposed them to direct sunshine, and found that
they sank to different depths in the snow. The black cloth

226 FRAGMENTS OF SCIENCE.

sank the deepest, the white did not sink at all. Franklin
inferred from his experiment that black bodies are tke best
absorbers, and white ones the worst absorbers, of radiant
heat. Let us test the generality of this conclusion. I have
here two cards, one of which is coated with a very dark
powder, and the other with a perfectly white one. I place
the powdered surfaces before the fire, and leave them there
until they have acquired as high a temperature as they ran
attain in this position. Which of the cards is most highlyi
heated ? It requires no thermometer to answer this ques
tion ? Simply pressing the back of the card, on which the
white powder is strewn, against my cheek or forehead, I
find it intolerably hot. Placipg the dark card in the same
position I find it cool. The white powder has absorbed far
more heat than the dark one. This simple result abolishes
a hundred conclusions which have been hastily drawn from
the experiment of Franklin. Again, here are suspended
two delicate mercurial thermometers at the same distance
from a gas-flame. The bulb of one of them is covered by a
dark substance, the bulb of the other by a white one. Both
bulbs have received the radiation from the flame, but the
white bulb has absorbed most, and its mercury stands much
higher than that of the other thermometer. I might vary
this experiment in a hundred ways, and show you that from
the darkness of a body you can draw no certain conclusion
i < 'Carding its power of absorption.

The reason of this simply is, that color gives us intelli
gence of only one portion, and that the smallest one, of
the rays impinging on the colored body. Were the rays
all luminous we might with certainty infer from the color
of a body its power of absorption ; but the great mass of
the radiation from our fire, our gas-flame, and even from
the sun itself, consists of invisible calorific rays, regard in:.';
which color teaches us nothing. A body may be highly trans
parent to one class of rays, and highly opaque to the othrr

RADIANT HEAT AND ITS RELATIONS. 227

class. Thus the white powder, which has shown itself so
powerful an absorber, has been specially selected on account
of its extreme perviousness to the visible rays, and its ex
treme imperviousness to the invisible ones ; while the dark
powder was chosen on account of its extreme transparency
to the invisible, and its extreme opacity to the visible rays.
In the case of the radiation from our fire, about 98 per cent,
of the whole emission consists of invisible rays ; the body,
therefore, which was most opaque to these triumphed as
an absorber, though that body was a white one. _

I would here invite you to consider the manner in
which we obtain from natural facts what may be called
their intellectual value. Throughout the processes of Na
ture there is interdependence and harmony, and the main
value of our science, considered as a mental discipline, con
sists in the tracing of this interdependence and the demon
stration of this harmon}\ The outward and visible phe
nomena are with us the counters of the intellect ; and our
science would not be worthy of its name and fame if it
halted at facts, however practically useful, and neglected
the laws which accompany and rule phenomena. Let us
endeavor, then, to extract from the experiment of Franklin
its full intellectual value, calling to our aid the knowledge
which our predecessors have already stored. Let us im
agine two pieces of cloth of the same texture, the one
black and the other white, placed upon sunned snow. Fix
ing our attention on the white piece, let us inquire whether
there is any reason to expect that it will sink into the
snow at all. There is knowledge at hand which enables
us to reply at once in the negative. There is, on the con
trary, reason to expect that after a sufficient exposure the
bit of cloth will be found on an eminence instead of in a
hollow ; that instead of a depression, we shall have a rela
tive elevation of the bit of cloth. For, as regards the lu
minous rays of the sun, the cloth and the snow are alike

228 FRAGMENTS OF SCIENCE.

powerless; the one cannot be warmed, nor the other
melted, by such rays. The cloth is white and the snow is
white, because their confusedly mingled particles and fibres
are incompetent to absorb luminous rays. Whether, then,
the cloth will sink or not depends entirely upon the dark
rays of the sun. Now the substance which absorbs the
dark rays of the sun with the greatest avidity is ice — or
snow, which is merely ice in powder. A less amount of
heat will be lodged in the cloth than in the surrounding
snow. The cloth must, therefore, act as a shield to the
snow on which it rests ; and in consequence of the more
rapid fusion of the exposed snow, the cloth must in due
time be left behind, perched upon an eminence like a gla
cier-table.

But though the snow transcends the cloth both as a
radiator and absorber, it does not much transcend it.
Cloth is very powerful in both these respects. Let us
now turn our attention to the piece of black cloth,' the
texture and fabric of which I assume to be the, same as
that of the white. For our object being to compare the
effects of color, we must, in order to study this effect in its
purity, preserve all other conditions constant. Let us then
suppose the black cloth to be obtained from the dyeing
of the white. The cloth itself, without reference to the
dye, is nearly as good an absorber of heat as the snow
around it. But to the absorption of the dark solar rays
by the undyed cloth is now added the absorption of the
whole of the luminous rays, and this great additional in
flux of heat is far more than sufficient to turn the balance
in favor of the black cloth. The sum of its actions on the
dark and luminous rays exceeds the action of the snow
on the dark rays alone. Hence the cloth will sink in the
snow, and this is the philosophy of Franklin's experi
ment.

Throughout this discourse the main stress has been laid

RADIANT HEAT AND ITS RELATIONS. 229

on chemical constitution, as influencing most powerfully
the phenomena of radiation and absorption. With regard
to gases, vapors, and to the liquids from which these va
pors are derived, it has been proved by the most varied
and conclusive experiments that the acts of radiation and
absorption are molecular — that they depend upon chemical
and not upon mechanical condition. In attempting to ex
tend this principle to solids I was met by a multitude of
facts obtained by celebrated experimenters, which seemed
flatly to forbid such extension. Melloni, for example, found
the same radiant and absorbent power for chalk and lamp
black. MM. Masson and Courtepee performed a most
elaborate series of experiments on chemical precipitates of
various kinds, and found that they one and all manifested
the same power of radiation. They concluded from their
researches, that where bodies are reduced to an extremely
fine state of division the influence of this state is so power
ful as entirely to mask and override whatever influence
may be due to chemical constitution.

But it appears to me that through the whole of these
researches a serious oversight has run, the mere mention
of which will show you what caution is essential in the
operations of experimental philosophy. Let me state
wherein I suppose this oversight to consist. I have here
a metal cube with two of its sides brightly polished. I
fill the cube with boiling water and determine the quan
tity of heat emitted by the two bright surfaces. One of
them far transcends the other as a radiator of heat. Both
surfaces appear to be metallic ; what, then, is the cause of
the observed difference in their radiative power ? Simply
this: I have coated, one of the surfaces with transparent
gum, through which, of course, is seen the metallic lustre
behind. Now this varnish, though so perfectly transparent
to luminous rays, is as opaque as pitch or lamp-black to
non-luminous ones. It is a powerful emitter of dark rays ;

230 FRAGMENTS OF SCIENCE.

it is also a powerful absorber. While, therefore, at the
present moment it is copiously pouring forth radiant heat
itself, it does not allow a single ray from the metal behind
to pass through it. The varnish then, and not the metal, is
the real radiator.

Now Melloni, and Masson, and Court6p6e, experimented
thus : they mixed their powders and precipitates with
gum-water, and laid them by means of a brush upon the
surfaces of a cube like this. True they saw their red pow
ders red, their white ones white, and their black ones black,
but they saw these colors through the coat of varnish
which encircled every particle of their powders. When,
therefore, it was concluded that color had no influence on
radiation, no chance had been given to it of asserting its
influence ; when it was found that all chemical precipitates
radiated alike, it was the radiation from a varnish common
to them all which showed the observed constancy. Hun
dreds, perhaps thousands, of experiments on radiant heat
have been performed in this way by various inquirers, but
I fear the work will have to be done over again. I am not,
indeed, acquainted with an instance in which an oversight
of so trivial a character has been committed in succession
by so many able men, and vitiated so large an amount of
otherwise excellent work.

Basing our reasonings, then, on demonstrated facts, we
arrive at the extremely probable conclusion that the envel
ope of the particles, and not the particles themselves, was
the real radiator in the experiments just referred to. To
reason thus, and deduce their more or less probable conse
quences from experimental facts, is an incessant exercise
of the student of physical science. But having thus fol
lowed for a time the light of reason alone through a series
of phenomena, and emerged from them with a purely intel
lectual conclusion, our duty is to bring that conclusion to
an experimental test. In this way we fortify our science,

RADIANT HEAT AND ITS RELATIONS. 231

sparing no pains, shirking no toil to secure sound materials
for the edifice which it is our privilege to raise.

For the purpose of testing our conclusion regarding the
influence of the gum I take two powders of the same physi
cal appearance ; one of them is a compound of mercury and
the other a compound of lead. On two surfaces of this
cube are spread these bright-red powders without varnish
of any kind. Filling the tube with boiling water, and de
termining the radiation from the two surfaces, one of them
is found to emit thirty-nine rays, while the other emits
seventy-four. This, surely, is a great difference. Here,
however, is a second cube, having two of its surfaces coated
with the same powders, the only difference being that now
the powders are laid on by means of a transparent gum.
Both surfaces are now absolutely alike in radiative power.
Both of them emit somewhat more than was emitted by
either of the unvarnished powders, simply because the gum
employed is a better radiator than either of them. Exclud
ing all varnish, and comparing white with white, I find
vast differences ; comparing black with black, I find them
also different; and when black and white are compared, in
some cases the black radiates far more than the white,
while in other cases the white radiates far more than the
black. Determining, moreover, the absorptive power of
those powders, it is found to go hand-in-hand with their
radiative power. The good radiator is a good absorber, and
the bad radiator is a bad absorber. From all this it is evi
dent that as regards the radiation and absorption of non-
luminous heat, color teaches us nothing ; and that even as
regards the radiation of the sun, consisting as it does main
ly of non-luminous rays, conclusions as to the influence of
color may be altogether delusive. This is the strict scien
tific upshot of our researches. But it is not the less true
that in the case of wearing apparel — and this for reasons
which I have given in analyzing the experiment of Frank-

232 FRAGMENTS OF SCIENCE.

lin — black dresses are more potent than white ones as ab
sorbers of solar heat.

Thus, in brief outline, I have brought before you a few
of the results of recent inquiry. If you ask me what is the
use of them, I can hardly answer you, unless you define the
term use. If you meant to ask me whether those dark
rays which clear away the Alpine snows will ever be ap
plied to the roasting of turkeys or the driving of steam-
engines, while affirming their power to do both, I would
frankly confess that they are not at present capable of
competing profitably with coal in these particulars. Still
they may have great uses unknown to me ; and when our
coal-fields are exhausted, it is possible that a more ethereal
race than ourselves may cook their victuals and perform
their work in this transcendental way. But is it necessary
that the student of science should have his labors tested by
their possible practical applications ? What is the prac
tical value of Homer's Iliad ? You smile, and possibly
think that Homer's Iliad is good as a means of culture.
There's the rub. The people who demand of science prac
tical uses, forget, or do not know, that it also is great as a
means of culture ; that the knowledge of this wonderful
universe is a thing profitable in itself, and requiring no
practical application to justify its pursuit. But while the
student of Nature distinctly refuses to have his labors
judged by their practical issues, unless the term practical
be made to include mental as well as material good, he
knows full well that the greatest practical triumphs have
been episodes in the search after pure natural truth. The
electric telegraph is the standing wonder of this age, and
the men whose scientific knowledge and mechanical skill
have made the telegraph what it is are deserving of all
honor. In fact, they have their reward, both in reputation
and in those more substantial benefits which the direct ser
vice of the public always carries in its train. But who, I

RADIANT HEAT AND ITS RELATIONS. 233

would ask, put the soul into this telegraphic body ? Who
snatched from heaven the fire that flashes along- the line ?
This, I am bound to say, was done by two men, the one a
dweller in Italy,1 the other a dweller in England, and, there
fore, not a thousand miles distant from the spot where I
now stand,8 who never in their inquiries consciously set a
practical object before them — whose only stimulus was
the fascination which draws the climber to a never-trodden
.peak, and would have made Csesar quit his victories to
seek the sources of the Nile. That the knowledge brought
us by those prophets, priests, and kings of science, is what
the world calls useful knowledge, the triumphant applica
tion of their discoveries proves. But science has another
function to fulfil, in the storing and the training of the hu
man mind ; and I would base my appeal to you on the
poor specimen which has been brought before you this
evening, whether any system of education at the present
day can be deemed even approximately complete in which
the knowledge of Nature is neglected or ignored.

1 Yolta. 2 Faraday.

X.

ON CHEMICAL KAYS AND THE STRUCT
URE AND LIGHT OF THE SKY.

A DISCOURSE.

DELIVERED IN THE ROYAL INSTITUTION OF GEEAT EEITAIN.

On Friday, January 15, I860.

" This is a very mysterious and a very beautiful phenomenon when
observed by the aid of a polariscope, consisting of a tourmaline plate,
with a slice of Iceland crystal or nitre, cut at right angles to the optic
axis, and applied on the side of the tourmaline furthest from the eye. In
a cloudless day, if the sky be explored in all parts by looking through
this compound plate, the polarized rings will be seen developed with more
or less intensity in every region but that nearest the sun and that most
distant from it — the maximum of polarization taking place on a zone of
the sky 90° from the sun, or in a great circle, having the sun for one of
its poles, so that the cause of polarization is evidently a reflection of the
sun's light on something. The question is, on what ? Were the angle of
maximum polarization 76° we should look to water or ice for the reflect
ing body. But though we were once of this opinion (art. Light, Encycl.
Mdropol. § 1143), careful observation has satisfied us that 90°, or there
abouts, is the correct angle, and that therefore, whatever be the body on
which the light has been reflected, if polarized by a single reflection, the
'polarizing angle ' must be 45°, and the index of refraction, which is the
tangent of that angle, unity ; in other words, the reflection would require
to be made in air upon air ! The only imaginable way in which this could
happen would be at the plane of contact of two portions of air differently
heated, such as might be supposed to occur at almost every point of the
atmosphere in a bright sunny day ; but against this there seems to be an
insuperable objection. The polarization is most regular and complete, as
we have lately been able to satisfy ourselves under the most favorable
possible atmospheric conditions, after sunset, in the bright twilight of a
summer night, with the sun some degrees below the horizon, and long
after all the tremor and turmoil of the air, due to irregular heating, must
have completely subsided. On the other hand, if effected by several suc
cessive reflections, what is to secure a large majority of them being in
one plane (in which case only their polarizing effect would accumulate) ;
and of those which become ultimately effective, what is there to deter
mine an ultimate deviation of 90° as that of the maximum ? The more
the subject is considered, the more it will be found beset with difficulties ;
and its explanation, when arrived at, will probably be found to carry
with it that of the blue color of the sky itself."

SIR JOHN HERSCHEL.

X.

ON CHEMICAL RAYS AND THE STRUCTURE AND
LIGHT OF THE SKY.

THE first physical investigation of any importance in
which, jointly with my friend Professor Knoblauch, I took
part, bore the title : " The Magneto-optic Properties of
Crystals, and the Relation of Magnetism and Diamagnetism
to Molecular Arrangement." 1 This investigation compelled
me to reflect upon the structure of crystals, on their optical
properties in relation to that structure, and more particu
larly on the striking phenomena exhibited by many of
them in the field of a sufficiently powerful magnet. These
were evidently due to the manner in which the molecules
of the crystals were built together by the force of crystal
lization ; and it was natural, if not necessary for me, to em
ploy such strength of imagination as I possessed in obtain
ing a mental picture of this molecular architecture. The
inquiry gave a tinge and bias to my subsequent scientific
thought, rendering, as it did, the conceptions and pursuits
of molecular physics pleasant to me. Its influence is to be
traced in most of my scientific work. The first lecture, for
example, which I ever delivered in this theatre, was " On
the Influence of Material Aggregation on the Manifestations
of Force ; " by " material aggregation " being meant the
way in which, by Nature or by Art, the molecules of mat-

1 Philosophical Magazine, July, 1850.

238 FRAGMENTS OF SCIENCE.

ter are arranged together. In 1853 I also published a
paper " On Molecular Influences," in which common heat
was made the explorer of organic structure. In the " Ba-
kerian Lecture," given before the Royal Society in 1855,
the same idea and phraseology crop out. The Bakerian
Lecture for 1864 bears the title " Contributions to Molec
ular Physics." And all through the investigations which
have occupied me during the last ten years, my wish and
aim have been to make radiant heat an instrument by
which to lay hold of the ultimate particles of matter.

The labors now to be considered lie in the same direc
tion. In the researches just referred to, tubes of glass and
brass were employed, called, for the sake of distinction,
" experimental tubes," in which radiant heat was acted
upon by the gases and vapors subjected to examination.
Two or three months ago, with a view of seeing what oc
curred within these tubes on the entrance of the gases or
vapors, it was found necessary to intensely illuminate their
interiors. The source of illumination chosen was the elec
tric light, the beam of which, converged by a suitable lens,
was sent along the axis of the tube. The dirt and filth in
which we habitually live were strikingly revealed by this
method 'of illumination. For, wash the tube as we might
with water, alcohol, acid, or alkali, until its appearance in
ordinary daylight was that of absolute purity, the delusive
character of this appearance was in most cases revealed by
the electric beam. In fact, in air so charged with sus
pended matter as that which supplies our lungs in London,
it is not possible to be more than approximately clean.

Vapors of various kinds were sent into a glass experi
mental tube, a yard in length, and about three inches in
diameter. As a general rule, the vapors were perfectly
transparent ; the tube, when they were present, appearing
as empty as when they were absent. In two or three cases,
however, a faint cloudiness sho\ved itself within the tube.

CHEMICAL RAYS. 239

This caused me a momentary anxiety, for I did not know
how far, in describing my previous experiments, actions
might have been ascribed to pure cloudless vapor, which
were really due to those newly-observed nebula?. Inter
mittent discomfort, however, is the normal feeling of the
investigator ; for it drives him to closer scrutiny, to greater
accuracy, and often, as a consequence, to new discovery.
It was soon found that the nebula3 revealed by the beam
-were also generated by the beam, and the observation
opened a new door into that region inaccessible to sense,
which embraces so much of the intellectual life of the phys
ical investigator.

What are those vapors of which we have been speak
ing ? They are aggregates of molecules, or small masses of
matter, and every molecule is itself an aggregate of smaller
parts called atoms. A molecule of aqueous vapor, for ex
ample, consists of two atoms of hydrogen and one of oxy
gen. A molecule of ammonia consists of three atoms of
hydrogen, and one of nitrogen, and so of other substances.
Tims the molecules, themselves inconceivably small, are
made up of distinct parts still smaller. When, therefore,
a compound vapor is spoken of, the corresponding mental
image is an aggregate of molecules separated from each
other, though still exceedingly near, each of these being
composed of a group of atoms still nearer to each other.
So much for the matter which enters into our conception of
a vapor.1 To this must now be added the idea of motion.
The molecules have motions of their own as wholes ; their
constituent atoms have also motions of their own, which
are executed independently of those of the molecules ; just

1 Newton seemed to consider that the molecules might be rendered
visible by microscopes ; but of the atoms he appears to have entertained
a different opinion. He finely remarks : "It seems impossible to see
the more secret and noble works of Nature within the corpuscles, by
reason of their transparency." — (Herschel, On Light, Art. 1145.)

240 FRAGMENTS OF SCIENCE.

as the various movements of the earth's surface are exe
cuted independently of the orbital revolution of our planet.

The vapor molecules are kept asunder by forces which,
virtually or actually, are forces of repulsion. Between
these elastic forces and the atmospheric pressure under
which the vapor exists, equilibrium is established as soon
as the proper distances between the molecules have been
assumed. If, after this, the molecules be urged nearer to
each "other by a momentary force, they recoil as soon as
the force is expended. If they be separated more widely
apart, when the separating force ceases to act they again
approach each other. The case is different as regards the
constituent atoms.

And here let it be remarked, that we are now upon the
very outmost verge of molecular physics ; and that I am
attempting to familiarize your minds with conceptions
which have not yet obtained universal currency even among
chemists ; which many chemists, moreover, might deem un
tenable. But, tenable or untenable, it is of the highest sci
entific importance to discuss them. Let us, then, look men
tally at our atoms grouped together to form a molecule.
Every atom is held apart from its neighbors by a force of
repulsion ; why, then, do not the mutually- rcpellant mem
bers of this group part company ? The molecules separate
from each other when the external pressure is lessened or
removed, but the atoms do not. The reason of this stabil
ity is that two forces, the one attractive and the other re
pulsive, are in operation between every two atoms ; and the
position of every atom — its distance from its fellows — is
determined by the equilibration of these two forces. If the
atoms come too near, repulsion predominates and drives
them apart; if too distant, attraction predominates and
draws them together. The point at which attraction and
repulsion are equal to each other is the atom's position of
equilibrium. If not absolutely cold — and there is no such

CHEMICAL RAYS. 241

thing as absolute coldness in our corner of Nature — the
atoms are always in a state of vibration, their vibrations
being executed to and fro across their positions of equilib
rium.

Into a vapor thus constituted, we have now to pour a
beam of light ; which most of you know to be a train of
minute waves, excited in, and propagated through, an al
most infinitely attenuated and elastic medium, which fills
all space, and which we name the ether. It is hardly neces
sary to remind you that these waves of light are not all of
the same size ; that some of them are much longer and
higher than others ; that the short waves and the long ones
move with the same rapidity through space, just as short
and long waves of sound travel with the same rapidity
through air, and that, therefore, the shorter waves must fol
low each other in quicker succession than the longer ones ;
that the different rapidities with which the waves of light
impinge upon the retina, or optic nerve, give rise in con
sciousness to differences of color • that there are, moreover,
numberless waves emitted by the sun and other luminous
bodies which reach the retina, but which are incompetent
to excite the sensation of light ; for, if the lengths of the
waves exceed a certain limit, or if they fall short of a cer
tain other limit, they cannot generate vision. And it is to
be particularly borne in mind, that the capacity to excite
vision does not depend so much on the strength of the
waves as on their periods of recurrence. I have, as many
of you know, permitted waves to enter my own eye, which,
if their energy were that of light, would have instantly and
utterly ruined the optic nerve, but which failed to produce
any impression whatever upon consciousness, because their
periods were not those competent to excite the retina.

The elements of all the conceptions with which we shall
have subsequently to deal are now in your possession. And
you will observe that, though we are speaking of things
11

iM2 FRAGMENTS OF SCIKM'K.

whirh lie entirely beyond the range of the senses, the con
ceptions are as truly mechanical as they would be if we
were dealing with ordinary masses of matter, and with
waves of sensible magnitude. No really scientific mind at
the present day will be disposed to draw a substantial dis
tinction between chemical and mechanical phenomena.
They differ from each other as regards the magnitude of
the masses involved ; but in this sense the phenomena of
astronomy diifer, also, from those of ordinary mechanics.
The main bent of the natural philosophy of a future age
will probably be to chasten into order, by subjecting it to
mechanical laws, the existing chaos of chemical phe
nomena.

Whether we see rightly or wrongly — whether our in
tellection be real or imaginary — it is of the utmost im
portance in science to aim at perfect clearness in the de
scription of all that comes, or seems to come, within the
range of the intellect. For, if we are right, clearness of
utterance forwards the cause of right ; while, if we are
wrong, it insures the speedy correction of error. In this
spirit, and with the determination at all events to speak
plainly, let us deal with our conceptions of ether-waves and
molecules. Supposing a wave, or a train of waves, to im
pinge upon a molecule so as to urge all its parts with the
same motion, the molecule would move bodily as a whole,
but because they are animated by a common motion there
\vould be no tendency of its constituent atoms to separate
from each other. Differential motions among the atoms
themselves would be necessary to effect a separation, and
if such motions be not introduced by the shock of the
waves, there is no mechanical ground for the decomposition
of the molecule.

Thus the conception of the decomposition of compound
molecules by the waves of ether comes to us recommended
by a priori probability. But a closer examination of the

CHEMICAL RAYS. 243

question compels us to supplement, if not materially to
qualify, this conception. It is a most remarkable fact that
the waves which have thus far been found most effectual in
shaking" asunder the atoms of compound molecules are
those of least mechanical power. Billows, to use a strong
comparison, are incompetent to produce effects which are
readily produced by ripples. It is, for example, the violet
and ultra-violet rays of the sun that are most effectual in
producing these chemical decompositions ; and, compared
with the red and ultra-red solar rays, the energy of these
" chemical rays " is infinitesimal. This energy would
probably in some cases have to be multiplied by millions
to bring it up to that of the ultra-red rays : and still the
latter are powerless where the smaller waves are potent.
We here observe a remarkable similarity between the be
havior of chemical molecules and that of the human retina.
The energy transmitted to the eye from a candle-flame half
a mile distant is more than sufficient to inform conscious
ness ; while waves of a different period, possessing twenty
thousand million times this energy, have been suffered to
impinge upon my own retina, with an absolute unconscious
ness of any effect whatever — mechanical, physiological,
chemical, or thermal.

If, then, the power of these smaller waves to unlock the
bonds of chemical union be not a result of their strength, it
must be, as in the case of vision, a result of their periods
of recurrence. But how are we to figure this action ? The
shock of a single wave produces no more than an infini
tesimal effect upon an atom or a molecule. To produce a
larger effect, the motion must accumulate, and for wave-
impulses to accumulate, they must arrive in periods iden
tical with the periods of vibration of the atoms on which
they impinge. In this case each successive wave finds the
atom in a position which enables that wave to add its shock
to the sum of the shocks of its predecessors. The effect is

•J i 1 FRAGMENTS OF SCIENCE.

mechanically the same as that due to the timed impulses
of a boy upon a swing. The single tick of a clock has no
appreciable effect upon the unvibrating and equally long
pendulum of a distant clock ; but a succession of ticks, each
of which adds, at the proper moment, its infinitesimal push
to the sum of the pushes preceding it, will, as a matter of
fact, set the second clock going. So likewise a single puff
of air against the prong of a heavy tuning-fork produces
no sensible motion, and, consequently, no audible sound ;
but a succession of puffs, which follow each other in periods
identical with the tuning-fork's period of vibration, will
render the fork sonorous. I think the chemical action of
light is to be regarded in this way. Fact and reason point
to the conclusion that it is the heaping up of motion on the
atoms, in consequence of their synchronism with the shorter
waves, that causes them to part company. This I take to
be the mechanical cause of these decompositions which are
effected by the waves of ether.

And now let us return to that faint cloudiness already
mentioned, from which, as from a germ, these considerations
and speculations have sprung. It has been long known that
light effected the decomposition of a certain number of
bodies. The transparent iodide of ethyl, or of methyl, for
example, becomes brown and opaque on exposure to light,
through the discharge of its iodine. The art of photography
is founded on the chemical actions of light ; so that it is
well known that the effects for which the foregoing theoretic
considerations would have prepared us, are not only proba
ble, but actual.

But the method employed in the experiments in which
the cloudiness above referred to was observed, and which
consists simply in offering the vapors of volatile substances
to the action of light, enables us not only to give such ex
periments a bcautfiul form, but also to give a great exten
sion to the operations of light, or rather of radiant force, as

CHEMICAL RAYS.

245

a chemical agent. It also enables us to illustrate in our
laboratories actions which have been hitherto performed
only in the laboratory of Nature. A few of these actions
of a representative character will now be brought before
you; and advantage will be taken of the fact that, in a
great number of cases, one or more of the substances into
which the waves of light break up
compound molecules are compar
atively involatile. The products
of decomposition require a greater
heat than is required by the va
pors from which they are derived
to keep them in the gaseous form ;
and hence, if the space in which
these new bodies are liberated be
of the 'proper temperature, they
wTill not remain in the vaporous
condition, but will precipitate
themselves as liquid particles, thus
forming visible clouds upon the
beam, to the action of which they
owe their existence.

The little flask, F, in the an
nexed figure, is stopped by a cork,
pierced in two places. Through
one orifice passes a narrow glass
tube, a, which terminates imme
diately under the cork; through
the other orifice passes a similar
tube, 5, descending to the bottom of the little flask, which
is filled to a height of about an inch with a transparent
liquid. The name of this liquid is nitrite of amyl, in every
molecule of which we have 5 atoms of ca.rbon, 11 of hydro
gen, 1 of nitrogen, and 2 of oxygen. Upon this group the
waves of our electric light will be immediately let loose.

246 FRAGMENTS OF SCIENCE.

The large horizontal tube that you see before you is called
an " experimental tube ; " it is connected with our small
flask ; between them, however, a stop-cock intervenes, by
means of which the passage between the flask and the ex
perimental tube can be opened or closed at pleasure. The
other tube, passing through the cork of the flask and de
scending into the liquid, is connected with a U-shaped ves
sel, filled with fragments of clean glass, covered with sul
phuric acid. In front of the U-shaped vessel is a narrow
tube stuffed with cotton-wool. At one end of the experi
mental tube is our electric lamp ; and here, finally, is an air-
pump, by means of which the tube has been exhausted.
\\V are now ready for experiment.

Opening the cock cautiously, the air of the room passes,
in the first place, through the cotton-wool, which holds
back the numberless organic germs and inorgam'6 dust-
particles floating in the atmosphere. The air, thus cleansed,
passes into the U-shaped vessel, where it is dried by the
sulphuric acid. It then descends through the narrow tube
to the bottom of the little flask, and escapes there through
a small orifice into the liquid. Through this it bubbles,
loading itself to some extent with the nitrite-of-amyl vapor,
and then the air and vapor enter the experimental tube
together.

The closest scrutiny would now fail to discover any
thing within this tube ; it is, to all appearance, absolutely
empty. The air and the vapor are both invisible. We
will permit the electric beam to play upon this mixture.
The lens of the lamp is so situated as to render the beam
slightly convergent, the focus being formed in the vapor
at about the middle of the tube. You will notice that the
tube remains dark for a moment after the turning on of the
beam ; but the chemical action will be so rapid that atten
tion is requisite to mark this interval of darkness. I igniic
the lamp ; the tube for a moment seems empty ; but sud-

CHEMICAL RAYS. 247

dcnly the beam darts through a luminous white cloud, which
has banished the preceding darkness. It has, in fact, shaken
asunder the molecules of the nitrite of amyl, and brought
down upon itself a shower of liquid particles which causes
it to flash forth in your presence like a solid luminous
spear. It is worth while to mark how this experiment
illustrates the fact that, however intense a luminous beam
may be, it remains invisible unless it has something to
shine upon. Space, though traversed by the rays from all
suns and all stars, is itself unseen. Not even the ether
which fills space, and whose motions are the light of the
universe, is itself visible.

You notice that the end of the experimental tube most
distant from the lamp is free from cloud. Now the nitrite-
of-amyl vapor is there also, but it is unaffected by the
powerful beam passing through it. Let us make the trans
mitted beam more concentrated by receiving it on a con
cave silver mirror, and causing it to return by reflection into
the tube. It is still powerless. Though a cone of light of
extraordinary intensity now traverses the vapor, no pre
cipitation occurs, no trace of cloud is formed. Why ? Be
cause the very small portion of the beam competent to de
compose the vapor is quite exhausted by its work in the
frontal portions of the tube. The great body of the light
which remains, after this sifting out of the few effectual
rays, has no power over the molecules of nitrite of amyl.
We have here, strikingly illustrated, what has been already
stated regarding the influence of period, as contrasted with
that of strength. For the portion of the beam which is here
ineffectual has probably more than a million times the ab
solute energy of the effectual portion. It is energy specially
related to the atoms that we here need, which specially re
lated energy being possessed by the feeble waves, invests
them with their extraordinary power. When the experi
mental tube is reversed so as to bring the undecomposed

248 FRAGMENTS OF SCIENCE.

vapors under the action of the unsifted beam, you have in
stantly this fine luminous cloud precipitated.

The light of the sun also effects the decomposition of
the uitrite-of-amyl vapor. A small room in the Royal
Institution, into which the sun shone, was partially dark
ened, the light being permitted to enter through an open
portion of the window-shutter. In the track of the beam
was placed a large plano-convex lens, which formed a fine
convergent cone in the dust of the room behind it. The
experimental tube was filled in the laboratory, covered
with a black cloth, and carried into the partially-dark
ened room. On thrusting one end of the tube into the
cone of rays behind the lens, precipitation within the cone
was copious and immediate. The vapor at the distant end
of the tube was shielded by that in front ; but on revers
ing the tube, a second and similar splendid cone was pre
cipitated.

Now let us pause for a moment and glance at the
ground over which we have passed. We have defined a
vapor as an aggregate of. molecules mutually repellent,
but hindered from indefinitely retreating from each other
by an external pressure. We have defined a molecule as
an aggregate of atoms maintained in positions of equi
librium by the equalized action of two opposing forces,
and always oscillating to and fro across those positions.
We have defined a beam of light as a train of innumerable
waves, and have illustrated their chemical action. We
have learned that it is not the magnitude or power of the
waves, so much as their periods of recurrence, that renders
them effectual as chemical agents. We have also seen
how the luminous beam is sifted by the vapor which it
decomposes, and deprived of those rays which are com
petent to effect the decomposition. The effects, moreover,
obtained with the electric beam are also produced by the
beams of the sun.

CHEMICAL RAYS. 249

And here I would ask you to make familiar to your
minds the idea that no chemical action can be produced by
a ray that does not involve the destruction of the ray. But
the term " ray " is unsatisfactory to us at present, when
our desire is to abolish all vagueness, and to affix a definite
physical significance to each of our terms. Abandoning
the term ray as loose and indefinite, we have to fix our
thoughts upon the waves of light ; and to render clear to
our minds that those waves which produce chemical action
do so by delivering up their own motion to the molecules
which they decompose. We have here forestalled to some
extent a question of great importance in molecular physics,
which, however, is worthy of being fixed more definitely in
your mind ; it is this : When the waves of ether are in
tercepted by a compound vapor, is the motion of the waves
transferred to the molecules of the vapor, or to the atoms
of the molecules ? We have thus far leaned to the con
clusion that the motion is communicated to the atoms ; for
if not to these individually, why should they be shaken
asunder ? The question, however, is capable of, and is
worthy of, another test, the bearing and significance of
which you will immediately appreciate.

As already explained, the molecules are held in their
positions of equilibrium by their mutual repulsion on the
one side, and by an external pressure on the other. Their
rate of vibration, if they vibrate at all, must depend upon
the elastic force which they mutually exert. If this force
be changed, the rate of vibration must change along with
it; and after the change the molecules could no longer
absorb the waves which they absorbed prior to the change.
Now, the elastic force between molecule and molecule is
utterly altered when a vapor passes to the liquid state.
Hence, if the liquid absorbs waves of the same period as its
vapor, it is a proof that the absorption is not effected by
the molecules. Let us be perfectly clear on this important

250 FRAGMENTS OF SCIENCE.

point. Those waves are absorbed whose vibrations syn
chronize with those of the molecules or atoms on which
they impinge ; a principle which is sometimes expressed by
saying that bodies radiate and absorb the same rays. This
great law, as you know, is the foundation of spectrum-
analysis ; it enabled Kirchhoff to explain the lines of Frauen-
hofer, and to determine the chemical composition of the
atmosphere of the sun. If, then, after such a change as
that involved in the passage of a vapor to the liquid state,
the same waves are absorbed as were absorbed prior to the
passage, it is a proof that the molecules, which must have
utterly changed their periods, cannot be the seat of the ab
sorption ; and we are driven to conclude that it is to the
atoms j whose rates of vibration are unchanged by the
change of aggregation, that the wave-motion is transferred.
If experiment should prove this identity of action on the
part of a vapor and its liquid, it would establish in a new
and striking manner the conclusion to which we have pre
viously leaned.

We wrill now resort to the experimental test. In front
of this experimental tube, wrhich contains a quantity of the
nitrite-of-amyl vapor, is placed a glass cell a quarter of an
inch in thickness, filled with the liquid nitrite of amyl. I
send the electric beam first through the liquid and then
through its vapor. The luminous power of this beam is
very great, but it can make no impression upon the vapor.
The liquid has robbed it completely of its effective waves.
When the liquid is removed chemical action immediately
commences, and in a moment we have the apparently
empty tube filled with this bright cloud, precipitated by
one portion of the beam, and illuminated by another. Thus
we uncover to some extent the secrets of this world of
molecules and atoms.

Instead of employing air as the vehicle by which the
vapor is carried into the experimental tube, we may em-

CHEMICAL RAYS. 251

ploy oxygen, hydrogen, or nitrogen. With hydrogen curi
ous effects are observed, due to the sinking of the clouds
through the extremely light gas in which they float. They
illustrate, but do not prove, the untenable notion of those
who say that the clouds of our own atmosphere could not
float if the cloud-particles were not little bladders instead
of full spheres. Before you is a tube filled with the nitrite-
of-amyl vapor, which has been carried into the tube by
hydrogen gas. On sending the beam through the tube a
delicate bluish-white cloud is precipitated. A few strokes
of the pump clear the tube of this cloud, but leave a resi
due of vapor behind. Again, turning on the beam we have
a second cloud, more delicate than the first. This may be
done half a dozen times in succession. A residue of vapor
will still linger in the tube sufficient to yield a cloud of ex
quisite delicacy, both as regards color and texture.

Besides the nitrite of amyl, a great number of other
substances might be employed, which, like the nitrite, have
been hitherto not known to be chemically susceptible to
light. This is, in fact, a representative case. One point
in addition I wish to illustrate, chiefly because the effect is
the same in kind as one of great importance in nature. Our
atmosphere contains carbonic-acid gas, which furnishes food
to the vegetable world. But this food, as many of you
know, could not be consumed by plants and vegetables
without the intervention of the sun's rays. As far as we
know, however, tbese rays are powerless upon the free car
bonic acid of our atmosphere ; the sun can only decompose
the gas when it is absorbed by the leaves of plants. In the
leaves the carbonic acid is in close proximity with sub
stances ready to take advantage of the loosening of the
molecules by the waves of light. Incipient disunion being
introduced by the solar rays, the carbon of the gas is seized
upon by the leaf and appropriated, while the oxygen is dis
charged into the atmosphere.

252 FRAGMENTS OF SCIENCE.

The experimental tube now before you contains a
quantity of a different vapor from that which we have
hitherto employed. The liquid from which this vapor is
derived is called the nitrite of butyl. On sending the elec
tric beam through the vapor, which has been carried in by
air, the chemical action is insensible. I add to the vapor a
quantity of air which has been permitted to bubble through
hydrochloric acid. When the beam is now turned on, so
rapid is the action and so dense the clouds precipitated,
that you could hardly, by an effort of attention, observe the
dark interval which preceded the precipitation of the cloud.
This enormous augmentation of the action is due to the
presence of the hydrochloric acid. Like the chlorophyl in
the leaves of plants, it takes advantage of the loosening of
the molecules of nitrite of butyl by the waves of the electric
light.

In these experiments we have employed a luminous
beam for two different purposes. A small portion of it has
been devoted to the decomposition of our vapors, while the
great body of the light has served to render luminous the
clouds resulting from the decomposition. It is possible to
impart to these clouds any required degree of tenuity, for
it is in our power to limit at pleasure the amount of vapor
in our experimental tube. When the quantity is duly
limited, the precipitated particles are at first inconceivably
small, defying the highest microscopic power to bring them
within the range of vision. Probably their diameters might
then be expressed in millionths of an inch. They grow
gradually, and as they augment in size they scatter a con
tinually increasing quantity of wave-motion, until finally
the cloud which they form becomes so luminous as to fill
this theatre with light. During the growth of the particles
the most splendid iridescences are often exhibited. Such
I have sometimes seen with delight and wonder in the
atmosphere of the Alps, but never any thing so gorgeous

STRUCTUKE AND LIGHT OF THE SKY. 253

as those which our laboratory experiments reveal. It is
not, however, with the iridescences, however beautiful they
may be, that we have now to occupy our thoughts, but
with other effects which bear upon the two great standing
enigmas of meteorology — the color of the sky and the polar
ization of its light.

It is possible, as stated, by duly regulating the quantity
of vapor, to make our precipitated particles grow from an
infinitesimal and altogether ultra-microscopic size to masses
of sensible magnitude ; and by means of these particles, in
a certain stage of their growth, we can produce a blue
which shall rival, if it does not transcend, that of the deepest
and purest Italian sky. Let this point be in the first place
established. Associated with our experimental tube is a
barometer, the mercurial column of which now indicates
that the tube is exhausted. Into the tube is introduced a
quantity of the mixed air and nitrite-of-butyl vapor sufficient
to depress the mercurial column one-twentieth of an inch ;
that is to say, the air and vapor together exert a pressure
of one six-hundredth of an atmosphere. I now add a quan
tity of air and hydrochloric acid sufficient to depress the
mercury half an inch farther, and into this compound and
highly-attenuated atmosphere I discharge the beam of the
electric light. The effect is slow ; but gradually within the
tube arises this splendid azure, which strengthens for a time,
reaches a maximum of depth and purity, and then, as the
particles grow larger, passes into whitish blue. This. ex
periment is representative, and it illustrates a general
principle. Various other colorless substances of the most
diverse properties, optical and chemical, might be employed
for this experiment. The incipient cloud in every case
would exhibit this superb blue ; thus proving to demonstra
tion that particles of infinitesimal size, without any color of
their own, and irrespective of those optical properties ex
hibited by the substance in a massive state, are competent
to produce the color of the sky.

254 FRAGMENTS OF SCIENCE.

But there is another subject connected with our firma
ment, of a more subtle and recondite character than even
its color. I mean that " mysterious and beautiful phenom
enon," 1 the polarization of the light of the sky. The po
larity of a magnet consists in its two-endedness, both ends,
or poles, acting in opposite ways. Polar forces, as most of
you know, are those in which the duality of attraction and
repulsion is manifested. And a kind of two-sidedness —
noticed by Huyghens, commented on by Newton, and dis
covered by a French philosopher, named Malus, in a beam
of light which had been reflected from one of the windows
of the Luxembourg Palace in Paris — receives the name of
polarization. We must now, however, attach a distinct
ness to the idea of a polarized beam, which its discoverers
were not able to attach to it. For in their day men's
thoughts were not sufficiently ripe, nor optical theory suffi
ciently advanced, to seize upon or express the physical
meaning of polarization. When a gun is fired, the explo
sion is propagated as a wave through the air. The shells
of air, if I may use the term, surrounding the centre of con
cussion, are successively thrown into motion, each shell
yielding up its motion to that in advance of it, and return
ing to its position of equilibrium. Thus, while the wave
travels through long distances, each individual particle of
air concerned in its transmission performs merely a small
excursion to and fro.2 In the case of sound, the vibrations
of the air-particles are executed in the direction in which
the sound travels. They are, therefore, called longitudinal
vibrations. In the case of light, on the contrary, the vibra
tions are transversal; that is to say, the individual particles
of ether move to and fro across the direction in which the
light is propagated. In this respect waves of light resem
ble ordinary water-waves, more than waves of sound. In

1 ncrschcl's Meteorology, Art. 233.

2 Lectures on Sound, p. 3. (Longmans.)

STRUCTURE AND LIGHT OF THE SKY. 255

the case of an ordinary beam of light, the vibrations of the
ether-particles are executed in every direction perpendicular
to it ; but let the beam impinge obliquely upon a plane-
glass surface, as in the case of Malus, the portion reflected
will no longer have its particles vibrating in all directions
round it. By the act of reflection, if it occur at the proper
angle, the vibrations are all confined to a single plane, and
light thus circumstanced is called plane polarized light.

A beam of light passing through ordinary glass executes
its vibrations within the substance exactly as it would do
in air, or in ether-filled space. Not so when it passes
through many transparent crystals. For these have also
their two-sidedness, the arrangement of their molecules
being such as to tolerate vibrations only in certain definite
directions. There is the well-known crystal tourmaline,
which shows a marked hostility to all vibrations executed
at right angles to the axis of the crystal. It speedily ex
tinguishes such vibrations, while those executed parallel to
the axis are freely propagated. The consequence is, that a
beam of light, after it has passed through any thickness of
this crystal, emerges from it polarized. So also as regards
the beautiful crystal known as Iceland spar, or as double-
refracting spar. In one direction, but in one only, it acts
like a piece of glass ; in all other directions it splits the
beam of light passing through it into two distinct halves,
both of which are perfectly polarized, their vibrations being
executed in two planes, at right angles to each other.

It is possible by a suitable contrivance to get rid of one
of the two polarized beams into which Iceland spar divides
an ordinary beam of light. This was done so ingeniously
and effectively by a man named Nicol, that the Iceland spar,
cut in his fashion, is now universally known as NicoPs prism.
Such a prism can polarize a beam of light, and if the beam,
before it impinges on the prism, be already polarized, in
one position of the prism it is stopped, while in another

256 FRAGMENTS OF SCIENCE.

position it is transmitted. Our way is now, to some extent,
cleared toward an examination of the light of the sky.
Looking at various points of the blue firmament through a
Nicol's prism, and turning the prism round its axis, we im
mediately notice variations of brightness. In certain posi
tions of the prism, and from certain points of the firmament,
the light appears to be freely transmitted ; while it is only
necessary to turn the prism round its axis through an angle
of 90° to materially diminish the intensity of the light. On
close scrutiny it is found that the difference produced by
the rotation of the prism is greatest when the sky is re
garded in a direction at right angles to that of the solar
rays through the air.

Let me describe a few actual observations made some
days ago on Primrose Hill. The sun was near setting, and
a few scattered neutral-tint clouds, wThich failed to catch
the dying light, were floating in the air. When these were
looked at across the track of the solar beams, it was pos
sible, by turning the Nicol round, to see them either as
white clouds on a dark ground, or as dark clouds on a bright
ground.1 In certain positions of the prisms the sky-light
was in great part quenched, and then the clouds, projected
against the darkness of space, appeared white. Turning
the Nicol 90° round its axis, the brightness of the sky was
restored, the clouds becoming dark through contrast with
this brightness. Experiments of this kind prove that the
blue light sent to us by the firmament is polarized, and that
the direction of most perfect polarization is perpendicular
to the solar rays. Were the heavenly azure like the light
scattered from a thick cloud, the turning of the prism would
have no effect upon it ; it would be transmitted equally dur
ing the entire rotation of the prism. The light of the sky is
in great part quenched, because it is in great part polarized.

1 1 was not aware when these words were written that this observation
was made by the indefatigable Brewster.

STRUCTURE AND LIGHT OF THE SKY. 257

When a luminous beam impinges at the proper angle
on a plane-glass surface it is polarized by reflection. It is
polarized, in part, by all oblique reflections ; but at one
particular angle, the reflected light is perfectly polarized.
An exceedingly beautiful and simple law, discovered by
Sir David Brewster, enables us readily to find the polarizing
angle of any substance whose refractive index is known.
This law was discovered experimentally by Brewster ; but
the Wave Theory of light renders a complete reason for
the law. A geometrical image of it is thus given : When
a beam of light impinges obliquely upon a plate of glass it
is in part reflected and in part refracted. At one particular
incidence the reflected and the refracted portions of the
beam are at right angles to each other. The angle of inci
dence is then the polarizing angle. It varies with the re
fractive index of the substance ; being for water 52-J, for
glass 57-J, and for diamond 68°.

It has been already stated that, in order to obtain the
most perfect polarization of the firmamental light, the sky
must be regarded in a direction at right angles to the solar
beams. This is sometimes expressed by saying that the
place of maximum polarization is at an angular distance of
90° from the sun. This angle, enclosed as it is between the
direct and reflected rays, comprises both the angles of inci
dence and reflection, supposing the polarization to be due
to a single reflection. Hence the angle of incidence is half
of 90°, or 45°. This is the atmospheric polarizing angle,
and the question is, what known substance possesses an
index of refraction to correspond with this polarizing angle ?
" If," says Sir John Herschel, " we knew this substance, we
might be tempted to conclude that particles of it, scattered
in the atmosphere, produce the polarization of the sky.
Were the angle of maximum polarization 76° (instead of
90°), we should look to water or ice, as the reflecting body,
however inconceivable the existence in a cloudless atmos-

258 FRAGMENTS OF SCIENCE.

phere and a hot summer day, of unevaporated particles of
water." But a polarizing angle of 45° corresponds to a
refractive index of 1 ; this means that there is no refraction
at all, in which case we ought to have no reflection. Brew-
ster, therefore, and others came to the conclusion that the
reflection was from the particles of air themselves. Dr.
Rubenson, of Upsala, made the angle enclosed between the
direct and reflected beams 90° 2' ; " the half of which," says
Mr. Buchan, in his excellent little " Handy Book of Me
teorology," " is so near the polarizing angle of air as to leave
no doubt that the light of the sky, as first stated by Brew-
ster, is polarized by reflection from the particles of air."

If you doubt the wisdom, acknowledge, at all events,
the faith in your capacity which has caused me to bring
so entangled a subject before you. I would fain believe,
however, that even the intellect which draws its culture
from a totally different source, may have its interest excited
in subjects like the present, dark and difficult though they
seem. I do not expect that you will grasp all the details
of this discussion ; but everybody present will, I think, see
the extremely important part hitherto played by the law
of Brewster in speculations as to the color and polarization
of the sky. Let me now endeavor to demonstrate in your
presence, firstly, and in confirmation of our former experi
ments, that sky-blue may be produced by exceedingly mi
nute particles of any kind of matter ; secondly, that polari
zation identical with that of the sky is produced by such
particles ; and thirdly, that matter in this fine state of di
vision, where its particles are small in comparison with the
height and span of a wave of light, releases itself completely
from the law of Brewster ; the direction of maximum polari
zation being absolutely independent of the polarizing angle
as hitherto defined.

Into this experimental tube, in the manner already de
scribed, I introduce a vapor which is decomposable by the

STRUCTURE- AND LIGHT OF THE SKY. 259

waves of light. The mixed air and vapor are sufficient to
depress the mercurial column one inch. I add to this mix
ture air, which has been permitted to bubble through dilute
hydrochloric acid, until the column is depressed thirty inches :
in other words, until the tube is full. And now I permit
the electric beam to play upon the mixture. For some
time nothing is seen. The chemical action is doubtless
progressing, and condensation is going on ; but the con
densing molecules have not yet coalesced to particles suffi
ciently large to reflect sensibly the waves of light. As
before stated — and the statement rests upon an experimental
basis — the particles here generated are at first so small that
their diameters would probably have to be expressed in
millionths of an inch ; while to form each of these particles
whole crowds of molecules are probably aggregated. Helped
by such considerations the intellectual vision plunges more
profoundly into atomic Nature, and shows us, among other
things, how far we are from the realization of Newton's
hope that the molecules might one day be seen by micro
scopes. While I am speaking, you observe this delicate blue
color, forming and strengthening within the experimental
tube. No sky-blue could exceed it in richness and purity ;
but the particles which produce this color lie wholly beyond
our microscopic range. A uniform color is here developed,
which has as little breach of continuity — which yields as
little evidence of the particles concerned in its production,
as that yielded by a body whose color is due to true mo
lecular absorption. This blue is at first as deep and dark
as the sky seen from the highest Alpine peaks, and for the
same reason. But it grows gradually brighter, still main
taining its blueness, until at length a whitish tinge mingles
with the pure azure ; announcing that the particles are now
no longer of that infinitesimal size which mainly scatters
the shortest waves.1

1 Possibly a photographic impression might be taken long before the
blue becomes visible, for the ultra-blue rays are first reflected.

260 FRAGMENTS OF SCIENCE.

The liquid here employed is the iodide of allyl, but I
might choose any one of a dozen substances here before
me to produce the effect. You have seen what may be
done with the nitrite of butyl. With nitrite of amyl, bisul
phide of carbon, benzol, benzoic ether, etc., the same blue
color may be produced. In all cases, where matter slowly
passes from the molecular to the massive state the transi
tion is marked by the production of the blue. More than
this : you have seen me looking at the blue color (I hardly
like to call it a blue " cloud," its texture and properties are
so different from ordinary clouds) through this bit of spar.
This is a Nicol's prism, and it is to be wished that one of
them could be placed in the hands of each of you. Now,
this blue that I have been regarding turns out to be, if the
expression be allowed, a bit of more perfect sky than the
sky itself. On looking across the illuminating beam as we
look across the solar rays in the atmosphere, we obtain not
only partial polarization, but perfect polarization. In one
position of the Nicol the blue light passes freely to the eye ;
in the other it is absolutely cut off, the experimental tube
being reduced to optical emptiness. It is well to place a
black surface behind the experimental tube, so as to prevent
foreign light from troubling the eye. In one position of
the prism this black surface is seen without softening or
qualification; for the particles within the tube are them
selves invisible, and the light which they scatter is quenched.
If the light of the sky were polarized with the same per
fection, on looking properly toward it through a Nicol we
should meet, not the mild radiance of the firmament, but
the unillumined blackness of space.

The construction of a Nicol's prism is such that it
allows the passage of vibrations which are executed in a
certain determinate direction, and these only. All vibra
tions executed at right angles to this direction are com
pletely stopped : while components only of those executed

STRUCTURE AND LIGHT OF THE SKY. 261

obliquely to it are transmitted. It is easy, therefore, to see
that, from the position in which the prism must be held to
transmit or to quench the light of our incipient cloud, we
can infer the direction of the vibrations of that light. You
will be able to picture those vibrations without difficulty.
Suppose a line drawn from any point of the " cloud " per
pendicular to the illuminating beam. The particles of ether
along that line, which carry the light from the cloud to the
eye, vibrate in a direction perpendicular both to the line
and to the beam. And if any number of lines be drawn
in the same way from the cloud, like the spokes of a wheel,
the particles of ether along all of them oscillate in the same
manner. Wherefore, if a plane surface be imagined cutting
the incipient cloud at right angles to its length, the vibra
tions discharged laterally are all parallel to this surface.
This is the plane of vibration of the polarized light.

Our incipient blue cloud is a virtual Nicol's prism, and,
between it and the real prism, we can produce all the
effects obtainable between the polarizer and analyzer of a
polariscope. When, for example, a thin plate of selenite,
which is crystallized sulphate of lime, is placed between
the Nicol and the incipient cloud, we obtain the splendid
chromatic phenomena of polarized light. The color of the
gypsum-plate, as many of you know, depends upon its
thickness. If this be uniform, the color is uniform. If, on
the contrary, the plate be wedge-shaped, thickening grad
ually and uniformly from edge to back, we have brilliant
bands of color produced parallel to the edge of the wedge.
Perhaps the best form of plate for experiments of this
character is that now in my hand, which was prepared for
me some years ago by a man of genius in his way, the late
Mr. Darker, of Lambeth. It consists of a plate of selenite
thin at the centre, and gradually thickening toward the
circumference. Placing this film between the Nicol and
the cloud, we obtain, instead of a series of parallel bands, a

L>C2 FRAGMENTS OF SCIENCE.

system of splendidly-colored rings. Precisely the same
phenomena are observed when we look at the blue firma
ment in a direction perpendicular to the solar rays.

We have thus far illuminated our artificial sky with
ordinary light. "We will now examine the effects produced
when the light which illuminates the particles is itself
polarized. In front of the electric lamp, and between it
and the experimental tube, is placed this fine Nicol's prism,
which is sufficiently large to embrace and to polarize the
entire beam. The plane of vibration of the light now
emergent from the prism, and falling upon the cloud, is
vertical ; and we find that this formless aggregate of infini
tesimal particles, without definite structure, is absolutely
incompetent to scatter the light upward or downward,
while it freely discharges the light horizontally, right and
left. I turn the polarizing Nicol so as to render the plane
of vibration horizontal ; the cloud now freely scatters the
light vertically upward and downward, but it is absolutely
incompetent to shed a ray horizontally to the right or left.

Suppose the atmosphere of our planet to be surrounded
by an envelope impervious to light, with an aperture on
the sunward side, through which a solar beam could enter.
Surrounded on all sides by air not directly illuminated, the
track of the sunlight would resemble that of the electric
beam in a dark space filled with our incipient cloud. The
course of the sunbeam would be blue, and it would dis
charge laterally, in all directions round it, light in precisely
the same polarized condition as that discharged from the
incipient cloud. In fact, the azure revealed by the sunbeam
would be the azure of such a cloud. And if, instead of
permitting the ordinary light of the sun to enter the aper
ture, a NicoPs prism were placed there, which should
polarize the sunlight on its entrance into our atmosphere,
the particles producing the color of the sky would act
precisely like those of our incipient cloud. In two directions

STRUCTURE AND LIGHT OF THE SKY. 263

we should have the solar light reflected ; in two others un-
reflected. In fact, out of such a solitary beam, traversing
the unilluminated air, we should be able to extract every
effect shown by our incipient cloud. In the production of
such clouds we virtually carry bits of the sky into our
laboratories, and obtain with them all the effects obtainable
in the open firmament of heaven.

The real sky is, as I have said, less perfect than our
artificial one may be made. For, mingled with the infini
tesimal particles which constitute the true matter of the
sky, there are others too coarse to scatter perfectly po
larized light at right angles to the solar beams. Hence,
when the brilliancy of the sky is diminished to the utter
most, there is still a residue of light ; the extinction is
partial, and not total, as in the case of our incipient cloud.
Let us consider this matter. The perfect polarization can
only be produced by excessively minute particles ; imagine
them growing gradually larger as they actually do in our
experiments. The extinction by the Nicol is perfect as
long as the polarization is complete. But what would you
expect? Manifestly, that after a time the polarization
would cease to be perfect. But here again the relation of
the size of the particles to the size of the waves must come
into play. In relation to the blue waves the particles are
larger than in relation to the red ; the blue waves, there
fore, will be the first liberated from a condition dependent
on the smallness of the particles. They will first escape
from the trammels of polarization ; and on their liberation
they exhibit an azure far purer and more brilliant than that
produced by the first precipitation of the particles. Could
we overarch ourselves with a sky of this color for a single
day, it would make us discontented with our present lack
lustre firmament ever afterward. It will be observed that
in all these cases reason and experiment go hand in hand,
the one predicting, the other verifying; every such vcrifi-

264 FRAGMENTS OF SCIENt i;

cation lending its weight of proof to the undulatory theory
on which the predictions are founded.

The selenite ring-system, already referred to, is a most
delicate reagent for the detection of polarized light. When
we look normally, or perpendicularly, at an incipient cloud,
the colors of the rings are most vividly developed, a dim
inution of the color being immediately apparent when
the incipient cloud is regarded obliquely. But let us con
tinue to look through the Nicol and selenite normally at
the cloud : the particles augment in size, the cloud becomes
coarser and whiter, the strength of the selenite colors be
coming gradually feebler. At length the cloud ceases to
discharge polarized light along the normal, and then the
selenite colors entirely disappear. If, now, the cloud be re
garded obliquely the colors are restored, very vividly, if not
with their first vividness and clearness. Thus the cloud
that has ceased to discharge polarized light at right angles
to the illuminating beam, pours out such light copiously in
oblique directions. The direction of maximum polariza
tion changes with the texture of the cloud.

But this is not all ; and to understand, even partially,
what remains, a word must be said regarding the appear
ance of the colors of our plate of selenite. If, as before
stated, the plate be of uniform thickness, its hue in polar
ized light is uniform. Suppose, then, that by arranging
the Nicol the color of the plate is raised to its maximum
brilliancy, and suppose the color produced to be green ; on
turning the Nicol round its axis the green becomes fainter.
When the angle of rotation amounts to 45° the color dis
appears ; we then pass what may be called a neutral posi
tion, where the selenite behaves, not as a crystal, but as a
bit of glass. Continuing the rotation, a color reappears,
but it is no longer green but red. This attains its maxi
mum at a distance of 45° from the neutral position, or, in
oilier words, at a distance of 90° from the position which

STRUCTURE AND LIGHT OP THE SKY. 265

showed the green at its maximum. At a further distance
of 45° from the position of maximum red, the color disap
pears a second time. We have there a second neutral
point, beyond which the green comes again into view, at
taining its maximum brilliancy at the end of a rotation of
180°. By the rotation of the Nicol, therefore, through an
angle of 90°, we produce a color complementary to that
with which we started.

As may be inferred from this result, the selenite ring-
system changes its character when the Nicol is turned.
It is possible to have the centre of the circle dark, the
surrounding rings being vividly colored. The turning of
the Nicol through an angle of 90° renders the centre bright,
while every point occupied by a certain color in the first
instance is occupied by the complement of that color in the
second. By curious internal actions, not here to be de
scribed, the cloud in our experimental tube sometimes
divides itself into sections of different textures. Some sec
tions are coarser than others, while it often happens that
some are iridescent to the naked eye, and others not.
Looking normally at such a cloud through the selenite and
Nicol, it often happens that in passing from section to sec
tion the whole character of the ring-system is changed.
You start with a section producing a dark centre and a
corresponding system of rings ; you pass through a neutral
point to another section and find there the centre bright,
and each of the first rings displaced by one of the comple
mentary color. Sometimes as many as four such rever
sions occur in the cloud of an experimental tube a yard
long. Now, the changes here indicated mean that in passing
from section to section of the cloud the plane of vibration
of the polarized light turns suddenly through an angle of
90° ; this change being entirely due to the different texture
of the two parts of the cloud.

You will now be able to understand, as far as it is ca^
12

266 FRAGMENTS OF SCIENCE.

pable of being understood, a very beautiful effect which,
under favorable circumstances, might be observed in our
atmosphere. This experimental tube contains an inch of
the iodide-of-allyl vapor, the remaining 29 inches necessary
to fill the tube being air, which has bubbled through aque
ous hydrochloric acid. Besides, therefore, the vapor of
iodide of allyl, we have those of water and of acid within
the tube. The light has been acting on the mixture for
some time, a beautiful incipient blue cloud being formed. As
before stated, the " incipient cloud " is wholly different in
texture and optical properties from an ordinary cloud ; but
it is possible to precipitate in the midst of the azure the
aqueous vapor so as to cause it to form in the tube a cloud
similar to the clouds of our atmosphere. An exhausted
vessel of about one-third of the capacity of the experi
mental tube is connected with it, the passage uniting both
being closed by a stop-cock. On opening this cock the
mixed air and vapor rush from the experimental tube into
the empty vessel ; and, in consequence of the chilling due
to rarefaction, the vapor in the experimental tube is pre
cipitated as a true cloud. What is the result ? Instantly
the centre of the system of colored rings becomes bright,
and the whole series of colors corresponding to definite ra
dial distances, complementary; While you continue to
look at the cloud, it gradually melts away as an atmos
pheric cloud might do in the azure of heaven. And there
is our azure also remaining behind. The coarser cloud
seems drawn aside like a veil, the blue reappears, the first
ring-system, with its dark centre and correspondingly col
ored circles, being restored.

Thus patiently you have accompanied me over a piece
of exceedingly difficult ground ; and I think, as a prudent
guide, we ought to halt upon the eminence we have now
attained. We might go higher, but the bowlders begin
here to be very rough. At a future day we shall, I doubt

STRUCTURE AND LIGHT OF THE SKY. £67

not, be able to overcome this difficulty, and to reach to-
g*ether a greater elevation.

THE SKY OF THE ALPS.

THE vision of an object always implies a differential
action on the retina of the observer. The object is dis
tinguished from surrounding space by its excess or defect
of light in relation to that space. By altering the illumi
nation, either of the object itself or of its environment, we
alter the appearance of the object. Take the case of clouds
floating in the atmosphere with patches of blue between
them. Any thing that changes the illumination of either
alters the appearance of both, that appearance depending,
as stated, upon differential action. Now the light of the
skv being polarized, may, as the reader of the foregoing
pages knows, be in great part quenched by a Nicol's
prism, while the light of a cloud, being unpolarizcd, cannot
be thus extinguished. Hence the possibility of very re
markable variations, not only in the aspect of the firma
ment, which is really changed, but also in the aspect of the
clouds which have that firmament as a background. It is
possible, for example, to choose clouds of such a depth of
shade that when the Nicol quenches the light behind them,
they shall vanish, being undistinguishable from the residual
dull tint which outlives the extinction of the brilliance of
the sky. A cloud less deeply shaded, but still deep enough,
when viewed with the naked eye, to appear dark on a
bright ground, is suddenly changed to a white cloud on a
dark ground by the quenching of the sky behind it. When
a reddish cloud at sunset chances to float in the region of
maximum polarization, the quenching of the sky behind it
causes it to flash with a brighter crimson. Last Easter eve
the Dartmoor sky, which had just been cleansed by a snow-

268 FRAGMENTS OF SCIENCE.

storm, wore a very wild appearance. Round the horizon it
was of steely brilliancy, while reddish cumuli and cirri
floated southward. When the sky was quenched behind
them these floating masses seemed like dull embers sud
denly blown upon ; they brightened like a fire. In the
Alps we have the most magnificent examples of crimson
clouds and snows, so that the effects just referred to may
be here studied under the best possible conditions. On
August 23, 1869, the evening Alpenglow was very fine,
though it did not reach its maximum depth and splendor.
Toward sunset I walked up the slopes to obtain a better
view of the Weisshorn. The side of the peak seen from the
Bel Alp, being turned from the sun, was tinted mauve ;
but I wished to see one of the rose-colored buttresses of the
mountain. Such was visible from a point a few hundred
feet above the hotel. The Matterhorn also, though for the
most part in shade, had a crimson projection, while a deep
ruddy red lingered along its western shoulder. Four dis
tinct peaks and buttresses of the Dom, in addition to its
dominant head — all covered with pure snow — were red
dened by the light of sunset. The shoulder of the Alphu-
bel was similarly colored, while the great mass of the Flet-
schorn was all a-glow, and so was the snowy spine of the
Monte Leone.

Looking at the Weisshorn through the Nicol, the glow
of its protuberance was strong or weak according to the
position of the prism. The summit also underwent a
change. In one position of the prism it exhibited a pale
white against a dark background ; in the rectangular posi
tion, it was a dark mauve against a light background. The
red of the Matterhorn changed in a similar manner ; but
the whole mountain also passed through striking changes
of definition. The air at the time was filled with a silvery
haze, in which the Matterhorn almost disappeared. This
could be wholly quenched by the Nicol, and then the

THE SKY OF THE ALPS. 269

mountain sprang forth with astonishing solidity and detach
ment from the surrounding air. The changes of the Dom
were still more wonderful. A vast amount of light could
be removed from the sky behind it, for it occupied the po
sition of maximum polarization. By a little practice with
the Nicol it was easy to render the extinction of the light,
or its restoration, almost instantaneous. When the sky was
quenched, the four minor peaks and buttresses, and the
summit of the Dom, together with the shoulder of the Al-
phubel, glowed as if set suddenly on fire. This was imme
diately dimmed by turning the Nicol through an angle of
90°. It was not the stoppage of the light of the sky behind
the mountains alone which produced this startling effect ;
the air between them and me was highly opalescent, and
the quenching of this intermediate glare augmented re
markably the distinctness of the mountains.

On the morning of August 24th similar effects were fine
ly shown. At 10 A. M. all three mountains, the Dom, the
Matterhorn, and the Weisshorn, were powerfully affected
by the Nicol. But in this instance also the line drawn to
the Dom being accurately perpendicular to the direction of
the solar shadows, and consequently very nearly perpen
dicular to the solar beams, the effects on this mountain were
most striking. The gray summit of the Matterhorn at the
same time could scarcely be distinguished from the opales
cent haze around it ; but when the Nicol quenched the
haze, the summit became instantly isolated, and stood out
in bold definition. It is to be remembered that in the pro
duction of these effects the only things changed are the
sky behind and the luminous haze in front of the moun
tains ; that these are changed because the light emitted
from the sky and from the haze is plane polarized light,1
and that the light from the snows and from the mountains
being sensibly unpolarized, is not directly affected by the
1 Defined at page 255.

270 FRAGMENTS OF SCIENCE.

Nicol. It will also be understood that it is not the interposi-
tion of the haze as an opaque body that renders the moun
tains indistinct, but that it is the UyJtt of the haze which
dims and bewilders the eye, and thus weakens the defini
tion of objects seen through it.

The results have a direct bearing upon what artists call
" aerial perspective." As we look from the summit of the
Aletschhorn, or from a lower elevation, at the serried crowd
of peaks, especially if the mountains be darkly colored —
covered with pines, for example — every peak and ridge is
separated from the mountains behind it by a thin blue haze
which renders the relations of the mountains as to distance
unmistakable. When this haze is regarded through the
Nicol perpendicular to the sun's rays, it is in many cases
wholly quenched, because the light which it emits in this
direction is wholly polarized. When this happens, aerial
perspective is abolished, and mountains very differently dis
tant appear to rise in the same vertical plane. Close to the
Bel Alp, for instance, is the gorge of the Massa, and beyond
the gorge is a high ridge darkened by pines. This ridge
may be projected upon the dark slopes at the opposite side
of the Rhone valley, and between both we have the blue
haze referred to, throwing the distant mountains far away.
But at certain hours of the day this haze may be quenched,
and then the Massa ridge and the mountains beyond the
Rhone seem almost equally distant from the eye. The one
appears, as it were, a vertical continuation of the other.
The haze varies with the temperature and humidity of the
atmosphere. At certain times and places it is almost as
blue as the sky itself; but to see its color, the attention
must be withdrawn from the mountains and from the trees
which cover them. In point of fact, the haze is a piece of
more or less perfect sky ; it is produced in the same man
ner, and is subject to the same laws, as the iirinament it
self. We live in the sky, not under it.

THE SKY OF THE ALPS. 271

These points were further elucidated by the deportment
of the selenite plate, with which the readers of the fore
going discourse are already acquainted. On some of the
sunny days of August the haze in the valley of the Rhone,
as looked at from the Bel Alp, was very remarkable. Tow-
ward evening the sky above the mountains opposite to my
place of observation yielded a series of the most splendidly-
colored iris-rings ; but on lowering the selenite until it had
the darkness of the pines at the opposite side of the Rhone
valley, instead of the darkness of space as a background,
the colors were not much diminished in brilliancy. I should
estimate the distance across the valley, as the crow flies, to
the opposite mountains, at nine miles ; so that a body of
air nine miles thick can, under favorable circumstances,
produce chromatic effects of polarization almost as vivid as
those produced by the sky itself.

Again : the light of a landscape, as of most other things,
consists of two parts: the one part comes purely from
superficial reflection, and this light is always of the same
color as that which falls upon the landscape ; the other
part comes to us from a certain depth within the objects
which compose the landscape, and it is this portion of the
total light which gives these objects their distinctive
colors. The white light of the sun enters all substances to
a certain depth, and is partially ejected by internal reflec
tion ; each distinct substance absorbing and reflecting the
light in accordance with the laws of its own molecular con
stitution. Thus the solar light is sifted by the landscape,
which appears in such colors and variations of color as,
after the sifting process, reach the observer's eye. Thus
the bright green of grass, or the darker color proper to the
pine, never comes to us alone, but is always mingled with
an amount of really foreign light derived from superficial
reflection. A certain hard brilliancy is conferred upon the
woods and meadows by this superficially-reflected light.

272 FRAGMENTS OF SCIENCE.

Under certain circumstances, it may be quenched by a
Nicol's prism, and we then obtain the true color of the grass
and foliage. Trees and meadows thus regarded exhibit a
richness and softness of tint which they never show as long
as the superficial light is permitted to mingle with the true
interior emission. The needles of the pines show this effect
very well, large-leaved trees still better ; while a glimmer
ing field of maize exhibits the most extraordinary variations
when looked at through the rotating Nicol.

Thoughts and questions like those here referred to took
me, in August, 1869, to the top of the Aletschhorn. The
effects described in the foregoing paragraphs were for the
most part reproduced in the summit of the mountain. I
scanned the whole of the sky with my Nicol. Both alone
and in conjunction with the selenite it pronounced the per
pendicular to the solar beams to be the direction of maxi
mum polarization. But at no portion of the firmament was
the polarization complete. The artificial sky produced in
the experiments recorded in the preceding discourse could,
in this respect, be rendered more perfect than the natural
one ; while the gorgeous " residual blue " which makes its
appearance when the polarization of the artificial sky ceases
to be perfect, was strongly contrasted with the lack-lustre
hue which, in the case of the firmament, outlived the ex
tinction of the brilliance. With certain substances, how
ever, artificially treated, this dull residue may also be ob
tained.

All along the arc from the Matterhorn to Mont Blanc
the light of the sky immediately above the mountains was
powerfully acted upon by the Nicol. In some cases the
variations of intensity were astonishing. I have already
said that a little practice enables the observer to shift the
Nicol from one position to another so rapidly as to render
the alternate extinction and restoration of the light imme
diate. When this was done along the arc to which I have

THE SKY OF THE ALPS.

273

referred, the alternations of light and darkness resembled
the play of sheet-lightning behind the mountains. My
notes state that there was an element of awe connected
with the suddenness with which the mighty masses, ranged
along the line referred to, changed their aspect and defi
nition under the operation of the prism.

XI.
DUST AND DISEASE.

A DISCOURSE.

DELIVEEED IN THE EOYAL INSTITUTION OF GEEAT BEITAIN.

January 21, 1870. With Additions.

"Tout iiiiasmc contagieux ales proprictes, 1* dc rcproduire son ana
logue dans une maladie qu'il a occasionnee ; 2° de sc repandre ct do
sYntrmlrc a, 1'infini, en vertu dc ee developpemcnt secondairc, c'est-a-
dire, aussi longtcmps qu'il existe unematiere propre a rccevoir le miasmc,
ct en i produirc un nouvcau. Cos deux proprietcs lui sont communes
avcc les germes dcs animaux et dcs plantes.

HlLDEBRAND.

XI.

ON DUST AND DISEASE.

Experiments on Dusty Air.

SOLAR light in passing through a dark room reveals its
track by illuminating the dust floating in the air. " The
sun," says Daniel Culverwell, " discovers atonies, though
they be invisible by candle-light, and makes them dance
naked in his beams." 3

In my researches on the decomposition of vapors by
light, I was compelled to remove these " atonies " and this
dust. It was essential that the space containing the vapors
should embrace no visible thing ; that no substance capable
of scattering the light in the slightest sensible degree
should, at the outset of an experiment, be found in the " ex
perimental tube " traversed by the luminous beam.

For a long time I was troubled by the appearance there
of floating dust, which though invisible in diffuse daylight
was at once revealed by a powerfully-condensed beam. Two
tubes were placed in succession in the path of the air : the
one containing fragments of glass wetted with concentrated
sulphuric acid ; the other, fragments of marble wetted with
a strong solution of caustic potash. To my astonishment
the dust passed through both. The air of the Royal Insti
tution sent through these tubes at a rate sufficiently slow

1 On a day of transient shadows there is something almost magical in
the rise and dissolution of the luminous beams among the scaffolding
poles of the Royal Albert Hall.

278 FRAGMENTS OF SCIENCE.

to dry it, and to remove its carbonic acid, carried into the
experimental tube a considerable amount of mechanically
suspended matter, which was illuminated when the beam
passed through the tube. The effect was substantially the
same when the air was permitted to bubble through the
liquid acid and through the solution of potash.

Thus, on October 5, 18G8, successive charges of air were
admitted through the potash and sulphuric acid into the ex
hausted experimental tube. Prior to the admission of the
air the tube was optically empty • it contained nothing
competent to scatter the light. After the air had entered
the tube, the conical track of the electric beam was in all
cases clearly revealed. This, indeed, was a daily observa
tion at the time to which I now refer.

I tried to intercept this floating matter in various ways ;
and on the day just mentioned, prior to sending the air
through the drying apparatus, I carefully permitted it to
pass over the tip of a spirit-lamp flame. The floating mat
ter no longer appeared, having been burnt up by the flume.
It was, therefore, of organic origin. I was by no means
prepared for this result ; for I had thought that the dust of
our air was, in great part, inorganic and non-combustible.

I had constructed a small gas-furnace, now much em
ployed by chemists, containing a platinum tube, which
could be heated to vivid redness.1 The tube contained a
roll of platinum gauze, which, while it permitted the air to
pass through it, insured the practical contact of the dust
with the incandescent metal. The air of the laboratory
was permitted to enter the experimental tube, sometimes
through the cold, and sometimes through the heated, tube
of platinum. The rapidity of admission was also varied.
In the first column of the following table the quantity of
air operated on is expressed by the number of inches which
the mercury gauge of the air-pump sank when the air en-
1 Pasteur was, I believe, the first to employ such a tube.

DUST AND DISEASE. 279

tercd. In the second column the condition of the platinum
tube is mentioned, and in the third the state of the air
which had entered the experimental tube.

Quantity of Air. State of Platinum Tubo. State of Experimental Tube.

15 inches Cold Full of particles.

15 " Red hot Optically empty.

The phrase " optically empty " shows that when the con
ditions of perfect combustion were present, the floating
matter totally disappeared. It was wholly burnt up, leav
ing no sensible residue. The experiment was repeated
many times, with the same invariable result.

The whole of the visible particles floating in the air of
London rooms being thus proved to be of organic origin,1
I sought to burn them up at the focus of a concave re
flector. One of the powerfully convergent mirrors em
ployed in my experiments on combustion by dark rays was
here made use of, but I failed in the attempt. Doubtless
the floating particles are in part transparent to radiant heat,
and are so far incombustible by such heat. Their rapid
motion through the focus also aids their escape. They do
not linger there sufficiently long to be consumed. A flame
it was evident would burn them up, but I at first thought
the presence of the flame would mask its own action among
the particles.

1 According to an analysis kindly furnished to me by Dr. Percy, the dust
collected from the walk of the British Museum contains fully 50 per cent,
of inorganic matter. I have every confidence in the results of this dis
tinguished chemist ; they show that the floating dust of our rooms is, as it
were, winnowed from the heavier matter. As bearing directly upon this
point, I may quote the following passage from Pasteur : " Mais ici sc
presente une remarque : la poussiere que 1'on trouve a la surface de tous
les corps est soumise constamment & des courants d'air, qui doivent sou-
lever ses particules les plus legeres, au nombre desquelles se trouvent, sans
doute, de preference les corpuscules organises, ceufs ou spores, moiiis
lourds gcneralement que les particules minerales."

280 FRAGMENTS OF SCIENCE.

In a cylindrical beam, which strongly illuminated the
dust of the laboratory, was placed an ignited spirit-lamp.
Mingling with the flame, and round its rim, were seen
curious wreaths of darkness resembling an intensely-black
smoke. On lowering the flame below the beam the same
dark masses stormed upward. They were at times blacker
than the blackest smoke that I have ever seen issuing from
the funnel of a steamer ; and their resemblance to smoke
was so perfect as to lead the most practised observer to
conclude that the apparently-pure flame of the alcohol-lamp
required but a beam of sufficient intensity to reveal its
clouds of liberated carbon.

But is the blackness smoke ? This question presented
itself in a moment. A red-hot poker was placed under
neath the beam, and from it the black wreaths also as
cended. A large hydrogen-flame was next employed, and
it produced those whirling masses of darkness far more
copiously than either the spirit-flame or poker. Smoke was
therefore out of the question.

"What, then, was the blackness ? It was simply that of
stellar space ; that is to say, blackness resulting from the
absence from the track of the beam of all matter competent
to scatter its light. When the flame was placed below the
beam, the floating matter was destroyed in situ ; and the
air, freed from this matter, rose into the beam, jostled aside
the illuminated particles, and substituted for their light the
darkness due to its own perfect transparency. Nothing
could more forcibly illustrate the invisibility of the agent
which renders all things visible. The beam crossed, un
seen, the black chasm formed by the transparent air, while
at both sides of the gap the thick-strewn particles shone
out like a luminous solid under the powerful illumina
tion.

But here a rather perplexing difficulty meets us. It is
not necessary to burn the particles to produce a stream of

DUST AND DISEASE. 281

darkness. Without actual combustion, currents may be
generated which shall exclude the floating matter, and
therefore appear dark amid the surrounding brightness. I
noticed this effect first on placing a red-hot copper ball be--
low the beam, and permitting it to remain there until its
temperature had fallen below that of boiling water. The
dark currents, though much enfeebled, were still produced.
They may also be produced by a flask filled with hot
water.

To study this effect a platinum wire was stretched
across the beam, the two ends of the wire being connected
with the two poles of a voltaic battery. To regulate the
strength of the current a rheostat was placed in the circuit.
Beginning with a feeble current the temperature of the
wire was gradually augmented ; but, before it reached the
heat of ignition, a flat stream of air rose from it, which
when looked at edgeways appeared darker and sharper than
one of the blackest lines of Fraunhofer in the solar spec
trum. Right and left of this dark vertical band the float
ing matter rose' upward, bounding definitely the non-lumi
nous stream of air. What is the explanation? Simply
this : The hot wire rarefied the air in contact with it, but
it did not equally lighten the floating matter. The con
vection current of pure air therefore passed upward among
the inert particles, dragging them after it right and left, but
forming between them an impassable black partition. This
elementary experiment enables us to render an account of
the dark currents produced by bodies at a temperature be
low that of combustion.

When the wire is white hot, it sends up a band of in
tense darkness. This, I say, is due to the destruction of
the floating matter. But even when its temperature does
not exceed that of boiling water, the wire produces a dark
ascending current. This, I say, is due to the distribution
of the floating matter. Imagine the wire clasped by the

282 FRAGMENTS OF SCIEXCE.

mote-filled air. My idea is that it heats the air and lightens
it, without in the same degree lightening the floating mat
ter. The tendency, therefore, is to start a current of clean
air through the mote-filled air. Figure the motion of the
air all round the wire. Looking at its transverse section
we should see the air at the bottom of the wire bending
round it right and left in two branch-currents, ascend
ing its sides and turning to fill the, partial vacuum created
above the wire. Now as each new supply of air, filled with
its motes, comes in contact with the hot wire, the clean
air, as just stated, is first started through the inert motes.
They are dragged after it, but there is a fringe of cleansed
air in advance of the motes. The two purified fringes of
tho two branch-currents unite above the wire, and, keep
ing the motes that once belonged to them right and left,
they form by their union the dark band observed in the
experiment. This process is incessant. Always the mo
ment the mote-filled air touches the wire this distribution
is effected, a permanent dark band being thus produced.
Could the air and the particles under the wire pass through
its mass we should have a vertical current of particles, but
no dark band. For here, though the motes would be left
behind at starting, they would hotly follow the ascending
current and thus abolish the darkness.

It has been said that when the platinum wire is intensely
heated, the floating matter is not only distributed, but de
stroyed. Let this be proved. I stretched a wire about 4
inches long through the air of an ordinary glass shade, rest
ing on its stand. Its lower rim rested on cotton-wool, which
also surrounded the rim. The wire was raised to a white
lu'jit by an electric em-rent. The air expanded, and some
of it was forced through the cotton-wool, while, when the
current was interrupted and the air within the shade cooled,
the expelled air in its return did not carry motes along with
it. At the beginning of this experiment the shade was

DUST AND DISEASE. 283

charged with floating matter ; at the end of half an hour it
was optically empty.

A second experiment was thus arranged : on the wooden
base of a cubical glass shade, measuring 11-J- inches a side,
upright supports were fixed, and from one support to the
other 38 inches of platinum wire were stretched in four
parallel lines. The ends of the platinum wire were soldered
to two stout copper wires, which passed through the base
of the shade and could be connected with a battery. As
in the last experiment, the shade rested upon cotton-wool.
A beam sent through the shade revealed the suspended
matter. The platinum wire was then raised to whiteness.
In five minutes there was a sensible diminution of the mat
ter, and in ten minutes it was totally consumed. Tin's
proves that when the platinum wire is sufficiently heated,
the floating matter, instead of being distributed, is destroyed.

But is not the matter really of a character which permits
of its destruction by the moderately-heated platinum wire ?
Here is the reply :

1. A platinum tube, with its plug of platinum gauze,
was connected with an experimental tube, through which a
powerful beam could be sent from an electric lamp placed
at its end. The platinum tube was heated till it glowed
feebly but distinctly in the dark. The experimental tube
was exhausted, and then filled with air which had passed
through the red-hot tube. A considerable amount of float
ing matter which had escaped combustion was revealed by
the electric beam.

2. The tube was raised to brighter redness and the air
permitted to pass slowly through it. Though diminished
in quantity, a certain amount of floating matter passed into
the exhausted experimental tube.

3. The platinum tube was rendered still hotter; a
barely perceptible trace of the floating matter now passed
through it.

284 FRAGMENTS OF SCIENCE.

4. The experiment was repeated, with the difference
that the air was sent more slowly through the red-hot tube.
The floating matter was totally destroyed.

5. The platinum tube was now lowered until it bordered
upon a visible red heat. The air sent through it still more
slowly than in the last experiment carried with it a cloud
of floating matter.

If, then, the suspended matter is destroyed by a bright-
red heat, much more is it destroyed by a flame, whose tem
perature is vastly higher than any here employed. So that
the blackness introduced into a luminous beam where a
flame is placed beneath it is due, as stated, to the destruc
tion of the suspended matter. At a dull-red heat, how
ever, and still more when only on the verge of redness, the
platinum tube permitted the motes to pass freely. In the
latter case the temperature was 800° or 900° Fahrenheit.
This was unable to destroy the suspended matter ; much
less, therefore, would a platinum wire heated to 212° be
competent to do so. Such a wire can only distribute the
matter, not destroy it.

The floating dust is revealed by intense local illumina
tion. It is seen by contrast with the adjacent illuminated
space ; the brighter the illumination the more sensible is
the difference. Now, the beam employed in the foregoing
experiments is not of the same brightness throughout its
entire transverse section, Pass a white switch, or an ivory
paper-cutter, rapidly across the beam, the impression of its
section will linger on the retina. The section seems to float
for a moment in the air as a luminous circle, with a rim much
brighter than its central portion. The core of the beam is
thus seen to be enclosed by an intensely-luminous sheath.
An effect complementary to this is observed when the beam
is intersected by the dark band from the platinum wire.
The brighter the illumination the greater must be the rela
tive darkness consequent on the withdrawal of the light.

DUST AND DISEASE. 285

Hence the cross-section of the sheath surrounds the dark
band as a darker ring.

Oxygen, hydrogen, nitrogen, carbonic acid, so prepared
as to exclude all floating particles, produce the darkness
when poured or blown into the beam. Coal-gas does the
same. An ordinary glass shade placed in the air with its
mouth downward permits the track of the beam to be seen
crossing it. Let coal-gas or hydrogen enter the shade by a
tube reaching to its top, the gas gradually fills the shade
from the top downward. As soon as it occupies the space
crossed by the beam, the luminous track is instantly abol
ished. Lifting the shade so as to bring the common bound
ary of gas and air above the beam, the track flashes forth.
After the shade is full, if it be inverted, the gas passes up
ward like a black smoke among the illuminated particles.

The air of our London rooms is loaded with this organic
dust, nor is the country air free from its presence. However
ordinary daylight may permit it to disguise itself, a suffi
ciently powerful beam causes dust suspended in air to ap
pear almost as a semi-solid. Nobody could, in the first
instance, without repugnance, place the mouth at the illu
minated focus of the electric beam and inhale the thickly-
massed dust revealed there. Nor is the repugnance abol
ished by the reflection that, although we do not see the
floating particles, we are taking them into our lungs every
hour and minute of our lives.

The Germ-Theory of Contagious Disease.

There is no respite to this contact with the floating mat
ter of the air ; and the wonder is, not that we should suffer
occasionally from its presence, but that so small a portion
of it, and even that but rarely diffused over large areas,
should appear to be deadly to man. And what is this por
tion ? It was some time ago the current belief that epidemic

280 FRAGMENTS OF SCIENCE.

diseases generally were propagated by a kind of malaria,
which consisted of organic matter in a state of motor-decay;
that when such matter was taken into the body through
the lungs, skin, or stomach, it had the power of spreading
there the destroying process which had attacked itself.
Such a power was visibly exerted in the case of yeast. A
little leaven was seen to leaven the whole lump, a mere
speck of matter in this supposed state of decomposition be
ing apparently competent to propagate indefinitely its own
decay. Why should not a bit of rotten malaria work in a
similar manner within the human frame ? In 1836 a very
wonderful reply was given to this question. In that year
( 'agnlard de la Tour discovered the yeast-plant, a living or
ganism, which, when placed in a proper medium, feeds, grows,
and reproduces itself, and in this way carries on the process
which we name fermentation. By this striking discovery
fermentation was connected with organic growth.

Schwann, of Berlin, discovered the yeast-plant inde
pendently about the same time; and in February, 1837, he
also announced the important result that, when a decoction
of meat is effectually screened from ordinary air, and sup
plied solely with calcined air, putrefaction never sets in.
Putrefaction, therefore, he affirmed to be caused by some
thing derived from the air, which something could be de
stroyed by a sufficiently high temperature. The results of
S\vann were confirmed by the independent experiments of
Helmholtz, Ure, and Pasteur, while other methods, pursued
by Schultze and by Schroeder and Dusch, led to the same
result. But as regards fermentation, the minds of chemists,
influenced probably by the great authority of Gay-Lussac,
fell back upon the old notion of matter in a state of decay.
It was not the living yeast-plant, but the dead or dyini;-
parts of it, which, assailed by oxygen, produced the fer
mentation. This notion was finally exploded by Pasteur,
lie proved that the so-called "ferments" are not such;

DUST AXD DISEASE. 287

that the true ferments are organized beings, which find in
the reputed ferments their necessary food.

Side by side with these researches and discoveries, and
fortified by them and others, has run the germ-theory of
epidemic disease. The notion was expressed by Kirchcr
and favored by Linngeus, that epidemic diseases are due
to germs which float in the atmosphere, enter the body, and
produce disturbance by the development within the body
of parasitic life. While it was still struggling against
great odds, this theory found an expounder and a defender
in the President of this institution. At a time when most
of his medical brethren considered it a wild dream, Sir
Henry Holland contended that some form of the germ-
theory was probably true. The strength of this theory
consists in the perfect parallelism of the phenomena of con
tagious disease with those of life. As a planted acorn
gives birth to an oak competent to produce a whole crop
of acorns, each gifted with the power of reproducing its
parent-tree ; and as thus from a single seedling a whole
forest may spring ; so, it is contended, these epidemic dis
eases literally plant their seeds, grow, and shake abroad
new germs, which, meeting in the human body their proper
food and temperature, finally take possession of whole
populations. There is nothing to my knowledge in pure
chemistry which resembles the power of self-multiplication
possessed by the matter which produces epidemic disease.
If you sow wheat you do not get barley ; if you sow small
pox you do not get scarlet fever, but small-pox indefinitely
multiplied, and nothing else. The matter of each con
tagious disease reproduces itself as rigidly as if it were (as
Miss Nightingale puts it) dog or cat.

*arasitic Diseases of Silk-worms. Pasteups Researches.

It is admitted on all hands that some diseases are the
product of parasitic growth. Both in man and lower crea-

288 FRAGMENTS OF SCIENCE.

tures, the existence of such diseases has been demonstrated.
I am enabled to lay before you an account of an epidemic
of this kind, thoroughly investigated and successfully corn-
batted by M. Pasteur. For fifteen years a plague had
raged among the silk-worms of France. They had sickened
and died in multitudes, while those that succeeded in spin
ning their cocoons furnished only a fraction of the normal
quantity of silk. In 1853 the silk culture of France pro
duced a revenue of one hundred and thirty millions of
francs. During the twenty previous years the revenue had
doubled itself, and no doubt was entertained as to its future
augmentation. The weight of the cocoons produced in
1853 was twenty-six millions of kilogrammes ; in 18G5 it
had fallen to four millions, the fall entailing in the single
year last mentioned a loss of one hundred millions of francs.
The country chiefly smitten by this calamity happened
to be that of the celebrated chemist, Dumas, now perpetual
secretary of the French Academy of Sciences. He turned
to his friend, colleague, and pupil, Pasteur, and besought
him with an earnestness which the circumstances rendered
almost personal, to undertake the investigation of the
malady. Pasteur at this time had never seen a silk-worm,
and he urged his inexperience in reply to his friend. But
Dumas knew too well the qualities needed for such an in
quiry to accept Pasteur's reason for declining it. "Je
mets," said he, " un prix extreme & voir votre attention
fixee sur la question qui interesse mon pauvre pays ; la
misere surpasse tout ce que vous pouvez imaginer."
Pamphlets about the plague had been showered upon the
public, the monotony of waste-paper being broken at rare
intervals by a more or less useful publication. " The
Pharmacopoeia of the Silk-worm," wrote M. Cornalia in
1860, "is now as complicated as that of man. Gases,
liquids, and solids have been laid under contribution.
From chlorine to sulphurous acid, from nitric acid to rum,

DUST AND DISEASE. 289

from sugar to sulphate of quinine — all has been invoked in
behalf of this unhappy insect." The helpless cultivators,
moreover, welcomed with ready trustfulness every new
remedy, if only pressed upon them with sufficient hardi
hood. It seemed impossible to diminish their blind confi
dence in their blind guides. In 1863 the French Minister
of Agriculture himself signed an agreement to pay 500,000
francs for the use of a remedy which its promoter declared
to be infallible. It was tried in twelve different depart
ments of France, and found perfectly useless. In no single
instance was it successful. It was under these circum-
.stances that M. Pasteur, yielding to the entreaties of his
friend, betook himself to Alais in the beginning of June,
1865. As regards silk husbandry, this was the most im
portant department in France, and it was also that which
had been most sorely smitten by the epidemic.

The silk-worm had been previously attacked by mus-
cardine, a disease proved by Bassi to be caused by a vege
table parasite. Though not hereditary, this malady was
propagated annually by the parasitic spores, which, wafted
by winds, often sowed the disease in places far removed
from the centre of infection. Muscardine is now said to
be very rare ; but for the last fifteen or twenty years a
deadlier malady has taken its place. A frequent outward
sign of this new disease are the black spots which cover
the silk-worms, hence the name p'ebrine, first applied to
the plague by M. de Quatrefages, and adopted by Pasteur.
Pebrine declares itself in the stunted and unequal growth
of the worms, in the languor of their movements, in their
fastidiousness as regards food, and in their premature
death. The track of discovery as regards the epidemic
is this: In 1849 Guerin Me*neville noticed in the blood
of silk-worms vibratory corpuscles which he supposed to
be endowed with independent life. Filippi proved him
wrong, and showed that the motion of the corpuscles was
13

LMJO FRAGMENTS OF Sl'IKNt'K.

the well-known Brownian motion. But Filippi himself
committed the error of supposing the corpuscles to be
normal to the life of the insect. They are really the cause
of its mortality — the form and substance of its disease.
This was well described by Cornalia ; while Lebert and
Frey subsequently found the corpuscles not only in the
blood, but in all the tissues of the insect. Osimo, in 1857,
discovered them in the eggs, and on this observation Yittu-
diani founded, in 1859, a practical method of distinguishing
healthy from diseased eggs. The test often proved falla
cious, and it was never extensively applied.

These corpuscles take possession of the intestinal canal,
and spread thence throughout the body of the worm.
They fill the silk cavities, the stricken insect often going
through the motions of spinning without any material to
answer to the act. Its organs, instead of being filled writh
the clear viscous liquid of the silk, are packed to disten-
tion by the corpuscles. On this feature of the plague Pas
teur fixed his entire attention. The cycle of the silk
worm's life is briefly this: From the fertile egg comes
the little worm, which grows, and casts its skin. This pro
cess of moulting is repeated two or throe times at subse-
qjient intervals during the life of the insect. After the last
moulting the worm climbs the brambles placed to receive
it, and spins among them its cocoon. It passes thus into
a chrysalis ; the chrysalis becomes a moth, and the moth
when liberated lays the eggs which form the starting-point
of a new cycle. Now Pasteur proved that the plague-cor
puscles might be incipient in the egg, and escape detec
tion ; they might also be germinal in the worm, and still
bailie the microscope. But as the worm grows, the cor
puscles grow also, becoming larger and more defined. In
the aged chrysalis they are more pronounced than in the
worm ; while in the moth, if either the egg or the worm
from which it comes should have been at all stricken, the

DUST AND DISEASE. 291

corpuscles infallibly appear, offering no difficulty of detec
tion. This was the first great point made out in 1865 by
Pasteur. The Italian naturalists, as aforesaid, recom
mended the examination of the eggs before risking their
incubation. Pasteur showed that both eggs and worms
might be smitten and still pass muster, the culture of such
eggs or such worms being sure to entail disaster. He made
the moth his starting-point in seeking to regenerate the race.
Pasteur made his first communication on this subject to
the Academy of Sciences in September, 1865. It raised
a cloud of criticism. Here, forsooth, was a chemist rashly
quitting his proper metier and presuming to lay down the
law for the physician and biologist on a subject which was
eminently theirs. " On trouva etrange que je fusse si peu
au courant de la question ; on m'opposa des travaux qui
avaient paru depuis longtemps en Italic, dont les resultats
montraient Pinutilite de mes efforts, et 1'impossibilite" d'ar-
river a un resultat pratique dans la direction que je m'etais
engage. Que mon ignorance fut grande au sujet des re-
cherches sans nombre qui avaient paru depuis quinze an-
nees." Pasteur heard the buzz, but he continued his work.
In choosing the eggs intended for incubation, the cultiva
tors selected those produced in the successful " educa
tions " of the year. But they could not understand the
frequent and often disastrous failures of their selected
eggs ; for they did not know, and nobody prior to Pasteur
was competent to tell them, that the finest cocoons may
envelope doomed corpusculous moths. It was not, how
ever, easy to make the cultivators accept new guidance.
To strike their imagination, and if possible determine their
practice, Pasteur hit upon the expedient of prophecy. In
1866 he inspected at St. Hippolyte-du-Fort fourteen differ
ent parcels of eggs intended for incubation. Having ex
amined a sufficient number of the moths which produced
these eggs, he wrote out the prediction of what would oc-

292 FRAGMENTS OF SCIENCE.

cur in 1867, and placed the prophecy as a sealed letter in
the hands of the Mayor of St. Hippolyte.

In 1867 the cultivators communicated to the mayor
their results. The letter of Pasteur was then opened and
read, and it was found that in twelve out of fourteen cases
there was absolute conformity between his prediction and
the observed facts. Many of the groups had perished to
tally ; the others had perished almost totally ; and this
was the prediction of Pasteur. In two out of the fourteen
cases, instead of the prophesied destruction, half an aver
age crop was obtained. Now, the parcels of eggs here re
ferred to were considered healthy by their owners. They
had been hatched and tended in the firm hope that the la
bor expended on them would prove remunerative. The appli
cation of the moth-test for a few minutes in 1866 would
have saved the labor and averted the disappointment. Two
additional parcels of eggs were at the same time submitted
to Pasteur. He pronounced them healthy ; and his words
were verified by the production of an excellent crop.
Other cases of prophecy still more remarkable, because
more circumstantial, are recorded in Pasteur's work.

Pasteur subjected the development of the corpuscles to
a searching investigation. With admirable skill and com
pleteness he examined the various modes by which the
plague is propagated. He obtained perfectly healthy
worms from moths perfectly free from corpuscles, and se
lecting from them 10, 20, 30, 50, as the case might be, he
introduced into the worms the corpusculous matter. It was
first permitted to accompany the food. Let us take a sin
gle example out of many. Rubbing up a small corpuscu
lous worm in water, he smeared the mixture over the mul
berry-leaves. Assuring himself that the leaves had been
eaten, he watched the consequences from day to day. Side
by side with the infected worms he reared their fellows,
keeping them as much as possible out of the wray of infec-

DUST AND DISEASE. 293

tion. These constituted his " lot tcmoign," his standard of
comparison. On the 16th of April, 1868, he thus infected
thirty worms. Up to the 23d they remained quite well.
On the 25th they seemed well, but on that day corpuscles
were found in the intestines of two of them. They first
form in the tunic of the intestine. On the 27th, or eleven
days after the infected repast, two fresh worms were exam
ined, and not only was the intestinal canal found in each
case invaded, but the silk-organ itself was found charged
with corpuscles. On the 28th, the twenty-six remaining
worms were covered by the black spots of pebrine. On the
30th, the difference of size between the infected and non-
infected worms was very striking, the sick worms being not
more than two-thirds of the size of the healthy ones. On
the 2d of May, a worm which had just finished its fourth
moulting was examined. Its whole body was so filled with
corpuscles as to excite astonishment that it could live.
The disease advanced, the worms died and were examined,
and on the llth of May only six out of the thirty remained.
They were the strongest of the lot, but, on being searched,
they also were found charged with corpuscles. Not one of
the thirty worms had escaped ; a single corpusculous meal
had poisoned them all. The standard lot, on the contrary,
spun their fine cocoons, and two only of their moths were
found to contain any trace of corpuscles, which had, doubt
less, been introduced during the rearing of the worms.

As his acquaintance with the subject increased, Pas
teur's desire for precision augmented, and he finally gives
the growing number of corpuscles seen in the field of his
microscope from day to day. After a contagious repast,
the number of worms containing the parasite gradually
augmented until finally it became cent, per cent. The
number of corpuscles would at the same time rise from 0 to
1, to 10, to 100, and sometimes even to 1,000 or 1,500 for a
single field of his microscope. He then varied the mode

L'Ol FRAGMENTS OF SCIENCE.

of infection. He inoculated healthy worms with the cor-
pusculous matter, and watched the consequent growth of
the disease. He showed how the worms inoculate each
other by the infliction of visible wounds with their claws.
In various cases he washed the claws, and found corpuscles
in the water. He demonstrated the spread of infection by
the simple association of healthy and diseased worms. The
diseased worms sullied the leaves by their dejections, they
also used their claws, and spread infection -in both ways.
It was no hypothetical infected medium that killed the
worms, but a definitely-organized and isolated thing. He
examined the question of contagion at a distance, and de
monstrated its existence. In fact, as might be expected
from Pasteur's antecedents, the investigation was exhaus
tive, the skill and beauty of his manipulation finding fitting
correlatives in the strength and clearness of his thought.

The following quotation from Pasteur's work clearly
shows the relation in which his researches stand to this
great question :

" Place," lie says, " the most skilful educator, even the most expert
microscopist, in presence of large educations which present the symp
toms described in our experiments ; his judgment will necessarily be er
roneous if he confines himself to the knowledge which preceded my re
searches. The worms will not present to him the slightest spot of
pebrine ; the microscope will not reveal the existence of corpuscles ; the
mortality of the worms will be null or insignificant ; and the cocoons
leave nothing to be desired. Our observer would, therefore, conclude
without hesitation that the eggs produced will be good for incubation.
The truth is, on the contrary, that all the worms of these fine crops have
been poisoned ; that, from the beginning, they carried in them the germ
of the malady ; ready to multiply it. -df In -yond measure in the chrysa
lides and the moths, thence to pass into the eggs and smite with sterility
the next generation. And what is the first causvj of the evil concealed
under so deceitful an exterior ? In our experiments we can, so to speak,
touch it with our fingers. It is entirely the eifect of a single corpuseu-
lous repast ; an effect more or less prompt according to the epoch of life
of the worm that has eaten the poisoned food."

DUST AND DISEASE. 295

Pasteur describes in detail his method of securing
healthy eggs, which is nothing less than a mode of restor
ing to France her ancient prosperity in silk husbandry.
And the justification of his work is to be found in the re
ports which reached him of the application, and the unpar*
alleled success of his method, at the time he was putting
his researches together for final publication. In France
and Italy his method has been pursued with the most sur
prising results. It was an up-hill fight which led to this
triumph, but opposition stimulated Pasteur, and thus, with
out meaning it, did good service. " Ever," he says, " since
the commencement of these researches, I have been ex*
posed to the most obstinate and unjust contradictions ; but
I have made it a duty to leave no trace of these contests in
this book." And, in reference to parasitic diseases, he uses
the following weighty words : " II est au pouvoir de 1'homme
de faire disparaitre de la surface du globe les maladies par-
asitaires, si, comme c'estma conviction, la doctrine des gene
rations spontanees est une chimere."

Pasteur dwells upon the ease with which an island like
Corsica, might be absolutely isolated from the silk-worm
epidemic. And, with regard to other epidemics, Mr. Simon
describes the extraordinary exemption of the Scilly Isles for
the ten years extending from 1851 to 1860. Of the 627
registration districts of England, one only had an entire es
cape from diseases which, in whole or in part, were preva
lent in all the others : " In all the ten years it had not a
single death by measles, nor a single death by small-pox,
nor a single death by scarlet fever. And why ? Not be
cause of its general sanitary merits, for it had an average
amount of other evidence of unhealthiness. Doubtless, the
reason of its escape was that it was insular. It was the
district of the Scilly Isles • to which it was most improb
able that any febrile contagion should come from without.
And its escape is an approximative proof that, at least for

290 FRAGMENTS OF SCIENCE.

those ten years, no contagium of measles, nor any contagium
of scarlet fever, nor any contagium of small-pox, had arisen
spontaneously within its limits." It may be added that
there were only seven districts in England in which no
death from diphtheria occurred, and that, of those seven S
districts, the district of the Scilly Isles was one. S

A second parasitic disease of silk-worms, called in France
laflacherie, coexistent with pebrine but quite distinct from
it, has also been investigated. Enough, however, has been
said to send such of you as are interested in these questions
to the original volumes for further information. To one
important practical point M. Pasteur, in a letter written to
me, directs attention :

" Permettez-moi de terminer ccs quclqucs lignes que jc dois dieter,
vaiiuMi que je suis par la maladie, en vous faisant observer que vous
rendriez service aux Colonies de la Grandc-Bretagne en repandant la
connaissance de ce livre, etdes principesque j'etablis touchant la maladie
des vers a soie. Beaucoup de ces colonies pourraient cultiver le miirier
avcc succes, et en jetant les yeux sur mon ouvrage vous vous convaincrez
qu'il est facile aujourd'hui, non-seulement d'eloigncr la maladio
, mais en outre de donner aux recoltes de la soie une prospe"rite
qu'elles u'ont jamais cue."

Origin and Propagation of Contagious Matter.

Prior to Pasteur, the most diverse and contradictory
opinions were entertained as to the contagious character of
p6brine ; some stoutly affirmed it, others as stoutly denied
it. But on one point all were agreed. " They believed in
the existence of a deleterious medium, rendered epidemic
by some occult and mysterious influence, to which was at
tributed the cause of the disease." Those acquainted with
medical literature will not fail to observe an instructive
analogy here. \Ve have on the one side accomplished
writers ascribing epidemic diseases to " deleterious media,"
which arise spontaneously in crowded hospitals and over

DUST AND DISEASE. 297

ill-smelling drains. According to them the matter of epi
demic disease is formed de novo in a putrescent atmosphere.
On the other side we have writers, clear, vigorous, with
well-defined ideas and methods of research, contending that
the matter which produces epidemic disease comes always
from a parent-stock. It behaves as germinal matter, and
they do not hesitate to regard it as such. They no more
believe in the spontaneous generation of such diseases than
they do in the spontaneous generation of mice. Pasteur,
for example, found that p£brine had been known for an in
definite time as a disease among silk-worms. The develop
ment of it which he combated was merely the expansion of
an already existing power, the bursting into open confla
gration of a previously smouldering fire. There is nothing
surprising in this ; for though epidemic disease requires a
special contagium to produce it, surrounding conditions
must have a potent influence on its development. Common
seeds may be duly sown, but the conditions of temperature
and moisture may be such as to restrict or altogether pre
vent the subsequent growth. Looked at, therefore, from
the point of view of the germ-theory, the exceptional energy
which epidemic disease from time to time exhibits is not
out of harmony with the method of Nature. You some
times hear diphtheria spoken of as if it were a new disease
of the last twenty years ; but Mr. Simon tells me that from
about three centuries ago, when tremendous epidemics of it
began to rage in Spain (where it was named Garrotillo),
and soon afterward in Italy, the disease has been well
known to all successive generations of doctors ; and that,
for instance, in or about 1758, Dr. Starr, of Liskeard, in a
communication to the Royal Society, particularly described
the disease, with all the characters which have recently
again become familiar, but under the name of morbus stran-
gulatorius, as then severely epidemic in Cornwall ; a fact
the more interesting as diphtheria, in its more modern re-

298 FRAGMENTS OF SCIEX< K.

appearance, again showed predilection for that remote
county. Many also believe that the black death of five
centuries ago, has disappeared as mysteriously as it came,
but Mr. Simon finds that it is believed to be prevalent at
this hour in some of the northwestern parts of India.

Let me here state an item of my own experience. When
I was at the Bel Alp last year the clergyman appointed to
that station received letters informing him of the breaking
out of scarlet fever among his children. He lived, if I re
member rightly, on the healthful eminence of Dartmoor,
and it was difficult to imagine how scarlet fever could have
been wafted to the place. A drain ran close to his house,
and on it his suspicions were manifestly fixed. Some of
our medical writers would fortify him in this notion, while
those of another school would deny to a drain, however
foul, the powor of producing a specific disease. After close
inquiry, he recollected that a hobby-horse had been used
both by his boy and another that a short time previously
had passed through scarlet fever. Drains and cesspools
are by no means in such evil odor as they used to be. A
fetid Thames and a low death-rate occur from time to time
together in London. For, if the special matter or germs of
epidemic disorder be not present, a corrupt atmosphere,
however obnoxious otherwise, will not produce the disorder.
Corrupted air may promote an epidemic, but cannot origi
nate it. On the other hand, through the transport of the
special germ or vims, disease may develop itself in regions
win TO the drainage is good and the atmosphere pure.

If you see a new thistle growing in your field you f»vl
sure that its seed has been wafted thither. Just as sure
does it seem that the contagious matter of scarlatina, or
any other contagious fever, has been transplanted to the
place where it newly appears. AYith a clearness and con-
clusiveness not to be surpassed Dr. "William Budd has
<l such diseases from place to place; showing how

DUST AND DISEASE. 299

they plant themselves at distinct foci among populations
subjected to the same atmospheric influences, just as grains
of corn might be carried in the pocket and sown. Hilde-
brand, to whose remarkable work, Du Typhus Contagieux,
Dr. cle Mussy has directed my attention, gives the following
striking case, both of the durability and the transport of
the virus of scarlatina : " Un habit noir que j'avais en visi
tant une malade attaqu<§e de scarlatine, et que je portai de
Yienne de Podolie, sans 1'avoir mis depuis plus d'un an et
demi, ine communiqua, des que je fus arrive", cette maladie
contagieuse, que je repandis ensuite dans cette province, ou
elle etait jusqu'alors presque inconnue." Some years ago
Dr. de Mussy himself was summoned to a country-house in
Surrey to see a young lady who was suffering from a dropsy,
evidently the consequence of scarlatina. The original dis
ease being of a very mild character had been quite over
looked, but circumstances were recorded which could leave
no doubt upon the mind as to the nature and cause of the
complaint. But then the question arose, how did the young
lady catch the scarlatina ? She had come there on a visit
two months previously, and it was only after she had been
a month in the house that she was taken ill. The house
keeper at once cleared up the mystery. The young lady
on her arrival had expressed a particular wish to occupy a
nice room in an isolated tower, and in that room six months
previously a visitor had been confined with an attack of
scarlatina. The room had been swept and whitewashed,
but the carpets had been permitted to remain.

Thousands of cases could probably be cited in which
the disease has shown itself in this mysterious way, but
where a strict examination has revealed its true parentage
and extraction. Is it then philosophical to take refuge in
the fortuitous concourse of atoms as a cause of specific dis
ease, merely because in special cases the parentage may be
indistinct? Those best acquainted with atomic Nature,

300 FRAGMENTS OF SCIENCE.

and who are most ready to admit, as regards even higher
things than this, the potentialities of matter, will be the
•last to accept these rash hypotheses.

The Germ- Theory applied to Surgery.

Not only medical but surgical science is now seeking
light and guidance from this germ-theory. Upon it the
antiseptic system of Professor Lister, of Edinburgh, is
founded ; and if the facts be correctly given, the results
are extraordinary. As already stated, the germ-theory of
putrefaction was started by Schwann, but the illustrations
of this theory adduced by Professor Lister are of such. pub
lic moment as not only to justify, but to render imperative,
their introduction here :

Schwann's observations, says Professor Lister, did not receive the
attention which they appear to me to have deserved. The fermentation
of sugar was generally allowed to be occasioned by the torula ccrevlsia; ;
but it was not admitted that putrefaction was due to an analogous
agency. And yet the two cases present a very striking parallel. In
each a stable chemical compound, sugar in the one case, albumen in the
other, undergoes extraordinary chemical changes under the influence of
an excessively minute quantity of a substance which, regarded chemi
cally, we should suppose inert. As an example of this in the case of
putrefaction, let us take a circumstance often witnessed in the treatment
of large chronic abscesses. In order to guard against the access of at
mospheric air, we used to draw off the matter by means of a canula and
trocar, such as you see here, consisting of a silver tube with a sharp-
pointed steel rod fitted into it, and projecting beyond it. The instru
ment, dipped in oil, was thrust into the cavity of the abscess, the trocar
was withdrawn, and the pus flowed out through the canula, care being
taken by gentle pressure over the part to prevent the possibility of
n-iruriritation. The canula was then drawn out with due precaution
against the reflux of air. This method was frequently successful as to
its immediate object, the patient being relieved from the mass of the ac
cumulated fluid, and experiencing no inconvenience from the operation.
But the pus was pretty certain to reaccumulate in course of time, and it
became necessary again and again to repeat the process. And unhappily

DUST AND DISEASE. 301

there was no absolute security of immunity from bad consequences.
However carefully the procedure was conducted, it sometimes happened,
even though the puncture seemed healing by first intention, that feverish
symptoms declared themselves in the course of the first or second day,
and, on inspecting the seat of the abscess, the skin was, perhaps, seen to
be red, implying the presence of some cause of irritation, while a rapid
reaccmnulation of the fluid was found to have occurred. Under these
circumstances, it became necessary to open the abscess by free incision,
when a quantity, large in proportion to the size of the abscess, say, for
example, a quart, of pus escaped, fetid from putrefaction. Now, how
had this change been brought about? Without the germ-theory, I
venture to say, no rational explanation of it could have been given. It
must have been caused by the introduction of something from without.
Inflammation of the punctured wound, even supposing it to have oc
curred, would not explain the phenomenon. For mere inflammation,
whether acute or chronic, though it occasions the formation of pus, does
not induce putrefaction. The pus originally evacuated was perfectly
sweet, and we know of nothing to account for the alteration in its quality
but the influence of something derived from the external world. And
what could that something be ? The dipping of the instrument in oil,
and the subsequent precautions, prevented the entrance of oxygen. Or
even if you allowed that a few atoms of the gas did enter, it would be
an extraordinary assumption to make that these could in so short a time
effect such changes in so large a mass of albuminous material. Besides,
the pyogenic membrane is abundantly supplied with capillary vessels,
through which arterial blood, rich in oxygen, is perpetually flowing;
and there can be little doubt that the pus, before it was evacuated at
all, was liable to any action which the element might be disposed to
exert upon it.

On the oxygen-theory, then, the occurrence of putrefaction under
these circumstances is quite inexplicable. But if you admit the germ-
theory, the difficulty vanishes at once. The canula and trocar having
been lying exposed to the air, dust will have been deposited upon them,
and will be present in the angle between the trocar and the silver tube,
and in that protected situation will fail to be wiped off when the instru
ment is thrust through the tissues. Thus when the trocar is withdrawn,
some portions of this dust will naturally remain upon the margin of the
canula, which is left projecting into the abscess, and nothing is more
likely than that some particles may fail to be washed off by the stream
of out-flowing pus, but may be dislodged when the tube is taken out,
and left behind in the cavity. The germ-theory tells us that these par-

302 FRAGMENTS OF SCIENCE.

tides of dust will be pretty sure to contain the germs of putrefactive
organisms, and if one such is left in the albuminous liquid, it will
rapidly develop at the high temperature of the body, and account for
all the phenomena.

But striking as is the parallel between putrefaction in this instance
and the vinous fermentation, as regards the greatness of the effort pro
duced, compared with the minuteness and the inertness, chemically
sp'.'aking, of the cause, you will naturally desire further evidence of the
similarity of the two processes. You can see with the microscope the
torula of fermenting must or beer. Is there, you may ask, any organism
to be detected in the putrefying pus ? Yes, gentlemen, there is. If any
drop of the putrid matter is examined with a good glass, it is found to
be teeming with myriads of minute jointed bodies, called vibrios, which
indubitably proclaim their vitality by the energy of their movements. It
is not an affair of probability, but a fact, that the entire mass of that
quart of pus has become peopled with living organisms as the result of
the introduction of the canula and trocar ; for the matter first let out
was as free from vibrios as it was from putrefaction. If this be so,
the greatness of the chemical changes that have taken place in the pus
ceases to be surprising. We know that it is one of the chief peculiari
ties of living structures that they possess extraordinary powers of effect
ing chemical changes in materials in their vicinity, out of all proportion
to their energy as mere chemical compounds. And we can hardly doubt
that the animalcules which have been developed in the albuminous liquid,
and have grown at its expense, must have altered its constitution, just
as we ourselves alter that of the materials on which we feed.1

Secured from the danger of putrefaction, it is amazing
how, under the hands of a really able surgeon, the human
ilesh and bones may be cut, torn, and crunched with im
punity. The accounts of the operations of our eminent
surirrons ivud like romance. On this, however, I must not
dwell further than to recommend to your attention a case
described in the BritisJi Medical Journal for the 14th of
January last. In the operations of Professor Lister care
is taken that every portion of tissue laid bare by the knife
shall be defended from germs ; that if they fall upon the
wound they shall be killed as they fall. With this in view

1 Introductory Lecture before the University of Edinburgh.

DUST AND DISEASE. 303

he showers upon his exposed surfaces the spray of diluted
carbolic acid, which is particularly deadly to the germs,
and he surrounds the wound in the most careful manner
with antiseptic bandages. To those accustomed to strict
experiment it is manifest that we have a strict experimenter
here — a man with a perfectly distinct object in view, which
he pursues with never-tiring patience and unwavering faith.
And the result, in his hospital practice, as described by him
self, has been, that even in the midst of abominations too
shocking to be mentioned here, and in the neighborhood
of wards where death was rampant from pyaemia, erysipe
las, and hospital gangrene, he was able to keep his patients
absolutely free from these terrible scourges. Let me here
recommend to your attention Professor Lister's "Intro
ductory Lecture before the University of Edinburgh," which
I have already quoted ; his paper on " The Effect of the
Antiseptic System of Treatment on the Salubrity of a Sur
gical Hospital ; " and the article in the British Medical
Journal, to which I have just referred.

If, instead of using carbolic-acid spray, he could sur
round his wounds with properly-filtered air, the result
would, he contends, be the same. In a room where the
germs not only float but cling to clothes and walls, this
would be difficult if not impossible. But surgery is ac
quainted with a class of wounds in which the blood is freely
mixed with air that has passed through the lungs, and it is a
most remarkable fact that such air does not produce putre
faction. Professor Lister, as far as I know, was the first to
give a philosophical interpretation of this fact, which he
decribes and comments upon thus :

I have explained to my own urind the remarkable fact that in simple
fracture of the ribs, if the lung be punctured by a fragment, the blood
effused into the pleural cavity, though freely mixed with air, undergoes
no decomposition. The air is sometimes pumped into the pleural cavity
in such abundance that, making its way through the wound in the pleura

304 FRAGMENTS OF SCIENCE.

costalis, it inflates the cellular tissue of the whole body. Yet this occa
sions no alarm to the surgeon (although if the blood in the pleura were to
putrefy, it would infallibly occasion dangerous suppurative pleurisy).
Why air introduced into the pleural cavity through a wounded lung
should have such wholly different effects from that entering directly
through a wound in the chest was to me a complete mystery until I heard
of the germ-theory of putrefaction, when it at once occurred to me that
it was only natural, that air should be filtered of germs by the air-pas
sages, one of whose offices is to arrest inhaled particles of dust, and pre
vent them from entering the air-cells.

I shall have occasion to refer to this remarkable hy
pothesis further on.

The advocates of the germ-theory, both of putrefaction
and epidemic disease, hold that both arise, not from the air,
but from something contained in the air. They hold, more
over, that " something " to be not a vapor nor a foreign
gas, nor indeed a molecule of any kind, but a particle.1
The term " particulate " has been used in the Reports of
the Medical Department of the Privy Council to describe
this supposed constitution of contagious matter ; ajnd Dr.
Sanderson's experiments render it in the highest degree
probable, if they do not actually demonstrate, that the virus
of small-pox is " particulate." Definite knowledge upon
this point is of exceeding importance, because in the treat
ment of particles methods are available -which it would be
futile to apply to molecules.

Application of JAtminow Beams to researches of tJtis
nature.

My own interference with this great question, while
sanctioned by eminent names, has been also an object of

1 As regards size, there is probably no sharp line of division between
molecules and particles ; the one gradually shades into the other. But
tin- dij-tinction that I would draw is this: the atom or the molecule, if
free, is always part of a gas, the particle is never so. A particle is a bit
of liquid or solid matter formed by the aggregation of atoms or molecules.

DUST AND DISEASE. 305

varied and ingenious attack. On this point I will only say
that when feeling escapes from behind the intellect, where
it is a useful urging force, and places itself in front of the
intellect, it is liable to produce glamour and all manner
of delusions. Thus my censors, for the most part, have lev
elled their remarks against positions which I never assumed,
and against claims which I never made. The simple his
tory of the matter is this : During the autumn of 1868 I
was much occupied with the observations referred to at the
beginning of this discourse. For fifteen years I had ha
bitually employed the electric light, making use of the
floating dust to reveal the paths of luminous beams ; but
until 1868, when I was driven to it, I did not intentionally
reverse the process and employ a luminous beam to reveal
and examine the dust. In a paper presented to the Royal
Society in December, 1869, 1 thus described the observa
tions which induced me to give more special attention to
the question of spontaneous generation and the germ-
theory of epidemic disease.

The Floating Matter of the Air.

Prior to the discovery of the foregoing action (the chemical action of
light upon vapors), and also during the experiments just referred to, the
nature of my work compelled me to aim at obtaining experimental tubes
absolutely clean upon the surface, and absolutely empty within. Neither
condition is, however, easily attained.

For however well the tubes might be washed and polished, and how
ever bright and pure they might appear in ordinary daylight, the electric
beam infallibly revealed signs and tokens of dirt. The air was always
present, and it was sure to deposit some impurity. All chemical pro
cesses, not conducted in a vacuum, are open to this disturbance. When
the experimental tube was exhausted it exhibited no trace of floating
matter, but on admitting the air through the U-tubes containing caustic
potash and sulphuric acid, a dust-cone more or less distinct was always re
vealed by the powerfully-condensed electric beam.

The floating motes resembled minute particles of liquid which had

306 FRAGMENTS OF SCIENCE.

been carried mechanically into the experimental tube. Precautions were
therefore taken to prevent any such transfer. They produced little or no
mitigation. I did not imagine at the time that the dust of the external
air could find such free pa'ssage through the caustic potash and the sul
phuric-acid tubes. But the motes really came from without. They also
passed with freedom through a variety of ethers and alcohols. In fact,
it requires long-continued action on the part of an acid first to wet the
motes and afterward to destroy them. By carefully passing the air
through the flame of a spirit-lamp or through a platinum tube heated to
bright redness, the floating matter was sensibly destroyed. It was there
fore combustible, in other words, organic matter. I tried to intercept it
by a large respirator of cotton-wool. Close pressure was necessary to
render the wool effective. A plug of the wool rammed pretty tightly into
the tube through which the air passed was finally found competent to
hold back the motes. They appeared from time to time afterward and
gave me much trouble ; but they were invariably traced in the end to
some defect in the purifying apparatus — to some crack or flaw in the
sealing-wax employed to render the tubes air-tight. Thus through proper
cine, but not without a great deal of searching out of disturbances, the
experimental tube, even when filled with pure air or vapor, contains
nothing competent to scatter the light. The space within it has the as
pect of an absolute vacuum.

An experimental tube in this condition I call optically empty.

The simple apparatus employed in these experiments will be at once
understood by reference to the figure on page 307. S S' is the glass ex
perimental tube which has varied in length from 1 to 5 feet, and which may
be from 2 to 3 inches in diameter. From the end S the pipe pp' passes to
an air-pump. Connected with the other end S' we have the flask F, con
taining the liquid whose vapor is to be examined ; then follows a U-tube,
T, filled with fragments of clean glass wetted with sulphuric acid ; then
a second U-tube, T', containing fragments of marble wetted with caustic
potash ; and finally a narrow straight tube, 1 1' , containing a tolerably
tightly-fitting plug of cotton-wool. To save the air-pump gauge from the
attack of such vapors as act on mercury, as also to facilitate observa
tion, a separate barometer tube was employed.

Through the cork which stops the flask F two glass tubes, a and ft, pa?s
air-tight. The tube a ends immediately under the cork ; the tube ft, on
the contrary, descends to the bottom of the flask and dips into the liquid.
The end of the tube b is drawn out so as to render very small the orifice
through which the air escapes into the liquid".

The experimental tube S S' being exhausted, a cock at the end S' is

308 FRAGMENTS OF SCIENCE.

carefully turned on. The air passes slowly through the cotton-wool, the
caustic potash, and the sulphuric acid in succession. Thus purified it
enters the flask F and bubbles through the liquid. Charged with vapor
it finally passes into the experimental tube, where it is submitted to ex
amination. The electric lamp L placed at the end of the experimental
tube furnished the necessary beam.

Wanting the cotton- wool the floating matter of the air
ran the gantlet of this system. The fact thus forced upon
my attention had a bearing too obvious to be overlooked.
It rendered at once evident to the senses why air filtered
through cotton-wool is incompetent to generate animalcular
life. The air is rendered by this treatment optically pure ;
in other words, freed from all floating matter, germs in
cluded. But the observations also revealed the great
liability to error in experiments of this nature. They
showed that without an amount of care which was hardly
to be expected in all cases, error would be inevitable. It
was especially manifest that the chemical method of
Schultze might lead to the 'most erroneous consequences ;
that neither acids nor alkalies had the power of rapid
destruction which they had been supposed to possess. In
short, the employment of the luminous beam rendered
evident the cause of success in experiments rigidly con
ducted like those of Pasteur ; while it made equally evident
the certainty of failure in experiments less severely and less
skilfully carried out.

Dr. Bennetts Experiments.

Take, for example, the well-conceived experiments of
Dr. Hughes Bennett, described before the Royal Society
of Surgeons in Edinburgh, on January 17, 18G8.1 Into
11 asks containing decoctions of liquorice-root, hay, or tea,
Dr. Bennett, by an ingenious method, forced air. The air
was driven through two U-tubes, the one containing a so-

1 British Medical Journal, 13, pt. ii. 1868.

DUST AND DISEASE. 309

lution of caustic potash, the other sulphuric acid. " All the
bent tubes," says Dr. Bennett, " were filled with fragments
of pumice-stone to break up the air, so as to prevent the
possibility of any germs passing through in the centre of
bubbles." The air also passed through a Liebig's bulb
containing sulphuric acid, and also through a bulb contain
ing gun-cotton.

It was only natural for Dr. Bennett to believe that his
bent tubes entirely cut off the germs. Previous to the
observations just referred to I also believed in their compe
tence to do this. But these observations destroy any such
notion. The gun-cotton, moreover, will fail to arrest the
whole of the floating matter unless it is tightly packed,
and there is no indication in Dr. Bennett's memoir that it
was so packed. On the whole, I should infer from the
mere inspection of the apparatus the very results which
Dr. Bennett has described — a retardation of the develop
ment of life, a total absence of it in some cases, and its
presence in others.

In his first series of experiments eight flasks were fed
with his sifted air, and five with common air. In ten or
twelve days all the five had fungi in them; while it re
quired from four to nine months to develop fungi in the
others. In one case, moreover, even after this interval, no
fungi appeared. In a second series of experiments there
was a similar exception. In a third series of experiments
he abandoned the cork stoppers used in the first and second
series, and employed glass stoppers. Flasks containing
decoctions of tea, beef, and hay, were filled with common
air, and other flasks with sifted air. In every one of the
former fungi appeared, and in not one of the latter. These
experiments simply ruin the doctrine that Dr. Bennett
finally espouses.

In all these cases the prepared air was forced into the
infusion when it was boiling hot. Dr. Bennett made a

310 FRAGMENTS OF SCIENH K.

fourth series of experiments, in which,- previous to forcing
in the air, he permitted the flasks to cool. Into four bottles
thus treated he forced prepared air, and after a time found
fungi in all of them. What is his conclusion ? Not that
the boiling hot liquid employed in his first experiments had
destroyed such germs as had run the gantlet of his ap
paratus ; but that air which, previous to being sealed up,
had been exposed to a temperature of 212° is too rare to
support life. This conclusion is so remarkable that it ought
to be stated in Dr. Bennett's own words: "It may be
easily conceived that air subjected to a boiling temperature
is so expanded as scarcely to merit the name of air, and
that it is more or less unfit for the purpose of sustaining
animal or vegetable life,"

Now numerical data are attainable here, and, as a
matter of fact, I live and flourish for a considerable portion
of each year in air of less density than that which Dr.
Bennett describes as scarcely meriting the name of air;
the Swiss men, women, children, flocks, herds, tadpoles,
grasshoppers, flowers, and grasses, do the same, while the
chamois rears its kids in air rarer still.

In a fifth series of experiments sixteen bottles were
filled with infusions. Into four of them, while cold, or
dinary unheated and unsifted air was pumped. In these
four bottles fungi were developed. Into four other bottles,
containing a boiling infusion, ordinary air was also pumped
—no fungi were here developed. Into four other bottles
containing an effusion which had been boiled and permitted
to cool, sifted air was pumped — no fungi were developed.
Finally, into four bottles containing a boiling infusion,
sifted air was pumped — no fungi were developed. Only,
therefore, in the four cases where the infusions wrere cold
infusions, and the air ordinary air, did fungi appear.

Dr. Bennett does not draw from these experiments the
conclusion to which they so obviously point. On them, on

DUST AND DISEASE. 311

the contrary, their author founds a defence of the doctrine
of spontaneous generation, and a general theory of sponta
neous development. So strongly was he impressed with
the idea that the germs could not possibly pass through his
potash and sulphuric-acid tubes, that the appearance of
fungi, even in a small minority of cases, where the air had
been sent through these tubes, was to him conclusive evi
dence of the spontaneous origin of such fungi. And he
accounts for the absence of life in many of his experi
ments by resorting to an hypothesis which will not bear
a moment's consideration. But now that we know that
organic particles may pass unscathed through alkalies and
acids, the experiments of Dr. Bennett are precisely what
ought, under the circumstances, to be expected. Indeed,
their harmony, with the conditions now revealed, is a proof
of the honestv and accuracy with which they were executed.
On another point also the luminous beam will cast a
light. Pasteur opened flasks upon the Mer de Glace, and,
being careful not to come between the wind and his flasks,
found the air incompetent, in the great majority of cases,
to generate life. M. Pouchet repeated Pasteur's experiment
in the Pyrenees, adding the precaution of holding the flasks,
when they were opened, above his head. The luminous
beam at once shows us the effect of this additional precau
tion. Let smoking brown paper be placed at the open
mouth of a glass shade so that the smoke shall ascend and
fill the shade. A beam sent through the shade forms a
bright track through the smoke. When the closed fist is
placed underneath the shade, a vertical wind of surprising
violence, considering the small elevation of temperature,
rises from the hand, displacing by comparatively dark air
the illuminated smoke. Such a wind infallibly rose from
M. Pouchet's body as he held his flasks above his head, and
thus the precaution of Pasteur of not coming between the
wind and the flask was annulled.

312 FRAGMENTS OF K'IKNCE.

Again, in order to utterly destroy all germs M. Poucbet
produced water from the combustion of hydrogen in air ;
but even in this water he found organisms. Had he seen,
however, as you have, the manner in which the air is clouded
with floating matter, would he have concluded that the
deportment of water which had been permitted to trickle
through such air could have the least influence in deciding
this great question ? I think not. Here is a quantity of
water produced and collected by allowing a hydrogen-flame
to play upon the polished bottom of a silver basin, in which
i< •<> had been placed. This water is clear in the common
light ; but in the condensed electric beam it is seen to be
laden with particles, so thick-strewn and minute, as to pro
duce a continuous cone of light. In passing through the
air the water loaded itself with this matter, and doubtless
became charged with incipient life.

Let me now draw your attention to another experiment
of Pasteur. He prepared twenty-one flasks, each contain
ing a decoction of yeast, filtered and clear. He boiled the
decoction, so as to destroy whatever germs it might contain,
and while the space above the liquid was filled with pure
steam he sealed his flasks with a blow-pipe. He opened ten
of them in the deep, damp caves of the Paris Observatory,
and eleven of them in the court-yard of the establishment.
Of the former, one only showed signs of life subsequently.
In nine out of the ten flasks no organisms of any kind
were developed. In all the others organisms speedily ap
peared.

Now here is an experiment conducted in Paris ; let us
see whether we cannot throw light upon it in London. I
place this large flask in the beam, and you see the luminous
track crossing it from side to side. The flask is filled with
the air of this room, charged with its germs and its dust,
and hence capable of illumination. But here is another
similar flask, which cuts a clear gap out of the beam. It is

DUST AND DISEASE. 313

filled with unfiltered air, and still no trace of the beam is
visible. Why ? By pure accident I stumbled on this flask
in our apparatus-room, where it had remained quiet for
some time. Here are three other flasks which have also
been kept quiet for a couple of days ; they are all optically
empty. The still air of the flasks has deposited its dust,
germs and all, and is itself practically free from suspended
matter. Hence, manifestly, the result of Pasteur.

I have had a chamber erected, the lower half of which
is of wood, its upper half being enclosed by four glazed
window-frames. The chamber tapers to a truncated cone
at the top* It measures in plan 3 ft. by 2 ft. 6 in., and its
height is 5 ft. 10 in. On the 6th of February this chamber
was closed, every crevice that could admit dust, or cause
displacement of the air, being carefully pasted over with
paper. The electric beam at first revealed the dust within
the chamber as it did in the air of the laboratory. The
chamber was examined almost daily ; a perceptible diminu
tion of the floating matter being noticed as time advanced.
At the end of a week the chamber was optically empty,
exhibiting no trace of matter competent to scatter the light.
But where the beam entered, and where it quitted the
chamber, the white circles stamped upon the interior sur
faces of the glass showed what had become of the dust. It
clung to those surfaces, and from them instead of from the
air, the light was scattered. If the electric beam were sent
through the air of the Paris caves, the cause of its impotence
as generator of life would, I venture to predict, be revealed.

These experiments illustrate the application of a lumi
nous beam to researches of this kind. They prove that the
germs which produce infusorial and fungoid life share the
fate of the ordinary visible dust with which they are inter
mixed ; that such germs attach themselves to the sides of
vessels, and fall gradually to the bottom of spaces filled
with perfectly still air. But I will now turn to a far more
14

314 FRAGMENTS OF SCIENCE.

interesting application of the luminous beam than any
hitherto described. My reference to Professor Lister's
interpretation of the fact that air which has passed through
the lungs cannot produce putrefaction is fresh in your mem
ories. He there assumed that the air was rendered innocu
ous by the filtering action of the lungs. Can this filtering
process be taken out of the region of assumption and placed
in that of demonstration ? It can.

Here is the concentrated beam with which we operated
at the commencement of this discourse. Its track through
the dust is luminous, and you have seen the blackness in
troduced when the dust is burnt, or otherwise removed. I
fill my lungs with ordinary air and breathe through a glass
tube across the beam. The condensation of the aqueous
vapor of the breath is here shown by the formation of a
luminous white cloud of delicate texture. It is necessary
to abolish this cloud, and this may be done by drying the
breath previous to its entering the beam ; or, still more
simply, by warming the glass-tube. When this is done the
luminous track of the beam is for a time uninterrupted,
because the dust returning from the lungs makes good, in
great part, the particles displaced. After some time, how
ever, an obscure disk appears in the beam, the darkness of
which increases, until finally, toward the end of the expira
tion, the beam is, as it were, pierced by an intensely black
hole, in which no particles whatever can be discerned. The
deeper air of the lungs is absolutely free from suspended
matter. It is therefore in the precise condition required by
Professor Lister's explanation. This experiment may'be
repeated any number of times with the same result. I think
it must be regarded as a crowning piece of evidence both
of the correctness of Professor Lister's views and of the
impotence, as regards vital development, of optically pure
air,

DUST AND DISEASE. 315

CoUon-wool Respirator.

I now empty my lungs as perfectly as possible, and
placing a handful of cotton-wool against my mouth and
nostrils, inhale through it. There is no difficulty in thus
filling the lungs with air. On expiring this air through a
glass tube, its freedom from floating matter is at once
manifest. From the very beginning of the act of expira
tion the beam is pierced by a black aperture. The first
puff from the lungs abolishes the illuminated dust, and puts
a patch of darkness in its place ; and the darkness con
tinues throughout the entire course of the expiration.
When the tube is placed below the beam and moved to
and fro, the same smoke-like appearance as that obtained
with a flame is observed. In short, the cotton-wool, when
used in sufficient quantity, and with due care, completely
intercepts the floating matter on its wray to the lungs.1

The application of these experiments is obvious. If a
physician wishes to hold back from the lungs of his patient,
or from his own, the germs or virus by which contagious
disease is propagated, he will employ a cotton-wool res
pirator. If perfectly filtered, attendants may breathe the
air unharmed. In all probability the protection of the lungs
and mouth will be the protection of the entire system. For
it is exceedingly probable that the germs which lodge in
the air-passages, or find their way with the saliva into the
stomach with its absorbent system, are those which sow in

1 Since the first publication of these results, Professor Lister has
availed himself of the filtering power of cotton-wool in the treatment of
wounds. He first destroys the germs adhering to the wool, and by a
proper lotion kills those that may be scattered on the flesh. The cleansed
wool placed upon the wound permits of a free diffusion of the air, but
entirely intercepts the germs, and thus keeps the blood perfectly sweet.
It is here essential that no matter from the wound should reach the out
side air, for such matter would open a highway to the organisms.

316 FRAGMENTS OF SCIENCE.

the body epidemic disease. If this be so, then disease can
be warded off by carefully-prepared filters of cotton-wool.
I should be most willing to test their efficacy in my own
person. But apart from all doubtful applications, it is per
fectly certain that various noxious trades in England may
be rendered harmless by the use of such niters. I have
had conclusive evidence of this from people engaged in
such trades. A form of respirator devised by Mr. Garrick,
a hotel proprietor in Glasgow, in which inhalation and ex
halation occur through two different valves, the one per
mitting the air to enter through the cotton-wool, and the
other permitting the exit of the air direct into the atmos
phere, is well adapted for this purpose. But other forms
might readily be devised.

Fireman's Respirator.

Smoke is often the fireman's greatest obstacle in his
efforts to save life ; I thought, therefore, of inventing a res
pirator for the use of firemen. Schroeder was the first to
use cotton-wool as a filter. To catch the atmospheric
germs, M. Pouchet employed a film of adhesive glycerine
spread upon glass ; while Dr. Stenhouse turned charcoal to
important account in respirators. By a combination of all
three a respirator of peculiar efficacy is obtained. For the
smoke of dried leaves the cotton-wool alone was found an
adequate protection ; but for the far more pungent smoke
of resinous deal it was found totally inadequate. At the
suggestion of a friend I moistened the wool with glycerine,
and found it a great improvement. It was the notion of
Pouchet in another form. Still about five minutes in dense
smoke was all that could be endured. I then associated
fragments of charcoal with the moistened cotton ; the effect
was excellent.1 Armed with a respirator of this kind, one
1 Mr. Ladd, of Beak Street, makes these respirators.

DUST AND DISEASE. 317

can breathe without annoyance in a space so crammed
with smoke, that a single inhalation without the respirator
would be intolerable. I wrote to the chief officer of the
Metropolitan Fire Brigade, asking him whether such a res
pirator would be useful. He replied to me that it would,
but added that he was aware of every invention of the kind
in all the countries of Europe, and that none had been
found of any use. At my invitation he was kind enough
to come to the Royal Institution with two firemen and an
assistant. The three latter, wearing such respirators, went
in succession into the smoke-filled space, and on returning,
stated that they had not experienced the slightest discom
fort, that they could have remained there all day long.
Captain Shaw himself repeated the experiment with the
same result. I am confident that sooner or later this res
pirator will be employed, to the great benefit of a class of
men' whose actions in critical circumstances I have often
had occasion to admire.

Application of Luminous Seams to Water.

The method of examination here pursued is also appli
cable to water. It is in some sense complementary to that
of the microscope, and may I think materially aid inquiries
conducted with that instrument. In microscopic examina
tion attention is directed to a small portion of the liquid,
and the aim is to detect the individual suspended particles.
By the present method a large portion o'f the liquid is il
luminated, its general condition being revealed, through
the light scattered by suspended particles. Care is taken
to defend the eye from the access of all other light, and,
thus defended, it becomes an organ of inconceivable deli
cacy. Indeed, an amount of impurity so infinitesimal as to
be scarcely expressible in numbers, and the individual par
ticles of which are so small as wholly to elude the micro-

318 FRAGMENTS OF SCIENCE.

scope, may, when examined by the method alluded to, pro
duce not only sensible but striking effects upon the eye.

I take, for instance, this bottle of water intended to
quench your lecturer's thirst. In the track of the beam it
simply reveals itself as dirty water. So you see that we
are invaded with dirt not only in the air we breathe, but
in the water we drink. And this water is no worse than
the other London waters. Thanks to the kindness of Pro
fessor Frankland, I have been furnished with specimens of
the water of eight London companies. They are all laden
with impurities mechanically suspended. But you will ask
whether filtering will not remove the suspended matter ?
The grosser matter, undoubtedly, but not the more finely-
divided matter. Here is water which has been passed four
times through a filter of bibulous paper, but it is still laden
with fine matter. Here, also, is a bottle kindly sent me by
Mr. Lipscomb, and passed once through his charcoal filter.
But the track of the beam through it is more luminous
than through air, because the quantity of matter suspended
in the water is greater than that suspended in air. Here
is another specimen courteously sent to me by the Silicated
Carbon Company. All the grosser matter has been re
moved, but it is thick with fine matter. Nine-tenths of the
light scattered by these particles is perfectly polarized in a
direction at right angles to the beam, and this release of
the particles from the ordinary law of polarization is a
demonstration of their smallness. I should say by far the
greater number of the particles concerned in this scattering
are wholly beyond the range of the microscope, and no or
dinary filter can intercept them. There is an aesthetic
pleasure in the drinking of a glass of cold sparkling water,
and I fear these experiments will destroy this pleasure if
you ever enjoyed it. And it is next to impossible by arti
ficial means to produce pure water. Mr. Hartley, for ex
ample, some time ago distilled water while it was sur-

DUST AND DISEASE. 319

rounded by hydrogen, but the water was not free from
floating matter. It is so hard to be clean in the midst of
dirt. Here, however, is an approach to pure water. It is
from the Lake of Geneva, and the bottle was carefully
filled for me by my distinguished friend Soret. The track
of the beam through it is of a delicate sky blue ; there is
scarcely a trace of grosser matter.

The purest water that I have seen — probably the purest
which has been seen hitherto — has been obtained from the
fusion of selected specimens of ice. But extraordinary
precautions are required to obtain this degree of purity.
An apparatus was devised and constructed by my assistant
for this purpose. Through the plate of an air-pump passes
the shank of a large funnel, attached to which below the
plate is a glass bulb. In the funnel is placed a block of the
most transparent ice, and over the funnel is a glass receiver.
This is first exhausted and refilled several times with air,
which has been filtered by its passage through cotton-wool,
the ice being thus surrounded by pure moteless air. But
the ice has previously been in contact with mote-filled air ;
it is, therefore, necessary to let it wash its own face, and
wash the bulb which is to receive the water of liquefaction.
The ice is permitted to melt, the bulb is filled and emptied
several times, until finally the large block dwindles to a
small one. We may be sure that all impurity has been
thus removed from the surface of the ice. These two bulbs
contain water obtained in this way, the purity of which is
the maximum hitherto attained. Still I should hesitate to
call the water absolutely pure. When the concentrated
beam is sent through it the track of the beam is not invis
ible, but of the most exquisitely delicate blue. This blue
is purer than that of the sky, so that the matter which pro
duces it must be finer than that of the sky. It may be,
and indeed has been, contended that this blue is scattered
by the very molecules of the water, and not by matter sus-

320 FRAGMENTS OF SCIENCE.

pendcd in it. But when we remember that this perfection
of blue is approached gradually through stages of less per
fect blue; and when we consider that a blue in all re
spects similar is demonstrably obtainable from particles
mechanically suspended, we should hesitate, I think, to
conclude that we have arrived here at the last stage of pu
rification. The evidence, I think, points distinctly to the
conclusion that, could we push the process of purification
still further, even this last delicate trace of blue would dis
appear.

Chalk - Water. Clartfs Softening Process.

But is it not possible to match the water of the Lake
of Geneva here in England ? Undoubtedly it is. We have
in England a kind of rock which constitutes at once an ex
ceedingly clean recipient and a natural filter, and from wrhich
we can obtain water extremely free from mechanical im
purities. I refer to the chalk-formation, in which large
quantities of water are held in store. Our chalk-hills are
in most cases covered with thin layers of soil, and with
very scanty vegetation. Neither opposes much obstacle
the entry of the rain into the chalk, where any organic
impurity which the water may carry in is soon oxidized
and rendered harmless. Those who have scampered like
myself over the downs of Hants and Wilts will remember
the scarcity of water in these regions. In fact, the rain
fall, instead of washing the surface and collecting in streams,
sinks into the fissured chalk and percolates through it, and
when this formation is suitably tapped we obtain water of
exceeding briskness and purity. Here is a large globe filled
with the water of a well near Tring. It is wonderfully free
from mechanical impurity ; indeed, it stands to reason that
water wholly withdrawn from surface contamination and
percolating through so clean a substance should be pure.
Sending a beam through this glass of water its purity is

DUST AND DISEASE. 321

conspicuous ; you see the track of the beam, but it is not
the thick and muddy track revealed in London waters. It
has been a subject much debated whether the supply of
excellent water which the chalk holds in store could not be
rendered available for London. Many of the most eminent
engineers and chemists have ardently recommended this
source, and have sought to show that not only is its
purity unrivalled, but that its quantity is practically inex
haustible. Data sufficient to test this are now, I believe,
in existence ; the number of wells sunk in the chalk is so
considerable and the quantity of water which they yield is
so well known.

But this water, so admirable as regards freedom from
mechanical impurity, labors under the disadvantage of
being very hard. It is rendered hard by the large quantity
of carbonate of lime which it holds in solution. The chalk-
water in the neighborhood of Watford holds in solution
about seventeen grains of carbonate of lime per gallon.
This, in the old terminology, used to be called seventeen
degrees of hardness. Now this hard water is bad for tea,
bad for washing ; it furs your boilers, because the lime
held in solution is precipitated by boiling. If the water be
used cold, its hardness must be neutralized at the expense
of soap before it will give a lather. These are serious ob
jections to the use of chalk-water in London. But they
are now successfully met by the experimental demonstration
that such water can be softened inexpensively, and on a
grand scale. I had long known the method of softening
water called Clark's process, but not until recently, under
the guidance of Mr. Homersham, did I see proof of its
larger applications. The chalk-water is softened for the
supply of the city of Canterbury ; at the Chiltern Hills it
is softened for the supply of Tring and Aylesbury. Carter-
ham also enjoys the luxury.

I have visited all these places, and made myself ac-

322 FRAGMENTS OF SCIENCE.

quainted with the works. At Canterbury there are three
reservoirs covered in and protected by a concrete roof and
layers of pebbles both from the summer's heat and the win
ter's cold. Each reservoir contains 120,000 gallons of chalk-
water. Adjacent to these reservoirs are others containing
pure slacked lime — the so-called " cream of lime." These
are filled with water, the lime and water being thoroughly
mixed by air forced in by an engine through apertures in
the bottom of the reservoir. The water thus well mixed
with the lime soon dissolves all of this substance that it is
capable of dissolving. The lime is then allowed to subside
to the bottom, leaving a perfectly clear lime-water behind.
The object is now to soften the chalk-water. Into the
empty reservoir is introduced a certain quantity of the clear
lime-water, and after this about nine times the quantity of the
chalk-water. The transparency immediately disappears —
the mixture of the two clear liquids becomes thickly turbid.
The carbonate of lime is precipitated, and the precipitate is
permitted to subside ; it is crystalline and heavy, and there
fore sinks rapidly. In about twelve hours you find a layer
of pure white carbonate of lime at the bottom of the reservoir,
with a water of extraordinary beauty and purity overhead.
A few days ago I pitched some halfpence into a reservoir
sixteen feet deep at the Chilton Hills. The sixteen feet
hardly perceptibly dimmed the coin. Had I cast a pin in,
it could, I am persuaded, have been seen at the bottom. By
this process of softening the water is reduced from about
seventeen degrees of hardness to three degrees of hardness.
It yields a lather immediately. Its temperature is constant
throughout the year. In the hottest summer it is cool, its
temperature being 20° above the freezing-point; and it
does not freeze in winter if conveyed in proper pipes. It
is not exposed to the contamination of either earth or air.
The reservoirs are covered ; a leaf cannot blow into the
water, no surface cnntiunination can reach it, it passes di-

DUST AND DISEASE. 323

rect from the main into the house-tap ; no cisterns are em
ployed, the supply is always fresh and pure. It is highly
charged with air. This is the kind of water which is sup
plied to the fortunate people of Tring, Caterham, and Can
terbury.

Let me, in conclusion, remind you that I do not con
sider the floating matter revealed by the electric beam to be
all living matter. I believe that only in exceptional cases,
such as those cited in the excellent reports of Dr. Angus
Smith, does the quantity of living matter suspended in the
air of our streets and rooms amount to more than a small
fraction of the total dust. But I believe it to be perfectly
well established that, during epidemics, air and water are
charged with the specific " materies morbi " by which the
disease is spread ; that these two media are, in fact, the
chief vehicles of its dissemination. I believe there are the
strongest grounds for holding the contagious matter to be
" particulate," and further, that the particles are to all in
tents and purposes germs / exhibiting as they do the fun
damental characteristic of propagating their own kind
through countless generations, and over vast geographical
areas. Their life and reproduction run parallel to, and are
an incident of the life of man himself. I do not doubt the
ability of these particles to scatter light, nor that the means
by which the visible floating dust of our air is arrested, and
which demonstrably arrest with it the germs of various
forms of fungoid and animalcular life, including those con
cerned in the phenomena of putrefaction, will also be found
effectual in arresting contagium.

The following extract from a private letter written to
me by Dr. William Budd, is so important, and its reasoning
is so cleat, that I asked and obtained the permission of its
exceedingly able writer to publish it :

" Another point of great practical importance is, as far

324 FRAGMENTS OF SCIENCE.

as possible, to appraise the respective shares which air and
water take in the great act of distribution. That both
cholera and typhoid fever are sometimes disseminated by
drinking-water has been amply proved. I have myself re
lated many instances of the fact, and have in my notes the
record of many others still more striking. But that water
is the sole or even the chief vehicle of cholera and typhoid
is a notion which, if I may trust my own experience, facts
do not warrant.

" Limiting myself, for the moment, to the case of typhoid,
I am in a position to state that all the worst and most wide
spread outbreaks of that fever which I have ever witnessed,
have occurred among communities supplied by drinking-
water which was absolutely blameless. Two illustrations
will suffice.

" I live in a town in which the divorce between sewage
and drinking-water has long been consummated. Bristol
is supplied with drinking-water which from its source in the
Mendips to the tap from wrhich it is delivered under high
pressure to the consumer, flows through conduits out of all
reach of sewage contamination.

" And yet typhoid fever has not only not ceased to exist
in Bristol, but about eight or ten years ago (before the
appointment of a health-officer), there occurred in the Parish
of St. James one of the worst outbreaks of this fever which
I have ever seen in the city. In the course of a circuit
which I took one morning with the late Dr. Pring (at that
time Poor Law Medical Officer) I saw within a compara
tively small area more than eighty cases of the disease.

" Now, with the exception of a single household, all the
patients were drinking the Mendip water ; the very same
\vat«-r which, as far as fever is concerned, more than 150,000
of their fellow-citizens outside the infected area were drink
ing with absolute impunity.

" Some four or five years ago I was sent for to advise

DUST AND DISEASE. 325

what measures should be taken to stay an outbreak of
typhoid fever which had occurred in a large convent about
two miles from Bristol. The inmates were divided into
three distinct divisions ; the largest being a reformatory for
girls, who occupied the central block of the building. Into
this reformatory the fever was brought by a girl already
suffering from it, and who had contracted it in a sea-side
place more than twenty miles off. From this girl the dis
ease spread until, at the date of my visit, more than fifty
girls were lying ill of it. From first to last the fever was
confined to the reformatory girls, and to persons in immedi
ate attendance upon them.

" Now, the facts as to the drinking-water were these :

" 1. The water was proved by examination of the well,
and by chemical analysis, to be entirely free from sewage
contamination.

" 2. The inmates of another large division of the con
vent, who remained entirely free from fever, drank the same
water as the girls among whom fever was raging like a
plague.

" 3. From the very time when disinfection was brought
to bear on the excreta the disease ceased to spread, although
the inmates of the infected division continued to drink the
same water as before.

" Lastly, nothing has since been done to the well — the
water remains what it was — but no fever has occurred in
the convent since.

" The evidence in both these cases is, as you see, of that
crucial, decisive order that admits of no reply.

" They show, at least, that typhoid fever may do its
worst where drinking-water takes absolutely no part in the
distribution of the poison.

"But if water be excluded, the air is the only other
possible vehicle by which a poison generated in the living
body can find its way back to other living bodies on a scale

,126 FRAGMENTS OF SCIENCE.

sufficiently large to cause the resulting disease to assume
an epidemic form.

" I may remark further that the infection of the air in
these two cases was obviously not the work of chance, but
only represented the effect of agencies which are always in
operation where this fever prevails.

" The phenomenon is, in fact, merely the expression of a
general law.

" The germs cast off in the liquid excreta of contagious
diseases rise into the air by no power of their own, but in
virtue of the very same physical conditions which cause the
germs of the great tribe of Infusoria, which, as their name
bespeaks, breed in liquids, to rise in swarms into the same
medium.

" If there were time or need, I could show, by evidence
quite as decisive, that all these statements apply equally to
cholera also.

" I do not know that there is any thing in these data to
suggest additional matter for your essay, but I have thought
it worth while to bring them under your notice, harmoniz
ing as they do with your own investigations which show
by such striking phenomena that air and water arc equally
objects of distrust.

" As to the germ-theory itself, that is a matter on which
I have long since made up my mind. From the day when
I first began to think upon these subjects, I have never had
a doubt that the specific cause of contagious fevers must be
living organisms.

" It is impossible, in fact, to make any statement bearing
upon the essence or distinctive characters of these fevers,
without using terms which are of all others the most distinc
tive of life. Take up the writings of the most violent oppo
nent of the germ-theory, and, ten to one, you will find them
full of such terms as ' propagation,' ' self-propagation,' l re
production,' * self-multiplication,' and so on. Try as he

DUST AND DISEASE. 327

may — if he has any thing to say of these diseases which is
characteristic of them — he cannot evade the use of these
terms or the exact equivalents of them. While perfectly
applicable to life and to living things, these terms express
qualities which are not only inapplicable to common chemi
cal agents, but, as far as I can see, actually inconceivable
of them."

XII.
LIFE AND LETTERS OF FARADAY.

BY DR. HENRY BENCE JONES.

[The Academy for May and June, 1870.]

Fame is the spur that the clear spirit doth raise
(That last infirmity of noble minds)
To scorn delights and live laborious days ;
But the fair guerdon when we hope to find,
And think to burst out into sudden blaze,
Comes the blind fury with the abhorred shears,
And slits the thin-spun life. But not the praise
Phoebus replied, and touched my trembling ears ;
Fame is no plant that grows on mortal soil,
Nor in the glistering foil
Set off to the world, nor in broad rumor lies,
But lives and spreads aloft by those pure eyes
And perfect witness of all-judging Jove."

MILTON.

XII.

LIFE AND LETTERS OF FARADAY.

UNDERTAKEN and executed in a reverent and loving
spirit, the work of Dr. Bence Jones makes Faraday the
virtual writer of his own life. Everybody now knows the
story of the philosopher's birth; that his father was a
smith ; that he was born at Newington Butts in 1791 ;
that he slid along the London pavements, a bright-eyed
errand-boy, with a load of brown curls upon his head and a
packet of newspapers under his arm ; that the lad's master
was a bookseller and bookbinder — a kindly man, who
became attached to the little fellow and in due time made
him his 'apprentice without fee ; that during his appren
ticeship he found his appetite for knowledge provoked and
strengthened by the books he stitched and covered. Thus
he grew in wisdom and stature to his year of legal man
hood, when he appears in the volumes before us as a writer
of letters, which reveal his occupation, acquirements, and
tone of mind. His correspondent was Mr. Abbott, a mem
ber of the Society of Friends, who, with a forecast of his
friend's greatness, preserved his letters and produced them
at the proper time.

In later years Faraday always carried in his pocket a
blank card on which he jotted down in pencil his thoughts
and memoranda. He made his notes in the laboratory,
in the theatre, and in the streets. This distrust of his
memory reveals itself in his first letter to Abbott. To a

332 FRAGMENTS OF SCIENCE.

proposition that no new inquiry should be started between
them before the old one had been exhaustively discussed,
Faraday objects. " Your notion," he says, " I can hardly
allow, for the following reason : ideas and thoughts spring
up in my mind which are irrevocably lost for want of
noting at the time." Gentle as he seemed, he wished to
have his own way, and he had it throughout his life.
Differences of opinion sometimes arose between the two
friends, and then they resolutely faced each other. "I
accept your offer to fight it out with joy, and shall in the
battle of experience cause not pain, but, I hope, pleasure."
Faraday notes his own impetuosity, and incessantly checks
it. There is at times something mechanical in his self-
restraint. In another nature it would have hardened into
mere " correctness " of conduct ; but his overflowing affec
tions prevented this in his case. The habit became a second
nature to him at last, and lent serenity to his later years.

In October, 1812, he was engaged by a Mr. De la
Roche as a journeyman bookbinder ; but the situation did
not suit him. His master appears to have been an austere
and passionate man, and Faraday was to the last degree
sensitive. All his life he continued so. He suffered at
times from dejection ; and a certain grimness, too, pervaded
his moods. " At present," he writes to Abbott, " I am as
serious as you can be, and would not scruple to speak a
truth to any human being, whatever repugnance it might
give rise to. Being in this state of mind, I should have
refrained from writing to you, did I not conceive from the
general tenor of your letters that your mind is, at proper
times, occupied upon serious subjects to the exclusion of
those that are frivolous." Plainly he had fallen into that
stern Puritan mood which not only crucifies the flesh, affec
tions, and lusts of him who harbors it, but is often a cause
of disturbed digestion to his friends.

About three months after his engagement with De la

FARADAY. 333

Roche, Faraday quitted him and bookbinding together.
He had heard Davy, copied his lectures, and written to him
entreating to be released from trade, which he hated, and
enabled to pursue science. Davy recognized the merit of
his correspondent, kept his eye upon him, and when oc
casion offered, drove to his door and sent in a letter offer
ing him the post of assistant in the laboratory of the Royal
Institution. He was engaged upon March 1, 1812, and on
the 8th we find him extracting the sugar from beet-root.
He joined the City Philosophical Society which had been
founded by Mr. Tatum in 1808. "The discipline was very
sturdy, the remarks very plain, and the results most valu
able." Faraday derived great profit from this little asso
ciation. In the laboratory he had a discipline sturdier still.
Both Davy and himself were at this time cut and bruised
by explosions of chloride of nitrogen. One explosion was
so rapid " as to blow my hand open, tear away a part of
one nail, and make my fingers so sore that I cannot use
them easily." In another experiment " the tube and re
ceiver were blown to pieces ; I got a cut on the head, and
Sir Humphry a bruise on his hand." And again, speaking
of the same substance, he says : " "When put in the pump
and exhausted, it stood for a moment, and then exploded
with a fearful noise. Both Sir H. and I had masks on, but
I escaped this time the best. Sir H. had his face cut in
two places about the chin, and a violent blow on the fore
head struck through a considerable thickness of silk and
leather." It was this same substance that blew out the
eye of Dulong.

Over and over again, even at this early date, we can
discern the quality which, compounded with his rare intel
lectual power, made him a great experimental philosopher.
This was his desire to see facts, and not to rest contented
with the descriptions of them. He frequently pits the eye
against the ear, and affirms the enormous superiority of the

S3 4 FRAGMENTS OF SCIENCE.

organ of vision. Late in life I have heard him say that he
could never have fully understand an experiment until he
had seen it. But he did not confine himself to experiment.
He aspired to be a teacher, and reflected and wrote upon
the method of scientific exposition. " A lecturer," he ob
serves, " should appear easy and collected, undaunted and
unconcerned : " still " his whole behavior should evince
respect for his audience." These recommendations were
afterward in great part embodied by himself. I doubt
his unconcern, but his fearlessness was often manifested.
It used to rise within him as a wave, which carried both
him and his audience along with it. On rare occasions
also, when he felt himself and his subject hopelessly unin
telligible, he suddenly evoked a certain recklessness of
thought, and without halting to extricate his bewildered
followers, he would dash alone through the jungle into
which he had unwittingly led them ; thus saving them from
ennui by the exhibition of a vigor which, for the time being,
they could neither share nor comprehend.

In October, 1813, he quitted England with Sir Hum
phry and Lady Davy. During hie absence he kept a
journal, from which copious and interesting extracts have
been made by Dr. Bence Jones. Davy was considerate,
preferring at times to be his own servant rather than
impose on Faraday duties which he disliked. But Lady
Davy was the reverse. She treated him as an underling ;
he chafed under the treatment, and was often on the point
of returning home. They halted at Geneva. De la Rive
the elder had known Davy in 1799, and by his writings in
the " Bibliotheque Britannique," had been the first to make
the English chemist's labors known abroad. He welcomed
Davy to his country residence in 1814. Both were sports
men, and they often went out shooting together. On these
occasions Faraday charged Davy's gun, while De la Hive
charged his own. Once the Gcnevese philosopher found

FARADAY. 335

himself by the side of Faraday, and in his frank and genial
way entered into conversation with the young man. It was
evident that a person possessing such a charm of manner
and such high intelligence could be no mere servant. On
inquiry De la Rive was somewhat shocked to find that the
soi-disant domestique was really preparateur in the labora
tory of the Royal Institution : and he immediately proposed
that Faraday thenceforth should join the masters instead
of the servants at their meals. To this Davy, probably out
of weak deference to his wife, objected ; but an arrangement
was come to that Faraday thenceforward should have his
food in his own room. Rumor states that a dinner in
honor of Faraday was given by De la Rive. This is a
delusion ; there was no such banquet ; but Faraday never
forgot the kindness of the friend who saw his merit when
he was a mere gar$on de laboratoire.1

He returned in 1815 to the Royal Institution. Here he
helped Davy for years ; he worked also for himself, and
lectured frequently at the City Philosophical Society. He
took lessons in elocution, happily without damage to his
natural force, earnestness, and grace of delivery. He was
never pledged to theory, and he changed in opinion as
knowledge advanced. With him life was growth. In those
early lectures we hear him say, " In knowledge, that man
only is to be contemned and despised who is not in a state
of transition." And again, " Nothing is more difficult and
requires more caution than philosophical deduction, nor is
there any thing more adverse to its accuracy than fixity of
opinion." Not that he was wafted about by every wind of

1 While confined last autumn at Geneva by the effects of a fall in the
Alps, my friends, with a kindness I can never forget, did all that friend
ship could suggest to render my captivity pleasant to me. M. de la Rive
then wrote out for me the full account, of which the foregoing is a con
densed abstract. It was at the desire of Dr. Bence Jones that I asked
him to do so. The rumor of a banquet at Geneva illustrates the ten
dency to substitute for the youth of 1814 the Faraday of later years.

33G FRAGMENTS OF SCIENCE.

doctrine ; but that he united flexibility with his strength.
In striking contrast with this intellectual expansiveness is
his fixity in religion, but this is a subject which cannot be
discussed here.

Of all the letters published in these volumes none
possess a greater charm than those of Faraday to his wife.
Here, as Dr. Bence Jones truly remarks, " he laid open all
his mind and the whole of his character, and what can be
made known can scarcely fail to charm every one by its
loveliness, its truthfulness, arid its earnestness." Abbott
and he sometimes swerved into word-play about love ; but
up to 1820, or thereabouts, the passion was potential
merely. Faraday's journal, indeed, contains entries which
show that he took pleasure in the assertion of his contempt
for love ; but these very entries became links in his destiny.
It was through them that he became acquainted with one
who inspired him with a feeling which only ended with his
life. His biographer has given us the means of tracing the
varying moods which preceded his acceptance. They reveal
more than the common alternations of light and gloom ; at
one moment he wishes that his flesh might melt and he
become nothing ; at another he is intoxicated with hope.
The impetuosity of his character was then unchastened by
the discipline to which it was subjected in after-years. The
very strength of his passion proved for a time a bar to its
advance, suggesting as it did to the conscientious mind of
Miss Barnard doubts of her capability to return it with
adequate force. But they met again and again, and at
each successive meeting he found his heaven clearer, until
at length he was able to say, " Not a moment's alloy of this
evening's happiness occurred. Every thing was delightful
to the last moment of my stay with my companion, because
she was so." The turbulence of doubt subsided, and a calm
and elevating confidence took its place. " What can I call
myself," ho writes to hor in a subsequent letter, " to convey

FARADAY. 337

most perfectly my affection and love for you ? Can I or
can truth say more than that for this world I am yours ? "
Assuredly he made his profession good, and no fairer light
falls upon his character than that which reveals his relations
to his wife. Never, I believe, existed a manlier, purer,
steadier love. Like a burning diamond it continued to shed
for six-and-forty years its white and smokeless glow.

Faraday was married on June 12, 1821 ; and up to this
date Davy appears throughout as his friend. Soon after
ward, however, disunion occurred between them, which,
while it lasted, must have given Faraday intense pain. It
is impossible to doubt the honesty of conviction with which
this subject has been treated by Dr. Bence Jones, and there
may be facts knowTi to him, but not appearing in these
volumes, which justify his opinion that Davy in those days
had become jealous of Faraday. This, which is the preva
lent belief, is also reproduced in an excellent article in
the March number of Fraser's Magazine. But the best
analysis I can make of the data fails to present Davy in
this light to me. The facts, as I regard them, are briefly
these :

In 1820, Oersted, of Copenhagen, made the celebrated
discovery which connects electricity with magnetism, and
immediately afterward the acute mind of Wollaston per
ceived that a wire carrying a current ought to rotate
round it own axis under the influence of a magnetic pole.
In 1821 he tried, but failed, to realize this result in the
laboratory of the Royal Institution. Faraday was not pres
ent at the moment, but he came in immediately afterward,
and heard the conversation of Wollaston and Davy about
the experiment. He had also heard a rumor of a wager
that Dr. Wollaston would eventually succeed.

This was in April. In the autumn of the same year
Faraday wrote a history of electro-magnetism, and repeated
for himself the experiments which he described. It was
15

338 FRAGMENTS OF SCIENCE.

while thus instructing himself that he succeeded in causing
a wire carrying an electric current to rotate round a mag
netic pole. This was not the result sought by Wollaston,
but it was closely related to it.

The strong tendency of Faraday's mind to look upon
the reciprocal actions of natural forces gave birth to his
greatest discoveries ; and we, who know this, should be
justified in concluding that, even had Wollaston not pre
ceded him, the result would have been the same. But in
judging Davy we ought to transport ourselves to his time,
and carefully exclude from our thoughts and feelings that
noble subsequent life which would render simply impossible
the ascription to Faraday of anything unfair. It would be
unjust to Davy to put our knowledge in the place of his,
or to credit him with data which he could not have pos
sessed. Rumor and fact had connected the name of Wol
laston with these supposed interactions between magnets
and currents. When, therefore, Faraday in October pub
lished his successful experiment without any allusion to
Wollaston, general, though really ungrounded, criticism
followed. I say ungrounded because, firstly, Faraday's ex
periment was not that of Wollaston, and secondly, Faraday,
before he published it, had actually called upon Wollaston,
and not finding him at home did not feel himself authorized
to mention his name.

In December Faraday published a second paper on the
same subject, from which, through a misapprehension, the
name of Wollaston was also omitted. Warburton and
others thereupon affirmed that Wollaston's ideas had been
appropriated without acknowledgment, and it is plain that
Wollaston himself, though cautious in his utterance, was
also hurt. Censure grew till it became intolerable. "I
hear," writes Faraday to his friend Stodart, " every day
more and more of these sounds, which, though only whis
pers to me, arc, I suspect, spoken aloud among scientific

FARADAY. 339

men." He might have written explanations and defences,
but he went straighter to the point. He wished to see the
principals face to face — to plead his cause before them per
sonally. There is a certain vehemence in his desire to do
this. He saw Wollaston, he saw Davy, he saw Warbur-
ton ; and I am inclined to think that it was the irresistible
candor and truth of character which these viva voce de
fences revealed, as much as the defences themselves, that
disarmed resentment at the time.

As regards Davy, another cause of dissension arose in
1823. In the spring of that year Faraday analyzed the
hydrate of chlorine, a substance once believed to be the
element chlorine, but .proved by Davy to be a compound of
that element and water. The analysis was looked over by
Davy, who then and there suggested to Faraday to heat
the hydrate in a closed glass tube. This was done, the
substance was decomposed, and one of the products of de
composition was proved by Faraday to be chlorine liquefied
by its own pressure. On the day of its discovery he com
municated this result to Dr. Paris. Davy, on being in
formed of it, instantly liquefied another gas in the same
way. Having struck thus into Faraday's inquiry, ought he
not to have left the matter in Faraday's hands ? I think
he ought. But, considering his relation to both Faraday
and the hydrate of chlorine, Davy, I submit, may be excused
for thinking differently. A father is not always wise enough
to see that his son has ceased to be a boy, and estrange
ment on this account is not rare ; nor was Davy wise enough
to discern that Faraday had passed the mere assistant
stage and become a discoverer. It is now hard to avoid
magnifying this error. But had Faraday died or ceased to
work at this time, or had his subsequent life been devoted
to money-getting instead of to research, would anybody
now dream of ascribing jealousy to Davy ? Assuredly
not. Why should he be jealous ? His reputation at this

340 FRAGMENTS OF SCIENCE.

time was almost without a parallel : his glory was without
a cloud. He had added to his other discoveries that of
Faraday, and after having been his teacher for seven years,
his language to him was this : " It gives me great pleasure
to hear that you are comfortable at the Royal Institution,
and I trust that you will not only do something good and
honorable for yourself, but also for science." This is not
the language of jealousy, potential or actual. But the
chlorine business introduced irritation and anger, to which,
and not to any ignobler motive, Davy's opposition to the
election of Faraday to the Royal Society is, I am per
suaded, to be ascribed.

These matters are touched upon with perfect candor
and becoming consideration in the volumes of Dr. Bence
Jones, but in " society " they are not always so handled.
Here a name of noble intellectual associations is surrounded
by injurious rumors which I would willingly scatter for
ever. The pupil's magnitude and the splendor of his posi
tion are too great and absolute to need as a foil the humilia
tion of his master. Brothers in intellect, Davy and Fara
day, however, could never have become brothers in feeling ;
their characters were too unlike. Davy loved the pomp
and circumstance of fame, Faraday the inner consciousness
that he had fairly won renown. They were both proud
men. But with Davy pride projected itself into the outer
world, while with Faraday it became a steadying and dig
nifying inward force. In one great particular they agreed.
Each of them could have turned his science to immense
commercial profit, but neither of them did so. The noble
excitement of research, and the delight of discovery, con
stituted their reward. I commend them to the reverence
which great gifts greatly exercised ought to inspire. They
were both ours, and through the coming centuries England
will be able to point with just pride to the possession of
men.

FARADAY. 341

The first volume of the " Life and Letters " reveals to
us the youth who was to be father to the man. Skilful,
aspiring, resolute, he grew steadily in knowledge and in
power. Consciously or unconsciously, the relation of action
to reaction was ever present to Faraday's mind. It had
been fostered by his discovery of magnetic rotations, and
it planted in him more daring ideas of a similar kind. Mag
netism he knew could be evoked by electricity, and he
thought that electricity, in its turn, ought to be capable of
evolution by magnetism. On August 29, 1831, his experi
ments on this subject began. He had been fortified by
previous trials, which, though failures, had begotten in
stincts directing him toward the truth. He, like every
strong worker, might at times miss the outward object, but
he always gained the inner light — education and expansion.
Of this Faraday's life was a constant illustration. By No
vember he had discovered and colligated a multitude of
the most wonderful and unexpected phenomena. He had
generated currents by currents ; currents by magnets, per
manent and transitory; and he afterward generated cur
rents by the earth itself. Arago's " Magnetism of Rota
tion," which had for years offered itself as a challenge to
the best scientific intellects of Europe, now fell into his
hands. It proved to be a beautiful but still special illustra
tion of the great principle of magneto-electric induction.
Nothing equal to this, in the way of pure experimental in
quiry, had previously been achieved.

Electricities from various sources were next examined,
and their differences and resemblances revealed. He thus
assured himself of their substantial identity. He then took
up conduction, and gave many striking illustrations of the
influence of fusion on conducting power. Renouncing pro
fessional work, from which at this time he might have de
rived an income of many thousands a year, he poured his
whole momentum into his researches. He was long en-

342 FRAGMENTS OF HCIKM K.

tangled in electro-chemistry. The light .of law was for a
time obscured by the thick umbrage of novel facts; but he
finally emerged from his researches with the great principle
of definite electro-chemical decomposition in his hands. If
his discovery of magneto-electricity may be ranked with
that of the pile by Volta, this new discovery may almost
stand beside that of definite combining proportions in
chemistry. He passed on to static electricity — its conduc
tion, induction, and mode of propagation. He discovered
and illustrated the principle of inductive capacity ; and,
turning to theory, he asked himself how electrical attrac
tions and repulsions are transmitted. Are they, like gravity,
actions at a distance, or do they require a medium ? If the
former, then, like gravity, they will act in straight lines ; if
the latter, then, like sound or light, they may turn a corner.
Faraday held, and his views are gaining ground, that his
experiments proved the fact of curvilinear propagation, and
hence the operation of a medium. Others denied this ; but
none can deny the profound and philosophic character of
his leading thought.1 The first volume of the researches
contains all the papers here referred to.

Faraday had heard it stated that henceforth physical
discovery would be made solely by the aid of mathematics ;
that we had our data, and needed only to work deductively.
Statements of a similar character crop out from time to
time in our day. They arise from an imperfect acquaintance
with the nature, present condition, and prospective vastness
of the field of physical inquiry. The tendency of natural
science doubtless is to bring all physical phenomena under
the dominion of mechanical laws ; to give them, in other
words, mathematical expression. But our approach to this
result is asymptotic ; and for ages to come — possibly for

1 In a very remarkable paper published in PoggendorfFs Annalen for
1857, Werner Siemens develops and accepts Faraday's theory of molecu
lar induction.

FARADAY. 343

all the ages of the human race — Nature will find room for
both the philosophical experimenter and the mathematician.
Faraday entered his protest against the foregoing statement
by labelling his investigations " Experimental Researches
in Electricity." They were completed in 1854, and three
volumes of them have been published. For the sake of
reference lie numbered every paragraph, the last number
being 3,362. In 1859 he collected and published a fourth
volume of papers under the title, " Experimental Researches
in Chemistry and Physics." Thus the apostle of experi
ment magnified his office.

The second volume of the Researches embraces memoirs
on the Electricity of the Gymnotus ; on the Source of Power
in the Voltaic Pile ; on the Electricity evolved by the Friction
of Water and Steam, in which the phenomena and principles
of Sir William Armstrong's Hydro-electric machine are
described and developed ; a paper on Magnetic Rotations,
and Faraday's letters in relation to the controversy it
aroused. The contribution of the most permanent value
here is that on the Source of Power in the Voltaic Pile. By
it the Contact Theory, pure and simple, was totally over
thrown, and the necessity of chemical action to the main
tenance of the current demonstrated.

The third volume of the Researches opens with a me
moir entitled, " The Magnetization of Light, and the Illu
mination of Magnetic Lines of Force." It is difficult even
now to affix a definite meaning to this title ; but the dis
covery of the rotation of the plane of polarization which it
announced seems pregnant with great results. The writ
ings of William Thomson on the theoretic aspects of the
discovery ; the excellent electro-dynamic measurements of
Wilhelm Weber, which are models of experimental com
pleteness and skill ; Weber's labors in conjunction with his
lamented friend Kohlrausch — above all, the researches of
Clerk Maxwell on the Electro-magnetic Theory of Light —

344 FRAGMENTS OF SCIENCE.

point to that wonderful and mysterious medium which is
the vehicle of light and radiant heat as the probable basis
also of magnetic and electric phenomena. The hope of
such a combination was first raised by the discovery here
referred to.1 Faraday himself seemed to cling with partic
ular affection to this discovery. He felt that there was
more in it than he was able to unfold. He predicted that
it would grow in meaning with the growth of science. This
it has done ; this it is doing now. Its right interpretation
will probably mark an epoch in scientific history.

Rapidly following it is the discovery of Diamagnetism,
or the Repulsion of Matter by a magnet. Brugmans had
shown that bismuth repelled a magnetic needle. Here he
stopped* Le Bailliff proved that antimony did the same.
Here he stopped. Seebeck, Becquerel, and others, also
touched the discovery. These fragmentary gleams excited
a momentary curiosity, and were almost forgotten, when
Faraday, independently, alighted on the same facts ; and,
instead of stopping, made them the inlets to a new and
vast region of research. The value of a discovery is to be
measured by the intellectual action it calls forth ; and it
was Faraday's good fortune to strike such lodes of scientific
truth as give some of the best intellects of the age occupa
tion.

The salient quality of Faraday's scientific character re
veals itself from beginning to end of these volumes : a union

1 A letter addressed to me by Professor Weber, on the 18th of last
March, contains the following reference to the connection here mentioned :
44 Die Hoffhung einer solchcn Combination ist durch Faraday's Entdeckung
dor Ihvhung dcr Polarisationsebene durch magnetische Directionskraft
zuerst, und sodann durch die Uebercinstimmung derjenigcn Geschwindig-
kcit, welche das Vcrhiiltniss der electro-dynamischen Einheit zur electro-
statischen ausdriickt, mit der Geschwindigkeit des Lichts angcregt
worden ; wnd mir schcint von alien Vrr.-m-hen, welche zur Verwirklichung
dieser Hoflhung gemacht worden sind, das von lljcrnn Maxwell gemachtc
am erfolgrcichstcn."

FARADAY. 345

of ardor and patience — the one prompting the attack, the
other holding him on to it till defeat was final or victory
assured. Certainty in one sense or the other was necessary
to his peace of mind. The right method of investigation
is, perhaps, incommunicable ; it depends on the individual
rather than on the system, and the mark is missed when
Faraday's researches are pointed to as merely illustrative
of the power of the inductive philosophy. The brain may
be filled with that philosophy, but without the energy and
insight which this man possessed, and which with him were
personal and distinctive, we should never rise to the level
of his achievements. His power is that of individual genius,
rather than of philosophic method ; the energy of a strong
soul expressing itself after its own fashion, and acknowl
edging no mediator between it and Nature.

The second volume of the " Life and Letters," like the
first, is an historic treasury as regards Faraday's work and
character, and his scientific and social relations. It contains
letters from Humboldt, Herschel, Hachette, De la Rive, Du
mas, Liebig, Melloni, Becquerel, Oersted, Pliicker, Du Bois-
Reymond, Lord Melbourne, Prince Louis Napoleon, and many
other distinguished men. I notice with particular pleasure
a. letter from Sir John Herschel in reply to a sealed packet
addressed to him by Faraday, but which he had permission
to open if he pleased. The packet referred to one of the
many unfulfilled hopes which spring up in the mind of fer
tile investigators :

" Go on and prosper, c from strength to strength,' like a
victor marching with assured step to further conquests ; and
be certain that no voice will join more heartily in the paeans
that already begin to rise, and will speedily swell into a
shout of triumph, astounding even to yourself, than that of
J. F. W. Herschel."

As an encourager of the scientific worker, this fine spirit
is still active.

346 FRAGMENTS OF SCIENCE.

Faraday's behavior to Melloni in 1835 merits a word of
notice. The young man was a political exile in Paris. He
had newly-fashioned and applied the thermo-electric pile,
and had obtained with it results of the greatest importance.
But they were not appreciated. With the sickness of dis
appointed hope, Melloni waited for the report of the Com
missioners appointed by the Academy of Sciences to exam
ine his labors. At length he published his researches in
the " Annales de Chimie." They thus fell into the hands
of Faraday, who, discerning at once their extraordinary
merit, obtained for their author the Rumford Medal of the
Royal Society. A sum of money always accompanies this
medal, and the pecuniary help was at this time even more
essential than the mark of honor to the young refugee.
Melloni' s gratitude was boundless :

" Et vous, monsieur," he writes to Faraday, " qui appar-
tenez a une society a laquelle je n'avais rien oflert, vous qui
me connaissiez & peine le nom ; vous n'avez pas demande
si j'avais des ennemis faiblcs ou puissants, ni calcule quel
en 6tait le nombre ; mais vous avez parle" pour 1'opprime
Stranger, pour celui qui n'avait pas le moindre droit u tant
de bienveillance, et vos paroles ont 6t6 accueillies favorable-
ment par des collegues consciencieux ! Je reconnais bien
hi des hommes dignes de leur noble mission, les ve>itables
repr6sentants de la science d'un pays libre et ge"n6reux."

Within the prescribed limits of this article it would be
impossible to give even the slenderest summary of Fara
day's correspondence, or to carve from it more than the
merest fragments of his character. His letters, written to
Lord Melbourne and others in 1836, regarding his pension,
illustrate his uncompromising independence. The Prime
Minister had offended him, but assuredly the apology de
manded and given was complete. I think it certain that,
notwithstanding the very full account of this transaction
given by Dr. Bence Jones, motives and influences were at

FARADAY. 347

work which even now are not entirely revealed. The min
ister was bitterly attacked, but he bore the censure of the
press with great dignity. Faraday, while he disavowed
having either directly or indirectly furnished the matter of
those attacks, did not publicly exonerate his lordship. The
Hon. Caroline Fox had proved herself Faraday's ardent
friend, and it was she who had healed the breach between
the philosopher and the minister. She manifestly thought
that Faraday ought to have come forward in Lord Mel
bourne's defence, and there is a flavor of resentment in one
of her letters to him on the subject. No doubt Faraday had
good grounds for his reticence, but they are to me unknown.

In 1841 his health broke down utterly, and he went to
Switzerland with his wife and brother-iri-law. His bodily
vigor soon revived, and he accomplished feats of walking-
respectable even for a trained mountaineer. The published
extracts from his Swiss journal contain many beautiful and
touching allusions. Amid references to the tints of the
Jungfrau, the blue rifts of the glaciers, and the noble Niesen,
towering over the Lake of Thun, we come upon the charm
ing little scrap which I have elsewhere quoted : " Clout-nail
making goes on here rather considerably, and is a very neat
and pretty operation to observe. I love a smith's shop, and
any thing relating to smithery. My father was a smith."
This is from his journal ; but he is unconsciously speaking
to somebody — perhaps to the world.

His descriptions of the Staub-bach, Giessbach, and of
the scenic effects of sky and mountain, are all fine and sym
pathetic. But amid it all,, and in reference to it all, he tells
his sister that " true enjoyment is from within, not from
without." In those days Agassiz was living under a slab
of gneiss on the glacier of the Aar. Faraday met Forbes
at the Grimsel, and arranged with him an excursion to the
" H6tel des Neuchatelois ; " but indisposition put the pro
ject out.

348 FRAGMENTS OF SCIEXCE.

From the Fort of Ham, in 1843, Faraday received a let
ter addressed to him by Prince Louis Napoleon Bonaparte.
He read this letter to me many years ago, and the desire,
shown in various ways by the French Emperor, to turn
modern science to account, has often reminded me of it
since. At the age of thirty-five the prisoner of Ham speaks
of " rendering his captivity less sad by studying the great
discoveries " which science owes to Faraday ; and he asks
a question which reveals his cast of thought at the time :
" What is the most simple combination to give to a voltaic
battery, in order to produce a spark capable of setting fire
to powder under water or under ground ? " Should the
necessity arise, the French Emperor will not lack at the
outset the best appliances of modern science ; while we, I
fear, shall have to learn the magnitude of the resources we
are now neglecting amid the pangs of actual war.1

One turns with renewed pleasure to Faraday's letters
to his wife, published in the second volume. Here surely
the loving essence of the man appears more distinctly than
anywhere else. From the house of Dr. Percy, in Birming
ham, he writes thus :

"Here — even here — the moment I leave the table I
wish I were with you IN QUIET. Oh, what happiness is
ours ! My runs into the world in this way only serve to
make me esteem that happiness the more."

And again • -

" We have been to a grand conversazione in the town-
hall, and I have now returned to my room to talk with you,
as the pleasantest and happiest thing that I can do. Noth
ing rests me so much as communion with you. I feel it
even now as I write, and catch myself saying the words
aloud as I write them/'

1 The u science " has since been applied with astonishing effect by
those who had studied it for more thoroughly than the Emperor oT the
French,

this, moreorec,
tore:

ier writing, I walk oat in the
with XT dear wife to enjoy
sceoei; of mfl that I save

a

O:

and Leers," some Ml
ladyhdesmbeshiawd
despise sect of CbrisliaK, know^ if IEWI

Oirist. Headds: c I do not think h at

•f~*A T$B4af~raf^^ r^F 4-l^A •vfe^'+nv^l ^MW^MM^^^ •v^f) v«a
. 1. 1 "7 M~ r -" ~~_ " .. 11 T

• idagaw,

two dianct tilings.0 He saw ckarly tie

of his pticolar faith. For his
mind ato leare no roan

' * " " * '.

yomh. His •!%•• mm cniraitational aid hereditary. It

L-J * «•• - _ ^_"«^ __ • -

..:. :.: .-;•;.. 11:5 : : ...5
of his ban ; and howerer its

_

It is orth :
andsosvit a

*• 1 1 •" 5 11 J " " * " T 1

would b a ^ secularist " were he no

-' : .. : . 5 :•".:;•:;•.: ; ...i -.:

accompabed by dc^mx JL lectnre defirered kiJutc Ac
City Phbsophkal Society in 171H, mmtm fci TI- twentr-
sii yearef age, expresses die liews regarding education
henteriaioed to theendof hislife «Firs

350 FRAGMENTS OF SCIENCE.

he says, "all theological considerations are banished from
the society, and of course from my remarks ; and whatever
I may say has no reference to a future state, or to the means
which are to be adopted in this world in anticipation of it.
Next, I have no intention of substituting any thing for re
ligion, but I wish to take that part of human nature which
is independent of it. Morality, philosophy, commerce, the
various institutions and habits of society, are independent
of religion, and may exist either with or without it. They
are always the same, and can dwell alike in the breasts of
those who from opinion are entirely opposed in the set of
principles they include in the term religion, or in those wTho
have none.

" To discriminate more closely, if possible, I will ob
serve that we have no right to judge religious opinions, but
the human nature of this evening is that part of man which
we have a right to judge ; and I think it will be found, on
examination, that this humanity — as it may perhaps be
(Called — will accord with what I have before described as
being in our own hands so improvable and perfectible."

Among my old papers I find the following remarks on
one of my earliest dinners with Faraday : " At two o'clock
he came down for me. He, his niece, and myself, formed
the party. ' I never give dinners,' he said. ' I don't know
how to give dinners, and I never dine out. But I should
not like my friends to attribute this to a wrong cause. I
act thus for the sake of securing time for work, and not
through religious motives, as some imagine.' He said
grace. I am almost ashamed to call his prayer a * saying '
of grace. In the language of Scripture, it might be de
scribed as the petition of a son, into w^hose heart God had
sent the Spirit of His Son, and who with absolute trust
asked a blessing from his father. We dined on roast beef,
Yorkshire pudding, and potatoes ; drank sherry, talked of
research and its requirements, and of his habit of keeping

FARADAY. 351

himself free from the distractions of society. He was bright
and joyful — boylike, in fact, though he is now sixty-two.
His work excites admiration, but contact with him warms
and elevates the heart. Here, surely, is a strong man. I
love strength, but let me not forget the example of its
union with, modesty, tenderness, and sweetness, in the char
acter of Faraday."

Faraday's progress in discovery, and the salient points
of his character, are well brought out by the wise choice of
letters and extracts published in these volumes. I will not
call the labors of the biographer final. So great a char
acter will challenge reconstruction. In the coming time
some sympathetic spirit, with the requisite strength, knowl
edge, and solvent power, will, I doubt not, render these
materials plastic, give them more perfect organic form, and
send through them, with less of interruption, the currents
of Faraday's life. " He was too good a man," writes his
present biographer, " for me to estimate rightly, and too
great a philosopher for me to understand thoroughly."
That may be, but the reverent affection to which we owe
the discovery, selection, and arrangement of the materials
here placed before us, is probably a surer guide than mere
literary skill. The task of the artist who may wish in
future times to reproduce the real though unobtrusive
grandeur, the purity, beauty, and childlike simplicity of
him whom we have lost, will find his chief treasury already
provided for him by Dr. Bence Jones's labor of love.

Library*

XIII.

AN

ELEMENTARY LECTURE ON MAGNETISM.

ADDEESS TO THE TEACHEES OF PKIMAKY SCHOOLS AT THE SOUTH
KENSINGTON MUSEUM.

April 30, 1861.

" Next in order I will proceed to discuss by what law of Nature it
coines to pass that iron can be attracted by that stone which the G reeks
call the Magnet from the name of its native place, because it has its origin
within the bounds of the country of the Magncsians. This stone is more
wondered at because it often produces a chain of [iron] rings hanging
down from it. Thus you may see five and more suspended in succession
and tossing about in the light airs, one always hanging from the other
and attached to its lower side, and each in turn one from the other ex
periencing the binding power of the stone : with such a continued cur
rent its force flics through all

"In things of this kind, many things must be established before you
can assign the true law of the thing in question, and it must be ap
proached by a very circuitous road ; wherefore all the more I call for an
attentive ear and mind." — LUCRETIUS, DC Jterum Natura, Lib. VI.,
Munro's Translation, p. 317.

This lecture is a plain statement of the elementary facts of magnet
ism, of one magnetic theory, and of the methods to be pursued in master
ing both. It has already circulated among the teachers mentioned on its
title-page, and I had some doubts as to the propriety of its insertion
here. But, on reading it, it seemed so likely to be helpful, that my
scruples disappeared. J. T.

MAGNETIC LINES OF FORCF.

From a Photograph by Professor MAYER, Lehigh University, United Slates.

XIII.

A LECTURE ON MAGNETISM.

WE have no reason to believe that the sheep or the dog-,
or, indeed, any of the lower animals, feel an interest in the
laws by which natural phenomena are regulated. A herd
may be terrified by a thunder-storm ; birds may go to roost,
and cattle return to their stalls during a solar eclipse ; but
neither birds nor cattle, as far as we know, ever think of
inquiring into the causes of these things. It is otherwise
with man. The presence of natural objects, the occurrence
of natural events, the varied appearances of the universe in
which he dwells, penetrate beyond his organs of sense, and
appeal to an inner power of which the senses are the mere
instruments and excitants. No fact is to him either final
or original. He cannot limit himself to the contemplation
of it alone, but endeavors to ascertain its position in a
series to which the constitution of his mind assures him it
must belong. He regards all that he witnesses in the
present as the efflux and sequence of something that has
gone before, and as the source of a system of events which
is to follow. The notion of spontaneity, by which in his
ruder .state he accounted for natural events, is abandoned;
the idea that Nature is an aggregate of independent parts
also disappears, as the connection and mutual dependence
of physical powers become more and more manifest : until
he is finally led, and that chiefly by the science of which
I happen this evening to be the exponent, to regard

358 J KAGMENTS OF SCIENCE.

Nature as an organic whole, as a body each of whose
members sympathizes with the rest, changing-, it is true,
from ages to ages, but without one real break of continuity,
or a single interruption of the fixed relations of cause and
effect.

The system of things which we call Nature is, however,
too vast and various to be studied first-hand by any single
mind. As knowledge extends there is always a tendency
to subdivide the field of investigation, its various parts be
ing taken up by different individuals, and thus receiving a
greater amount of attention than could possibly be bestowed
on them if each investigator aimed at the mastery of the
whole. East, west, north, and south, the human mind
pushes its conquests ; but the centripetal form in which
knowledge, as a whole, advances, spreading ever wider on
all sides, is due in reality to the exertions of individuals,
each of whom directs his efforts, more or less, along a single
line. Accepting, in many respects, his culture from his
fellow-men, taking it from spoken words and from written
books, in some one direction, the student of Nature must
actually touch his work. He may otherwise be a dis
tributor of knmvlfluv, but not a creator, and fails to attain
that vitality of thought and correctness of judgment which
direct and habitual contact with natural truth can alone
impart.

One large department of the system of Nature which
forms the chief subject of my own studies, and to which it
is my duty to call your attention this evening, is that of
physics, or natural philosophy. This term is large enough
to cover the study of Nature generally, but it is usually
restricted to a department which, perhaps, lies closer to
our perceptions than any other. It deals with the phe
nomena and laws of light and boat — with the phenomena
and laws of magnetism and electricity — with those of
sound — with the pressures and motions of liquids and

A LECTUIIE ON MAGNETISM. 359

gases, whether in a state of translation or of undulation.
The science of mechanics is a portion of natural philosophy,
though at present so large as to need the exclusive atten
tion of him who would cultivate it profoundly. Astronomy
is the application of physics to the motions of the heavenly
bodies, the vastness of the field causing it, however, to be
regarded as a department in itself. In chemistry physical
agents play important parts. By heat and light we cause
bodies to combine, and by heat and light we decompose
them. Electricity tears asunder the locked atoms of com
pounds, through their power of separating carbonic acid into
its constituents ; the solar beams build up the whole vege
table world, and .by it the animal, while the touch of the
self-same beams causes hydrogen and chlorine to unite with
sudden explosion and form by their combination a powerful
acid. Thus physics and chemistry intermingle, physical
agents being employed by the chemist as a means to an
end ; while in physics proper the laws and phenomena of
the agents themselves, both qualitative and quantitative,
are the primary objects of attention.

My duty here to-night is to spend an hour in telling how
this subject is to be studied, and how a knowledge of it is
to be imparted to others. When first invited to do this, I
hesitated before accepting the responsibility. It would be
easy to entertain you with an account of what natural phi
losophy has accomplished. I might point to those applica
tions of science regarding which we hear so much in the
newspapers, and which we often find mistaken for science
itself. I might, of course, ring changes on the steam-
engine and the telegraph, the electrotype and the photo
graph, the medical applications of physics, and the million
other inlets by which scientific thought filters into prac
tical life. That would be easy compared with the task
of informing you how you are to make the study of physics
the instrument of your own culture, how you are to pos-

360 FRAGMENTS OF SCIENCE.

sess its facts and make them living- seeds which shall
take root and grow in the mind, and not lie like dead
lumber in the store-house of memory. This is a task much
heavier than the mere cataloguing of scientific achieve
ments ; and it is one which, feeling my own want of time
and power to execute it aright, I might well hesitate to
accept

But let me sink excuses, and attack the work to the
best of my ability. First and foremost, then, I would ad
vise you to get a knowledge of facts from actual observa
tion. Facts looked at directly are vital ; when they pass
into words half the sap is taken out of them. You wish,
for example, to get a knowledge of magnetism ; well, pro
vide yourself with a good, book on the subject, if you can,
but do not be content with what the book tells you ; do
not be satisfied with its descriptive woodcuts ; see the
actual thing yourself. Half of our book-writers describe
experiments which they never made, and their descrip
tions often lack both force and truth ; but no matter how
clever or conscientious they may be, their written words
cannot supply the place of actual observation. Every fact
has numerous radiations, which are shorn off by the man
who describes it. Go, then, to a philosophical instrument-
maker, and give, according to your means, for a straight
bar-magnet, say, half a crown, or, if you can afford it, five
shillings for a pair of them ; or get a smith to cut a length
of ten inches from a bar of steel an inch wide and half an
inch thick ; file its ends decently, harden it, and get some
body like myself to magnetize it. Two bar-magnets are
better than one. Procure some darning-needles such as
these. Provide yourself also witli a little unspun silk ;
which will give you a suspending fibre void of torsion ;
make a little loop of paper or of wire, thus, and attach your
fibre to it. Do it neatly. In the loop place your darning-
needle, and bring the two ends or poles, as they are called,

A LECTURE ON MAGNETISM. 361

of your magnet successively up to either end of the needle.
Both the poles, you find, attract both ends of the needle.
Replace the needle by a bit of annealed iron wire, the same
effects ensue. Suspend successively little rods of lead,
copper, silver, or brass, of wood, glass, ivory, or whalebone ;
the magnet produces no sensible effect upon any of these
substances. You thence infer a special property in the
case of steel and iron. Multiply your experiments, how
ever, and you will find that some other substances besides
iron are acted upon by your magnet. A rod of the metal
nickel, or of the metal cobalt, from which the blue color
used by painters is derived, exhibits powers similar to those
observed with the iron and steel.

In studying the character of the force you may, how
ever, confine yourself to iron and steel, which are always
at hand. Make your experiments with the darning-needle
over and over again ; operate on both ends of the needle ;
try both ends of the magnet. Do not think the work stu
pid ; you are conversing with Nature, and must acquire a
certain grace and mastery over her language ; and these
practice can alone impart. Let every movement be made
with care, and avoid slovenliness from the outset. In every
one of your experiments endeavor to feel the responsibility
of a moral agent. Experiment, as I have said, is the lan
guage by which we address Nature, and through which she
sends her replies ; in the use of this language a lack of
straightforwardness is as possible and as prejudicial as in
the spoken language of the tongue. If you wish to become
acquainted with the truth of Nature, you must from the first
resolve to deal with her sincerely.

Now remove your needle from its loop, and draw it from
end to end along one of the ends of the magnet ; resuspend
it, and repeat your former experiment. You find the result
different. You now find that each extremity of the magnet
attracts one end of the needle and repels the other. The
16

36-2 FRAGMENTS OF SCIENCE.

simple attraction observed in the first instance is now re
placed by a dual force. Repeat the experiment till you
have thoroughly observed the ends which attract and those
which repel each other.

Withdraw the magnet entirely from the vicinity of your
needle, and leave the latter freely suspended by its fibre.
Shelter it as well as you can from currents of air, and if
you have iron buttons on your coat or a steel penknife in
your pocket, beware of their action. If you work at night,
beware of iron candlesticks, or of brass ones with iron rods
inside. Freed from such disturbances, the needle takes up
a certain determinate position. It sets its length nearly
north and south. Draw it aside from this position and let
it go. After several oscillations it will again come to it.
If you have obtained your magnet from a philosophical-in
strument maker, you will see a mark on one of its ends.
Supposing, then, that you drew your needle along the end
thus marked, and that the eye-end of your needle was the
last to quit the magnet, you will find that the eye turns to
the south, the point of the needle turning toward the north.
Make sure of this, and do not take this statement on my
authority.

Now take a second darning-needle like the first, and
magnetize it in precisely the same manner : freely sus
pended it also will turn its point to the north and its eye
to the south. Your next step is to examine the action of
the two needles which you have thus magnetized upon each
other.

Take one of them in your hand, and leave the other sus
pended ; bring the eye-end of the former near the eye-end
of the latter ; 'the suspended needle retreats : it is repelled.
Make the same experiment with the two points, you obtain
the same result, the suspended needle is repelled. Now
cause the dissimilar ends to act on each other — you have
:it< ruction — point attracts rye and eye attracts point. Pmvo

A LECTURE ON MAGNETISM. 363

the reciprocity of this action by removing- the suspended
needle, and putting the other in its place. You obtain the
same result. The attraction, then, is mutual, and the re
pulsion is mutual, and you have thus demonstrated in the
clearest manner the fundamental law of magnetism, that
like poles repel, and that unlike poles attract each other.
You may say that this is all easily understood without do
ing ; but do it, and your knowledge will not be confined to
what I have uttered here.

I have said that one end of your magnet has a mark
upon it ; lay several silk fibres together, so as to get suffi
cient strength, or employ a thin silk ribbon, and form a loop
large enough to hold your magnet. Suspend it ; it turns
its marked end toward the north. This marked end is that
which in England is called the north pole. If a common
smith has made your magnet, it will be convenient to deter-
mine its north pole yourself, and to mark it with a file.
You vary your experiments by causing your magnetized
darning-needle to attract and repel your large magnet ; it
is quite competent to do so. In magnetizing the needle, I
have supposed the eye-end to be the last to quit the marked
end of the magnet ; that end of the needle is a south pole.
The end which last quits the magnet is always opposed in
polarity to the end of the magnet with which it has been in
contact. Brought near each other they mutually attract,
and thus demonstrate that they are unlike poles.

You may perhaps learn all this in a single hour ; but
spend several at it, if necessary; and remember, under
standing it is not sufficient: you must obtain a manual
aptitude in addressing Nature. If you speak to your fellow-
man, you are not entitled to use jargon. Bad experiments
are jargon addressed to Nature, and just as much to be dep
recated. A manual dexterity in illustrating the interaction
of magnetic poles is of the utmost importance at this stage
of your progress, and you must not neglect attaining this

3 04 FRAGMENTS OF SCIENCE.

power over your implements. As you proceed, moreover,
you will be tempted to do more than I can possibly suggest.
Thoughts will occur to you which you will endeavor to fol
low out ; questions will arise which you will try to answer.
The same experiment may be twenty things to twenty
people. Having witnessed the action of pole on pole
through the air, you will perhaps try whether the magnetic
power is not to be screened off. You use plates of glass,
wood, slate, pasteboard, or gutta-percha, but find them all
pervious to this wondrous force. One magnetic pole acts
upon another through these bodies as if they were not
present. And should you become a patentee for the regu
lation of ships' compasses, you will not fall, as some pro
jectors have done, into the error of screening off the mag
netism of the ship by the interposition of such substances.

If you wish to teach a class you must contrive that the
effects which you have thus far witnessed for yourself shall
be witnessed by twenty or thirty pupils. And here your
private ingenuity must come into play. You will attach
bits of paper to your needles, so as to render their move
ments visible at a distance, denoting the north and south
poles by different colors, say green and red. You may also
improve upon your darning-needle. Take a strip of sheet-
steel, the rib of a lady's stays will answer, heat it to vivid
redness and plunge it into cold water. It is thereby hard
ened, rendered, in fact, almost as brittle as glass. Six
inches of this, magnetized in the manner of the darning-
needle, will be better able to carry your paper indexes.
Having secured such a strip, you proceed thus :

Magnetize a small sewing-needle and determine its
poles ; or, break half an inch or an inch off your magnetized
darning-needle, and suspend it by a fine silk fibre. The
sewing-needle or the fragment of the darning-needle is now
to be used as a test-needle to examine the distribution of
the magnetism in your strip of steel. Hold the strip up-

A LECTURE ON MAGNETISM. 365

right in your left hand, and cause the test-needle to ap
proach the lower end of your strip; one end is attracted,
the other is repelled. Raise your needle along the strip ;
its oscillations, which at first were quick, become slower ;
opposite the middle of the strip they cease entirely ; neither
end of the needle is attracted ; above the middle the test-
needle turns suddenly round, its other end being now at
tracted. Go through the experiment thoroughly ; you thus
learn that the entire lower half of the strip attracts one end
of the needle, while the entire upper half attracts the oppo
site end. Supposing the north end of your little needle to
be that attracted below, you infer that the entire lower half
of your magnetized strip exhibits south magnetism, while
the entire upper half exhibits north magnetism. So far,
then, you have determined the distribution of magnetism in
your strip of steel.

You look at this fact, you think of it ; in its suggestive-
ness the value of the experiment chiefly consists. The
thought arises, " What will occur if I break my strip of
steel across in the middle ? Shall I obtain two magnets,
each possessing a single pole ? " Try the experiment ;
break your strip of steel, and test each half as you tested
the whole. The mere presentation of its two ends in suc
cession to your test-needle suffices to show you that you
have not a magnet with a single pole, that each half pos
sesses two poles with a neutral point betwreen them. And
if you again break the half into two other halves, you will
find that each quarter of the original strip exhibits precisely
the same magnetic distribution as the strip itself. You
may continue the breaking process ; no matter how small
your fragment may be, it still possesses two opposite poles
and a neutral point between them. Well, your hand ceases
to break where breaking becomes a mechanical impossi
bility ; but does the mind stop there ? No : you follow
the breaking process in idea when you can no longer realize

366 FRAGMENTS OF SCIENCE.

it in fact ; your thoughts wander amid the very atoms of
your steel, and you conclude that each atom is a magnet,
and that the force exerted by the strip of steel is the mere
summation or resultant of the forces of its ultimate par
ticles.

Here, then, is an exhibition of power which we can call
forth or cause to disappear at pleasure. We magnetize our
strip of steel by drawing it along the pole of a magnet ;
we can demagnetize it, or reverse its magnetism, by prop
erly drawing it along the same pole in the opposite direc
tion. What, then, is the real nature of this wondrous
change ? What is it that takes place among the atoms of
the steel when the substance is magnetized ? The question
leads us beyond the region of sense, and into that of imagi
nation. This faculty, indeed, is the divining-rod of 'the man
of science. Not, however, an imagination which catches
its creations from the air, but one informed and inspired by
facts, capable of seizing firmly on a physical image as a
principle, of discerning its consequences, and of devising
means whereby these forecasts of thought may be brought
to an experimental test. If such a principle be adequate to
account for all the phenomena, if from an assumed cause
the observed facts necessarily follow, we call the assump
tion a theory, and, once possessing it, we can not only re
vive at pleasure facts already known, but we can predict
others wluch we have never seen. Thus, then, in the prose
cution of physical science, our powers of observation, mem
ory, imagination, and inference, are all drawn upon. We
observe facts and store them up ; imagination broods upon
these memories, and by the aid of reason tries to discern
their interdependence. The theoretic principle flashes, or
slowly dawns upon the mind, and then the deductive fac
ulty interposes to carry out the principle to its logical con
sequences. A perfect theory gives dominion over natural
facts; and even an assumption which can only partially

A LECTURE ON MAGNETISM. 367

stand the test of a comparison with facts, may be of emi
nent use in enabling us to connect and classify groups of
phenomena. The theory of magnetic fluids is of this latter
character, and with it we must now make ourselves familiar.

With the view of stamping the thing more firmly on
your minds, I will make use of a strong and vivid image.
In optics, red and green are called complementary colors ;
their mixture produces white. Now I ask you to imagine
each of these colors to possess a self-repulsive power ; that
red repels red, and that green repels green ; but that red
attracts green and green attracts red, the attraction of the
dissimilar colors being equal to the repulsion of the similar
ones. Imagine the two colors mixed so as to produce
white, and suppose two strips of wood painted with this
white ; what will be their action upon each other ? Sus
pend one of them freely as we suspended our darning-
needle, and bring the other near it ; what will occur ? The
red component of the strip you hold in your hand will re
pel the red component of your suspended strip, but then it
will attract the green ; and the forces being equal they neu
tralize each other.. In fact, the least reflection shows you
that the strips will be as indifferent to each other as two
unmagnetized darning-needles would be under the same
circumstances.

But suppose, instead of mixing the colors, we painted
one half of each strip from centre to end red, and the other
half green, it is perfectly manifest that the two strips would
now behave toward each other exactly as our two magnet
ized darning-needles — the red end would repel the red and
attract the green, the green would repel the green and at
tract the red; so that, assuming two colors thus related to
each other, wTe could by their mixture produce the neutral
ity of an unmagnetized body, while by their separation we
could produce the duality of action of magnetized bodies.

But you have already anticipated a defect in my con-

3C8 FRAGMENTS OF SCIENCE.

ception ; for if we break one of our strips of wood in the
middle we have one half entirely red and the other entirely
green, and with these it would be impossible to imitate the
action of our broken magnet. How, then, must we modify
our conception? We must evidently suppose each atom
of wood painted green on one face and red on the opposite
one. If this were done the resultant action of all the atoms
would exactly resemble the action of a magnet. Here, also,
if the two opposite colors of each atom could be caused
to mix so as to produce white, we should have, as before,
perfect neutrality.

Substitute in your minds for these two self-repellant
and mutually attractive colors two invisible self-repellant
and mutually attractive fluids, which in ordinary steel are
mixed to form a neutral compound, but which the act of
magnetization separates from each other, placing the oppo
site fluids on the opposite faces of each atom, and you have
a perfectly distinct conception of the celebrated theory of
magnetic fluids. The strength of the magnetism excited is
supposed to be proportional to the quantity of neutral fluid
decomposed. According to this theory nothing is actually
transferred from the exciting magnet to the excited steel.
The act of magnetization consists in the forcible separation
of two powers which existed in the steel before it was mag
netized, but which then neutralized each other by their coa
lescence. And if you test your magnet after it lias excited
a hundred pieces of steel, you will find that it has lost no
force — no more, indeed, than I should lose had my words such
a magnetic influence on your minds, as to excite in them a
strong resolve to study natural philosophy. I should, in
fact, be the gainer by my own utterance and by the reac
tion of your strength ; and so also the magnet is the gainer
by the reaction of the body which it magnetizes.

Look now to your excited piece of steel ; figure each
atom to your minds with its opposed fluids spread over its

A LECTURE ON MAGNETISM. 369

opposite faces. How can this state of tilings be perma
nent ? The fluids, by hypothesis, attract each other ;
what, then, keeps them apart ? Why do they not instantly
rush together across the equator of the atom, and thus neu
tralize each other ? To meet this question, philosophers
have been obliged to infer the existence of a special force
which holds the fluids asunder. They call it coercive
force; and it is found that those kinds of steel which offer
most resistance to being magnetized, which require the
greatest amount of coercion to tear their fluids asunder,
are the very ones which offer the greatest resistance to the
reunion of the fluids after they have been once separated.
Such kinds of steel are most suited to the formation of per
manent magnets. It is manifest, indeed, that without
coercive force a permanent magnet would not be at all pos
sible.

You have not forgotten that, previous to magnetizing your
darning-needle, both its ends were attracted by your mag
net ; and that both ends of your bit of iron wire were acted
upon in the same way. Probably also long before this you
will have dipped the end of your magnet among iron filings,
and observed how they cling to it, or into a nail-box, and
found how it drags the nails after it. I know very well
that if you are not the slaves of routine, you will have by
this time done many things that I have not told you to do,
and thus multiplied your experience beyond what I have
indicated. You are almost sure to have caused a bit of
iron to hang from the end of your magnet, and you have
probably succeeded in causing a second piece to attach
itself to the first, a third to the second ; until finally the .
force has become too feeble to bear the weight of more.
If you have operated with nails, you may have observed
that the points and edges hold together with the greatest
tenacity ; and that a bit of iron clings more firmly to the
corner of your magnet than to one of its flat surfaces. In

370 FRAGMENTS OF SCIENCE.

short, you will, in all likelihood, have enriched your expe
rience in many ways without any special direction from
me.

Well, the magnet attracts the nail, and that nail attracts
a second one. This proves that the nail in contact with
the magnet has had the magnetic quality developed in it
by that contact. If it be withdrawn from the magnet, its
power to attract its fellow-nail ceases. Contact, however,
is not necessary. A sheet of glass or paper, or a space
of air, may exist between the magnet and the nail ; the
latter is still magnetized, though not so forcibly as when
in actual contact. The nail then presented to the magnet
is itself a temporary magnet. That end which is turned
toward the magnetic pole has the opposite magnetism of
the pole which excites it ; the end most remote from the
pole has the same magnetism as the pole itself, and be
tween the two poles the nail, like the magnet, possesses a
magnetic equator.

Conversant as you now are with the theory of magnetic
fluids, you have already, I doubt not, anticipated me in
imagining the exact condition of the iron under the in
fluence of the magnet. You picture the iron as possessing
the neutral fluid in abundance, you picture the magnetic
pole, when brought near, decomposing the fluid ; repelling
the fluid of a like kind with itself, and attracting the unlike
fluid ; thus exciting in the parts of the iron nearest to itself
the opposite polarity. But the iron is incapable of becoming
a permanent magnet. It only shows its virtue as long as
the magnet acts upon it. What, then, does the iron lack
which the steel possesses? It lacks coercive force. Its
fluids arc separated with ease, but, once the separating
cause is removed, they flow together again and neutrality
is restored. Your imagination must be quite nimble in
picturing these changes. You must be able to see the
fluids dividing and reuniting according as the magnet is

A LECTURE ON MAGNETISM. 3?1

brought near or withdrawn. Fixing a definite pole in your
imagination, you must picture the precise arrangement of
the two fluids with reference to this pole. And you must
not only be well drilled in the use of this mental imagery
yourself, but you must be able to arouse the same pictures
in the minds of your pupils, and satisfy yourself that they
possess this power of placing actually before themselves
magnets and iron in various positions, and describing the
exact magnetic state of the iron in each particular case.
The mere facts of magnetism will have their interest im
mensely augmented by an acquaintance with those hidden
principles whereon the facts depend. Still, while you use
this theory of magnetic fluids to track out the phenomena
and link them together, be sure to tell your pupils that it
is to be regarded as a symbol merely — a symbol, more
over, which is incompetent to cover all the facts,1 but which
does good practical service while we are waiting for the
actual truth.

This state of excitement into which the soft iron is
throw^n by the influence of the magnet, is sometimes called
" magnetization by influence." More commonly, however,
the magnetism is said to be " induced " in the soft iron,
and hence this way of magnetizing is called "magnetic
induction." Now, there is nothing theoretically perfect in
Nature : there is no iron so soft as not to possess a certain
amount of coercive force, and no steel so hard as not to be
capable, in some degree, of magnetic induction. The
quality of steel is in some measure possessed by iron, and
the quality of iron is shared in some degree by steel. It is
in virtue of this latter fact that the unmagnetized darning-

1 This theory breaks down when applied to diamagnetic bodies, which
are repelled by magnets. Like soft iron, such bodies are thrown into a
state of temporary excitement in virtue of which they are repelled, but
any attempt to explain such a repulsion by the decomposition of a fluid
will demonstrate its own futility.

372 FRAGMENTS OF SCIENCE.

needle was attracted in your first experiment ; and from
this you may at once deduce the consequence that, after the
steel has been magnetized, the repulsive action of a magnet
must be always less than its attractive action. For the
repulsion is opposed by the inductive action of the magnet
on the steel, while the attraction is assisted by the same
inductive action. Make this clear to your minds, and
verify it by your experiments. In some cases you can
actually make the attraction due to the temporary mag
netism overbalance the repulsion due to the permanent
magnetism, and thus cause two poles of the same kind
apparently to attract each other. When, however, good
hard magnets act on each other from a sufficient distance,
the inductive action practically vanishes, and the repulsion
of like poles is sensibly equal to the attraction of unlike
ones.

I dwell thus long on elementary principles, because
they are of the first importance, and it is the temptation
of this age of unhealthy cramming to neglect them. Now
follow me a little further. In examining the distribution
of magnetism in your strip of steel, you raised the needle
slowly from bottom to top, and found what we called a
neutral point at the centre. Now does the magnet really
exert no influence on the pole presented to its centre?
Let us see.

Fio. 1.

Let S N, Fig. 1, be your magnet, and let n represent a
particle of north magnetism placed exactly opposite the

A LECTURE ON MAGNETISM. 373

middle of the magnet. Of course this is an imaginary case,
as you can never in reality thus detach your north mag
netism from its neighbor. What is the action of the two
poles of the magnet on n ? Your reply will of course be
that the pole S attracts n while the pole N repels it.
Let the magnitude and direction of the attraction be ex
pressed by the line n m, and the magnitude and direction
of the repulsion by the line n o. Now the particle n being
equally distant from S and N, the line n o, expressing the
repulsion, will be equal to m n, which expresses the attrac
tion, and the particle n, acted upon by two such forces,
must evidently move in the direction p n, exactly midway
between m n and n o. Hence you see that, although there
is no tendency of the particle n to move toward the mag
netic equator, there is a tendency on its part to move
parallel to the magnet. If instead of a particle of north
magnetism we placed a particle of south magnetism op
posite to the magnetic equator, it would evidently be urged
along the line n q / and if instead of two separate particles
of magnetism we place a little magnetic needle, containing
both north and south magnetism, opposite the magnetic
equator, its south pole being urged along n q, and its north
along n p, the little needle will be compelled to set itself
parallel to the magnet S N. Make the experiment, and
satisfy yourselves that this is the case.

Substitute for your magnetic needle a bit of iron wire,
devoid of permanent magnetism, and it will set itself ex
actly as the needle does. Acted upon by the magnet, the
wire, as you know, becomes a magnet and behaves as such ;
it will, of course, turn its north pole toward p, and south
pole toward q, just like the needle.

But supposing you shift the position of your particle of
north magnetism, and bring it nearer to one end of your
magnet than to the other, the forces acting on the particle
are no longer equal ; the nearest pole of the magnet will

374 FRAGMENTS OF SCIKV i

act more powerfully on the particle than the more distant
one. Let S N, Fig. 2, be the magnet and n the particle
of north magnetism in its new position. "Well, it is
repelled by N, and attracted by S. Let the repulsion be
represented in magnitude and direction by the line n o,
and* the attraction by the shorter line n m. The resultant
of these two forces will be found by completing the par
allelogram m n o p, and drawing its diagonal n p. Along
n p, then, a particle of north magnetism would be urged
by the simultaneous action of S and N. Substituting a

FIG. 2.

S I

particle of south magnetism for ny the same reasoning
would lead to the conclusion that the particle would be
urged along n q, and if we place at n a short magnetic
needle, its north pole will be urged along n p, its south
pole along n q, and the ouly position possible to the
needle, thus acted on, is along the line p q, which, as you
see, is no longer parallel to the magnet. Verify this by
actual experiment.

In this way we might go round the entire magnet, and
considering its two poles as two centres from which the
force emanates, we could, in accordance with ordinary me
chanical principles, assign a definite direction to the mag
netic needle at every particular place. And substituting,
as before, a bit of iron wire for the magnetic needle, the
positions of both will be the same.

A LECTURE ON MAGNETISM. 375

Now, I think, without further preface, you will be able
to comprehend for yourselves, and explain to others, one
of the . most interesting effects in the whole domain of
magnetism. Iron filings you know are particles of iron,
irregular in shape, being longer in some directions than in
others. For the present experiment, moreover, instead of
the iron filings, very small scraps of thin iron wire might be
employed. I place a sheet of paper over the magnet ; it is
all the better if the paper be stretched on a wooden frame,
as this enables us to keep it quite level. I scatter the
filings, or the scraps of wire, from a sieve upon the paper,
and tap the latter gently, so as to liberate the particles for
a moment from its friction. The magnet acts on the filings
through the paper, and see how it arranges them ! They
embrace the magnet in a series of beautiful curves, which
are technically called magnetic curves, or lines of magnetic
force. Does the meaning of these lines yet flash upon
you ? Set your magnetic needle or your suspended bit of
wire at any point of one of the curves, and you will find
the direction of the needle or of the wire to be exactly that
of the particle of iron, or of the magnetic curve at the
point. Go round and round the magnet ; the direction of
your needle always coincides with the direction of the curve
on which it is placed. These, then, are the lines along
which a particle of south magnetism, if you could detach it,
would move to the north pole, and a bit of north magnetism
to the south pole ; they are the lines along which the de
composition of the neutral fluid takes place, and in the case
of the magnetic needle, one of its poles being urged in one
direction, and the other pole in the opposite direction, the
needle must necessarily set itself as a tangent to the curve.
I will not seek to simplify this subject further. If there
be any thing obscure or confused or incomplete in my
statement, you ought now, by patient thought, to be able
to clear, away the obscurity, to reduce the confusion to

370 FRAGMENTS ,OF SCIENCE.

order, and to supply what is needed to render the explana
tion complete. Do not quit the subject until you thor
oughly understand it ; and if you are able to look with
your mind's eye at the play of forces around a magnet, and
see distinctly the operation of those forces in the produc
tion of the magnetic curves, the time which we have spent
together has not been spent in vain.

In this thorough manner we must master our materials,
reason upon them, and, by determined study, attain to clear
ness of conception. Facts thus dealt with exercise an
expansive force upon the boundaries of thought ; they
widen the mind to generalization. We soon recognize a
brotherhood between the larger phenomena of Nature and
the minute effects which we have observed in our private
chambers. Why, we inquire, does the magnetic needle set
north and south? Evidently it is compelled to do so by
the earth; the great globe which we inherit is itself a
magnet. Let us learn a little more about it. By means of
a bit of wax or otherwise attach your silk fibre to your
magnetic needle by a single point at its middle, the needle
will thus be uninterfered with by the paper loop, and will
enjoy to some extent a power of dipping its point or its
eye below the horizon. Lay your magnet on a table, and
hold the needle over the equator of the magnet. The
needle sets horizontal. Move it toward the north end of
the magnet; the south end of the needle dips, the dip
augmenting as you approach the north pole, over which
the needle, if free to move, will set itself exactly vertical.
Move it back to the centre, it resumes its horizontal it y ;
pass it on toward the south pole, its north end now dips,
and directly over the south pole the needle becomes ver
tical, its north end being now turned downward. Thus
we learn that on the one side of the magnetic equator the
north end of the needle dips ; on the other side the south
end dips, the dip varying from nothing to ninety degrees. If

A LECTURE OX MAGNETISM. 377

we go to the equatorial regions of the earth with a suit
ably-suspended needle, we shall find there the position of
the needle horizontal. If we sail north, one end of the
needle dips ; if we sail south, the opposite end dips ; and
over the north or south terrestrial magnetic pole the needle
sets vertical. The south magnetic pole has not yet been
found, but Sir James Ross discovered the north magnetic
pole on the 1st of June, 1831. In this manner we estab
lish a complete parallelism between the action of the earth
and that of an ordinary magnet.

The terrestrial magnetic poles do not coincide with the
geographical ones ; nor does the earth's magnetic equator
quite coincide with the geographical equator. The direc
tion of the magnetic needle in London, which is called the
magnetic meridian, encloses an angle of 24 degrees with
the true astronomical meridian, this angle being called the
Declination of the needle for London. The north pole of
the needle now lies to the west of the true meridian ; the
declination is westerly. In the year 1660, however, the
declination was nothing, while before that time it was
easterly. All this proves that the earth's magnetic con
stituents are gradually changing their distribution. This
change is very slow ; it is technically called the secular
change, and the observation of it has not yet extended over
a sufficient period of -time to enable us to guess, even ap
proximately, at its laws.

Having thus discovered, to some extent, the secret of
the earth's power, we can turn it to account. I hold in my
hand a poker formed of good soft iron ; it is now in the
line of dip, a tangent, in fact, to the earth's line of magnetic
force. The earth, acting as a magnet, is at this moment
constraining the two fluids of the poker to separate, making
the lower end of the poker a north pole, and the upper
end a south pole. Mark the experiment : I hold the knob
uppermost, and it attracts the north end of a magnetic

378 FRAGMENTS OF SCIENCE.

needle. I now reverse the poker, bringing its knob under
most ; the knob is now a north pole and attracts the south
end of a magnetic needle. Get such a poker and carefully
repeat this experiment ; satisfy yourselves that the fluids
shift their position according to the manner in which the
poker is presented to the earth. It has already been stated
that the softest iron possesses a certain amount of coercive
force. The earth, at this moment, finds in this force an an
tagonist which opposes the full decomposition of the neu
tral fluid. The component fluids may be figured as meet
ing an amount of friction, or possessing an amount of ad
hesion, which prevents them from gliding over the atoms
of the poker. Can we assist the earth in this case ? If we
wish to remove the residue of a powder from the interior
surface of a glass to which the powder clings, we invert
the glass, tap it, loosen the hold of the powder, and thus
enable the force of gravity to pull it down. So also by
tapping the end of the poker we loosen the adhesion of
the fluid to the atoms and enable the earth to pull them
apart. But, what is the consequence? The portion of
fluid which has been thus forcibly dragged over the atoms
refuses to return when the poker has been removed
from the line of dip; the iron, as you see, has become
a permanent magnet. By reversing its position and
tapping it again we reverse its magnetism. A thoughtful
and competent teacher will well know how to place these
remarkable facts before his pupils in a manner which will
excite their interest ; he will know, and if not, will try to
learn, how, by the use of sensible images, more or less gross,
to give those he teaches definite conceptions, purifying
these conceptions more and more as the minds of his pupils
become more capable of abstraction. He will cause his
logic to run like a line of light through these images, and
by thus acting he will cause his boys to march at his
side with a profit and a joy, which the mere exhibition of

A LECTURE ON MAGNETISM. 379

facts without principles, or the appeal to the bodily senses
and the power of memory alone, could never inspire.

As an expansion of the note at page 371, the following extract may
find a place here :

" It is well known that a voltaic current exerts an attractive force
upon a second current, flowing in the same direction ; and that when the
directions are opposed to each other the force exerted is a repulsive one.
By coiling wires into spirals, Ampere was enabled to make them produce
all the phenomena of attraction and repulsion exhibited by magnets, and
from this it was but a step to his celebrated theory of molecular cur
rents. He supposed the molecules of a magnetic body to be surrounded
by such currents, which, however, in the natural state of the body mu
tually neutralized each other, on account of their confused ' grouping.
The act of magnetization he supposed to consist in setting these molecu
lar currents parallel to each other ; and, starting from this principle, he
reduced all the phenomena of magnetism to the mutual action of electric
currents.

" If we reflect upon the experiments recorded in the foregoing pages
from first to last, we can hardly fail to be convinced that diamagnetic
bodies operated on by magnetic forces possess a polarity " the same in
kind as, but the reverse in direction of that acquired by magnetic bodies."
But, if this be the case, how are we to conceive the physical mechanism
of this polarity ? According to Coulomb's and Poisson's theory, the act
of magnetization consists in the decomposition of a neutral magnetic
fluid ; the north pole of a magnet, for example, possesses an attraction
for the south fluid of a piece of soft iron submitted to its influence, draws
the said fluid toward it, and with it the material particles with which the
fluid is associated. To account for diamagnetic phenomena this theory
seems to fail altogether ; according to it, indeed, the oft-used phrase, " a
north pole exciting a north pole, and a south pole a south pole," involves
a contradiction. For if the north fluid be supposed to be attracted tow
ard the influencing north pole, it is absurd to suppose that its presence
there could produce repulsion. The theory of Ampere is equally at a loss
to explain diamagnetic action ; for if we suppose the particles of bismuth
surrounded by molecular currents, then, according to all that is known
of electro-dynamic laws, these currents would set themselves parallel to,
and in the same direction as those of the magnet, and hence attraction,
and not repulsion, would be the result. The fact, however, of this not

380 FRAGMENTS OF SCIEXCE.

being the case proves that these molecular currents are not the mechan
ism by which diumagnetic induction is effected. The consciousness of
this, I doubt not, drove M. Weber to the assumption that the phenomena
of diamagnetism are produced by molecular currents, not directed) but
actually excited in the bismuth by the magnet. Such induced currents
would, according to known laws, have a direction opposed to those of the
inducing magnet, and hence would produce the phenomena of repulsion.
To carry out the assumption here made, M. Weber is obliged to suppose
that the molecules of diamagnetic bodies are surrounded by channels, in
which the induced molecular currents, once excited, continue to flow
without resistance." — Diamagnctism and Nar/nc-cryslattic Action, pp. ISO,
137.

XIV.
SHORTER ARTICLES.

SLATES.— DEATH BY LIGHTNING.— SCIENCE AND SPIRITS.—
VITALITY.— ADDITIONAL REMARKS ON MIRACLES.

SLATES.

(Part of a Lecture delivered in the Royal Institution of Great Britain,
June 6, 1856.)

WHEN the student of physical science has to investigate
the character of any natural force, his first care must be to
purify it from the mixture of other forces, and thus study
its simple action. If, for example, he wishes to know how
a mass of liquid would shape itself, if at liberty to follow
the bent of its own molecular forces, he must see that these
forces have free and undisturbed exercise. We might, per
haps, refer him to the dew-drop for a solution of the ques
tion ; but here we have to do, not only with the action of
the molecules of the liquid upon each other, but also with
the action of gravity upon the mass, which pulls the drop
downward and elongates it. If he would examine the
problem in its purity, he must do as Plateau has done, de
tach the liquid mass from the action of gravity ; he would
then find the shape to be a perfect sphere. Natural pro
cesses come to us in a mixed manner, and to the unin-
structed mind are a mass of unintelligible confusion. Sup
pose half a dozen of the best musical performers to be placed
in the same room, each playing his own instrument to per
fection, but no two playing the same tune ; though each in
dividual instrument might be a source of perfect music, still
the mixture of all would produce mere noise. Thus it is
with the processes of Nature. Here mechanical and mo
lecular laws intermingle and create apparent confusion.
Their mixture constitutes what may be called the noise of

384 FRAGMENTS OF SCIENCE.

natural laws, and it is the vocation of the man of science to
resolve this noise into its components, and thus to detect
the " music " in which the foundations of Nature are laid.

The necessity of this detachment of one force from all
other forces is nowhere more strikingly exhibited than in the
phenomena of crystallization. Here, for example, is a so
lution of common sulphate of soda or Glauber salt. Look
ing into it mentally, we see the molecules of that liquid,
like disciplined squadrons under a governing eye, arranging
themselves into battalions, gathering round distinct centres,
and forming themselves into solid masses, which after a time
assume the visible shape of the crystal now held in my hand.
I may, like an ignorant meddler wishing to hasten matters,
introduce confusion into this order. This may be done by
plunging a glass rod into the vessel ; the consequent action
is not the pure expression of the crystalline forces ; the
molecules rush together with the confusion of an unorgan
ized mob, and not with the steady accuracy of a disciplined
host. In this mass of bismuth also we have an example of
confused crystallization ; but in the crucible behind me a
slower process is going on : here there is an architect at
work " who makes no chips, no din," and who is now build
ing the particles into crystals, similar in shape and structure
to those beautiful masses which we see upon the table. By
permitting alum to crystallize in this slow way, we obtain
these perfect octahedrons ; by allowing carbonate of lime
to crystalize, Nature produces these beautiful rhomboids ;
when silica crystallizes, we have formed these hexagonal
prisms capped at the ends by pyramids ; by allowing salt
petre to crystallize we have these prismatic masses, and
when carbon crystallizes, we have the diamond. If we wish
to obtain a perfect crystal, we must allow the molecular
forces free play : if the crystallizing mass be permitted to
rest upon a surface it will be flattened, and to prevent this
a small crystal must be so suspended as to be surrounded

SLATES. 385

on all sides by the liquid, or, if it rest upon the surface, it
must be turned daily so as to present all its faces in succes
sion to the working builder.

In building up crystals these little atomic bricks often
arrange themselves into layers which are perfectly parallel
to each other, and which can be separated by mechanical
means ; this is called the cleavage of the crystal. The crys
tal of sugar I hold in my hand thus far escaped the solvent
and abrading forces which sooner or later determine the
fate of sugar-candy. I readily discover that it cleaves with
peculiar facility in one direction. Again, I lay my knife
upon this piece of rock-salt, and with a blow cleave it in
one direction. Laying the knife at right angles to its
former position, the crystal cleaves again; and finally,
placing the knife at right angles to the two former positions,
we find a third cleavage. Rock-salt cleaves in three di
rections, and the resulting solid is this perfect cube, which
may be broken up into any number of smaller cubes. Ice
land spar also cleaves in three directions, not at right angles,
but oblique to each other, the resulting solid being a rhom
boid. In each of these cases the mass cleaves with equal
facility in all three directions. For the sake of complete
ness I may say that many crystals cleave with unequal fa
cility in different directions: heavy spar presents an ex
ample of this kind of cleavage.

Turn we now to the consideration of some other phe
nomena to which the term cleavage may be applied. Beech,
deal, and other woods, cleave with facility along the fibre,
and this cleavage is most perfect when the edge of the axe
is laid across the rings which mark the growth of the tree.
If you look at this bundle of hay severed from a rick, you
will see a sort of cleavage in it also ; the stalks lie in paral
lel planes, and only a small force is required to separate
them laterally. But we cannot regard the cleavage of the
tree as the same in character as that of the hay-rick. In
17

386 FRAGMENTS OF SCIENCE.

the one case it is the molecules arranging themselves ac
cording to organic laws which produce a cleavable struct
ure, in the other case the easy separation in one direction
is due to the mechanical arrangement of the coarse sensible
masses of the stalks of hay.

This sand-stone rock was once a powder, more or less
coarse, held in mechanical suspension by water. The pow
der was composed of two distinct parts, fine grains of sand
and small plates of mica. Imagine a wide strand covered by
a tide, or an estuary with water which holds such powder in
suspension : how wTill it sink ? The rounded grains of sand
wrill reach the bottom first, because they encounter least re
sistance, the mica afterward, and when the tide recedes we
have the little plates shining like spangles upon the surface
of the sand. Each successive tide brings its charge of
mixed powder, deposits its duplex layer day after day, and
finally masses of immense thickness are piled up, which by
preserving the alternations of sand and mica tell the tale
of their formation. Take the sand and tnica, and mix them
together in water, and allow them to subside ; they will ar
range themselves in the manner indicated, and by repeating
the process you can actually build up a mass which shall be
the exact counterpart of that presented by Nature. Now this
structure cleaves with readiness along the planes in which
the particles of mica are strewn. Specimens of such a rock
sent to me from Halifax, and other masses from the quarries
of Over Darwen in Lancashire, are here before you. With
a hammer and chisel I can cleave them into flags ; indeed,
these flags are employed for roofing purposes in the districts
from which the specimens have come, and receive the name
of " slate-stone." But you will discern without a word
from me, that this cleavage is not a crystalline cleavage
any more than that of a hay-rick. It is molar, not molec
ular.

This, so far as I am aware of, has never been imagined,

SLATES. 387

and it lias been agreed among geologists not to call such
splitting as this cleavage at all, but to restrict the term to
a phenomenon of a totally different character.

Those who have visited the slate-quarries of Cumberland
and North Wales will have witnessed the phenomenon to
which I refer. We have long drawn our supply of roofing-
slates from such quarries ; school-boys ciphered on these
slates, they were used for tombstones in church-yards, and
for billiard-tables in the metropolis ; but not until a com
paratively late period did men begin to inquire how their
wonderful structure was produced. What is the agency
which enables us to split Honister Crag, or the cliffs of
Snowdon, into laminae from crown to base ? This question
is at the present moment one of the great difficulties of
geologists, and occupies their attention perhaps more than
any other. You may wonder at this. Looking into the
quarry of Penrhyn, you may be disposed to offer the ex
planation I heard given two years ago. " These planes of
cleavage," said a friend who stood beside me on the quarry's
edge, " are the planes of stratification which have been
lifted by some convulsion into an almost vertical position."
But this was a mistake, and indeed here lies the grand diffi
culty of the problem. The planes of cleavage stand in most
cases at a high angle to the bedding. Thanks to Sir Roder
ick Murchison, I am able to place the proof of this before
you. Here is a specimen of slate in which both the planes
of cleavage and of bedding are distinctly marked, one of
them making a large angle with the other. This is com
mon. The cleavage of slates, then, is not a question of
stratification ; what, then, is its cause ?

In an able and elaborate essay published in 1835, Pro
fessor Sedgwick proposed the theory that cleavage is due
to the action of crystalline or polar forces subsequent to the
consolidation of the rock. " We may affirm," he says, " that
no retreat of the parts, no contraction of dimensions in pass-

388 I'KACMKNTS OF SCIENCE.

ing to a solid state, can explain such phenomena. They
appear to me only resolvable on the supposition that crystal
line or polar forces acted upon the whole mass simultane
ously in one direction and with adequate force." And again,
in another place : " Crystalline forces have rearranged whole
mountain-masses, producing a beautiful crystalline cleavage,
passing alike through all the strata." ] The utterance of
such a man struck deep, as it ought to do, into the minds
of geologists, and at the present day there are few who do
not entertain this view either in whole or in part.3 The
boldness of the theory, indeed, has, in some cases, caused
speculation to run riot, and we have books published on the
action cf polar forces and geologic magnetism, which rather
astonish those who know something about the subject. Ac
cording to this theory, whole districts of North Wales and
Cumberland, mountains included, are neither more nor less
than the parts of a gigantic crystal. These masses of slate
were originally fine mud, composed of the broken and
abraded particles of older rocks. They contain silica, alu
mina, potash, soda, and mica, mixed mechanically together.
In the course of ages the mixture became consolidated, and
the theory before us assumes that a process of crystalliza
tion afterward rearranged the particles and developed in it
a single plane of cleavage. Though a bold, and I think in
admissible, stretch of analogies, this hypothesis has done

1 Transactions of the Geological Society, scr. ii. vol. iii. p. 477.

2 In a letter to Sir Charles Lyell, dated from the Cape of Good Hope
February 20, 1836, Sir John Herschel writes as follows : " If rocks have
been so heated as to allow of a commencement of crystallization, that is
to say, if they have been heated to a point at which the particles can be
gin to move among themselves, or at least on their own axes, some gen
eral law must then determine the position in which these particles will
rest on cooling. Probably that position will have some relation to the
direction in which the heat escapes. Now, when all or a majority of par
ticles of the same nature have a general tendency to cue position, that
must of course determine a cleavage plane."

SLATES. 389

good service. Right or wrong, a thoughtfully - uttered
theory has a dynamic pow.er which operates against intel
lectual stagnation; and even by provoking opposition is
eventually of service to the cause of truth. It would, how
ever, have been remarkable if, among the ranks of geolo
gists themselves, men were not found to seek an explana
tion of slate-cleavage involving a less hardy assumption.

The first step in an inquiry of this kind is to seek facts.
This has been done, and the labors of Daniel Sharpe (the
late President of the Geological Society, who, to the loss
of science and the sorrow of all who knew him, has so sud
denly been taken away from us), Mr. Henry Clifton Sorby,
and others, have furnished us with a body of facts associated
with slaty cleavage, and having a most important bearing
upon the question.

Fossil shells are found in these slate-rocks. I have here
several specimens of such shells in the actual rock, and oc
cupying various positions in regard to the cleavage planes.
They are squeezed, distorted, and crushed ; in all cases the
distortion leads to the inference that the rock which con
tains these shells has been subjected to enormous pressure
in a direction at right angles to the planes of cleavage.
The shells are all flattened and spread out in these planes.
Compare this fossil trilobite of normal proportions with
these others which have suffered distortion. Some have
lain across, some along, and some oblique to the cleavage of
the slate in which they are found ; but in all cases the dis
tortion is such as required for its production a compressing
force acting at right angles to the planes of cleavage. As
the trilobites lay in the mud, the jaws of a gigantic vice ap
pear to have closed upon them and squeezed them into the
shapes you see.

We sometimes find a thin layer of coarse, gritty mate
rial, between two layers of finer rock, through which and
across the gritty layer pass the planes of lamination. The

390 I'll AC MK NTS OF SCIENCE.

coarse layer is found bent by the pressure into sinuosities
like a contorted ribbon. Mr. Sorby has described a striking
case of this kind. This crumpling can be experimentally
imitated; the amount of compression might, moreover, be
roughtly estimated by supposing the contorted bed to be
stretched out, its length measured and compared with the
shorter distance into which it has been squeezed. We find
in this way that the yielding of the mass has been consider
able.

Let me now direct your attention to another proof of
pressure ; you see the varying colors which indicate the
bedding on this mass of slate. The dark portion is gritty,
being composed of comparatively coarse particles, which,
owing to their size, shape, and gravity, sink first and con
stitute the bottom of each layer. Gradually, from bottom
to top the coarseness diminishes, and near the upper sur
face we have a layer of exceedingly fine mud. It is the
mud thus consolidated from which are derived the German
razor-stones, so much prized for the sharpening of surgical
instruments. When a bed is thin, the fine white mud is
permitted to rest upon a slab of the coarser slate in contact
with it : when the bed is thick it is cut into slices, which
are cemented to pieces of ordinary slate, and thus rendered
stronger. The mud thus deposited is, as might be ex
pected, often rolled up into nodular masses, carried for
ward, and deposited among coarser material by the rivers
from which the slate-mud has subsided. Here are such
nodules enclosed in sandstone. Everybody, moreover, who
has ciphered upon a school-slate must remember the whitish-
green spots which sometimes dotted the surface of the
slate, and over which the pencil usually slid as if the spots
were greasy. Now these spots are composed of the finer
mud, and they could not, on account of their fineness, bite
the pencil like the surrounding gritty portions of the slate.
Here is a beautiful example of these spots : you observe

SLATES. 391

them 011 the cleavage surface in broad round patches. But
turn the slate edgeways and the section of each nodule is
seen to be a sharp oval, with its longer axis parallel to the
cleavage. This instructive fact has been adduced by Mr.
Sorby. I have made excursions to the quarries of Wales
and Cumberland, and to many of the slate-yards of London,
and found the fact general. Thus we elevate a common
experience of our boyhood into evidence of the highest
significance as regards a most important geological problem.
From the magnetic deportment of these slates, I was led to
infer that these spots contain a less amount of iron than the
surrounding dark slate. An analysis was made for me by
Mr. Hambly in the laboratory of Dr. Percy at the School of
Mines, with the following result :

ANALYSIS OF SLATE.
Dark Slate, two Analyses.

1. Percentage of iron 5.85

2. " " 6.13

Mean 5.99

Whitish-green Slate,

1. Percentage of iron 3.24

2. " " 3.12

Mean 3.18

According to these analyses, the quantity of iron in the
dark slate immediately adjacent to the greenish spot is
nearly double the quantity contained in the spot itself.
This is about the proportion which the magnetic experi
ments suggested.

Let me now remind you that the facts brought before
you are typical — each is the representative of a class. We
have seen shells crushed ; the unhappy trilobites squeezed,
beds contorted, nodules of greenish marl flattened ; and all
these sources of independent testimony point to one and
the same conclusion, namely, that slate-rocks have been

C92 FRAGMENTS OF SCIENCE.

subjected to enormous pressure in a direction at right angles
to the planes of cleavage.

In reference to Mr. Sorby's contorted bed, I have said
that by supposing it to be stretched out and its length
measured, it would give us an idea of the amount of yield
ing of the mass above and below the bed. Such a measure
ment, however, would not give the exact amount of yielding.
I hold in my hand a specimen of slate with its bedding
marked upon it ; the lower portions of each layer being
composed of a comparatively coarse gritty material some
thing like what you may suppose the contorted bed to be
composed of. Now, in crossing these gritty portions^ the
cleavage turns, as if tending to cross the bedding at an
other angle. When the pressure began to act, the inter
mediate bed, which is not entirely unyielding, suffered
longitudinal pressure ; as it bent, the pressure became grad
ually more lateral, and the direction of its cleavage is ex
actly such as you would infer from an action of this kind — it
is neither quite across the bed nor yet in the same direction
as the cleavage of the slate above and below it, but inter
mediate between both. Supposing the cleavage to be at
right angles to the pressure, this is the direction which it
ought to take across these more unyielding strata.

Thus we have established the concurrence of the phe
nomena of cleavage and pressure — that they accompany
each other ; but the question still remains, Is the pressure
sufficient to account for the cleavage ? A single geologist,
as far as I am aware, answers boldly in the affirmative.
This geologist is Sorby, who has attacked the question in
the true spirit of a physical investigator. Call to mind the
cleavage of the flags of Halifax and Over Darwen, which is
caused by the interposition of layers of mica between the
gritty strata. Mr. Sorby finds plates of mica to be also a
constituent of slate-rock. He asks himself, what will be
the effect of pressure upon a mass containing such plates

SLATES. 393

confusedly mixed up in it ? It will be, he argues, and he
argues rightly, to place the plates with their flat surfaces
more or less perpendicular to the direction in which the
pressure is exerted. He takes scales of the oxide of iron,
mixes them with a fine powder, and on squeezing the mass
finds that the tendency of the scales is to set themselves at
right angles to the line of pressure. Along the planes of
weakness produced by the scales the mass cleaves.

By tests of a different character from those applied by
Mr. Sorby, it might be shown how true his conclusion is,
that the effect of pressure on elongated particles or plates
will be such as he describes it. But while the scales must
be regarded as a true cause, I should not ascribe to them a
large share in the production of the cleavage. I believe
that, even if the plates of mica were wholly absent, the
cleavage of slate-rocks would be much the same as it is at
present.

Here is a mass of pure white wax : it contains no mica
particles, no scales of iron, nor any thing analogous to them.
Here is the self-same substance submitted to pressure. I
would invite the attention of the eminent geologists now
before me to the structure of this wax. No slate ever ex
hibited so clean a cleavage ; it splits into laminas of sur
passing tenuity, and proves at a single stroke that pressure
is sufficient to produce cleavage, and that this cleavage is
independent of intermixed plates or scales. I have pur
posely mixed this wax with elongated particles, and am
unable to say at the present moment that the cleavage is
sensibly affected by their" presence — if any thing, I should
say they rather impair its fineness and clearness than pro
mote it.

The finer the slate is the more perfect will be the re
semblance of its cleavage to that of the wax. Compare
the surface of the wax with the surface of this slate from
Borrodale in Cumberland. You have precisely the same

394 FRAGMENTS OF SCIENCE.

features in both : you see flakes clinging to the surfaces of
each, which have been partially torn away in cleaving.
Let any close observer compare these two effects, he will,
I am persuaded, be led to the conclusion that they are the
product of a common cause.1

But you will ask me how, according to my view, does
pressure produce this remarkable result. This may be
stated in a very few words :

There is no such thing in Nature as a body of perfectly
homogeneous structure. I break1 this clay which seems so
uniform, and find that the fracture presents to my eyes in
numerable surfaces along which it has given way, and it
has yielded along those surfaces because in them the cohe
sion of the mass is less than elsewhere. I break this mar
ble, and even this wax, and observe the same result ; look
at the mud at the bottom of a dried pond ; look to some of
the ungravelled walks in Kensington Gardens on drying af
ter rain — they are cracked and split, and, other circumstances
being equal, they crack and split where the cohesion is least.
Take then a mass of partially consolidated mud. Such a
mass is divided and subdivided by interior surfaces along
which the cohesion is comparatively small. Penetrate the
mass in idea, and you will see it composed of numberless
irregular polyhcdra bounded by surfaces of weak cohesion.
Imagine such a mass subjected to pressure — it yields and
spreads out in the direction of least resistance ; a the little

1 I have usually softened the wax by warming it, kneaded it with the
fingers, and pressed it between thick plates of glass previously wetted.
At the ordinary summer temperature the pressed wax is soft, and tears
rather than rlcaves ; on this account, I cool my compressed specimens in
a mixture of pounded ice and salt, and when thus cooled they split beau
tifully.

2 It is scarcely necessary to say that, if the mass were squeezed equal
ly in all directions, no laminated structure could be produced ; it must
have room to yield in a lateral direction. Mr. Warren De la Rue informs
me that he once wished to obtain white-lead in a fine granular state, and

SLATES. 395

polyhedra become converted into lamina?, separated from
each other by surfaces of weak cohesion, and the infallible
result will be a tendency to cleave at right angles to the
line of pressure.

Further, a mass of dried mud is full of cavities and fis
sures. If you break dried pipe-clay you see them in great
numbers, and there are multitudes of them so small that you
cannot see them. A flattening of these cavities must take
place in squeezed mud, and this must to some extent facili
tate the cleavage of the mass in the direction indicated.

Although the time at my disposal has not permitted me
duly to develop these thoughts, yet for the last twelve
months the subject has presented itself to me almost daily
under one aspect or another. I have never eaten a biscuit
during this period without remarking the cleavage devel
oped by the rolling-pin. You have only to break a biscuit
across, and to look at the fracture, to see the laminated
structure. We have here the means of pushing the anal
ogy further. I invite you to compare the structure of this
slate, which was subjected to a high temperature during
the conflagration of Mr. Scott Russell's premises, with that
of a biscuit. Air or vapor within the slate has caused it
to swell, and the mechanical structure it reveals is precisely
that of a biscuit. During these inquiries I have received
much instruction in the manufacture of puff-paste. Here
is some such paste baked under my own superintendence.
The cleavage of our hills is accidental cleavage, but this is
cleavage with intention. The volition of the pastry-cook
has entered into its formation. It has been his aim to pre
serve a series of surfaces of structural weakness, along
which the dough divides into layers. Puff-paste in prepa-

to accomplish this he first compressed it. The mould was conical, and
permitted the lead to spread out a little laterally. The lamination was
as perfect as that of slate, and it quite defeated him in his effort to ob
tain a granular powder.

39G FRAGMENTS OF SCIENCE.

ration must not be handled too much ; it ought, moreover,
to be rolled on a cold slab, to prevent the butter from melt
ing, and diffusing itself, thus rendering the paste more ho
mogeneous and less liable to split. Puff-paste is, then,
simply an exaggerated case of slaty cleavage.

The principle which I have enunciated is so simple as
to be almost trivial ; nevertheless, it embraces not only the
cases mentioned, but, if time permitted, it might be shown
you that the principle has a much wider range of applica
tion. When iron is taken from the puddling-furnace it is
more or less spongy, an aggregate in fact of small nod
ules : it is at a welding heat, and at this temperature is
submitted to the process of rolling. Bright, smooth bars
are the result. But, notwithstanding the high heat, the
nodules do not perfectly blend together. The process of
rolling draws them into fibres. Here is a mass acted upon
by dilute sulphuric acid, which exhibits in a striking man
ner this fibrous structure. The experiment was made by
my friend Dr. Percy, without any reference to the question
of cleavage.

Break a piece of ordinary iron, and you have a granular
fracture ; beat the iron, you elongate these granules, and
finally render the mass fibrous. Here are pieces of rails
along which the wheels of locomotives have slidden ; the
granules have yielded and become plates. They exfoliate
or come off in leaves ; all these effects belong, I believe,
to the great class of phenomena of which slaty cleavage
forms the most prominent example.1

[I would now lay more stress on the lateral yielding,
referred to in the note at the bottom of page 394, accompa
nied as it is by tangential sliding, than I was prepared to
do when this lecture wras given. This sliding is, I think,
the principal cause of the planes of weakness both in
pressed wax and slate-rock. J. T. 1871.]

1 For some further observations on this subject by Mr. Sorby and
myself, see Philosophical Magazine for August, 1856.

DEATH BY LIGHTNING.

PEOPLE in general imagine, when they think at all about
the matter, that an impression upon the nerves — a blow,
for example, or the prick of a pin — is felt at the moment it
is inflicted. But this is not the case. The seat of sensa
tion is the brain, and to it the intelligence of any impression
made upon the nerves has to be transmitted before this
impression can become manifest in consciousness. The
transmission, moreover, requires time, and the consequence
is, that a wound inflicted on a portion of the body distant
from the brain is more tardily appreciated than one inflicted
adjacent to the brain. By an extremely ingenious experi
mental arrangement, Helmholtz has determined the velocity
of this nervous transmission, and finds it to be about one
hundred feet a second, or less than one-tenth of the velocity
of sound in air. If, therefore, a whale fifty feet long were
wounded in the tail, it would not be conscious of the injury
till half a second after the wound had been inflicted.1 But
this is not the only ingredient in the delay. There can
scarcely be a doubt that to every act of consciousness be
longs a determinate molecular arrangement of the brain —
that every thought or feeling has its physical correlative in
that organ ; and nothing can be more certain than that
every physical change, whether molecular or mechanical,
requires time for its accomplishment. So that, besides the

1 A most admirable lecture on the velocity of nervous transmission
has been published by Dr. Du Bois-Raymond in the Proceedings of the
Royal Institution for 1866, vol. iv. p. 575.

398 FRAGMENTS OF SCIENCE.

interval of transmission, a still further time is necessary for
the brain to put itself in order — for its molecules to take
up the motions or positions necessary to the completion of
consciousness. Helmholtz considers that one-tenth of a
second is demanded for this purpose. Thus, in the case of
the whale above supposed, we have first half a second con
sumed in the transmission of the intelligence through the
sensor nerves to the head, one-tenth of a second consumed
by the brain in completing the arrangements necessary to
consciousness, and, if the velocity of transmission through
the motor be the same as that through the sensor nerves,
half a second in sending a command to the tail to defend
itself. Thus one second and a tenth would elapse before
an impression made upon its caudal nerves could be re
sponded to by a whale fifty feet long.

Now, it is quite conceivable that an injury might be
inflicted which would render the nerves unfit to be the con
ductors of the motion which results in sensation ; and if
such a thing occurred, no matter how severe the injury
might be, we should not be conscious of it. Or it may
be that, long before the time required by the brain to
complete the arrangement necessary to consciousness, its
power of arrangement might be wholly suspended. In
such a case also, though the injury might be of a nature
to cause death, this would occur without feeling of any
kind. Death in this case would be simply the sudden
negation of life, without any intervention of consciousness
whatever.

Doubtless there are many kinds of death of this char
acter. The passage of a musket-bullet through the brain
is a case in point ; and the placid aspect of a man thus killed
is in perfect accordance with the conclusion which might be
drawn a priori from the experiments of Helmholtz. Cases
of insensibility, moreover, are not uncommon which do not
result in death, and after which the persons affected have

DEATH BY LIGHTNING. 399

been able to testify that no pain was felt prior to the loss
of consciousness.

The time required for a rifle-bullet to pass clean through
a man's head may be roughly estimated at a thousandth of
a second. Here, therefore, we should have no room for
sensation, and death would be painless. But there are
other actions which far transcend in rapidity that of the
rifle-bullet. A flash of lightning cleaves a cloud, appearing
and disappearing in less than a hundred-thousandth of a
second, and the velocity of electricity is such as would carry
it in a single second over a distance almost equal to that
which separates the earth and moon. It is well known
that a luminous impression once made upon the retina en
dures for about one-sixth of a second, and that this is the
reason why we see a ribbon of light when a glowing coal
is caused to pass rapidly through the air. A body illumi
nated by an instantaneous flash continues to be seen for the
sixth of a second after the flash has become extinct ; and
if the body thus illuminated be in motion, it appears at
rest at the place where the flash falls upon it. The color-
top is familiar to most of us. By this instrument a disk
with differently-colored sectors is caused to rotate rapidly ;
the colors blend together, and, if they are chosen in the
proper proportions, when the motion is sufficiently rapid
the disk appears white. Such a top, rotating in a dark room
and illuminated by an electric spark, appears motionless,
each distinct color being clearly seen. Professor Dove has
found that a flash of lightning produces the same effect.
During a thunder-storm he put a color-top in exceedingly
rapid motion, and found that every flash revealed the top
as a motionless object with its colors distinct. If illuminated
solely by a flash of lightning, the motion of all bodies on
the earth's surface would, as Dove has remarked, appear
suspended. A cannon-ball, for example, would have its
flight apparently arrested, and would seem to hang motion-

400 FRAGMENTS OF SCIENCE.

less in space as long as the luminous impression which re
vealed the ball remained upon the eye.

If, then, a rifle-bullet move with sufficient rapidity to
destroy life without the interposition of sensation, much
more is a flash of lightning competent to produce this effect.
Accordingly, we have well -authenticated cases of people
being struck senseless by lightning who, on recovery, had
no memory of pain. The following circumstantial case is
described by Hemmer :

On June 30, 1788, a soldier in the neighborhood of
Mannheim, being overtaken by rain, placed himself under
a tree, beneath which a woman had previously taken
shelter. He looked upward to see whether the branches
were thick enough to afford the required protection, and,
in doing so, was struck by lightning, and fell senseless to
the earth. The woman at his side experienced the shock
in her foot, but was not struck down. Some hours after
ward the man revived, but remembered nothing about
what had occurred, save the fact of his looking up at the
branches. This was his last act of consciousness, and he
passed from the conscious to the unconscious condition
without pain. The visible marks of a lightning-stroke
are usually insignificant : the hair is sometimes burnt ;
slight wounds are observed; while, in some instances,
a red streak marks the track of the discharge over the
skin.

Under ordinary circumstances, the discharge from a
small Leyden-jar is exceedingly unpleasant to myself.
Some time ago I happened to stand in the presence of a
numerous audience, with a battery of fifteen large Leyden-
jars charged beside me. Through some awkwardness on
my part, I touched a wire leading from the battery, and
the discharge went through my body. Life was absolutely
blotted out for a very sensible interval, without a trace of
pain. In a second or so consciousness returned ; I saw my-

DEATH BY LIGHTNING. 401

self in the presence of the audience and apparatus, and, by
the help of these external appearances, immediately con
cluded that I had received the battery discharge. The in
tellectual consciousness of my position was restored with
exceeding rapidity, but not so the optical consciousness.
To prevent the audience from being alarmed, I observed
that it had often been my desire to receive accidentally
such a shock, and that my wish had at length been fulfilled.
But while making this remark, the appearance which my
body presented to myself was that of a number of separate
pieces. The arms, for example, were detached from the
trunk, and seemed suspended in the air. In fact, memory
and the power of reasoning appeared to be complete long
before the optic nerve was restored to healthy action. But
what I wish chiefly to dwell upon here is, the absolute pain-
lessness of the shock ; and there cannot be a doubt that, to
a person struck dead by lightning, the passage from life to
death occurs without consciousness being in the least de
gree implicated. It is an abrupt stoppage of sensation,
unaccompanied by a pang.
July 8, 1865.

SCIENCE AND SPIRITS.

THEIR refusal to investigate " spiritual phenomena " is
often urged as a reproach to scientific men. I here propose
to give a sketch of an attempt to apply to the " phenom
ena " those methods of inquiry which are found available
iu dealing with natural truth.

Some time ago, when the spirits were particularly
active in this country, a celebrated philosopher was invited,
or rather entreated, by one of his friends to meet and ques
tion them. He had, however, already made their acquaint
ance, and did not wish to renew it. I had not been so
privileged, and he therefore kindly arranged a transfer of
the invitation to me. The spirits themselves named the
time of meeting, and I was conducted to the place at the
day and hour appointed.

Absolute unbelief in the facts was by no means my con
dition of mind. On the contrary, I thought it probable
that some physical principle, not evident to the spiritualists
themselves, might underlie their manifestations. Extraor
dinary effects are produced by the accumulation of small
impulses. Galileo set a heavy pendulum in motion by the
well-timed puffs of his breath. Ellicot set one clock going
by the ticks of another, even when the two clocks were
separated by a wall. Preconceived notions can, moreover,
vitiate, to an extraordinary degree, the testimony of even
veracious persons. Hence my desire to witness those ex
traordinary phenomena, the existence of which seemed
placed beyond a doubt by the known veracity of those who
li;i;l Avitnessed and described them. The meeting took

SCIENCE AND SPIRITS. 403

place at a private residence in the neighborhood of Lon
don. My host, his intelligent wife, and a gentleman who
may be called X., were in the house when I arrived. 1
was informed that the " medium " had not yet made her
appearance ; that she was sensitive, and might resent sus
picion. It was therefore requested that the tables and
chairs should be examined before her arrival, in order to be
assured that there was no trickery in the furniture. This
was done ; and I then first learned that my hospitable host
had arranged that the seance should be a dinner-party.
This was to me an unusual form of investigation ; but I
accepted it, as one of the accidents of the occasion.

The " medium " arrived — a delicate-looking young lady,
who appeared to have suffered much from ill health. I
took her to dinner and sat close beside her. Facts were
absent for a considerable time, a series of very wonderful
narratives supplying their place. The duty of belief on
testimony was frequently insisted on. X. appeared to be
a chosen spiritual agent, and told us many surprising
things. He affirmed that, when he took a pen in his hand,
an influence ran from his shoulder downward, and impelled
him to write oracular sentences. I listened for a time,
offering no observation. "And now," continued X., " this
power has so risen as to reveal to me the thoughts of others.
Only this morning I told a friend what he was thinking of,
and what he intended to do during the day." Here, I
thought, is something that can be at once tested. I said
immediately to X. : " If you wish 'to win to your cause an
apostle, who will proclaim your principles to the world
without fear, tell me what I am now thinking of." X.
reddened, and did not tell me my thought.

Some time previously I had visited Baron Reichenbach,
in Vienna, and I now asked the young lady who sat beside
me, whether she could see any of the curious things which
he describes — the light emitted by crystals, for example ?

404 FRAGMENTS OF SCIENCE.

Here is the conversation which followed, as extracted from
my notes, written on the day following the seance:

Medium. — " Oh, yes ; but I see light around all
bodies."

I. — " Even in perfect darkness ? "

Medium. — " Yes ; I see luminous atmospheres round all
people. The atmosphere which surrounds Mr. R. C. would
fill this room with light."

I. — " You are aware of the effects ascribed by Baron
Reichenbach to magnets ? "

Medium. — " Yes ; but a magnet makes me terribly ill."

I. — " Am I to understand that, if this room were per
fectly dark, you could tell whether it contained a magnet,
without being informed of the fact ? "

Medium. — " I should know of its presence on entering
the room."

Z— "How?"

Medium. — " I should be rendered instantly ill."

I. — " How do you feel to-day ? "

Medium. — " Particularly well ; I have not been so well
for months."

I. — " Then, may I ask you whether there is, at the
present moment, a magnet in my possession ? "

The young lady looked at me, blushed, and stammered,
" No ; I am not en rapport with you."

I sat at her right hand, and a left-hand pocket, within
six inches of her person, contained a magnet.

Our host here deprecated discussion, as it " exhausted
the medium." The wonderful narratives were resumed ;
but I had narratives of my own quite as wonderful. These
spirits indeed, seemed clumsy creations, compared with
those with which my own researches had made me familiar.
I therefore began to match the wonders related to me by
other wonders. A lady present discoursed on spiritual
atmospheres, which she could see as beautiful colors when

SCIENCE AND SPIRITS. 405

she closed her eyes. I professed myself able to see similar
colors, and more than that, to be able to see the interior of
my own eyes. The medium affirmed that she could see
actual waves of light coming from the sun. I retorted that
men of science could tell the exact number of waves
emitted in a second, and also their exact length. The
medium spoke of the performances of the spirits on musical
instruments. I said that such performance was gross, in
comparison with a kind of music which had been discovered
some time previously by a scientific man. Standing at a
distance of twenty feet from a jet of gas, he could command
the flame to emit a melodious note ; it would obey, and
continue its song for hours. So loud was the music emitted
by the gas-flame, that it might be 'heard by an assembly of
a thousand people. These were acknowledged to be as
great marvels as any of those of spiritdom. The spirits
were then consulted, and I was pronounced to be a first-
class medium.

During this conversation a low knocking was heard
from time to time under the table. These were the spirits'
knocks. I was informed that one knock, in answer to a
question, meant " No ; " that two knocks meant " Not
yet ; " and that three knocks meant " Yes." In answer to
the question whether I was a medium, the response was
three brisk and vigorous knocks. I noticed that the knocks
issued from a particular locality, and therefore requested
the spirits to be good enough to answer from another
corner of the table. They did not comply ; but I was
assured that they would do it, and much more, by-and-by.
The knocks continuing, I turned a wine-glass upside down,
and placed my ear upon it, as upon a stethoscope. The
spirits seemed disconcerted by the act ; they lost their
playfulness, and did not quite recover it for a considerable
time.

Somewhat weary of the proceedings, I once threw my-

406 FRAGMENTS OF SCIENCE.

self back against my chair, and gazed listlessly out of the
window. While thus engaged, the table was rudely pushed.
Attention was drawn to the wine, still oscillating in the
glasses, and I was asked whether that was not convincing.
I readily granted the fact of motion, and began to feel the
delicacy of my position. There were several pairs of arms
upon the table, and several pairs of legs under it ; but how
was I, without offence, to express the conviction which I
really entertained? To ward off the difficulty, I again
turned a wine-glass upside down and rested my ear upon it.
The rim of the glass was not level, and the hair on touch
ing it caused it to vibrate and produce a peculiar buzzing
sound. A perfectly candid and warm-hearted old gentle
man at the opposite side of the table, whom I may call A.,
drew attention to the sound, and expressed his entire belief
that it was spiritual. I, however, informed him that it was
the moving hair acting on the glass. The explanation was
not well received, and X., in a tone of severe pleasantry,
demanded whether it was the hair that had moved the
table. The promptness of my negative probably satisfied
him that my notion was a very different one.

The superhuman power of the spirits was next dwelt
upon. The strength of man, it was stated, was unavailing
in opposition to theirs. No human power could prevent
the table from moving when they pulled it. During the
evening this pulling of the table occurred, or rather was
attempted, three times. Twice the table moved when my
attention was withdrawn from it ; on a third occasion, I
tried whether the act could be provoked by an assumed air
of inattention. Grasping the table firmly between my
knees, I threw myself back in the chair, and waited, with
eyes fixed on vacancy, for the pull. It came. For some
seconds it was pull spirit, hold muscle ; the muscle, how
ever, prevailed, and the table remained at rest. Up to the
present moment, this interesting fact is known only to the
partirular spirit in (|iirstion and myself.

SCIENCE AND SPIRITS. 407

A species of mental scene-painting, with which my own
pursuits had long rendered me familiar, was employed to
figure the changes arid distribution of spiritual power.
The spirits were provided with atmospheres, which com
bined with and interpenetrated each other, considerable
ingenuity being shown in demonstrating the necessity of
time in effecting the adjustment of the atmospheres. In
fact, just as in science, the senses, time, and space, con
stituted the conditions of the phenomena. A rearrange
ment of our positions was proposed and carried out ; and
soon afterward my attention was drawn to a scarcely
sensible vibration on the part of the table. Several persons
were leaning on the table at the time, and I asked permis
sion to touch the medium's hand. " Oh, I know I tremble,"
was her reply. Throwing one leg across the other, I ac
cidentally nipped a muscle, and produced thereby an in
voluntary vibration of the free leg. This vibration, I knew,
must be communicated to the floor, and thence to the
chairs of all present. I therefore intentionally promoted it.
My attention was promptly drawn to the motion ; and a
gentleman beside me, whose value as a witness I was par
ticularly desirous to test, expressed his belief, that it was
out of the- compass of human power to produce so strange
a tremor. " I believe," he added earnestly, " that it is
entirely the spirits' work." " So do I," added, with heat,
the candid and warm-hearted old gentleman A. " Why,
sir," he continued, " I feel them at this moment shaking
my chair." I stopped the motion of the leg. " Now, sir,"
A. exclaimed, " They are gone." I began again, and A.
once more ejaculated. I could, however, notice that there
were doubters present, who did not quite know what to
think of the manifestations. I saw their perplexity ; and,
as there was sufficient reason to believe that the disclosure
of the secret would simply provoke anger, I kept it to
myself,

408 FRAGMENTS OF SCIENCE.

Again a period of conversation intervened, during which
the spirits became animated. The evening was confessedly
a dull one, but matters appeared to brighten toward its
close. The spirits were requested to spell the name by
which I am known in the heavenly world. Our host com
menced repeating the alphabet, and when he reached the
letter " P " a knock was heard. He began again, and the
spirits knocked at the letter " O." I was puzzled, but
waited for the end. The next letter knocked down was
" E." I laughed, and remarked that the spirits were going
to make a poet of me. Admonished for my levity, I was
informed that the frame of mind proper for the occasion
ought to have been superinduced by a perusal of the Bible
immediately before the seance. The spelling, however,
went on, and sure enough I came out a poet. But matters
did not end here. Our host continued his repetition of the
alphabet, and the next letter of the name proved to be
" O." Here was manifestly an unfinished word ; and the
spirits were apparently in their most communicative mood.
The knocks came from under the table, but no person pres
ent evinced the slightest desire to look under it. I asked
whether I might go underneath ; the permission was
granted ; so I crept under the table. Some tittered ; but
the candid old A. exclaimed, " He has a right to look into
the very dregs of it, to convince himself." Having pretty
well assured myself that no sound could be produced under
the table without its origin being revealed, I requested our
host to continue his questions. He did so, but in vain. He
adopted a tone of tender entreaty ; but the " dear spirits "
had become dumb dogs, and refused to be entreated. I
continued under that table for at least a quarter of an hour,
after which, with a feeling of despair as regards the pros
pects of humanity never before experienced, I regained my
chair. Once there, the spirits resumed their loquacity, and
dubbed me " Poet of Science."

SCIENCE AND SPIRITS. 409

This, then, is the result of an attempt made by a scien
tific man to look into these spiritual phenomena. It is not
encouraging ; and for this reason : The present promoters
of spiritual phenomena divide themselves into two classes,
one of which needs no demonstration, while the other is
beyond the reach of proof. The victims like to believe, and
they do not like to be undeceived. Science is perfectly
powerless in the presence of this frame of mind. It is,
moreover, a state perfectly compatible with extreme intel
lectual subtlety and a capacity for devising hypotheses
which only require the hardihood engendered by strong
conviction, or by callous mendacity, to render them impreg
nable. The logical feebleness of science is not sufficiently
borne in mind. It keeps down the weed of superstition,
not by logic but by slowly rendering the mental soil unfit
for its cultivation. When science appeals to uniform ex
perience, the spiritualist will retort, " How do you know
that a uniform experience will continue uniform ? You tell
me that the sun has risen for six thousand years : that is
no proof that it will rise to-morrow ; within the next twelve
hours it may be puffed out by the Almighty." Taking this
ground, a man may maintain the story of " Jack and the
Bean-stalk " in the face of all the science in the world.
You urge, in vain, that science has given us all the knowl
edge of the universe which we now possess, while spiritual
ism has added nothing to that knowledge. The drugged
soul is beyond the reach of reason. It is in vain that im
postors are exposed, and the special demon cast out. He
has but slightly to change his shape, return to his house,
and find it " empty, swept, and garnished." •

December 10, 1864.

18

VITALITY.

THE origin, growth, and energies of living things are
subjects which have always engaged the attention of think
ing men. To account for them it was usual to assume a
special agent, to a great extent free from the limitations
observed among the powers of inorganic Nature. This
agent was called the vital force / and, under its influence,
plants and animals were supposed to collect their materials
and to assume determinate forms. Within the last twenty
years, however, our ideas of vital processes have undergone
profound modifications ; and the interest, and even dis
quietude, which the change has excited in some minds arc
amply evidenced by the discussions and protests which are
now common regarding the phenomena of vitality. In
tracing out these phenomena through all their modifications
the most advanced philosophers of the present day declare
that they ultimately arrive at a single source of power,
from which all vital energy is derived ; and the disquieting
circumstance is that this source is not the direct fiat of a
supernatural agent, but a reservoir of what, if we do not
accept the creed of Zoroaster, must be regarded as inor
ganic force. In short, it is considered as proved that all
the energy which we derive from plants and animals is
drawn from the sun.

A few years ago, when the sun was affirmed to be the
source of life, nine out of ten of those who are alarmed by
the form which this assertion has latterly assumed, would
have assented, in a general way, to its correctness,. Their
assent, however, was more poetical than scientific, and they

VITALITY. 4H

were by no means prepared to see a rigid mechanical sig
nification attached to their words. This, however, is the
peculiarity of modern conclusions : that there is no creative p .,
energy whatever in the vegetable or animal organism, but
that all the power which we obtain from the muscles of
men and animals, as much as that which we develop by
the combustion of wood or coal, has been produced at the
sun's expense. The sun is so much colder that we may
have our fires ; he is also so much colder that we may have
our horse-racing and Alpine climbing. It is, for example,
certain that the sun has been chilled to an extent capable
of being accurately expressed in numbers, in order to fur
nish the power which lifted this year a certain number of
tourists from the vale of Chamouni to the summit of Mont
Blanc.

To most minds, however, the energy of light and heat
presents itself as a thing totally distinct from ordinary me
chanical energy. But either of them can be derived from
the other. By the friction of wood a savage can raise it
to the temperature of ignition ; by properly striking a piece
of iron a skilful blacksmith can cause it to glow, and thus,
by the rude agency of his hammer, he generates light and
heat. This action, if carried far enough, would produce the
light and heat of the sun. In fact the sun's light and heat
have actually been referred to the fall of meteoric matter
upon his surface ; and whether the sun is thus supported or
not, it is perfectly certain that he might be thus supported.
Whether, moreover, the whilom molten condition of our
planet was, as supposed by eminent men, due to the collision
of cosmic masses or not, it is perfectly certain that the mol
ten condition might be thus brought about. [If, then, solar
light and heat can be produced by the impact of dead mat
ter, and if from the light and heat thus produced we can
derive the energies which we have been accustomed to call
vital, it indubitably follows that vital energy may have a \
proximately mechanical origin.

412 FRAGMENTS OF SCIENCE.

In what sense, then, is the sun to be regarded as the
origin of the energy derivable from plants and animals ?
Let us try to give an intelligible answer to this question.
AVater may be raised from the sea-level to a high elevation,
and then permitted to descend. In descending it may be
made to assume various forms — to fall in cascades, to spurt
in fountains, to boil in eddies, or to flow tranquilly along a
uniform bed. It may, moreover, be caused to set complex
machinery in motion, to turn mill-stones, throw shuttles,
work saws and hammers, and drive piles. But every form
of power here indicated would be derived from the original
power expended in raising the water to the height from
\\liirh it fell. There is no energy generated by the ma
chinery ; the work performed by the water in descending
is merely the parcelling out and distribution of the work
expended in raising it. In precisely this sense is all the
energy of plants and animals the parcelling out and distri
bution of a power originally exerted by the sun. In the
case of the water, the source of the power consists in the
forcible separation of a quantity of the liquid from a low
level of the earth's surface and its elevation to a higher
position, the power thus expended being returned by the
water in its descent. In the case of vital phenomena, the
source of power consists in the forcible separation of the
atoms of compound substances by the sun. We name the
force which draws the water earthward " gravity," and that
which draws atoms together " chemical affinity ; " but these
different names must not mislead us regarding the qualita
tive identity of the two forces. They are both attract:
and, to the intellect, the falling of carbon atoms against
oxygen atoms is not more difficult of conception than the
fulling of water to the earth.

The building up of the vegetable, thcii) is effected by
the sun through the reduction of chemical compounds. TJte
phenomena of animal life are more or less coii'j'l»'<tt<.<l

VITALITY. 413

reversals of these processes of reduction. We eat the vege
table, and we breathe the oxygen of the air, and in our
bodies the oxygen which had been lifted from the carbon
and hydrogen by the action of the sun again falls toward
them, producing animal heat and developing animal forms.
Through the most complicated phenomena of vitality this
law runs : the vegetable is produced while a weight rises,
the animal is produced while a weight falls. But the ques
tion is not exhausted here. The water employed in our
first illustration generates all the motion displayed in its
descent, but the form of the motion depends on the charac
ter of the machinery interposed in the path of the water.
In a similar way the primary action of the sun's rays is
qualified by the atoms and molecules among which their
energy is distributed. Molecular forces determine the form
which the solar energy will assume. In the separation of
the carbon and oxygen this energy may be so conditioned
as to result in one case in the formation of a cabbage, and
in another case in the formation of an oak. So also as
regards the reunion of the carbon and the oxygen, the mo
lecular machinery through which the combining energy
acts may, in one case, weave the texture of a frog, while
in another it may weave the texture of a man.

The matter of the animal body is that of inorganic Na
ture. There is no substance in the animal tissues which is
not primarily derived from the rocks, the water, and the
air. Are the forces of organic matter, then, different in
kind from those of inorganic matter ? The philosophy of
the present day negatives the question. It is the com
pounding in the organic world of forces belonging equally
to the inorganic that constitutes the mystery and the mir
acle of vitality. Every portion of every animal body may
be reduced to purely inorganic matter. A perfect reversal
of this process of reduction would carry us from the inor
ganic to the organic ; and such a reversal is at least con-

414 . FRAGMENTS OF SCIEN* K.

ceivable. The tendency, indeed, of modern science is to
break down the wall of partition between organic and inor
ganic, and to reduce both to the operation of forces which
are the same in kind, but whose combinations differ in com
plexity.

Consider now the question of personal identity, in rela
tion to this of molecular form. Twenty-six years ago,
Mayer, of Heilbronn, with that power of genius which
breathes large meanings into scanty facts, pointed out that
the blood was " the oil of life," the combustion of which,
like that of coal in grosser cases, sustained muscular action.
The muscles are the machinery by which the dynamic power
of the blood is brought into play. Thus the blood is con
sumed. But the whole body, though more slowly than the
blood, wastes also, so that after a certain number of years
it is entirely renewed. How is the sense of personal iden
tity maintained across this flight of molecules ? To man as
we know him, matter is necessary to consciousness, but the
matter of any period may be all changed, while conscious
ness exhibits no solution of continuity. Like changing
sentinels, the oxygen, hydrogen, and carbon that depart
seem to whisper their secret to their comrades that arrive,
and thus, while the Non-ego shifts the Ego remains intact.
Constancy of form in the grouping of the molecules, and
not constancy of the molecules themselves, is the correlative
of this constancy of perception. Life is a wave which in
no two consecutive moments of its existence is composed
of the same particles.

Supposing, then, the melocules of the human body
instead of replacing others, and thus renewing a preexist
ing form, to be gathered first hand from Nature and put
together in the same relative positions as those which they
occupy in the body ; that they have the self- same forces and
distribution of forces, the self-same motions and distribution
of motions — would this organized concourse of molecules

VITALITY, 415

stand before us as a sentient thinking being ? There seems
no valid reason to believe that it would not. Or, supposing
a planet carved from the sun, and set spinning round an
axis, and revolving round the sun at a distance from him
equal to that of our earth, would one of the consequences
of its refrigeration be the development of organic forms ?
I lean to the affirmative. Structural forces are certainly
in the mass, whether or not those forces reach to the extent
of forming a plant or an animal. In an amorphous drop of
water lie latent all the marvels of crystalline force ; and
who will set limits to the possible play of molecules in a
cooling planet ? If these statements startle, it is because
matter has been denned and maligned by philosophers and
theologians who were equally unaware that it is, at bottom,
essentially mystical and transcendental.

Questions such as these derive their present interest in
great part from their audacity, which is sure, in due time, to
disappear. And the sooner the public dread is abolished
with reference to such questions the better for the cause of
truth. As regards knowledge, physical science is polar.
In one sense it knows, or is destined to know, every thing.
In another sense it knows nothing. Science knows much
of this intermediate phase of things that we call Nature, of
which it is the product ; but science knows nothing of the
origin or destiny of Nature. Who or what made the sun,
and gave his rays their alleged power ? Who or what made
and bestowed upon the ultimate particles of matter their
wondrous power of varied interaction ? Science does not
know : the mystery, though pushed back, remains unaltered.
To many of us who feel that there are more things in
heaven and earth than are dreamt of in the present phi
losophy of science, but who have been also taught, by
baffled efforts, how vain is the attempt to grapple with
the inscrutable, the ultimate frame of mind is that of
Goethe:

41 G FRAGMENTS OF SCIENCE.

" Who dares to name His name,
Or belief in Him proclaim,
Veiled in mystery as lie is, the All-enfolder ?
Gleams across the mind His light,
Feels the lifted soul His might,
Dare it then deny His reign, the All-upholder? "

One or two interpolations excepted, the foregoing brief
article was written on an Alpine slope in the summer of
1863. Seven years afterward I was singularly interested
to learn, that nearly 300 years ago, in explaining the actions
and energies of the human body, Descartes employed
similar imagery and expressed similar views as far as the
knowledge of his time allowed. Professor Huxley, who
possesses a reading faculty which I can but envy, has pub
lished in his " Lay Sermons " the following remarkable
extracts from the " Trait6 de 1'Homme : "

"In proportion as these spirits" (the animal spirits) "enter the cavi
ties of the brain, they pass thence into the pores of its substance, and from
these pores into the nerves ; where, according as they enter, or even
only tend to enter, more or less, into one than into another, they have
the power of altering the figure of the muscles into which the nerves are
inserted, and by this means of causing all the limbs to move. Thus, as
you may have seen in the grottoes and the fountains in royal gardens,
the force with which the water issues from its reservoir is sufficient to
move various machines, and even to make them play instruments, or
pronounce words, according to the different disposition of the pipes which
lead the water.

" And, in truth, the nerves of the machine which I am describing may
very well be compared to the pipes of these water-works ; its muscK.s
and its tendons to the other various engines and springs which seem to
move them ; its animal spirits to the water which impels them, of which
the heart is the fountain ; while the cavities of the brain are the central
office. Moreover, respiration and other such actions as are natural and
usual in the body, and which depend on the course of the spirits, are
like the movements of a clock, or of a mill, which may be kept up by the
ordinary flow of water.

VITALITY. 417

" The external objects which, by their mere presence, act upon the
organs of the senses ; and which, by this means, determine the corporal
machine to move in many different ways, according as the parts of the
brain are arranged, are like the strangers who, entering into some of the
grottoes of those water-works, unconsciously cause the movements which
take place in their presence. For they cannot enter without treading upon
certain planks so arranged that, for example, if they approach a bathing
Diana, they cause her to hide among the reeds ; and if they attempt to
follow her, they see approaching a Neptune, who threatens them with his
trident ; or if they try some other way, they cause some monster who
vomits water into their faces, to dart out ; or like contrivances, according
to the fancy of the engineers who have made them. And lastly, when
the rational soul is lodged in this machine, it will have its principal seat
in the brain, and will take the place of the engineer, who ought to be
in that part of the works with which all the pipes are connected, when
he wishes to increase, or to slacken, or in some way to alter, their move
ments."

" All the functions which I have attributed to this machine " (the
body), " as the digestion of food, the pulsation of the heart and of the
arteries ; the nutrition and the growth of the limbs ; respiration, wake-
fulness, and sleep ; the reception of light, sounds, odors, flavors, heat, and
such like qualities, in the organs of the external senses ; the impression
of the ideas of these in the organ of common-sense and in the imagina
tion ; the retention, or the impression, of these ideas on the memory ;
the internal movements of the appetites and the passions ; and lastly,
the external movements of all the limbs, which follow so aptly, as well
the action of the objects which are presented to the senses, as the im
pressions which meet in the memory, that they imitate as nearly as
possible those of a real man : I desire, I say, that you should consider
that these functions in the machine naturally proceed from the mere
arrangement of its organs, neither more nor less than do the movements
of a clock, or other automaton, from that of its weights and its wheels ;
so that, so far as these are concerned, it is not necessary to conceive any
other vegetative or sensitive soul, nor any other principle of motion, or
of life, than the blood and the spirits agitated by the fire which burns
continually in the heart, and which is no wise essentially different from
all the fires which exist in inanimate bodies."

ADDITIONAL REMARKS ON MIRACLES.

AMONG the scraps of manuscript written at the time
when Mr. Mozley's work occupied my attention I find the
following reflections :

With regard to the influence of modern science which
Mr. Mozley rates so low, one effect of it is certainly to en
hance the magnitude of many of the recorded miracles, and
to increase proportionably the difficulties of belief. The
ancients knew but little of the vastness of the universe.
The Rev. Mr. Kirkman, for example, has shown what inad
equate notions the Jews entertained regarding the " firma
ment of heaven ; " and Professor Airy refers to the case of
a Greek philosopher who was persecuted for hazarding the
assertion, then deemed monstrous, that the sun might be as
large as the whole country of Greece. The concerns of a
universe, regarded from this point of view, were vastly
more commensurate with man and his concerns than those
of the universe which science now reveals to us ; and hence
that to suit man's purposes, or in compliance with his
prayers, changes should occur in the order of the universe,
was more easy of belief in the ancient world than it can
be now. In the very magnitude which it assigns to natural
phenomena, science has augmented the distance between
them and man, and increased the popular belief in their or
derly progression. As a natural consequence, the demand

REMARKS ON MIRACLES. 419

for evidence is more exacting than it used to be, whenever
it is affirmed that such order has been disturbed.

Let us take as an illustration the miracle by which the
victory of Joshua over the Amorites was rendered complete,
where the sun is reported to have stood still for " a whole
day" upon Gibeon, and the moon in the valley of Ajalon.
An Englishman of average education at the present day
would naturally demand a greater amount of evidence to
prove that this occurrence took place than would have sat
isfied an Israelite in the age succeeding that of Joshua.
For, to the one, the miracle probably consisted of the stop
page of a ball of fire less than a yard in diameter, while to
the other it would be the stoppage of an orb fourteen hun
dred thousand times the earth in size. And, even accept
ing the interpretation which instructed divines now put
upon this text, that Joshua dealt with what was apparent
merely, but that what really occurred was the suspension
of the earth's rotation, I think a greater reserve in accept
ing the miracle, and a right to demand stronger evidence
in support of it, will be conceded to a modern man of sci
ence than would have sufficed for an ancient Jew.

There is a scientific imagination as well as an historic
imagination, and when, by the exercise of the former, the
stoppage of the earth's rotation is clearly realized, the
event assumes proportions so vast in comparison with the
result to be obtained by it that belief reels under the reflec
tion. The energy here involved is equal to that of six trill
ions of horses working for the whole of the time employed
by Joshua in the destruction of his foes. The amount of
power thus expended would be sufficient to supply every
individual of an army a thousand times the strength of that
of Joshua, with a thousand times the fighting-power of
each of Joshua's soldiers, not for the few hours necessary to
the extinction of a handful of Amorites, but for millions
of years. All this wonder is silently passed over by the

420 FRAGMENTS OF SCIENCE.

sacred historian, confessedly because he knew nothing
about it. Whether, therefore, we consider the miracle as
purely evidential, or as a practical means of vengeance, the
same lavish squandering of energy stares the scientific man
in the face. If evidential, the energy -was wasted, because
the Israelites knew nothing of its amount ; if simply de
structive, then the ratio of the quantity lost to that em-
plo}recl may be inferred from the foregoing figures.

To other miracles similar remarks apply. Transferring
thought from our little sand-grain of an earth to the im
measurable heavens, where countless worlds, with their
freights of life, probably revolve unseen, the very suns which
warm them being barely seen by us across abysmal space ;
reflecting that beyond these sparks of solar fire suns innu-
moruble may lie, whose light can never stir the optic nerve
at all ; and, bringing this conception face to face with the
idea that the Builder and Sustainer of it all should contract
himself to a burning bush, or behave in other familiar ways
ascribed to him — it is easy to understand how astounding
the incongruity must appear to the scientific man. Did
this credulous prattle of the ancients about miracles stand
alone ; were it not locally associated with words of imper
ishable wisdom, and with examples of moral grandeur un
matched elsewhere in the history of the human race, both
the miracles and their " evidences " would have long since
ceased to be the transmitted inheritance of intelligent men.
Under the pressure of the awe which this universe inspires,
well may we exclaim in David's spirit, if not in David's
words: u When I consider the heavens the work of thy
fingers, the moon, and the stars, which thou hast ordained;
what is man that thou shouldst be mindful of him, or the
son of man that thou shouldst so regard him ? "

If you ask me who is to limit the outgoings of Al
mighty power, my answer is, not I. If you should urge
that if the Builder and the Maker of this universe chose to

REMARKS ON MIRACLES. 421

stop the rotation of the earth, or to take the form of a
burning bush, there is nothing to prevent him from doing
so, I am not prepared to contradict you. I neither agree
with you nor differ from you, for it is a subject of which I
know nothing. But I observe that in such questions re
garding Almighty power, your inquiries relate, not to that
power as it is actually displayed in the universe, but to the
power of your own imagination. Your question is, not has
the Omnipotent done so and so ? or is it in the least likely
that the Omnipotent should do so and so ? but, is my imagi
nation competent to picture a being able and willing to do
so and so ? I am not prepared to deny your competence.
To the human mind belongs the faculty of enlarging and
diminishing, of distorting and combining indefinitely the
objects revealed by the senses, or by its own consciousness.
It can imagine a mouse as large as an elephant, an elephant
as large as a mountain, and a mountain as high as the stars.
It can separate congruities and unite incongruities. We
see a fish and we see a woman ; we can drop one half of
each, and unite in idea the other two halves to a mermaid.
We see a horse and we see a man ; we are able to drop one
half of each, and unite the other two halves to a centaur.
Thus also the pictorial representations of the Deity, the
bodies and wings of cherubs and seraphs, the hoofs, horns,
and tail of the Evil One, the joys of the blessed, and the
torments of the damned, have been elaborated from mate
rials furnished to the imagination by the senses. And it
behooves you and me to take care that our notions of the
Power which rules the universe are not mere fanciful or ig
norant enlargements of human power. The capabilities of
what you call your reason are not denied. By the exercise
of the power here adverted to, and which may be called
the mytliologic imagination^ you can picture to yourself a
being able and willing to do any and every conceivable
thing. You are right in saying that in opposition to this

422 FRAGMENTS OF SCIENCE.

power science is of no avail. Mr. Mozley would call it
" a weapon of air." The man of science, however, while
accepting the figure, would probably reverse its parts,
thinking that it is not science which is here the thing of
air, but the unsubstantial figment of the imagination to
which its solidity is opposed.

TIIE END.

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THE ORIGIN OF CIVILIZATION;

OR, THE

PRIMITIVE CONDITION OF MAN.
By SIR JOHN LTIBBOCK, Bart, M, P., F. R. S.

38O Tages. Illustrated..

Tliis interesting work is the fruit of many years' research
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scribing the conditions of those tribes of men who are lowest
in the scale of development.

" This interesting work — for it is intensely so in its aim, scope, and the
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or the natural history of the human species ; the complete science of man,
body and soul, including sex, temperament, race, civilization, etc." — Provi
dence Press.

"A work which is mo?t comprehensive in its aim, and most admirable in
its execution. The patience and judgment bestowed on the book are every
where apparent ; the mere list of authorities quoted giving evidence of wide
and impartial reading. The work, indeed, is not only a valuable one on ac
count of the opinions it expresses, but it is also most serviceable as a book
of reference. It offers an able and exhaustive table of a vast array of facts,
which no single student could well obtain for himself, and it has not been
made the vehicle for any special pleading on the part of the author." —
London Atlienceum.

" The book is no cursory and superficial review ; it goes to the very heart
of the subject, and embodies the results of all the later investigations. It ia
replete with curious and quaint information presented in a compact, luminous,
and entertaining form." — Albany Evening Journal.

"The treatment of the subject is eminently practical, dealing more with
fact than theory, or perhaps it will be more just to say, dealing only with
theory amply sustained by tact." — Detroit Free Press.

"This interesting and valuable volume illustrates, to some extent, the
way in which the modern scientific spirit manages to extract a considerable
treasure from the chaff and refuse neglected or thrown aside by former in
quirers." — London Saturday Review.

D. APPLETON & CO... Publishers.

D. Appleton & Company^ Publications.

LAY SEEMO^S,
ADDKESSES, AND KEYIEWS,

BY THOMAS HENRY HUXLEY.
Cloth, 12mo. 390 pages. Price, $1.75

Tnis is the latest and most popular of the works of this in
trepid and accomplished English thinker. The American edition
of the work is the latest, and contains, in addition to the English
edition, Professor Huxley's recent masterly address on " Spon
taneous Generation," delivered before the British Association for
the Advancement of Science, of which he was president.
The following is from an able article in the Independent :

The " Lay Sermons, Addresses, and Reviews " is a book to be read
by every one who would keep up with the advance of truth — as well by
those who are hostile as those who are friendly to his conclusions. In
it, scientific and philosophical topics are handled with consummate abil
ity. It is remarkable for purity of style and power of expression. No
where, in any modern work, is the advancement of the pursuit of that
natural knowledge, which is of vital importance to bodily and mental
well-being, so ably handled.

Professor Huxley is undoubtedly the representative scientific man of
the age. His reverence for the right and devotion to truth have estab
lished his leadership of modern scientific thought. He leads the beliefs
and aspirations of the increasingly powerful body of the younger men of
science. His ability for research is marvellous. There is possible no more
equipoise of judgment than that to which he brings the phenomena of
Nature. Besides, he is not a mere scientist. His is a popularized phi-
losophy ; social questions have been treated by his pen in a manner most
masterly. In his popular addresses, embracing the widest range of top
ics, he treads on ground with which he seems thoroughly familiar.

There are those who hold the name of Professor Huxley as synony
mous with irreverence and atheism. Plato's was so held, and Galileo's,
and Descartes's, and Newton's, and Faraday's. There can be no greater
mistake. No man has greater reverence for the Bible than Huxley. No
one more acquaintance with the text of Scripture. He believes there is
definite government of the universe ; that pleasures and pains are distrib
uted in accordance with law ; and that the certain proportion of evil
woven up in the life even of worms will help the man who thinks to bear
his own share with courage.

In the estimate of Professor Huxley's future influence upon science,
his youth and health form a large element. He has just passed his forty,
fifth year. If God spare his life, truth can hardly fail to be the gainer
from a mind that is stored with knowledge of the laws of the Creator's
operations, and that has learned to love all beauty and hate ail rileness of
Nature and art.

SPENCER'S SYSTEM OF PHILOSOPHY.

THE PHILOSOPHY OF EVOLUTION.

By HERBERT SPENCER.

This great system of scientific thought, the most original and important men
tal undertaking of the age, to which Mr. Spencer has devoted his life, is now well
advanced, the published volumes being: First Principle*, The Principles of Bi-
otoyy, two volumes, and The Principles of Psychology, vol. i., which will bo
shortly printed.

This philosophical system differs from all its predecessors in being solidly
based on the sciences of observation and induction ; in representing the order
and course of Nature ; in bringing Nature and man, life, mind, and society, under
one great law of action ; and in developing a method of thought which may serve
for practical guidance in dealing with the affairs of life. That Mr. Spencer is the
man for this great work will be evident from the following statements :

41 The only complete and systematic statement of the doctrine of Evolution
with which I am acquainted is that contained in Mr. Herbert Spencer's 4 System
of Philosophy ; ' a work which should be carefully studied by all who desire to
know whither scientific thought is tending."— T. H. HUXLEY.

44 Of all our thinkers, he is the one who has formed to himself the largest new
scheme of a systematic philosophy."— Prof. MASSON.

44 If any individual influence is visibly encroaching on Mills in this country, it
is his."— Ibid.

44 Mr. Spencer is one of the most vigorous as well as boldest ItLokers that
English speculation has yet produced."— JOHN STUART MILL.

44 One of the acutest metaphysicians of modern times."— Ibid.

44 One of our deepest thinkers."— Dr. JOSEPH D. HOOKER.

It is questionable if any thinker of finer calibre has appearo'l in our coun
try."1 — GEORGE HENRY LEWES.

44 He alone, of all British thinkers, has organized a philosophy."— Rid.

44 He is as keen an analyst as is known in the history of philosophy ; I do not
except either Aristotle or Kant."— GEORGE RIPLET.

44 If we were to give our own judgment, we should say that, since Newton,
there has not in England been a philosopher of more remarkable speculative and
•ystematizing talent than (in spite of some errors and some narrowness) Mr. Her
bert Spencer."— London- Saturday Review.

" We cannot refrain from offering our tribute of respect to one who, whether
(or the extent of his positive knowledge, or for the profundity of his speculative
insight, has already achieved a name second to none in the whole range of Eng
lish philosophy, and whose works will worthily sustain the credit of Eogllsk
thought in the present generation."— Westminster Itevitw.

D. APPLETON & CO.'S PUBLICATIONS.
ON

THE ORIGIN OF SPECIES

BY

Means of Natural Selection ;

OR,

THE PRESERVATION OF FAVORED RACES

IN THE

STRUGGLE FOR LIFE.

BY

ZD-A-IVWIIT, -A.. OVC.

One Volume. 12mo. Cloth. $2.00.

" His first point is to show that species are in many cases not well
defined, and that the whole order of natural history seems to be in a
state of mutation, by reason of constant variations. Thus even under
domestication, important changes may be introduced by intercrossing,
by selection of the best individuals for propagation, by crossing parent*
marked by however slight, but favorable peculiarities.

"His second point is what he terms the universal and necessary
struggle for existence. This follows from the high geometrical ratio
of increase common to all beings. If there were no catastrophes,
any one of the existing species would be sufficiently numerous in a
few thousand years to cover the whole earth, to the exclusion of every
thing else.

" His third point is to prove that this struggle is directed by the
law of natural selection. Even the races of domestic animals may be
constantly improved and modified by choosing the best individuals
for propagation. Nature brings the same discipline to bear upon the
whole domain of animal and vegetable life. She seizes at once upon
any slight variation that is favorable, and perpetuates it ; in the uni-
rersal pressure, any variation that is injurious is immediately extin
guished."

THE DESCENT OF MAN,

AND

SELECTION IN RELATION TO SEX.

BY

CHAS. DABWIN, M. A., F. E, S.
Two Vols., 12mo.

PRICE, . ... . $4.00

In these volumes Mr. Darwin has brought forward all the facts and
arguments which science has to offer in favor of the doctrine that man
has arisen by gradual development from the lowest point of animal life.
He had originally intended this work as a posthumous publication, but
the extensive acceptance of the views unfolded in his book on the " Origin
of Species " induced him to believe that the public were ripe for the most
advanced deductions from his theory of "Natural Selection." Aside from
the logical purpose which Mr. Darwin had in view, his work is an original
and fascinating contribution to the most interesting portion of natural
history. -

From the London Spectator.

"For our part, we find Dr. Darwin's vindication of the origin of man a far moro
wonderful vindication of Theism than Paley's 'Natural Theology,' though we do
not know, BO reticent is his style, whether or not he conceives it himself.''
From the Citizen and Sound Table.

" Even the charge of atheism, which was so violently urged against Mr. Dar
win, is now rarely hoard, and theologians, whose orthodoxy is unquestioned, hftve
ventured to admit that it is possible to believe both in Christianity and the Dar
winian theory at the game time."

From the Charleston Courier.

"No one can rise from an ordinarily attentive consideration of Mr. Darwin's
treatise, without being impressed, not only" with the extent and depth of the.
knowledge which lie lias attained upon the subject under treatment, and his long,
unwearied labor in collecting facts, but also with his possession of qualities
equally rare — the true scientific temper, the transparent candor, and the truth-
Becking soberness, with which he expresses to you his conclusions, and the pro-
C6M60 07 which he reaches them.

" Whether you like his discourse or not — though yon may refuse to acquiesce
in his conclusions — still you are compelled to bear your witness, that lhi< man
has not been laboring to find facts to support a preconceived theory, but that the
theory Is the irrepressible outgrowth of his accumulated facts."
From the Evening Bulletin.

" This theory is now indorsed by many eminent scientists, who at first com
bated it, including Sir Charles Lyell, probably the most learned of living geolo-
gists. and even by a class of Christian divines like Dr. MK'osh. who think that
certain theories of cosmogony, like the nebular hypothesis and the law of evolu
tion, may be accepted without doing violence to faith."

Sent free, by mail, to any address in the U. S., on receipt of the price.

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Works publisJwd by D. Appleton <& Co.

HEAT,

CONSIDERED AS A MODE OF MOTION,

Being a Course of Twelve Lectures delivered before the
Royal Institution of Great Britain.

BY JOHN TYNDALL, F. E. S.,

rnOFESSOB Or NATtrRAL PHILOSOPHY IN THE EOYAL INSTITUTION— AUTHOK 3» COB
"GLAOIKKS OF THE ALTS," ETC.

With One Hundred Illustrations. Svo, 480 pages. Price, $2.

Prom the American Journal of Science.— With all the skill which has
made Faraday the master of experimental science in Great Britain, Professor Tyndall
enjoys the advantage of a superior general culture, and is thus enabled to set forth hia
philosophy with all the graces of eloquence and the finish of superior diction. With a
simplicity, and absence of technicalities, which render his explanations lucid to un
scientific minds, and at the same time a thoroughness and originality by which he in
structs the most learned, he unfolds all the modern philosophy of heat. His work takes
rank at once as a classic upon the subject.

New York Times. — Professor Tyndall's course of lectures on heat is one of the
most beautiful illustrations of a mode of handling scientific subjects, which is com
paratively new, and which promises the best results, both to science and to literature
generally ; we mean Ae treatment of subjects in a style at once profound and popu
lar. The title of Professor Tyndall's work indicates the theory of heat held by him,
and indeed the only one now held by scientific men— it is a mode of motion.

Boston Journal.— He exhibits the curious and beautiful workings of nature iu
n most delightful manner. Before the reader particles of water lock themselves or fly
asunder with a movement regulated like a dance. They form themselves into liquid
flowers with fine serrated petals, or into rosettes of frozen gauze ; they bound upward
In boiling fountains, or creep slowly onward in stupendous glaciers. Flames burst into
music and sing, or cease to sing, as the experimenter pleases, and metals paint them
selves upon a screen in dazzling hues as the painter touches his canvas.

New York Tribune. — The most original and important contribution that has
yet been made to the theory and literature of thermotics.

Scientific American.— The work is written in a charming style, and is th«
most valuable contribution to scientific literature that his been published in many
years. It is the most popular exposition of the dynamical theory of heat that has yet
appeared. The old material theory of heat may be said to be defunct.

Louisville Democrat.— This is one of the most delightful scientific works we
htre ever met. The lectures are so full of life and spirit that we can almost imagine
Uxe lecturer before us, and see his brilliant experiments in every stage of their progress.
The theory is so carefully and thoroughly explained that no one can fail to understand
tt. Such books as these create a love for science.

Independent. — Professor Tyndall's expositions and experiments are remarkably
ttjoughtful, ingenious, clear, and convincing; portions of the book have almost th«
Interest of a romance, so startling aro the descriptions and elucidations.

Wwks of Herbert Spencer published by D. .Appleton d' Co.
A NEW SYSTEM OF PHILOSOPHY.

FIRST PRINCIPLES.

1 VoL Larg-e 12mo. 515 Pages. Price $2 50.

CONTENTS :
PART FIRST.— Tim Unknowable.

Ciiaptei i. Religion and Science; IL Ultimate Eeligious Ideas; IU.
Ultimate Scientific Ideas; IV. The Relativity of all Knowledge; V Th«
Reconciliation.

PART SECOND — Laws of the Knowable.

I. Laws in General; IL The Law of Evolution; III. The same con
tinued; IV. The Causes of Evolution; V. Space, Tune, Matter, Motion, and
Force; VL The Indestructibility of Matter ; VII. The Continuity of Motion ;
VIII. The Persistence of Force ; IX. The Correlation and Equivalence of
Forces; X. The Direction of Motion ; XI. The Rhythm of Motion; XII. The
Conditions Essential to Evolution ; XIII. The Instability of the Homoge
neous ; XIV. The Multiplication of Effects ; XV. Differentiation «»nd Inte
gration ; XVI. Equilibration ; XVII. Summary and Conclusion.

In the first part of this work Mr. Spencer defines the province, limits, and
relations of religion and science, and determines the legitimate scope of
philosophy.

In part second he unfolds those fundamental principles which have been
arrived at within the sphere of the knowable ; which are true of all order*
of phenonema, and thus constitute the foundation of all philosophy. The
law of Evolution, Mr. Spencer maintains to be universal, and he has here
worked it out as the basis of his system.

These First Principles are the foundation of a system of Philosophy
bolder, more elaborate, and comprehensive perhaps, than any other which
oat been hitherto designed in England. — British Quarterly Review.

A work lofty in aim and remarkable in execution. — Comhill Mayazinc.

In the works of Herbert Spencer we have the rudiments of a positiye
Theology, and an immense step toward the perfection of the science of Psy
chology. — Christian Examiner.

If we mistake not, HI spite of the very negative character of his own re
mits, he has foreshadowed some strong arguments for tlie doctrine of a po»-
ti»e Christian Theology. — New Englander.

AB far as the frontiers of knowledge, where the Intellect may go, there ft
BO living man whoso jruidance may more safely be trusted. —
MriAfc

Work* <tf Herbert Spencer published, by D. AppUtcn & Co.
TJie Philosophy of Herbert Spencer.

THE

PRINCIPLES OF BIOLOGY

Vol. I. 475 pages. (Now in press.)

CONTENTS:
PART I. — THE DATA OP BIOLOGY.

L Organic Matter. — II. The actions of Forces on Organic Matter. — III. Th«
re-actions of Organic Matter on Forces. — IV. Proximate Definition of
Life. — V. The Correspondence between Life and its Circumstances. —

VI. The Degree of Life varies as the Degree of Correspondence.—

VII. The Scope of Biology.

PART II. — THE INDUCTIONS OF BIOLOGY.

L Growth. — II. Development. — III. Function. — IV. Waste and Repair. —
V. Adaptation,— VI. Individuality.— VII. Genesis.— VIII. Heredity.-

IX. Variation. — X. Genesis, Heredity, and Variation — XI. Classifica
tion. — XII. Distribution.

PART III. — THE EVOLUTION OP Lnra.

I. Preliminary. — II. General Aspects of the Special-creat ion-hypothesis. —
III. General Aspects of the Evolution-hypothesis. — IV. The Arguments
from Classification. — V. The Arguments from Embryology. — VI. The
Arguments from Morphology. — VII. The Arguments from Distribution,
— VIII. How is Organic Evolution caused ? — IX. External Factors. —

X. Internal Factors. — XI. Direct Equilibration. — XII. Indirect Equili
bration. — XIII. The Cooperation of the Factors. — XFV. The Converg
ence of the Evidences.

All these works are rich In materials for forming intelligent opinions, even where
we are unable to agree with those put forth by the author. Much may be learned from
Jjem in departments in which our common Educational system is very deficient. The
active citizen may derive from them accurate systematized information concerning hia
highest duties to society, and the principles on which they are based. He may gain
dearer notions of the value and bearing of evidence, and be better able to distinguish
between facts and inferences. He may find common things suggestive of wiser thought
—nay, we will venture to say of truer emotion — than before. By giving us fuller rcali-
tations of liberty and justice his writings will tend to increase onr self-reliance in the
treat emergency of civilization to which we have been summoned — Atlantic Montfilv

D. APPLETON & CO:S PUBLICATIONS.
THE

Correlation and Conservation of Forces.

WITH AN

.INTRODUCTION AND BEIEF BIOGRAPHICAL NOTIOES
By EDWARD L> YOUMANS, M.D. 12mo, 490 pages.

CONTENTS.

L By W. R. GROVE. The Correlation of Physical Forces.
IL By Prof. HELMHOLTZ. The Interaction of Natural Forces.
HI. By J. R. MATER. 1. Remarks on the Forces of Inorganic Xature.

2. On Celestial Dynamics.

3. On the Mechanical Equivalent of Her<t.

IV. By Dr. FARADAY. Some Thoughts on the Conservation of Forces.
V. By Prof. LIEBIO. The Connection and Equivalence of Forces.
VI. By Dr. CARPENTER. The Correlation of the Physical and Vital Forces

"This work is a very welcome addition to our scientific literature, and will I*
l>articularly acceptable to those who wish to obtain a popular, but at tho Bame time
precise and clear view of what Faraday justly calls the highest law in physical science,
the principle of the conservation of force. Sufficient attention has not been paid to the
publication of collected monographs or memoirs upon special subjects. Dr. Youmans'
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hope his excellent example may be followed in other branches of science." — American
Journal of Science.

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Correlation and Conservation of Forces? In this volume we have the answer, and
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""We here have the original expositions of the new Philosophy of Forces, accompa
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Quarterly Review.

" This is, perhaps, the most remarkable book of the age. "We have here the latest
discoveries, and the highest results of thought concerning the nature, laws, and con-
Elections of the forces of the universe. No higher or more sublime problem can engage
the intellect of man than is discussed by these doctors of science intent alone on anir
lag at the truth."— Detroit Free Press.

'This work presents a praiseworthy specimen of complete and faithful authorship,
and iU publication at thie time will form an epoch in tha experience of ninny thinking
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