judge of the total scientific achievement of any age, the standpoint
of a succeeding age is desirable. We may, however, transport
ourselves in idea into the future, and thus survey with more or less
completeness the science of our time. We sometimes hear it decried,
and contrasted to its disadvantage with the science of other times. I
do not think that this will be the verdict of posterity. I think, on
the contrary, that posterity will acknowledge that in the history of
science no higher samples of intellectual conquest are recorded than
those which this age has made its own. One of the most salient of
these I propose, with your permission, to make the subject of our
consideration during the coming hour.
It is now generally admitted that the man of to-day is the child and
product of incalculable antecedent time. His physical and
intellectual textures have been woven for him during his passage
through phases of history and forms of existence which lead the mind
back to an abysmal past. One of the qualities which he has derived
from that past is the yearning to let in the light of principles on
the otherwise bewildering flux of phenomena. He has been described by
the German Lichtenberg as 'das rastlose Ursachenthier'--the restless
cause-seeking animal--in whom facts excite a kind of hunger to know
the sources from which they spring. Never, I venture to say, in the
history of the world has this longing been more liberally responded
to, both among men of science and the general public, than during the
last thirty or forty years. I say 'the general public,' because it is
a feature of our time that the man of science no longer limits his
labours to the society of his colleagues and his peers, but shares, as
far as it is possible to share, with the world at large the fruits of
enquiry.
The celebrated Robert Boyle regarded the universe as a machine; Mr.
Carlyle prefers regarding it as a tree. He loves the image of the
umbrageous Igdrasil better than that of the Strasburg clock. A
machine may be defined as an organism with life and direction outside;
a tree may be defined as an organism with life and direction within.
In the light of these definitions, I close with the conception of
Carlyle. The order and energy of the universe I hold to be inherent,
and not imposed from without, the expression of fixed law and not of
arbitrary will, exercised by what Carlyle would call an Almighty
Clockmaker. But the two conceptions are not so much opposed to each
other after all. In one fundamental particular they at all events
agree. They equally imply the interdependence and harmonious
interaction of parts, and the subordination of the individual powers
of the universal organism to the working of the whole.
Never were the harmony and interdependence just referred to so clearly
recognised as now. Our insight regarding them is not that vague and
general insight to which our fathers had attained, and which, in early
times, was more frequently affirmed by the synthetic poet than by the
scientific man. The interdependence of our day has become
quantitative--expressible by numbers--leading, it must be added,
directly into that inexorable reign of law which so many gentle people
regard with dread. In the domain now under review men of science had
first to work their way from darkness into twilight, and from twilight
into day. There is no solution of continuity in science. It is not
given to any man, however endowed, to rise spontaneously into
intellectual splendour without the parentage of antecedent thought.
Great discoveries grow. Here, as in other cases, we have first the
seed, then the ear, then the full corn in the ear, the last member of
the series implying the first. Thus, as regards the discovery of
gravitation with which the name of Newton is identified, notions more
or less clear concerning it had entered many minds before Newton's
transcendent mathematical genius raised it to the level of a
demonstration. The whole of his deductions, moreover, rested upon the
inductions of Kepler. Newton shot beyond his predecessors; but his
thoughts were rooted in their thoughts, and a just distribution of
merit would assign to them a fair portion of the honour of discovery.
Scientific theories sometimes float like rumours in the air before
they receive complete expression. The doom of a doctrine is often
practically sealed, and the truth of one is often practically
accepted, long prior to the demonstration of either the error or the
truth.
Perpetual motion was discarded before it was proved to be opposed to
natural law; and, as regards the connection and interaction of natural
forces, intimations of modern discoveries are strewn through the
writings of Leibnitz, Boyle, Hooke, Locke and others.
Confining ourselves to recent times, Dr. Ingleby has pointed out to me
some singularly sagacious remarks bearing upon this question, which
were published by: an anonymous writer in 1820. Roget's penetration
was conspicuous in 1829. Mohr had grasped in 1837 some deep-lying
truth. The writings of Faraday furnish frequent illustrations of his
profound belief in he unity of nature. 'I have long,' he writes in
1845, 'held an opinion almost amounting to conviction, in common, I
believe, with other lovers of natural knowledge, that the various
forms under which the forces of matter are made manifest have one
common origin, or, in other words, are so directly related and
mutually dependent, that they are convertible, as it were, one into
another, and possess equivalence of power in their action.' His own
researches on magneto-electricity, on electro-chemistry, and on the
'magnetisation of light led him directly to this belief. At an early
date Mr. Justice Grove made his mark upon this question. Colding,
though starting from a metaphysical basis, grasped eventually the
relation between heat and mechanical work, and sought to determine it
experimentally. And here let me say, that to him who has only the
truth at heart, and who in his dealings with scientific history keeps
his soul unwarped by envy, hatred, or malice, personal or national,
every fresh accession to historic knowledge must be welcome. For
every new-comer of proved merit, more especially if that merit should
have been previously overlooked, he makes ready room in his
recognition or his reverence. But no retrospect of scientific
literature has as yet brought to light a claim which can sensibly
affect the positions accorded to two great Path-hewers, as the Germans
call them, whose names in relation to this subject are linked in
indissoluble association. These names are Julius Robert Mayer and
James Prescott Joule.
In his essay on 'Circles' Mr. Emerson, if I remember rightly,
pictured intellectual progress as rhythmic. At a given moment
knowledge is surrounded by a barrier which marks its limit. It
gradually gathers clearness and strength until by-and-by some thinker
of exceptional power bursts the barrier and wins a wider circle,
within which thought once more entrenches itself. But the internal
force again accumulates, the new barrier is in its turn broken, and
the mind finds itself surrounded by a still wider horizon. Thus,
according to Emerson, knowledge spreads by intermittent victories
instead of progressing at a uniform rate.
When Dr. Joule first proved that a weight of one pound, falling
through a height of seven hundred and seventy-two feet, generated an
amount of heat competent to warm a pound of water one degree
Fahrenheit, and that in lifting the weight so much heat exactly
disappeared, he broke an Emersonian 'circle,' releasing by the act an
amount of scientific energy which rapidly overran a vast domain, and
embodied itself in the great doctrine known as the 'Conservation of
Energy.' This doctrine recognises in the material universe a constant
sum of power made up of items among which the most Protean
fluctuations are incessantly going on. It is as if the body of Nature
were alive, the thrill and interchange of its energies resembling
those of an organism. The parts of the 'stupendous whole' shift and
change, augment and diminish, appear and disappear, while the total of
which they are the parts remains quantitatively immutable. Immutable,
because when change occurs it is always polar--plus accompanies minus,
gain accompanies loss, no item varying in the slightest degree without
an absolutely equal change of some other item in the opposite
direction.
*****
The sun warms the tropical ocean, converting a portion of its liquid
into vapour, which rises in the air and is recondensed on mountain
heights, returning in rivers to the ocean from which it came. Up to
the point where condensation begins, an amount of heat exactly
equivalent to the molecular work of vaporisation and the mechanical
work of lifting the vapour to the mountain-tops has disappeared from
the universe. What is the gain corresponding to this loss? It will
seem when mentioned to be expressed in a foreign currency. The loss
is a loss of heat; the gain is a gain of distance, both as regards
masses and molecules. Water which was formerly at the sea-level has
been lifted to a position from which it can fall; molecules which have
been locked together as a liquid are now separate as vapour which can
recondense. After condensation gravity comes into effectual play,
pulling the showers down upon the hills, and the rivers thus created
through their gorges to the sea. Every raindrop which smites the
mountain produces its definite amount of heat; every river in its
course develops heat by the clash of its cataracts and the friction of
its bed. In the act of condensation, moreover, the molecular work of
vaporisation is accurately reversed. 'Compare, then, the primitive
loss of solar warmth with the heat generated by the condensation of
the vapour, and by the subsequent fall of the water from cloud to sea.
They are mathematically equal to each other. No particle of vapour
was formed and lifted without being paid for in the currency of solar
heat; no particle returns as water to the sea without the exact
quantitative restitution of that heat. There is nothing gratuitous in
physical nature, no expenditure without equivalent gain, no gain
without equivalent expenditure. With inexorable constancy the one
accompanies the other, leaving no nook or crevice between them for
spontaneity to mingle with the pure and necessary play of natural
force. Has this uniformity of nature ever been broken? The reply is:
'Not to the knowledge of science.'
What has been here stated regarding heat and gravity applies to the
whole of inorganic nature. Let us take an illustration from
chemistry. The metal zinc may be burnt in oxygen, a perfectly
definite amount of heat being produced by the combustion of a given
weight of the metal. But zinc may also be burnt in a liquid which
contains a supply of oxygen--in water, for example. It does not in
this case produce flame or fire, but it does produce heat which is
capable of accurate measurement. But the heat of zinc burnt in water
falls short of that produced in pure oxygen, the reason being that to
obtain its oxygen from the water the zinc must first dislodge the
hydrogen. It is in the performance of this molecular work that the
missing heat is absorbed. Mix the liberated hydrogen with oxygen and
cause them to recombine; the heat developed is mathematically equal to
the missing heat. Thus in pulling the oxygen and hydrogen asunder an
amount of heat is consumed which is accurately restored by their
reunion.
This leads up to a few remarks upon the Voltaic battery. It is not my
design to dwell upon the technical features of this wonderful
instrument, but simply, by means of it, to show what varying shapes a
given amount of energy can assume while maintaining unvarying
quantitative stability. When that form of power which we call an
electric current passes through Grove's battery, zinc is consumed in
acidulated water; and in the battery we are able so to arrange matters
that when no current passes no zinc shall be consumed. Now the
current, whatever it may be, possesses the power of generating heat
outside the battery. We can fuse with it iridium, the most refractory
of metals, or we can produce with it the dazzling electric light, and
that at any terrestrial distance from the battery itself.
We will now, however, content ourselves with causing the current to
raise a given length of platinum wire, first to a blood-heat, then to
redness, and finally to a white heat. The heat under these
circumstances generated in the battery by the combustion of a fixed
quantity of zinc is no longer constant, but it varies inversely as the
heat generated outside. If the outside heat be nil, the inside heat
is a maximum; if the external wire be raised to a blood-heat, the
internal heat falls slightly short of the maximum. If the wire be
rendered red-hot, the quantity of missing heat within the battery is
greater, and if the external wire be rendered white-hot, the defect is
greater still. Add together the internal and external heat produced
by the combustion of a given weight of zinc, and you have an
absolutely constant total. The heat generated without is so much lost
within, the heat generated within is so much lost without, the polar
changes already adverted to coming here conspicuously into play. Thus
in a variety of ways we can distribute the items of a never-varying
sum, but even the subtle agency of the electric current places no
creative power in our hands.
Instead of generating external heat, we may cause the current to
effect chemical decomposition at a distance from the battery. Let it,
for example, decompose water into oxygen and hydrogen. The heat
generated in the battery under these circumstances by the combustion
of a given weight of zinc falls short of what is produced when there
is no decomposition. How far short? The question admits of a
perfectly exact answer. When the oxygen and hydrogen recombine, the
heat absorbed in the decomposition is accurately restored, and it is
exactly equal in amount to that missing in the battery. We may, if we
like, bottle up the gases, carry in this form the heat of the battery
to the polar regions, and liberate it there. The battery, in fact is
a hearth on which fuel is consumed; but the heat of the combustion,
instead of being confined in the usual manner to the hearth itself,
may be first liberated at the other side of the world.
And here we are able to solve an enigma which long perplexed
scientific men, and which could not be solved until the bearing of the
mechanical theory of heat upon the phenomena of the Voltaic battery
was understood. The puzzle was, that a single cell could not
decompose water. The reason is now plain enough. The solution of an
equivalent of zinc in a single cell develops not much more than half
the amount of heat required to decompose an equivalent of water, and
the single cell cannot cede an amount of force which it does not
possess. But by forming a battery of two cells instead of one, we
develop an amount of heat slightly in excess of that needed for the
decomposition of the water. The two-celled battery is therefore rich
enough to pay for that decomposition, and to maintain the excess
referred to within its own cells.
Similar reflections apply to the thermo-electric pile, an instrument
usually composed of small bars of bismuth and antimony soldered
alternately together. The electric current is here evoked by warming
the soldered junctions of one face of the pile. Like the Voltaic
current, the thermo-electric current can heat wires, produce
decomposition, magnetise iron, and deflect a magnetic needle at any
distance from its origin. You will be disposed, and rightly disposed,
to refer those distant manifestations of power to the heat
communicated to the face of the pile, but the case is worthy of closer
examination. In 1826 Thomas Seebeck discovered thermo-electricity,
and six years subsequently Peltier made an observation which comes
with singular felicity to our aid in determining the material used up
in the formation of the thermo-electric current. He found that when a
weak extraneous current was sent from antimony to bismuth the junction
of the two metals was always heated, but that when the direction was
from bismuth to antimony the junction was chilled. Now the current in
the thermo-pile itself is always from bismuth to antimony, across the
heated junction--a direction in which it cannot possibly establish
itself without consuming the heat imparted to the junction. This heat
is the nutriment of the current. Thus the heat generated by the
thermo-current in a distant wire is simply that originally imparted to
the pile, which has been first transmuted into electricity, and then
retransmuted into its first form at a distance from its origin. As
water in a state of vapour passes from a boiler to a distant
condenser, and there assumes its primitive form without gain or loss,
so the heat communicated to the thermo-pile distils into the subtler
electric current, which is, as it were, recondensed into heat in the
distant platinum wire.
In my youth I thought an electro-magnetic engine which was shown to me
a veritable perpetual motion--a machine, that is to say, which
performed work without the expenditure of power. Let us consider the
action of such a machine. Suppose it to be employed to pump water
from a lower to a higher level. On examining the battery which works
the engine we find that the zinc consumed does not yield its full
amount of heat. The quantity of heat thus missing within is the exact
thermal equivalent of the mechanical work performed without. Let the
water fall again to the lower level; it is warmed by the fall. Add
the heat thus produced to that generated by the friction, mechanical
and magnetical, of the engine; we thus obtain the precise amount of
heat missing in the battery. All the effects obtained from the
machine are thus strictly paid for; this 'payment for results' being,
I would repeat, the inexorable method of nature.
No engine, however subtly devised, can evade this law of equivalence,
or perform on its own account the smallest modicum of work. The
machine distributes, but it cannot create. Is the animal body, then,
to be classed among machines? When I lift a weight, or throw a stone,
or climb a mountain, or wrestle with my comrade, am I not conscious of
actually creating and expending force? Let us look at the antecedents
of this force. We derive the muscle and fat of our bodies from what
we eat. Animal heat you know to be due to the slow combustion of this
fuel. My arm is now inactive, and the ordinary slow combustion of my
blood and tissue is going on. For every grain of fuel thus burnt a
perfectly definite amount of heat has been produced. I now contract
my biceps muscle without causing it to perform external work. The
combustion is quickened, and the heat is increased; this additional
heat being liberated in the muscle itself. I lay hold of a 56 lb.
weight, and by the contraction of my biceps lift it through the
vertical space of a foot. The blood and tissue consumed during this
contraction have not developed in the muscle their due amount of heat.
A quantity of heat is at this moment missing in my muscle which would
raise the temperature of an ounce of water somewhat more than one
degree Fahrenheit. I liberate the weight: it falls to the earth, and
by its collision generates the precise amount of heat missing in the
muscle. My muscular heat is thus transferred from its local hearth to
external space. The fuel is consumed in my body, but the heat of
combustion is produced outside my body. The case is substantially the
same as that of the Voltaic battery when it performs external work, or
produces external heat. All this points to the conclusion that the
force we employ in muscular exertion is the force of burning fuel and
not of creative will. In the light of these facts the body is seen to
be as incapable of generating energy without expenditure, as the
solids and liquids of the Voltaic battery. The body, in other words,
falls into the catagory of machines.
We can do with the body all that we have already done with the
battery--heat platinum wires, decompose water, magnetise iron, and
deflect a magnetic needle. The combustion of muscle may be made to
produce all these effects, as the combustion of zinc may be caused to
produce them. By turning the handle of a magneto-electric machine a
coil of wire may be caused to rotate between the poles of a magnet. As
long as the two ends of the coil are unconnected we have simply to
overcome the ordinary inertia and friction of the machine in turning
the handle. But the moment the two ends of the coil are united by a
thin platinum wire a sudden addition of labour is thrown upon the
turning arm. When the necessary labour is expended, its equivalent
immediately appears. The platinum wire glows. You can readily
maintain it at a white heat, or even fuse it. This is a very
remarkable result. From the muscles of the arm, with a temperature of
100 degrees, we extract the temperature of molten platinum, which is
nearly four thousand degrees. The miracle here is the reverse of that
of the burning bush mentioned in Exodus. There the bush burned, but
was not consumed--here the body is consumed, but does not burn. The
similarity of the action with that of the Voltaic battery when it
heats an external wire is too obvious to need pointing out. When the
machine is used to decompose water, the heat of the muscle, like that
of the battery, is consumed in molecular work, being fully restored
when the gases recombine. As before, also, the transmuted heat of
the muscles may be bottled up, carried to the polar regions, and there
restored to its pristine form.
*****
The matter of the human body is the same as that of the world around
us; and here we find the forces of the human body identical with those
of inorganic nature. Just as little as the Voltaic battery is the
animal body a creator of force. It is an apparatus exquisite and
effectual beyond all others in transforming and distributing the
energy with which it is supplied, but it possesses no creative power.
Compared with the notions previously entertained regarding the play of
'Vital force' this is a great result. The problem of vital dynamics
has been described by a competent authority as 'the grandest of all.'
I subscribe to this opinion, and honour correspondingly the man who
first successfully grappled with the problem. He was no pope, in the
sense of being infallible, but he was a man of genius whose work will
be held in honour as long as science endures I have already named him
in connection with our illustrious countryman Dr. Joule. Other
eminent men took up this subject subsequently and independently, but
all that has been done hitherto enhances instead of diminishing the
merits of Dr. Mayer.