paper on the production of heat by Voltaic electricity. In it he
announced the law that the calorific effects of equal quantities of
transmitted electricity are proportional to the resistance overcome by
the current, whatever may be the length, thickness, shape, or
character of the metal which closes the circuit; and also proportional
to the square of the quantity of transmitted electricity. This is a
law of primary importance. In another paper, presented to, but
declined by, the Royal Society, he confirmed this law by new
experiments, and materially extended it. He also executed experiments
on the heat consequent on the passage of Voltaic electricity through
electrolytes, and found, in all cases, that the heat evolved by the
proper action of any Voltaic current is proportional to the square of
the intensity of that current, multiplied by the resistance to
conduction which it experiences. From this law he deduced a number of
conclusions of the highest importance to electrochemistry.
It was during these enquiries, which are marked throughout by rare
sagacity and originality, that the great idea of establishing
quantitative relations between Mechanical Energy and Heat arose and
assumed definite form in his mind. In 1843 Mr. Joule read before the
meeting of the British Association at Cork a. paper' On the Calorific
Effects of Magneto-Electricity, and on the Mechanical Value of Heat.'
Even at the present day this memoir is tough reading, and at the time
it was written it must have appeared hopelessly entangled. This, I
should think, was the reason why Faraday advised Mr. Joule not to
submit the paper to the Royal Society. But its drift and results are
summed up in these memorable words by its author, written some time
subsequently: 'In that paper it was demonstrated experimentally, that
the mechanical power exerted in turning a magneto-electric machine is
converted into the heat evolved by the passage of the currents of
induction through its coils; and, on the other hand, that the motive
power of the electromagnetic engine is obtained at the expense of the
heat due to the chemical reaction of the battery by which it is
worked.' [Footnote: Phil. Mag. May, 1845.] It is needless to dwell
upon the weight and importance of this statement.
Considering the imperfections incidental to a first determination, it
is not surprising that the 'mechanical values of heat,' deduced from
the different series of experiments published in 1843, varied widely
from each other. The lowest limit was 587, and the highest 1,026
foot-pounds, for 1 degree Fahr. of temperature.
One noteworthy result of his enquiries, which was pointed out at the
time by Mr. Joule, had reference to the exceedingly small fraction of
the heat actually converted into useful effect in the steam-engine.
The thoughts of the celebrated Julius Robert Mayer, who was then
engaged in Germany upon the same question, had moved independently in
the same groove; but to his labours due reference will be made on a
future occasion. [Footnote: See the next Fragment.] In the memoir now
referred to, Mr. Joule also announced that he had proved heat to be
evolved during the passage of water through narrow tubes; and he
deduced from these experiments an equivalent of 770 foot-pounds, a
figure remarkably near the one now accepted. A detached statement
regarding the origin and convertibility of animal heat strikingly
illustrates the penetration of Mr. Joule, and his mastery of
principles, at the period now referred to. A friend had mentioned to
him Haller's hypothesis, that animal heat might arise from the
friction of the blood in the veins and arteries. 'It is
unquestionable,' writes Mr. Joule,' that heat is produced by such
friction; but it must be understood that the mechanical force expended
in the friction is a part of the force of affinity which causes the
venous blood to unite with oxygen, so that the whole heat of the
system must still be referred to the chemical changes. But if the
animal were engaged in turning a piece of machinery, or in ascending a
mountain, I apprehend that in proportion to the muscular effort put
forth for the purpose, a _diminution_ of the heat evolved in the system
by a given chemical action would be experienced.' The italics in this
memorable passage, written, it is to be remembered, in 1843, are Mr.
Joule's own.
The concluding paragraph of this British Association paper equally
illustrates his insight and precision, regarding the nature of
chemical and latent heat. 'I had,' he writes, 'endeavoured to prove
that when two atoms combine together, the heat evolved is exactly that
which would have been evolved by the electrical current due to the
chemical action taking place, and is therefore proportional to the
intensity of the chemical force causing the atoms to combine. I now
venture to state more explicitly, that it is not precisely the
attraction of affinity, but rather the mechanical force expended by
the atoms in falling towards one another, which determines the
intensity of the current, and, consequently, the quantity of heat
evolved; so that we have a simple hypothesis by which we may explain
why heat is evolved so freely in the combination of gases, and by
which indeed we may account "latent heat" as a mechanical power,
prepared for action, as a watch-spring is when wound up. Suppose, for
the sake of illustration, that 8 lbs. of oxygen and 1 lb. of hydrogen
were presented to one another in the gaseous state, and then exploded;
the heat evolved would be about 1 degree Fahr. in 60,000 lbs. of
water, indicating a mechanical force, expended in the combination,
equal to a weight of about 50,000,000 lbs. raised to the height of one
foot. Now if the oxygen and hydrogen could be presented to each other
in a liquid state, the heat of combination would be less than before,
because the atoms in combining would fall through less space.' No
words of mine are needed to point out the commanding grasp of
molecular physics, in their relation to the mechanical theory of heat,
implied by this statement.
Perfectly assured of the importance of the principle which his
experiments aimed at establishing, Mr. Joule did not rest content with
results presenting such discrepancies as those above referred to. He
resorted in 1844 to entirely new methods, and made elaborate
experiments on the thermal changes produced in air during its
expansion: firstly, against a pressure, and therefore performing work;
secondly, against no pressure, and therefore performing no work. He
thus established anew the relation between the heat consumed and the
work done. From five different series of experiments he deduced five
different mechanical equivalents, the agreement between them being far
greater than that attained in his first experiments. The mean of them
was 802 foot-pounds. From experiments with water agitated by a
paddle-wheel, he deduced, in 1845, an equivalent of 890 foot-pounds.
In 1847 he again operated upon water and sperm-oil, agitated them by a
paddle-wheel, determined their elevation of temperature, and the
mechanical power which produced it. From the one he derived an
equivalent of 781.6 foot-pounds; from the other an equivalent of 782.1
foot-pounds. The mean of these two very close determinations is 781.8
foot-pounds.
By this time the labours of the previous ten years had made Mr. Joule
completely master of the conditions essential to accuracy and success.
Bringing his ripened experience to bear upon the subject, he executed
in 1849 a series of 40 experiments on the friction of water, 50
experiments on the friction of mercury, and 20 experiments on the
friction of plates of cast-iron. He deduced from these experiments
our present mechanical equivalent of heat, justly recognised all over
the world as 'Joule's equivalent.'
There are labours so great and so pregnant in consequences, that they
are most highly praised when they are most simply stated. Such are
the labours of Mr. Joule. They constitute the experimental foundation
of a principle of incalculable moment, not only to the practice, but
still more to the philosophy of Science. Since the days of Newton,
nothing more important than the theory, of which Mr. Joule is the
experimental demonstrator, has been enunciated.
I have omitted all reference to the numerous minor papers with which
Mr. Joule has enriched scientific literature. Nor have I alluded to
the important investigations which he has conducted jointly with Sir
William Thomson. But sufficient, I think, has been here said to show
that, in conferring upon Mr. Joule the highest honour of the Royal
Society, the Council paid to genius not only a well-won tribute, but
one which had been fairly earned twenty years previously. [Footnote:
Lord Beaconsfield has recently honoured himself and England by
bestowing an annual pension of 200 pounds on Dr. Joule.]
********************
XX. THE COPLEY MEDALIST OF 1871.
DR. JULIUS ROBERT MAYER was educated for D the medical profession. In
the summer of 1840, as he himself informs us, he was at Java, and
there observed that the venous blood of some of his patients had a
singularly bright red colour. The observation riveted his attention;
he reasoned upon it, and came to the conclusion that the brightness of
the colour was due to the fact that a less amount of oxidation
sufficed to keep up the temperature of the body in a hot climate than
in a cold one. The darkness of the venous blood he regarded as the
visible sign of the energy of the oxidation.
It would be trivial to remark that accidents such as this, appealing
to minds prepared for them, have often led to great discoveries.
Mayer's attention was thereby drawn to the whole question of animal
heat. Lavoisier had ascribed this heat to the oxidation of the food.
'One great principle,' says Mayer, 'of the physiological theory of
combustion, is that under all circumstances the same amount of fuel
yields, by its perfect combustion, the same amount of heat; that this
law holds good even for vital processes; and that hence the living
body, notwithstanding all its enigmas and wonders, is incompetent to
generate heat out of nothing.'
But beyond the power of generating internal heat, the animal organism
can also generate heat outside of itself. A blacksmith, for example,
by hammering can heat a nail, and a savage by friction can warm wood
to its point of ignition. Now, unless we give up the physiological
axiom that the living body cannot create heat out of nothing, 'we are
driven,' says Mayer, 'to the conclusion that it is the total heat
generated within and without that is to be regarded as the true
calorific effect of the matter oxidised in the body.'
From this, again, he inferred that the heat generated externally must
stand in a fixed relation to the work expended in its production. For,
supposing the organic processes to remain the same; if it were
possible, by the mere alteration of the apparatus, to generate
different amounts of heat by the same amount of work, it would follow
that the oxidation of the same amount of material would sometimes
yield a less, sometimes a greater, quantity of heat. 'Hence,' says
Mayer, 'that a fixed relation subsists between heat and work, is a
postulate of the physiological theory of combustion.'
This is the simple and natural account, given subsequently by Mayer
himself, of the course of thought started by his observation in Java.
But the conviction once formed, that an unalterable relation subsists
between work and heat, it was: inevitable that Mayer should seek to
express it numerically. It was also inevitable that a mind like his,
having raised itself to clearness on this important point, should push
forward to consider the relationship of natural forces generally. At
the beginning of 1842 his work had made considerable progress; but he
had become physician to the town of Heilbronn, and the duties of his
profession limited the time which he could devote to purely scientific
enquiry. He thought it wise, therefore, to secure himself against
accident, and in the spring of 1842 wrote to Liebig, asking him to
publish in his 'Annalen' a brief preliminary notice of the work then
accomplished. Liebig did so, and Dr. Mayer's first paper is contained
in the May number of the 'Annalen' for 1842.
Mayer had reached his conclusions by reflecting on the complex
processes of the living body; but his first step in public was to
state definitely the physical principles on which his physiological
deductions were to rest. He begins, therefore, with the forces of
inorganic nature. He finds in the universe two systems of causes
which are not mutually convertible;--the different kinds of matter and
the different forms of force. The first quality of both he affirms to
be indestructibility. A force cannot become nothing, nor can it arise
from nothing. Forces are convertible but not destructible. In the
terminology of his time, he then gives clear expression to the ideas
of potential and dynamic energy, illustrating his point by a weight
resting upon the earth, suspended at a height above the earth, and
actually falling to the earth. He next fixes his attention on cases
where motion is apparently destroyed, without producing other motion;
on the shock of inelastic bodies, for example. Under what form does
the vanished motion maintain itself? Experiment alone, says Mayer,
can help us here. He warms water by stirring it; he refers to the
force expended in overcoming friction. Motion in both cases
disappears; but heat is generated, and the quantity generated is the
equivalent of the motion destroyed. 'Our locomotives,' he observes
with extraordinary sagacity, 'may be compared to distilling apparatus:
the heat beneath the boiler passes into the motion of the train, and
is again deposited as heat in the axles and wheels.
A numerical solution of the relation between heat and work was what
Mayer aimed at, and towards the end of his first paper he makes the
attempt. It was known that a definite amount of air, in rising one
degree in temperature, can take up two different amounts of heat. If
its volume be kept constant, it takes up one amount: if its pressure
be kept constant it takes up a different amount. These two amounts
are called the specific heat under constant volume and under constant
pressure. The ratio of the first to the second is as 1: 1.421. No
man, to my knowledge, prior to Dr. Mayer, penetrated the significance
of these two numbers. He first saw that the excess 0.421 was not, as
then universally supposed, heat actually lodged in the gas, but heat
which had been actually consumed by the gas in expanding against
pressure. The amount of work here performed was accurately known, the
amount of heat consumed was also accurately known, and from these data
Mayer determined the mechanical equivalent of heat. Even in this
first paper he is able to direct attention to the enormous discrepancy
between the theoretic power of the fuel consumed in steam-engines, and
their useful effect.
Though this paper contains but the germ of his further labours, I
think it may be safely assumed that, as regards the mechanical theory
of heat, this obscure Heilbronn physician, in the year 1842, was in
advance of all the scientific men of the time.
Having, by the publication of this paper, secured himself against what
he calls 'Eventualitaeten,' he devoted every hour of his spare time
to his studies, and in 1845 published a memoir which far transcends
his first one in weight and fulness, and, indeed, marks an epoch in
the history of science. The title of Mayer's first paper was,
'Remarks on the Forces of Inorganic Nature.' The title of his second
great essay was, 'Organic Motion in its Connection with Nutrition.' In
it he expands and illustrates the physical principles laid down in his
first brief paper.
He goes fully through the calculation of the mechanical equivalent of
heat. He calculates the performances of steam-engines, and finds that
100 lbs. of coal, in a good working engine, produce only the same
amount of heat as 95 lbs. in an unworking one; the 5 missing lbs.
having been converted into work. He determines the useful effect of
gunpowder, and finds nine per cent. of the force of the consumed
charcoal invested on the moving ball. He records observations on the
heat generated in water agitated by the pulping engine of a paper
manufactory, and calculates the equivalent of that heat in
horse-power. He compares chemical combination with mechanical
combination--the union of atoms with the union of falling bodies with
the earth. He calculates the velocity with which a body starting at
an infinite distance would strike the earth's surface, and finds that
the heat generated by its collision would raise an equal weight of
water 17,356' C. in temperature. He then determines the thermal
effect which would be produced by the earth itself falling into the
sun. So that here, in 1845, we have the germ of that meteoric theory
of the sun's heat which Mayer developed with such extraordinary
ability three years afterwards. He also points to the almost
exclusive efficacy of the sun's heat in producing mechanical motions
upon the earth, winding up with the profound remark, that the heat
developed by friction in the wheels of our wind and water mills comes
from the sun in the form of vibratory motion; while the heat produced
by mills driven by tidal action is generated at the expense of the
earth's axial rotation.
Having thus, with firm step, passed through the powers of inorganic
nature, his next object is to bring his principles to bear upon the
phenomena of vegetable and animal life. Wood and coal can burn;
whence come their heat, and the work producible by that heat? From
the immeasurable reservoir of the sun. Nature has proposed to herself
the task of storing up the light which streams earthward from the sun,
and of casting into a permanent form the most fugitive of all powers.
To this end she has overspread the earth with organisms which, while
living, take in the solar light, and by its consumption generate
forces of another kind. These organisms are plants. The vegetable
world, indeed, constitutes the instrument whereby the wave-motion of
the sun is changed into the rigid form of chemical tension, and thus
prepared for future use. With this prevision, as shall subsequently
be shown, the existence of the human race itself is inseparably
connected. It is to be observed that Mayer's utterances are far from
being anticipated by vague statements regarding the 'stimulus' of
light, or regarding coal as 'bottled sunlight.' He first saw the full
meaning of De Saussure's observation as to the reducing power of the
solar rays, and gave that observation its proper place in the doctrine
of conservation. In the leaves of a tree, the carbon and oxygen of
carbonic acid, and the hydrogen and oxygen of water, are forced
asunder at the expense of the sun, and the amount of power thus
sacrificed is accurately restored by the combustion of the tree. The
heat and work potential in our coal strata are so much strength
withdrawn from the sun of former ages. Mayer lays the axe to the root
of the notions regarding 'vital force' which were prevalent when he
wrote. With the plain fact before us that in the absence of the solar
rays plants cannot perform the work of reduction, or generate chemical
tensions, it is, he contends, incredible that these tensions should be
caused by the mystic play of the vital force. Such an hypothesis
would cut off all investigation; it would land us in a chaos of
unbridled phantasy.
'I count,' he says, 'therefore, upon your agreement with me when I
state, as an axiomatic truth, that during vital processes the
conversion only, and never the creation of matter or force occurs.'
Having cleared his way through the vegetable world, as he had
previously done through inorganic nature, Mayer passes on to the other
organic kingdom. The physical forces collected by plants become the
property of animals. Animals consume vegetables, and cause them to
reunite with the atmospheric oxygen. Animal heat is thus produced;
and not only animal heat, but animal motion. There is no
indistinctness about Mayer here; he grasps his subject in all its
details, and reduces to figures the concomitants of muscular action. A
bowler who imparts to an 8-lb. ball a velocity of 30 feet, consumes
in the act one tenth of a grain of carbon. A man weighing 150 lbs,
who lifts his own body to a height of 8 feet, consumes in the act 1
grain of carbon. In climbing a mountain 10,000 feet high, the
consumption of the same man would be 2 oz. 4 drs. 50 grs. of carbon.
Boussingault had determined experimentally the addition to be made to
the food of horses when actively working, and Liebig had determined
the addition to be made to the food of men. Employing the mechanical
equivalent of heat, which he had previously calculated, Mayer proves
the additional food to be amply sufficient to cover the increased
oxidation.
But he does not content himself with showing, in a general way, that
the human body burns according to definite laws, when it performs
mechanical work. He seeks to determine the particular portion of the
body consumed, and in doing so executes some noteworthy calculations.
The muscles of a labourer 150 lbs. in weight weigh 64 lbs; but when
perfectly desiccated they fall to 15 lbs. Were the oxidation
corresponding to that labourer's work exerted on the muscles alone,
they would be utterly consumed in 80 days. The heart furnishes a
still more striking example. Were the oxidation necessary to sustain
the heart's action exerted upon its own tissue, it would be utterly
consumed in 8 days. And if we confine our attention to the two
ventricles, their action would be sufficient to consume the associated
muscular tissue in 3.5 days. Here, in his own words, emphasised in
his own way, is Mayer's pregnant conclusion from these calculations:
'The muscle is only the apparatus by means of which the conversion of
the force is effected; but it is not the substance consumed in the
production of the mechanical effect.' He calls the blood 'the oil of
the lamp of life;' it is the slow-burning fluid whose chemical force,
in the furnace of the capillaries, is sacrificed to produce animal
motion. This was Mayer's conclusion twenty-six years ago. It was in
complete opposition to the scientific conclusions of his time; but
eminent investigators have since amply verified it.
Thus, in baldest outline, I have sought to give some notion of the
first half of this marvellous essay. The second half is so
exclusively physiological that I do not wish to meddle with it. I
will only add the illustration employed by Mayer to explain the action
of the nerves upon the muscles. As an engineer, by the motion of his
finger in opening a valve or loosing a detent, can liberate an amount
of mechanical motion almost infinite compared with its exciting cause,
so the nerves, acting upon the muscles, can unlock an amount of
activity, wholly out of proportion to the work done by the nerves
themselves.
As regards these questions of weightiest import to the science of
physiology, Dr. Mayer, in 1845, was assuredly far in advance of all
living men.