mechanical theory of heat in the most fearless and precise manner to
vital processes. He also embraced the other natural agents in his
chain of conservation. In 1853 Mr. Waterston proposed, independently,
the meteoric theory of the sun's heat, and in 1854 Professor William
Thomson applied his admirable mathematical powers to the development
of the theory; but six years previously the subject had been handled
in a masterly manner by Mayer, and all that I have said about it has
been derived from him. When we consider the circumstances of Mayer's
life, and the period at which he wrote, we cannot fail to be struck
with astonishment at what he has accomplished. Here was a man of
genius working in silence, animated solely by a love of his subject,
and arriving at the most important results in advance of those whose
lives were entirely devoted to Natural Philosophy. It was the
accident of bleeding a feverish patient at Java in 1840 that led Mayer
to speculate on these subjects. He noticed that the venous blood in
the tropics was of a brighter red than in colder latitudes, and his
reasoning on this fact led him into the laboratory of natural forces,
where he has worked with such signal ability and success. Well, you
will desire to know what has become of this man. His mind, it is
alleged, gave way; it is said he became insane, and he was certainly
sent to a lunatic asylum. In a biographical dictionary of his country
it is stated that he died there, but this is incorrect. He recovered;
and, I believe, is at this moment a cultivator of vineyards in
Heilbronn.
====================
June 20, 1862.
While preparing for publication my last course of lectures on Heat, I
wished to make myself acquainted with all that Dr. Mayer had done in
connection with this subject. I accordingly wrote to two gentlemen
who above all others seemed likely to give me the information which I
needed. [Footnote: Helmholtz and Clausius.] Both of them are Germans,
and both particularly distinguished in connection with the Dynamical
Theory of Heat. Each of them kindly furnished me with the list of
Mayer's publications, and one of them [Clausius] was so friendly as to
order them from a bookseller, and to send them to me. This friend, in
his reply to my first letter regarding Mayer, stated his belief that I
should not find anything very important in Mayer's writings; but
before forwarding the memoirs to me he read them himself. His letter
accompanying them contains the following words: 'I must here retract
the statement in my last letter, that you would not find much matter
of importance in Mayer's writings: I am astonished at the multitude of
beautiful and correct thoughts which they contain;' and he goes on to
point out various important subjects, in the treatment of which Mayer
had anticipated other eminent writers. My other friend, in whose own
publications the name of Mayer repeatedly occurs, and whose papers
containing these references were translated some years ago by myself,
was, on the 10th of last month, unacquainted with the thoughtful and
beautiful essay of Mayer's, entitled 'Beitraege zur Dynamik des
Himmels,' and in 1854, when Professor William Thomson developed in so
striking a manner the meteoric theory of the sun's heat, he was
certainly not aware of the existence of that essay, though from a
recent article in 'Macmillan's Magazine' I infer that he is now aware
of it. Mayer's physiological writings have been referred to by
physiologists--by Dr. Carpenter, for example--in terms of honouring
recognition. We have hitherto, indeed, obtained fragmentary glimpses
of the man, partly from physicists and partly from physiologists; but
his total merit has never yet been recognised as it assuredly would
have been had he chosen a happier mode of publication. I do not think
a greater disservice could be done to a man of science, than to
overstate his claims: such overstatement is sure to recoil to the
disadvantage of him in whose interest it is made. But when Mayer's
opportunities, achievements, and fate are taken into account, I do not
think that I shall be deeply blamed for attempting to place him in
that honourable position, which I believe to be his due.
Here, however, are the titles of Mayer's papers, the perusal of which
will correct any error of judgment into which I may have fallen
regarding their author. 'Bemerkungen ueber die Kraefte der unbelebten
Natur,' Liebig's 'Annalen,' 1842, Vol. 42, p. 231; 'Die Organische
Bewegung in ihrem Zusammenhange mit dem Stoffwechsel,' Heilbronn,
1845; 'Beitraege zur Dynamik des Himmels,' Heilbronn, 1848;
'Bemerkungen ueber das Mechanische Equivalent der Waerme,' Heilbronn,
1851.
====================
IN MEMORIAM.--Dr. Julius Robert Mayer died at Heilbronn on March 20,
1878, aged 63 years. It gives me pleasure to reflect that the great
positionwhich he will for ever occupy in the annals of science was
first virtually assigned to him in the foregoing discourse. He was
subsequently hosen by acclamation a member of the French Academy of
Sciences; and he received from the Royal Society the Copley medal-its
Highest reward. [Footnote: See 'The Copley Medalist for 1871,' p.479.]
====================
November 1878.
At the meeting of the British Association at Glasgow in 1876--that is
to say, more than fourteen years after its delivery and
publication--the foregoing lecture was made the cloak for an unseemly
personal attack by Professor Tait. The anger which found this
uncourteous vent dates from 1863, when it fell to my lot to maintain,
in opposition to him and a more eminent colleague, the position which
in 1862 I had assigned to Dr. Mayer. [Footnote: See 'Philosophical
Magazine' for this and the succeeding years.] In those days Professor
Tait denied to Mayer all originality, and he has since, I regret to say,
never missed an opportunity, however small, of carping at Mayer's
claims. The action of the Academy of Sciences and of the Royal Society
summarily disposes of this detraction, to which its object, during his
lifetime, never vouchsafed either remonstrance or reply.
Some time ago Professor Tait published a volume of lectures entitled
'Recent Advances in Physical Science,' which I have reason to know has
evoked an amount of censure far beyond that hitherto publicly
expressed. Many of the best heads on the continent of Europe agree in
their rejection and condemnation of the historic portions of this
book. In March last it was subjected to a brief but pungent critique
by Du Bois-Reymond, the celebrated Perpetual Secretary of the Academy
of Sciences in Berlin. Du Bois-Reymond's address was on 'National
Feeling,' and his critique is thus wound up: 'The author of the
"Lectures" is not, perhaps, sufficiently well acquainted with the
history on which he professes to throw light, and on the later phases
of which he passes so unreserved (schroff) a judgment. He thus
exposes himself to the suspicion--which, unhappily, is not weakened by
his other writings--that the fiery Celtic blood of his country
occasionally runs away with him, converting him for the time into a
scientific Chauvin. Scientific Chauvinism,' adds the learned
secretary, 'from which German investigators have hitherto kept free,
is more reprehensible (gehaessig) than political Chauvinism, inasmuch
as self-control (_sittliche Haltung_) is more to be expected from men of
science, than from the politically excited mass.' [Footnote: Festrede,
delivered before the Academy of Sciences of Berlin, in celebration of
the birthday of the Emperor and King, March 28, 1878.]
In the case before this 'expectation' would, I fear, be doomed to
disappointment. But Du Bois-Reymond and his countrymen must not
accept the writings of Professor Tait as representative of the thought
of England. Surely no nation in the world has more effectually shaken
itself free from scientific Chauvinism. From the day that Davy, on
presenting the Copley medal to Arago, scornfully brushed aside that
spurious patriotism which would run national boundaries through the
free domain of science, chivalry towards foreigners has been a guiding
principle with the Royal Society.
On the more private amenities indulged in by Professor Tait, I do not
consider it necessary to say a word.
********************
XVII. CONTRIBUTIONS TO MOLECULAR PHYSICS.
[Footnote: A discourse delivered at the Royal Institution, March 18,
1864--supplementing, though of prior date, the Rede Lecture on
Radiation.]
HAVING on previous occasions dwelt upon the enormous differences which
exist among gaseous bodies both as regards their power of absorbing
and emitting radiant heat, I have now to consider the effect of a
change of aggregation. When a gas is condensed to a liquid, or a
liquid congealed to a solid, the molecules coalesce, and grapple with
each other by forces which are insensible as long as the gaseous state
is maintained. But, even in the solid and liquid conditions, the
luminiferous aether still surrounds the molecules: hence, if the acts
of radiation and absorption depend on them individually, regardless of
their state of aggregation, the change from the gaseous to the liquid
state ought not materially to affect the radiant and absorbent power.
If, on the contrary, the mutual entanglement of the molecular by the
force of cohesion be of paramount influence, then we may expect that
liquids will exhibit a deportment towards radiant heat altogether
different from that of the vapours from which they are derived.
The first part of an enquiry conducted in 1863-64 was devoted to an
exhaustive examination of this question. Twelve different liquids
were employed, and five different layers of each, varying in thickness
from 0.02 of an inch to 0.27 of an inch. The liquids were enclosed,
not in glass vessels, which would have materially modified the
incident heat, but between plates of transparent rock-salt, which only
slightly affected the radiation. The source of heat throughout these
comparative experiments consisted of a platinum wire, raised to
incandescence by an electric current of unvarying strength. The
quantities of radiant heat absorbed and transmitted by each of the
liquids at the respective thicknesses were first determined. The
vapours of these liquids were subsequently examined, the quantities of
vapour employed being rendered proportional to the quantities of
liquid previously traversed by the radiant heat. The result was that,
for heat from the same source, the order of absorption of liquids and
of their vapours proved absolutely the same. There is no known
exception to this law; so that, to determine the position of a vapour
as an absorber or a radiator, it is only necessary to determine the
position of its liquid.
This result proves that the state of aggregation, as far at all events
as the liquid stage is concerned, is of altogether subordinate
moment--a conclusion which will probably prove to be of cardinal
importance in molecular physics. On one important and contested point
it has a special bearing. If the position of a liquid as an absorber
and radiator determine that of its vapour, the position of water fixes
that of aqueous vapour. Water has been compared with other liquids in
a multitude of experiments, and it has been found, both as a radiant
and as an absorbent, to transcend them all. Thus, for example, a
layer of bisulphide of carbon 0.02 of an inch in thickness absorbs 6
per cent, and allows 94 per cent of the radiation from the red-hot
platinum spiral to pass through it; benzol absorbs 43 and transmits 57
per cent. of the same radiation; alcohol absorbs 67 and transmits 33
per cent, and alcohol, as an absorber of radiant heat, stands at the
head of all liquids except one. The exception is water. A layer of
this substance, of the thickness above given, absorbs 81 per cent, and
permits only 19 per cent. of the radiation to pass through it. Had no
single experiment ever been made upon the vapour of water, its
vigorous action upon radiant heat might be inferred from the
deportment of the liquid.
The relation of absorption and radiation to the chemical constitution
of the radiating and absorbing substances was next briefly considered.
For the first six substances in the list of liquids examined, the
radiant and absorbent powers augment as the number of atoms in the
compound molecule augments. Thus, bisulphide of carbon has 3 atoms,
chloroform 5, iodide of ethyl 8, benzol 12, and amylene 15 atoms in
their respective molecules. The order of their power as radiants and
absorbents is that here indicated, bisulphide of carbon being the
feeblest, and amylene the strongest of the six. Alcohol, however,
excels benzol as an absorber, though it has but 9 atoms in its
molecule; but, on the other hand, its molecule is rendered more
complex by the introduction of a new element. Benzol contains carbon
and hydrogen, while alcohol contains carbon, hydrogen and oxygen.
Thus, not only does atomic _multitude_ come into play in absorption and
radiation--atomic _complexity_ must also be taken into account. I would
recommend to the particular attention of chemists the molecule of
water; the deportment of this substance towards radiant heat being
perfectly anomalous, if the chemical formula at present ascribed to it
be correct.
Sir William Herschel made the important discovery that, beyond the
limits of the red end of the solar spectrum, rays of high heating
power exist which are incompetent to excite vision. The discovery is
capable of extension. Dissolving iodine in the bisulphide of carbon,
a solution is obtained which entirely intercepts the light of the most
brilliant flames, while to the ultra-red rays of such flames the same
iodine is found to be perfectly diathermic. The transparent
bisulphide, which is highly pervious to invisible heat, exercises on
it the same absorption as the perfectly opaque solution. A hollow
prism filled with the opaque liquid being placed in the path of the
beam from an electric lamp, the light-spectrum is completely
intercepted, but the heat spectrum may be received upon a screen and
there examined. Falling upon a thermo-electric pile, its invisible
presence is shown by the prompt deflection of even a coarse
galvanometer.
What, then, is the physical meaning of opacity and transparency as
regards light and radiant heat? The visible rays of the spectrum
differ from the invisible ones simply in period. The sensation of
light is excited by waves of aether shorter and more quickly recurrent
than the non-visual waves which fall beyond 'the extreme red. But why
should iodine stop the former and allow the latter to pass? The
answer to this question no doubt is, that the intercepted waves are
those whose periods of recurrence coincide with the periods of
oscillation possible to the atoms of the dissolved iodine. The
elastic forces which keep these atoms apart compel them to vibrate in
definite periods, and, when these periods synchronise with those of
the aethereal waves, the latter are absorbed. Briefly defined, then,
transparency in liquids, as well as in gases, is synonymous with
discord, while opacity is synonymous with accord, between the periods
of the waves of aether and those of the molecules on which they
impinge.
According to this view transparent and colourless substances owe their
transparency to the dissonance existing between the oscillating
periods of their atoms and those of the waves of the whole visible
spectrum. From the prevalence of transparency in compound bodies, the
general discord of the vibrating periods of their atoms with the
light-giving waves of the spectrum, may be inferred; while their
synchronism with the ultra-red periods is to be inferred from their
opacity to the ultra-red rays. Water illustrates this in a most
striking manner. It is highly transparent to the luminous rays, which
proves that its atoms do not readily oscillate in the periods which
excite vision. It is highly opaque to the ultra-red undulations,
which proves the synchronism of its vibrating periods with those of
the longer waves.
If, then, to the radiation from any source water shows itself
eminently or perfectly opaque, we may infer that the atoms whence the
radiation emanates oscillate in ultra-red periods. Let us apply this
test to the radiation from a flame of hydrogen. This flame consists
mainly of incandescent aqueous vapour, the temperature of which, as
calculated by Bunsen, is 3259°C, so that, if the penetrative power of
radiant heat, as generally supposed, augment with the temperature of
its source, we may expect the radiation from this flame to be
copiously transmitted by water. While, however, a layer of the
bisulphide of carbon 0.07 of an inch in thickness transmits 72 per
cent. of the incident radiation, and while every other liquid
examined transmits more or less of the heat, a layer of water of the
above thickness is entirely opaque to the radiation from the hydrogen
flame. Thus we establish accord between the periods of the atoms of
cold water and those of aqueous vapour at a temperature of 3259°C. But
the periods of water have already been proved to be ultra red--hence
those of the hydrogen flame must be sensibly ultra-red also. The
absorption by dry air of the heat emitted by a platinum spiral raised
to incandescence by electricity is insensible, while that by the
ordinary undried air is 6 per cent. Substituting for the platinum
spiral a hydrogen flame, the absorption by dry air still remains
insensible, while that of the undried air rises to 20 per cent. of
the entire radiation. The temperature of the hydrogen flame is, as
stated, 3259°C; that of the aqueous vapour of the air 20°C. Suppose,
then, the temperature of aqueous vapour to rise from 20°C. to 3259°C,
we must conclude that the augmentation of temperature is applied to an
increase of amplitude or width of swing, and not to the introduction
of quicker periods into the radiation.
The part played by aqueous vapour in the economy of nature is far more
wonderful than has been hitherto supposed. To nourish the vegetation
of the earth the actinic and luminous rays of the sun must penetrate
our atmosphere; and to such rays aqueous vapour is eminently
transparent. The violet and the ultra-violet rays pass through it
with freedom. To protect vegetation from destructive chills the
terrestrial rays must be checked in their transit towards stellar
space; and this is accomplished by the aqueous vapour diffused through
the air. This substance is the great moderator of the earth's
temperature, bringing its extremes into proximity, and obviating
contrasts between day and night which would render life insupportable.
But we can advance beyond this general statement, now that we know the
radiation from aqueous vapour is intercepted, in a special degree, by
water, and, reciprocally, the radiation from water by aqueous vapour;
for it follows from this that the very act of nocturnal refrigeration
which produces the condensation of aqueous vapour at the surface of
the earth--giving, as it were, a varnish of water to that
surface--imparts to terrestrial radiation that particular character
which disqualifies it from passing through the earth's atmosphere and
losing itself in space.
And here we come to a question in molecular physics which at the
present moment occupies attention. By allowing the violet and
ultra-violet rays of the spectrum to fall upon sulphate of quinine and
other substances Professor Stokes has changed the periods of those
rays. Attempts have been made to produce a similar result at the
other end of the spectrum--to convert the ultra-red periods into
periods competent to excite vision--but hitherto without success. Such
a change of period, I agree with Dr. Miller in believing, occurs when
the limelight is produced by an oxy-hydrogen flame. In this common
experiment there is an actual breaking up of long periods into short
ones--a true rendering of unvisual periods visual. The change of
refrangibility here effected differs from that of Professor Stokes;
firstly, by its being in the opposite direction--that is, from a lower
refrangibility to a higher; and, secondly, in the circumstance that
the lime is heated by the collision of the molecules of aqueous
vapour, before their heat has assumed the radiant form. But it cannot
be doubted that the same effect would be produced by radiant heat of
the same periods, provided the motion of the aether could be rendered
sufficiently intense. [Footnote: This was soon afterwards
accomplished. See the section on 'Transmutation of Rays'.] The
effect in principle is the same, whether we consider the lime to be
struck by a particle of aqueous vapour oscillating at a certain rate,
or by a particle of aether oscillating at the same rate.
By plunging a platinum wire into a hydrogen flame we cause it to glow,
and thus introduce shorter periods into the radiation. These, as
already stated, are in discord with the atomic vibrations of water;
hence we may infer that the transmission through water will be
rendered more copious by the introduction of the wire into the flame.
Experiment proves this conclusion to be true. Water, from being
opaque, opens a passage to 6 per cent. of the radiation from the
spiral. A thin plate of colourless glass, moreover, transmits 68 per
cent. of the radiation from the hydrogen flame; but when the flame
and spiral are employed, 78 per cent. of the heat is transmitted.
For an alcohol flame Knoblauch and Melloni found glass to be less
transparent than for the same flame with a platinum spiral immersed in
it; but Melloni afterwards showed that the result was not
general--that black glass and black mica were decidedly more
diathermic to the radiation from the pure alcohol flame. Melloni did
not explain this, but the reason is now obvious. The mica and glass
owe their blackness to the carbon diffused through them. This carbon,
as first proved by Melloni, is in some measure transparent to the
ultra-red rays, and I have myself succeeded in transmitting between 40
and 50 per cent. of the radiation from a hydrogen flame through a
layer of carbon which intercepted the light of an intensely brilliant
flame. The products of combustion of alcohol are carbonic acid and
aqueous vapour, the heat of which is almost wholly ultra-red. For
this radiation, then, the carbon is in a considerable degree
transparent, while for the radiation from the platinum spiral, it is
in a great measure opaque. The platinum wire, therefore, which
augmented the radiation through the pure glass, augmented the
absorption of the black glass and mica.
No more striking or instructive illustration of the influence of
coincidence could be adduced than that furnished by the radiation from
a carbonic oxide flame. Here the product of combustion is carbonic
acid; and on the radiation from this flame even the ordinary carbonic
acid of the atmosphere exerts a powerful effect. A quantity of the
gas, only one-thirtieth of an atmosphere in density, contained in a
polished brass tube four feet long, intercepts 50 per cent. of the
radiation from the carbonic oxide flame. For the heat emitted by
lampblack, olefiant gas is a far more powerful absorber than carbonic
acid; in fact, for such heat, with one exception, carbonic acid is the
most feeble absorber to be found among the compound gases. Moreover,
for the radiation from a hydrogen flame olefiant gas possesses twice
the absorbent power of carbonic acid, while for the radiation from the
carbonic oxide flame, at a common pressure of one inch of mercury, the
absorption by carbonic acid is more than twice that of olefiant gas.
Thus we establish the coincidence of period between carbonic acid at a
temperature of 20°C. and carbonic acid at a temperature of over
3000°C, the periods of oscillation of both the incandescent and the
cold gas belonging to the ultra-red portion of the spectrum.