impossible it is to determine the effect of temperature pure and
simple on the transmission of radiant heat if different sources of
heat be employed. Throughout such an examination the same oscillating
atoms ought to be retained. This is done by beating a platinum spiral
by an electric current, the temperature meanwhile varying between the
widest possible limits. Their comparative opacity to the ultra-red
rays shows the general accord of the oscillating periods of the
vapours referred to at the commencement of this lecture with those of
the ultra-red undulations. Hence, by gradually heating a platinum wire
from darkness up to whiteness, we ought gradually to augment the
discord between it and these vapours, and thus augment the
transmission. Experiment entirely confirms this conclusion. Formic
nether, for example, absorbs 45 per cent. of the radiation from a
platinum spiral heated to barely visible redness; 32 per cent. of the
radiation from the same spiral at a red heat; 26 per cent. of the
radiation from a white-hot spiral, and only 21 per cent. when the
spiral is brought near its point of fusion. Remarkable cases of
inversion as to transparency also occur. For barely visible redness
formic aether is more opaque than sulphuric; for a bright red heat
both are equally transparent; while, for a white heat, and still more
for a higher temperature, sulphuric aether is more opaque than formic.
This result gives us a clear view of the relationship of the two
substances to the luminiferous aether. As we introduce waves of
shorter period the sulphuric aether augments most rapidly in opacity;
that is to say, its accord with the shorter waves is greater than that
of the formic. Hence we may infer that the atoms of formic aether
oscillate, on the whole, more slowly than those of sulphuric aether.
When the source of heat is a Leslie's cube coated with lampblack and
filled with boiling water, the opacity of formic aether in comparison
with sulphuric is very decided. With this source also the positions of
chloroform and iodide of methyl are inverted. For a white-hot spiral,
the absorption of chloroform vapour being 10 per cent, that of iodide
of methyl is 16; with the blackened cube as source, the absorption by
chloroform is 22 per cent, while that by the iodide of methyl is only
19. This inversion is not the result of temperature merely; for when
a platinum wire, heated to the temperature of boiling water, is
employed as a source, the iodide continues to be the most powerful
absorber. All the experiments hitherto made go to prove that from
heated lampblack an emission takes place which synchronises in an
especial manner with chloroform. For the cube at 100' C, coated with
lampblack, the absorption by chloroform is more than three times that
by bisulphide of carbon; for the radiation from the most luminous
portion of a gas-flame the absorption by chloroform is also
considerably in excess of that by bisulphide of carbon; while, for the
flame of a Bunsen's burner, from which the incandescent carbon
particles are removed by the free admixture of air, the absorption by
bisulphide of carbon is nearly twice that by chloroform. _The removal
of the carbon particles more than doubles the relative transparency of
the chloroform_. Testing, moreover, the radiation from various parts
of the same flame, it was found that for the blue base of the flame
the bisulphide of carbon was most opaque, while for all other parts of
the flame the chloroform was most opaque. For the radiation from a
very small gas flame, consisting of a blue base and a small white tip,
the bisulphide was also most opaque, and its opacity very decidedly
exceeded that of the chloroform when the source of heat was the flame
of bisulphide of carbon. Comparing the radiation from a Leslie's cube
coated with isinglass with that from a similar cube coated with
lampblack, at the common temperature of 100°C, it was found that, out
of eleven vapours, all but one absorbed the radiation from the
isinglass most powerfully; the single exception was chloroform.
It is worthy of remark that whenever, through a change of source, the
position of a vapour as an absorber of radiant heat was altered, the
position of the liquid from which the vapour was derived underwent a
similar change.
It is still a point of difference between eminent investigators
whether radiant heat, up to a temperature of 100°C, is monochromatic
or not. Some affirm this; some deny it. A long series of experiments
enables me to state that probably no two substances at a temperature
of 100°C. emit heat of the same quality. The heat emitted by
isinglass, for example, is different from that emitted by lampblack,
and the heat emitted by cloth, or paper, differs from both. It is
also a subject of discussion whether rock-salt is equally diathermic
to all kinds of calorific rays; the differences affirmed to exist by
some investigators being ascribed by others to differences of
incidence from the various sources employed. MM. de la Provostaye
and Desains maintain the former view, Melloni and M. Knoblauch
maintain the latter. I tested this point without changing anything
but the temperature of the source; its size, distance, and
surroundings remaining the same. The experiments proved rock-salt to
be coloured thermally. It is more opaque, for example, to the
radiation from a barely visible spiral than to that from a white-hot
one.
In regard to the relation of radiation to conduction, if we define
radiation, internal as well as external, as the communication of
motion from the vibrating atoms to the aether, we may, I think, by
fair theoretic reasoning, reach the conclusion that the best radiators
ought to prove the worst conductors. A broad consideration of the
subject shows at once the general harmony of this conclusion with
observed facts. Organic substances are all excellent radiators; they
are also extremely bad conductors. The moment we pass from the metals
to their compounds we pass from good conductors to bad ones, and from
bad radiators to good ones. Water, among liquids, is probably the
worst conductor; it is the best radiator. Silver, among solids, is
the best conductor; it is the worst radiator. The excellent
researches of MM. de la Provostaye and Desains furnish a striking
illustration of what I am inclined to regard as a natural law--that
those atoms which transfer the greatest amount of motion to the
aether, or, in other words, radiate most powerfully, are the least
competent to communicate motion to each other, or, in other words, to
propagate by conduction readily.
********************
XVIII. LIFE, AND LETTERS OF FARADAY.
1870.
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 ran 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 apprenticeship 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 manhood, 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 member of the
Society of Friends, who, with a forecast of his correspondent'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 Abbot. To
a proposition that no new enquiry 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 almost mechanical in his
self-restraint. In another nature it would have hardened into mere
'correctness' of conduct; but his overflowing affections prevented
this in his case. The habit of self control 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 affections and lusts of him who harbours it,
but is often a cause of disturbed digestion to his friends.
About three months after his engagement with De la 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 recognised the
merit of his correspondent, kept his eye upon him, and, when occasion
offered, drove to his door and sent in a letter, offering him the post
of assistant in the laboratory of the Royal Institution. He was
engaged March 1, 1813, 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 valuable.' Faraday
derived great profit from this little association. In the laboratory
he had a discipline sturdier still. Both Davy and himself were at
this time frequently 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 receiver 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 forehead 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 intellectual power, made
Faraday 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 organ of vision. Late in life I have heard him say
that he could never 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 observes, 'should appear easy and
collected, undaunted and unconcerned:' still 'his whole behaviour
should evince respect for his audience.' These recommendations were
afterwards 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 unintelligible, 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 vigour which, for the time being, they could neither
share nor comprehend.
In October 1813 he quitted England with Sir Humphry and Lady Davy.
During his 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 'Bibliothéque Britannique,' had been the first to make
the English chemist's labours known abroad. He welcomed Davy to his
country residence in 1814. Both were sportsmen, and they often went
out shooting together. On these occasions Faraday charged Davy's gun
while De la Rive charged his own. Once the Genevese philosopher found
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 enquiry De la Rive was somewhat shocked
to find that the _soi-disant domestique_ was really _préparateur_ in the
laboratory 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. Rumour states
that a dinner in honour 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 _garcon de
laboratoire_. [Footnote: 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 friendship 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 condensed abstract. It was at the desire
of Dr. Bence Jones that I asked him to do so. The rumour of a banquet
at Geneva illustrates the tendency to substitute for the youth of 1814
the Faraday of later years.]
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 anything more adverse to its accuracy than fixity of
opinion.' Not that he was wafted about by every wind of doctrine; but
that he united flexibility with his strength. In striking contrast
with this intellectual expansiveness was 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, and its earnestness.' Abbott
and he sometimes swerved into wordplay 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 that he might 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. Everything 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,' he
writes to her in a subsequent letter, 'to convey 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 afterwards, 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 known 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 prevalent belief, is also reproduced in an
excellent article in the March number of 'Framer'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 afterwards the
acute mind of Wollaston perceived that a wire carrying a current ought
to rotate round its own axis under the influence of a magnetic pole.
In 1821 'he tried, but failed, to realise this result in the
laboratory of the Royal Institution. Faraday was not present at the
moment, but he came in immediately afterwards and heard the
conversation of Wollaston and Davy about the experiment. He had also
heard a rumour 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 while thus instructing himself that he
succeeded in causing a wire, carrying an electric current, to rotate
round a magnetic pole. This was not the result sought by Wollaston,
but it was closely related to that result.
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 preceded 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 possessed. Rumour and fact had connected the name of Wollaston
with these supposed interactions between magnets and currents. When,
therefore, Faraday in October published his successful experiment,
without any allusion to Wollaston, general, though really ungrounded,
criticism followed. I say ungrounded because, firstly, Faraday's
experiment 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 authorised 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 whispers to me, are, I suspect, spoken
aloud among scientific 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 personally.
There was a certain vehemence in his desire to do this. He saw
Wollaston, he saw Davy, he saw Warburton; and I am inclined to think
that it was the irresistible candour and truth of character which
these viva voce defences 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 analysed 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 decomposition was proved by
Faraday to be chlorine liquefied by its own pressure. On the day of
its discovery he communicated this result to Dr. Paris. Davy, on
being informed of it, instantly liquefied another gas in the same way.
Having struck thus into Faraday's enquiry, 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
estrangement 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 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 honourable 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 persuaded, to be
ascribed.