SEQUEL TO THE EPOCH OF YOUNG AND FRESNEL. RECEPTION OF THE
UNDULATORY THEORY.
WHEN Young, in 1800, published his assertion of the Principle of
Interferences, as the true theory of optical phenomena, the
condition of England was not very favorable to a fair appreciation
of the value of the new opinion. The men of science were strongly
pre-occupied in favor of the doctrine of emission, not only from a
national interest in Newton's glory, and a natural reverence for his
authority, but also from deference towards the geometers of France,
who were looked up to as our masters in the application of
mathematics to physics, and who were understood to be Newtonians in
this as in other subjects. A general tendency to an atomic
philosophy, which had begun to appear from the time of Newton,
operated powerfully; and {112} the hypothesis of emission was so
easily conceived, that, when recommended by high authority, it
easily became popular; while the hypothesis of luminiferous
undulations, unavoidably difficult to comprehend, even by the aid of
steady thought, was neglected, and all but forgotten.
Yet the reception which Young's opinions met with was more harsh
than he might have expected, even taking into account all these
considerations. But there was in England no visible body of men,
fitted by their knowledge and character to pronounce judgment on
such a question, or to give the proper impulse and bias to public
opinion. The Royal Society, for instance, had not, for a long time,
by custom or institution, possessed or aimed at such functions. The
writers of "Reviews" alone, self-constituted and secret tribunals,
claimed this kind of authority. Among these publications, by far the
most distinguished about this period was the _Edinburgh Review_;
and, including among its contributors men of eminent science and
great talents, employing also a robust and poignant style of writing
(often certainly in a very unfair manner), it naturally exercised
great influence. On abstruse doctrines, intelligible to few persons,
more than on other subjects, the opinions and feelings expressed in
a Review must be those of the individual reviewer. The criticism on
some of Young's early papers on optics was written by Mr.
(afterwards Lord) Brougham, who, as we have seen, had experimented
on diffraction, following the Newtonian view, that of inflexion. Mr.
Brougham was perhaps at this time young enough[96\9] to be somewhat
intoxicated with the appearance of judicial authority in matters of
science, which his office of anonymous reviewer gave him: and even
in middle-life, he was sometimes considered to be prone to indulge
himself in severe and sarcastic expressions. In January, 1803, was
published[97\9] his critique on Dr. Young's Bakerian Lecture, _On
the Theory of Light and Colors_, in which lecture the doctrine of
undulations and the law of interferences was maintained. This
critique was an uninterrupted strain of blame and rebuke. "This
paper," the reviewer said, "contains nothing which deserves the name
either of experiment or discovery." He charged the writer with
"dangerous relaxations of the principles of physical logic." "We
wish," he cried, "to recall philosophers to the strict and severe
methods of investigation," describing them as those pointed out by
Bacon, Newton, and the like. Finally, Dr. Young's speculations {113}
were spoken of as a hypothesis, which is a mere work of fancy; and
the critic added, "we cannot conclude our review without entreating
the attention of the Royal Society, which has admitted of late so
many hasty and unsubstantial papers into its _Transactions_;" which
habit he urged them to reform. The same aversion to the undulatory
theory appears soon after in another article by the same reviewer,
on the subject of Wollaston's measures of the refraction of Iceland
spar; he says, "We are much disappointed to find that so acute and
ingenious an experimentalist should have adopted the wild optical
theory of vibrations." The reviewer showed ignorance as well as
prejudice in the course of his remarks; and Young drew up an answer,
which was ably written, but being published separately had little
circulation. We can hardly doubt that these Edinburgh reviews had
their effect in confirming the general disposition to reject the
undulatory theory.
[Note 96\9: His age was twenty-four.]
[Note 97\9: _Edin. Review_, vol. i. p. 450.]
We may add, however, that Young's mode of presenting his opinions
was not the most likely to win them favor; for his mathematical
reasonings placed them out of the reach of popular readers, while
the want of symmetry and system in his symbolical calculations,
deprived them of attractiveness for the mathematician. He himself
gave a very just criticism of his own style of writing, in speaking
on another of his works:[98\9] "The mathematical reasoning, for want
of mathematical symbols, was not understood, even by tolerable
mathematicians. From a dislike of the affectation of algebraical
formality which he had observed in some foreign authors, he was led
into something like an affectation of simplicity, which was equally
inconvenient to a scientific reader."
[Note 98\9: See _Life of Young_, p. 54.]
Young appears to have been aware of his own deficiency in the power
of drawing public favor, or even notice, to his discoveries. In
1802, Davy writes to a friend, "Have you seen the theory of my
colleague, Dr. Young, on the undulations of an ethereal medium as
the cause of light? It is not likely to be a popular hypothesis,
after what has been said by Newton concerning it. He would be very
much flattered if you could offer any observations upon it, _whether
for or against it_." Young naturally felt confident in his power of
refuting objections, and wanted only the opportunity of a public
combat.
Dr. Brewster, who was, at this period, enriching optical knowledge
with so vast a train of new phenomena and laws, shared the general
aversion to the undulatory theory, which, indeed, he hardly overcame
{114} thirty years later. Dr. Wollaston was a person whose character
led him to look long at the laws of phenomena, before he attempted
to determine their causes; and it does not appear that he had
decided the claims of the rival theories in his own mind. Herschel
(I now speak of the son) had at first the general mathematical
prejudice in favor of the emission doctrine. Even when he had
himself studied and extended the laws of dipolarized phenomena, he
translated them into the language of the theory of moveable
polarization. In 1819, he refers to, and corrects, this theory; and
says, it is now "relieved from every difficulty, and entitled to
rank with the fits of easy transmission and reflection as a general
and simple physical law;" a just judgment, but one which now conveys
less of praise than he then intended. At a later period, he remarked
that we cannot be certain that if the theory of emission had been as
much cultivated as that of undulation, it might not have been as
successful; an opinion which was certainly untenable after the fair
trial of the two theories in the case of diffraction, and
extravagant after Fresnel's beautiful explanation of double
refraction and polarization. Even in 1827, in a _Treatise on Light_,
published in the _Encyclopædia Metropolitana_, he gives a section to
the calculations of the Newtonian theory; and appears to consider
the rivalry of the theories as still subsisting. But yet he there
speaks with a proper appreciation of the advantages of the new
doctrine. After tracing the prelude to it, he says, "But the
unpursued speculations of Newton, and the opinions of Hooke, however
distinct, must not be put in competition, and, indeed, ought
scarcely to be mentioned, with the elegant, simple, and
comprehensive theory of Young,--a theory which, if not founded in
nature, is certainly one of the happiest fictions that the genius of
man ever invented to grasp together natural phenomena, which, at
their first discovery, seemed in irreconcileable opposition to it.
It is, in fact, in all its applications and details, one succession
of _felicities_; insomuch, that we may almost be induced to say, if
it be not true, it deserves to be so."
In France, Young's theory was little noticed or known, except
perhaps by M. Arago, till it was revived by Fresnel. And though
Fresnel's assertion of the undulatory theory was not so rudely
received as Young's had been, it met with no small opposition from
the older mathematicians, and made its way slowly to the notice and
comprehension of men of science. M. Arago would perhaps have at once
adopted the conception of transverse vibrations, when it was
suggested by his fellow-laborer, Fresnel, if it had not been that he
was a member of the {115} Institute, and had to bear the brunt of
the war, in the frequent discussions on the undulatory theory; to
which theory Laplace, and other leading members, were so vehemently
opposed, that they would not even listen with toleration to the
arguments in its favor. I do not know how far influences of this
kind might operate in producing the delays which took place in the
publication of Fresnel's papers. We have seen that he arrived at the
conception of transverse vibrations in 1816, as the true key to the
understanding of polarization. In 1817 and 1818, in a memoir read to
the Institute, he analysed and explained the perplexing phenomena of
quartz, which he ascribed to a _circular polarization_. This memoir
had not been printed, nor any extract from it inserted in the
scientific journals, in 1822, when he confirmed his views by further
experiments.[99\9] His remarkable memoir, which solved the
extraordinary and capital problem of the connexion of double
refraction and crystallization, though written in 1821, was not
published till 1827. He appears by this time to have sought other
channels of publication. In 1822, he gave,[100\9] in the _Annales de
Chimie et de Physique_, an explanation of refraction on the
principles of the undulatory theory; alleging, as the reason for
doing so, that the theory was still little known. And in succeeding
years there appeared in the same work, his theory of reflection. His
memoir on this subject (_Mémoire sur la Loi des Modifications que la
Réflexion imprime à la Lumière Polarisée_,) was read to the Academy
of Sciences in **1823. But the original paper was mislaid, and, for a
time, supposed to be lost; it has since been recovered among the
papers of M. Fourier, and printed in the eleventh volume of the
Memoirs of the Academy.[101\9] Some of the speculations to which he
refers, as communicated to the Academy, have never yet
appeared.[102\9]
[Note 99\9: Hersch. _Light_, p. 539.]
[Note 100\9: _Ann. de Chim._ 1822, tom. xxi. p. 235.]
[Note 101\9: Lloyd. _Report on Optics_, p. 363. (Fourth Rep. of
Brit. Ass.)]
[Note 102\9: Ib. p. 316, _note._]
Still Fresnel's labors were, from the first, duly appreciated by
some of the most eminent of his countrymen. His _Memoir on
Diffraction_ was, as we have seen, crowned in 1819: and, in 1822, a
Report upon his _Memoir on Double Refraction_ was drawn up by a
commission consisting of MM. Ampère, Fourier, and Arago. In this
report[103\9] Fresnel's theory is spoken of as confirmed by the most
delicate tests. The reporters add, respecting his "theoretical ideas
on the particular kind of undulations which, according to him,
constitute light," that "it would be impossible for them to
pronounce at present a decided {116} judgment," but that "they have
not thought it right to delay any longer making known a work of
which the difficulty is attested by the fruitless efforts of the
most skilful philosophers, and in which are exhibited in the same
brilliant degree, the talent for experiment and the spirit of
invention."
[Note 103\9: _Ann. Chim._ tom. xx. p. 343.]
In the meantime, however, a controversy between the theory of
undulations and the theory of moveable polarization which M. Biot
had proposed with a view of accounting for the colors produced by
dipolarizing crystals, had occurred among the French men of science.
It is clear that in some main features the two theories coincide;
the intervals of interference in the one theory being represented by
the intervals of the oscillations in the other. But these intervals
in M. Biot's explanations were arbitrary hypotheses, suggested by
these very facts themselves; in Fresnel's theory, they were
essential parts of the general scheme. M. Biot, indeed, does not
appear to have been averse from a coalition; for he allowed[104\9]
to Fresnel that "the theory of undulations took the phenomena at a
higher point and carried them further." And M. Biot could hardly
have dissented from M. Arago's account of the matter, that Fresnel's
views "_linked together_"[105\9] the oscillations of moveable
polarization. But Fresnel, whose hypothesis was all of one piece,
could give up no part of it, although he allowed the usefulness of
M. Biot's formulæ. Yet M. Biot's speculations fell in better with
the views of the leading mathematicians of Paris. We may consider as
evidence of the favor with which they were looked upon, the large
space they occupy in the volumes of the Academy for 1811, 1812,
1817, and 1818. In 1812, the entire volume is filled with a memoir
of M. Biot's on the subject of moveable polarization. This doctrine
also had some advantage in coming early before the world in a
didactic form, in his _Traité de Physique_, which was published in
1816, and was the most complete treatise on general physics which
had appeared up to that time. In this and others of this author's
writings, he expresses facts so entirely in the terms of his own
hypothesis, that it is difficult to separate the two. In the sequel
M. Arago was the most prominent of M. Biot's opponents; and in his
report upon Fresnel's memoir on the colors of crystalline plates, he
exposed the weaknesses of the theory of moveable polarization with
some severity. The details of this controversy need not occupy us;
but we may observe that this may be considered as the last struggle
{117} in favor of the theory of emission among mathematicians of
eminence. After this crisis of the war, the theory of moveable
polarization lost its ground; and the explanations of the undulatory
theory, and the calculations belonging to it, being published in the
_Annales de Chimie et de Physique_, of which M. Arago was one of the
conductors, soon diffused it over Europe.
[Note 104\9: _Ann. Chim._ tom. xvii. p. 251.]
[Note 105\9: "Nouait".]
It was probably in consequence of the delays to which we have
referred, in the publication of Fresnel's memoirs, that as late as
December, 1826, the Imperial Academy at St Petersburg proposed, as
one of their prize-questions for the two following years, this,--"To
deliver the optical system of waves from all the objections which
have (as it appears) with justice been urged against it, and to
apply it to the polarization and double refraction of light." In the
programme to this announcement, Fresnel's researches on the subject
are not alluded to, though his memoir on diffraction is noticed;
they were, therefore, probably not known to the Russian Academy.
Young was always looked upon as a person of marvellous variety of
attainments and extent of knowledge; but during his life he hardly
held that elevated place among great discoverers which posterity
will probably assign him. In 1802, he was constituted Foreign
Secretary of the Royal Society, an office which he held during life;
in 1827 he was elected one of the eight Foreign Members of the
Institute of France; perhaps the greatest honor which men of science
usually receive. The fortune of his life in some other respects was
of a mingled complexion. His profession of a physician occupied,
sufficiently to fetter, without rewarding him; while he was Lecturer
at the Royal Institution, he was, in his lectures, too profound to
be popular; and his office of Superintendent of the _Nautical
Almanac_ subjected him to much minute labor, and many petulant
attacks of pamphleteers. On the other hand, he had a leading part in
the discovery of the long-sought key to the Egyptian hieroglyphics;
and thus the age which was marked by two great discoveries, one in
science and one in literature, owed them both in a great measure to
him. Dr. Young died in 1829, when he had scarcely completed his
fifty-sixth year. Fresnel was snatched from science still more
prematurely, dying, in 1827, at the early age of thirty-nine.
We need not say that both these great philosophers possessed, in an
eminent degree, the leading characteristics of the discoverer's
mind, perfect clearness of view, rich fertility of invention, and
intense love of knowledge. We cannot read without great interest a
letter of {118} Fresnel to Young,[106\9] in November, 1824: "For a
long time that sensibility, or that vanity, which people call love
of glory, is much blunted in me. I labor much less to catch the
suffrages of the public, than to obtain an inward approval which has
always been the sweetest reward of my efforts. Without doubt I have
often wanted the spur of vanity to excite me to pursue my researches
in moments of disgust and discouragement. But all the compliments
which I have received from MM. Arago, De Laplace, or Biot, never
gave me so much pleasure as the discovery of a theoretical truth, or
the confirmation of a calculation by experiment."
[Note 106\9: I was able to give this, and some other extracts, from
the then unedited correspondence of Young and Fresnel, by the
kindness of (the Dean of Ely) Professor Peacock, of Trinity College,
Cambridge, whose Life of Dr. Young has since been published.]
Though Young and Fresnel were in years the contemporaries of many
who are now alive, we must consider ourselves as standing towards
them in the relation of posterity. The Epoch of Induction in Optics
is past; we have now to trace the Verification and Application of
the true theory.