Thomas Young (scientist)

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Thomas Young, frontispiece from The Life of Thomas Young (1855) by George Peacock

Thomas Young (13 June 177310 May 1829) was an English genius and polymath, admired by, among others, William Herschel and Albert Einstein. He is famous for having partly deciphered Egyptian hieroglyphs (specifically the Rosetta Stone) before Jean-Francois Champollion eventually expanded on his work.


  • A permanent alteration of form limits the strength of materials with regard to practical purposes, almost as much as fracture; since, in general, the force which is capable of producing this effect is sufficient, with a small addition, to increase it till fracture takes place.
  • I have resolved to confine my studies and my pen to medical subjects only. For the talents which God has not given me, I am not responsible, but those which I possess, I have hitherto cultivated and employed as diligently as my opportunities have allowed me to do ; and I shall continue to apply them with assiduity, and in tranquillity, to that profession which has constantly been the ultimate object of all my labours.
  • I met with an accident about five weeks ago in London, which has prevented my walking ever since, and I think I broke one of the metatarsal bones; this has been a favourable circumstance, for it has increased my literary application in a considerable degree. I have been studying, not the theory of the winds, but of the air, and I have made observations on harmonics which I believe are new. Several circumstances unknown to the English mathematicians which I thought I had first discovered, I since find to have been discovered and demonstrated by the foreign mathematicians; in fact, Britain is very much behind its neighbours in many branches of the mathematics: were I to apply deeply to them, I would become a disciple of the French and German school; but the field is too wide and too barren for me.
    • Letter to Dr. Bostock (June, 1798) as quoted by George Peacock, Life of Thomas Young (1855)
  • This statement appears to us to be conclusive with respect to the insufficiency of the undulatory theory, in its present state, for explaining all the phenomena of light. But we are not therefore by any means persuaded of the perfect sufficiency of the projectile system: and all the satisfaction that we have derived from an attentive consideration of the accumulated evidence, which has been brought forward, within the last ten years, on both sides of the question, is that of being convinced that much more evidence is still wanting before it can be positively decided. In the progress of scientific investigation, we must frequently travel by rugged paths, and through valleys as well as over mountains. Doubt must necessarily succeed often to apparent certainty, and must again give place to a certainty of a higher order; such is the imperfection of our faculties, that the descent from conviction to hesitation is not uncommonly as salutary, as the more agreeable elevation from uncertainty to demonstration. An example of such alternations may easily be adduced from the history of chemistry. How universally had phlogiston once expelled the aërial acid of Hooke and Mayow. How much more completely had phlogiston given way to oxygen! And how much have some of our best chemists been lately inclined to restore the same phlogiston to its lost honours! although now again they are beginning to apprehend that they have already done too much in its favour. In the mean time, the true science of chemistry, as the most positive dogmatist will not hesitate to allow, has been very rapidly advancing towards ultimate perfection.
    • Miscellaneous Works: Scientific Memoirs (1855) Vol. 1, ed. George Peacock & John Leitch, p. 249
  • When I was a boy, I thought myself a man. Now that I am a man, I find myself a boy.
    • as quoted by Horatio B. Williams, Thomas Young, The Man and Physician, J. Opt. Soc. Am. 20, 35-49 (1930).

"Outlines of Experiments and Inquiries Respecting Sound and Light" (1800)[edit]

From the Philosophical Transactions In a Letter addressed to Edward Whittaker Grey, M.D. Sec. R.S. Read January 16th

  • The well known elevation of the pitch of wind instruments, in the course of playing, sometimes amounting to half a note, is not, as is commonly supposed, owing to any expansion of the instrument, for this should produce a contrary effect, but to the increased warmth of the air in the tube.
  • It may hereafter be considered how far the excellent experiments of Count Rumford, which tend very greatly to weaken the evidence of the modern doctrine of heat, may be more or less favourable to one or the other system of light and colours.
  • It is surprising that so great a mathematician as Dr. Smith could have entertained for a moment, an idea that the vibrations constituting different sounds should be able to cross each other in all directions, without affecting the same individual particles of air by their joint forces: undoubtedly they cross, without disturbing each other's progress; but this can be no otherwise effected than by each particle's partaking of both motions. If this assertion stood in need of any proof, it might be amply furnished by the phenomena of beats, and of the grave harmonics observed...

An Introduction to Medical Literature, Including a System of Practical Nosology (1823)[edit]

  • There is no study more difficult than that of physic: it exceeds, as a science, the comprehension of the human mind: and those who blunder onwards, without attempting to understand what they see, are often very nearly on a level with those, who depend too much on imperfect generalisations, applied to facts, which can scarcely be subjected to any well marked analogy. Hence it may happen, that talents and labour may become useless for want of a proper direction... To assist in furnishing the student with a sufficient direction... is the principal object of this work.
    • p. 2
  • Physic is one of those departments, in which there is frequent necessity for the exercise of an incommunicable faculty of judgment, and a sagacity, which may be called transcendental, as extending beyond the simple combination of all that can be taught by precept. Nor is there any other mode of cultivating these powers, than by pursuing a much more extensive range of elementary study, than appears, to a common and superficial observer, to be in any way connected with the immediate objects of the profession.
    • p. 5

Quotes about Young[edit]

  • I may here refer to a curious mathematical calculation by Dr. Thomas Young, to the effect, that if three words coincide in two different languages, it is ten to one they must be derived in both cases from some parent language, or introduced in some other manner. "Six words would give more," he says, "than seventeen hundred to one, and eight near 100,000, so that in these cases the evidence would be little short of absolute certainty."
  • Reflexion, refraction, the formation of images by lenses. the mode of operation of the eye, the spectral composition and recomposition of the different kinds of light the invention of the reflecting telescope, the first foundations of colour theory, the elementary theory of the rainbow pass us by in procession, and finally come his of the colours of thin films as the origin of the next great theoretical advance, which had to await, over a hundred years, the coming of Thomas Young.

Life of Thomas Young (1855)[edit]

by George Peacock
  • It is now more than twenty years since I somewhat rashly undertook to write the Life of Dr. Young. ...The undertaking was consequently abandoned, and it was proposed to transfer it to other hands; but it was not found easy to secure the services of a person who possessed sufficient scientific knowledge to enable him to write the life of an author whose works were so various in their character and not unfrequently so difficult to understand and analyse, as those of Dr. Young.
    • Preface, p. vii
  • It was the kindred science of sound which had suggested to Young his principle of interference, and he was under a similar obligation to the same science for the suggestion of the principle which formed the first step in the solution of the great problem of double refraction.
    • Ch. XII Optical Discoveries.—Second Epoch, p.375
  • We propose... to call the attention of our readers to some of the more remarkable Memoirs, or Philosophical Essays, of Dr. Young, which have not elsewhere been noticed; selecting those which are distinguished... or which are otherwise calculated to show the extraordinary capacity which he possessed of solving the most difficult problems in the applications of mathematics to natural philosophy, by processes apparently the most inadequate to the purpose. He never confined himself to the beaten track of a systematic investigation. We find in his writings no symmetrical formula or analytical refinements. There is no seeking after generalities, when the particular question which he has in hand does not require them; whilst every expedient is freely resorted to, however irregular and unusual, if it serves the purpose which he has in view. Important and difficult steps are passed over as manifest, terms are neglected as insignificant, analogies take the place of proofs, and we are surprised to find ourselves at the end of an investigation, even within the limits of space which would commonly be deemed hardly sufficient to master the difficulties which meet us at the beginning. But his rare sagacity hardly ever deserts him; and though he has occasionally been led to hasty and premature conclusions, or committed mistakes in numerical calculations, from the brevity and rapidity of his processes, yet nothing can be more surprising than the general soundness of his views of mechanical principles and their applications, and the correctness both of his philosophical and numerical results.
    • Ch. 15 Miscellaneous Memoirs, pp.416-417
  • A Memoir on Hydraulics, printed in the Philosophical Transactions for 1808, was introductory to another in the same Collection for the following year, on the Functions of the Heart and Arteries. The connection between these subjects was considered by him... sufficiently close to give them both a professional character, and thus to exempt them from the restriction which he had imposed upon the class of publications which alone should be allowed to appear under his own name. ...Few persons can be found ...with a union of acquirements so remote from each other as to be able to prosecute an inquiry of this nature, or to judge of the correctness of the conclusions to which it leads; but as such it was exactly suited to Dr. Young, who delighted in questions so obscure and difficult, where his various knowledge and bold spirit of speculation had full room for their exercise.
    • Ch. XV Miscellaneous Memoirs, p. 417

"The History of Young's Discovery of the Theory of Colors" (1875)[edit]

Alfred M. Mayer, "The History of Young's Discovery of the Theory of Colors," The American Journal of Science and Arts (April, 1875) Third Series, Volume IX, No. 52, pp. 251-267.
  • The first publication by Young of his theory of color appeared in a Bakerian Lecture entitled, "On the Theory of Light and Colors," which Young read before the Royal Society on Nov. 12 1801. ...
    The fact that Young, the founder of the undulatory theory of light, in this Bakerian Lecture, in which it has been said that he laid the foundations of that doctrine, should set forth his views in a series of postulates followed by citations from the writings of Newton, to give them weight and proof, may justly surprise those who have trusted to the second-hand information derived from carelessly-complied text books and from hastily prepared popular lectures. But then, where would be the pugilistic charm of the popular lecturer on the undulatory theory of light, if Newton, his champion, the violent defender of the emanation cause, should decline to enter as a contestant? ...
    Young's hypothesis imagines each sensitive point of the retina to contain particles capable of vibrating in perfect unison to those vibrations causing three principal colors (red, yellow, and blue, in this the first publication of his hypothesis) "and that each of the particles is capable of being put in motion, less or more forcibly, by undulations differing less or more from a perfect unison." This would suppose such a triple molecular constitution of each nerve fibril as to cause the three species of its constituent molecules (or the atoms forming the molecules) to be in tune with the three rates of vibration corresponding respectively to the undulations of the ether causing red, yellow, and blue. He afterward says: "and each sensitive filament of the nerve may consist of three portions, one for each principal color." We have here a conception of the mode of action of an ætherial vibration on the retinal nerve fibrils which has not been described by those who have given accounts of Young's theory of color. ...the statements made by Young in the foregoing paper concerning his color hypothesis were entirely hypothetical not having been based on any observation or experiment either of his own or of others...
  • The next publication by Young on his theory of color... a paper read by him before the Royal Society, on July 1, 1802... "An account of some cases of the production of colours, not hitherto described." ...
    Young changed his three elementary color-sensations from red, yellow, and blue, to red, green, and violet, in consequence of Dr. Wollaston's correction of the description of the prismatic spectrum." ...
    Wollaston... only observed imperfectly the dark lines of the spectrum, now known as Fraunhofer's lines, but he imagined he saw a spectrum... divided into four distinct and separated "primary divisions." He at once inferred and erroneously that Newton's analysis... was false; that no orange or yellow exists... but between the red and the blue there exists only a "yellowish green." ...Young made a similar but even greater error in his description... I imagine that when Wollaston's sharp eye caught the glimpse of the divided spectrum he naturally thought... that the dark lines were the dividing lines of the pure simple colors of the solar spectrum. ...
    Young in finally selecting red, green and violet as the three elementary color-sensations was not, as Helmholtz states, guided in their choice "by the consideration that the extreme colors of the spectrum occupied the privileged positions," but selected those colors on hearing of Wollaston's supposed complete analysis of the sun's light into red, greenish blue and violet colors, separated from each other in the spectrum by dark spaces.
  • We hear no more from Young about his theory of colors until 1807, when he published the first volume of his celebrated work, "A Course of Lectures on Natural Philosophy and the Mechanical Arts." ...Young gives a concise statement of his views on the analysis of the sensations of color and supports these views with conclusive experiments with rotating colored discs; but, strange to say, he omits from this account... all mention of the physiological explanation of it which he gave in the Bakerian Lecture of 1801. ...
    [I]n the Natural Philosophy we read that, "The sensations of various kinds of light may also be combined in a still more satisfactory manner by painting the surface of a circle with different colours... and causing it to revolve with such rapidity, that the whole may assume the appearance of a single tint, or of a combination of tints, resulting from the mixture of the colours." These experiments were evidently first made by Young; and are fully described in the text and perfectly illustrated... in the plates of Young's work. These experiments have been carefully repeated by Helmholtz, Maxwell, and others, and of their general accuracy there is no doubt. We can readily imagine the delight with which Young must have viewed these beautiful experiments, which, however, together with other truths unfolded by him, were destined to remain unnoticed, "until a later generation, by slow degrees, arrived at the discovery of his discovery."

"The Century's Progress in Physics" (1897)[edit]

Henry Smith Williams, "The Century's Progress in Physics," Part I, "The Impoderables," Harper's New Monthly Magazine (July, 1897) Volume 95, Issue 566, p. 254-265.
  • There were giants abroad in the world of science in the early days of our century, Herschel, Lagrange, and Laplace; Cuvier, Brongniart, and Lamarck; Humboldt, Goethe, Priestley—what need to extend the list?—the names crowd upon us. But among them all there was no taller intellectual figure than that of a young Quaker who came to settle in London and practise the profession of medicine in the year 1801. The name of this young aspirant to medical honors and emoluments was Thomas Young. He came fresh from professional studies at Edinburgh and on the Continent, and he had the theory of medicine at his tongue's end; yet his medical knowledge, compared with the mental treasures of his capacious intellect as a whole, was but as a drop of water in the ocean.
    Incidentally the young physician was prevailed upon to occupy... the chair of Natural Philosophy at the Royal Institution, which Count Rumford had founded, and of which Davy was then Professor of Chemistry—the institution whose glories have been perpetuated by such names as Faraday and Tyndall, and which the Briton of to-day speaks of as the "Pantheon of Science."
  • As early as 1793, when he was only twenty, Young had begun to communicate papers to the Royal Society of London, which were adjudged worthy to be printed in full in the Philosophical Transactions; so it is not strange that he should have been asked to deliver the Bakerian Lecture before that learned body the very first year after he came to London. The lecture was delivered November 12, 1801. Its subject was "The Theory of Light and Colors," and its reading marks an epoch in physical science; for here for the first time was brought forward convincing proof of that undulatory theory of light... which holds that light is not a corporeal entity, but a mere pulsation in the substance of an all-pervading ether, just as sound is a pulsation in the air, or in liquids or solids.
    Young had... advocated this theory at an earlier date, but it was not until 1801 that he hit upon the idea which enabled him to bring it to anything approaching a demonstration. It was while pondering over the familiar but puzzling phenomena of colored rings into which white light is broken when reflected from thin films—Newton's rings...—that an explanation occurred to him which at once put the entire undulatory theory on a new footing. With that sagacity of insight which we call genius, he saw of a sudden that the phenomena could be explained by supposing that when rays of light fall on a thin glass part of the rays being reflected from the upper surface other rays reflected from the lower surface might be so retarded in their course through the glass that the two sets would interfere...
    By following up this clew with mathematical precision, measuring the exact thickness of the plate and the space between the different rings of color, Young was able to show mathematically what must be the length of pulsation for each of the different colors of the spectrum. He estimated that the undulations of red light... must number about 37,640 to the inch, and pass any given spot at a rate of 463 millions of millions of undulations in a second, while the extreme violet numbers 59,750 undulations to the inch or 735 millions of millions to the second.
  • Young... examined the colors that are produced by scratches on a smooth surface, in particular testing the light from "Mr. Coventry's exquisite micrometers," which consist of lines scratched on glass at measured intervals. These microscopic tests brought the same results as the other experiments. The colors were produced at certain definite and measurable angles, and the theory of interference of undulations explained them perfectly, while, as Young affirmed... no other theory hitherto advanced could expIain them at all. Taking all the evidence together Young declared that he considered the argument he had set forth in favor of the undulatory theory of light to be sufficient and decisive.
  • This doctrine of interference of undulations was the absolutely novel part of Young's theory. The all compassing genius of Robert Hooke had... very nearly apprehended it more than a century before, as Young himself points out, but... even with the sagacious Hooke it was only a happy guess... and utterly ignored by all others. Young did not know of Hooke's guess until he himself had fully formulated the theory, but he hastened then to give his predecessor all the credit that could possibly be adjudged his due... To Hooke's contemporary, Huyghens, who was the originator of the general doctrine of undulation as the explanation of light, Young renders full justice also. For himself he claims only the merit of having demonstrated the theory which these and a few others of his predecessors had advocated without full proof.

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