Source on Thomas Young (scientist)

“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."”

“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.”