EULOGY ON THOMAS YOUNG. 141 



be neglected, and which, moreover, became a matter of imperative dnty 

 when the question referred to the immortal author of the Natural Phi- 

 losophy,* (the Frinciinaf) The pcDalty of retaliation was applied to him 



* It seems impossible to make this sentence intelligible, nnless Tve suppose the " im- 

 luortal author " spoken of to be Newton, and by consequence that the title Natural Philos- 

 opln/ was a slip of the writer's pen for Frincipia. Yet the stipposition that the hostility 

 of the Edinburgh lleview was at all called forth by any want of courtesy toward New- 

 Ton in the writings of Young is wholly unsupported by anything in Young's papers, 

 in which he cites the views of Newton with the greatest respect. — Tr^vnslator. 



Xewton's support of the emission theori/ of light. — The authority of names can never bo 

 of any avail to the truly inductive philosopher; his motto is emphatically "ji!(//;HS r« 

 verba." But there has been alwaj'S a pi"opensity among writers on the subject to dwell 

 on such authority, and to array great names on either side of any of those controverted 

 points which have divided the scientific worhl. Perhajis, where the question is purely 

 one of opinion, and refers simply to hypotheses upheld for what they are worth as 

 such, the weight of a name may not be unworthy of due estimation : great experience 

 and high genius may add value to a pure hi/pothesis, though it could not to a positive 

 <onclusioii . In regard to theories of light tJais has l)een conspicuously exemplitied, and 

 during a long continuance of controversial discussion it has been a matter of triumph 

 to the opponents of the nndulatory the(n-y that the authority of Newton is on their 

 side. And even Arago, as well as some other supporters of it, have spoken as if regret- 

 ting that they were thus constrained to put themselves in antagonism to Newton. 

 They have pictured two rival theories, the one headed by Newton and supported by 

 Laplace, Biot, Brewster, and Potter; the other uplield in opposition to thembyHuy- 

 gliens, Hooke, Euler, Fresnel, Young, Airy, and all the Cambridge school. 



But a very slight inquiry into the real facts entirely dispels this view of the case. In 

 particular. Dr. Young himself, in projiosiug his iheory, so far from opiiosing the Newto- 

 nian views, expressly endeavors to conciliate attention l)y claiming the weight of New- 

 ton's anthority on his own side; thus, in his paper "On the theory of light and colors," 

 (Phil. Trans., 1801,) he commences by highly extolling the optical researches of New- 

 ton, and then observes, " Those who are attached, as they may be, with the greatest 

 justice, to every doctrine which is stamped with the Newtonian approbation, will proba- 

 idy be disposed to bestow on these considerations (i. e., his own views) so much the 

 more of their attention as they shall appear to coincide more nearly with Newton's 

 opinion." He then proceeds to examine in detail a number of passages from Newton's 

 writings, in which the theory of waves is distinctly upheld and even applied with some 

 precision to the explanation of various phenomena of light, illustrated by their analo- 

 gies to those of sound. 



It is perfectly true that Newton, in the actual investigation of several phenomena of 

 light, adopts other hypotheses than those of waves, and chiefly the idea of light 

 (whatever may be its nature) being subject to certain attractions and repulsions, to 

 certain bendiugs when approaching near the edges of solid bodies, to certain peculiar 

 modifications or changes in its nature recurring periodically at certain minute inter- 

 vals along the length of a ray, to the idea of a ray having "sides" endued with dif- 

 ferent properties ; in a word, a variety of conceptions which he introduces for the pur- 

 pose of giving some kind of imaginary physical representation of the modus operandi in 

 eacli of the several curious experimental cases which he had examined. In all these 

 There is no unity or community of principle ; there is at least nothing like the spirit of 

 theory, no continual recurrence to one leading idea, no perpetual a])peal to any one 

 principle, however imaginary, but an attemptin each isolated case to frame something 

 like an isolated hypotliesis to suit it, and in some way to represent its phenomena, 

 though without any attempt to connect them with the others. It may perhaps be said 

 that all the.se various suppositions agree in supposing light to be matcrud, to be some- 

 thing emitted from the luminous source. But on a closer examination it seems far 

 from certain that even this can be maintained. The only part of these investigations, 

 ])erhaps,in which anything very positive of this kind is distinctly introduced, is when 

 Newton investigates the laws of refraction on the express supposition of small mole- 

 cules attracted by the molecules of the medium. But in this instance it has been truly 

 observed tliat, at the time when Newton wrote, no mathematical method existed by 

 which this kind of action could be reduced to calculation, except those involving the 

 action of attractive force. To give, then, a mathematical theory of ordinary reflection 

 and refraction, he was necessitated to make use of this method. When ho came to in- 

 vestigate those more recondite phenomena which he (very appi'opriately to their «j;- 

 j7«re)J^ nature) called " inflecti(m," the idea most naturally and obviously presented was, 

 that some power or influence, analogous to attraction and repulsion, existing in the 

 edge of an opaque body to bend out of their course rays passing very rear it, and this 

 might seem to imply the materiality of those rays. A^kind of alternating action of this 

 sort, which he imagined necessary to account for a part of theefiect, would, however, 

 hardly be reconcilable to the idea of direct emission. It would be a difficult matter 



