570 Professor Tyndall [Jan. 22, 



filled with a medium of so fickle and vibratory a nature. Were we to 

 take the trouble of refuting him lie might tell us, ' my opinion is changed, 

 and I have abandoned that hypothesis. But here is another for you.' 

 We demand if the world of science which Newton once illuminated is 

 to be as changeable in its modes as the world of fashion, which is 



directed by the nod of a silly woman or a pampered fop ? We 



have a right to demand that the hypothesis shall be so consistent with 

 itself as not to require perpetual mending and patching ; that the 

 child we stoop to play with shall be tolerably healthy, and not of the 

 puny and sickly nature of Dr. Young's productions, which have 

 scarcely stamina to subsist until the fruitful parent has furnished us 

 with a new litter, to make way for which he knocks on the head, 

 or more barbarously exposes, the first." He taunts Young with 

 claiming the inheritance of Newton's queries, " vainly imagining that 

 he fulfils this destination by ringing changes on these hypotheses, 

 arguing from them, as if they were experiments or demonstrations, 

 twisting them into a partial coincidence with the clumsy imaginations 

 of his own brain, and pompously parading what Newton left as hints, 

 in a series of propositions, with all the affectation of system." 



To Brougham's coarse invective Young replied in a masterly and 

 exhaustive letter. A single copy, and one only, was sold by its pub- 

 lisher. There were at that time in the ranks of science no minds 

 competent to understand the controversy. The poison worked with- 

 out an antidote, and, for thirteen years, Young and his researches on 

 light had no place in public thought. His discoveries remained ab- 

 solutely unnoticed until their re-discovery by Fresnel lifted the pall 

 which for so many years had been thrown over this splendid genius. 



Young lectured for two years at the Eoyal Institution, and he 

 afterwards threw the lectures into a permanent form in a quarto volume 

 of 750 pages with 40 plates, and nearly 600 figures and maps. He also 

 produced at the same time a second volume of the same magnitude, 

 embracing his optical and other memoirs, and a most elaborate classed 

 catalogue of works and papers, accompanied by notes, extracts, and 

 calculations. For this colossal work Young was to receive lOOOZ. 

 His publisher, however, became bankrupt, and he never touched the 

 money. His lectures constitute a monument of Young's power almost 

 equal to that of his original memoirs. They are replete with profound 

 reflections and suggestions. In his eighth lecture, on "Collision," 

 the term energy, now in such constant use, is first introduced and 

 defined. By it he was able to avoid, and enable us to avoid, the con- 

 fusion which had crept into scientific literature by the incautious em- 

 ployment of the word force. The theory now known as the Young- 

 Helmholtz theory, which refers all the sensations of colour to three 

 primary sensations — red, green, and violet — was clearly enunciated by 

 Young in his thirty-seventh lecture, on " Physical Optics." His views 

 of the nature of heat were original and correct. He regarded the 

 generation of heat by friction as an unanswerable confutation of the 



