KINETIC OR MECHANICAL VIEW OF NATUUH 37 



for the purpose of serving as the carrier of a definite 

 kind of wave - motion — to he endowed with most mys- 

 terious, seemingly contra(Hctory properties.^ Neverthe- 

 less the development of this conception, the desire to 

 define more minutely the properties of this fictitious 

 sul)stance of wliich we have no direct perception, wime 

 in the course of the century to guide more and more the 

 work of experimentalists as well as theorists. We meet 

 with objections in the beginning, when the conception was 

 first introduced, such as were urged by many chemical 

 philosophers when Dal ton reintroduced and formulated 



(Tait, 'Light,' p. 192). Sir G. G. 

 Stokes tells us " that in a course 

 of conversation with Sir David 

 Brewster, who had just returned 

 from France, where lie witnessed 

 the celebrated experiment by which 

 F(»ucault had just proved experi- 

 mentally that light travels faster 

 in air than in water, he asked him 

 wliat his objection was to the 

 theory of undulations, and he 

 found he was staggered by the 

 idea in limine of filling space with 

 some substance merely in order 

 that 'that little twinkling star,' 

 as he expressed himself, should be 

 able to send his light to us" 

 ('Burnett Lectures on Light,' p. 

 15). 



^ It is known that the two phil- 

 osophers who in the middle of the 

 century did more than any others to 

 introduce the positive or exact spirit 

 into general thinking and into 

 philosophical literature, Auguste 

 Comte and John Stuart Mill, were 

 both opposed to the theory of an 

 ether. Huxley, in speaking of 

 Comte, exclaims : " What is to be 

 thought of the contemporary of 

 Young and of Fresnel who never 

 misses an opportunity of casting 

 scorn upon the hypothesis of an 

 ether — the fundamental basis not 



only of the undulatory theory of 

 light, but of so much else in 

 modern physics, and whose con- 

 tempt for the intellects of .some of 

 the strongest men of his generation 

 was such that he puts forward the 

 mere existence of niglit :« a refuta- 

 tion of the undulatory theory ? " 

 (See 'Philosophic Positive,' vol. ii. 

 p. 440, anil Huxley, ' Lay Sermons,' 

 J). 134.^ The fourteenth chapter 

 of Mill's 'System of Logic,' written 

 originally in the beginning of the 

 'forties, but subsequently anno- 

 tated with reference to some of 

 AVliewell's criticisms, contains a 

 lengthy discussion of the hypoth- 

 esis of an ether. Mill says (vol. ii. 

 ]). 21, seventh edition): " What has 

 most contributed to accredit the 

 hypothesis of a physical medium 

 for the conveyance of light is the 

 certiiin fact that light travels, that 

 its communication is not instan- 

 taneous but requires time, and that 

 it is intercepted by intervening 

 objects. There are analogies be- 

 tween its j)henomena iind those of 

 the mechanical motion of a solid or 

 fluid substance. But we are not 

 entitled to ivs^iume that mechanical 

 motion is the only i)owcr in nature 

 capable of exhibiting the.se attri- 

 butes." 



