KINETIC OK MECHANICAL VIEW OF NATLKE. 11 



firmed, tliat light takes time to travel from one point 

 ill space to another. Wherever time is involved in a 

 phenomenon, motion of something is suggested, and 

 this something, as well as the nature of its motion, 

 become subjects of speculation. At the beginning of 5. 

 the nineteenth century two distinct theories existed andemusion 



theoriea. 



regarding these matters. Both had succeeded in ex- 

 ])laining and calculating satisfactorily a large number 

 of the phenomena of light as exhibited by mirrors and 

 lenses, as well as in optical instruments and crystals. 

 One of these theories, the so-called emission, emanation, 

 or corpuscular theory of light, held that luminous 

 bodies send out minute particles which travel in 

 straight lines, and, impinging upon the eye, create the 

 sensation of light. The rival hypothesis, the undul- 

 atory or vibratory theory, held light to consist in 

 the periodic wave-motion of a substance called ether, 

 which was supposed to exist everywhere, filling all 

 space and interpenetrating all ponderable matter. Both e. 

 theories are kinetic or mechanical theories, and for their theories 



kinetic. 



development require the analysis of certain modes of 

 motion. Both liad to formulate their respective 

 notions as to the something that moved. Both could 

 point to analogies in other domains of natural science. 

 There existed at that time similar corpuscular ex- 

 planations of the phenomena of heat, of electricity 



velocity tliey move, how (li.staut William Huggins (1S6S), Kox-Tiil- 



they are from u.s, and mucli else ' bot, and others. That Doppler's 



he-sidex," a jjrediction which, since principle i.s really none otiier than 



the invention of spectrum analysis U()mer".s was )-emarked by P. G. 



and various controversies connected Tait in 'Light' ^•2nd eil., p. '220). 



witli the subject, has been brilliantly ^ See also Hoscnborgor, ' Gescli. d. 



verified by the discoveries of Sir Physik,' vol. iii. p. 708 Kq(j. 



