ON MATTER AND FORCE. 13 



of an aether. It was, however, in his ideas of 

 light that Newton held the imponderable 

 materiality of force. Descartes said that light 

 consisted of small particles emitted by the 

 luminous body. He compares these particles 

 to balls, and endeavours to explain, by means 

 of this comparison, the laws of reflection and 

 refraction. Hooke proposed the theory of 

 undulations, and asserted that light consisted in 

 a quick, short, vibratory motion propagated in a 

 homogeneous medium. 



Huygens says Whewell would have esta- 

 blished the undulatory theory, but Newton, 

 though at first by no means averse to the 

 assumption of an aBther as the vehicle of 

 luminiferous undulations, and even to the last 

 considering the assumption of an sether as 

 highly probable, and its vibrations as important 

 parts of the phenomena of light, yet made the 

 emission ideas the leading part of his optical 

 doctrines. " His disciples found it more easy 

 to conceive the motions of a particle than the 

 propagation of a wave, and the general ascen- 

 dency of the Newtonian doctrines led to a 

 belief in the materiality of light." 



Newton's ideas of the actual emission of some 



