AND THE THEORY OF LIGHT. 49 



media, for there seems to be some uncertainty on the 

 subject in the scientific mind. One scientific writer 

 says :* " From the foregoing we conclude, then, that the 

 peculiar colour and refrangibility belonging to each kind 

 of homogeneous light are permanent and original afiec- 

 tions not generated by the changes which light undergoes 

 in refractions or reflections ; and therefore that these pro- 

 perties are inherent in the rays previous to their separa- 

 tion by experiments." 



Another says : '^ The dispersion of light into the colours 

 of the spectrum, consequent on its refraction through a 

 prism, is explained by supposing that transparent bodies 

 attract difierent sorts of light unequally ; their refraction 

 is therefore unequal; and thus, on their emergence from 



the refracting medium, the rays become dispersed 



According to the undulatory theory the production of 

 coloured light is supposed to be owing to the difierent 

 velocities with which the particles of ether vibrate; and 

 thus a distinct sensation is escited in the eye analogous to 

 that which is experienced by the ear from the dififerent 

 velocities with which the undulations of the atmosphere 

 are propagated. As high notes and low notes result from 

 the different velocities of these aerial undulations, so the 

 different colours owe their origin to the unequal velocities 

 with which the ether vibrates .... The different refrangi- 

 bility of hght, and the prismatic dispersion consequent 

 upon it, admit of being very easily explained ; for a wave 

 that vibrates with a higher velocity than another will 

 suffer a different refraction from that suffered by the latter, 

 if the two waves be transmitted through the same medium, 

 as ejff. g7\ through glass. "f 



These arguments presuppose that it has been demon- 

 strated that different velocities exist inherently in the 



* Treatise on Liglit and Vision, by the Rev. H. Lloyd, p. 198. 

 t Peschel's Elements of Physics, pp. 90, 91. 



SER. III. VOL. I. H 



