112 COSMOS. 



For Arago's observations have shown that refraction in the prism 

 is not altered by the relation of the velocity of light to that 

 of the earth's motion. All the measurements coincide in the 

 result, that the light of those stars towards which the earth is 



systeme des ondes, consistait done a expliquer, comment la 

 vitesse de propagation des rayons de differentes couleurs dans 

 les corps differents pouvait etre dissemblable et servir a rendre 

 compte de 1'inegalite de refraction de ces rayons ou de la dis- 

 persion. On a montre recemment que cette difficulte n'est 

 pas insurmontable ; qu'on pent constituer T Ether dans les 

 corps inegalement denses de maniere que des rayons a ondu- 

 lations dissemblables s ? y propagent avec des vitesses inegales : 

 reste a determiner, si les conceptions des geometres a cet egard 

 sont conformes a la nature des choses. Voici les amplitudes 

 des ondulations deduites experimentalement d'une serie de 

 faits relatif aux interferences : 



mm 



Violet 0-000423 



Jaune 0-000551 



Eouge 0-000620 



La vitesse de transmission des rayons de differentes couleurs 

 dans les espaces celestes est la meme dans le systeme des 

 ondes et tout-a-fait independante de 1'etendue ou de la vitesse 

 des ondulations." 



"According to the mathematical theory of a system of 

 waves, rays of different colours, having unequal undulations, 

 must nevertheless be transmitted through ether with the 

 same velocity. There is no difference in this respect from 

 the mode of propagation of waves of sound which are 

 transmitted through the atmosphere with equal velocity. 

 This equality of transmission in waves of sound may be well 

 demonstrated experimentally by the uniformity of effect pro- 

 duced by music at all distances from the source whence it 

 emanates. The principal, I may say the only objection, ad- 

 vanced against the undulatory theory, consisted in the diffi- 

 culty of explaining how the velocity of the propagation of rays 

 of different colours through different bodies could be dissimi- 

 lar, while it accounted for the inequality of the refraction of the 

 rays or of their dispersion. It has been recently shown that 



