114 COSMOS. 



On comparing the velocities of solar, stellar, and terres- 

 trial light, which are all equally refracted in the prism, 

 with the velocity of the light of frictional electricity, we 

 are disposed, in accordance with Wheatstone's ingeniously 

 conducted experiments, to regard the lowest ratio in which 

 the latter exceeds the former as 3:2. According to the lowest 

 results of Wheatstone's optical rotatory apparatus, electric 



nes de rayons pareils, mais obscurs par defaut ou par exces 

 de vitesse. A plus de vitesse correspond une moindre refrac- 

 tion, comme moins de vitesse entraine une refraction plus 

 grande. Ainsi chaque rayon rouge visible est accompagne de 

 rayons obscurs de la meme nature, qui se refractent les uns 

 plus, les autres moins que lui : ainsi il existe des rayons dans 

 les stries noires de la portion rouge du spectre ; la merne chose 

 doit etre admise des stries situees dans les portions jaunes, 

 vertes, bleues- et violettes." 



*" I showed many years ago, by direct observations, that the 

 rays of those stars towards which the earth moves, and the rays 

 of those stars from which it recedes, are repeated in exactly 

 the same degree. Such a result cannot be reconciled with the 

 theory of emission, unless we make the important admission 

 that luminous bodies emit rays of all velocities, and that only 

 rays of a determined velocity are visible, these alone being 

 capable of impressing the eye with the sensation of light. In 

 the theory of emission, the red, yellow, green, blue, and violet 

 solar rays, are respectively accompanied by like rays, which 

 are, however, dark from deficiency or excess of velocity. 

 Excessive velocity is associated with a slight degree of re- 

 fraction, while a smaller amount of velocity involves a slighter 

 degree of refraction. Thus, every visible red ray is accom- 

 panied by dark rays of the same nature, of which some are 

 more, and others less, refracted than the former ; there are 

 consequently rays in the black lines of the red portion of the 

 spectrum ; and the same must be admitted in reference to the 

 lines situated in the yellow, green, blue, and violet portions." 

 Arago, in the Comptes rendus de V Acad. des Sciences, t. xvi. 

 1843, p. 404. Compare also t. viii. 1839, p. 326, and Pofs- 

 son, Traite de Mecanique, ed. ii. 1833, t. i. 168. Accord- 

 .iig to the undulatory theory, the stars emit waves of extremely 

 various transverse velocities of oscillations. 



