86 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 con- 

 ducted 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 

 light traverses 288,000 miles in a second.* If we reckon 

 189,938 miles for stellar light, according to Struve's observ- 

 itions on aberration, we obtain the difference of 95,776 miles 

 as the greater velocity of electricity in one second. 



These results are apparently opposed to the views ad- 

 vanced by Sir William Herschel, according to which solar 

 xnd stellar light are regarded as the effects of an electro- 

 magnetic process a perpetual northern light. I say ap- 

 parently, for no one will contest the possibility that there 

 may be several very different magneto-electrical processes in 

 the luminous cosmical bodies, in which light the product 

 of the process may possess a different velocity of propaga- 

 tion. To this conjecture may be added the uncertainty of 

 the numerical result yielded by the experiments of Wheat- 

 stone, who has himself admitted that they are not sufficient- 

 ly established, but need further confirmation before they can 



associated with a slight degree of refraction, while a smaller amount of 

 velocity involves a slighter degree of refraction. Thus every visible 

 red ray is accompanied by dark rays of the same nature, of which some 

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

 quently 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 yel- 

 low, green, blue, and violet portions." Arago, in the Comptes Rendus 

 de V Acad, des Sciences, t. xvj., 1843, p. 404. Compare also t. viii., 1839, 

 p. 326, and Poisson, Trail6 de Mfcanique, ed. ii., 1833, t. i., % 168. Ac- 

 cording to the undulatory theory, the stars emit waves of extremely 

 various transverse velocities of oscillations. 



* Wheatstone, in the Philos. Transact, of the Royal Soc.for 1834, p. 

 589, 591. From the experiments described in this paper, it would ap 

 pear that the human eye is capable of perceiving phenomena of light, 

 whose duration is limited to the millionth part of a second (p. 591). 

 On the hypothesis referred to in the text, of the supposed analogy be- 

 tween the light of the sun and polar light, see Sir John Herschel's Re- 

 suits of Astron. Observ. at the Cape of Good Hope, 1847, p. 351. Arago, 

 in the Comptes Rendus pour 1838, t. vii., p. 956, has referred to the in- 

 genious application of Breguet's improved Wheatstone's rotatory ap- 

 paratus for determining between the theories of emission and undula- 

 tion, since, according to the former, light moves more rapidly through 

 water than through air, while, according to the latter, it moves more 

 rapidly through air than through water. (Compare also Comptes Ren- 

 dug pour 1850, t. xxx., p. 489-495, 556.) 



