VELOCITY OF LIGHT. 115 



light traverses 288000 miles in a second. 5 * If we reckon 

 189938 miles for stellar light, according to Struve's observa- 

 tions on aberration, we obtain the difference of 95776 miles 

 as the greater velocity of electricity in one second. 



These results are apparently opposed to the views advanced 

 by Sir William Herschel, according to which solar and stellar 

 light are regarded as the effects of an electro-magnetic pro- 

 cess a perpetual northern light. I say apparently, 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 propagation. To this conjec- 

 ture may be added the uncertainty of the numerical result 

 yielded by the experiments of Wheatstone, who has himself 

 admitted that they are not sufficiently established, but need 

 further confirmation before they can be satisfactorily compared 

 with the results deduced from observations on aberration and 

 on the satellites. 



The attention of physicists has been powerfully attracted to 

 the experiments on the velocity of the transmission of elec- 



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

 1834, pp. 589, 591. From the experiments described in this 

 paper it would appear that the human eye is capable of per- 

 ceiving phenomena of light, whose duration is limited to the 

 millionth part of a second (p. 591). On the hypothesis re- 

 ferred to in the text, of the supposed analogy between the light 

 of the sun and polar light, see Sir John Herschel's Results 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 ingenious application of Breguet's improved 

 Wheatstone' s rotatory apparatus for determining between the 

 theories of emission and undulation, 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 Compte* re-ndua 

 pour 1850, t. xxx. pp. 489-495, 556.) 



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