PORTION OF THE COSMOS. VELOCITY OF LIGHT. 75 



result, that the light of the stars towards which the Earth is 

 advancing has the same index of refraction, as the light of 

 the stars from which the Earth is receding. Speaking in the 

 language of the emission hypothesis, the celebrated observer 

 we have just named said, that bodies send forth rays of all 

 velocities, but that among these different velocities there is 

 only one which can awaken the sensation of light. ( 144 ) 



If we compare the velocities of solar, sidereal, and terres- 

 trial light, which all comport themselves exactly in the same 

 manner in the prism, with the velocity of the current of 

 friction-electricity, we are inclined to assign to the latter, 

 according to the experiments devised with admirable in- 

 genuity by Wheatstone, a velocity superior to the former 

 in the ratio of at least 3 to 2. According to the lowest 

 results of Wheatstone' s optical rotating apparatus, the elec- 

 tric current traverses 288000 English statute miles, or 

 250000 geographical miles, in a second. ( 145 ) If, then, we 

 reckon with Struve for sidereal light in the aberration- 

 observations 166196 geographical miles in a second, we get 

 a difference of 83804 geographical miles in a second for the 

 greater velocity of the electric current. 



This result appears to contradict the previously mentioned 

 view of William Herschel, which regarded the light of the 

 sun and of the fixed stars as perhaps the effect of an electro- 

 magnetic process, a perpetual Aurora. I say appears to 

 contradict ; for it cannot be deemed impossible that, in the 

 different luminous bodies of space, there may be several 

 magneto-electric processes very different in kind, and in 

 which the light produced by the process may have a different 

 rate of propagation. To this possible conjecture must be 

 added the uncertainty of the numerical result obtained with 



