140 ANNUAL OF SCIENTIFIC DISCOVERY. 



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. 

 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. If we com- 

 pare the velocities of solar, sidereal and terrestrial 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 

 ingenuity by Wheatstone, a velocity superior to the former in the ratio 

 of at least three to two. According to the lowest results of Wheat- 

 stone's optical rotating apparatus, the electric current traverses 288,000 

 English statute miles, or 250,000 geographical miles, in a second. If, 

 then, we reckon with Strove for sidereal light in the aberration observa- 

 tions 166,196 geographical miles in a second, we get a difference of 

 83,804 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 can- 

 not 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 differ- 

 ent rate of propagation. To this possible conjecture must be added the 

 uncertainty of the numerical result obtained with Wheatstone's appa- 

 ratus, which result he himself regards as " not sufficiently established, 

 and as requiring fresh confirmation," in order to be compared satisfac- 

 torily with the deductions from aberrations and satellite observations. 

 Later experiments, made by Walker, in the United States, on the veloc- 

 ity of the propagation of electricity, on the occasion of his telegraphic 

 determination of the longitudes of Washington, Philadelphia, New 

 York and Cambridge, have excited a lively interest in the minds of 

 physical inquirers.* 



Measurements made Avith conductors 1050 English statute miles, or 

 968 geographical miles, in length, gave, from 18 equations of condi- 

 tion, the rate of propagation of the hydro-galvanic current at only 18,700 

 statute, or 16,240 geographical miles in a second, that is, fifteen times 

 slower than the electric current in Wheatstone's rotating disc appa- 

 ratus. As in Walker's remarkable experiments two wires were not 

 used, and but half the conduction, according to the common expression, 

 took place through the moist body of the earth, it might seem a justi- 

 fiable supposition that the velocity of the propagation of electricity is 

 dependent on the nature as well as on the dimensions of the medium. In 

 the voltaic current bad conductors become more heated than good con- 

 ductors, and electric discharges are very variously complicated phe- 

 nomena, as appears by the latest experiments of Reiss. The now 

 prevailing views of what is commonly called " connection through the 

 earth'* are opposed to the view of linear conduction between the 



* Annual Scientific Discovery, 1850, Vol. I., pp. 12i 127. 



