358 HISTORY OF ASTRONOMY. 



and the preceding clock pause, longer at Washington 

 than at Cambridge, and the excess on the Washington 

 register will measure twice the time consumed in the 

 transmission of the signals between the two stations. 



Thus, in the following figure, let the upper line rep- 

 resent a portion of the Washington time scale, corre- 

 sponding to 15, 16, etc., seconds, and the lower line the 



Washington, _J5 * J7 18 



Cambridge,' . g _ _ -^ fl ^- 



same for Cambridge, each division being a little later 

 than the corresponding one for Washington. Then if 

 an arbitrary signal is made at Cambridge between 16 and 

 17 seconds, and printed at A, the record on the Wash- 

 ington scale will be at B, and the interval from 16 to B 

 will exceed that from 16 to A by twice the time con- 

 sumed in the transmission of the signals from Cambridge 

 to Washington. 



In the observations of January, 1849, Professor 

 Walker detected a difference in the registers of the papers 

 at the several stations, and it indicated a velocity of the 

 electric wave of 18,800 miles per second.* 



On the 31st of October, 1849, similar experiments 

 were repeated between Washington and Cincinnati, in- 

 dicating a velocity of only 16,000 miles per second.f 



Dr. B. A. Gould has discussed the same experiments, 

 and has deduced from the observations of January 23d a 



* Proceedings Am. Phil. Soc., vol. V., p. 76. 

 f Astronomical Journal, vol. I., p. 55. 



