APPLICATION OP THE ELECTRIC TELEGRAPH. 357 



The difference of longitude between Greenwich and 

 Paris for nearly thirty years had been assumed to be 

 9m. 21s.5 ; and this result is now concluded to have been 

 too great by an entire second of time. 



The time occupied in the transmission of the electric 

 current was found to be Os.086 at Greenwich, and Os.079 

 at Paris, the distance being about 300 miles. 



DETERMINATION OP THE VELOCITY OP THE ELECTRIC 

 CURRENT. 



The experiments of January 23d, 1849, between Cam- 

 bridge, New York, Philadelphia, and Washington, 

 afforded an approximate determination of the velocity 

 of the electric fluid. If the fluid requires no time for 

 its transmission, then the star signals given at either 

 station ought to be similarly printed at all the stations ; 

 and the fraction of a second registered upon any one 

 scale should be identically the same as upon every other. 

 But if the fluid requires time for its transmission, these 

 fractions will be different. Suppose the clock to be at 

 "Washington ; that an arbitrary signal is made at Cam- 

 bridge ; and that the time required for the transmission 

 of a signal between the two places is the thirtieth of a 

 second. Then the clock pause will be registered at Cam- 

 bridge -f-yth of a second after it took place and was re- 

 corded at Washington, and the arbitrary signal pause 

 will be recorded at Cambridge as soon as it is made, or 

 s^-th o f a second before it reaches Washington. We 

 shall thus have the interval between the signal pause 



