ON THE DETERMINATION OF TRANSATLANTIC LONGITUDES. 



the intervention of a relay-magnet at the sending station, and acts through a i«-!a. 

 magnet at the receiving station, it is evident that the difference of time registered by 

 the two chronograph-sheets will express not only the difierenot of longitude and thrf 

 transmission time, but also the uncompensated resistance of the relay-magnet If the 

 difference of local times which obtains when such signals are sent from Cambridge to 



Duxbury is subtracted from the difference of local times when such signals are sent 

 from Duxbury to Cambridge, the remainder will represent not merely twice the trans- 

 mission time, but twice the transmission time increased by twice the resistance of the 

 relay-magnet. This. accounts for the large value of the appai nt transmission time 

 derived from the sidereal clock-signals when compared with the transmission time 

 indicated by hand-signals or by the Mean Time Clock-signals. 



The St. Pierre and Brest cables, when combined, make a total length of thirty-thrt 

 hundred and twenty-nine nautical miles. The total resistance of the cable between 

 Duxbury and St. Pierre amounts to 8980.51 ohms; the total resistance of the cab* 

 between St. Pierre and Brest (the greater diameter of the wire overbalancing the in- 

 creased length) is only 8152.80 ohms. When the resistance of the galvanometer 

 added to the sum of the above-named resistances, the whole resistance between Dux- 





1 



bury and Brest is found to be 18321.31 ohms. The degree of 



by saying that the gutta-percha resistance between Duxbury and St. Pierre is 1,722,70* 



megohms, and between St. Pierre and Brest 6,204,900 megohms; in all, 7,927^ ) 

 megohms. It appears that the transmission time of the electrical signals through this 

 cable is .816 of a second. It would be a hasty conclusion, however, to suppose tha 

 the velocity of electricity is 4,080 miles a second, or that it has any velocity 



or lio-ht 



mission 



which we speak of the velocity of a cannon-ball or of the velocity of 

 There is an advantage in substituting for the word nebo* the phrna. 



defining the velocity of electricity as 



d 





f 



any particular case divided by the time. The peculiarity of the motn.n 



distance to be traversed by the electricity had been greater, not only wool. a. add* 



tional time have been required for the additional distance, but more tune woul , e- 



,t distance. Ohm, in his admirable but too ^^ £ 



-^. 7 -«r>hn iCoifp maihemultwh, beat oeiu , aiu i 



published in 1827, under the title Du 9*~**" £ "P the abjee. of the 



treating of the permanent state of the galvanic cucmt, take u, j 



distribution of tensions in the variable state of the circmt, and arnves at tins 



quired for the fi 



-*<»**« 



a 



nx + a2(rn* m -~i 



i . •»( / +*) e p 



21 



** 



