APPLICATION OF THE ELECTKIC TELEGRAPH. 353 



servation here employed, the velocity of the electric 

 current is insensible for the distance between Berlin and 

 Frankfort ; a distance which, by the circuitous route of the 

 telegraph, amounts to about 300 English miles. 



In November, 1853, the difference of longitude be- 

 tween the observatories of Greenwich and Brussels was 

 determined by means of the electric telegraph. A gal- 

 vanic telegraph needle was mounted in the observatory 

 at Brussels in close proximity to the transit-clock, nearly 

 as in the Greenwich observatory. The signals to be 

 made were simple deviations of the needle, produced 

 directly by the galvanic current through the long com^ 

 municating wire. 



It was arranged that the observations should be divided 

 into two series : that in the first series an observer from 

 Brussels (M. Bouvy) should observe both the galvanic 

 signals and the transits for correcting the transit clock at 

 Greenwich, while an observer from Greenwich (Mr. Dun- 

 kin) made the corresponding observations at Brussels ; 

 that this series should be continued till satisfactory ob- 

 servations had been obtained upon at least three even- 

 ings ; that the observers should then be reversed, and the 

 second series be observed in the same manner. The 

 signals were to occupy one hour in each evening, from 

 lOh. to llh. Brussels mean solar time, each hour being 

 divided into four quarters. The contacts of wires for 

 completing galvanic circuit were to be made at Green- 

 wich and with a Greenwich battery in the first and third 

 quarters, and at Brussels with a Brussels battery in the 



