116 COSMOS. 



tricity, recently conducted in the United States by Walker 

 during Ihe course of his electro-telegraphic determinations of 

 the terrestrial longitudes of Washington, Philadelphia, New 

 York, and Cambridge. According to Steinheil's description of 

 these experiments, the astronomical clock of the Observatory 

 at Philadelphia was brought to correspond so perfectly with 

 Morse's writing apparatus on the telegraphic line, that this 

 clock marked its own course by points on the endless paper 

 fillets of the apparatus. The electric telegraph instantaneously 

 conveys each of these clock times to the other stations, indi- 

 cating to these the Philadelphia time by a succession of similar 

 points on the advancing paper fillets. In this manner arbitrary 

 signs, or the instant of a star's transit, may be similarly noted 

 down at the station by a mere movement of the observer's finger 

 on the stop. " The special advantage of the American method 

 consists," as Steinheil observes, " in its rendering the determi- 

 nation of time independent of the combination of the two senses, 

 sight and hearing, as the clock notes its own course, and indicates 

 the instant of a star's transit (with a mean error, according to 

 Walker's assertion, of only the 70th part of a second.) A 

 constant difference between the compared clock times at Phila- 

 delphia and at Cambridge is dependent upon the time occupied 

 by the electric current in twice .traversing the closed circle 

 between the two stations." 



Eighteen equations of condition, from measurements made 

 on conducting wires of 1050 miles, gave for the velocity of 

 transmission of the hydro-galvanic current 18700 miles, 57 



67 Steinheil in Schumacher's Astr. Nachr., no. 679 (1849), 

 s. 97-100; Walker in the Proceedings of the American Philo- 

 sophical Society, vol. v. p. 128. (Compare earlier propositions 

 of Pouillet in the Comptes rendus, t. xix. p. 1386.) The more 

 recent ingenious experiments of Mitchel, Director of the Obser- 

 vatory at Cincinnati (Gould's Astron. Journal, Dec. 1849, p. 3, 

 On the velocity of the electric ivave\ and the investigations of 



