76 SPECIAL RESULTS IN THE URANOLOGICAL 



Wheatstone's apparatus, which result he himself regards as 

 "not sufficiently established, and as requiring fresh confir- 

 mation" in order to be compared satisfactorily with the de- 

 ductions from aberration- and satellite- observations. 



Later experiments made by Walker in the United States 

 of North America on the velocity of the propagation of elec- 

 tricity, on the occasion of his telegraphic determinations of 

 the longitudes of Washington, Philadelphia, New York, and 

 Cambridge, have excited a lively interest in the minds of 

 physical enquirers. According to Steiuheil's description of 

 these experiments, the astronomical clock of the Observatory 

 at Philadelphia was connected with Morse's writing appa- 

 ratus on the line of telegraph in such manner, that the clock's 

 march noted itself by points on the endless strip of paper of 

 the apparatus. The electric telegraph carries each of these 

 points instantaneously to the other stations, and gives them 

 the Philadelphia time by similar points on their moving strips 

 of paper. Arbitrary signals, or the instant of the passage of 

 a star, may be noted in the same manner by the observer, by 

 merely touching or pressing an index with his finger. The 

 material advantage of this American method consists, as 

 Steinheil expresses it, " in its making the determination of 

 time independent of the connection of the two senses, 

 sight and hearing ; as the clock's march notes itself, and the 

 instant of the star's passage is given direct (to within a mean 

 error of the 70th part of a second, as Walker states) by the 

 movement of the observer's finger. A constant difference 

 between the compared clock-marks of Philadelphia and 

 Cambridge is produced by the time which the electric cur- 

 rent requires to traverse twice the closed circuit between the 

 two stations/' 



