[ 284. ] 



XXXIV. On the Velocity of the Electrical Wave or Current 

 through a Metallic Circuit. By O. M, Mitchel, Director 

 of the Cincinnati Observatory^ . 



THE machinery now in use in the Cincinnati Observatory, 

 for the conversion of lime into space, furnishes the means 

 of executing the most delicate experiments in the record of 

 minute fractions of time. The sidereal clock is made to re- 

 cord its beats on a metallic disc, revolving beneath a steel 

 recording pen fixed in position. The disc which carries the 

 metal plate is made to revolve with uniform velocity, and 

 receives the stroke of the recording pen without affecting its 

 motion. A second pen, situated direcdy opposite the first, is 

 placed under the control of the observer at the transit or 

 other instrument, and gives him the means of recording any 

 observed phaenomenon with all the accuracy with which the 

 eye can seize the instant of its occurrence. 



On the completion of this machinery, several months since, 

 my attention was called to the velocity of electrical currents 

 in their passage along the telegraphic wires and through the 

 ground, as being involved in the determination of differences 

 of longitude by signals, transmitted telegraphically. 



On the evening of the 12th of November, a series of expe- 

 riments was performed at the Observatory, to determine the 

 velocity of the electrical wave in its passage along the tele- 

 graphic wires. The long circuit involved in these experi- 

 ments was formed as follows: — 



From the main battery in the O'Rielly Telegraph Office, 

 Cincinnati, along one wire to the observatory, a distance of 

 one mile; thence, by the continuation of the same wire, to 

 Pittsburg ; thence, returning on a second wire, to the obser- 

 vatory ; thence, through the receiving magnet, to a ground 

 wire; thence, one mile, through the ground, to the main bat- 

 tery in Cincinnati. 



The following is the plan on which the experiments were 

 conducted. The sidereal clock was so arranged that its pen- 

 dulum closed a local circuit, operating on the time-pen and 

 recording the alternate clock-beats or seconds, on a metal 

 plate placed on the revolving disc already described. This 

 connexion remained unchanged during the entire course of 

 the experiments, and this pen is called hereafter the standard 

 pen. 



A receiving magnet was made to close a short local circuit 

 (equal in power and length to the former), which operated on 

 the observation pen, causing it to strike its point into the metal 



* From the American Astronomical Journal, No. 2, December 13, 1849. 



