THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



NOVEMBER 1876. 



XLI. On a Method of Measuring the Contour of Electric Waves 

 passing through Telegraph Lines. By Robert Sabine *. 



YARIOUS methods have during the last forty years been 

 suggested and put in practice with the view of ascertain- 

 ing the time which elapses between starting electricity into one 

 end of a conductor, and the instant when the advancing wave 

 acquires strength to do the work necessary to give some indi- 

 cation at the other end. 



Sir William Thomson, in his admirable paper on the " Theory 

 of the Electric Telegraph," has clearly shown that, in any form of 

 conductor with any given receiver, the time required for a wave 

 to give a signal is dependent upon the induction and the resist- 

 ance of the line, or what is termed its " retardation." It may also 

 be stated that, with any given line, this time is dependent both 

 upon the sensitiveness and the resistance of the indicating- 

 instrument ; by decreasing the sensitiveness or by increasing 

 the resistance interposed by the instrument, the observed time 

 is increased. Professor Wheatstone, in his celebrated expe- 

 riment with the rotating mirror, measured the time which 

 the discharged contents of his Ley den jar required to gather 

 tension enough to spring over one tenth of an inch of air after 

 it had passed through 440 yards of copper wire. Had he in- 

 creased the length either of the spark or of the copper wire, he 

 would necessarily have increased the observed time also. To- 

 day any attempt to measure the velocity of an electric wave 

 by frictional electricity would scarcely be expected to afford 



* Communicated by the Author. 

 Phil. Mag. S. 5. Vol. 2. No. 12. Nov. 1876. Y 



