THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



MA Y 1876. 



XLI. On a Method of Measuring very small Intervals of Time. 

 By Mr. Robert Sabine*. 



THE method I am going to describe of determining any 

 very small interval of time which elapses between two 

 successive mechanical actions, I believe to be trustworthy when 

 proper precautions are used, It is based upon the fact that a 

 charged Ley den jar or other form of accumulator f can only 

 be discharged at a certain definite rate through a given 

 circuit. 



It is common knowledge that if a telegraph cable or accu- 

 mulator have an electrostatic capacity of f farads, and the 

 resistance to leakage or discharge between its two sides be R 

 ohms, the time (t seconds) required for any initial charge of 

 the potential P to diminish to a remainder at the potential p 

 will be 



p 

 t=fR log e — seconds, 



assuming that all the electricity which we have to deal with 

 resides upon the coatings and that it is free to be discharged. 

 This proportion, otherwise expressed, is commonly used for 

 finding the insulation resistances of submarine cables when 

 their capacities are known and the initial charge is allowed to 

 leak or discharge through the dielectric alone during a given 

 umber of minutes. 

 In employing this method for the measurement of time, it is 



Communicated by the Author, 

 t Commonly called a " condenser." 



Phil. Mag. S. 5. Vol. 1. No. 5. May 1876. 2 A 



