.S7A' WILLIAM SIEMENS, F.R.S. 55 



Mi-. \\\ -nior Siemens in the value of the constant, proving that he 

 started with another unit. Mr. Werner Siemens's method has been 

 fully developed in " Poggendorff 's Annalen," vol. 102. 



In dealing with cylindrical jars, or with cables, this formula may 

 be written more simply thus : 



I.C 



A = n 



In our experiments the inductive capacity of a Leyden jar is 

 measured by the deflection of a galvanometer needle. If the 

 deflection of the needle is caused by a current of very short 

 duration, the quantity of the electricity passing through the 

 galvanometer is equal to 



A 



sm = . 

 v- __ . 



~r~ 



In practice it is found to be very difficult to read with sufficient 

 accuracy the sudden deflection of a needle, and we prefer for 

 practical use an instrument which we have placed before the 

 Section, enabling us to obtain a rapid succession of charging or 

 discharging currents which in passing through the galvanometer 

 produce a steady deflection of the needle, capable of being read 

 with great accuracy. The value of these deflections is calculated 

 by means of the following formula : 



If A is the angle through which the sine galvanometer has to 

 be turned to bring the needle to zero, C the number of charges or 

 discharges per second, E the electromotive power of the battery, 

 we have 



sin A* 



K= ^E~ 



* 



or if KI is the unit capacity of a jar and A the corresponding 



* In this case the amount of charge is represented by a constant deflection, 

 and therefore by sin A, whilst above, where it was given by one swing of the 



^ 

 needle, it is equal to sin - . 



