GAUGAIN'S DISCHARGE ELECTROMETER. 201 



measured, it is advantageous to connect this body to the electrometer 

 by a bad conductor, such as a cotton thread, in order to retard the 

 discharges. As a general rule, a complete discharge is not effected, 

 and there remains on the system of conductors a residual charge 

 incapable of giving contact to the gold-leaf in the electrometers ; 

 this residue may be measured by various methods, on which we need 

 not enter.* 



If the cotton thread connects the electrometer, not with an 

 electrified body, but with a source at constant potential, or with a 

 conductor of large capacity, such as a battery, the number of dis- 

 charges in unit time measures the yield of electricity, and therefore 

 the strength of the current which traverses the wire. 



On the other hand, if the potential of the source is very high 

 compared with the variable potential of the gold-leaf during the 



Fjg. 159- 



alternating insulation and discharge, the yield is proportional to the 

 potential of the source. This experiment furnishes thus a very simple 

 means of comparing potentials of the magnitude of those we meet 

 with in the phenomena of statical electricity. 



If the discharge electrometer is connected with a closed con- 

 ducting cylinder (58), we might also compare electrical charges the 

 division, for instance, of electricity between two conductors of any 

 given shape ; it would be only necessary to count the number of 

 discharges which each of them gives, after they have been in contact, 

 when it is introduced into the cylinder. 



825. CAPILLARY ELECTROMETER. This very delicate instrument, 

 invented by M. Lippmann,f enables us to determine the difference of 



* MASCART. Traite d'Electricite Statique, Vol. i., p. 417. 1876. 

 t LIPPMANN. Ann. de Chim. et de Phys. [5], Vol. v., p. 494. 1873. 



