1892.] 



On measuring High Electrical Resistances. 



341 



resultant fault or point of zero potential ; and for measuring the in- 

 sulation of the circuit while the pressure is on. 



Connections. The method consists in connecting the quadrants of 

 an ordinary quadrant electrometer to the terminals of a source of 

 fairly high E.M.F., while the aluminium vane or needle is connected 

 to earth. 



The resistance to be determined is connected to one side of this 

 arrangement, and a variable resistance of the same order of magnitude 

 to the other side, the free ends of each being connected to earth. 



The centre of the battery, or other source of E.M.F., is then earthed 

 for a short time, bringing the needle to the zero reading, and, after 

 the removal of this earth connection, the needle will travel to one 

 side or the other, unless the resistance to the passage of electricity 

 from each pole to earth is exactly equal, in which case the needle will 

 remain permanently at zero. 



By observing the motion and varying the comparison resistance 

 accordingly, this balance is soon arrived at, if within the range of 

 variation provided. 



The arrangement is shown in the figure, where B is the battery or 

 other source of E.M.F., Q the quadrants, N the needle, X the un- 

 known resistance, and B the variable resistance. The earth contacts 

 are shown by E. 



Diagram of connections for electrostatic balance for very high resistances, 

 opposite quadrants of electrometer are not shown. 



The 



Principle. The method depends upon the well-known fact that 

 every source of electricity produces equal quantities of what are 



