110 Systems of Conductors [CH. iv 



where q llt -^ are supposed calculated for = 0. Since F 2 = 0, we have from 

 equation (56), 



so that Q 



shewing that for small values of 0, Q is directly proportional to 6. 



Let us suppose that we join the first pair of quadrants (conductor 1) 

 to a condenser of known capacity T which is entirely outside the electro- 

 meter. Since the needle (3) is entirely screened by the quadrants the value 

 of q l3 remains unaltered, while q n will become q n + T. If & is now the 

 deflection of the needle, we have 



so that, by combination with the last equation, we have 



i\_ r 

 & e ' 



If 6" is the deflection obtained by joining the pairs of quadrants to the 

 terminals of a battery of known potential difference jD, we have from 

 equation (56), 



CV - 

 V *~ ])' 



and on substituting this value for CV 3j our equation becomes 



__ 



& e 



giving Q in terms of the known quantities F, D and the three readings 

 0, 0' and 0". 



REFERENCES. 



On the Theory of Systems of Conductors : 



MAXWELL. Electricity and Magnetism. Chapter in. 



On the Theory and Use of Electrostatic Instruments : 



J. J. THOMSON. Elements of the Mathematical Theory of Electricity and Magnet- 

 ism. Chapter in. 

 MAXWELL. Electricity and Magnetism. Chapter xin. 



