MAGNETISM 



If the throw due to this is 6 any other throw will indicate 



flow of 



10 KG 



coulombs. 



In carrying out a test on a ring it is first demagnetised by 

 reversals, as already described in the magnetometer method. Thru 

 a small current A 1 is established in the coil A,prodocing within it 

 afield H 1 = 4 7 rNA 1 /10. If this creates induction \\ 1 through tin- 

 secondary coil the flow of electricity in the ballistic galvanometer 



will be -rjr-i and if the throw is O l 



It 



/iB, 



TT 



whence 



. 



Unless the primary coil A is very close in every turn to the iron 

 a correction must fee subtracted from Bj for the induction through 

 the space between wire and iron. If the mean area of the coil i> 

 S'and the cross-section of the iron i>S. the amount to lu-siiht ra< -ted 

 from B A to give the induction in the iron is (>' S) II r But the 

 correction is very small. 



The current in A is then inerea>ed by an addition of \ 

 amperes. This increases the field by H 2 , and the induction bv B., 

 measured by the new throw of the ballistic galvanometer. The 



