on Magnetic Testing,. 



each of the currents in the coil. This will be seen from fig. 2, 

 which exhibits ?ome results obtained on testing a specimen 

 steel. OABCD is the magnetization curve for the 



Fi ff . 2. 



of 



material in the neutral condition. If now, starting with 

 the specimen in this condition, the strength of the field is 

 changed from to B^, the induction becomes B x ; that is to 

 say, the point A on the curve is arrived at. Now let the 

 current in the magnetizing coil be reversed. The induction 

 changes from -f-Bj to — B x ; the kick of a ballistic galvano- 

 meter connected to a secondary coil wound on the specimen 

 would be proportional to 2B X . If the field is once more 

 reversed the induction becomes -f B x ; that is, after the 

 double reversal the point A is once more reached. Let now 

 the field be gradually increased from +H X to + H 2 , and the 

 induction in the specimen will follow the curve from A to B. 

 If after arriving at the point B the field is changed from 

 + H 2 to — H 2 , the induction changes from +B 2 to —Bo ; 

 the kick of the galvanometer is therefore proportional 

 to 2B 2 . Following this procedure the complete curve may 

 be traced out. 



