on Magnetic Testing. 9 



reversing a number of times, a, magnetizing field of 11 c.G.s. 

 units in a solenoid containing a specimen of steel in the 

 freshly annealed condition. It will be seen that the change 

 of induction brought about by the first reversal is 7572 c.G.s. 

 units, whereas that brought about by the tenth is 6248 c.G.s. 

 units. Hence the induction calculated from the first throw 

 of a ballistic galvanometer connected to a secondary coil 

 wound on the helix would be over 20 per cent, in excess of 

 that which is characteristic of the material when in the cyclic 

 condition. 



Table II. 



Val ue of H in 



Induction in 



Change of 

 Induction 



c.G.s. units. 



c.G.s. units. 



on reversitl. 



+ 11 



4186 



7572 



-11 



3386 



6859 



+ 11 



3473 



6746 



-11 



3273 



6559 



+ 11 



3286 



6484 



-11 



3198 



6S96 



+ 11 



3198 



6359 



-11 



3161 



6285 



+ 11 



3126 



6250 



-11 



3124 



6248 



+ 11 



3124 





The table shows that the results of tests which have been 

 carried out on annealed steel are very approximately correct, 

 even though the specimen had not been submitted to the 

 process of reversals, provided that the magnetizing current 

 has been reversed nine or ten times previous to the galvano- 

 meter-throw being observed. A magnetization curve so 

 obtained would, however, lie slightly above the curve which 

 is characteristic of the material when in the truly neutral 

 condition. 



Fig. 4 shows the magnitude of the " Sensitive State ** 

 induced in a specimen of steel by cooling from room temper 

 rature to that of liquid air boiling under normal conditions 

 (about —190° C). Curve I. is the magnetization curve 

 for the material at room temperature when in the neutral 

 condition. This curve having been obtained, the specimen 

 was subjected to the neutralizing process and brought to the 



