IRON, STEEL, AND NICKEL TUBES IN THE MAGNETIC FIELD. 555 



was also measured after the magnetic strain experiments were made, was found on trial 

 to have in no way changed its behaviour. 



To see what other changes could be produced, the steel tube (No. VII.) was 

 annealed by being allowed to cool over night slowly in lime from a temperature of a 

 dull red heat. It was then set up in the usual way, and the changes of volume in 

 various fields measured. For purposes of easy comparison the volume changes accom- 

 panying definite fields of the tube in its three conditions are given in the immediately 

 preceding table. The second column reproduces the column under VII. (brass cap) of 

 the table on p. 537 ; the third column gives the results obtained on March 4th ; aud 

 the fourth column the measurements of March 11th after the tube had been annealed. 



A glance at the volume changes in the first and second conditions of the tube 

 shows the extraordinary character of the mysterious change which must have occurred 

 in the molecular stability of the tube. In its second condition the tube behaves more 

 after the fashion that might have been expected, although the magnitude of the volume 

 change is considerably greater than in the case of Tube VI. The effect of annealing is 

 greatly to diminish the magnitude and to make Tube VII. much more like the others. 

 Probably, then, the difficulty of tracing out any marked law of volume change in the 

 transition from tube to tube in the case of steel is due to heterogeneity and unequal 

 tempering in the original bar. 



VOL. XXXVIII. PART III. (NO. 13). 4 F 



