OX TRANSIENT ELECTRIG CURRENTS. Obi 



r = 0.77. For the latter, it is near the field giving the maximum tran- 

 sient current. Had the field been stronger, the curve for the thick 

 wire would have lain far above that for the thin wire. 



In the preceding experiment, we found that the maximum point 

 of the curve was shifted into stronger i\c]d* as the radius of the wire was 

 increased. This shews that if the magnetizing field be kept constant, 

 a large amount of twist must be applied to the thin wire in order to 

 produce the maximum current. The angle of twist corresponding to 

 the maximum current as found from the present set of experiments 

 are as follows : — 



For r=1.00, angle of twist corresponding to max. cur. = 36° 

 „=0.77, „ 44° 



„ = 0.62, „ 60° 



„=o.44, „ ir. 



Thus the angle of twist at which the maximum current occurs 

 becomes greater as the radius of the wire becomes smaller. 



Professor Ewing* in discussing the apparent discrepancy in the 

 direction of the transient current as obtained by him and by Matteucci 

 attributes it to the fact that in Matteucci's experiments, the amount 

 of twist as well as the magnetization of the iron bar were so great that 

 the Villari critical point had been passed. Unfortunately Matteucci's 

 experiments were performed at a time when the current was not 

 measured in units now in general use. It is now impossible to 

 know the exact value of his magnetizing field ; but it is no doubt 

 true, since the iron bars examined by him, were over 5 mm. thick, 

 that the pull and push produced by twisting were very great ; and 

 judging from the number of Grove cells he used, the magnetizing 

 field must have been strong. According to the experiments of Pro- 

 fessor Ewing, the Villari critical point comes earlier with strong 

 than with weak stresses. Thus it is quite probable that in Matteucci's 



* Proc. H. S., 1884. 



