THE THERMO-ELECTRIC EFFECTS OF LONGITUDINAL STRESS IN IRON. ^\ 



the maximum and minimum points, agitation imparted to the wire 

 tends to shift the representative points lower in the diagram on the 

 "on" branch, while it is just the opposite on the "off" branch. 

 Below and up to the maximum point on the " on " branch the 

 representative points are shifted upwards, and beyond the minimum 

 points on the two branches shifted downwards though to very small 

 extents. If the effect of agitation is solely to shake out the traces of 

 hysteresis, then such an experiment as the above can be regarded as 

 one which would contribute much towards the understanding of the 

 nature of the hysteresis itself. 



§ 15. The above experiment was varied in such a way that 

 throughout either "on " or "off" branch the wire was kept undisturbed 

 or tapped, while throughout the other branch tapped or kept un- 

 disturbed. The results, obtained with a piece of wire cut from the 

 same bundle as above but with quite a different experimental arrange- 

 ment, are shown in Fig. 15, PI. Ill, in which the curves for un- 

 disturbed conditions are drawn in full lines and those for agitated 

 conditions in dotted lines. An inspection of the figure will show 

 that the full " off" branch, when taken in conjunction with the full 

 " on," would make up a complete cyclic curve obtained in the usual 

 way, while the dotted " on " with the dotted " off" make up a com- 

 plete cyclic curve obtainable by continually tapping the wire. 



In the above experiment the order of the processes gone through 

 is that indicated in the figure by arrow heads. Experiments made 

 specially showed that the general character of the curves is indepen- 

 dent of the order, that is to say, we obtain the same results when we 

 go through, first the " on " branch without agitation, next the " off" 

 with it, then the " on " again with it, and lastly the "off" without 

 it. This is consistent with the result at the end of § 13. 



§ 16. All the foregoing experiments show very well with what 



