126 



Prof. J. A. Ewing. 



A to B gave + 7. By restoring 5° of positive torsion a state was 

 reached in which reversals of the battery gave no transient currents. 



§ 16. The effects which are obtained by twisting and untwisting 

 after the longitudinal magnetising force is removed are somewhat 

 more complex than those already described, on account of the fact 

 that a gradual shaking out of the residual magnetism takes place, 

 which is not, however, complete even after many twistings. For 

 example : — 



Transient Circular 

 current. magnetisation. 



At +60°, reverse A to B. +76 +38 



Break A sensibly +38 



-18 +20 



+ 60° to 



0° 



„ 



-60 



-60 „ 







„ 



+ 60 



+ 60 „ 







„ 



-60 



-60 „ 







„ 



+ 60 



+ 60 „ 



-60 



-60 „ 



+ 60 



-19 + 1 



+ 4 +5 



+ 12 +17 



-4 +13 



- 8 +o 



+ 4 +9 



+ 8 +17 



-11 +6 



+ 11 +17 



Ten more complete wistings ; then 



+ 60° to -60° - 9 +16 



-60 „ +60 +8 +8 



It is interesting to notice that the circular magnetisation has, so to 

 speak, received a permanent set to the side on which its earliest and 

 greatest value lay. 



§ 17. Another experiment, to show the production of circular out 

 of residual longitudinal magnetism : — 



Transient Circular 

 current. magnetisation. 



Make and break A at 0° . . . 



Then, 0° to +60° +18 +18 



At +60, remake A +20 +38 



§ 18. The following table shows the relative amounts of circular 

 magnetism developed in an iron wire (the wire of § 2), with one. 

 constant amount of torsion (60°) by different intensities of longitu- 

 dinal magnetising force. It will be noticed that a maximum of effect 

 is passed at about 15 or 16 c.g.s. units. 



