MAGNETIC EFFECTS OF TWIST. 181 



this area. An incomplete cycle for ± 20 7r indicates an approximate 

 area of 10,000 w. At these very high twists, the wire must of course 

 be severely strained ; the great regularity of the magnetic effect is, 

 in the circumstances, all the more remarkable. 



With these results before us, a very natural enquiry was as to 

 the existence of similar peculiarities in the case of longitudinally 

 magnetised nickel wire. Mr. Imagawa had time only for a few experi- 

 ments, but these were enough to establish the existence of the pecu- 

 liarity. The most complete results of these experiments are given in 

 Table III. The first column gives the twists in ordinary degrees or 

 in multiples of tt ; the second and third columns give, as in Table I, 

 the going and returning measurements of the magnetic condition of 

 the wire ; and the fourth column gives the differences between the 

 corresponding numbers in the second and third columns. The num- 

 bers are not given in absolute measure, but simply in terms of the 

 scale unit.* The wire used was 0*85 millimetres in diameter and 52 

 centimetres in length. Thus the twists as given correspond to twists 

 per centimetre of ± 0°'58 , ± 0°-87 , ± 1°-16 , ± l°-73 , ± 2°-32 , 

 ±3°-47 , ±6°-94 , ±17°-3. 



The results are graphically shown in Plate II., the twists being 

 taken as abscissae and the relative intensities as ordinate«. All the 

 curves are double-looped, and are nearly symmetrica] for the higher 

 cyclic twists. For the first five cycles, namely, ± 30° , ± 45° , 

 ± 60° , ± 90° , ± 120° , there is true magnetic lag, the return 

 curve at either limit always being above the other. In the curve for 

 ± 180° , ± 2 TT , and ± 5 tt 3 how r ever, the magnetic lag becomes 

 negative. This change in algebraic sign is also shown by the signs 

 of the numbers in column four of Table III, as will be at once seen 



* Mr. Imagawa has, indeed, left no record of the constants of the magnetising coil which he 

 used, so that it is impossible to reduce the numbers to absolute measure. So far as the present 

 discu-sion is concerned, this is, however, of no real importance. 



