by twisting Magnetized Iron and Nickel Wires. 129 



The current produced in iron wire caused an appreciable 

 deflexion of the galvanometer in a field of 200 units, and in 

 the same direction as for lower fields. On raising the 

 magnetizing force to 300 or 400 units, no current of measur- 

 able strength was produced. If the transient current becomes 

 reversed in direction, the deflexion of the galvanometer 

 becoming null in field of 300 units, an appreciable throw of 

 the mirror should have been noticed in the opposite direction 

 for § = 400 or =500. Judging from the fact that no such 

 change is observed, it seems probable that the current never 

 becomes reversed even bj further increasing the magnetizing 

 force. The current thus appears to decrease asymptotically 

 with the increase of magnetizing field. Professor Ewing 

 also arrived at a similar conclusion. 



The next point to be investigated was the effect of various 

 amounts of twist on the transient current. There are two 

 ways of examining the proposed problem. We may either 

 ■vary the magnetizing field, while the twist is kept constant, 

 and work out separately for different twists ; or we may keep 

 the magnetizing force constant while the twist is made to 

 vary. 



Both these cases have been tried. The first case was tried 

 with iron wire of different thicknesses, and the result is 

 shown graphically in fig. 3. The thinner wire was twisted 

 through ±15°, ±20°, ±30°, and ±60° (September 25, 

 1888). All these curves show that the current increases 

 with the increase of twist. The maximum point remains 

 nearly in the same magnetizing field for three small twists, 

 but is shifted toward stronger field as the twist is increased. 

 A similar tendency will also be noticed in the curves obtained 

 for the wire of *73 millim. radius (September 22, 1888). 

 The rate of decrease of the current as the field is increased 

 becomes more rapid for the thick than for the thin wire. 



Similar experiments performed on nickel wire of 0*43 

 millim. radius are shown graphically in fig. 1 (dotted lines). 

 They are for the twists of 30° and 60° respectively. The 

 increase of the current with the increased twist is quite 

 apparent, but nothing definite can be said about the shifting 

 of the position of maximum transient current. After a 

 certain strength of the magnetizing force, the current in- 

 creases so gradually, that without very delicate measurement 

 it is difficult to know exactly where the maximum point i^ 

 situated. 



To examine how the current increases with the increase of 

 twist, I had recourse to the second mode of investigation, i. e. t 



Phil. Mag. S. 5. Vol. 29. No. 176. Jan. 1890. K 



