120 Mr. H. Nagaoka on the Effects of Torsion and 



It might at first sight appear that this arrangement might 

 prevent the longitudinal stress being applied uniformly for 

 various angles of the twist, because of the friction of the rod 

 against the Vs. To test this point the wire was fixed by the 

 screw and the longitudinal pull applied by known loads hung 

 on below. The upper end of the wire was fastened to a spring- 

 balance, by means of which any variations of stress could at 

 once be detected. With a given load, the wire was twisted 

 through various angles ; but scarcely any sensible variation 

 of longitudinal stress was indicated. 



The magnetic experiments were conducted in the following 

 manner : — At first a constant current was made to pass through 

 the magnetizing coil and the magnetometer-zero was deter- 

 mined. The M'ire was then placed in position, and was first 

 twisted through 180° in what we call the positive direction ; 

 although it may be stated once for all that the positive direc- 

 tion means the first chosen direction, whether that is, so to 

 speak, with the magnetizing current or against it. Then 

 after a complete revolution in the opposite direction, it was 

 brought back to its original position. This process was 

 repeated till the changes became nearly cyclic. Then at every 

 successive 20° of twist, the deflexion of the magnetometer- 

 magnet as given by the scale-reading was taken and noted, 

 the reading being observed by means of a telescope. Each 

 complete set of experiments was made in a constant magnetic 

 field, while the wire was subjected to gradually-increasing 

 longitudinal stresses. The results thus obtained are given in 

 C.Gr.S. electromagnetic units, though such reduction is not 

 necessary in experiments of this kind. The observed values 

 of the intensity 3 for successive 60° of twist are given in the 

 Appendix. In the figures showing the changes of magneti- 

 zation, the abscissse denote the amount of twist, while the 

 ordinates represent the intensity of magnetization 3. 



The first experiment was made with a nickel wire 40 centim. 

 long, and 1 millim. thick. The wire was deprived of its initial 

 magnetism by heating it red-hot. It was then placed vertically, 

 and so came under the influence of a magnetic field of '34 

 C.G.S. units. With a steady load of "64 kilog. the wire 

 was subjected to repeated twisting and untwisting. After 

 six such operations, the changes became nearly cj-'clic, and 

 the following readings of deflexions were taken at the seventh 

 cycle : — 



