&8 Messrs. K. Honda and T. Terada on the Change of 



(b) Measurement of the Change of Rigidity by 

 Barns' s method. 



The same specimens, on the other hand, were tested by the 

 differential method used by Barus *, in which the wires were 

 first twisted and then magnetized. In onr experiments, 

 instead of the magnetic wire, a copper one was used for the 

 compensation of the twist at no field, in order to avoid any 

 ambiguity caused by the magnetization of the compensating 

 wire. The specimens were cut from the previous samples 

 into about one-third of their lengths. The copper wire was 

 so chosen that its total twist for a given couple was nearly 

 equal to that of the magnetic specimen to be tested. The 

 two wires were connected in the same line by a copper rod of 

 moderate diameter with a small mirror attached to it, and 

 hung vertically from a torsion circle. The lower end of the 

 specimen was also rigidly connected to another copper rod. 

 To this rod, a rigid pin was perpendicularly fixed, the ends 

 of which slid in the vertical grooves cut on the inside of a 

 flat hollow cylinder at the centre of the lower torsion circle. 

 In this way, the tension applied to the pan hanging on the 

 lower end of the lower copper rod was transmitted inde- 

 pendently of the twist. The upper and lower ends of this 

 connected system could therefore be twisted to any desired 

 amount by means of the torsion circles, while the tension was 

 constantly acting on the wire. A magnetizing coil, whose 

 length was 30 cm. and Aim— 379*7, was placed co-axially 

 with the lower wire, which was, in our case, the specimen to 

 be tested. The coil had a small resistance of 0'6H, so that 

 the effect of heating was negligibly small, though the water- 

 jacketed arrangement was dispensed with. A long scale 

 distance of 6'797 m. was used to increase the sensitiveness 

 of the arrangement. The sensitiveness w<as such that a 

 deflexion of 1 scale-division corresponded to a change of total 

 twist of 15""2. 



To stop the vibration of the mirror, a short brass wire was 

 fixed horizontally to the vertical copper rod a little below the 

 reflecting mirror and bent downward. Just below it, a small 

 mercury cup w r as placed, into which the wire dipped. 



Our method of observation was as follows : — First the 

 torsion circles were adjusted so that the magnetic field 

 produced no deflexion of the mirror. The readings of both 

 circles for this position corresponded to those of the untwisted 

 state of the wire. Next the lower circle was twisted by 



* Barns, Joe. tit. 



