MAMXETlZA'l'IiiN of XK'KKL. ^^5 



torsion and detorsion, uotwith.stunding the alj.suliite coiistuncy of the 

 magnetizing force botli in diivction and magnitude. This critical 

 vahie of the load seems to vary with the fstreno'th of the mag-netizinf 

 field, becoming greater as the Held is increased. All these points Avill 

 be described in the following pages. 



I must here expi'ess my tlianks to Dr. C. G. Knott, for his kind 

 suggestions during the course of experiments. 



The intensity of magnetization was measured by a direct inagnet- 

 ometric metliod. The magnetometer consisted of a small mirror 

 hung by a spider thread 11 cms long. This was geometrically fixed 

 in position on a wooden plank according to Thomson's method of the 

 hole, slot, plane. Levelling was effected by three base-screws. In 

 front of the magnetometer a lamp was placed, and the image of the 

 slit was reflected on a circular scale. Its radius was 1 metre, and 

 it was so placed that the magnetometer was just at its centre. The 

 wire to be examined was set vertically due east of the magnetometer. 

 The upper end of the wire was level with the centre of the magneto- 

 meter mirror. i'o each end of the wire, a short stout brass wire was 

 brazed. I'he lower of these was bent into a hook, so that a pan 

 holding the weight could be hung from it. The uppei- one was 

 ri\eted to a strong brass rod projecting from the middle of tlie side 

 of a table, w iiich rested on stone piers. The nickel wire* was sur- 

 rounded by a magnetizing c(nl rl5 cms. long. The resistance of the 

 (;oil was IS*. (I Ohms, and the strength of the held for a current of one 

 ampere was 138.4 C < J. .S. units. The magnetizing current was sent 

 from 1:^ Daniel I cells, and its strength was adjusted by means of a 

 liquid slide, and measured by a tangent galvanometer. 



• This mre contained 1.7 per cent, of iron, Ijesides small rjuantities of carbon as iuipuiutics. 



