166 Dr. E. Taylor Jones on 



annealed soft iron (of diameter 0586 millim.) could be drawn, 

 which fitted accurately in front and more loosely behind. 

 The friction was thus only a fraction of 1 gramme weight. 



The end of the wire was also carefully polished and, as well 

 as the opposite small pole-face, examined and measured with 

 a Zeiss microscope. 



With a magnetizing current of 25 amperes, the weight 

 supported in this case was 249 grms. weight ; this corresponds 

 to a pull of 92*39 kilogs. weight per sq. centim. (1314 lb. wt. 

 per sq. inch). 



The maximum value of the magnetization was, moreover, 

 determined by means of an isthmus consisting of a bundle of 

 50 pieces of the same wire pushed through the former pole- 

 pieces of 78° 28' vertical angle. This value was found to be 

 about 1800 C.G-.S. 



Taking also 500 grms. weight as the approximate value of 



1 P 1 

 the integral - I TLdL we have from these data the values of 



ffj* 



B 2 — H 2 , and of B — H = 47rl ; from these were deduced the 



values 



B= 61,900 C.G.S. 



H= 39,300 „ 



These experiments were extended still further by drawing out 

 the wire to a thickness of 0*2412 millim., and narrowing 

 down the hole in the pole-piece correspondingly. 



After the wire had been once more annealed in a spirit-flame 

 and its end ground plane, the weight supported with a 

 current of 40 amperes was 52*5 grms. weight, corresponding 

 to a pull of 114*9 kilogs. weight per sq. centim. (1634 lb. 

 wt. per sq. inch). 



Hence follow, as above, the values 



B = 74,200 C.G.S. 

 H= 51,600 „ 



and the permeability is only 



^=B/H = 1*44. 



The calculated value of H from the Stefan-Ewing loga- 

 rithmic formula is 50,450 C.G.S., assuming that the conical 

 pole-pieces are uniformly magnetized with a maximum inten- 

 sity of 1800 C.G.S. To this must be added about 750 G.G.S. 

 due to the direct action of the coils of the electromagnet with 



