334 Mr. R. H. M. Bosanquet on Electromagnets. 



As I propose shortly to undertake further experiments, I will 

 only indicate the nature of the general conclusions. 



Curves of Magnetic Besistance of Bars I, and II. 



—I 1 1 1 \ — I 1 — \ 1 i — I 1 1 — \ 1 — I \ 



5000 10 000 15,000 20,000 



The magnetic resistance for each bar can be expressed as 

 the sum of a resistance due to its form, and a quantity formed 

 by dividing the length by /ju, the permeability of the metal*. 

 The form-resistance for different bars may be approximately 

 represented by 



•37rl0- ,006] ^ 



These constants are determined from the minimum resistances 

 of the above bars, assuming that a further metal resistance, 

 due to jx = 3000, is to be subtracted from the values found. 



The formula agrees with the values obtained from the bar 

 and the 18 pieces (Phil. Mag. May 1883), when corrected for 

 the erroneously assumed value of F (/ in that paper). The 

 error due to the value of H is not worth considering, as most 

 of it appears in numerator and denominator. These errors all 

 fall on the value of A in the formula 



Arl0~ kl r. 



A would come to about *36 after correction. But k is un- 

 affected by the errors, depending only on the ratio of the 

 observed quantities. ^ And taking as the result there that the 

 ratio of the form-resistances of the bar and of one of the 1 8 

 pieces is 2 : 3, we find at once £= -006139. The agreement 

 of both constants is quite as close as can be expected. 



As to/, it obviously follows a general course similar to p, 

 except irregularities in the lower inductions, which I take to 

 be connected with residual magnetism. But it can never 



* The initial value of /x for I. would be about 240 (very near Bowland's 

 value 232 for his magnetic ring), that for LL. about 270. Both bars had 

 been repeatedly magnetized to saturation. 



