258 Mr. R. H. M. Bosanquet on Permanent Magnetism. 



53 = 553 gives from Rowland's table //. = 800 nearly, whence 



28 # 5 



-^— is to be subtracted, = "036 ; 



Air resistance ='303 centim. 

 = '32Rsay. 



In the steel R is very nearly 1 centim. 



With the above values for the air resistances we can deter- 

 mine the resistance of the steel from the ratio of deflections 

 when joined and separate. Let r be the resistance of each 

 piece. Then 



18r + -32 _ tan 13° 

 18(r + '47)~tanl°-8~ ? 

 whence 



r=-0555; 

 and resistance of unit length 



_ r 1 



1-58 ~ 28-5' 

 whence 



^ = 28-5. 



Direct Determination of Permeability (//,) of Steel Compound 



Magnet. 

 The magnet was enclosed in a paper case, joined up, and 

 wound with 180 coils. The currents employed did not dis- 

 turb the permanent magnetism. 



Current. Mean displacement. 



•48 ampere. 2°'0, from 12° to 14°. 



(The deflection was really observed from zero 13° in opposite 

 directions ; and it amounted to 4 o, 0.) 



Change of moment = 497. 



(The moment of the bar joined up is 3120.) 



Total resistance = 1*4 centim. 



Subtracting air resistance = *3 centim. 

 Resistance of steel =1*1 centim. 



Resistance of unit length = _ L) . = ^ 

 & 28*5 26 



/*=26*. 



* Since the above was written I have subjected the num. I ers to a 

 careful scrutiny, and made another determination of /a directly, having 

 discovered a possible source of error in the above. The resulting num- 

 bers all lie between 30 and 32. 



