Permanent Magnetism. 315 



18 pieces of soft iron. 



A = 37 inches. 



I. II. III. 



Current 1*0 4-2 5'36 amperes. 



Deflection ... 0°-7 3°'0 3°-75 



Moment 165-2 708 885-77 



8 28-1 120-74 151 



x -44645 -43714 -44607 for one piece. 



fi 410 460 480 



2a -46590 -45654 -46610 



Mean value of 2a =-46285 



Corresponding value of 2aB/ ... ='45592 

 From II. alone 2«K' =-44970 



I. has little weight, because of the smallness of the observed 

 deflection; III. because the current was too much for the coils 

 and the apparatus was heated. The value derived from II. 

 alone is therefore to be preferred. I adopt 13°*1 and 1°'8 for 

 the deflections of the steel compound bar, joined up and sepa- 

 rate. In deducing the moments from these, h must be taken 

 = 41 inches. The condition was very permanent; but the 

 moments were lower than they are now. 



Then we have, if r be the resistance of one piece, 



1 8?- + -30 2 _ 

 l% + -456)~ 

 Taking first the mean of I., II., III. for the soft iron; then 



1-58 = 3^52' /*= 30,52 - 



Taking II. alone for the soft iron, 



18r + -302 



whence 



18(r + -450) 

 ^=31-06. 



135, 



Direct determination of permeability of the permanent 



magnet. 



Deflections 

 Moments ... 



A = 34 inches. 



Current 

 1-33 ampere. 

 9°. 9 



'.'.'..... 2566-7 



Reversed. 



21°-33 

 5743-7 



Diff. of moments 3177*0 



