the Magnetic Properties of Iron. 



255 



Consequently 



/, - I = 36-74 1 8-62 3 + i (^?) 2 1 = 3,080 gramme cms.' 



and 



G fi -G 1 = 36-74 x 8-62 x 981 = 310,000 dyne cms./radians, 



hence 



' O, = (^l«.080)+»10^p(l-'8y_ 706> ooo dyne cms./radians. 



l-18 2 -0-782 2 J 



Now one division on the B scale = -0086 radians, therefore 

 restoring couple per division = 706,000 x - 0086 = 6,090 dyne cms. 

 Average of results by two methods =6,120 dyne cms. per div. 



Then, as previously stated, a specimen of iron whose maximum 

 permeability was known, having been determined by the ballistic 

 galvanometer method, was placed in the instrument, and the BH 

 curve obtained for it in the arbitrary units fixed by the scale 

 divisions. This curve, corrected for demagnetisation, is shown 

 in Fiof. 5. 



It is seen that the permeability is a maximum in the neigh- 

 bourhood of H=28 divs. and B = 16 divs. 



The approximate values of B and H in C.G.S. units corre- 

 sponding to those scale readings were then determined from 

 the equations 



(1) Moment in dyne cms. 1/6 x 6,120 = --__-' . H, 



(2) B = Hfi = H0/x, 



4-7T 



