-H'®'* 



Iron under Small Periodic Magnetizing Forces. 237 



the approximate formula given by Searle and Bedford * on 



the assumptions that p, is constant and that -=- does not 

 vary over the section 



dt ~ Sirp' \dt) ' 



where X is the eddy-current loss per c.c, 



A the area of section of the rod or wire, 

 and p the specific resistance of the iron ; 



where T is the period of the alternations, 

 and E is the eddy-current loss per c.c. per cycle. 

 Substitute for B and perform the integration, 



E = -^- Bfa . 2tt 2 [1 + 96 3 2 + 25 V] 



07Tp 



where » 2 = B^ 2 [1 + % 3 2 + 256 5 2 ]. (» is the quantity which 

 has been referred to before as the " effective induction/') 

 E having been calculated, the hysteresis U is given by 



U=I-D. 



5. The first specimen experimented upon was a bundle of 

 iron wires of low permeability, which were taped together to 

 form a long circular cylinder, the details of which are given 

 below. A coil was wound on the centre of the bundle for 

 measuring the induction produced in the iron. Four different 

 frequencies were employed, namely, 50, 28, 15*5, and 8*5. 



Details of Iron Wire Bundle. 



Number of wires 46. 



Mean diameter of wires 0*0789 cm, 



Sectional area of iron 0*2250 sq. cm. 



Length of wires 307 cm. 



Specific resistance at 12°*5 C. 1*366 x 10 4 . 



Turns on central coil 400. 



Details of Magnetizing Solenoid. 



Length of solenoid 170 cm. 



Internal diameter of windings. 1'6 cm. q.p. 

 Constant of solenoid H = 53-37 C. 



* G. F. C. Searle and T. G. Bedford, Phil. Trans, cxcviii. p. 33, 

 1902, App. 1. 



Phil. Mag. S. 6. Vol. 13. No. 74. Feb. 1907. S 



