96 



PROCEEDINGS OF SECTION A. 



lamina of annealed transformer iron of whicli the details are as 



follows : — 



Internal diameter ... ... ... 7'5(j cm. 



External diameter ... ... ... 10"16 cm. 



Mass ... ... ... ... ... 913 grams 



Density ... ... ... ... 7 70 



Length of magnetio circuit ... ... 27*86 cm. 



Section of magnetic circuit ... ... •01225 cm'. 



Thickness ... ... ... ... 03275 cm. 



No. of primary turns ... ... 125 



No. of secondary turns ... ... 10 or 20 



Specific resistance of the iron at 15°C 13600. 

 Its magnetic properties, statically determined by Ewing and 



Classen's method, are given below. U representing the hysteresis 



loss per c.c. per cycle — 



The values of U, which were required for values of Bma^. inter- 

 mediate to and beyond the above four values of Bj^.,^ , were obtained 

 as follows : — On a large sheet of squared jDaper we plotted from the 

 above the log U against log B,„.,;^. The four points lay on a line 

 nearly straight with slight but regular curvature. From this line, 

 when extended, all the values of U, made use of in the tables that are 

 to follow, were calculated. 



5. The arrangement of the appai'atus by means of which th6 first 

 three series of results given below were obtained was practically 

 identical with that already described by one of us.* 



The magnetizing current was obtained from a four-pole rotary 

 converter supplied with direct current from storage cells. The speed 

 was regulated by means of a rheostat in its field circuit, and by varying 

 the number of cells used while it was continuously determined by 

 means of a chronograph. The magnetizing current was adjusted to 

 any required value by means of a Kelvin Balance and an adjustable 

 inductance. The reducing factor of the galvanometer used with the 

 wave tracer was determined by means of a Clark cell and a megohm. 



The second three series of results were obtained by means of a 

 new wave tracer, the commutator of which was attached to the spindle 

 of a 3 2-pole alternate current generator, whose armature is surface 

 wound, and which was driven by a direct current shunt motor. The 

 A.C. generator supplied the magnetizing current. The other details 

 of the arrangement were exactly as for the first three series. 



From both these sources we obtained a magnetizing current of 

 approximately sine wave form, but the variation from the sine form in 

 the two was essentially different. 



Thus if the magnetizing force was — 



H = H, { sin o)t -\- 7/^ sin 3 {od — <^,) -(- h-, sin 5 (o)^ — (f).) 



&c.} 



in the case of the rotary converter h. was negative while in that of 

 the generator Ji^ was positive. 



* Lyle. Variation of Magnetic Hystere.sis-with Frequency. Phil. Mag., Jan., 1905. 



