On the Magnetic Hysteresis of Cobalt. 271 



Distance Wire 

 Current. was moved. 



1-45 1*5 cm. 



104 2-2 



0-80 4-2 



•57 6-5 



•45 8-0 



•38 12-0 



•12 10-5 



These results are of course quite rough, but the same 

 general result is obtained as in the first experiments. The 

 direct comparison of a ballistic and a magnetometric curve for 

 the same bar would show that they approximately agree, since 

 the factors causing variation of the equivalent length will affect 

 both delimitations in the same way ; preliminary experiments 

 have confirmed this. It is hoped to examine bars bent into 

 incomplete rings and other forms. 



The kind assistance of Mr. L. Gr. Walter, B.A., in the earlier 

 experiments is gratefully acknowledged. 



X XVIII. On the Magnetic Hysteresis of Colalt. By J. A. 

 Fleming, M.A., JJ.Sc, F.R.S., Professor of Electrical 

 Engineering in University College, London, A. W. Ashton, 

 B.Sc, 1851 Exhibition Scholar, and H. J. Tomlinson, 

 Salomons Scholar, University College, London*. 



[Plates VII. & VIII.] 



ALTHOUGH determinations have been made of the mag- 

 netic constants of cobalt by other observers, we have 

 not been able to find any very complete set of observations 

 on the magnetic hysteresis values of cobalt of known chemical 

 composition corresponding to various cyclical magnetic forces 

 of known range or maximum value. Having in our possession 

 a cobalt ring of supposed fairly pure commercial cobalt, a 

 series of magnetic experiments were undertaken with it, the 

 results of which are embodied in the following tables and 

 diagrams (see Plates VII. & VIII.). 



A rectangular sectioned circular ring of the metal was cast 

 for us by Messrs. H. Wiggin & Co. of Birmingham, and 

 turned up true in the lathe. The dimensions of the ring 

 were then carefully measured and the mean values were 

 found to be as follow : — 



* Communicated by the Physical Society : read June 23, 1899. 



