326 Mr. H. A. Rowland on the Magnetic Permeability 



form, between which, as the metal contracts, vacant spaces may 

 be left. As the specific gravity of my rings approaches to that 

 of the pure metals precipitated by hydrogen, I consider it 

 evidence of their purity. The dimensions of the rings and their 

 other constants are given below : — 



Ring.' 



Weight in 

 vacuo, in 

 grammes. 



Loss in 

 water at 

 4° C, in 

 grammes. 



Specific 

 gravity. 



Mean dia- 

 meter, in 

 centimetres. 



Nickel, No. I 



Nickel, No. II 



21823 



io-bii 



4-681 



2-4560 



1 1435 

 •5346 



8-886 

 8-887 

 8-7553 

 8-7550 



3-28 



2-48 

 1-81 



Cobalt, No. I. 



Cobalt, No. II 





Ring. 



Mean cir- 

 cumference, 

 in centi- 

 metres. 



Number of 



coils of wire 



on ring. 



Coils per 

 metre of 

 circumfe- 

 rence. 



Area of 



section, in 

 square cen- 

 timetres. 



Nickel, No. I 



Nickel, No. II. 



Cobalt, No. I. 



Cobalt, No. II 



10-304 



7-791 

 5-686 



318 



243 

 158 



3086 



3119 

 2779 



•2384 



•1467 

 •09403 



Up to the present time only the rings whose dimensions are 

 given have been used. 



The following Tables from the nickel ring No. I. leave little 

 to be desired in point of regularity, and confirm the fact proved 

 in my first paper, that the laws deduced for iron hold also for 

 nickel, and also confirm the value given in my other paper for 

 the maximum value of magnetization of nickel. But the most 

 important thing that they show is the effect of heat upon the 

 magnetization of nickel; and Table III. contains the first nume- 

 rical data yet obtained on the effect of heat on the magnetic pro- 

 perties of any substance. 



As all the rings were wound with two layers of wire, a slight 

 correction was made in the value of 53 for the lines of inductive 

 force which passed through the air and not through the metal. 

 In all the experiments of this paper greater care was used to 

 obtain T than in the first paper. Each value of 43, %$, and T is 

 the mean of four readings. In all the Tables I have left the 

 order of the observations the same as that in which they were 

 made, and have also put down the date, as I now have reason to 

 suspect that the leaving of a ring in the magnetized state in 

 which it is after an experiment will in time affect its properties 

 to a small extent. Let me here remark that the time necessary 

 to simply make the observations is only a very small fraction of 

 that required to prepare for them and to afterwards discuss 



