MAGNETIC PERMEABILITY OF NICKEL AND COBALT 



69 



at present I have not found any law connecting these two, and doubt 

 if any exact relation exists, though as a general rule the value of the 

 constant is greater in those curves where the permeability is least. 



In a short abstract in the ' Telegraphic Journal/ April 1, 1874, of a 

 memoir by M. Stefan, it is stated " that the resistance of iron and 

 nickel to magnetization is at first very great, then decreases to a mini- 

 mum value, which is reached when the induced magnetic moment is 

 become a third of its maximum." This will do for a very rough approx- 

 imation, but is not accurate, as will be seen from the following Table 

 of this ratio from my own experiments : 



The average of these is, if we include Bessemer steel with the iron, as 

 it is more iron than steel: 



Hence the place of greatest permeability will vary with the kind of 

 metal. From these, however, we can approximate to the value of 6 in 

 the formula; for we have 



27,000 f AT- i i ^ 11,000 

 for Iron, b = - ; for Nickel, * = = ; 

 p " 



for Cobalt, b = 26,000. 



In Table V we have the results for cobalt in the magnetic state. 

 We here find the same effect of magnetization as we have before found 

 for iron and nickel. 



