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

 suring a plot of the curve, or from the empirical equation 



yu,=Bsin ^ ^ j 



when we know the values of the constants. In this case 



#, ~ c 



P^ _ C^(2B 2 -3/^ + ^(£, + 6) ^W^f 

 in which 



In all these the upper signs are to be taken for all values of «£), 



less than ^ , and the lower signs for greater values. 



On applying these formulae to the observations, I have found 

 that the corrections will in no way influence my conclusions, 

 being always very small j but at the same time the calculation 



shows that it would be well to diminish the ratio — as much as 



a 



possible. In all my rings this ratio did not depart very much 



from x-jr ; but I would advise future experimenters to take it at 

 o'o 



least as small as — : the amount of correction will be very 

 nearly proportional to the square of -• 



Summary. 



The following laws have been established entirely by my own 

 experiments, though in that part of (2) which refers to iron I 

 have been anticipated in the publication by Dr. Stoletow (Phil. 

 Mag. Jan. 1873). When any measurements are given, they are 

 on the metre, gramme, second system. 



(1) Iron, nickel, and cobalt, in their magnetic properties at 

 ordinary temperatures, differ from each other only in the quan- 

 tity of those properties and not in the quality. 



(2) As the magnetizing-force is increased from upwards, 

 the resistance of iron, nickel, and cobalt to magnetization de- 

 creases until a minimum is reached, and after that increases 

 indefinitely. This minimum is reached when the metal has 

 attained a magnetization of from *24 to *38 of the maximum of 

 magnetization of the given metal. 



