Properties, Specific Resistance, and Hardness of Steel. 367 



/. Like the T. E. H., so also the specific resistance of steel 

 approximates to the value of this constant for soft iron. Upon 



the value found for the ratio m p L , however, not much 



reliance can be placed, the factors involved being too small to 

 admit of accurate determination. 



With cast iron no experiments were made. 



IX. Remarks on the above, considered as auxiliary to the de- 

 termination of the relation between hardness and magnetic 

 moment. 



In this place I will avail myself of the experiments of Ruths 

 on the relation between hardness and magnetic moment, 

 these being perhaps the most comprehensive. With suffi- 

 cient approximation for our purpose, we will put the T. E. H. 

 of glass-hard rods =120 : 10 6 , that of the yellow annealed = 

 40 : 10 6 , of the blue =20 : 10 6 ; and with these as abscissae and 

 Ruth's values for the corresponding permanent magnetic 

 moments ("in millions of absolute units," mg.-mm.-sec. 

 syst.) as ordinates, suppose the curves belonging to each of 

 the barsf to be constructed. These curves are given in fig. 6, 

 the attached number referring to the ratio between the length 

 and diameter of each rod. 



I will omit the interesting deductions which Ruths makes 

 from his data, these going beyond our present purpose. 



From an inspection of the curves we derive the following 

 important result, — viz. that, like the electrical properties of 

 steel and its specific gravity, so also the maximum of perma- 

 nent magnetism is largely modified by the different degrees . 

 of glasshardness of the bar (i. e. those lying above yellow- 

 annealed and scarcely distinguishable mechanically). In the 

 second place, the results of Ruths, being obtained from com- 

 paratively thick bars, are largely influenced by structure. In 

 view of these facts, I deem the hope by no means too sanguine, 

 that, if to avoid complications from structure we experiment 

 on thin rods, the maximum of permanent magnetism may be 

 empirically expressed in terms of the dimensions and T. E. H. 

 only — that, furthermore, from the parallelism discovered in 



tinuously increases as the rod passes from a condition of saturated longi- 

 tudinal to a condition of saturated circular magnetization. 



The result above enunciated has therefore probably even a more general 

 signification. 



t The data employed are those obtained by Ruths for rods 120 millims. 

 long and 1-7, 2-4, 2 9, 3*8, 4 9, 59 millims. respectively in diameter, with 

 very powerful magnetizing forces. 



