1 

 342 Dr. C. Barns on the Relation between the Thermoelectric 



Treve and Durasssier*, and Grayf. All these observers, 

 however, have classified steel, with reference to its hardness, 

 either simply into hard and soft, or have accepted the colours 

 of the oxide film of the tempered bar as a criterion of distinc- 

 tion sufficient for their purposes. It seemed, therefore, that 

 the most probable method of further elucidating the magnetic 

 subject referred to would consist in attempting to find some 

 method by which the hardness of steel can be more distinctly 

 and more rationally expressed. My endeavour was, in other 

 words, to give the very vague notion hardness as applied to 

 steel a quantitative signification. So long, however, as the 

 ultimate nature of hardness does not admit of accurate defini- 

 tion, it is sufficient for the accomplishment of this end to exa- 

 mine some of the other properties of steel which likewise vary 

 with its hardness, and by considering the magnetic moment, 

 co3teris paribus, as dependent on the former, to eliminate, as 

 it were, the notion of hardness between them. My attempt 

 is, in short, to find an expression for the more complicated 

 functions of hardness, cceteris paribus, in terms of the more 

 simple. Of the latter the thermoelectric properties and the spe- 

 cific resistance of steel, both admitting of accurate and easy de- 

 termination, appear most suitable. 



As, however, the experiments on hardness and the elec- 

 trical properties of steel alluded to, although only introduc- 

 tory in their character, gave rise to a number of new results, 

 I determined to publish them separately. To obtain as com- 

 plete a picture as possible of these phenomena, I have made 

 free use of all the information on the subject within my reach. 

 In each case the author borrowed from is cited. 



II. Apparatus for Hardening Thin Steel Wire. 



For reasons which become apparent below J, the principal 

 experiments of the following paper are confined to thin rods 

 cut from the same coil. The rather difficult task of hardening 

 these homogeneously throughout their length, without giving 

 rise to a change in their chemical composition (either from 

 oxidation or carburation), I believe I have accomplished by 

 the aid of the following apparatus. 



A glass tube 200 to 300 millims. long, 8 millims. wide, was 

 provided at a distance of about 80 millims. from one end with 

 two opposite apertures a a (PI. XI. fig. 1), each about 3 millims. 

 in diameter. This part was then surrounded by a cork A, 

 perforated perpendicularly to the axis of the tube in a manner 



* Ami. de Chim. ct de Phys. (5) v. p. 266, 1875. 

 t Phil. Mag. [5] vi. pp. 321-323, 1878. 

 \ Difficulties duo to structure, vi.de vii., d. 



