and Electrical Resistance of Iron. 233 



kinson and Le Chatelier in the papers already cited shows that 

 in each case they would be more strictly satisfied by a con- 

 tinuous curve like those here given.) 



The annealing of specimen A has reduced its specific 

 resistance considerably. 



With specimen B, the further annealing at 1150° has but 

 slightly altered it from the condition as regards specific re- 

 sistance in which it was after the annealing at 840°. 



The temperature-coefficients and specific resistance at 0° 

 and 1000° are given at the foot of Tables XI. and XII. 



As regards the resistance-changes both of specimens A 

 and B, and of the soft commercial iron previously tested : — 

 The resistance rises with rising temperature at a rate which 

 increases fairly uniformly till a specific resistance of about 

 100,000 C.G.S. units is reached. Here the maximum slope of 

 the curve occurs at a point but few degrees below the critical 

 temperature. The rate of increase of resistance then falls off 

 rapidly, so that at 1000° the temperature-coefficient is about 

 •0024 and the specific resistance 118,000. 



With specimen B, which, judging from the low value of its 

 specific resistance at 0° (10,050 C.Gr.S. units) and from the 

 high value ( # 0057 at 0°) of its temperature-coefficient, should 

 be a sample of very pure iron, the maximum coefficient after 

 annealing at 1150° was *0204 at about 765°. The number of 

 observations on this resistance-temperature curve (18 H.) 

 make it perhaps permissible to note its irregularities a little 

 more closely. A flat part of the curve will be noticed be- 

 tween 830° and 900°, and the temperature-coefficient, which 

 remains tolerably constant over this range, has at 865° the 

 value '0068. (Dr. Hopkinson gave "0067 as the coefficient 

 of iron above the critical temperature.) The points of maxi- 

 mum curvature 800° and 920° seem to be in agreement with 

 the minima of the permeability curve (No. 13) ohtained at 

 the same time. 



The above experiments were carried out in the laboratories 

 of the Physical Institute of the Polytechnicum, Zurich ; and 

 the author takes this opportunity of expressing his gratitude 

 to the director, Prof. H. F. Weber, for encouragement received 

 throughout the progress of the work. 



Zurich, March 1897. 



