Brown. — Action of Ficsible Cutouts. 357 



These results are sufficient to show that my metals are 

 ■"commercial pure tin." It would have been interesting, no 

 doubt, to have made a complete analysis of the metals ; but 

 for this purpose what is really required is the specific resist- 

 ance and the fusing-temperature of the material, and to this 

 I accordingly devoted my attention. Here sundry difficulties 

 cropped up. The first determination of the specific resistance 

 (po) gave a value about 25 per cent, less than that of Mat- 

 thiessen, the English standard. My values will be seen to be 

 of the order of 106 x 10 ~ 6 ohms per cubic centimetre at 

 0° C. for tin wire, confessedly impure, hard-drawn into wire 

 of about 36 mils ; Matthiessen gives the numeric as 13-19 for 

 " tin, pressed." Matthiessen's value 1 find to be confirmed 

 by Fleming ;* my own value, approximately, by Kirchoff and 

 Hausemann— 10 : 67 at 15° C. (10 018 at 0° C, reducing by my 

 formula for temp, coef.) ; Lorenz, at 0° C, 10781 (taking 

 mercury as 91074) ; Becquerel (1846), given by Weiller 

 (1885), 11-6 (cf. with mercury), 94-079; 10-71 (cf . with silver), 

 150. Tin pure ; banca drawn into wire, 9-821. 



A similar disagreement is apparent with regard to the 

 temperature coefficient, the authorities I have been able to 

 consult giving as follows (writing, instead of the usual for- 

 mula, the coefficients for the temperature divided by 100, 

 which gives handier numbers and is more convenient for my 

 purposes) : — 



Matthiessen, [l + 3628 (4) + 00636 (m) 2 ] , from 0° to 100° : 

 calculated bv mvselr from his conductivity coefficient at 

 0°, 50°, and i00° C.+ 



Fleming, about [l + 0-4085 (m) + 00345 (m)*] , from 0° to 

 200° : calculated from the curves given (Elect. : 3rd July, 

 1896, p. 30), P at 0° = 13-1 ; 100 D = 189 ; 200° = 256. 



Lorenz, [l + 0-432 (^jo)] : calculated from values at 0° and 

 100° of conductivity. 



Benolt (1873), [l + 04028 (4) + 005326 (mY] ■ 



My own value for fuse- wire A (annealed) is — 



[1 + 0-421 (4) + 0-0398 die)] , 



the curve fitting the equation very well indeed. My value, 

 however, is dependent upon the thermometer errors very 

 largely, especially the quadratic term. Since 0° and 100° are 

 the fiducial points, it is better to take the change of resistance 

 for this range. Thus we have — 



* Friday Evening Discourse, Rov. Ins?., 5ih June, 1896. 

 t Trans. E.SL, 1862. 



