188 Conducting Powers of Metals at Different Temperatures. 



Temperatures 

 observed. 



Temperatures 

 calculated. 



97°-8 C. 



Differences 



Readings of 



b 



index of rheo-stat. 



0°-00 C, 



89 

 85 

 84 

 83 

 74 

 10 

 65 

 60 

 55 



55 



51 



47 



34 

 23 

 22 

 18 

 15 



•40 

 •20 

 •75 

 •87 

 •58 

 •30 

 •90 

 •80 

 •80 

 •00 



•64 

 •40 

 •75 

 •63 



•7- 



•54 

 •00 



-0 

 1 

 1 

 1 

 3 

 3 

 4 

 4 

 8 

 3 

 2 

 2 

 1 

 

 



+ 

 



•10 

 •30 

 •25 

 •13 

 •92 

 •70 

 •10 

 •20 

 •20 



•00 



•86 

 •60 

 •85 

 •37 

 •30 

 •44 



•00 



398-0 



360-0 



341-0 



339-0 



335-3 



293-* 



273-5 



•J 5 3-6 



280-6 



207-6 

 2o4-4 



170 



113-0 



627 

 58-5 



39-7 

 23-7 



that 



The author considers these results as justifying the conclusion 



is constant, and ascribes the differences in the third column 



dt 



to inequality of temperature in the oil bath, a bad conductor of 

 heat, during the cooling. To this inference we object, because 

 in the first place there is no presumption in the nature of the 'case 



dr % 



that -77 is constant for different temperatures, and in the second 



place, the equality of temperature being well established at the 

 upper limit of 97°*8 C., the differences in question ought, if they 



depended 



to have been greatest in 



the first and most rapid stages of the cooling, whereas the differ- 

 ences are then very small. We therefore regard these residuals 



dr 



as indicating for jr a variable value containing terms of the first 



and even of the second powers at least of the elevation of tem- 

 perature above 0°- C. For practical purposes indeed the variation 



dr 



of ~r may perhaps be neglected. For purposes of exact science 



so far as appears from the paper before us, it certainly cannot be. 



dr 



Proceeding on the principle that ~tj is constant, experiments 



were next instituted on the different metals. An annealed silver 



dv 



wire gave tt = 04444, the whole resistance at 12°'75 C. being 



116184. Hence we have, 



Increment of resistance for 1° C, . . 0*4444 



Whole resistance at 12° 75 C, . . 116-184 



" " " 0°C, . . . 110 518 



