and the Influence oj Temperature on the Resistance of Metals. 201 



of " a" the temperatures at which the resistances have been 



w — 1 

 observed. These will be found by using the formula a— — - — . 



In Table VI. I have given M. Siemens' s Table of the resistances 

 of mercury for different temperatures, together with the value of 

 the coefficient u a " for each of the observations. The resistance 

 of mercury at 0° C. is taken = 1 . 



Table VI. 



T. 



Resistance. 



Coefficient 







18-51 

 28-19 

 41-29 

 57-34 

 97-29 



100 



1 -0i 66 

 1 0263 

 10391 

 1-0548 

 10959 



0000897 

 0-000933 

 0-000947 

 0000956 



0000986 



If the formula w = l+at were correct, the values found for 

 " a " ought all to be equal ; but as there is a gradual increment 

 in the values there can be no doubt that a formula with two 

 terms, as w = l + at + bt q , will express the resistances for different 

 temperatures much better. 



The increase of resistance of mercury between 0° and 100° is, 

 according to 



Becquerel. Siemens. Matthiessen Schroder van der 



and von Bose. Kolk*. 



10*3 per cent. 9'85 per cent. 9 # per cent. 8-6 per cent. 



M. Siemens' s value is deduced from 12 observations ; Schroder 

 van der Kolk's from 29 ; von Bose's and my own from 96. 

 Again, M. Siemens deduces from 14 observations that the resist- 

 ance of copper between 0° and 100° increases in direct ratio with 

 the increase of temperature ; whereas von Bose and myself de- 

 duce from 332 observations that the formula for the resistance 

 of copper must be w= 1 + at -f- M 2 . Our experiments are almost 

 finished ; we hope that they will be published before the end of 

 the yeax*. 



8. Page 105 (2nd paper), M. Siemens states, " What induced 

 Mr. Matthiessen to make at the end of his paper the following asser- 

 tion lam not able to judge, as he does not give the grounds on which 

 he bases it : — ' it has been generally assumed that the conducting 

 power of all copper wire, whether pure or commercial , varies with an 

 increase of temperature to the same degree, which, however, is far 

 from the truth.' " Two reasons for my having made the above 

 * Poggendorffs Annalen, vol. ex. p. -152. 



Phil. Mug. S. 4. Vol. 22. No. 146. Sept. 1861. P 



