SCIENCE AND PRACTICE. 



267 



fixed point of temperature, at which alone the standard of 

 comparison is just. 



The conducting power of a metal, at any temperature, 

 t C., whose conducting power at the freezing point of water 

 is 100, is expressed by 



C= 100 + at + 



yt 



etc. 



Arndsten, Matthiessen, and others, have made very elabo- 

 rate experiments to determine the constants, a, |3, &c. for 

 the different inetals. Matthiessen's experiments being of 

 later date are the most trustworthy. The means of his 

 results for some of the metals, reduced from many obser- 

 vations by the method of least squares, are given in the 

 following table : 



Metals. 



Silver ... 

 Copper ... 



Gold 



Zinc 



Cadmium. 



Tin 



Lead 



Arsenic . . . 

 Antimony 

 Bismuth 



Mean of all. 



Co-efficients. 



100 

 100 

 100 

 100 

 100 

 WO 

 100 

 100 

 100 

 100 



0,38278 t 

 0,38701 t 

 0,36745 t 

 0,37047 t 

 0,36871 t 

 0,36029 t 

 0,38756 t 

 0,38996 t 

 0,39826 t 

 0,35216 t 



+ 0,0009848^ 

 4- 0,0009009* 2 

 + 0,0008443 P 

 + 0,0008274 P 

 + 0,0007575 t* 

 + 0,0006136 rf 2 

 + 0,0009146 rf 2 

 + 0,0008879 * 2 

 + 0,0010364^ 

 + 0,0005728 t 2 



100 0,37647 t + 0,0008340 ^ 



From the above table it becomes evident that for all the 

 pure metals, in a solid state, the values of the constants a 

 and |3 are nearly uniform, and agree, within the limit which 

 may reasonably be assigned to errors of observation, with 

 the mean of all given at the foot of the table. The law may 

 therefore be considered as established that the conducting 

 powers of all pure metals, in a solid state, decrease, in the 

 same ratio, between C. and 100 C. A still better agree- 



