Note. — The curves for the conductivity of heat and electricity are taken 

 from Plate xiv. of the Report on Copper- Tin Alloys, above referred to. 

 The latter curve should, however, be moved slightly to the left, as Mat- 

 thiessen's numbers represent volumes, and not weights, per cent, of copper. 



The earlier results, which were obtained by observations on 

 blocks of alloy 18 millims. square and 7 millims. thick, have 

 since been verified (except in the case of pure copper, 

 which as originally given is too low) by a series of disks 

 24 millims. in diameter and 3 millims. thick, formed in the 

 lathe, or, in the case of the very brittle ones, by filing. 



The close agreement between the conductivity for heat and 

 electricity has, as is well known, been pointed out by Wiede- 

 mann and Franz *; but as the similarity has hitherto, I believe, 

 only been observed in isolated cases, the above results on an 

 extended series of alloys may be of interest. 



Calvert and Johnson claim a high degree of accuracy for 

 their results ; but they were subjected to adverse criticism, as 

 Wiedemann \ objected to the apparatus they adopted and to 

 the small size of the bars employed. It is therefore the more 

 important to point to the almost absolute identity of the two 

 curves representing phenomena of which the manifestations 

 are so different. 



The respective values of the alloys were ascertained by 

 placing the metal to be examined on one side of the balance 

 and by superposing a graduated wedge-shaped scale of zinc 

 over the opposing coil, as has already been described by Prof. 



• PoggendorfTs Annalen, vol. lxxxix. [1853], pp. 497 

 t Ibid. vol. cviii. [1859], pp. 393-407. 



-531. 



