On the Induction-Balance Effect of Copper-Tin Alloys. 551' 



giving me a chance of correcting my omission regarding your 

 researches on the influence of light on vegetation." 



I hope with this explanation of the cause of the delay, you will 

 now allow me to assert my claim, especially as Dr. Allman*, in 

 a note of November 13th, says, • ■ you are quite right in assert- 

 ing your claim to priority " &c.,and "you are liberty to make 

 what use you please of my letter. " 



As a very early investigator into those most interesting 

 phenomena, I cannot afford to allow my discoveries to be un- 

 recognized, without an appeal. It is highly satisfactory to' 

 find this supported by so high an authority as Professor All- 

 mann, who in his letter of the 9th November writes : — " I have 

 been refreshing my memory of your researches, by reading 

 your published account of them ; and their completeness and 

 conclusiveness render my regret the greater, that I had not 

 given them the recognition they so well merit." 

 I am, Gentlemen, 



Your obedient Servant, 



Robert Hunt, F.R.S. 



LXIY. On an Analogy between the Conductivity for Heat 

 and the Induction-Sal ance Effect of Copper-Tin Alloys. 

 By W. Chandler Roberts, F.R.S.* 



IN a paper submitted to the Society in June last, I pointed 

 out that the results obtained when copper-tin alloys are 

 examined by the aid of the induction-balance does not cor- 

 respond with Matthiessen's determinations of the electric con- 

 ductivities of the same alloys. The nature of the induction- 

 curve remained therefore more or less obscure ; but I have 

 recently observed a remarkable resemblance between my own 

 results t and those given by Calvert and Johnson J for the 

 conductivity of heat, which had hitherto escaped me, as the 

 authors did not plot their figures. The following diagram 

 shows the relation of the curve published by me in July last 

 with those of Calvert and Johnson and Matthiessen respec- 

 tively, which I find for the first time placed in juxtaposition 

 in a valuable report on the copper- tin alloys recently issued 

 by the United-States Government^ 



* Communicated by the Physical Society, having been read on 

 November 8th. 



t Phil. Mag. (5) vol. viii. p. 57, 1879. 



% Phil. Trans, vol. cxlviii. 1858, p. 349. 



§ Report made under the Direction of the Committee on Metallic 

 Alloys. Washington, 1879. 



