393 



The third general law of Prof. Forbes states that the vibrations 

 are proportional within certain limits to the difference of the con- 

 ducting powers of the metals for heat, the metal having the least 

 conducting power being necessarily the coldest." The evidence ad- 

 duced against the first law appears to destroy this one also. The 

 author however proceeds further, and reverses the conditions deemed 

 essential by Prof. Forbes. Silver stands at the head of conductors ; 

 using it as the cold metal, he has obtained distinct tones with hot 

 rockers of brass, copper and iron, placed upon it. These and other 

 experiments show that the third general law is, like the two others, 

 untenable. Prof. Forbes further states that two of the metals, bis- 

 muth and antimony, are perfectly inert ; the author has however ob- 

 tained distinct tones with both of these substances. He finally 

 enters also into an examination of the arguments of Prof. Forbes 

 against the views supported by Faraday, and shows how the facts 

 adduced against the said views become, when duly considered, strong 

 corroborative evidence of their correctness. 



1. "The following letter from Prof. Dove to the Earl of Rosse, 

 was read from the Chair," 



Berlin, Jan. 7, 1854. 



My lord, — The vast stock of observations daily gathered by 

 British Observatories for the promotion of terrestrial physics, always 

 impressed me, as a scientific man, with gratitude towards a nation 

 so worthy of the happy privilege of interrogating nature in every 

 part of the globe. To day, at the receipt of the unhoped-for honour 

 awarded to me by the Royal Society (the Copley Medal), for labours 

 in a great measure grounded on those observations, I feel myself called 

 upon to express a more personal, and still deeper, sense of gratitude. 

 May I beg of your Lordship to communicate to the Council and 

 the Society my most respectful thanks for the approbation bestowed 

 upon the result of my exertions ? 



I am, my Lord, 

 Your Lordship's most obedient Servant^ 



To the Earl of Rosse, H. W. Dove. 



President of the Royal Society. 



2. " The following letter from Prof. Hansteen to Col. Sabine, was 

 also read." 



Observatory at Christiania, January 6, 1854. 



Dear Sir, — At the end of last year I calculated formulse of inter- 

 polation for dilFerent places in Europe, at which I had collected a 

 sufficient number of observations of the magnetical inclination : 



i=i^+x^(t-'to)y + (t-toyz, , (L) 



Proceedings of the Royal Society. Vol. VL No. 102. 29 



