342 



The following remarkable experiment of Mr. Hopkins of Cam- 

 bridge *, which is considered by him to be confirmatory of the sliding 

 theory of De Saussure as opposed to De Charpentier's dilatation 

 theory, receives a ready explanation on the principles which I have 

 laid down in this note. It is indeed a necessary result of them. 

 " Mr. Hopkins placed a mass of rough ice, confined by a square 

 frame or bottomless box, upon a roughly chiselled flag stone, which 

 he then inclined at a small angle, and found that a slow but uni- 

 form motion was produced, when even it was placed at an incon- 

 siderable slope." This motion, which Mr. Hopkins attributed to 

 the dissolution of the ice in contact with the stone, would, I appre- 

 hend, have taken place if the mass had been of lead instead of ice ; 

 and it would have been but about half as fast, because the linear 

 expansion of lead is only about half that of ice. 



II. "Reply of the President and Council of the Royal Society 

 to an application from the Lords of the Committee of Privy 

 Council for Trade, on the subject of Marine Meteorological 

 Observations." 



[This Letter was communicated to the Society in pursuance of a 

 resolution of the Council. The Secretary explained that it had been 

 drawn up by the Treasurer, Colonel Sabine, and submitted, before 

 final adoption by the Council, to several Fellows of the Society spe- 

 cially conversant with the subjects to which it refers.] 



Royal Society, Somerset House, 

 February 22, 1855. 



SIB, In the month of June last, the Lords of the Committee of 

 the Privy Council for Trade caused a letter to be addressed to the 

 President and Council of the Royal Society, acquainting them that 

 their Lordships were about to submit to Parliament an estimate for 

 an Office for the Discussion of the Observations on Meteorology, to 



* I have quoted the above account of it from Professor Forbes's book, p. 419. 



