404 Intelligence and Miscellaneous Articles. 



when diluted, gives an abundant precipitate with chloride of barium. 

 It differs from brochantite in containing more water ; therefore, as 

 its external aspect is also quite different, it deserves to form a 

 separate species. It is to be noticed that Berthier formerly analyzed 

 an amorphous brochantite from Mexico, in which he had found as 

 much water as in Langite, while its colour was green like that of 

 other brochantites. 



Langite gave on analysis — 



Oxygen. Ratios. 



Sulphuric acid 1677 10"0 3 



Oxide of copper . .. 65'92 13\31 



Lime 0-83 0*2 M3'6 4 



Magnesia 0*29 01 J 



Water 16" 19 14'4 4 



100-00 



which corresponds to the formula 



4CuO, S0 3 + 4HO. 

 This formula requires — 



Sulphuric acid 1 706 



Oxide of copper 67'59 



Water 15*35 



100-00 



It thus only differs from brochantite by containing one more equiva- 

 lent of water. — Comptes Rendus, October 10, 1864. 



ON THE HISTORY OF ENERGETICS. 



To the Editors of the Philosophical Magazine and Journal. 



University of Glasgow, 



Gentlemen, October 5, 1864. 



So far as I know, the earliest introduction of a distinct term to 



denote the mechanical form of what is now called " potential energy " 



is due to Carnot, who, in a scarce and little-known essay on Machines 



in general, uses the phrase "force vive virtuelle" in that sense. ' 



The step which I took in 1853, of applying the distinction between 

 "Actual Energy" and ''Potential Energy," not to motion and me- 

 chanical power alone, but to all kinds of physical phenomena, was 

 suggested to me, I think, by Aristotle's use of the words dvva/us and 

 evepyeia. 



I am, Gentlemen, 



Your most obedient Servant, 



W. J. Macquorn Rankine. 



Erratum in October Number. 



In Prof. Rankine's paper on Stream-lines, Equation II., 

 db , _ db 

 dy dx 



, db , db 

 for read 



