MR. Davy's experiments, Sic. 15J 



which gives (p=z MY xMgt=:M{Vxgt.) And Mly, if 



the agent poflefs inertia,, its mafs muft alfo be confidered. 



Thus, in the cafe of a horfe vvhofe mafs is H, moving along 



with the velocity V during the time /, and railing the mafs 



M, we (hall have <?) = (M x H) V x M ^ ^ And from fimilai: 



principles formula may be inveftigated to reprefent the power 



of a firft movar in more complicated cafes. 



It will after all, be proper to diftinguifh carefully between Power expen4el 

 .1 1 .1 . • r-^ 1 • I and power ufe- 



the quantity of power expended, and that portion ot it which fuHy employed 



is uftfully employed: but a due confideration of this would require to be 



too widely extend the limits of the prefent communication. »«^"g**"^=»* 



Indeed I ought to apologize to yourfelf, and the fcientifie 



part of your readers, for dwelling fo long as I have done 



upon topics which are well known to all who are converlant 



in the theory of mechanics: but if thofe, for whofe ufe this 



letter is chiefly intended, Ihall derive fome precife information,, 



or add to the (lock of their pra6lical knowledge, by any hints 



of mine, I (hall not fearieing heavily cenfured for having *^, 



entered thus into minutiae. 



' I am. Sir, 



Your's very refpeflfully, 



OLINTHUS GREGORY. 



Royal Mil. Academy, Woolwich, 

 June lOth, 1805. 



II. 



An Account of fome Analyiical Experiments on a Mineral 

 Production from Detonflurc cmfifimg principalli/ of Alumine 

 and Water. By Humpiirv DAvf, Efcj. F. It. S, Profejjbr 

 of Cheniijlrj/ in the Royal Injlitution, From the Philofophical 

 Tranfaciions in IS05 . * 



. I, Preliminary Obftrvations, 



JL HIS foflil was found many years ago by Dr. Wavell, in aHiftory of a 

 quarry near Barnftaple : Mr. Hatchett, who vifited the place ^°^*^* 

 in 1796, defcribed it as <illin;]j fome of (he cavities and veins 

 in a rock of foft argillaceous fchilU When ^rft made known, 



it 



^'" f * * 



