On the Nature oftfi^ Earths. 273 



can be but small, and every part of it can be made by a 

 common ship carpenter, and be repaired bv him at sea if 

 damaged by shot. It will take up but little' room, only that 

 of a half-barrel cask; and it is of a nature so analogous to 

 that kmd of machinery to which sailors are accustomed, thai 

 It can be readily understood and managed by them. 



In order to render the description of my double capstan 

 more clear, I annex a sketch of it, as fitted up in the man- 

 ner proposed. I am, sir, your very humble servant, 



^ ^ J' WlTLEY BOSWELL. 



io C. Taylor, M.D. Sec. 



Reference to the Eugravlng of Mr. Bosweli's improved 

 Capstan, to preverit the Necessity of surgtnrr. Plate VI 1 1 

 Fig. 5. ^ . 



A Represents the larger or common capstan used on 

 board ships. 



B Another capstan of less dimensions, placed in a similar 

 manner. 



C The coils of the messenger passing alternatelv round 

 the large and small capstans, but with their direct'ion re- 

 versed on the different barrels, so that they may cross each 

 cither ni the interval between them. 



DDDD Projecting rings round each capstan or barrel, 

 so fixed on the two barrels, that those on one barrel should 

 be exactly opposite the middle of the intervals between those 

 on the other barrel. 



L. On the Nature of the Earths. 



To Mr. Tilloch. 

 sin, 



The result of the late experiments by Messrs. Davy, Ber- 

 zehus*, and Pontm, has only confirmed the idea entertained 

 by Lavoisier and others with regard to the nature of earths 

 ind alkahs, which were suspected to be merely metallic 



• Pfiil, Mag. vol. xxxi. p. 149, 

 Vol. 31. No, 124. Sept. Ib08. S oxidcs 



