486 Scientific News, jicceunts of Books, (3c. 



The theory of the machine of Cit. Trouville is deduced from the preceding formula, 

 fuppofmg the fpring to have a fall equal to the height of the great afpiratnr, to which it 

 fupplies water ; and that the firft fmall afpirator draws from the fpring, and empties itfelf 

 into the refervoir of ttic fecond afpirator ; that this difgorges into the rcfervoir of the third, 

 and fo forth j all theff efFe£ls producing each other by appropriate machinery. 



SCIENTIFIC NEWS, ACCOUNTS OF BOOKS, Sic. 



Klaproth'a Analytical Ejfays. 



XT will undoubtedly afford much fatisfacftion to the cultivators of philofophical chc- 

 miftry, to be informed, that a tranflarion of the above work, by the learned editor of 

 Gren's Principles of Modern ■Chemijlry, is in the prefs, and will fliortly appear. 



Jlfiiltiplicatien of Engravings in Relief. 



Mr. George Gray, of Newcaftle upon Tyne, has prefented me with fome fpecimens of 

 a very ufeful application, of the art of taking impreflions In foil, or leaf metal. They con- 

 Cft of three blocks ; the firft about three inches fquare, containing fixteen lines of pica 

 italic, formed by imprefling a leaf of tin foil upon the face of the printers types, fet up in 

 the ufual manner. The tin foil is ftrengthened by plaifter of Paris poured into the conca- 

 vity, to the thicknefs of a little more than half an inch. This block is not as (harp as the 

 type itfelf j but affords impreffions on paper perfe£lly legible, and about as neat as common 

 ballads are ufually printed. The fecond is an impreffion taken in brafs foil, from a wood 

 cut of Beivicke, 25 inches long, and near i\ inch broad. A folution of fal ammoniac was 

 applied to the concave fide, and lead then poured in, which confequently adhered, and 

 gave the requifite ftrength. It is very (haip, but the face has been bended in taking off; 

 fo that it is not cafy to print from it. The third is a fmall figure of a (hip, within a 

 bounding line of three quarters of an inch fquare. It is made in the fame manner with 

 brafs foil, and though the engraving abounds with fine ftrokes, it affords an ' impreffion 

 which could not, I think, be diftinguifhed from another taken from the' original. 



It may perhaps be true, that this art is rather inferior to the method of moulding and 

 cafting, defcribed at page 6^ of the fecond Volume of this Journal. But it requires lefs of 

 preparation, as well as of (kill, and with fome improvements in the foil, the manipulations 

 and the ftrengthening, may probably exceed the other method in precifion and effeft. -, 



Rational 



