4^8 ^ liolalory Hydiaulic Engine. 



*4t* Many engineers have exercifed their talepts in cpntrlving machines which fliould 

 ralfe water without the alternate aiflion of the pump ; but I do not recolleft having feen 

 any conftru6i;ion precifely the fame as that of my correfpondent. In the Recueil des Ma- 

 chines et Inventions approinees par V Academie Royale des Sciences, torn. I. page 103, there is 

 a machine by the celebrated M. Amontons, for raifing water by a drum or cylinder, fixed 

 with its axis horizontal, and an ellipfis revolving in it againft two flaps or valves attached 

 to the cylinder i the efF;;cl of which was to afford two pair of variable fpaces fimilar to the 

 engine before us. It is dated 1699. 



Mr. Thomas Dickinfon in 1790 obtained a patent for a new engine on a rotatory prin- 

 ciple, of which the contrivance (hews a mind habituated to mechanical rcfearch and in- 

 vention. The principal organ confiils of a cylinder, in which another eccentric cylinder 

 revolves, leaving a gibbous fpace on one fide, and out of this laft cylinder iffues two Aiders 

 crofling each other, and fo contrived as to length and other expedients, that they fweep 

 the cavity, and afford variable fpaces for the introduftion and extrufion of water. The 

 drawings may be feen in the fecond Volume of the Repertory bf Arts, and the whole 

 differs very much from the invention of my correfpondent. 



The adtion of fteam againft flaps or valves between two concentric cylinders, .forms part 

 of fome imperfect defcriptions in the fpecifications of the celebrated James Watt, and 

 there is alfo a contrivance of this kind loofely defcribed in the firft volume of the Irifli 

 Tranfa£lions, by John Cooke, Efq. 



I fhall not attempt to difcufs the relative values of thefe Inventions, either with regard to 

 each other, or to the engines more generally ufed. The advantage of an inceffant or con- 

 tinued motion is admitted by all mechanics, and might be eafily difplayed. But in engines 

 like every one of the foregoing, the difficulties of ftuffing or packing the parts which move 

 in contadV, and the confiderable fridion and wear they rauft be fubjedt to, unlefs im- 

 proved far beyond their prefent ftate, are fo great, that I think few pradlical men would 

 venture to undertake them. I do by no means prefume to fay, that they are on that ac- 

 cpunt ufekfs. Undoubtedly they may be claffcd at leaft with thofe produfts of the under- 

 ftanding, by which our knowledge and mental habits are improved, and which form a ftock 

 whence the moft ftriking and unforefeen difcoveries are occafionally drawn. Sheep were 

 noarked, loadftones were examined, and the covers of kettles were blown off many ages 

 before the art of printing, the mariner's compafs, and the fteam engine were thought of. 



W. N. 



Account 



