Comparifon of the Steam Engines of Newcomen'and of IVaii. '231 



the boiler opened as before ; the confequence of which is, that the pifton again defcends, 

 and in this manner the alternations repeatedly take place. ' i '' 



The principal augmentation of power in this engine, ccmipared with that of Newcomen, 

 appears to arife from the cylinder not being cooled by the injeiElion water, and its beinij 

 practicable to ufe fteam fomewhat ftronger than the prefTure of the atmofphere. In general 

 thefe engines are worked by fleam, which would fupport a column of four or fivejnches of 

 mercury befides the prelTure of the atmofphere, and I have fometimes feen the gage as hi»h 

 as eight inches. But whether the comparative profit of the additional work was fuch as to 

 repay the extraordinary confumption of fuel in fuch cafes may be doubted ; and indeed I fup- 

 pofe this praflice is never adopted but when the work of a manufadlory is fuch as to eiceed 

 the power or rate of the engine conftrufled for performing it. 



The mofl: ample information refpeiling thefe improvedfteam engines, which rs to be met 

 with in print, is found in the Nouvelle Architecflure Hydraulique ofProny. 



When we contemplnte thefe engines together with the fimpler engine of Savery, one of the 

 tnoft ftriking differences, is, that the latter is not embarraffed with tlie weight and expence 

 of the beam and counterpoife. I believe that the fly was firft introduced by Meffrs. Watt 

 and Boulton, as an equalizer of the adlion in fteam engines, which in various conftru£tions 

 renders a counterpoife unneceflary, but is faid to diminilh- the power by loading the work 

 ■with friction and refiftance. Of this however I can fay nothing from my own experience 

 or obfervation. The counterpoife is alfo unneceflary in the engines called doubl'e engines,, 

 in which the fteam is made to a£l alternately on each fide of the pifton, by proper communi- 

 cation from the boiler, while the fpacc into which the pifton is to move is made to com- 

 municate with the condenfing veflel, where a conftant injeftion is maintained. I was alfo 

 informed, in the year 1794, that fome engines had been conftrudled without the beam ; biit 

 the archite£l from whom I had the information did not ftate the particulars. 



The injeQion water and elaftic fluid are difpofed of in Newcomen's engine with fcarceljr 

 any lofs of power, becaufe the former flows fpontaneoufly through the eduftion-pipe-, and, 

 the latter is driven out by a very flight effort of the fteam againit the atmofphere. Wa'tt*s. 

 engine could not have an edudion-pipe unlefs the column were at leaft 34 or 35 feet 1011^,. 

 to exclude the atmofphere, and even in that cafe there could be no fnift to deliver the elaftic 

 fluid. It was therefore neceflary there fliould be an air-pump to carxy off both > and this is 

 a load upon the engine equal to the amount of the friction of thefe additional parts and 

 the whole weight of the edudion water. I am not well informed of this laft cj^uantity; but 

 fuppofe it to be about one eightieth * part of the power of the engine. 



The fteam-engine for which a patent has lately been granted to Mr. Sadler, is worked 

 without a lever or beam, and confequently has not the inertia of that h.avy mafs to over- 

 come. The greateft part of its adion is performed by the elaftlcity of ftsam ; but the moft 

 remarkable character of his invention is, that part of the fteam previous to its condenfation is 

 employed a fecond time in another cylinder, the pifton of which is fubje6l to the prelfure of 

 the atmofphere. By this fecond application it not only performs the ofEce of an an -pump 

 in a very accurate manner, but llkewife adds to the total amount of force in the uiuchuie. 



* Suppofing the injeftion water to be about -j-^ff of the magnitude of the cylinder within, aud that, 

 tjie ftroke would ralfe \ of the fame magnitude of water through its own length. 



PlataX.. 



