«S{B Defirtptkn of an Improtfmetff in the Steam Engittt. 



tators by condenfing his fteam in a cold veffel at a diftance from the working cylinder. The 

 bther improvements in the mechanifm in the furnace, in the double ftroke, &c. &c. 

 though highly valuable and honourable to the fkill and contrivance of the inventors, ap- 

 pear to be of fubordinate importance, and in many particulars are little more than thofe 

 variations of fafhion which in mechanics, as well as other lefs important departments of 

 human induftry, are more or lefs prevalent. 



It was among the early improvements of the (learn engine, to feed the boiler out of that 

 hot water which was afforded by the condertfation of the fteam along with the ftream of 

 inje£lion. When the boiler receives a quantity of cold water, it becomes neceflary either 

 to increafe the fire, or to admit the engine to work whh lefs effedl: from the diminifhed 

 quantity or elafticity of the fteam produced; and when the water thus fupplied is afforded 

 in the manner juft mentioned, it will be hotter the lefs the injeQion, and the contrary. 

 But there is a mean which muft be attended to in the adjuftment of this heat. A fparing 

 injeftion will not afford a good vacuum, and therefore the engine will work with dimi- 

 nifhed effect ; and a copious injeftion will afford water at a low temperature to the boiler; 

 When the adjuftment is at the beft, the water of the fupply is not hotter than the hand can 

 fcear, that is to fay, about 120°. It becomes therefore an obje£l of value, to afcertain the 

 means by which the condenfation of the fteam may be rendered as perfeCt as the intro- 

 dudllon of cold water can make it, and at the fame time, that a greater part of the heat 

 it imparts may be employed in raifmg the temperature of the water intended for the 

 boiler. 



Plate VIII. reprefents a feftion of the parts of a double engine; that is to fay, an en- 

 gine in which the pifton is alternately impelled by the elafticity of fteam ading above and 

 below. A A is the great cylinder in which the pifton moves ; O, P, are the ftearrl 

 boxes, or mttaliic receptacles, into which the fteam is firft introduced from the boiler 

 by pipes at O and P, not reprefented in the figure. They contain each two valves, 

 B, C, and />, c, which are opened or {hut by the ufual apparatus attached to the working 

 beam ; d,d'\s the paffage to D D the condenfer, terminating in H the air pump. E F G 

 are the additional parts of which the new improvement confifts. 



Let us then fuppofe the engine in a£tual work, the valve b in the lower fteam box being 

 open, and c (hut, while B in the upper fteam box is (hut, and C open. From this difpo- 

 fition fteam will ru(h in from the boiler through /, beneath the pifton, while the other 

 fteam which had been admitted before above the pifton, will "have a communication through 

 L, C, K and d, to D the condenfer, where a conftant injection J being kept up, it becomes 

 condenfed and leaves a vacuum. Confequently the pifton muft rife by the whole force of 

 the fteam beneath. When it has arrived near the top of the cylinder, the valves in the 

 fteam boxes b and C are (hut, and the others B and c are opened ; fo that the fteam froift 

 the boiler ru(hes through L into the fpace above the pifton, while the other fteam beneath 

 paffes through /, f'and k to the condenfer, where it affumes the denfe form and leaves a 

 vacuum, into which the pifton is urged in its defcent. When the dcfcent is completed, 



the 



