Additional NolC^\ 401 



. ^' Aiiotlier advaiUnge was, that the cylinder, not being nuule so 

 cold as in Savary's method, much le.s steam was lost in lillin;^ it 

 after each condensation. . 



**The machine, however, still remained imperfect^ for the cold 

 water thrown into tlie cylinder accjuircd heat tVom the steam it 

 condensed, and being in a Vessel exhausted of air, it produccil 

 steam itself, which, in part, resisted the action of the atmosphere 

 on the piston } were this remedied by throwing in more cold 

 water, the destruction of stea n in the iicx.t filling of the cylinder 

 would be proportionably increased. It has, therefore, in practice, 

 been found advisable not to load these engines witli culumns of 

 water weighing more than seven pounds for each square inch cf 

 the area of the piston. The bulk of water, when converted int,o 

 steam, remained unknown, until Mr. J. Watt, then of Glasgow, in 

 17G4, determined it to be about 1800 times more rare than water. 

 It soon occurred to Mr. Watt, that a perfect engine w culd be that 

 in which no steam should be condensed in filling the cyhnder, and 

 in which the ^eam should be so perfectly cooled as to produce 

 neaily a perfect vacuum. 



*' Mr. Watt having ascertained the degree of heat in which 

 water boiled in vacuo, and under progressive degrees of pressure, 

 and instructed by Dr. Black's discovery of latent heat, having cai- 

 culated the quantity of cold water necessary to condense certain 

 quantities of steam so far as to produce the exhaustion required, 

 he made a communication from tlie cylinder to a cold vessel pre- 

 viously exhausted of air and water, into which the steam rushed, 

 by its elasticity, and became immediately condensed. He tJien 

 adapted a cover to the cylinder, and admitted steam above tlie 

 piston to press it down instead of "air, and^^tead of applying wa- 

 ter, he used oil or grease to fill the pores of tho oakum. :.nd Lo 

 lubricate the cylinder. 



" He next applied a pump to extract the injection water, il:e 

 condensed steam, and the air, from the condensing- vessel, eveiy 

 stroke of the enoine. 



o 



" To prevent the cooling of the cylinder by the contact of 

 the external air, he surrounded it with a case containing steam, 

 which he again protected by a covering of matters which conduct 

 heat slow ly. 



" This construction presented an ea-y means of regulating the 

 power of the engine, for tlie steam being the acting po\\ er, as the 

 pipe which admits it from the boiler is more or le:,3 opened, a 

 greater or smaller qumtitv c:in enter du)!ng the time ui a if.oke. 



Vol. I ' •l-^y 



