S/A WILLIAM SIEMENS, F.R.S. 51 



its form. Great honour, however, is due to Fulton, Stephenson, 

 Nasmyth, and others, for having adapted the same to the most 

 important purposes. 



The steam-engine of Watt was composed of four organic parts, 

 which were pointed out on a working model before the meeting, 

 namely : 1. The furnace, or chamber of combustion, with its 

 flues and chimney. 2. The boiler, or steam generator. 3. The 

 Mi .mi-vessel, or cylinder, wherein the elastic force of the steam is 

 imparted to the piston, or other first moving parts of the 

 machinery. 4. The condenser, where the elastic force of the 

 steam is destroyed by abstracting its latent heat, by injection of 

 cold water, or by exposure of cooled metallic surfaces. In the 

 case of high-pressure engines, it would seem that the condenser 

 was suppressed ; but it might be said, that this class of engines 

 makes use of one great common condenser, namely, the atmo- 

 sphere ; the separate condenser possessing only the advantage 

 of relieving the working piston of the opposing atmospheric 

 pressure. The only essential improvement of the steam-engine 

 that has been introduced since the time of "Watt consists in 

 working the steam expansively, whereby a considerable economy 

 has been attained ; but it is well known that Watt foresaw the 

 advantages that would be realized in this direction, and was pre- 

 vented only by insufficiency of the mechanical means at his 

 disposal from realising the same. 



The lofty superstructure proved the soundness of the foundation 

 Watt had laid ; and it would seem hopeless to change the same, 

 unless it could be proved that the very principle regarding the 

 nature of heat, whereon Watt had built, had given way to another 

 more comprehensive principle. The engine of Watt was based 

 upon the material theory of heat that prevailed at his time, and 

 almost to the present day. According to this theory, steam was 

 regarded as a chemical compound of water and the supposed im- 

 ponderable fluid " heat," which possessed amongst others the pro- 

 perty of occupying under atmospheric pressure nearly 1700 times 

 the bulk of the water contained in it. The Boulton and Watt 

 condensing engine took the full advantage of this augmentation of 

 volume, which effected a proportionate displacement of piston, and 

 the condensation of the steam obviated all resisting pressure to 

 the piston. 



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