Intelligence and Miscellaneous Articles. 309 



To estimate the improvement thus effected by Mr. Woolf, by him- 

 self alone, without aid from any other engineers, and whilst he was 

 opposed by many, the performance of the engines previously used in 

 Cornwall must be examined. 



Mr. Watt first introduced his engines into Cornwall in 1/78, in 

 place of Newcomen's atmospheric engines, which had been introduced 

 there about fifty years before, but had never raised more than eight 

 or nine millions. Mr. Watt did twice as much with his first engines, 

 and three times as much, after he had applied his method of working 

 expansively, for which he had a patent in 1782. It consists in stop- 

 ping the supply of steam from the boiler to the cylinder, when the 

 piston has only moved through a portion of its course, leaving it to be 

 impelled through the remainder, by the expansive action of the steam 

 already admitted into the cylinder, without any further expenditure 

 of steam from the boiler. 



Mr. Watt proposed in 1782 to work his engines by stopping the 

 supply of steam when the piston had only moved one-fourth of its 

 course, leaving three-fourths of the course to be performed by the ex- 

 pansive action ; and although the force exerted by the steam during 

 that expansion must continually decrease, nevertheless 2-^ times 

 more power would be exerted on the whole than would be exerted 

 by the same steam, if it acted without expansion. But it was found 

 that such an extent of expansive action could not be realized in prac- 

 tice, because the steam used by Mr. Watt, when expanded to fill a 

 quadruple space, becomes too feeble to impel a piston with effect. 



Mr. Watt never retained the steam in his boilers much above the 

 pressure of the atmosphere ; they were always supplied with water 

 through upright pipes, open at top to the atmosphere, and the lower 

 ends immersed beneath the surface of the water in the boilers ; the 

 open ends of the feeding pipes being only eight feet high above that 

 surface, the steam could not by any chance be retained in the boiler 

 beyond 3-£- pounds per square inch more elastic than the atmospheric 

 air : that was Mr. Watt's practice, and his successors in business at 

 Soho still continue it. The term low-pressure steam can only with 

 propriety be applied to the steam produced by such boilers. 



Mr. Watt's engines with such boilers cannot be made to exert a 

 competent power to drain deep mines, unless the supply of steam to 

 the cylinder is continued until the piston has run through more than 

 half its course ; and on an average in practice, low-pressure steam is 

 only expanded so much as to fill one and a half time the space it 

 occupies in the cylinder, at the moment when the supply was cut off: 

 even with that moderate extent of expansive action, the steam will 

 exert nearly one half more power than would be exerted by the same 

 steam acting without expansion, as it must do if the supply from the 

 boiler to the cylinder were continued until the piston terminated its 

 course. 



open air without any clothing. See a description of the cylinders, Philoso- 

 phical Magazine, vol. xlvi. pp. 116, 236, 319, & 398 ; and the performance for 

 each month is stated in the Numbers of the succeeding volumes up to the 

 end of 1818. 



Mr. Watt's 



