SECT, i.] THE STEAM ENGINE. 27 



condensing in a separate vessel ; and it necessarily involved a method of clearing 

 the condenser of air and water. The application of the principle could be ren- 

 dered perfect only by keeping the cylinder as hot as the steam, and the condenser 

 as cold as it could be done with economy ; and the methods proposed by Mr. Watt 

 for accomplishing these objects are at once novel and efficient. 



The idea of using steam pressure was not new, not even when applied to a piston, 

 (see art. 12.) but the application of it in a close cylinder by means of a stuffing 

 box, such as Smeaton had applied to the air pump, was a new mode of construc- 

 tion, which, it may be inferred, was intended in the engine specified, though it is 

 not described. The scheme of a rotary steam vessel, or steam wheel, was also first 

 made public in this specification, though in a very imperfect manner. 



27. Mr. Watt's steam wheel not answering on trial, his next object seems to 

 have been to convert the reciprocating motion of the piston rod into a rotary one. 

 Methods for this purpose had been contrived by Hulls and Fitzgerald ; and patents 

 had been obtained for similar ones by Stewart in 1769, and by Washborough in 

 1778, also by Steed in 1781, for the simple crank motion. 



Notwithstanding the existence of these methods, Mr. Watt obtained a patent for 

 five others in 1781, one of which was the sun and planet wheel motion, which he 

 used for some time on account of the crank being Steed's patent. 



In 1782 Mr. Watt obtained another patent, embracing various methods of 

 applying steam. First, for an expansive steam engine, with six different con- 

 trivances for equalizing the power ; secondly, the double power steam engine, in 

 which the steam is alternately applied to press on each side of the piston, while 

 a vacuum is formed on the other ; thirdly, a new compound engine, or method of 

 connecting together the cylinders and condensers of two or more distinct engines, 

 so as to make the steam which has been employed to press on the piston of the 

 first, act expansively upon the piston of the second, &c. ; and thus derive an 

 additional power to act either alternately or conjointly with that of the first cylinder; 

 fourthly, the application of toothed racks and sectors to the end of the piston or 

 pump rods, and to the arches of the working beams, instead of chains ; fifthly, 

 a new reciprocating semirotative engine, and a new rotative engine or steam 

 wheel. 



By the double engine the same cylinder was rendered capable of doing double 

 the quantity of work in the same time, the steam pressure acting, and condensation 

 taking place, both during the ascent and descent of the piston. Simple as this 

 change appears, after being made, it is attended with many striking advantages ; 

 it renders the power nearly uniform, diminishes the proportion of cooling surface, 

 a less boiler is necessary, and it reduces the bulk and weight of the engine. 



Of the modes of regulating the power of steam engines, the most effective were, 



