SECT, i.] THE STEAM ENGINE. 9 



ultimately render the air saturated with vapour ; but even then it would not be 

 more than an air engine, and a very indifferent one, being exceedingly complex. 



1705. THOMAS NEWCOMEN. 



10. The trials of Savery's engines made known their defects, yet evidently 

 strengthened the idea that steam could be effectively applied to raise water ; and 

 the immense expense of raising water from deep mines so embarrassed their pro- 

 prietors, that there were most powerful incentives at that period to engage in 

 further researches on the subject. To this stimulus we are indebted for another 

 construction of the steam engine, by Thomas Newcomen, a smith, of Dartmouth, 

 who, in conjunction with John Cawley, a plumber of the same place, and Captain 

 Savery, obtained letters patent for the invention in 1705. 1 The novelty of this 

 construction consists entirely in condensing the steam below an air-tight piston, in 

 a cylindrical vessel having an open top ; and the idea was very probably taken 

 from the project of Papin in 1695 (see art. 6) ; for it appears that Newcomen was 

 in correspondence with Dr. Hook on the subject, to whom the speculations of Papin 

 were well known ; but the mode of effecting the object was entirely different from 

 Papin's. It consists in admitting steam below a piston ; and, at first, the steam 

 was condensed by applying cold water to the outside of the cylinder ; but injection 

 of cold water by a jet into the interior was soon found to be a more effective 

 method, and is said to have been discovered by accident. 2 The following is a 

 description of the engine, as far as it was improved by Newcomen. B represents 

 the boiler with its furnace for producing steam ; and at a small height above the 

 boiler is a steam cylinder, C, of metal, bored to a regular diameter, and closed at 

 the bottom, the top remaining open. A communication is formed between the 

 boiler and the bottom of the cylinder, by means of a short steam pipe, S. The 

 lower aperture of this pipe is shut by the plate p, which is ground flat, so as to 

 apply very accurately to the whole circumference of the orifice. This plate is called 

 the regulator, or steam cock, and it turns horizontally on an axis a, which passes 

 through the top of the boiler, and is fitted steam-tight ; and has a handle to 

 open and shut it. 



1 Switzer says, on report, that Newcomen was as early in his invention as Savery. Sys. of 

 Hydros ii. 342. 



2 Desaguliers' Experimental Philosophy, ii. p. 533. The piston was kept tight by a quantity 

 of water on the top of it ; and as they were working by condensing from the outside, they were 

 surprised to see the engine make several strokes very quickly, and found that it was owing to a 

 hole in the piston letting down water to condense the steam. This suggested the idea of injection. 



B 



