HYDRAULICS. 211 



bursting, when the safety valve was loaded too 

 much. 



But the greatest defect of this machine is the 

 great waste of steam, and, consequently, of fuel. 

 For when the steam is admitted to the top of the 

 cold water in the receiver, it is condensed with 

 great rapidity ; and the water does not begin to 

 yield to its pressure, until its surface be so hot as 

 not to condense any more steam : it then descends, 

 but, as thus, a new part of the side of the receiver 

 is exposed to the steam, more is condensed, so that 

 a condensation of the steam is going on all the 

 while the water is descending. This is repeated 

 at every stroke, as the receiver is cooled every 

 time it is filled with water. 



Mr. Savary succeeded in raising water to small 

 heights, and erected several engines in different 

 parts of England ; but he failed in deep mines. 

 Many attempts have been made to correct these 

 defects, but hitherto without much success. 



At a time when almost all the most valuable 

 mines in England were coming to a stand, for want 

 of more powerful or cheaper machines than were 

 then known, Newcomen and Cauly conceived the 

 project of applying a piston with a lever and other 

 machinery. They joined with Savary, in procur- 

 ing a patent for it in 1705, and executed many 

 engines which were of vast utility to the mining 

 concerns, occasioning the continuance of mines 

 that must have been neglected, and the opening of 

 new ones. 



Fig. 2. exhibits a section of Newcomen's engine: 

 a is the boiler built in brick-work. In the top of 

 the boiler is a steam-pipe, c, communicating with 

 the cylinder b, which is of metal, and is bored very 

 truly. The lower aperture of this pipe is shut by 



p 2 



