THE STEAM-ENGINE. 



tubes, B, C, connected with the boiler, D, below. On 

 the boiler being heated, 

 steam passes through 

 the pivot tubes into the 

 cylinder, from which it 

 escapes by the holes, F, 

 in the tubes, E, E. In 

 escaping, it rushes out 

 with great force, and by 

 its reaction on the sides 

 of the tubes opposite the 

 holes, it forces them and 

 the cylinder to revolve 

 in a contrary direction. 



In 1543, a Spaniard, 

 Blasco de Garay, is said 

 to have propelled a boat 

 in Barcelona harbour by 

 the power evolved from a 

 caldron of boiling water; 



Fig. 6. 



and in the beginning of the I7th century, various 

 attempts seem to have been made to make use of 

 steam. The only notice of steam-power at this 

 time, however, which is interesting to us, occurs 

 later on in the century. In 1663, the Marquis of 

 Worcester, during his confinement in the Tower, 

 wrote his famous book, A Century of the Names 

 and Scantlings of such Inventions as at present I 

 can call to mind to have tried and perfected. 

 Under the name of ' Fire-waterwork,' he describes 

 a machine for raising water by means of steam, 

 which appears to have been actually at work at 

 Vauxhall in 1656. 



In 1698, Captain Savery obtained a patent for a 

 steam-engine, which was the first used to any 

 extent in doing work, most earlier engines having 

 been little better than scientific toys. His 

 engines seem to have been employed for some 

 years in the drainage of mines in Cornwall 

 and Devonshire. The essential improvement 

 in them over the older ones was the use of a 

 boiler separate from the vessel in which the 

 steam did its work. One vessel, in all former 

 engines, had served both purposes. 



In all the attempts at pumping-engines hitherto 

 made, including Savery's, the steam acted directly 

 upon the water to be moved without any intervening 

 part. To Dr Papin, a celebrated Frenchman, is due 

 the idea of the piston. It was first used by him in a 

 model constructed in 1690, where the cylinder was 

 still made to do duty also as a boiler ; but in an 

 improved steam-pump invented about 1700 he 

 used it as a diaphragm floating on the top of the 

 water in a separate vessel, or cylinder, and the 

 steam, by pressing on the top of it, forced the 

 water out of the cylinder at the other end. 



The next great step in advance was made about 

 1705 in the 'atmospheric' engine, conjointly in- 

 vented by Newcomen, Cawley, and Savery. This 

 machine held its own for nearly seventy years, 

 and was very largely applied to mines, so that it 

 will be worth while to give a somewhat more 

 detailed description of it than of the others. 



In this engine, which is shewn in fig. 7, the 

 previous inventions of the separate boiler, and of 

 the cylinder with its movable steam-tight piston, 

 are utilised, although in a new form. The ' beam, 

 which has ever since been used in pumping- 

 engines, was used for the first time, and for the 

 first time also the condensation of the steam was 

 made an instantaneous process, instead of a slow 



and gradual one. The boiler, B, is placed over a 

 furnace ; from it a pipe conveys the steam to the 

 cylinder, C, immediately connected with the boiler, 



Fig. 7- 



the supply of steam being regulated by the valve, 

 V. The level of the water in the boiler is ascer- 

 tained by the gauge-cocks, G, G, and the pressure 

 of the steam by the safety-valve, SV. The piston, 

 P, works in the cylinder, C, and is kept tight by a 

 stream of water issuing through a pipe regulated 

 by a stop-cock, T, and supplied from a cistern, C'. 

 From the same cistern, the water for condensing 

 is supplied to the cylinder by the pipe, A ; the 

 water of condensation is led from the interior of 

 the cylinder by a pipe to a cistern, S, this being 

 placed at a considerable distance below the 

 cylinder, in order to balance the atmospheric 

 pressure, which would otherwise force the water 

 up the pipe into the vacuum created in the 

 cylinder. The air which gains access to the 

 cylinder with the steam is allowed to pass off 

 through the snifting-valve, H, which opens up- 

 wards. The piston-rod, M, is connected by a 

 chain to a quadrant placed at the end of a beam, 

 which vibrates on a centre, I ; the pump-rod, N, 

 is attached in a similar manner to the other end 

 of the beam. A second and smaller pump supplies 

 the cistern, C', through the pipe, EE. The opera- 

 tion of the engine is as follows : The fire being 

 Droperly raised, and steam freely formed, the valve, 

 V, is opened, to allow the entrance of the steam 

 nto the cylinder. Although the pressure of the 

 steam is at most not more than that of the 

 atmosphere, the pump-rod, N, with its counter- 

 weights, is so much heavier than the piston-rod, 

 that it at once falls, and consequently raises the 

 end, M, preparatory to another stroke. The 

 regulator-valve, V, is now shut, and the stop-cock, 

 R, on the pipe, A, being opened, the cold water is 

 injected, and condenses the steam. But as a 

 vacuum is made by the condensation of the steam, 

 the pressure of the air, acting with a force equal 

 to nearly 15 Ibs. per square inch on the surface of 

 the piston, carries it down to the bottom of the 



423 



