246 EIGHTEENTH CENTURY. FT. in. 



120 years before Christ ; and Baptiste Porta in 1580, Solo- 

 mon de Cans in 1615, and the Marquis of Worcester in 

 1663, all tried to make use of steam to do work. Again, in 

 1690 and 1698, a Frenchman named Papin and an English- 

 man, Captain Savery, tried to make steam-engines to raise 

 water out of mines. But the only one of all these engines 

 which we need describe here was that which fell into the 

 hands of Watt, and which was made by a man named New- 

 comen in 1705. A plan of Newcomen's engine is given in 

 Fig. 41. Its working depended on the pressure of the 

 atmosphere (explained p. 123) on the piston at one end of 

 the beam, and the weight of the lump of iron, e, at the other 

 end. 



The lever-beam of this engine is balanced in such a 

 way that when it is not at work the weight e pulls it down 

 on the side away from the engine, and the piston,/,/, is drawn 

 up to the top of the cylinder, as in the figure. To set the 

 engine going a fire is lighted under the boiler, and the 

 tap or stopcock, a, is opened, so that the steam rises into 

 the cylinder, driving out the air through the air-vent, c. As 

 soon as the cylinder is full of steam, a is turned off, and the 

 stopcock, b, turned on. Immediately a small jet of cold 

 water from the tank T rushes through b into the cylinder, 

 turning the steam back into a few drops of water, which flow 

 out with the cold water down the pipe d. Now notice, the 

 cylinder is quite empty ; for the steam drove out the air, and 

 the cold water carried the steam away with it, while no air can 

 come in at c or d, because the little valves in them are kept 

 shut by the weight of the atmosphere outside. So there is 

 nothing to hoi J up the piston, which is being heavily pressed 

 down by the air above it. The consequence is, down it 

 comes to the bottom of the cylinder, dragging with it the 



