JAMES WATT. 



state of steam is numerically designated. The latter, he says, 

 is about two thousand times as great as the former ; which is 

 not far from a correct account of the expansive force that steam 

 exerts under the ordinary pressure of the atmosphere. One 

 measure of water, it is found, in such circumstances, will pro- 

 duce about seventeen hundred measures of steam. 



The next person whose name occurs in the history of the 

 steam-engine, is Denis Papin, a native of France, but who 

 spent the part of his life during which he made his principal 

 pneumatic experiments in England. Up to this time, the 

 reader will observe, the steam had been aj^plied directly to the 

 surface of the water, to raise which, in the form of a jet, by 

 such pressure, appears to have been almost the only object 

 contemplated by the employment of the newly-discovered 

 power. It was Papin who first introduced a piston into the 

 tube or cylinder which rose from the boiler. This contrivance, 

 which forms an essential part of the common sucking-pump, is 

 merely, as the reader probably knows, a block fitted to any 

 tube or longitudinal cavity, so as to move freely up and down 

 in it, yet without permitting the passage of any other substance 

 between itself and the sides of the tube. To this block a rod 

 is generally fixed ; and it may also have a hole driven through 

 it, to be gTiarded by a valve, opening upwards or downwards, 

 according to the object in view. Long before the time or 

 Papin it had been proposed to raise weights, or heavy bodies 

 of any kind, by suspending them to one extremity of a handle 

 or cross-beam attached at its other end to the rod of a piston 

 moving in this manner in a hollow cylinder, and the descent of 

 which, in order to produce the elevation of the weights, was to 

 be effected by the pressure of the superincumbent atmosphere 

 after the counterbalancing air had been by some means or other 



