PHYSICS OF THE EIGHTEENTH CENTURY. 



299 



rangement, constructed an engine mainly upon the principle formerly 

 proposed by Papin. This engine, as being the immediate forerunner 

 of Watt's engine, requires a word of explanation. Its mode of action, 

 may be gathered from Fig. 146, in which a represents the boiler, from 

 which steam passed into the cylinder c through the opening e when 



FIG. 146. NEWCOMEN'S ENGINE. 



the cock k was opened, which was originally done by hand, as the 

 piston h was drawn up by the weight of the pump-rod m and counter- 

 poise /, attached to the other end of the beam. In the lower part 

 of the cylinder, which in the figure is shown as if partly broken away, 

 in order to exhibit its interior, were two other apertures, one of which, 

 d, communicated with a cistern, , of cold water, which being ad- 

 mitted into the cylinder when the latter was full of steam and the 

 communication with the boiler closed, caused the condensation of 

 the steam. It will be seen that here again the steam is simply the 

 means for readily obtaining a vacuum, in consequence of its property 

 of condensing into water by the application of cold. Any desired 

 power could be obtained by this machine, not by increasing the ten- 

 sion of the steam, but by enlarging the diameter of the cylinder. The 



