212 RECOLLECTIONS OF FORTY YEARS. 



use. According to Salomon de Cans' s plan the 

 motive steam was to be engendered in the vessel 

 containing the water and by means of this same 

 water. In Savery 's engine there were two separate 

 chambers, one containing the water and the other, 

 which may be called the boiler, the steam. This 

 steam, when a sufficient quantit} 7 has been generated, 

 finds its way to the upper part of the water chamber 

 by a communicating tube which can be opened at will 

 by means of a tap. It exercises a downward pressure 

 upon the liquid surface, and forces it back into a 

 vertically ascending tube, the lower orifice of which 

 must always be beneath this surface, for otherwise 

 the steam itself would escape. 



"In Salomon de Caus's engine, as soon as the 

 presence of the steam has produced its effect, a work- 

 man has to make good the water which has been 

 driven out by means of an orifice in the upper part of 

 the metallic sphere which opens and shuts at discre- 

 tion. All that then remains to be done is to keep the 

 fire going. In Savery's engine the water is let in, not 

 by a workman, but by atmospheric pressure. 



" In short, Savery sought to utilise steam for driv- 

 ing water into a vertical tube, but Salomon de Cans 

 had done precisely the same thing eighty-three years 

 before. Savery, again, effected the vacuum which 

 brought about the suction by the cooling of the steam. 

 This was a very important matter, but Denis Papin 

 had long before drawn attention to it." 



