2 6 HER OES O F INVENTION AND DISCO VER V. 



so loaded as to resist the expansive force of the steam up to a 

 certain point, while at the same time, it must give way and 

 allow free vent to the pent-up element, long before it can have 

 acquired sufficient strength to burst the boiler. The safety- 

 valve, however, was not introduced into the steam-engine either by 

 Papin, or for some years after his time. It was employed by him 

 only in the apparatus still known by the name of his digester, a 

 contrivance for producing a very powerful heat in cookery and 

 chemical preparations, by means of highly-concentrated steam. 

 We now come to the engine invented by Captain Savery in 

 1698. This gentleman, we are told, having one day drank a 

 flask of Florence wine at a tavern, afterwards threw the empty 

 flask upon the fire, when he was struck by perceiving that the 

 small quantity of liquid still left in it very soon filled it with 

 steam, under the influence of the heat. Taking it up again 

 while thus full of vapour, he now plunged it, with the mouth 

 downwards, into a basin of cold water, which happened to be 

 on the table ; by which means the steam being instantly con- 

 centrated, a vacuum was produced within the flask, into which 

 the water immediately rushed up from the basin. According to 

 another version of the story, it was the accidental circumstance 

 of his immersing a heated tobacco-pipe into water, and perceiving 

 the water immediately rush up through the tube, on the concen- 

 tration by the cold of the warm and thin air, that first suggested 

 to Savery the important use that might be made of steam, or any 

 other gas expanded by heat, as a means of creating a vacuum. 

 He did not, however, employ steam for this purpose in the same 

 manner that Papin had done. Instead of a piston moving 

 under the pressure of the atmosphere through the vacuum 

 produced by the concentration of the steam, he availed himself 

 of such a vacuum merely to permit the rise of the water into it 



