CATALOG OF THE MECHANICAL COLLECTIONS 27 



spheres that were held together only by the pressure of the atmosphere 

 upon them when they had been put lightly together and the air 

 pumped from between them. The model shows two teams of eight 

 horses, each straining against the other to pull the hemispherical cups 

 apart. 



The model is exhibited in this series to indicate that the develop- 

 ment of the atmospheric steam engines following this date depended 

 upon the knowledge that the atmosphere exerts a fluid pressure upon 

 every surface within it. 



Reference. Gaspare Schotts : Experimenta Nova, 1672. 



PAPIN PISTON ENGINE, c. 1690 



U.S.N.M. no. 308466 ; model ; made in the Museum ; not illustrated. 



Denis Papin, a French physician, was the first to demonstrate the 

 suitability of using steam to produce a vacuum in a cylinder under 

 a piston in a manner that the pressure of the atmosphere would force 

 down the piston and thus do work that could be applied usefully. 

 The elements of the later successful atmospheric steam engines were 

 present in the Papin engine, but he never solved the problem of 

 regularly repeating the cycle of the engine. 



The model shows a machine (rather than an engine) in which a 

 number of weights on a platform are raised by a rope running 

 through overhead pulleys to a piston in a vertical cylinder. A quan- 

 tity of water heated in the cylinder filled the space below the piston 

 with steam, which, when allowed to condense, formed a vacuum under 

 the piston and permitted the pressure of the atmosphere to force 

 down the piston and raise the platform. 



Shown in the model is a "digester", or pressure cooker, equipped 

 with a weighted-lever plug safety valve, an important device in- 

 vented by Papin. 



References, The New Digester, London, 1681 ; La Maniere D^AmoUr 

 les Os, etc., 1682. 



SAVERY STEAM ENGINE, 1698 



U.S.N.M. no. 307238; photograph of drawing; gift of the Science Museum, 

 London ; not illustrated. 



The following is from the Catalogue of the Mechanical Engineering 

 Collection in the Science Museum, London, 1919: "In 1698 Thomas 

 Savery patented an apparatus 'for raising of water and occasioning 

 motion to all sort of mill works, by the impellant force of fire.' No 

 drawing of the arrangement was deposited, but the following year 

 a model of the machine was shown at the Royal Society, and is 

 illustrated in the Philosophical Transactions. 



"The apparatus in its simplest form consisted of a high pressure 

 boiler supplying steam to a receiver, which was provided with suc- 

 tion and delivery pipes and the corresponding valves. By means of 



