16 BULLETIN 119, U. S. NATIONAL MUSEUM. 



The great demand which resulted for steam engines, after the 

 introduction of Watt's engines, stimulated other inventors, the 

 most prominent of whom probably was Jonathan Hornblower, who 

 in 1781 patented and constructed the compound single-acting engine 

 with a high-pressure cylinder placed between the low-pressure 

 cylinder and the beam center. On account of the low boiler pressure 

 in use at that time, this engine proved less economical than the Watt 

 engine, and since it made use of the separate condenser was an 

 infringement of Watt's patent of 1769. 



Upon the expiration of the Watt patent, that is, about 1800, an 

 advance began in the development of the steam engine which is still 

 continuing. The vacuum became of relatively less importance; in 

 fact, with the high-pressure engine it was sometimes dispensed with 

 entirely. One of the first to advocate and introduce the high-pres- 

 sure engine was Eichard Trevithick, who patented in 1802 a semi- 

 portable engine of this type. The application of this engine to the 

 locomotive was probably the most important step. 



Model of Hero's Rotary Steam Engine. Deposited by the United States 

 Department of the Interior. 



The philosopher, Hero, of Alexandria, Egypt, prepared a treat- 

 ise entitled " Spiritalia seu Pneumatica." In it are described a 

 number of interesting forms of water and heat engines, and among 

 the latter an apparatus moved by the force of steam somewhat as 

 represented in the model. This earliest of steam engines, which 

 Hero called " aeolipile," consisted of a globe suspended between 

 trunnions through one of which steam enters through pipes from a 

 boiler below. The hollow-bent arms projecting from the globe 

 cause the vapor to issue in such a direction that the reaction pro- 

 duces a rotary movement of the globe, just as the rotation of reaction 

 water wheels is produced by outflowing water. 



Cat. No. 244,887 U.S.N.M. 



Model of Dr. Denis Papin's Atmospheric Steam Engine, A. D. 1690. De- 

 posited by the United States Department of the Interior. 



The apparatus proposed by Dr. Papin consists of an open-topped 

 metal cylinder fitted with a piston and piston rod. A small quantity 

 of water is placed in the bottom of the cylinder and heated by a fire 

 placed underneath until the steam generated forces the piston to rise 

 to the top. The fire was then removed and the steam gradually 

 condensed, forming a vacuum within the cylinder, and thus causing 

 the piston to move downward by air pressure with such force as to 

 enable it by the aid of a rope and overhead pulley to lift a weight. 



