2Q BULLETIN 173, U. S. NATIONAL MUSEUM 



pounds of coal burned, while the Watt engine, with separate con- 

 denser and operating expanding, performed 66.0 million foot-pomids 

 of work from the same weight of fuel. 



This much of the story of the steam engine is illustrated in the 

 Museum by a series of models, with relevant photographs and 

 drawings, under the caption : 



THE STORY OF THE STEAM ENGINE 

 150 A. D. TO 1777 



HERON'S TURBINE, c. 150 A. D. 

 Plate 10, Fioubb 1 



U.S.N.M. no. 308462 ; model ; made in the Museum ; photograph no. 17133. 



This model is a pictorial adaptation of the aeolipile described (in 

 Pneumatica) by Heron of Alexandria who lived in the first century. 



The model consists of a light hollow ball supported on its axis 

 between two trunnions, one of which is hollow. The ball carries four 

 bent nozzles in a plane perpendicular to the line of its axis. Steam, 

 generated in a boiler below, is carried to the ball through the hollow 

 trunnion and escapes through the nozzles. The reaction on the 

 nozzles, due to the steam issuing from them, turns the ball. 



Heron of Alexandria (Egypt), a Greek philospher, who lived some 

 time between 50 B. C. and 150 A. D., left a number of treatises 

 (Pneumatica, Aittomatopoiika, Belopoiika, Cheirohalistra, Metrica, 

 Dioptia, and Katoptrica) in which are collected most of the knowl- 

 edge of his time in the fields of theoretical and applied mechanics. 



BRANCA TURBINE, c. 1629 



U.S.N.M. no. 308464 ; model ; made in the Museum ; not illustrated. 



Giovanni Branca, a chemist of Loretto, Italy, suggested a steam 

 engine in which a jet of steam issuing from a nozzle was directed 

 against the blades of a paddle wheel. This is the earliest suggestion 

 of an impulse turbine. 



The model shows such a wheel connected to the pestles of a chem- 

 ist's stamp mill. The nozzle is attached directly to a spherical copper 

 boiler. 



Eeference, Le Machine, Kome, 1668. 



DEMONSTRATION OF THE "WEIGHT OF THE ATMOSPHERE", 1654 



U.S.N.M. no. 30S645 ; model ; made in the Museum ; not illustrated. 



This is a simplified pictorial model of Otto von Guericke's spec- 

 tacular demonstration before the burghers of Magdeburg, in which he 

 showed the great force required to separate two large hollow hemi- 



