CATALOG OF THE MECHANICAL COLLECTIONS 175 



CALORIC, OR HOT-AIR, ENGINES 



Turbines driven by hot air or hot gases are very old. Heron 

 (Alexandria, 50 A. D.) described a simple hot-air reaction turbine 

 that mysteriously animated dancing figures when an altar fire was 

 lighted: Leonardo da Vinci (Florence, c. 1490) in his notes and 

 sketches suggested the chimney- jack or chimney-gas turbine to utilize 

 the hot gases from a fire to turn a roasting spit; and Guillaume 

 Amontons (France, 1699) had an atmospheric "fire wheel" in which 

 a heated column of air was made to drive a wheel. Some chimney 

 jacks, toys, and the small exhaust-gas turbines used to drive super- 

 chargers for automobile and aircraft engines are probably the only 

 present-day uses of this form of hot-air engine. 



The use of heated air expanding in a cylinder against a piston 

 to perform work is just as old. The recent development, however, 

 dates from the British patent of Glazebrook (1797), followed by 

 Cayley (1807) and Stirling (1826), and reached its peak about 

 1850-1860 following Ericsson's demonstrations of 1845-1855. These 

 engines in their simplest form consist of two chambers filled with 

 air or gas and connected by pipes with the opposite ends of a 

 cylinder in which a piston reciprocates as the bodies of air in the 

 chambers are alternately expanded and contracted by heating and 

 cooling the chambers. This is the form of Stirling's engine. The 

 great number of hot-air engine designs are but variations of this 

 idea. Some compress the air before or after heating, others sepa- 

 rate the heaters from the chambers, or discharge the air at the 

 end of the stroke; some use screens and baffles as regenerative heat- 

 ers; and others use moistened air, mixtures of steam and air, and 

 water pistons to cut down friction and abrasion. 



John Ericsson (1803-1858), who applied the screw propeller to 

 ship propulsion and designed the U. S. S. Monitor^ of Civil War 

 fame, devoted a large part of his life to the development of the hot- 

 air engine. As early as 1826 he made one at Havre, France, which 

 he demonstrated unsuccessfully at London. In 1833 he patented 

 a regenerator to utilize the heat in the exhausted air to preheat the 

 new supply of cold air. He continued his experiments after coming 

 to America in 1839 and built eight hot-air engines between 1840 and 

 1850. He gradually increased the size of his engines and in 1851 

 built the ninth (at a cost of $17,000), which had a 2-foot stroke 

 and two compressing cylinders of 4-foot diameter. He claimed an 

 economy of 1 horsepower-hour from 11 ounces of coal. Two large 

 engines working satisfactorily in factories at New York received 

 favorable notice in the press and enabled Ericsson to obtain the sup- 

 port necessary to construct a ship propelled by a caloric engine with 

 \four 168-inch working cylinders and four 137-inch compressing 



