Figure 9. — Stirling air engine, 1845. Although the Stirlings had been experi- 

 menting with the regenerative cycle for nearly 30 years, their first practical 

 engine was built around 1844. One of two air vessels is shown cut away. 

 The air that is used as the working fluid is transferred alternately from the 

 space above the displacer piston through the generator to the space below it; 

 meanwhile, air is supplied to and returned from the working cylinder, shown 

 beUveen the two air vessels. (From Minutes of Proceedings of the Institution oj 

 Civil Engineers, 1845, ^°'- 4' P^- 24.) 



Benjamin Cheverton, not as dogmatic as Mr. 

 Hawksley, thought the principle of the regenerator 

 faulty. He agreed that caloric was not consumed 

 when work was produced, but he pointed out that 

 "the change takes place, not in the quantity, but in 

 the intensity of heat." He was groping in the direc- 

 tion of the concept of availability, and he was the 

 first to admit that his argument was circumspect for 

 "want of an adequate terminology." ^' 



»" Ibid., pp. 316-317. 



Captain Fitzroy, of the Royal Navy, sometime 

 captain of the renowned Beagle, said that the chief 

 argument against the imputed fallacy was the fact 

 that the Ericsson had "actually been propelled . . . 

 through the water." The relative economy of air 

 and steam was, he said, "entirely another question." '''' 



Karl Wilhelm Siemens — later Sir William, whose 

 name is associated with the regenerative furnace for 

 metallurgical purposes that he was soon to intro- 



™ Ibid., p. 350. 



PAPER 20: JOHN ERICSSON AND THE AGE OF CALORIC 



57 



