104 THE ADDRESSES, LECTURES, ETC., OF 



the best advantage those stores of potential energy in the shape 

 of fuel which have providentially been placed at our disposal. 



AIE-ENGINES. 

 To THE EDITOR OF "ENGINEERING." 



SIR, In your article of last week on "Air-Engines" you 

 inadvertently do scanty justice to the Institution of Civil 

 Engineers, in alluding to their state of ignorance regarding the 

 theory of air-engines and the dynamical theory of heat prior 

 to the year 1854, when the late Professor Rankine read his 

 Paper on " Air-Engines " before the British Association. When 

 in 1845 the merits of Dr. Stirling's economiser were discussed 

 before the Institution, the dynamical theory of heat was not 

 known, and in consideration of this circumstance it was only 

 natural that no just appreciation could be formed of the scope 

 and utility of that most interesting appliance, the economiser, the 

 mere physical conception of which may be traced back almost to 

 antiquity. 



Dr. Stirling introduced his air-engine under the title of the 

 Paradox Engine, because, with many others, he believed that it 

 involved the realisation of perpetual motion, allowance being 

 made for the incidental losses of heat. 



When however in 1852, Captain Ericsson appeared upon the 

 stage with his regenerative air-engine, and re-asserted the same 

 fallacy under which Stirling had been labouring, the Council of 

 the Institution determined to sift the question to the bottom, and 

 knowing that I had paid much attention to kindred subjects 

 requested me to prepare a critical paper on air-engines, which was 

 read accordingly during the session 1852-53. At that time the 

 believers in the dynamical theory of heat, might be counted on 

 your fingers, and I could hardly have selected a more unpopular 

 title for my paper than "On the Conversion of Heat into 

 Mechanical Effect." * Being convinced, however, that the new 



* Published in the Scientific Papers of Sir William Siemens, Vol. I., p. 29. 



