820 TRANSACTIONS OF SECTION G. 



of the regenerator to be an entire fallacy, and did not believe that the power 

 derived from the expansion of air by heat could be used eftectively, and then be 

 recovered and used again. Mr. Hawksley considered that the machine involved 

 a mechanical fallacy and that the regenerator produced no mechanical effect 

 whatever. Mr. Rendel was the President at the meeting which dealt with Mr. 

 Cheverton's paper, and, in view of the great differences of opinion on the subject, 

 he stated that ' he would not have the meeting arrive at a hasty or erroneous 

 conclusion on the question of this engine, and he therefore suggested that Mr. 

 Siemens should draw up a paper on the subject, and that the members should 

 collect, for a future meeting, all the information within their reach, in order to 

 the calm and deliberate discussion of the question.' This resulted in the further 

 meeting of May 17, 1853, when papers were read by Manby, Leslie, and Siemens. 

 The paper by Manby consists of the summary of a discussion by M. Galy- 

 Cazalet, which took place in Paris in 1852. M. Galy-Cazalet comes to the conclu- 

 sion that the regenerator involves a fallacy, and he concludes : ' There appears 

 to be at present so much doubt of the utility of the regenerator that it would be 

 wise to abandon its use for a time, and by trials with a more simple form of 

 caloric engine establish the fact either of the superiority or of the inferiority of 

 heated air in comparison with steam as a motive power.' Mr. Leslie, on the 

 contrary, in his paper upholds vigorously the accuracy of the principle of the re- 

 generator or economiser. He comes to the conclusion that it is based on true 

 principles and is attended in practice with real economy of heat, and consequently 

 of fuel. In this conclusion he is doubtless correct ; the regenerator is useful and 

 does economise heat. But Leslie goes much further than this ; he appears to 

 support Stirling in tlie fallacy that the regenerator may be made indefinitely 

 useful. Stirling states : — • 



'And thus it appears that by applying air successively to a series of bodies 

 reg;ularly increasing in temperature, and moving it alternately from one end of the 

 series to the other, it may be heated and cooled ten times, with an expenditure 

 of caloric which would barely have heated it once, it if had been applied at once, 

 to the hottest body (i.e., beyond the series). It is evident also that if the series 

 had been composed of twenty points, or bodies, having a difference of temperature 

 of five degrees, the air might be heated andcooled twenty times at no greater expense 

 of caloric. Nay it is evident that by multiplying the members of the series 

 indefinitely air could be heated and" expanded and made to do work at no 

 appreciable expense. But let no mathematician be alarmed with the idea of a 

 perpetual motion, or the creation of power. There are many enemies to contend 

 with in the air engine besides friction, which alone prevents perpetuity in some 

 mechanical motions. We have no means, without consuming a part of our power, 

 of applying the air so closely to the apparatus as to make it absolutelv assume the 

 temperature of the bodies to which it is applied. There is, therefore," a loss in the 

 very act of heating and cooling.' 



Leslie comes to the conclusion that Stirling is right, but that an air engine 

 without a regenerator would be a much less effective and economical application 

 of heat than the steam engine. Leslie gives some interesting particulars of the 

 later air engines of James Stirling. lie states that an engine of 45 h.p. was 

 started in March 1843 at the Dundee Foundry ; that in December 1845— two 

 years and nine months after starting— one air-"vessel gave way, and in May 1846 

 another failed, and in January 1847 a third failed. This information was supplied 

 to him by Mr. David Mudie, one of the lessees of the foundry. 



We now come to Siemens' paper ' On the Conversion of Heat into Mechanical 

 Effect,' and for the first time we find the engineer guided by an intelligible principle. 

 Siemens discussed the material theory of heat, and accepted unreservedly the 

 dynamical theory, for which he gives a large measure of credit to Joule. This is 

 the first of the Institution papers in which I find the name of Joule. Siemens 

 mentions Carnot, Clapeyrou, Holtzman of Mannheim, Joule, Helmholtz, Meyer, 

 Rankiue, and Professor Thomson. Curiously enough, although Siemens mentions 

 Carnot and the other philosophers who dealt with the Carnot principle, including 



