I'KESIDENTIAL ADDRESS. 819 



the large engines of the hot-air ship • Ericsson ' in America, the engines having 

 air cylinders of no less than 14 feet diameter. Four papers were read in this 

 year: ' On the Use of Heated Air as a Motive Power,' by Benjamin Cheverton ; 

 ' On the Caloric Engine,' by Charles Manby ; ' On the Principle of the Caloric 

 Air Heated Engine,' by James Leslie, M.Inst.C.E. ; and ' On the Conversion of 

 Heat into Mechanical Effect,' by Charles William Siemens, A.M.I.C.E. 



Cheverton evidently considers, from his paper referring to Stirling and Ericsson, 

 that ' Both parties also rest the efficiency of their engines on the repeated use of 

 caloric. They contend that in recovering from the ejected hot air the caloric 

 which gave it superior tension, and employing it in heating the injected air, " it 

 is made to operate over and over again." Mr. Ericsson aspires to embody a new 

 principle in motive mechanics — no less, to use his own words, than " that the pro- 

 duction of mechanical force by heat is unaccompanied by the loss of heat," except 

 such as arises from radiation, or other practically unavoidable waste.' Cheverton 

 rejects this idea, but, strangely enough, does not appear aware of the work either 

 of Cainot or of Joule. He comes to the conclusion, however, that ' caloric, doubt- 

 less, is in all its aspects a manifestation of force, and unquestionably, as a me- 

 chanical agent, of a dynamic force, and therefore is directly amenable to the third 

 law of motion.' He appears to think that heat is accompanied with molecular 

 activity, but is puzzled by what he accepts to be a fact, that in the steam engine 

 the whole of the heat of the steam as it comes from the boiler is found in the 

 condenser. With regard to the steam, he says : ' Undoubtedly, in respect to the 

 materiality of caloric, if it be material, it is transferred intact to the condenser, 

 yet in its passage it may have parted with force, which it cannot communicate 

 again.' He comes to the conclusion that the change may take place not in the 

 quantity, but in the intensity of heat. Here he resembles Carnot; but it appears 

 to him impossible to arrive at any useful theory of the heat engine, because he 

 states : ' . . . for every investigation leads to the conclusion that the effect of 

 caloric is independent at least of the chemical, if not also of the physical, consti- 

 tution of bodies. But economy of fuel is a different question from the economy 

 of caloric ; it is altogether a practical matter, and can only be determined by ex- 

 periment ; for this, and, indeed, most other points of practice, are too intractaljle 

 to come within the grasp of the most powerful calculus.' In the discussion a com- 

 munication was read from Sir George Cay ley, in the course of which he states, with 

 regard to the regenerator : ' There can exist no doubt of the effective re-application 

 of heat to an almost unlimited extent by this beautiful invention, due originally 

 to Mr. Stirling, and now carried out to a greater extent by Captain Ericsson.' 

 Sir George Cayley discussed the difficulties of Ericsson's engine, but be accepts 

 the principle that heat may give work and yet be used over and over again prac- 

 tically undiminished. Armstrong did not express himself upon the theory at all, 

 but he was doubtful as to the advantage of the air engine compared with the steam 

 engine, although he believed that it was practicable to recover and use over again 

 a large proportion of the heat applied, and he thought the balance of economy, so 

 far as heat was concerned, would be found in favour of air. Siemens agreed to 

 some extent in the advantages of a regenerator, but he showed clearly that expan- 

 sion doing work was accompanied by a diminution of temperature, and stated that 

 this heat had to be replaced by the fire. Bidder was of opinion ' that no theoretical 

 advantage was obtained in using heated air instead of vaporised water as a motive 

 power, and it was incapable of being applied practically with as much con- 

 venience.' It is most interesting to note that Dr. Faraday joined in this discussion. 

 He said very little, and I will give his remarks complete. Dr. Faraday said : 

 ' Twenty years ago he had directed his attention to this question, and from theo- 

 retical views he had been induced to hope for the successful employment of heated 

 air as a motive power ; but even then he saw enough to discourage his sanguine 

 expectation, and he had, with some diffidence, ventured to express his conviction 

 of the almost unconquerable practical difficulties surrounding the case, and of the 

 fallacy of the presumed advantages of the regenerator. He still retained his 

 doubts as to the success of the innovation, and feared the eventual results, even 

 of Captain Ericsson's spirited and ingenious efforts.' Brunei considered the use 



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