ON THE PHYSICAL VIEW OF NATURE. 



135 



mechanical value and the availability of heat existed, 

 had to be largely altered, and corrected notions laid 

 down, frequently as a result of prolonged discussion. 1 

 As an example, I may refer to the controversy between 

 Him and Zeuner as to the cause of the great discrepancy 

 between the theoretical and practical figures referring to 

 the work in the steam-cylinder, the so-called " Water or 

 Iron " controversy. 2 



But whilst it must be admitted that the corrected 

 views regarding the nature of heat the preservation 



1 The best account of the prac- 

 tical bearings of the mechanical 

 theories of Rankine and Clausius 

 is to be found in Prof. Unwin's 

 " Forrest Lecture," delivered 2nd 

 May 1895, before the Institute of 

 Civil Engineers, and published in 

 the ' Electrician,' vol. xxxv. p. 46 

 s'jq. and p. 77 sqq. He there refers 

 to the great discrepancy between 

 the "rational" and the "experi- 

 mental" theories, and to Hirn's 

 experiments and practical results, 

 notably with the "steam-jacket," 

 and his introduction of " super- 

 heating " in 1855. " No doubt 

 the rational theory altogether 

 underrated the enormous facility 

 of heat-exchange, which arises out 

 of the contact between a conduct- 

 ing cylinder-wall and a vapour in a 

 condition of the greatest instability, 

 and liable to condense or evaporate 

 on the slightest change of thermal 

 condition " (p. 50). The several con- 

 troversies through which Clausius 

 defended and gradually elucidated 

 the somewhat obscure statement 

 which he gave of the so - called 

 second law of thermo-dynamics may 

 be studied with advantage in the 

 2nd edition of his collected Memoirs 

 (' Die mechanische Warmetheorie,' 

 Braunschweig, vol. i., 1876), where 

 his replies to criticisms of Holtz- 



mann, Decher, Zeuner, Rankine, 

 Wand, and Tait are most instruc- 

 tive. A good account is also given 

 in Baynes's ' Lessons on Thermo- 

 dynamics,' Oxford, 1878, p. 103 

 sqq. 



2 See Prof. Unwin, loc. cit., p. 

 79. " On the appearance of Islier- 

 wood's researches in 1863, the dis- 

 crepancy between the rational 

 theory and the results of experi- 

 ment were recognised by Rankine 

 and others. But the conditions of 

 the steam - cylinder condensation 

 are so complex that for a long time 

 the more theoretical writers prac- 

 tically ignored both Hirn's and 

 Isherwood's results. Zeuner per- 

 haps had pushed the rational theory 

 to the furthest limit of detail, and 

 with the greatest insight into prac- 

 tical conditions. But it was not 

 till 1881 that he began to explicitly 

 admit the largeness and importance 

 of the condensing action of the 

 cylinder. Zeuner then was disposed 

 to attribute initial condensation to 

 the presence of a permanent and 

 not inconsiderable maas of water in 

 the clearance space of the engine. 

 ... In opening a discussion with 

 Hirn in 1881, Zeuner wrote that 

 if the presence of water in the 

 clearance space was conceded, the 

 Alsatian calculations would be 



