Ill 



influenced by the existence or non-existence of certain mutual 

 Strains among the Particles composing them." The second was a 

 remarkable paper on " The Elasticity and Strength of Spiral Springs 

 and of Bars subjected to Torsion." In this paper the action of a 

 spiral spring was explained, and important principles connected with 

 the subject of torsion were brought forward. These papers were 

 published in the ' Cambridge and Dublin Mathematical Journal,' 

 November, 1848. 



The third was, perhaps, yet more remarkable. It was contributed 

 to the Royal Society of Edinburgh, and was on " The Parallel Roads 

 or Terraces of Lochaber (Glenroy)." These remarkable terraces or 

 shelves had attracted much attention. Darwin, Lyell, David Milne, 

 Sir G. Mackenzie, Agassiz, Sir Thomas Dick Lauder, and others 

 had discussed the causes of their formation. James Thomson, how- 

 ever, gave in this paper Avhat is now the accepted explanation. 



Curiously, Professor Tyndall seems not even to have known of 

 the existence of the paper when he gave his admirable exposition of 

 this wonderful natural formation at the Royal Institution in 1876. 

 He attributes the explanation of the Parallel Roads to Jamieson, 

 1863 ; whereas the whole theory had been given by Thomson in 

 1848 in the paper just mentioned with details as to necessary climatic 

 circumstances, not noticed by Tyndall. 



In January, 1849, he communicated to the Royal Society of Edin- 

 burgh a paper of great importance, which was printed in the 

 ' Transactions ' of the Society, and was afterwards republished, with 

 some slight alterations by the author, in the ' Cambridge and Dublin 

 Mathematical Journal,' November, 1850. The title of this paper was 

 " Theoretical Considerations on the Effect of Pressure in lowering 

 the Freezing Point of Water." The principles expounded in this 

 paper were afterwards, in 1857, used as the foundation of his well- 

 known explanation of the plasticity of ice, discovered by Forbes ; and 

 later, from 1857 onwards, for several years, the whole subject afforded 

 him much food for thought ; and extensions and developments in 

 various directions followed. The paper of 1849 was of great intrinsic? 

 importance. In it, by the application of Carnot's principle, an abso- 

 lutely unsuspected physical phenomenon was discovered and predicted, 

 and the amount of lowering of the freezing point of water was cal- 

 culated. The phenomenon was shortly after experimentally tested 

 and confirmed by his brother, Lord Kelvin. 



But the paper has another title to interest, which is not so generally 

 known. In it for the first time Carnot's principle was stated, and 

 Carnot's cycle described, in words carefully chosen, so as not to 

 involve the assumption of the material theory of heat, or rather, as 

 Thomson himself puts it, the supposition of the "perfect conservation 

 of heat." 



