1890.] on The Scientific Work of Joule. 5 



Working under the same conditions, hydrogen was shown to be reduced 

 a small amount in temperature, air somewhat more (about 0'3^), and 

 carbonic acid a much greater amount. A repetition of Joule and 

 Thomson's experiment was shown by means of a 100 feet coil of lead 

 pipe, compressed hydrogen, air, and carbonic acid gas being employed, 

 and the original results verified in each case. The effect of this 

 research was to enable Joule and Thomson to formulate a great im- 

 provement on the gaseous laws ; for instead of the product of the 

 volume and pressure being strictly proportional to the absolute tem- 

 perature, as it had been hitherto believed to be, they found that a 

 new term was involved, which is equivalent to a constant divided by 

 the absolute temperature and multiplied by the volume. 



In conclusion, Prof. Dewar read the following letter, which he had 

 received from Sir Lyon Playfair in response to his request for some 

 reminiscences of Joule : — 



Dear Dewar, 20^/i Jan., 1890. 



You ask for some of my memories of Joule from 1842 to 1845, 

 when I was Professor of Chemistry at the Royal Institution in 

 Manchester. The great Dalton died in the autumn of 1844, and had 

 long been President of the Manchester Philosophical Society. He 

 naturally gave impulse to the study of science in that town, where 

 there was an active band of young workers in research. 



Joule was, even then, foremost among these ; and the names of 

 Binney, Williamson, Schunck, Angus Smith, Young, and others show 

 that the spirit of scientific inquiry was active. We were also 

 stimulated by the fact that Baron Liebig and Bunsen came to pay me 

 visits during that time ; they were men to excite research. 



Joule was a man of singular simplicity and earnestness. We 

 used to meet at each other's houses at supper, to help the progress of 

 our work by discussion. Joule was an earnest worker, and was then 

 engaged on his experiments on the mechanical equivalent of heat. 

 He took me to his small laboratory to show me his experiments, and 

 I of course quickly recognised that my young friend the brewer was a 

 great philosopher. We jointly worked upon questions of far less 

 importance than his great central discovery, but he was equally 

 interested. I was very anxious that he should devote his life to 

 science, and persuaded him to become candidate for the Professorship 

 of Natural Philosophy at St. Andrews. He was on the point of 

 securing this, but his slight personal deformity was an objection in 

 the eyes of one of the electors ; and St. Andrews lost the glory of 

 having one of the greatest discoverers of our age. 



When Joule first sent an account of his experiments to the Royal 

 Society, the paper was referred, among others, to Sir Charles Wheat- 

 stone, who was my intimate personal friend. Wheatstone was an 

 eminently fair man and a good judge, but the discovery did not then 

 recommend itself to his mind. For a whole Sunday afternoon we 

 walked on Barnes Common, discussing the experiments and their 



