xHi Annual Report of tJie Council. 



Thermodynamics could be founded on Joule's discovery of the- 

 convertibility of heat and work, and on Carnot's theorem altered 

 to include Joule's law. Meanwhile Joule had made more perfect 

 determinations of the Mechanical Equivalent of Heat, and his 

 memoir, published in the Philosophical Transactions for 1850, 

 gives 772 foot-pounds as the most correct result. It was Lord 

 Kelvin's suggestion that Joule's initial J should be used as the 

 symbol for the mechanical equivalent of heat ; this was adopted 

 by Rankine and by Clausius who had independently recognised 

 the truth of Joule's work. 



In 1 85 1 Lord Kelvin was elected an honorary member of 

 this Society. In 1852 he visited Joule at Salford and began the 

 joint investigation on the cooling which gases undergo when 

 forced under pressure through a small orifice. The result, 

 predicted by Kelvin, required all the experimental skill of Joule 

 to establish, but " The Joule-Thomson effect " is now in every 

 day use in the preparation of liquid air. 



In 1855 Joule visited Kelvin and brought out his process of 

 welding metals by means of an electric current, the first 

 experiment being made in the Professor's Laboratory at Glasgow. 



In 1856 the friends began at Joule's house their joint 

 research on the rise of temperature of bodies moving rapidly 

 through the air, and read the actual rise of a thermometer 

 whirled through the air. 



Of the dozen memoirs and notes communicated by Lord 

 Kelvin to this Society, the one which has attracted most public 

 attention is that on the size of molecules read on March 22nd, 

 1870. In this paper Kelvin gave several methods by which an 

 inferior limit to the size of molecules might be calculated. The 

 electric attraction between metallically-connected plates of zinc 

 and copper, found for plates of measurable thickness and at 

 measurable distances asunder, would not permit of the plates 

 being brought within a distance of a four-hundred-milHonth of a 

 centimetre from each other. Plates so thin and so near would 

 rush into chemical combination. The augmentation of energy 



