Oct. 26, 1882] 



NA TURE 



619 



rate thermometers ; and whil=t Regnault was doing the 

 same thing in France Mr. Joule produced, with the 

 assistance of Mr. Dancer, instrument maker, of Man- 

 chester, the first English thermometers possessing such 

 accuracy as the mercury-in-glass thermometer is capable 

 of. Some of them were forwarded to Prof. Graham and 

 to Prof. Lyon Playfair : and the production of these in- 

 struments was in itself a most important contribution to 

 scientific equipment. 



As the direct experiment of friction of a fluid is dependent 

 on no hypothesis, and appears to be wholly unexceptionable, 

 it was used by Mr. Joule repeatedly in modified forms. 

 The stirring of mercury, of oil, and of water with a 

 paddle, which was turned by a falling weight, was com- 

 pared, and solid friction, the friction of iron on iron under 

 mercury, was tried ; but the simple stirring of water 

 seemed preferable to any, and was employed in all his 

 later determinations. 



In 1S47 Mr. Joule was married to Amelia, daughter of 

 Mr. John Grimes, Comptroller of Customs, Liverpool. 

 His wife died early (1854), leaving him one son and one 

 daughter. 



The meeting of the British Association at Oxford in 

 this year, proved an interesting and important one. 

 Here Joule read a fresh paper "On the Mechanical 

 Equivalent of Heat." Of this meeting Sir William 

 Thomson writes as follows to the author of this notice : — 



" I made Joule's acquaintance at the Oxford meeting, 

 and it quickly ripened into a life-long friendship. 



" I heard his paper read in the section, and felt strongly 

 impelled at first to rise and say that it must be wrong 

 because the true mechanical value of heat given, suppose 

 in warm water, must, for small differences of temperature, 

 be proportional to the square of its quantity. I knew 

 from Carnot that this must be true (and it is true ; only 

 now I call it ' motivity,' to avoid clashing with Joule's 

 'mechanical value.') But as I listened on and on, I 

 saw that (though Carnot had vitally important truth, 

 not to be abandoned) Joule had certainly a great truth 

 and a great discovery, and a most important measure- 

 ment to bring forward. So instead of rising with my 

 objection to the meeting I waited till it was over, and 

 said my say to Joule himself, at the end of the meeting. 

 This made my first introduction to him. After that I 

 had a long talk over the whole matter at one of the con- 

 versaziones of the Association, and we became fast 

 friends from thenceforward. However, he did not tell 

 me he was to be married in a week or so ; but about a 

 fortnight later I was walking down from Chamounix to 

 commence the tour of Mont Blanc, and whom should I 

 meet walking up but Joule, with a long thermometer in 

 his hand, and a carriage with a lady in it not far off. He 

 told me he had been married since we had parted at 

 Oxford ! and he was going to try for elevation of tempera- 

 ture in waterfalls. We trysted to meet a few days later 

 at Martigny, and look at the Cascade de Sallanches, to 

 see if it might answer. We found it too much broken 

 into spray. His young wife, as long as she lived, took 

 complete interest in his scientific work, and bcth she and 

 he showed me the greatest kindness during my visits to 

 them in Manchester, for our experiments on the thermal 

 effects of fluid in motion, which we commenced a few 

 years later." 



''Joule's paper at the Oxford meeting made a grea 

 sensation. Faraday was there and was much struck with 

 it, but did not enter fully into the new views. It was 

 many years after that before any of the scientific chiefs 

 began to give their adhesion. It was not long after, when 

 Stokes told me he was inclined to be a Joulite." 



" Miller, or Graham, or both, were for years quite in- 

 credulous as to Joule's results, because they all depended 

 on fractions of a degree of temperature — sometimes very 

 small fractions — his boldness in making such large con- 

 clusions from such very small observational effects, is 

 almost as noteworthy and admirable as his skill in ex- 

 torting accuracy from them. I remember distinctly at 

 the Royal Society, I think it was either Graham or Miller, 

 saying simply he did not believe Joule, because he had 

 nothing but hundredths of a degree to prove his case by." 



The friendship formed between Joule and Thomson in 

 1847 grew rapidly. A voluminous correspondence was 

 kept up between them, and several important researches 

 were undertaken by the two friends in common. Their 

 first joint research was on the thermal effects experienced 

 by air rushing through small apertures. The results of 

 this investigation give for the first time an experimental 

 basis for the hypothesis assumed without proof by Mayer 

 as the foundation for an estimate of the numerical rela- 

 tion between quantities of heat and mechanical work, and 

 they show that for permanent gases the hypothesis is very 

 approximately true. Subsequently Joule and Thomson 

 undertook more comprehensive investigations on the 

 thermal effects of fluids in motion, and on the heat ac- 

 quired by bodies moving rapidly through the air. They 

 found the heat generated by a body moving at one mile 

 per second through the air sufficient to account for its 

 ignition. The phenomena of "shooting stars" were 

 explained by Mr. Joule in 1S47 by the heat developed by 

 bodies rushing into our atmosphere. 



It is impossible within the limits to which this sketch 

 is necessarily confined, to speak in detail of the many 

 researches undertaken by Mr. Joule on various physical 

 subjects. Even of the most interesting of these a very 

 brief notice must suffice for the present. 



Molecular physics, as I have already remarked, early 

 claimed his attention. Various papers on electrolysis of 

 liquids, and on the constitution of gases, have been the 

 result. A very interesting paper on "Heat and the Consti- 

 tution of Elastic Fluids " was read before the Manchester 

 Literary and Philosophical Society in 1848. In it he 

 developed Daniel Bernoulli's explanation of air pressure by 

 the impact of the molecules of the gas on the sides of the 

 vessel which contains it, and from very simple considera- 

 tions he calculated the average velocity of the particles 

 requisite to produce ordinary atmospheric pressure at 

 different temperatures. The average velocity of the par- 

 ticles of hydrogen at 32° F. he found to be 6055 feet per 

 second, the velocities at various temperatures being pro- 

 portional to the square roots of the numbers which 

 express those temperatures on the absolute thermo- 

 dynamic scale. 



His contribution to the theory of the velocity of sound 

 in air was likewise of great importance, and is distin- 

 guished alike for the acuteness of his explanations of 

 the existing causes of error in the work of previous experi- 



