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The Athenaeum Club - JDF has read an account of the BAAS Dublin meeting and Professor Powell's [Baden Powell] account of Melloni's [Macedonio Melloni] and JDF's experiments: 'His chief object seems to have been to make out the accuracy of his own papers, and he certainly mistakes Melloni's results as completely as it is possible to do when he makes him say that there are two distinct kinds of heat. On the contrary there are an infinite variety which pass into one another insensibly. He equally mistakes my results when he makes them to depend upon Mr Murphy's [Robert Murphy, Elementary Principles of the Theories of Electricity, Heat, and Molecular Actions, 1833] Integration. This is precisely Biot's [Jean Baptiste Biot] objection, viz that the two positions of the plates are not symmetrical as regards the effect of conduction [JDF gives a diagram showing the angles of the plates]. Granted at once. But will the mathematical gentlemen only have the goodness to see the experiment tried and they will see that the effect is of an order quite superior to any effect of conduction whatever - that it is independent of the distances of the plates from one another, which requires, no nicety of adjustment, so that the integration (if practicable) will go for nothing. I have really a right to insist that my experiments shall be seen before they are judged. I admit all the mathematical perturbations, but the chief cause is as clearly developed as the influence of the moon on the tides'. The tables have turned in Paris in favour of JDF's theory: 'Arago [Dominique F J Arago], Libri [Guglielmo Libri] and Dulong [P. L. Dulong] have taken up my cause, Biot is at last silenced'. Could WW point out to Mr Murphy [Robert Murphy] 'that in the case of Depolarization by the mica plate there is the most perfect symmetry (mathematically) which he can desire'.

Edinburgh - JDF did his best to look after Professor Plücker [Julius Plücker] of Bonn: 'He seemed pleased with my optical apparatus which is now pretty complete and in the Airy [George Airy] fashion'. Thanks WW for reading his memorandum for the Philosophical Magazine [on heat]. Professor Powell [Baden Powell] 'much to my gratification, disclaims in toto the colour which the reporter has given to his account of my experiments in the Phil. Mag....I don't know what Murphy [Robert Murphy] says. It is only lately that I have grown jealous of any little credit my polarizing might bring me'. JDF is sorry he has not acted sooner on WW's suggestions for tides but will endeavour to get it established. George Airy has asked JDF for advice on taking magnetic observations, can WW make sure he received JDF's reply. He spent a day with Mr Harcourt [Vernon Harcourt] and urged him to work hard in securing a good attendance at Bristol for the forthcoming BAAS meeting: 'I think the place ill chosen, but yet that it may be one of the best in point of science'. What does WW think of Lord Brougham's book?: 'it is certainly remarkable'. WW should not enlarge his mechanics which JDF still expects it to sell well in Edinburgh. JDF still hopes to publish on the Pyrenean hot waters. He has been examining his thermometer in Bessel's [Friedrich Bessel] way 'which does not do much credit to Troughton [Edward Troughton] and Simms [William Simms] 'standard''.