Nantes - JDF spoke to Arago [Dominique F. J. Arago] about the tide observations - at least regarding those being made this month: 'he had represented the matter in the strongest terms in the Chamber of Deputies as you may have seen by the newspaper - he read an extract from your letter, and told the minister of Marine that what was doing in England put him to the blush, and quoted yours and Mr Lubbock's [John W Lubbock] Papers. With regard to the Brest observations he assures me that they are half-printed and going on'. JDF was not so successful regarding Arago's magnetical observations 'which I much fear he will never print'. Arago 'lives in a perpetual turmoil, in which science has no serious part, and yet he seems to feel that he was born for that and not for the petty concerns of daily objurgations'. Biot [Jean Baptiste Biot] attacked JDF's experiments on polarised heat 'in most unmeasured terms: this pleased JDF 'because it shewed how much importance he attached to them'. Biot regretted that JDF had not brought his apparatus with him so as to repeat the experiments: However, JDF offered to repeat them 'with the aid of a few bits of Mica to shew the chief results to Melloni [Macedonio Melloni, who argued that light and radiant heat are effects directly produced by two different causes]...This I did, and afterwards more at large to Mr Libri [Guglielmo Libri] who has taken up my cause very warmly and is perfectly satisfied'. JDF was astonished that even though Biot and Melloni attacked his experiments, neither of them 'had attempted to repeat one of the experiments'. There would have been a meeting at the Institute last week in which Libri was to defend JDF. The only person doing anything of value is 'as usual' Poisson, who is just bringing out his book on heat: 'I know of nothing else doing at the moment in Paris'. JDF has 'never seen anything connected with the origin of Gothic which appeared to me nearly so interesting as the Abbey of Fontevrault and the church at Candes'.
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 - Thanks WW for his book on the Doctrine of Limits [The Doctrine of Limits with its Applications Namely Conic Sections, the First Three Sections of Newton, the Differential Calculus, 1838], and congratulates him on his award of the Royal Society Medal for his work on tides. JDF has had news that John Herschel is soon to return [from the Cape in South Africa]. JDF has been working hard on the subject of Heat: 'I have got an unexceptionable method of measuring Indices of Refraction of heat (which you are probably aware has hitherto been unsuccessfully attempted - numerically I mean, -) by observing the critical angle of Total Reflection, a method which may probably one day be so far improved as to give the means of analyzing a ray of heat into its component fasciculi between definite limits of refrangibility. In the next place I have worked out numerically the law of Depolarization which when the length of a wave is given will give the retardation and vice versa'. Macedoni Melloni began his long paper on depolarization by trying to 'pick holes' in JDF's experiments 'very ungraciously and substitute his own for them', but 'he ends in confirming all my results and adding almost nothing of his own, with a single exception viz. he finds all kinds of heat equally polarizable; I find it less so as the Temp. is lower - obviously a point of great importance for Theory'. His discrepancy with Melloni concerns the experimental set-up: 'Melloni instead of using my excessively thin polarizing bundles of mica split by heat, employs the old piles of distinct mica plates as I first used them. the fact is the heat in being polarized passes through so much mica, that it loses its distinctive character and whatever be the source consists at last only of that kind of heat which mica is capable of transmitting'. Conversely, JDF's extra thin mica piles 'suffers heat from different sources to pass with almost equal readiness. so there is an end of the puzzle'.