Copy letter from Herbert Rix, to Clifford S Estes, Walnut Hill, Woburn, Massachusetts, U.S.A 'Dear Sir, I am afraid we are too overwhelmed with work to look up the bibliography of your subject, which would be a matter of some difficulty and involve considerable expenditure of time. I may mention, however, that there are some papers in the "Complete Rendus" of the Paris Academy which might be useful to you, as, for instance, vol. 86 (1878), p. 1019 (paper by Muchot); also 24th May, 1880; also vol. 91 (1880), p 388 (paper by Pifre). I am, yours truly, H Rix Asst. Sec. R.S. [Assistant Secretary, Royal Society]'. 28 May 1894