Copy letter, from Sir John Herschel to John Tyndall, dated at Collingwood Copy of letter, copied as part of the correspondence project led by Colonel John Herschel FRS following the death of his father. Thanks for paper on action of rays 'of high refrangibility' on gases and vapors. Attempts to understand reflection of wave motion on particles with diameters 'incomparably smaller' than length of wave. 23 October 1870