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. Thinks John Tyndall's work on polarization will lead to remarkable discovery. Discusses production of rainbow, parallels to Isaac Newton's explanation of black spot on a soap bubble, and problems in John Tyndall's undulatory theory explanation of reflection. In John Tyndall's experiments, what are nebulous particles produced by light in gas or vapor? 2 December 1868