Copy letter, from Sir John Herschel to William Thomson, 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 William Thomson for pageproofs of his work on analytical dynamics. Compliments work on Isaac Newton's view of nature of luminous ether. Gives own views on ether and motion theory of heat. 22 November 1864