Copy letter, from Sir John Herschel to Jacques Babinet, dated at Slough Copy of letter, copied as part of the correspondence project led by Colonel John Herschel FRS following the death of his father. Responds to Jacques Babinet's 1832-8-25 with comments about the optical properties of tourmaline. John Frederick William Herschel also talks about his astronomical work, including the collimator on his telescope and his double star work. 12 September 1832