Copy letter, from Sir John Herschel to Charles Wheatstone, dated at [Collingwood] Copy of letter, copied by Robert Sabine [Charles Wheatstone's son-in-law] as part of the correspondence project led by Colonel John Herschel FRS following the death of his father. Checked by Isabella Herschel in 1876. Makes some amendments in John Frederick William Herschel's request for information [see John Frederick William Herschel's 1845-4-6]. 15 April 1845