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. The continuation of magnetic and meteorological observatories is under question, and Charles Wheatstone's instrument for observing atmospheric electricity should be part of the discussion. 6 April 1845