Copy of draft letter, from Sir John Herschel to William Hasledine Pepys, dated at Collingwood Copy of draft letter, copied as part of the correspondence project led by Colonel John Herschel FRS following the death of his father. Asks WP to recall the particulars of an experimental session [see WP's 1823-3-11] where John Frederick William Herschel tried to demonstrate the polarization of light by an electrical current in a coil of wire. 9 November 1845