Copy of draft letter, from Sir John Herschel to Thomas Davidson, 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. Outlines the differences between the telescope of his own father and that of Lord Oxmantown [William Parsons]. Comments on various lenses. Sends him a little work of his own on telescopes. 9 February 1862