Copy letter, from Sir John Herschel to William Henry Smyth, 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. Advises William Henry Smyth on best ways to make a 'darkening glass' for solar observations. Also suggests method for delineating sunspots. Hopes William Henry Smyth will attend Nautical Almanac meeting and support his points. Completes two telescope mirrors and observes Uranian satellites. Asks William Henry Smyth to look for a double star between Beta1 and Beta2 Capricorni. 8 August 1830