Before revision: History A record by William Herschel (1738–1822), shows he observed dichromatism with a solution of ferrous sulphate and tincture of nutgall in 1801 when working on an early solar telescope, but he did not recognise the effect.The History of the Telescope - By Henry C. King - Page 141 Kreft Marko (2007).
After revision: Weblinks Kreft SamoHistory A record by William Herschel (1738–1822), shows he observed dichromatism with a solution of ferrous sulphate and tincture of nutgall in 1801 when working on an early solar telescope, but he did not recognise the effect.The History of the Telescope - By Henry C. King - Page 141 Kreft Marko (2007).