Sir John Frederick William Herschel, 1st Baronet was an English polymath, mathematician, astronomer, chemist, inventor, and experimental photographer who invented the blueprint. Herschel originated the use of the Julian day system in astronomy. He named seven moons of Saturn and four moons of Uranus – the planet discovered by his father Sir William Herschel. His "Preliminary Discourse" (1831), which advocated an inductive approach to scientific experiment and theory-building, was an important contribution to the philosophy of science. He published a catalogue of his astronomical observations in 1864, the "General Catalogue of Nebulae and Clusters".