John Herschel

Sir John Frederick William Herschel, 1st Baronet was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint, and did botanical work. Herschel originated the use of the Julian day system in astronomy. He named seven moons of Saturn and four moons of Uranus – the seventh planet, discovered by his father Sir William Herschel. He made many contributions to the science of photography, and investigated colour blindness and the chemical power of ultraviolet rays. His Preliminary Discourse, which advocated an inductive approach to scientific experiment and theory-building, was an important contribution to the philosophy of science.

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Sir John Herschel used a solar wedge attached to his telescope to observe the Sun in the mid 19th century. A solar wedge reflects 4.5% of sunlight towards the eyepiece and a second glass filter reduces the Sun's white light by a factor of 1,000 or more