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Images Dated 20th May 1987

Choose from 13 pictures in our Images Dated 20th May 1987 collection for your Wall Art or Photo Gift. All professionally made for Quick Shipping.


Isaac Newtons design for a reflecting telescope Featured 20 May 1987 Image

Isaac Newtons design for a reflecting telescope

Diagram of Sir Isaac Newton's design for a reflecting telescope. Known also as the Newtonian telescope. It worked by concentrating light by reflection from a parabolic mirror, instead of by refraction through a lens. Newton (1642-1727) first displayed this telescope to King Charles II, based on a design of 1668. It had a focal length of 15 cm and could magnify 30-40 times. Inadequate mirrors meant that the Newtonian reflector was not as refined as contemporary refracting telescopes, until 1722, when James Hadley ground a quality parabolic mirror. This drawing was published in the Philosophical Transactions of the Royal Society in 1672

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