Newtonian telescope Newtonian telescope The Newtonian telescope, also called the Newtonian reflector or just the Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton (1642–1727), using a concave primary mirror and a flat diagonal secondary mirror. Newton's first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope. The Newtonian telescope's simple design makes it very popular with amateur telescope makers. Newton's idea for a reflecting telescope was not new. Galileo Galilei and Giovanni Francesco Sagredo had discussed using a mirror as the image forming objective soon after the invention of the
Reflecting instrument presented his reflecting quadrant in 1731. Halley noted that Hadley's design was quite similar to the earlier Newtonian instrument. As a result of this inadvertent secrecy, Newton's invention played little role in the development of reflecting instruments. What is remarkable about the octant is the number of persons who independently invented the device in a short period of time. John Hadley and Thomas Godfrey both get credit for inventing the octant. They independently developed the same instrument around 1731. They were not the only ones, however. In Hadley's case, two instruments were designed. The first was an instrument very similar