section_path: Mechanical devices/Telescopes
section_name: Telescopes
paragraph_text: Telescopes
  
  Refracting telescopes first appeared in the Netherlands in 1608, apparently the product of spectacle makers experimenting with lenses. The inventor is unknown, but Hans Lipperhey applied for the first patent, followed by Jacob Metius of Alkmaar. Galileo was one of the first scientists to use this tool for his astronomical observations in 1609. The reflecting telescope was described by James Gregory in his book Optica Promota (1663). He argued that a mirror shaped like the part of a conic section, would correct the spherical aberration that flawed the accuracy of refracting telescopes. His design, the " Gregorian telescope ", however, remained un-built.
  
  In 1666, Newton argued that the faults of the refracting telescope were fundamental because the lens refracted light of different colors differently. He concluded that light could not be refracted through a lens without causing chromatic aberrations. From these experiments Newton concluded that no improvement could be made in the refracting telescope. However, he was able to demonstrate that the angle of reflection remained the same for all colors, so he decided to build a reflecting telescope. It was completed in 1668 and is the earliest known functional reflecting telescope. 50 years later, Hadley developed ways to make precision aspheric and parabolic objective mirrors for reflecting telescopes, building the first parabolic Newtonian telescope and a Gregorian telescope with accurately shaped mirrors. These were successfully demonstrated to the Royal Society.