Newton's Reflecting Telescope

Timeline

1. 1668Trinity College, Cambridge · CambridgeUnable to overcome chromatic aberration in refracting lenses, Newton cast and polished his own concave speculum metal primary mirror and used an angled flat secondary to direct the converging beam to a side-mounted eyepiece, completing a working prototype of a few inches' aperture in autumn 1668, capable of resolving Jupiter's moons and the phases of Venus. The instrument was known only to a few Cambridge friends, and its performance was still inferior to later improved models.
2. 1671London (Royal Society) · LondonIn autumn 1671 Newton built another reflecting telescope that was 'manifestly superior' (tube about 7 inches, aperture about 2.25 inches). After reports circulated through Isaac Barrow and others, the Society asked him to send it for inspection. The instrument arrived in London that December, and a written record dated December 26 described the pinhole-scale eyepiece aperture on the side and the focusing screw at the base.
3. 1672Whitehall and London · LondonIn January 1672 the Society announced that the telescope had been examined at Whitehall by Charles II, Brouncker, More, Wren, Hooke, and others, and asked Henry Oldenburg to write to Huygens in Paris describing the design to establish Newton's priority. Newton was promptly elected a Fellow of the Royal Society, and around the same time published his theory of colored light, bringing the reflecting telescope and his optical research together into the European scientific network.