Newton's Reflecting Telescope (Astronomy Plate XXVI)

Figure 9 (shown here) depicts Newton’s design of the reflecting telescope, first built in 1668. Newton first conceived of the reflecting telescope as an alternative to the refracting telescope at age 23 as he worked on optics. Newton reported that "by their mediation Optick instruments might be brought to any degree of perfection imaginable, provided a Reflecting substance could be found, which would polish as finely as Glass, and reflect as much light, as glass transmits, and the art of communicating to it a Parabolick figure be also attained…."

Denis Diderot (1713-1784)
Encyclopédie. Volume 5 Astronomy (Sciences – Mathématiques – Astronomie), Plate XXVI.
Paris: Briasson [etc.], 1751-1772