Gregorian telescope

The Gregorian telescope is named after the James Gregory design, which appeared in his 1663 publication Optica Promota (The Advance of Optics).

Similar theoretical designs have been found in the writings of Bonaventura Cavalieri (Lo Specchio Ustorio (On Burning Mirrors), 1632[2]) and Marin Mersenne (L'harmonie universalle, 1636[3]).

Gregory's early attempts to build the telescope failed, since he had no practical skill himself and could find no optician capable of actually constructing one.

[4] It was not until ten years after Gregory's publication, aided by the interest of experimental scientist Robert Hooke, that a working instrument was created.

The Gregorian design solved the problem of viewing the image in a reflector by allowing the observer to stand behind the primary mirror.