James Gregory's OPTICA PROMOTA

translated and annotated by
Ian Bruce

Gregory's original book has no table of contents. The 59 Theorems on optics and various notes are set out in consecutive pdf files suitable for a quick down-load. Most of the optical section and the astronomical appendix of 30 Theorems have not appeared in English before, and may be of interest to historians of optics and astronomy. The book was published in 1663 in London.


Definitions & Introductory Material. Link to this document by clicking here. You can do likewise to access any section; use the browser 'Back' arrow to return to this screen.

Propositon 1.
A discussion of the law of refraction independent of Descartes.

Propositions 2 to 6
The Law of Refraction for Dense Ellipsoids & Hyperboloids.

Propositions 7 to 17
The generation of spheroidal and conoidal surfaces from conic sections and the behaviour of lighr rays passing through them.

Propositions 18 to 27
Image formation by mirrors and lenses with spheroidal and hyperboloidal surfaces.

Propositions 28 to 36
A miscellany of theorems; the eye in optics; power in a cone of rays; Alhazen's problem; image viewing, etc.

Propositions 37 to 43
Important results for the use of paraxial rays in image formation.

Propositions 44 to 51
Image formation for lenses and mirrors with elliptic and hyperbolic surfaces derived from ray diagrams.

Propositions 52 to 59
More complex optical structures including a detailed description of the design of the first ever reflecting telescope, and a single lens telescope are given. One may presume that the former was the inspiration for Newton's reflecting telescope.

Astronomical Appendix Propositions 60 - 78.
The theorems are concerned with the mathematics of observational astronomy - computing parallax, spherical trigonometry involving Napier's Rules, etc. The curious reader should investigate these in situ, as they are too detailed to list here.

Astronomical Appendix Propositions 79 - 90.
Parallax methods are introduced for measuring the earth/moon distance, the earth/sun distance involving the transits of Venus and or Mercury, and the distance to nearby stars, tracking comets, etc.

Ian Bruce. August 2006 latest revision. Copyright : I reserve the right to publish this translated work in book form. However, if you are a student, teacher, or just someone with an interest, you can copy part or all of the work for personal or educational use.