The Practical Astronomer Comprising illustrations of light and colours--practical descriptions of all kinds of telescopes--the use of the equatorial-transit--circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy

CHAPTER VII.

Chapter 1352 wordsPublic domain

ON THE METHOD OF GRINDING AND POLISHING OPTICAL LENSES AND SPECULA.

1. Directions for grinding lenses for eye-glasses, microscopes, &c.--2. Method of casting and grinding the specula of reflecting telescopes--Compositions for speculum metal--To try the figure of the metal--To adjust the eye-hole of Gregorian reflectors--To center the specula--To center lenses. _page_ 432-442.