The Illuminating and Magnifying Powers and Prices of Newtonian, Gregorian, Cassegranian, and Herschelian Reflectors, and Galilean, Huygenian, and Achromatic Telescopes, of from 3 Inches to 7 Feet Focus, being Calculated and Described in Plain Terms which all Persons may easily understand. To which will be added, An Appendix from the Writings of SIR ISAAC NEWton, Sir WILLIAM HERSCHEL, &c. and Original Communications from Eminent Practical Opticians of the present time, on the Construction and Use of Telescopes. LONDON: PRINTED BY J. MOYES, GREVILLE STREET. CHAP. I. ON READING GLASSES FOR PER- SONS WHOSE EYES ARE IMPAIRED BY II. SPECTACLES WITH PLAIN GLASSES. III. CASES OF PERSONS WHO COULD NOT 20 and 34 THE MAGNIFYING GLASSES REQUIRED The time that the First Glasses of 36 To keep Glasses perfectly clean Advice to Buyers of Telescopes How to adjust an Opera Glass for various |