CONTENTS. 



HISTORICAL SKETCH OF THE TELESCOPE. MEMOIR DIVIDED INTO SIX SECTIONS :— 

 § 1. Gbinding and Polishing the Mireors . . . . . . .2 



1. Experiments on a metal speculum. Corrosion by aqua regia ; voltaic grinding . 2 



2. Silvering glass. Foucault's and Cimeg's processes ; details of silrering a mirror ; thick- 



ness and durability of silver films ; their use in daguerreotyping . . 2 



3. Grinding and polishing glass. Division of subject . . . . .6 



a. Peculiarities of glass ; effects of pressure ; effects of heat ; oblique mirrors . 6 



b. Emery and rouge ; elutriation of emery . . . . . .10 



c. Tools of iron, lead, pitch ; the gauges ; the leaden tool ; the iron tool ; the pitch 



polisher . . . . . . . . . .10 



d. Methods of examination ; two tests, eyepiece and opaque screen ; appearance of 



spherical surface ; oblate spheroidal surface ; hyperbolic surface ; irregular 

 surface ; details of tests ; atmospheric movements ; correction for parallel rays 

 by measure ; appearances in relief on mirrors . . . . .13 



e. Machines ; Lord Rosse ; Mr. Lassell ; spiral stroke machine ; its construction and 



use ; the foot-power ; method of local corrections ; its advantages and disad- 

 vantages ; machine for local corrections ; description and use . . .19 



4. Eyepieces, plane mirrors, and test objects . . . . . .26 



§ 2. The Telescope Mounting ......... 2T 



Stationary eyepiece ; method of counterpoising . . . . . . 2t 



a. The tube ; the mirror support ; air sac ; currents in the tube 



b. The supporting frame . . . . . . . .31 



§ 3. The Clock Movement . . . . . . "■ . . .33 



a. The sliding plateholder ; the frictionless slide . . . . .33 



6. The clepsydra ; the sand-clock . . . . . . .36 



c. The sun camera . . . . . . . . .40 



§ 4. The Obseevatory ......... 



a. The building ........ 



b. The dome ; its peculiarities ...... 



c. The observer's chair ....... 



§ 5. The Photographic Laboratory . . . . • . • 



a Description of the apartment ...... 



b. Photographic processes ; washed plates ; difSculties of celestial photography 



§ 6. The Photographic Enlarger ....... 



a. Low powers ; use of a concave mirror, its novelty and advantages ; of the making 

 of reverses ........ 



h. High powers; microscopic photography . 



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