CONTENTS. 



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



§ 1. (jRiNDiNG AND Polishing the Mirrors ...... 



1. Ej-perimentx on a metal apeculum. Corrosion by aqua regia ; voltaic griiuliiig 



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



ness and durability of silver films ; their use in daguerreotyping 



3. Gi-inding and polishing glass. Division of subject .... 



a. Peculiarities of glass ; effects of pressure ; effects of licat ; oblique mirrors 

 6. Emery and rouge ; elutriation of emery ..... 



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



polisher ......... 



d. Methods of e.xiuiiiiKitioM ; two tests, eyepiece and opacpic screen ; appearance of 



spherical surface; oliiate spheroidal surface; hyperbolic surface; irregular 

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

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



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 . 



4. Eyepieces, plane mirrors, and test objects 

 § 2. The Telescope Mounting .... 



Stationary eyepiece ; method of counterpoising . 



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



b. The supporting frame 



§ 3. The Clock Movement .... 



a. The sliding plateholder ; the frictionless slide 



b. The clepsydra ; the sand-clock 



c. The sun camera . . . ■ 



§ 4. The Observatory . . . • • 



a. The building . . . ■ 



b. The dome ; its peculiarities 



c. The observer's chair 



§ 5. The Photographic Laboratoky 



a Description of the apartment 



b. Photographic i)rocesscs ; washed plates ; difficult: 



§ fi. The Photographic Enlarger 



a. Low powers ; use of a concave mirror, its novelty 



of reverses . . . ■ 



b. High powers ; microscopic photography . 



es of celestial photography 

 and advantages ; of the makin 



2 

 2 



2 



6 



6 



10 



10 



13 



19 



26 



27 



27 

 28 

 31 



33 

 33 

 36 

 40 



41 

 41 

 44 

 45 



46 



46 

 47 



51 



51 

 54 



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111 



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