366 SEC. 11. ASTRONOMY. 



exposure by an alteration of the width of opening in the shutter, or by 

 increasing or diminishing the tension of the spring. 



The telescopic camera, attached to a bracket by means of two ring-clips or 

 couplings, accurately turned, providing a motion in arc for the camera tube, 

 read off by suitable scale and vernier, is bolted to the end of the declination 

 axis of the 



Equatorial Mounting. This in outline resembles instruments constructed 

 on the German plan, but is " universal,'' i.e., admits of adjustment for any 

 latitude up to 80, either North or South of the Equator. A novel contrivance 

 has been introduced for retaining clock gearing for great variations of lati- 

 tude. Briefly the instrument combines all the most recent appliances for 

 convenience of manipulation, and, though massive as regards construction, it 

 may fairly be called portable. Eleven of these instruments have been sent to 

 various parts of the world, without, it is believed, one single mishap. 



1853. Complete Transit of Venus Astronomical Equip- 

 ment, as used by the English expeditions. 



The Astronomer Royal. 



1853a. One of the Telescopes used in the " Transit of 



Venus " Expedition. 



The French Commission for Observing the Transit of Venus 

 in 1874. 



1853b. One of the Photographic Apparatus used in the 

 " Transit of Venus " Expedition. 



The French Commission for Observing the Transit of Venus 

 in 1874. 



1853c. Photographic Revolver, used in observing the 

 transit of Venus. M. Janssen, Member of the Institute, Paris. 



1853d. Photographic Impressions, obtained with the 

 revolver. M. Janssen, Member of the Institute, Paris. 



1854. Short Focus Mirror, spherical, for telescopes, cor- 

 rected by two lenses of homogenous media, for reflecting telescopes 

 and astro-photography. With pamphlet. 



Professor Carl Wenzel Zenger, Prague. 



1855. Aplanatic Object Glass, 4" aperture, 76" focal 

 distance, for photographing the heavenly bodies. 



C. A. Steinheil, Sons, Munich. 



The objective is free from chemical focus, gives perfectly correct and 

 flat images, and is not affected by disturbing reflexions. Each half is achro- 

 matic, and consists of two cemented lenses. 



1855a. Perfect Diagonal Planes (2), for reflecting tele- 

 scopes. Adam Hilger. 



1855b. Bight- Angle Prisms (2), for total reflection. 



Adam Hilger. 



