61 



Remarks on Photographing the Solar 

 Eclipse of 12th December, 1890. 



By D. B. Adamson. 



[Read February 3, 1891] 



I lay before you to-night some photo-negatives of the late solar 

 eclipse, also a photographic enlargement of one of the same. The 

 instrument used in taking them being a Newtonian reflector of 

 12|- in. aperture. Although with this instrument (when armed 

 with the solar diagonal and dark glass) we can gaze on the sun's 

 disc very comfortably, I found that a further reduction of the 

 light would be required for the purpose of photography. Know- 

 ing that eclipses do not wait for any one, I set about making 

 preparations and experiments a week before hand. My flrst at- 

 tempt was with a diminished aperture and a very short exposure 

 (one which might almost be termed instantaneous), using a com- 

 mon dry plate. On developing this I was somewhat surprised to 

 find that on the centre of the plate (where a black disc should 

 have been) there was only a circle of clear glass more transparent 

 than the surrounding parts of the plate, the gelatine having 

 quite disappeared from the exposed part. My next idea was to 

 remove the silver from the face of the small speculum (having 

 spare ones), and to place behind this a piece of black woollen 

 cloth, in hopes of reducing, if not altogether getting rid of, the 

 double reflection. I found that this gave a very cool reflection, 

 but still so distinctly double that it was of no use for my pur- 

 pose, so I replaced the small silvered speculum. I next removed 

 the silver from the large speculum (having a duplicate of same;, 

 leaving only the bare glass to give the reflection, and by reducing 

 the aperture of the telescope to seven inches, I succeeded in pro- 

 ducing the photos as you see them. Although the slowest dry 

 plates were used, and the exposure was almost instantaneous 

 (being the time occupied by a one and three-quarter inch hole in 

 a slide falling past a similar hole at the focus of the telescope), 

 still it was too long, but by using a very weak developer the 

 photos came out fairly sharp. My plan of procedure was in the 

 flrst place to watch for the first contact, which took place at 

 11 h. 21 m. 3 s. a.m. This was very sharp and clear, the atmo- 

 sphere being fairly steady. I next gave my attention to plioto- 

 graphing, taking five negatives at various stages of the eclipse, 

 my desire being to obtain one as nearly central as possible. This, 



