OP ARTS AND SCIENCES. 



35 



of a dark disk upon a bright ground and of a bright disk upon a darker 

 ground, observations for the diameter were continued for several days 

 succeeding the transit. Since it was only possible to observe both 

 points of tangency of the inclined lines with the disk of the planet on 

 one side of the vertical lines, the elimination of the effect of an error 

 in the position angle of the line x^ does not here take place. Care 

 was taken, however, to make the setting for the zero of position as 

 exact as possible. 



The followins: results were obtained. 



TABLE X. 



If these observations can be trusted we may conclude : — 

 («.) That the difference in the value of the diameter at the dis- 

 tance unity, due to irradiation on Dec. 6, and on the days immediately 

 following, is not far from 0"A. 



(b.) That up to a certain point this difference increases with the 

 angular increase in the distance of the planet from the sun. This in- 

 crease, however, is probably not quite as great as the observations 

 seem to indicate. On Dec. 26 and Jan. 1 the atmospheric conditions 

 were not favorable to good observations. 



Report by S. C. Chandler, Jr. 



The following determinations of the diameter of Venus during the 

 transit on Dec. 6, 1882, were made by Professor Rogers's plan of 

 transits over inclined lines, with the "West Equatorial. The telescope 

 had been prepared for solar observation by the maker, Mr. John 

 Clacey, by smoking the front of the crown and the back of the flint 

 lens of the object-glass ; a process which he finds affords a better effect 

 than a silver film, the image being sharper and the effect of contrast 

 with the sky more agreeable. The result in the present instance was 

 completely satisfactory. The obscuration produced by the double 

 smoke film was sufficient to render a shade glass unnecessary with the 

 power used, which was about 180 diameters. 



