SUMMARY OF RESULTS AND SUGGESTIONS. 167 



DETERMINATIONS OF THE BRIGHTNESS OF THE CORONA. 



PHOTOGRAPHS OF THE LANDSCAPES. No previous experiments 

 of a like nature having been made, it may be considered that 

 the exposures adopted were fortunately chosen for their special 

 purpose of recording the rate of decline of sunlight during the 

 progress of the partial phase and also of giving a comparison 

 between the light of the sky immediately before and that 

 immediately after totality. It should be borne in mind, how- 

 ever, that the darkness during other eclipses seems often to 

 have been more intense, and it would certainly be well to take 

 at least two or three exposures after totality, say at intervals 

 of every two minutes and compare them with similar exposures 

 made at corresponding intervals before totality. 



When testing the light of the full moon for comparison with 

 that of the corona it would seem that very careful note should 

 be made of time and place and general conditions. It might 

 be instructive also if such tests were made at more than one 

 lunation. The actual altitude of the place of observation may 

 be of some importance in face of the fact that the intensity of 

 moonlight rapidlv increases with elevation on leaving the 

 earth's surface. JoHN M ^ CQy 



INTEGRATING PHOTOGRAPHS. Previous to the eclipse of 1896 

 the question of obtaining a measurement of the intensity of 

 the light of the corona by means of photography was raised 

 by Mr. Maunder, and experiments with a view to its deter- 

 mination formed part of his programme and that of Mr. Lunt 

 at Vadso. These experiments, though differing in detail, had 

 for their fundamental idea the exposing a plate behind a 

 graduated screen, and the- same principle was made use of 

 in an experiment carried out by Mr. Moore and Mr. Johnson 

 at Benares in 1898. 



The experience gained in measuring this and comparison 

 photographs has suggested the possibility that better results 

 may be obtained by discarding the screen and exposing a plate 

 in sections to the light of the corona, giving exposures of 

 varying lengths to the different sections. Trial exposures of 

 similar plates to a standard light could then be made with 

 similar development, and the results compared by means of 

 the density of the deposits on the films. 



Whichever method be adopted it should be used at all the 

 stations of the B. A. A. during the ellipse of 1900, under as 

 far as possible identical conditions, and in that case it can 

 hardly fail to give a satisfactory measure of the total light of 

 the corona. The apparatus required is exceedingly simple, so 

 that the experiment would be within the reach of those who 

 do not care to undertake more ambitious work. - 



