336 PROFESSOR L. BECKER ON THE DISTRIBUTION OF 



After my return to the Observatory 1 photographed the moon on three nights 

 with the eclipse apparatus and approximately at the same zenith distance the sun 

 had at the eclipse. The atmosphere was exceptionally transparent for Glasgow on 

 the first and third nights. I used plates returned from Kalaa and I developed them 

 in the same way and at the same temperature as the eclipse photographs. 



(a) Brightness of Corona. The plates show, just as the eclipse photographs, a 

 background due to diffused light. I compared the intensity of the background 

 of the lunar photographs with those on the eclipse negatives, picking out those 

 exposures which showed the same density of background in both. The durations of 

 exposure give then the ratio of the light of the sky when illuminated by the corona 

 and that when illuminated by the moon, and this equals the ratio of the total light 

 emitted by the corona and the moon, provided the diffused light at the eclipse is 

 exclusively due to the corona and the relative intensities of the two spectra are the 

 same. Assuming ZOLLNER'S observations of the luminosity of lunar phases in terms 

 of that of full moon, I find from 17 comparisons that the total light of the corona 

 equals seven full moons. The comparison belongs to blue- violet rays. 



(6) The Intensity of the Corona in Terms of Lunar Intensity. Let i a be the 

 intensity of the region of the moon which lies north and south of Grimaldi and close 

 to the edge of the moon. I compared the blackness of this region on the photograph 

 with that of the corona on that photograph which was equally long exposed and 

 through the same aperture, and measured the distances of points of the corona at 

 which both showed the same degree of blackness. With the reduced distances I 

 calculate, by formula (D), i/c, which equals ijc. Instead of i a , which belongs to 

 phase angle a, I introduce i g , the intensity of the Grimaldi region at mean full moon, 

 and find log i f /c equal to 2'543 from nine photographs on October 18, 2'578 from 

 three photographs on November 14, and 2'532 from 17 photographs on November 15. 

 The mean 2'551 belongs to h = 122, and at this distance from the sun's limb the 

 intensity of the corona equals that of the Grimaldi region at mean full moon. 

 Therefore the constant of formula (D) is Iqg c = 12'228 2'551 + log i g = 9'677 + log i g . 

 For want of suitable apparatus I am unable to measure i g in terms of the average 

 intensity of lull moon, but I am led to expect by integration of the intensity formula 

 and comparison with the total light of the corona (seven full moons) that i g is about 4. 

 i t = 4 would make the intensity of the corona at a distance of 0'23 diameter equal to 

 that of full moon, a result which is quite at variance with that cited by LANGLEY.* 



' The 1900 Solar Eclipse Expedition.' 



