45 
observations of the intensity of total daylight, give the 
separate intensities of diffused and direct sunlight. Owing 
to the very rapid changes which occurred constantly in the 
condition of the solar disc from passing clouds, only a few 
isolated sets of these double observations, made when the 
disc was free from cloud, are of value. 
These observatious are, however, sufficient to indicate 
that the rate of diminution and increase of intensity of the 
chemically active rays in the direct sunlight is proportional 
to the changes of area in the exposed portion of the sun’s 
surface. 
Apparent 
Solar Time. 
Chemical Intensities. 
Total. Diffuse. Direct. 
Fraction of 
Disc visible. 
7h. 57m 
.0-948... 
...0-788.. 
....0-160.. 
0-94 
8h. 29m.. 
,0-183... 
...0-146.. 
....0-037.. 
....0-43 
8h. 45m 
.0-113... 
.. 0-090.. 
....0-023.. 
....0-17 
9h. 0m 
. 0 - 000 ... 
...o-ooo.. 
....o-ooo.. 
,... 0-00 
9h. 16m 
.0-152... 
...0-124.. 
....0-028.. 
....0-21 
From these numbers it 
appears 
that the differences ob- 
served between the 
curves 
of total 
chemical intensity and 
area of solar disc must be due to variations in the intensity 
of the diffused light; and the rapid diminution observed 
during the first part of the eclipse may be explained by the 
dark body of the moon cutting off the light from the highly 
luminous portion of sky lying on one side of the sun’s disc. 
I have to thank Mr. Baxendell for his kindness in fur- 
nishing me with the astronomical data required in the above 
calculation. 
PHYSICAL AND MATHEMATICAL SECTION. 
October 13th, 1868. 
Mr. Thomas Carrick in the Chair. 
“ On Observations of Atmospheric Ozone,” by J. Baxen- 
dell, F.B.A.S. [This paper was afterwards read at the 
Ordinary Meeting of the Society held on the 20th October, 
1868. See page 21.] 
