474 
MESSES. EOSCOE AND THOEPE ON THE MEASUEEMENT OF THE 
sity of the uneclipsed sun calculated from the mean curve in fig. 2. Column IV. shows 
the relation of this intensity to the sun’s altitude, the chemical intensity immediately 
before first contact being taken as unity. Column V. gives the immediate results of 
the photochemical observations during the eclipse. Column YI. shows these results cal- 
culated from the mean curve in fig. 4 ; column VII. the same corrected for variation 
in the sun’s altitude ; column VIII. the same referred to the total chemical intensity 
immediately before first contact as unity. Lastly, Column IX. shows the magnitude of 
the eclipse at the times of observation, the unobscured sun being regarded as unity. 
Table V. 
I. 
II. 
III. 
IV. 
V. 
VI. 
VII. 
VIII. 
IX. 
h m 
12 44 
28 08 
0-153 
0-998 
0-134 
0-140 
0-140 
0-915 
0-961 
12 54 
27 34 
0-151 
0-987 
0-143 
0-132 
0-134 
0-876 
0-880 
1 16 
26 17 
0-143 
0-935 
0-098 
0-098 
0-105 
0-686 
0-637 
1 24 
25 49 
0-140 
0-915 
0-094 
0-078 
0-085 
0-555 
0-534 
2 2 
22 35 
0-121 
0-791 
0-000 
0-000 
0-000 
0-000 
0-000 
2 9 
21 43 
0-115 
0-752 
0-024 
0-019 
0-025 
0-165 
0-127 
2 25 
20 03 
0-107 
0-699 
0-033 
0-033 
0-047 
0-307 
0-338 
2 34 
18 56 
0-101 
0-660 
0-047 
0-047 
0-071 
0-464 
0-498 
2 44 
17 42 
0-095 
0-621 
0-057 
0-057 
0-092 
0-601 
0-602 
2 54 
16 33 
0-088 
0-575 
0-064 
0-064 
0-111 
0-725 
0-736 
3 4 
15 14 
0-081 
0-529 
0-062 
0-071 
0-134 
0-876 
0-861 
The relation of columns VIII. and IX. is graphically represented in fig. 5, the unbroken 
line representing the magnitude of the eclipse, the abscissae represent the time, and the 
ordinates the corresponding chemical intensity and area of exposed disk. 
From these observations we deduce the law that the diminution in the total chemical 
intensity of the sun’s light during an eclipse is directly proportional to the magnitude of 
the obscuration. 
We now proceed to investigate the influence respectively exerted by the (1) diffused 
and (2) direct radiation. 
Table VI. contains the results of the determinations of chemical intensity of diffused 
light. 
Column I. gives the apparent solar times of observations ; column II. the correspond- 
ing solar altitude ; column III. the chemical intensity of diffused light calculated from 
the mean curve in fig. 3 obtained from the observations of Dec. 19, 20, 21. Column IV. 
gives the relation of this intensity to the sun’s altitude, the chemical intensity of the 
diffused light immediately before first contact being taken as unity. Column V. gives 
the immediate results of the determinations of chemical intensity of the diffused light 
during the eclipse. Column VI. shows these results calculated from the mean curve in 
fig. 5 ; column VII. the same corrected for variation in altitude ; column VIII. the same 
referred to the chemical intensity of diffused light immediately before first contact as 
unity. Column IX. shows the magnitude of the eclipse at the time of observation, the 
unobscured sun being regarded as unity. 
