CHEMICAL INTENSITY OE TOTAL DAYLIGHT IN ECLIPSE OF 1870. 
473 
Table IV. 
Hour. 
Altitude. 
Sky. 
Sun. 
Total. 
Cloud. 
Remarks. 
h m 
9 3 
n , 
16 31 
0-085 
0-011 
0-096 
2 
Bar. 29-27 inches. 
9 54 
22 33 
0-096 
0-027 
0-123 
o 
*J 
10 54 
26 44 
0-105 
0-055 
0-160 
2 
Pure blue sky. 
12 0 
29 09 
0-107 
0-066 
0-173 
3-4 
12 24 
28 45 
0-105 
0-070 
0-175 
3 
Large cumuli over Etna and on horizon. 
12 34 
28 29 
0-090 
0-050 
0-140 
— 
12 44 
28 08 
0-090 
0-044 
0-134 
4 
12 54 
27 34 
0-077 
0-066 
0-143 
4 
Sun close to clouds. 
1 4 
27 00 
[0-084] 
6 
Sun overcast. 
1 16 
26 17 
0-053 
0-045 
0-098 
6 
Sun unclouded. 
1 24 
25 49 
0-043 
0-051 
0-094 
7 
Yellow light strongly marked. 
1 40 
24 25 


No exposure: sun overcast. 
The disk was overcast during the time of totality by clouds ; the paper, however, was exposed for 
the entire time of totality, but not the slightest action was evident, Alt. 22° 41-22° 31'. 
2 9 
2 25 
21 43 
20 03 
0-023 
0-010 
0-024 
0-033 
3 
Sun unclouded. 
2 34 
18 56 
0-028 
0-019 
0-047 
2-3 
? 5 
2 44 
17 42 
0-035 
0-022 
0-057 
2-3 
?? 
2 54 
16 33 
0-041 
0-023 
0-064 
2-3 
» 
3 4 
15 14 
0-062 
3 
3 20 
Sun clouded over. 
These results are graphically represented in figs. 4 and 4 a. 
Table V. shows the relation of the total chemical intensity to the area of the solar disk 
obscured. The following approximate method, which we have employed for determin- 
ing the relative area of the sun eclipsed at the times of observation, is sufficiently accu- 
rate for our purpose. Three large disks were cut from a stout and uniformly thick sheet 
of paper, two to represent the solar, the third the lunar disk, their radii being in the 
ratio of the apparent semidiameters of the sun and moon on the day of the eclipse. 
Each of the sun-cards was accurately weighed on a chemical balance ; and on one the 
ratios of the intervals elapsing between first contact and the various times of observation 
before totality were pointed off along a diameter, and the edge of the lunar disk advanced 
successively to these points, and the segments cut off and weighed. The total weight of 
the solar disk into the weights of the various segments gives approximately the area of 
the sun covered at the corresponding time of observation. In a similar manner the ap- 
proximate areas after totality were obtained. This method of procedure, which neglects 
the influence of the moon’s motion and of the earth’s motion of rotation, is of course 
crude ; but as the commencement of the eclipse occurred near noon, the error thus intro- 
duced may certainly be disregarded for areas covered up to l h 24 m , the time of the last 
observation taken before totality. To the areas thus obtained for the times of observa- 
tion after totality we have applied the necessary corrections, for which we are indebted 
to Mr. Seabroke. 
Column I. gives the apparent solar times of observation ; column II. the correspond- 
ing altitude of the sun. Column III. shows the corresponding total chemical inten- 
