1460 
indicated by the numbers 1 to 12, and ares representing the moon’s 
limb in a series of positions. The width of the sickle-shaped strips 
bounded by these ares, is ‘/,, of the sun’s radius, excepting the 
strips a, 6, ed, for, which ais 
In 40°/, minutes the moon’s limb accomplished a distance equal 
to the sun’s apparent radius; so the strips a, 6, c, d, required 
1, > 40°/, minutes each for reappearing from behind the moon, 
the strips e to w took */,,X 40°, minutes each. On our curve (Plate 
XI Le.) we read the successive increments of the radiation, corre- 
sponding to the series of sickle-shaped strips. We shall denote these 
increments by the same letters as the strips. 
The increment a is entirely due to radiation from zone 1; the 
increment 6 to radiation from the zones 1 and 2, etc. 
Let us indicate by a, the average intensity of the radiation with 
which a unit of disk-surface, belonging to zone », supplies our 
thermopile. Then the increment A, for instance, will be composed 
as follows: 
he Ona OFF ae oe Om. 
8,,6, ete. being the surfaces of the parts that the corresponding 
