346' - Mr. Schroeter's Observations 
This, and the mathematical certainty that the phsenomenon 
is, in fact, nothing but a real twilight in the lunar atmo- 
sphere, will be farther evinced by the following theoretical 
deductions, in which the same mode of computing as was used 
in the observations on Venus, will be adopted, with this dif- 
ference, that the angle / c g, fig. 7, Tab. VI. = A c F,is equal to 
the angle D c E, or the geocentric elongation of the moon 
from the sun. 
1. According to the above observation, we find that the 
twilight at both cusps measured, from c to k , fig. 1 and 2, Tab, 
VIII. 20 lines = 1/ 20". The apparent diam. of the moon 
being at 6 h P. M. == 31' 18" ; whence the twilight must have 
extended over an arc of the limb, measuring 4 0 53' 23" ; and, 
if the real diam. of the moon be assumed at 465 geogr. miles, 
this extent must have answered to ic^| of these miles. 
2. But we have seen that f c, fig. 7, Tab. VI. or the mea- 
sured projection of the twilight, is by no means the true dis- 
tance of its farther edge /, from the terminating border g. 
This distance, therefore, must be found by the following com- 
putation : 
Long, of the moon, Feb. 24, 6 h P. M. = 12 s 7 0 3/ 22" 
Long, of the sun - - - - = 11 5 52 22 
Difference of Long. = 1 1 47 o 
= 3i° 47' o" 
Latitude of the moon = o 22 17 
Log. cos. 31° 47' o'' = L. 9,9294424 
+ L °g- cos. o 22 17 = L. 9,9999908 
Log. dist. of d from the © = L. 9,9 294332 
= 3*° 47' 7" 
