on the Atmosphere of the Moon . 347 
Thus was the above the amount of the angle/cg*, fig. 7 ; and 
as the sin. of the arc fg = si n.fc x si n.fcg, then 
Log. sin ./ c = L. 4 0 53' 23" = L. 8,9306436 
-f Log. sm.f eg = L.31 47 7 = L. 9,7215942 
L. sin./g- = 8,6522378 
which gives fg = 2 0 34' 25" 
Whence I infer, that the breadth of the lunar twilight from 
the terminating border to where it loses itself in, and assumes 
the faint appearance of, the light reflected from our earth, 
measures, in a direction perpendicular to the aforesaid border, 
2 0 34' 25", equal to a breadth of 105 lines, or lo^- geogr. 
miles. 
3. Hence, admitting that the laws of the inflection of light 
are the same in the moon as on our earth and Venus, it will 
be easy to compute the perpendicular height of the inferior 
and more dense part of the lunar atmosphere h d , fig. 9, Tab. 
VII. ; the angler, in the right angled triangle dc e , = i° 17' 6", 
and the radius b c = 234 geogr. miles, or 891914 toises, being 
given ; whence 
Log. rad. 5 = L. 891914 = L. 5>95°3 210 
— Log. cos. i° if 6" — L. 9,9998908 
5>95° 43 02 = 892140 
— be — 891914 
d b ~ 226 
So that the inferior more dense part of the moons atmo- 
sphere, measures, in perpendicular height, not more than 
226 toises, or 1356 Paris feet; that inferior part, namely, 
