on the Planet Venus . 1 
163 
angle at the earth = 12 0 42' 19" 
compl. of the angle at Venus = 17 42 17 
Now the crepuscular light of Venus, the measure being consi- 
dered as a chord, extended 15 0 19' ; then consequently it is, 
log. sin. 15 0 19' o" - 9,421857 
log. sin. 17 42 17 - 9,483033 
log. sin. 8,904890 
= 4 0 36' 28" 
To so much, therefore, amounts the arch of a great circle, 
over which the crepuscule of Venus's atmosphere extends, as 
far as it can be distinguished on our earth, under favourable 
circumstances. According to my former computation, it came 
to 4 0 38' 30" : wherefore the whole difference , certainly very incon- 
siderable to be given as an instance of inaccuracy, amounts only 
to 2 minutes; and it is surely quite superfluous to include 
seconds in a calculation, which, from the circumstances of the 
observation, can only be depended on to several minutes. 
If it be wished to take this opportunity of determining the 
arch, how far the points of the horns project on account of the 
apparent diameter of the sun seen from Venus, put the semi- 
diameter of the sun seen from the earth at the abovementioned 
time, deducting 3" for irradiation, = 16' 3", 3 = 963", 3 
log- 9 6 3>3 “ 2,983762 
log. dist. o = 9>997766 
log. dist. ? a o 
2,981528 
9,857040 
