on the Planet Venus. 
1 73 
What seems to deserve further attention in this phenome- 
non, is the circumstance, that I have seen this extremely brighter 
border at the edge , not only about the time of Venus’s greatest di- 
gressions from the sun , when she appears to us half enlightened, or 
more , but also equally well very near the conjunction ; and parti- 
cularly plain in the year 1790, when she had the very smallest cres- 
cent phase, not amounting to more than from 4 to 6 seconds in 
breadth. 
Were it not for this remarkable circumstance, I should look 
for the cause solely in the greater quantity of light, which, 
when the planet has the phase of being half, or almost half 
illuminated, falls quite or nearly perpendicular through its 
atmosphere, on the surface which appears to us the edge, and 
is reflected back from this surface into the atmosphere, by 
which it is again reflected, and in various ways refracted, so 
that at the edge, against which we look by an oblique long 
line through the atmosphere, we see an exceeding quantity of 
light, being that of the planet and its atmosphere at the same time; 
but the abovementioned observation seemed to make it pro- 
bable, that, as I have always believed, the appearance chiefly 
depends on optical fallacy, yet this still requires further inves- 
tigation. However, though we are as little acquainted with 
the natural constitution of the ball of the planet, in respect to 
its power of reflecting more or less light, as with the species of 
the refraction there, yet it seems contrary to all analogy, that 
the atmosphere of this heavenly body should be an opaque 
cover, capable of reflecting more light than the solid body it- 
self ; yet that we should see the external edge, not faintly 
expressed, in the manner of an atmosphere, but sharply termi- 
nated ; and, on the other hand , the boundary of light, under 
