158 Mr. Schroeter’s new Observations 
the diameter of the sun seen from Venus 
in aphel. = 43' 51", 6 
in perihel. = 44' e8",i 
I really do not see, therefore, how the diameter of the sun 
seen from Venus could be expressed generally, and with respect 
to every part of her orbit, more accurately, than as 44', the 
quantity taken for the calculation. And indeed equally unim- 
portant, must be considered 
2. The remark on my computation of the penumbra. The 
sense of the note on that subject, which I have given, p. 313 
(Phil. Trans, for 1792), is plain enough, that, as the sun is seen 
in Venus under an angle of 44', the penumbra, assuming the 
diameter of Venus = 60", can amount only to ©",38 in the 
middle of her disc; but that as Venus, when her diameter is so 
large, can only appear under the phase of a crescent, the pe- 
numbra can scarcely amount to ^ of a second in the perpen- 
dicular diameter on the line of the cusps. Instead of o",38, or 
still more accurately o ,/ ,384, by an error of writing or compu- 
tation o "36 was set down : but what does this inconsiderable 
difference, of ~ sec. impede in the conclusion, that the penum- 
bra at the boundary of light on the disc, or in the perpendicular 
direction on the line of the horns , is imperceptible ? and how 
could so unimportant a matter deserve the least notice ? 
3. With respect to the twilight itself of Venus* s atmosphere, and 
the computation of it, the paper in question contains, p. 16 and 
17, three objections: ( a ) that I had overlooked the penumbra, 
which, in the projection I have given of the crepuscule 15 0 19' 
is said to amount to more than 2°-§-, or, as this error of com- 
putation was corrected in my copy, to T 1 1' 4 f ,6 ; (b) that my 
7-feet speculum must be tarnished, because I have measured the 
