on the Planet Penns. 
131 
That the decrease of light toward the boundary of illumi- 
nation, whereby that part of thfe disc becomes extremely dim, 
is no deception, appeared now evidently ; for whilst the planet 
faintly glimmered through the clouds, I could often see only y 
of her illumined part, reckoning from the outer edge, and 
sometimes only half. 
5 h 55'- Venus shining out for a short time between the 
clouds, the same appearance with full certainty ; ^nd I re- 
marked also again a slight darker indentation at the southern 
horn ; but the scene was by no means so striking as both evenings 
before. 
5 h 59' > the appearance changed ; and 
6 h 7', this was found to be confirmed ; but I could not with 
certainty discover a separate point of light ; sometimes, how- 
ever, though but seldom, there seemed a glimpse of it at the 
southern horn. Immediately afterwards Venus was covered 
with clouds. 
6 h 30' to 6 h 45'. Venus shining in a clear sky, her southern 
horn was again, as at tf 6', rounded exactly like the northern ; 
and with powers 160, 209, and 370, and a distinct image, I 
found no trace of a separate point of light. Comparing this 
third observation with the two former ones, it agrees very well 
to the minute ; for now the southern horn had nearly the same 
appearance of being like the northern, at 6 h 30', as it had the 
preceding evening at 7 h 12', and therefore 42 minutes earlier; 
but in general it was evident that the appearance remained no 
longer exactly the same as on the two evenings before ; and 
this difference may be easily explained by the very probable 
supposition of a libration, and that it is not a single mountain 
which occasions the appearance, but a considerable ridge, with 
S 2 
