ON THE LIGHT OF THE MOON AND OF THE PLANET JUPITER. 263 
theory, and if we reduce the phases of the Moon to full, by means of the proportions 
derived from observation, and given on p. 256, we have, 
O for v = 180°.0 Lo O for v = 180°.0 
Log. ~ — = 0.548 : = 0.0 
gei O for v = 111?.2 . d O for v = 169°.1 pene 
O' for v! = 180°.0 0" for v" — 1809.0 
Log. = 0.284. Log. - = 0.008; 
^5 e for of = 111°.9 "TË o" for v = 169°.1 
and thence, 
LI H 1 Oy 
— === — Venus and Moon, full phase, 
pl 6.441 0, 
(39) 
à . i 
E — idcm Jupiter and Moon, ` 
p" 7.094 Oo 
where 6,, ©; , ©,” represent the values of O for each body when fuil phased. 
That Venus and Jupiter very much exceed the Moon in their capacity for reflecting 
light, is evident from the above. It would seem, moreover, that in this respect Venus 
nearly resembles Jupiter, provided that Lambert's reduction for phase is applicable; it 
is, perhaps, questionable whether this can be admitted. 
Seidel* has collected and discussed with great care a very large number of photo- 
metric comparisons of Venus and Jupiter, and has deduced for ratio of their respec- 
tive albedos, 
d 
i 2 = 0.958. 
vi 
Our results, if we adopt the numbers in (39), give 
M. — 0,908. 
p 
Both depend on Lamberts phase-correction ; but since they have been obtained at 
nearly the same average relative position of the Earth, Sun, and planets, the agreement 
proves little, as regards the question of the reliability of the phase-correction. ‘The 
uncertainty, however, does not admit of remedy, for although Venus, like the Moon, 
presents itself successively in every phase, it is only when at a considerable angular 
distance from the Sun that it can be well observed. Its low altitude, and the strong 
twilight surrounding it, throw a doubt over all evening or morning eier made 
in the neighborhood of either conjunction with the Sun; but the fact of its being visible 
* Untersuchungen über die Lichtstürke der Planeten Venus, Mars, Jupiter, und Saturn, p. 52. 
