284 ON THE LIGHT OF THE MOON AND OF THE PLANET JUPITER. 
those before investigated. Thus all the experiments agree in indicating that the planet 
reflects to the Earth more than twice as much light as would have been expected from 
a priori considerations. The disproportion is the more remarkable on account of the 
bright bands, and especially of the brilliant white spots occasionally seen on the surface 
ofJupiter. From the best estimates which I have been able to make, the whitest bands 
are brighter than the average surface in a proportion larger than 3: 2. 
- This has been ascertained by drawing belts of different intensity upon a sphere held 
at a distance of twelve or fifteen feet from the eye, and, judging of their resemblance 
to the belts upon Jupiter, by viewing the two objects alternately. The contrast of 
tints having been decided upon, the sphere was afterwards compared with paper of dif- 
ferent shades placed at suitable distances from a lamp to give a similar contrast. The 
ratio of the squares of the distances furnished a measure of the quantities of light 
given by each. : 
Assuming that the dusky belts, at the time when the comparisons were made, (in 
April, 1860,) occupied one fourth of the surface, I have found, 
Albedo of principal dusky belts aid 
Albedo of rest of surface Cu eps 
Albedo of actual surface of Jupiter Yo 
Albedo of J upiter if destitute of dark belts ` 1.13 ' 
The average brilliancy of the surface, exclusive of the dark belts, is about interme- 
diate between the bright and the dark belts; hence, 
Albedo of narrow, very white belts 
See = 1.13 1.51 = 1.70. 
General albedo of whole surface x 
From the accounts which many observers have given of the brightness of the white 
faculee, it seems quite possible that their light may be even more than double that of 
the rest of the surface, and that the darker spots are in an equal degree fainter. 
By admitting that Jupiter shines in part by native light, it is of course easy to 
explain its apparent excess of brightness. ‘The planet is probably enveloped in a 
dense mantle of clouds, and we know that in our own atmosphere the luminosity 
of the clouds is a well-established fact. The more brilliant auroral exhibitions, too, 
are unquestionable evidence that the Earth itself shines with a certain amount of 
native light, and to suppose a similar property in Jupiter is introducing no very improb- 
able hypothesis. On the other hand, the phenomena of the transits of the shadows of 
the satellites of Jupiter over its disc show that the greater part, certainly, of the light ` 
