ON THE LIGHT OF THE MOON AND OF THE PLANET JUPITER. 229 
assumes a bluish cast due to the effect of contrast in intensity and quantity rather 
than of actual color. Arago,* to account for the supposed bluish tints of the Mare 
Crisium and Mare Serenitatis on the Moon, suggests that the general tint of the latter 
is yellowish. That the moonlight has no decided tinge of red appears from casual 
remarks made by Sir John Herschel in the account of his comparisons of various 
stars with the image of the Moon formed in the focus of a lens. For instance, to 
observations made April 27, 1836, the note is added, “ The Moon's image is too yellow 
for B Crucis," T a star elsewhere described as white. And again, “y Crucis" (a red 
star) *is too red for the Moon." 
By comparing images reflected from a silvered glass globe, I have found that the 
color of moonlight more nearly resembles that of the flame of a “blue-light” or 
* Bengola" light than that of any other artificial light which was tried, — indeed, 
no difference could be perceived between the “ Bengola” and the Moon in this 
respect. The whitest part of the flame of the Carcel or French * moderateur" lamps 
is decidedly red, contrasted with the image of the moon; that of a candlet or com- 
mon oil-lamp appears of a dingy, yellowish red. The Drummond light is of a golden 
yellow when contrasted with sunlight. I have not recognized, in point of color, any 
considerable difference between the light of the Moon, Jupiter, Venus, and the Sun, 
when tested by this method. 
The following description by Mr. De la Rue, in October, 1856, would make the 
general hue of Jupiter yellowish rather than blue: — 
“The southern belt of Jupiter appeared, on most occasions on which I have ob- 
served it, to be somewhat darker than the northern, which has always been more 
diffuse and more broken up by intervals and streaks; the northern also has invariably 
been the broader of the two. Both belts are unmistakably brown as compared with 
the general tint of the planet, which about the poles has a decidedly yellow hue, and 
more obviously so towards the north. Besides the very conspicuous broad belts, there 
were observed several delicate and faint streaks extending to a greater or less distance 
across the disc, but seldom entirely across it; these faint streaks just under the north 
belt were decidedly yellow.” § | 
* Pop. Astron., Eng. Trans., Vol. IL p. 287. Set also the explanation applied by Mr. Grove to the ap- 
pearance presented by Jupiter. Monthly Notices Royal Astr. Soc., Vol. XVII. p. 13. 
T Obs. Cape of Good Hope, p. 360. 
I See also the remark of Arago. “One of the principal sources of error seems to me to be the difficulty of 
comparing the white light of the Sun or of the Moon, which then looks bluish, by contrast with the reddish 
light of a candle." — Popular Astron., Eng. Trans., Vol. II. p. 288. 
$ Monthly Notices Astr. Soc., Vol. XVII. p. 5. 
VOL. VIII. 30 
