IX. 
Comparison of the Light of the Sun and Moon. 
By GEORGE P. BOND. 
(Communicated September 11, 1860.) 
Iw the preceding memoir, allusion has been made to the values found by Bouguer 
and Wollaston for the ratio between the light received at the Earth from the Sun and 
the Full Moon. The numbers given by them respectively are: — 
Bouguer,* ee S = 300 000, 
Wollaston,f . S ‘ : ; $ ; ; S — 801 072. 
The discordance is large enough to excite a doubt whether they may not both be 
entirely illusory; it will not, then, be uninteresting to re-examine,the processes which 
these eminent physicists have followed in their investigations, and to add the results of 
new experiments depending on quite different methods. 
The method of Bouguer is thus described by Arago: — 
* On the day of observation, the Sun being at an altitude of 31°, and his rays enter- 
ing a dark chamber through a hole +, of an inch in diameter, he placed a concave 
lens in front of this aperture, which diminished the intensity of the solar rays by caus- 
ing them to diverge. 
“Then receiving this divergent light on a screen, at a distance where it was weak- 
ened in the proportion of 1 to 11664, he found it equal to that of a candle situated at 
the distance of 17 inches from the screen. 
“ Repeating this experiment at night with the moonlight and the same concave lens, 
. the Moon being full and also at an altitude of 31^, Bouguer perceived that the light, 
when it had been made to diverge e of an inch, or when it had been weakened 
* Traité d'Optique, p. 87; E T Phil. Trans., 1829, p. Sé, 
i Popular Astronomy, English Translation, Vol II. p. ee The distances have been reduced by the 
caesi: ad to Np measures. ` 
