292 COMPARISON OF THE LIGHT OF THE SUN AND MOON. 
was compared. It is not clear that these dissimilar conditions may not have occa- 
sioned some disturbance in the results. Bouguer, by using the same aperture upon 
both objects, has avoided this risk of error. It is, however, to be remarked, that the 
point of divergence as noticed by Wollaston is in the comparison between the Moon 
and the candle-light. For the Sun, they find respectively, 
Wollaston, Sunlight — 5563 Candles at 1 English foot distance. 
Bouguer, DI = 5774 66 Së [4 
But on the other hand, 
1 
Wollaston, Moonlight — 144 Candle at 1 English foot distance. 
Bouguer, e A c & “ 
52 
Lambert* has compared the Moon with the light of a tallow-candle, and found the 
latter, at a distance of 1 foot English, 44 times as bright as moonlight. My own 
experiments give 62 for the same ratio, using a wax candle. 
Though no great reliance can be placed on the constancy of the candle-light used in 
the different experiments, yet it is to be noticed that Wollaston’s result diverges widely 
from the mean of the other determinations, and in a direction and to an amount which 
would be sufficiently well explained by supposing that the atmospheric extinction had 
not been considered, in reducing the observations of the Moon; in the other experi- 
ments, its influence was much less sensible. 
Wollaston has also attempted a comparison of the light of the Sun and of Sirius 
and a Lyrz, by using, as an intermediate standard, the image of a candle reflected from 
a small thermometer-bulb, equalizing it first with the image of the Sun reflected from 
a similar bulb placed at a suitable distance, and then with the star. The images both 
of the Sun and of the star were viewed through a telescope provided with a colored 
screen to give them the same tint with the candle-light. The atmospheric extinction 
has been eliminated by making the observations at nearly equal altitudes. 
The mean result, supposing none of the incident light to be absorbed by the bulbs 
reflecting the Sun's image, is: — 
Sun’s light — 11 839 533 000 x the light of Sirius; 
but allowing for the loss of nearly half the Sun's light in reflection, Wollaston finds 
Sun's light — 20 000 000 000 X the light of Sirius. 
* Beer, Grundriss des Photometrischen Caleüles, p. 71. 
