COMPARISON OF THE LIGHT OF THE SUN AND MOON. 291 
Hence 5,563 is the number of candles which, being placed at the distance of 12 
inches, will give a light equal to that of the Sun. 
“VI. Observations of the Light of the Moon compared with that of a Candle by Means of Shadows. 
Distance, in Inches, of the Candle from a Screen, | 
Date:of the Observation: Remarks. when its Light is equal to that of (+ 
1799, May 16 8 Elongation 1703° ETC p 
| jc. Jede dT e Ful 144 
Hence 
(mm uu X Candle when placed at the distance of twelve feet, 
and 
2 
© = 5568 X Se, Moons. 
12 
— 801,072 Moons." 
In two particulars which may have exercised a considerable influence, Wollaston's 
experiments seem to be less deserving of confidence than those of Bouguer. 
It does not appear that, in the former, the extinction of light by the Earth's atmos- 
phere has been allowed for. The Sun was in a high northern declination, and the 
Moon far to the south of the equator; indeed, at the date of the second observation, 
in its extreme southern declination of 28°, with a meridian altitude in the latitude of 
London of only 10° or 11°. Unless, then, special care was taken to observe the Sun 
when equally near the horizon, of which there is no evidence, RA UU thio 
moonlight must have been relatively much too faint by reason of the ordinary atmos- 
pheric extinction. At the date of the last comparison, it must have been from this 
cause less than half as bright as it would have been at the meridian altitude of the 
Sun, and still fainter, if we take into account the smoky atmosphere of London, where 
the experiments were probably made. * POS ; 
Another objectionable feature is the means employed for diminishing the ae 
by admitting it only through a very small aperture, while for the Moon the full disc 
* Supposing each to have been observed when near the meridian, the effect of atmospheric extinction would 
have been to cause the Moon to appear, in the mean of the comparisons, too faint relatively to the Sun, in the 
proportion 6:10. Wollaston's ratio of sunlight to moonlight would then be 
0.6 x 801072 — 480 643, 
or 
S — 480 643. 
