COMPARISON OF THE LIGHT OF THE SUN AND MOON. 295 
This, again, is not entitled to much confidence, principally because the experiments 
for determining the absorption of sunlight by the ed surface of the globe failed 
to give a satisfactory result. 
Of the different methods tried, that which seemed best fitted for the purpose will 
now be described ; — the results of other attempts will be omitted, because they were 
in part only preliminary trials, and in some instances they were vitiated through neg- 
lect of precautions to which due attention was afterwards given. It should, however, 
be noticed that they all indicate a value of S less than 500 000. 
The standard illuminator was a single Bengola light, those of the same size and 
manufacture being used throughout. 
1860, July 1. A fine sky, perfectly clear. A glass globe, B;, having a reflecting 
surface of silver, (applied by Liebig's process,) 10".16 in diameter was placed in the 
open air exposed to the sunlight. The brightness of the image of the Sun formed at 
its virtual focus was compared with a single Bengola light, by receiving the light of 
both objects upon a small reflecting sphere, which was moved towards one or the other 
until their images, seen in it side by side, were judged to be equal; the distances of 
the globes from each other and from the Bengola were then measured, and the observa- 
tion repeated. 
ft. 
h m 
4 45 Sid. time. Bengola to Photometer, 15 
Globe B; $ 20 
4 50 ei Bengola to Photometer, 21.2 
Globe Ð; e 24.4 
4 55 e Bengola to Photometer, 18.4 
Globe B; " 21.5 
On each occasion a new Bengola was burned, and the position of B; was altered so 
as to expose a new portion of its surface to the Sun. 
1860, July 14. Clear. Observations on same image in D; continued. 
fi 
3 45 Mean solar time. Bengola to Photometer, .28.0 
Globe Bb; e 80.6 - 
3 50 = Bengola to Photometer, 40.5 
Globe B; S 52.2 
The sensible equality in the intensity of the light reflected in different directions 
from the globe B, was tested experimentally by comparing with the photometer the im- 
age of the Sun reflected from it with the Sun image in a similar globe of smaller 
