224 ON THE LIGHT OF THE MOON AND OF THE PLANET JUPITER. 
The proportions between the intensity of the chemical rays from the Sun and those 
from the Moon and Jupiter, were next ascertained. For the Sun and Moon the propor- 
tion found was the ratio 340,000 to 1. Comparisons were also made between the 
Moon and the Earth's landscape, indicating that the latter has a somewhat feebler 
photographie power than the Moon. 
No satisfactory explanation of the superior chemical energy of the light of Jupiter 
having presented itself, attention was next directed to the relative intensity of the 
visual rays from the same objects. 
In the account of these experiments an exposition is first given of the photometric 
formule required in the discussion of the observations, with particular reference to the 
relative brightness of the Sun, and of the Moon or planets illuminated by it, as seen 
from the Earth. Different writers have arrived at very discordant representations of 
the ratio of the quantity of light afforded by the full Moon compared with sunlight, 
supposing none to be lost in reflection from its surface. Attention has been given to 
the cause of the discrepancies, and to the effect of changes in the phase of the Moon 
or planet in modifying both the amount of light transmitted to the Earth, and its 
distribution over the illuminated area. 
The changes of moonlight at the several phases, computed from Lambert's and Eu- 
lers theories, compared with Herschel's series of photometric determinations made in 
1836 at the Cape of Good Hope, were found to bear scarcely any resemblance to the 
observed values. This discordance was confirmed by a new series of experiments, agree- 
ing closely in their indications with those of Herschel. The fact that the two series were 
originally destined for quite different purposes, adds to the force of this confirmation. 
Of the two theories, Lambert's deviates the least from the truth, still, however, making 
the half-moon from two to three times too bright; and since it is based upon a prin- 
ciple found experimentally to be generally true for opaque substances, it would seem 
that the constitution of the Moon's surface in respect to its reflective properties is 
peculiar. The brightness somewhat suddenly increasing when it approaches opposi- 
tion, as though the greater number of the reflecting facets of its asperities were dis- 
posed at right angles to the radius vector of the orbit, causing a sudden glance of 
light analogous to that which we may see in micaceous rocks. 
It deserves notice that such a tendency would also accord with the actual distribu- 
tion of light at full moon; for, in this case, the brightness ought to increase towards 
the margin of the disc, as it actually does, whereas Lambert's theory requires that it 
should decrease. | 
Jupiter, on the other hand, agrees sufficiently well with Lambert’s theory, as 
