240 ON THE LIGHT OF THE MOON AND OF THE PLANET JUPITER. 
brighter than the surface of the globe enveloped by it. Jupiter is brightest at the 
centre, but we perhaps never obtain a view of its solid nucleus, nor even of the denser 
regions of its atmosphere. 
A more serious discordance from Lambert’s formula is presented in comparing the 
observed and computed quantity of light received from the Moon at its several phases. 
In 1836, Sir J. Herschel, during his stay at the Cape of Good Hope, compared the 
Moon's image, formed by a lens, by means of an apparatus constructed for the purpose, 
with sixty-nine of the brightest fixed stars, at various phases between the elongations 
105° and 262^. The object immediately in view, which was the comparison of the 
light of the stars, by employing the lunar image merely as a temporary standard, 
and subsequently eliminating the uncertainty of its variations by referring all the 
stars to one of the brightest of their number, was satisfactorily accomplished, and 
furnished a most valuable series of photometric determinations. If the light of these 
stars be taken as àn invariable standard, it is evident from Herschel's reductions, that 
- that of the Moon experiences a much more rapid degradation at the phases on either 
side of full than can be accounted for by the formula * of which he has made use to cor- 
rect the light received from the phase to full moonlight, and we shall presently see that 
Lambert's does not afford a materially better representation. On the other hand, if 
the moonlight, reduced to full, is assumed to be consistent with theory, then we must 
infer with Herschel, that the effect of the increasing phase on the general illumination 
of the sky enfeebles the starlight in a very anomalous way, and so as to make it im- 
possible to obtain absolute results as originally proposed. He found that the influ- 
ence in question might be represented by supposing that *the effective impression 
of a star on the retina is inversely as the square of the illumination of the ground of 
the sky on which it is seen projected," + adding, however, that he was by no means 
prepared for the enormous extent of the influence which the results indicated. 
Referring to the details of the investigation, it will be seen that, while the fact of a 
well-marked discrepancy is placed beyond doubt by Herschel's investigations, it may be 
accounted for DCH well, so far e the representation of the observations is con- 
cerned, by ote it to EES variations of moonlight not recognized in the com- 
dii : Geer SC if, pros of supposing, with Euler and Herschel, that 
moonlight varies with the area of the projection of i i ' 
to the Man at a given phase, that is, S ës v iion Beau: egen ee 
2 y, we adopt, within the limits of 
* Results of Astr. Obs. at the Cape of Good Hope, 
See p. 237 (16). 
t Ibid., p. 368. 
p.956. The formula is substantially the same as Euler's. 
