Prof. Leslie on the Light of the Moon and the Planets. 899 
midity attracted from the ocean ; but that the Moon, being much 
nearer to our Earth, drew her nutriment only from the lakes, 
whose waters in exhaling, carried along with them portions of 
mud and other impurities, which partly encrusted and obscured 
her surface. Had the delineation been more precise, we could 
perhaps have marked the spread of such incrustation during the 
course of three thousand years. This mythological notion, how- 
ever, is favourable to the hypothesis of the gradual change of 
the Moon’s surface. 
It deserves to be noticed, that the phosphorescent quality 
which we have thus been led, by a strict process of induction, 
to ascribe to the Moon, is not altogether a new proposition. 
Such an idea was started by Licetus, Professor of Philosophy at 
Bologna, soon after the discovery of the singular stone known 
by that name. But, not supported by any proofs, his opinion 
seems to have been soon neglected, and at length forgotten. It 
is barely mentioned in Riecioii’s Great Collection *. 
But recent discoveries in optics furnish another demonstration, 
that the moon shines by her native light. All rays reflected 
from glass or water, or generally from the surface of any body 
not of a metallic nature, become polarized. To acquire this 
modification, the light emitted directly from the Sun, a candle, 
or the fire, must undergo such a reflexion. But the rays of the 
Moon affect the very same disposition, and therefore must not 
have previously suffered reflexion at her surface. This ingenious 
and conclusive remark I owe to my celebrated friend M. Arago, 
who first communicated to me in conversation, at Paris in 1814. 
I have since repeatedly verified it, and have found that Venus 
and the other bright planets possess the same property. 
The theory of lunar phosphorescence accords with the vari- 
ous phenomena. Three or four days after change, the very 
thin lucid crescent seems to embrace a dark grey circle, suffu- 
* Heinrich, in his curious book on Phosphorescence, conjectures that the light 
of comets is of the same nature as that of the Bolognian stone, and hints that not 
only the Moon and the Earth, but all the planets, are more or less phosphorescent. 
Schroter, Harding, and other practical astronomers, from the phenomena exhibited 
by the Moon and Venus, were led to believe that the planets possessed a peculiar 
light, independent of that of the Sun. These details serve to complete the history 
of the idea of lunar phosphorescence first started by Licetus, and here brought for- 
ward by Professor Leslie, in so novel, interesting, and striking a manner.— Edit. 
