Prof. Leslie on the L ight of the Moon and the Planets. 3 9i 
portion of the sun’s light which the moon can remit to us, would be 
500 x 210,000, or 105 million times diminished. Yet the quan- 
tity of attenuated light which we actually receive from the moon, 
exceeds this measure seven or eight hundred times. In fact, the 
light from the moon is equal, if not superior, to what could have 
reached us, if every point of her surface had performed the most 
perfect reflexion. JBouguer inferred from his observations, that 
it amounts to between the 250,000th and the 300,000th part 
of the direct light of the sun ; and I found it, by the first ap- 
plication of my photometer, to approach to the 150,000th part, 
while we have seen that the portion of the solar beams which 
could ever be reflected from the Moon, exceeds not the 210,000th 
part of the total incidence. We are thus forced to conclude, 
that the light from the Sun, at the Moon’s surface, is almost 
entirely absorbed, but exerts a power to cause the projection of 
a still greater quantity of luminous particles, which had lain com- 
bined with her substance. From some broad spaces, this latent 
light is feebly emitted, while, from certain lucid spots, it is dis- 
charged with extreme profusion. In short, we are compelled 
to admit, that the body of the Moon is really a phosphorescent * 
substance like the Bolognian stone, which, excited by the calo- 
rific illumination of the Sun, is made to shed its native light. 
Nor are instances wanted of analogous effects. The mineral 
just mentioned, or the sulphate of barytes, was first observed 
near two centuries ago, to shine spontaneously after being ex- 
posed to the rays of the Sun. Various calcined or incinerated 
* Phosphoric bodies are those which shine spontaneously in the dark. To this 
class belong phosphorus itself, and many substances in a certain stage of putrefac- 
tion, such as meat, fish, wood, &c. But the term phosphorescent is applied to sub- 
stances which become lucid for a short time, on being exposed to any strong light. 
This property was first remarked in the famous Bolognian stone,— the sulphate of 
barytes or heavy spar , — which being suspected, from its ponderous nature, to con- 
tain silver, was roasted in contact with charcoal and other inflammable matters, 
for the purpose of extracting the ore. A similar preparation is made with calcined 
oyster-shells, which, being pounded and mixed with the third part of their weight 
of the flowers of sulphur, are rammed into a crucible, and subjected for half an 
hour to a red heat. 
To the class of phosphorescent bodies likewise belong a numerous catalogue of 
minerals, which, when heated, shine with different colours in the dark. Most sub- 
stances, as I have shewn in a former paper, are caused to emit various coloured 
light, by a powerful electrical excitement. 
