432 Scientific Intelligence. 
may. Extremes of heat and cold, dry and wet weather are unknown. 
Injurious drought and heavy rains are rare. Within the last thirteen 
years, there have been eight destructive fires in the city, seven of which 
were followed by rain more or less heavy.. These facts are mentioned 
as probable confirmation of Professor Espy’s doctrine upon the sub- 
ject; but whether true or not, let every one judge for himself. 
Natchez, Aug. 12, 1846. 
2. Variations in the climate of France; (L’Institut, No. 647.)—M. 
Dureau de Lamalle, in May last, read a memoir before the French 
Academy, in which he contested the value of the citations taken from 
ancient authors by M. Fuster adduced to prove that the mean tempera- 
ture of France had diminished. 
V. Astronomy. 
1. Atmosphere of the Moon ; (from an article on the Physical Con- 
stitution of the Moon, by Prof. E. Loomis, in the Sidereal Messenger, 
Cincinnati, i, p. 20.)—Whether we observe the moon with the naked 
eye or with the most powerful telescope, we have no difficulty in say- 
ing precisely where day ceases and night begins. The shadows of the 
lunar mountains are dark as midnight.—The transition seems instanta- 
neous from midnight to noonday. We conclude that the moon has no 
twilight—or rather the legitimate conclusion is, that the moon has no 
twilight which can be appreciated by this mode of observation. More 
refined methods of observation have disclosed the existence of a feeble 
twilight. If there was no atmosphere, the line which joins the extrem- 
ities of the horns of the new moon should pass exactly through the 
centre of the disc—that is, the ring of light should be an exact semi- 
circle. . By observing the moon when her phases were extremely fal- 
cated, Schréter discovered a faint glimmering light extending from both 
the cusps beyond the semicircle. The greatest breadth of this twilight 
was two seconds, corresponding to about two miles on the moon’s sur- 
face.— We admit then that the moon has a twilight, extending about two 
miles in breadth, from which we compute that the height of the denser 
part of the moon’s atmosphere is 1500 feet. 
When the edge of the moon’s disc approaches a star, the instant be- 
fore its disappearance, its light must pass through the moon’s atmos- 
phere, if there be any, and suffer refraction. The light of the star, 
instead of moving in a straight line, must be bent behind the moon, and 
the star must be seen later than it would be without refraction. ‘The 
effect must take place at emersion; the star must re-appear 
sooner thant it should if there were no refraction—in other words, the 
aur of an occultation is diminished by refraction. Now it is easy 
to bri ing aoe to the test of experiment. We can compute the 
