1819.] Scientific Intelligence. 385 
view, when really behind the moon’s disc, by the refraction of 
her atmosphere. The emersion was not observed, the star hav- 
ing come into view about half a minute earlier than was expected. 
he observation was made with a Newtonian reflector, of six 
inches aperture, and a very distinct power of 100: with this 
power, the star, before contact, presented a minute, round, well- 
defined disc, whose contact with, and change of place upon, the. 
moon’s limb, were most distinctly observed. 
J. B. Emmett. 
—2 EP 
*, * The existence of alunar atmosphere is duubtful, and has been denied alto- 
gether by some astronomers. If it does exist, its tenuity must be extreme, as the 
brilliancy of stars for the most part is not in the least diminished by it. See in 
particular Col. Beaufoy’s observations on this subject, Annals of Philosophy, 
ii, 225, et passim, j 
XI. Mr. Murray on Dew, and on the Temperature of the Sea. 
(To Dr. Thomson.) 
SIR, Paris, Feb. 15, 1819. 
I was convinced of the truth of the late Dr. Wells’s theory of 
the formation of dew from the first perusal of his very ingenious 
essay. Time has confirmed, not weakened the impression. 
On the 5th of last month in crossing the Bochetta from Genoa 
to Turin, at half-past seven o’clock, a.m. with a still atmosphere 
and serene sky, I noted the following observation, which cannot 
I think be explained in any other way than upon the principles 
laid down by Dr. Wells. The external atmosphere was 27° 
Fahr.; that within the coach 54°. The windows had been 
shut for a considerable time. The exterior surface of the 
glass was dry, the inner covered with a thin crust of ice, though 
exposed to this medium of 54°. I lowered one of the side win- 
dows about half an inch ; this had the effect of causing the ice 
to disappear very shortly. I explain the phenomenon in the 
following manner: The exterior surface of the glass radiated 
caloric to the heavens more promptly than it received the warm 
impressions from within, in consequence of which the respirable 
vapour condensed upon the inner surface passed into the state 
of ice. Onadmitting the external air, a current was established, 
and the ice dissolved, though it lowered the temperature consi- 
derably. The ball of the thermometer in contact with the ice 
within still supported a temperature of 54°. I should add to 
these that no ice formed on the surface of the front windows, and 
these were overshadowed by the covert of the cabriolet. Now 
Dr. Wells has clearly proved that a cloudy sky, or the prevalence 
of winds, are circumstances unfavourable to the formation of 
dew; and that an agitated atmosphere not only prevents the 
deposition of dew and the formation of hoar frost, ice, &c. but 
dissolves them as soon as formed. 
Dr. Davy’s ingenious researches on the temperature of the 
sea will no doubt be appreciated by the navigator. By this 
account we are focined of the approximation of shoals by a 
Vou. XIII. N° V. 2B 
