Natural-Philosophical Collections. 337 
ing through the northern signs. By considering the relative positions of the sun 
and moon with that of the earth, and the small angle subtended by the latter 
during the first four days of the moon’s age, when the phenomenon is exhibited 
to the best advantage, the dull copper colour seen on the moon’s opaque body in 
clear weather, particularly when near the horizon after sunset, appears to be ef- 
fected by means of the solar rays re‘lected to the regions of the moon, from 
the extensive water in the Kithiopic Ocean and the Great South Sea, according 
as the earth advances in its annual motion round the sun: as it is well known 
the reflected solar rays from water are extremely bright, and as they proceed 
through a clear atmosphere in the direction of the moon, it is probable that they 
produce a faint light upon the dark part of her dise. In the opposite season of 
the year, when the sun’s declination is north, there is more heat in this latitude, 
and consequently more vapours in the atmosphere, which intercept the incident 
and reflected solar rays, and do away their effect; nor is the moon’s angular 
position in the heavens so convenient to receive them as in autumn and winter. 
Cold in southern latitudas as far as 56 or 57 degrees, is said by late voyagers 
to be a mere chimera, aud that snow is scarcely ever seeri on the ground in these 
parallels, although reverse to nature in comparison of the low temperature and 
rigour of the winter in the same parallels in the northern hemisphere ; therefore, 
snow on the ground in South America, or the Cape of Good Hope, or New 
Holland in any part of the year, cannot be the means of conveying the sun’s re- 
flected rays to the regions of the moon; nor is the snow in North America so 
Situated during our winter, as to cause light from the earth to be reflected from 
the dark part of the moon’s disc, as has been supposed by some modern philo- 
Sophers, 
The reflected light from the unilluminated part of the moon in her first quarter, 
as before mentioned, is sufficient to establish the fact of the existence of an at- 
tenuated lunar atmosphere, which, according to the ingenious calculations of the 
celebrated M. Schroeter of Lilienthal, canuot be much less than a mile anda 
ahalfin height. If the moon were a mere cinder, as some would have her to 
be, and without any atmosphere, is it possible that the light she receives from 
the earth could be reflected to it from the dark part of her dise >—_ Phil. Mag. 
Mr Faraday’s Experiments on Flint-Glass for Achromatic Experiments.— 
A paper by Mr Faraday was read at the Royal Society on the 19th November, 
giving a short account of the experiments made at the expense of government to 
obtain more perfect glass for optical instruments. ‘The paser commenced by 
stating, that, although glass had been brought to ample perfection for domestic 
purposes, yet for optical instruments it was far from being perfect. This fact 
was too well known; and it was a singular circumstance, that-the first telescope 
maker (Mr. Dollond) had not been able to obtain a perfect disc of the circum- 
ference of four and a-half inches for an achromatic telescope in the last five years, 
nor one of five and a-half inches in the last ten years. The want of an improved 
glass for optical instruments was so much felt, that, in 1525, a committee was 
appointed to make experiments, in order to ascertain if an improvement could be 
made. His Majesty’s government afterwards ordered every facility to be given, 
and stated, that the expence incurred in the experiments should be paid out of 
the treasury. A furnace had been erected in the Falcon Glass Works, and sub- 
sequently one at the Royal Institution, where the experiments had been carried 
on with the greatest assiduity. The paper now read was intended as a summary 
of these proceedings. The experiments gone into were briefly glanced at, and 
discoveries had been made which had brought the manufacture of glass for 
_.optical purposes to nearly a perfect state, the faults so long complained of, viz. 
of the glass being wavy, reely, &c. being remedied to a great extent. ‘The most 
_ perfect homog2nzous glass obtained by these experiments was found to act per- 
fectly. fhe paper went into minor details, The experiments are still going on. 
din. Journal of Science, No. Ti. ; 
