12 
POPULAR SCIENCE REVIEW. 
the small concave reflectors as the large mirror of the telescope, 
Lord Rosse found that such a deviation of his galvanometer as 
the full moon gave appeared to indicate an elevation of tempe- 
rature of the lunar surface, as we have previously mentioned, 
through 500° Fahrenheit, allowance being made for the imperfect 
absorption of the sun’s rays by the lunar surface. 
No evidence was afforded of cosmical heat. Had there been 
such, and it could have penetrated our atmosphere, a certain 
heat-effect would have been constantly exhibited, independently 
of the phase of illumination. On one night, however, when 
the moon was two days old, and the air clear and calm, no per- 
ceptible impulse was imparted to the needle. It is reasonable 
to suppose that, under favourable circumstances for revealing it, 
some internal warmth would show itself, small though its 
^amount might be ; for although the moon, from its large radiating 
surface and small mass, doubtless parted rapidly with the heat 
of the previous existence of which we see evidence in its 
volcanic crust, yet it can hardly have cooled down to the low 
temperature of space, and if it has not, the dark body of the 
moon ought to exhibit warmth not manifested by the regions 
of sky surrounding it. It is conceivable, however, that any 
such that might come towards us would be absorbed in the 
higher strata of our atmosphere. 
Since Lord Rosse’s observations were made, renewed atten- 
tion has been given to the subject by physicists on the continent. 
During the past summer, M. Bailie, of the Paris cole Polytech- 
nique, verified preceding conclusions as to the evidence of lunar 
radiation ; and, by an experiment similar to one of Lord Rosse’s, 
determined that the full moon gave as much heat to his pile as a 
cube of boiling water 6^ centimetres square at a distance of 
35 metres. A Thompson’s galvanometer was employed, and the 
rays were condensed by a concave mirror of 39 centimetres’ 
aperture.* M. Marie-Davy, after fruitlessly trying to affect a 
dilatation thermometer by the moon’s rays, condensed by a 
three-foot lens, mounted an extremely sensitive thermopile in 
the eyepiece of an equatorial telescope of nine inches’ aperture, 
erected in the garden of the Paris Observatory. A little 
trouble was caused by the influence of some iron ribs of the 
dome covering the instrument, but the effects of these were 
avoided by comparing each deviation of the galvanometer 
needle with the mean of the two readings before and after it. 
Observations \yere made on five days between the 9th and 20th 
of October last, the fourth and fifteenth days of the moon’s 
age. Like Lord Rosse, M. Marie-Davy obtained effects increas- 
iug in magnitude with the degree of illumination ; and knowing 
“ Comptes rendus,” lxix. 900. 
