Any one desirous of carrying out a careful study of the Moon’s surface must be provided with a good map, and for general purposes none is so convenient or accessible as Webb’s, reduced from Beer and Mädler’s _Mappa Selenographica_ published in 1837, of which another reproduction is given in Lardner’s _Astronomy_. Those, however, who would desire to study the Moon with the utmost attention to detail must provide themselves with Schmidt’s map published in 1878 at the expense of the German Government. When it is stated that this map represents the Moon on a circle 7½ feet in diameter, the size and amount of detail in it will be readily understood. Special books on the Moon furnishing numerous engravings and detailed descriptions have been written by Carpenter and Nasmyth (jointly) and by Neison. Various attempts have been made to determine the amount of light reflected by the Moon, and also the question whether it yields any measurable amount of heat. As regards the light of the full Moon compared with that of the Sun, the estimates range from 1/300000 to 1/800000, a discrepancy not perhaps greater than might be expected under the circumstances of the case. With respect to the heat possessed by, or radiated from the Moon’s surface, the conclusions of those who have attempted to deal with the matter are less consistent. As regards the surface of the Moon itself Sir John Herschel was of opinion that it is heated at least to the temperature of boiling water, but that owing to the radiant heat having to pass through our atmosphere, which acts as an obstacle, it is no wonder that it should be difficult for us to become conscious of its existence. In 1846 Melloni, by concentrating the rays of the Moon with a lens 3 feet in diameter, thought he detected a sensible elevation of temperature; and in 1856 C. P. Smyth at Teneriffe, but with inferior instrumental appliances, arrived at the same conclusion. Though Professor Tyndall in 1861 obtained a contrary result, yet the most recent experiments by the younger Earl of Rosse, Professor Langley, and others, all tend to show that the Moon does really radiate a certain infinitesimally small amount of heat. Perhaps, however, it will be best to give Langley’s ideas as to this in his own words:—“While we have found abundant evidence of heat from the Moon, every method we have tried, or that has been tried by others, for determining the character of this heat appears to us inconclusive; and without questioning that the Moon radiates heat earthward from its soil, we have not yet found any experimental means of discriminating with such certainty between this and reflected heat that it is not open to misinterpretation.” It is obvious from the foregoing that we on the Earth need not concern ourselves very much about lunar heat; and I will only add that F. W. Very, by an ingenious endeavour to localise the Moon’s radiant heat, has been able, he thinks, to establish the fact that on the part of the Moon