Page:The Moon (Pickering).djvu/135

Rh the snow has increased in area and conspicuousness. This is the normal course upon the Moon, but if we turn to Plate 5C, instead of having increased still further in conspicuousness, as we should have expected it to do, it has returned more nearly to the appearance that it had on Plate 5A. This is the case notwithstanding the fact that on Plate 5C the snow about Menelaus [2.1, 6.1] and Manilius [2.9, 6.4] is more conspicuous in both cases than it is on Plate 5B. This apparent change in Plinius is probably not due to the melting of the snow, but is merely an effect of photographic contrast. It is quite possible, however, that a visual study of it under sufficiently favourable atmospheric conditions might lead to interesting results.