Lunar photography was introduced as long ago as 1858 by _Lewis Morris Rutherfurd_ (1816-1892), the well-known American astronomer; but for years very little was done in this matter, although Rutherfurd secured fairly good photographs. Rutherfurd, De la Rue, and the older astronomical photographers took photographs of the entire Moon, but this plan was abandoned in favour of what Miss Clerke calls “bit by bit photography.” About 1890 this method was introduced, and has been followed with success by _Maurice Loewy_ (born 1833), and his assistant, Pusiex, at the Paris Observatory; by _Ladislas Weinek_ at Prague; by the astronomers of the Lick Observatory; and by _William Henry Pickering_ (born 1858), the distinguished astronomer of Harvard, whose discoveries and investigations have created quite a new interest in lunar astronomy. These investigations were commenced in 1891 at Arequipa, on the slope of the Andes, in Peru. An occultation of Jupiter, witnessed by W. H. Pickering on October 12, 1892, gave support to the view that a very tenuous lunar atmosphere does exist. In 1900 he established, near Mandeville, Jamaica, a temporary astronomical station, where he obtained many excellent photographs. Totally he secured eighty plates. These appeared, as the first complete photographic lunar atlas ever published, in his work ‘The Moon’ (1903), in which he sums up all his observations since 1891, and concludes that “the evidence in favour of the idea that volcanic activity upon the Moon has not yet ceased is pretty strong, if not fairly conclusive.” Pickering points out that the density of the lunar atmosphere is not greater than one ten-thousandth of that at the Earth’s surface, and, under these circumstances, water cannot exist above freezing-point, which of course brings us to the subject of snow. He considers that snow is observed on the mountain peaks and near the poles of the Moon, and he believes his conclusion to be verified by observations on the well-known crater, Linné. He brings forward evidence of the probable existence on the Moon of organic life, pointing out that the difference between the conditions of the Earth and the Moon is not so great as that above and below the ocean on our own planet. He has collected evidence of the existence of something resembling vegetation on the Moon “coming up, flourishing, and dying, just as vegetation springs and withers on the Earth.”