Page:The Moon (Pickering).djvu/101

Rh We may summarize the results of these four eclipses in the following table:

Figures 1 and 2 of Plate G represent the floor of Plato. They are on a scale of $h$, or about thirty-two miles to the inch, and are enlarged from the same negatives that were used in printing Plates 9C and 7D, with which they may be compared. These are the first photographs published, so far as I am aware, showing the details of the floor so that they may be clearly distinguished. The best ones hitherto issued are those of the Paris Observatory, Plates 11, 23 and 34, and of "Weinek's Atlas," Plates 7 and 8. We have now reached a position, I believe, where the details of the bright streaks on the floor of this formation can be better studied by means of photography than they can from drawings made even under the most favourable atmospheric conditions. This is chiefly because photography enables us to obtain much greater contrasts than the eye is capable of detecting, and also perhaps somewhat because the eye is dazzled by the brightness of the more brilliant portions of the Moon. For delicate detail, such as that involved in depicting the smaller craters on the floor, photography, of course, cannot compete with the eye. Still, in both Figures 1 and 2 we can readily locate the positions of craterlets numbers 1, 2, 3 and 4 (see upper figure, page 40).

Comparing these photographs with some taken at the Harvard station on Mount Wilson in California in 1890, and at Arequipa in 1894 and 1897, we find that no change in the markings has taken place since 1897, and only a slight change since the earlier photographs were taken. This change, however, is interesting if real. Each of the four craters whose numbers are given above is indicated by a bright spot upon the photographs. The brightest spot on the floor, however, situated in the southeastern part—that is, the upper right-hand region—does not show on any of the photographs taken in 1890. It was faint in 1894 and conspicuous in 1897. It does not correspond with any important craterlet visible in 1892, but coincides exactly, judging by the bright streaks, with a certain craterlet which was most conspicuous in the earlier observations of Plato made from 1869 to 1884, and is designated as 9 on the upper figure, page 40, This craterlet could not be found, although carefully looked for in 1892. Whether it has now reappeared