Page:The Moon (Pickering).djvu/88

60 be seen with a five-inch telescope under favourable conditions. At first, therefore, it appeared doubtful if our photographs could be used to advantage.

Four negatives were selected, however, and enlarged to the same scale as the drawings, and are reproduced beside them on the plates. The first photograph, it will be noticed, was taken 2.6 days after lunar sunrise, or 1.6 days later than the first drawing. In the same way the second photograph was taken 1.0 day later than the second drawing, the third photograph 1.5 days later than the third drawing, and the fourth photograph 0.9 day before the fourth drawing.

A casual glance at the drawings shows, in Figure 1, Plate E, near the bottom of the picture and within the crater, a number of markings that may be described as more or less canal-like. At the same time there are numerous fine lines, which probably merely represent cracks in the surface, and which later disappear under a higher Sun. In Figiu-e 3, and Plate F, Figure 5, however, the real canals come out. In Figure 8 they have again become invisible. It is at first a little difficult to recognise any particular region on all of the different photographs and drawings, but a portion of the crater walls and the three central peaks can be found in every case, and starting from these the other regions may always be identified.

There is a dark kite-shaped marking on the planet Mars, shown near the bottom of Plate D, Figure 12, which is known as the Syrtis major. If Plate F, Figure 5, be inverted, at least two such dark markings will be found upon it. In Plate D, Figure 11, a dark peninsula-like marking to the right of the centre is known as the Solis lacus. Above it and half surrounding it is a dark semicircular region. Canals radiate from it in various directions. If Figure 5 be again inverted, the counterpart of this marking will be found just below its centre. In both cases the canals radiate from the centre to an incomplete dark circumference, and in both cases the intervening bright region is darkest on the side of the darkest exterior.

It has been said that the canals of Mars never end save in a sea or another canal. That this is not quite true is shown by a canal seen just above the centre of Figure 12. This fading out into nothingness seems to be rather more frequent, however, upon the Moon, several such instances occurring in Figure 5. In both Figures 3 and 5 rounded lakes or oases are found at the junctions of some of the canals. In Figure 5 a little lake is seen above and to the left of the centre, without any connecting canals, but in Figure 3, drawn a month later, the canals belonging to it are shown intersecting like an X, although