“It must have been a great curiosity in the days when the moon was inhabited, and I suppose that scientific ‘lunarians’ organized expeditions to explore it.” “Perhaps, if you choose to regard it in that way. Now look again at the _Mare Humorum_. You perceive that its eastern side is lined with mountains and crater rings, while near the center of the northern border there is a conspicuous ring with a bright line running from the southern edge to the center. This is one of the most beautiful of lunar formations, and is named Gassendi. It is a favorite object for those who study the moon with telescopes on account of the great variety and singularity of the details visible within the ring. When you become a selenographer and possess your own telescope you will find few things more interesting to study than Gassendi. “Next let us take up photograph No. 12. Here the moon is once more a little ‘older’ than before, and the sunrise line has again advanced a little eastward. This advance does not appear so rapid when the terminator is near the moon’s limb, because, on account of the rounding away of the lunar globe, the illuminated surface is foreshortened from our point of view on the earth. In this photograph you perceive that the wonderful shining mountain Aristarchus has become even brighter than it was before, or at least it is more conspicuous on account of the appearance of what seems to be a short ray shooting out from it in a southeasterly direction. There is also a light spot just below it which is caused by a little mountain group called the Harbinger Mountains. The bright ray connects Aristarchus with its neighbor Herodotus, of which I spoke a little while ago. There is a very remarkable feature of the moon here, not shown in the photograph, but to which I must briefly refer. It is an enormous cleft, or crack, or, if you please, cañon, which starts from Herodotus, whose northern wall seems to have been broken through to give passage to it, and goes winding across the surface of the _Oceanus Procellarum_ with several sharp turns and angles for a total distance of nearly a hundred miles. What produced this remarkable chasm on the moon it is difficult to say. Some have suggested that it may once have been the bed of a river, but there are many serious objections to that view. Nevertheless, there seems to be little doubt that if we were to visit the moon we should find, in many ways, a striking resemblance between this prodigious cañon and that of the Colorado River.” “And are not all these things so ancient, as far as you can tell, that, like the terrible volcanic rings, they might have been formed before the appearance of inhabitants upon the moon?” [Illustration: NO. 12. SEPTEMBER 4, 1903; MOON’S AGE 13.27 DAYS. ] “They certainly seem to be very ancient, and I cannot deny the _possibility_ of what you say.”