whereas we could hardly expect to note any, save by the merest accident, in two or three hundred years. To come now to the last, and, according to some, the most decisive piece of evidence in favour of the theory that the moon's crust is still under the influence of volcanic forces. On May 19, 1877, Dr. Hermann J. Klein, of Cologne, observed a crater more than two miles in width, where he felt sure that no crater had before existed. It was near the centre of the moon's visible hemisphere, and not far from a well-known crater called Hyginus. At the time of observation it was not far from the boundary between the light and dark parts of the moon: in fact, it was near the time of sunrise at this region. Thus the floor of the supposed new crater was in shadow--it appeared perfectly black. In the conventional language for such cases made and provided (it should be stereotyped by selenographers, for it has now been used a great many times since Schroeter first adopted the belief that the great crater Cassini, thirty-six miles in diameter, was a new one) Dr. Klein says, "The region having been frequently observed by myself during the last few years, I feel certain that no such crater existed in the region at the time of my previous observations." He communicated his discovery to Dr. Schmidt, who also assured him that the region had been frequently observed by himself during the last few years, and he felt certain that no such crater, &c., &c. It is not in the maps by Lohrman and by Beer and Maedler, or in Schroeter's drawings, and so forth. "We know more," says a recent writer, singularly ready to believe in lunar changes; "we know that at a later period, with the powerful Dorpat telescope, Maedler carefully re-examined this particular region, to see if he could detect any additional features not shown in his map. He found several smaller craterlets _in other parts_" (the italics are mine), "but he could not detect any other crater in the region where Dr. Klein now states there exist a large crater, though he did find some very small hills close to this spot." "This evidence is really conclusive," says this very confident writer, "for it is incredible that Maedler could have seen these minute hills and overlooked a crater so large that it is the second largest crater of the score in this region." Then this writer comes in, of course, in his turn, with the customary phrases. "During the six years, 1870-1876, I most carefully examined this region, for the express purpose of detecting any craters not shown by Maedler," and he also can certify that no such crater existed, etc., etc. He was only waiting, when he thus wrote, to see the crater for himself. "One suitable evening will settle the matter. If I find a deep black crater, three miles in diameter, in the place assigned to it by Dr. Klein, and when six years' observation convinces me no such crater did exist, I shall know that it must be new."