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THE MOON'S SURFACE.
By F. H. LORING.

Modern advances in science demand attention to matters that are quite outside the conventional range of related subjects. For example, investigations of atomic structure has led the student into astronomical phenomena; yet the atom is considered as properly belonging to the domain of chemistry. Even so remote a subject as the surface of the moon becomes in a sense linked with atomic physics.

The moon's surface has been the object of much study and some speculation. The cause of the few mountain ranges on the moon, or more particularly the cause of the formation of so many thousand craters affords a problem of considerable interest.

It would appear that the craters had been formed by the bombardment of the moon's surface by huge explosive shells, rather than that the formations had been due to the action of pent-up gases which, in escaping, had thrown up molten material.

In the case of volcanic eruptions, as seen on the earth, stream-formations of lava should be in great evidence on the moon, owing to the large size of the craters there present, whereas, few, if any such lava flows appear on the moon.

The volcanic theory of the mountains or particularly the craters of the moon, has given way to the meteoric-bombardment theory. It has been suggested that meteorites, in striking the moon without there being any appreciable atmosphere thereon, would, in consequence, strike her surface at great velocities (say, 12 to 44 miles per second), and the energy of impact would render the meteorites instantaneously gaseous. This means practically bomb explosions, as indicated analogously above.

H. E. Ives (Astrophysical Journal, 1919, Vol. 50, p. 245), has said: "The explanation readiest to hand-that the rings, pits

and peaks are the result of volcanic action— does not appear to be adequate when closely studied. While superficially similar in appearance to terrestrial volcanoes, the lunar

craters exhibit significant differences of structure from these. The crater floors are lower than the surrounding country instead of higher, as they are in most terrestrial volcanoes, the central peak is often missing, and the amount of material piled up in the ring mountain is less than would be deposited there by volcanoes we know. It has, however, been pointed out by W. H. Pickering that the volcanoes of Hawaii are quite similar to the lunar configurations."

Ives, in his paper, has shown photographic reproductions of bombarded territory, produced by bombs having been dropped from aeroplanes in war experiments. Comparing the pits and their attendant rings, as photographed at high elevation from an aeroplane, with telescopic photographs of lunar areas, the resemblance is remarkably striking. In fact, so closely do some of the photographs of the bomb craters resemble some of the lunar craters, that it is difficult to distinguish between them. Photographic reproductions of the moon's surface are shown in so many books on astronomy it is unnecessary to introduce them here.

It will be noticed than on the moon there are overlapping craters which would be difficult to explain on the purely volcanic theory, whereas, from the bombardment theory, this overlapping would be expected.

Ives has pointed out (loc. cit.), that the velocity at impact would give rise to the meteorites being suddenly raised to a temperature amounting to thousands of degrees centigrade, sufficient to render them instantaneously gaseous. That is to say, an cannot be dogmatic), the velocity at would at least account for the circular formations, as the gases would expand in all