Rensselaer Union, Volume 8, Number 46, Rensselaer, Jasper County, 3 August 1876 — Some of the Favorite Lunar Studies. [ARTICLE]

Some of the Favorite Lunar Studies.

There are two lunar spots which the selenographer regards with special favor, because of the evidence they seem to give of change. One is a crater lying on the so-called Sea of Serenity, which some popular lunar observers regard as the left eye of the Man in the Moon. Here there was once a deep crater nearly seven miles aeross, a very distinct and obvious feature even with the small telescope (l ess d'ah four inches in aperture) used by Beer and Madlerin forming thoir celebrated chart, But, ten years ago, the skillful astronomer Schmidt, a selenographer of selenographers—who has, in fact* given the best energies of his life to moon-gazing—found this crater missing. When he announced the fact to the scientific world, other astronomers, armed with very powerful instruments, looked for~the crater which had been so clearly seen with Madler’s small telescope; but though they found a crater, it was nothing like the crater described by Madler. The present crater is scarcely two miles in diameter, and only just visible with powerful telescopes; all aronnd it there is a shallow depression, oc. cupying a region about as large as the whole crater had been before. It seems impossible to doubt that a great change has taken place I. here, and • the question arises whether the change has been produced by volcanic activity or otherwise. 'Sir John HersChel pronounced somewhat in favor of the former hypothesis. “ The most conjecture,” said he, “as to the cause of this disappearance seems to be the filling up of the crater from beneath by an effusion of viscous lava, which, overflowing the rim on all sides, may have so flowed down the outside slope as to efface its ruggedness, and convert it into a gradual declivity, casting no stray shadows.”, But how tremendous the volcanic energy required to fill with lava a crater nearly seven miles in diameter and more than half a mile deep. The volcanic hypothesis seems on this account utterly incredible, for if such energy resided in the moon’s interior we should find her whole surface continually changing. Far more probable sfeems tne idea that the wall of this crater has simply fallen in, scattering its fragments over what had been the floor of the crater. The forces at work on the moon are Quite competent to throw down steep crater walls like those which seem formerly to have girt al>out this deep cavity. Under the tremendous and long-lasting heat of the lunar midday

sun, the rock substance of the moon’s surface must expand, while during the intense cold of the lunar night a correspond, ing contraction must take place, under the influence of this alternate expansion and contraction the strongest of the lunar crater-walls must be tending to their downfall. Their substance must be gradually crumbling away. From time to time large masses must topple over, and occasionally long ranges of crater-wall must be brought to the ground. It seems conceivable enough, certainly far more probable than any other interpretation which has been offered, that the craterwall first missed by Schmidt was destroyed in this way. The other favorite region of stenographers is a much larger one—the great walled plain called Plato, and by the older astronomers the Greater Black Lake, sixty miles in diameter, and surrounded by mountains, some of which rise nearly 2,500 yards above the level of the floor.— Spectator.