Centrifugal force, in combination with the gravity of the Moon’s crust, confined the internal lunar atmosphere to a blanket which we estimated at about fifty miles in thickness over the inner surface of this buried world. This atmosphere rarefies rapidly as one ascends the higher peaks, with the result that these are constantly covered with perpetual snow and ice, sending great glaciers down mighty gorges toward the central seas. It is this condition which has probably prevented the atmosphere, confined as it is within an almost solid sphere, from becoming superheated, through the unthinkable ages that this condition must have existed. The Earth seasons are reflected but slightly in the Moon, there being but a few degrees difference between summer and winter. There are, however, periodic wind-storms, which recur with greater or less regularity once each sidereal month, due, I imagine, to the unequal distribution of crater openings through the crust of the Moon, a fact which must produce an unequal absorption of heat at various times and in certain localities. The natural circulation of the lunar atmosphere, affected as it is by the constantly-changing volume and direction of the sun’s rays, as well as the great range of temperature between the valleys and the ice-clad mountain peaks, produces frequent storms of greater or less violence. High winds are accompanied by violent rains upon the lower levels and blinding snowstorms among the barren heights above the vegetation line. Rains which fall from low-hanging clouds are warm and pleasant; those which come from high clouds are cold and disagreeable, yet however violent or protracted the storm, the illumination remains practically constant—there are never any dark, lowering days within the Moon, nor is there any night. CHAPTER III HUMAN QUADRUPEDS Of course we did not reach all these conclusions in a few moments, but I have given them here merely as the outcome of our deductions following a considerable experience within the Moon. Several miles from the ship rose foothills which climbed picturesquely toward the cloudy heights of the loftier mountains behind them, and as we looked in the direction of these latter, and then out across the forest, there was appreciable to us a strangeness that at first we could not explain, but which we later discovered was due to the fact that there was no horizon, the distance that one could see being dependent solely upon one’s power of vision. The general effect was of being in the bottom of a tremendous bowl, with sides so high that one might not see the top.