We did not rise much above five hundred feet from the opening of the well through which we had come from outer space when I descried an excellent landing place and determined to descend. This was readily accomplished, and we made a safe landing close to a large forest and near the bank of a small stream. Then we opened the forward hatch and stepped out upon the deck of _The Barsoom_, the first Earth Men to breathe the air of Luna. It was, according to Earth time, eleven A.M., January 8, 2026. I think that the first thing which engaged our interest and attention was the strange, and then, to us, unaccountable luminosity which pervaded the interior of the Moon. Above us were banks of fleecy clouds, the undersurfaces of which appeared to be lighted from beneath, while, through breaks in the cloud banks we could discern a luminous firmament beyond, though nowhere was there any suggestion of a central incandescent orb radiating light and heat as does our sun. The clouds themselves cast no shadows upon the ground, nor, in fact, were there any well-defined shadows even directly beneath the hull of the ship or surrounding the forest trees which grew close at hand. The shadows were vague and nebulous, blending off into nothingness at their edges. We ourselves cast no more shadows upon the deck of _The Barsoom_ than would have been true upon a cloudy day on Earth. Yet the general illumination surrounding us approximated that of a very slightly hazy Earth day. This peculiar lunar light interested us profoundly, but it was some time before we discovered the true explanation of its origin. It was of two kinds, emanating from widely different sources, the chief of which was due to the considerable radium content of the internal lunar soil, and principally of the rock forming the loftier mountain ranges, the radium being so combined as to diffuse a gentle perpetual light which pervaded the entire interior of the Moon. The secondary source was sunlight, which penetrated to the interior of the Moon through the hundreds of thousands of huge craters penetrating the lunar crust. It was this sunlight which carried heat to the inner world, maintaining a constant temperature of about eighty degrees Fahrenheit.