If the Moon has no air, and no liquids of any sort, it seems impossible that its surface can maintain any form of life, either vegetable or animal, analogous to those on the Earth. In fact, nothing indicating life has been detected on the Moon--our satellite looking like a barren, lifeless desert. If life is to be found there at all, it must be of a very elementary nature. Aside from the want of air and water to sustain it, the climatic conditions of our satellite are very unfavorable for the development of life. The nights and days of the Moon are each equal to nearly fifteen of our days and nights. For fifteen consecutive terrestrial days the Sun's light is absent from one hemisphere of the Moon; while for the same number of days the Sun pours down on the other hemisphere its light and heat, the effects of which are not in any way mitigated by an atmosphere. During the long lunar nights the temperature must at least fall to that of our polar regions, while during its long days it must be far above that of our tropical zone. It has been calculated that during the lunar nights the temperature descends to 23° below zero, while during the days it rises to 468°, or 256° above the boiling point. It has been a question among astronomers whether changes are still taking place at the surface of the Moon. Aside from the fact that change, not constancy, is the law of nature, it does not seem doubtful that changes occur on the Moon, especially in view of the powerful influences of contraction and dilatation to which its materials are submitted by its severe alternations of temperature. From the distance at which we view our satellite, we cannot expect, of course, to be able to see changes, unless they are produced on a large scale. Theoretically speaking, the largest telescopes ever constructed ought to show us the Moon as it would appear to the naked eye from a distance of 40 miles; but in practice it is very different. The difficulty is in the fact that, while we magnify the surface of a telescopic image, we are unable to increase its light; so that, practically, in magnifying an object, we weaken its light proportionally to the magnifying power employed. The light of the Moon, especially near the terminator, where we almost always make our observations, is not sufficiently bright to bear a very high magnifying power, and only moderate ones can be applied to its study. What we gain by enlarging an object, we more than lose by the weakening of its light. Besides, a high magnifying power, by increasing the disturbances generally present in our atmosphere, renders the telescopic image unsteady and very indistinct. On the whole, the largest telescopes now in existence do not show us our satellite better than if we could see it with the naked eye from a distance of 300 miles or more. At such a distance only considerable changes would be visible.