In Appleton's Cyclopædia, article "The Moon," it is stated that "Schröter (about 1800) claimed to have discovered indications of vegetation on the surface of the moon. These consist of certain traces of a greenish tint which appear and reappear periodically; much as the white spots covering the polar regions of Mars.... As we are able, under the most favorable conditions, to use upon the moon telescopic powers which have the effect of bringing the satellite to within one hundred and fifty to one hundred and twenty miles of us, we should doubtless notice any such marked changes on her surface as the passage of the seasons produces, for example, on our own globe." Very recently (August 12, 1894), it has been stated, Professor Gathmann has observed a peculiar green spot about forty by seventy miles in area near the crater of Tycho Brahe, "on the northwestern edge of the satellite's upper limb," which had disappeared twenty-two hours afterwards. We understand, of course, that the moon's librations, by the variation of position of the lunar body, enable us to see, at times, around the edge of this satellite somewhat, so that, instead of observing only one-half, we can in this way see nearly six-tenths of her surface, but not at the same time, of course. When the moon is dark it occupies a position between the earth and the sun, and only its opposite face is illuminated. In this position the attraction of solar gravity and the attraction of the electrically opposite solar electrosphere both accumulate their forces upon the moon's atmosphere in the same line as the repulsion of the earth's similar electricity, so that the lunar moisture and atmosphere are, at this part of her subordinate orbit, most powerfully forced away from the direction of the earth. As the moon now proceeds towards her first quarter, the terrestrial repulsion drives her atmosphere radially outward, while solar gravity and electrical attraction tend to hold it in the direction of the sun. The result will be an electrospheric libration, so to speak, and the moon's atmosphere and moisture will be carried around towards its illuminated face and, to some extent, will overlap the area of terrestrial repulsion. But as the moon advances this will gradually diminish, soon cease, and finally be reversed as it again approaches darkness. We can now understand why the green surface, if it really was due to vegetation, appeared along the lunar margin at the time described above, and also that the observation of planetary occultations "at the unilluminated edge of the young moon" was the very worst part of the moon and its orbit in which to look for air or moisture; as the sun's influence is then directly away from the unilluminated surface of the moon, and his "pull" would have, in fact, still further denuded the very portion most persistently examined, and where this absence of atmosphere was especially noted.