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Page:Popular Science Monthly Volume 34.djvu/171

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NEW LIGHT ON A LUNAR MYSTERY.

and it comes from that center of astronomical interest, the Lick Observatory. Prof. Holden believes that he has discovered, if not one of the same objects described by Herschel, a phenomenon of the same kind. It is hardly necessary to say that Prof. Holden has not discovered a lunar volcano in action, but the extraordinary appearance that he has seen sufficiently accounts for Herschel's mistake. It will be best to quote the Lick Observatory director's own words from his letter on the subject to "The Observatory," an English astronomical journal:

"I have never been able to understand how Herschel, the keenest of observers, could have been deceived in this observation until the night of July 15th of this year, when I was looking at the moon with the great telescope. At the southern extremity of the Alps, in the dark portion of the disk, not far from the terminator, I saw an illumination of the crest of a high peak which was extraordinarily and incredibly bright. . . . No part of this illumination seemed less bright than a first-magnitude star, and, taken altogether, it was the brightest object I have ever seen in the sky. It was apparently ten times as bright as neighboring portions of the moon's surface. Its yellow light was tinged in places with the purple due to the secondary spectrum of the objective; and, viewed as a whole, it presented the appearance of a vast conflagration—something quite foreign to the brilliant white of the rest of the moon's surface.

"It would have required no stretch of the imagination to have supposed it to be a tremendous eruption of a range of lunar volcanoes. . . . Observations on this and the succeeding nights showed that it was in fact due to a specially brilliant and favorable illumination of a mountain-ridge near the southern termination of the lunar Alps.

"I have now no doubt that the observation of Sir William Herschel referred to similar appearances."

Prof. Holden then refers to a similar, though less brilliant, display that was witnessed in 1843 by Dr. Gerling, of Marburg, apparently at the same spot on the moon.

I may add that there are at least two other recorded apparitions of this sort which were seen in that neighborhood, but evidently not in exactly the same place. The first was observed by Schroeter, the German selenographer, in 1788. He saw in the shadow of the great range of the lunar Alps, at the eastern foot of the mountains, a bright point, as brilliant as a fifth-magnitude star, which disappeared after he had watched it for fifteen minutes. Subsequently, when the region where this light appeared had become fully illuminated by the rising sun, Schroeter perceived, where the light had been, a round shadow on the surface of the moon, which was sometimes gray and sometimes black.