NEW LIGHT ON A LUNAR MYSTERY. 159 



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 extraordi- 

 nary appearance that he has seen sufficiently accounts for Her- 

 schel's mistake. It will be best to quote the Lick Observatory 

 director's own words from his letter on the subject to " The Ob- 

 servatory," an English astronomical journal : 



" I have never been able to understand how Herschel, the keen- 

 est 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 ex- 

 traordinarily and incredibly bright. . . . No part of this illumi- 

 nation 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 conflagra- 

 tion — 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 favor- 

 able illumination of a mountain-ridge near the southern termina- 

 tion 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, dis- 

 play that was witnessed in 1843 by Dr. Gerling, of Marburg, ap- 

 parently at the same spot on the moon. 



I may add that there are at least two other recorded appari- 

 tions of this sort which were seen in that neighborhood, but evi- 

 dently 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 min- 

 utes. Subsequently, when the region where this light appeared 

 had become fully illuminated by the rising sun, Schroeter per- 

 ceived, where the light had been, a round shadow on the surface 

 of the moon, which was sometimes gray and sometimes black. 



