258 The Lunar Taurus (S.) and Argwus — Occultations. 



E. side, where there is a small crater of 6-|°. Proclus, more 

 than 18 miles across, is of difficult measurement in depth from 

 its position. Schroter, from a rough attempt, considered it 

 about 11,000 feet j B. and M. thought it exceeded 8300 feet 

 on the W., which is the deeper side. The ring (using that 

 expression in its stricter sense) is, after Aristarchus, the most 

 luminous in the moon, having 8° of light in its S., and 9° in its 

 N. portion ; the interior has only 4°. It is a remarkable fact 

 that, with so much brilliancy, it is barely to be distinguished 

 on the night-side. From its position Schroter inferred that it 

 ought to be nearly as conspicuous after the full as Aristarchus 

 before it — he found its site, however, either quite dark or very 

 feebly illuminated ; and much less conspicuous than the less 

 brilliant and worse situated Manilius and Menelaus ; in total 

 eclipse, too, it disappeared while other spots retained their 

 visibility. B. and M., who agree with him as to the fact, 

 explain it from the narrowness of the ring, which renders it 

 imperceptible with such low powers as are alone suitable for 

 examining the details of the dark hemisphere. 



The restricted breadth in this instance of the highly re- 

 flective portion is a curious and suggestive fact, though it is 

 difficult to assign any probable explanation of it. If the upper- 

 most ridge of the wall were of especial elevation, and exhibited 

 a graduated brilliancy, we might be led to the idea of a sub- 

 sequent " weathering" from the action of a low-lying atmo- 

 spheric stratum. But such is not the case, and the inference 

 would be totally at variance with appearances elsewhere. Nor 

 is it easy to see, in the face of many adverse instances, how 

 that particular part would be liable to a bleaching process from 

 more rapid cooling, or from the escape of vapour. If, on the 

 contrary, we should incline to the supposition of an original 

 difference in material, it is difficult to conceive how, amid the 

 violent disturbance of an eruption on so extended a scale, any 

 separate layer of matter could be so regularly deposited, and 

 on so limited a space. The last discharge, possibly of ashes, 

 might have a very distinct character, but would hardly exhibit 

 itself merely as the summit of a lofty ring. We may, perhaps, 

 collect that if we see its pristine condition, it never could have 

 been one of great fluidity. But it must be admitted that the 

 subject of lunar eruption is at present enveloped in much 

 obscurity. 



OCCULTATIONS. 



May 2nd, k Cancri, 5 mag., 7h. 53m. to 8h. 37m.— 4th, 36 

 Sextantis, llh. lm. to llh. 52m. 



