80 Intelligence and Miscellaneous Articles. 



NOTICE OF TRACKS OF EllUPTIVE ACTION IN THE MOON. 

 BY THE REV. T. W. AVEBB. 



The inquiry as to the continuance of volcanic or explosive action 

 on the surface of the moon must be admitted to be a very interesting 

 one. Astronomers are generally agreed as to its entire cessation on 

 any conspicuous scale ; but tliis would not necessarily infer the im- 

 possibility, or even improbabilit}', of minor eruptions, which might 

 still continue to result from a diminished but not wholly extinguished 

 force. Till the publication of the labours of Beer and Miidler, the 

 necessary data for the determination of the question were very im- 

 perfect ; and since that time the general impression would seem to 

 be adverse to the idea of any physical change. Before, however, it is 

 entirely acquiesced in, it may be well to see whether any evidence 

 of an opposite nature exists. Want of leisure has hitherto prevented 

 me from entering upon the subject in any other than the most Inci- 

 dental manner ; but I would request permission to direct attention to 

 one or two regions where an accurate investigation might be desirable. 



One of these is the spot named Cichus, near tlie south extremity 

 of the Mare Nubium. Here, many years ago, In comparing Schroter's 

 drawings with the moon, I was struck with the apparent enlargement 

 of the small crater which has defaced one side of the ring. On pro- 

 curing the map of Beer and Miidler, I found that they had also seen 

 it enlarged. Could we in this instance depend upon the older draw- 

 ings, we might reasonably infer the probability of a change since 

 the year 1792. Schroter was, undoubtedly, a coarse draftsman ; but 

 still he was faithful and careful, nor does there seem any appearance, 

 but the reverse, that his designs were copied from one another to save 

 trouble ; if not, the agreement of three separate figures seems fair 

 evidence that this little crater was not then of its present magnitude. 



The second case seems more satisfactory. It is that of the spot 

 Messier, in the Mare Fcecunditatis, where two small craters lie side 

 by side at the end of two parallel white streaks, resembling the di- 

 vided tail of a comet. In consequence of an observation of Schroter, 

 Beer and Miidler directed their attention especially to this region, 

 and examined It more than 300 times between the years 1829 and 

 1837, with the result that the two craters were perfectly and sin- 

 gularly alike in size, shape, height of ring, depth of cavity, and even 

 the position of some peaks upon the rings. I cannot say that I have 

 ever been able to obtain a perfectly distinct view of this spot, from 

 atmospheric causes ; but every sight i have had of It has strength- 

 ened my Impression that this remarkable similarity no longer exists. 

 I first noticed a difference in the aspect of the two craters in 1855, 

 Nov. 14. Since that time. In the occasional use of four instruments 

 of very dift'ereut size and power (one an object-glass of 5| inches 

 by Alvan Clark, now in my possession), I have invariably felt con- 

 vinced that neither in size, form, nor depth are those two craters any 

 longer precisely similar, but that, on tlie contrary, under suitable 

 angles of illumination, such as must have repeatedly occurred during 

 the 300 examinations by Beer and Miidler, the difference between 

 them is obviously so great as to indicate some permanent alteration 

 in the surface during the space of twenty years. — Proceedings of 

 the Royal Astronomical Society, vol. xix. p. 234. 



