360 Neighbourhood of the Lunar Spot, Mare Crisium. 



craters. The aspect of the district is then so changed, that 

 its correct identification as to details requires actual measure- 

 ment. These great discrepancies, they observe, might easily 

 lead to the idea of casual atmospheric obscurations or other 

 changes; but continuous and persevering observation shows 

 that they are all periodical, and so entirely dependent upon the 

 angle of incident light, that an ephemeris of these phenomena 

 might be constructed to serve for every lunation. Vegetation 

 has been suggested, according to B. and M., by several astro- 

 nomers, as the cause of these appearances ; if so, it would 

 require to be of a nature to run its course in a single lunation. 

 In favour of this idea it might be alleged that many valleys of 

 a precisely similar character are to be met with, especially 

 nearer the Poles, that show no such grey tint, but preserve 

 their bright aspect under high illumination.* All this, how- 

 ever, is little to be depended upon ; and it must be admitted 

 that vegetation, in the absence of air and water, is to us incom- 

 prehensible. It had already occurred to Schroter that the 

 moon, from the very slight inclination of its equator to its 

 orbit, could possess scarcely any change of seasons; and that 

 therefore the functions dependent with us upon summer and 

 winter, might there be discharged by its lengthened day and 

 night; so that vegetation might be concerned in the change 

 of colour for which some spots are remarkable as contrasted 

 with others, in proportion to the increased anglo of the sun's 

 rays. (Jruithuisen, as might have been expected from him, 

 pushed the matter much further. He distinguished the grey 

 spots into three classes, each, as he fancied, characterised by 

 a "flora" of its own. 1. — Small levels of a very dark hue, 

 which undergo no change, and may possibly be covered with 

 forests of conifers ! 2. — Numberless dark spots which acquire 

 a deeper tone under the advancing light, among which ho 

 classes the Paludcs Amain' of Hovel, the very region we are 

 now discussing. 3. — The grey plains, which gradually grow 

 darker after sunrise, probably from the dispersion of a low 

 mist. And besides these ho noticed traces of another kind of 

 lunar flora, teqnirmg great attention to be perceived, reaching 

 as far as 2-7' of JN. latitude, and gradually creeping up the 

 valleys among the mountains as (lie sun attains its greatest 



height. Prom all this lie concludes that there is a lunar 

 ■ tation (Annprised between 65° N. and 55°S. latitude, most 



luxuriant. ne;ir the equator, and preserving an analogy between 



increasing relative height and Latitude similar to that which 

 obtains on the earth. Our readers could not be much won- 



* It CHcapod ~B. ami M. flint near tho Poles the sun's altitude would never be 

 sulliciciit to admit of a fair comparison. 



