32 Lunar Details. 



The E. portion of M. Hcemus, which runs off into the 

 M. Vwporum, attains a less elevation than the other end, and 

 can scarcely be termed mountainous. In concluding their 

 description of this region, B. and M. remark the striking and 

 unmistakeable contrasts of reflective power that are here 

 crowded into a small space., and are many of them independent 

 of the relief of the surface. In general the mountains are 

 bright, and the valleys dark. Yet, under an oblique illumina- 

 tion, it is obvious how slight or imperceptible a difference of 

 level is frequently combined with great inequality of light, 

 while in other far more uneven regions, such as those lying JST. 

 of the M. Serenitatis, and the Carpathian Mts., not to mention 

 the S.W. Quadrant, an uniform degree of brightness prevails. 

 Is this, they inquire, to be ascribed to some peculiar cause 

 in the original formation of the moon, or to some persistent 

 reason ? This district seems to them highly worthy of a 

 more careful and less fragmentary investigation than it has 

 yet received ; they content themselves, however, with remark- 

 ing that they have repeatedly thought that the separate 

 portions of the surface nowhere show a clear and decided 

 " light-tone," but rather an almost inextricable mixture, as 

 though from a mechanical union of specks of light and dark- 

 ness. It does not seem very likely that a larger instrument 

 than that used by B. and M. (which had barely 4| inches of 

 aperture) would be of any great service in unravelling these 

 mysteries, since the superfluous amount of light in the 

 brighter portions would produce a dazzling, rather than a 

 discriminating effect. But with the addition of a lightly- 

 tinted screen-glass, great apertures might prove very efficient ; 

 though an objection may possibly lie against the employment 

 of a coloured medium in very delicate observations, from the 

 partial absorption it must exercise on light, the composition of 

 which is uncertain : in this point of view an interesting experi- 

 ment might be tried, by the successive introduction of a 

 number of differently tinted screens of equal depth, the result 

 of which might possibly be the detection of colours in the 

 moon, too delicate to be otherwise recognized. But — excepting 

 for such an investigation — it is probable that the employment 

 of an unsilvered glass speculum might produce the most satis- 

 factory result. On this subject the reader may be referred to 

 Dr. Draper's experience, recorded in our last number; and 

 there seems reason to beheve that an instrument of this kind, 

 ensuring the defining power which is the result of large aper- 

 tures, without either an overpowering glare of light, or any 

 objectionable mode of lessening it, might be found of especial 

 value in lunar observation. 



