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LUNAR CELESTIAL PHENOMENA.

Accordingly, if on the moon there were an atmo-sphere constituted like ours, and sufficient in quantityto cover the moon’s surface to a depth of about 5|miles of uniform specific gravity equal to that of ourair at the sea-level, then such an atmosphere underthe moon’s smaller attracting power would expand sogreatly that the half nearest the moon would extendto a height of about 22 miles.* At the mean level ofthe moon’s surface,—that is, a level correspondingpretty nearly to our sea-level, so as to be as muchabove the greatest lunar depressions as below thegreatest lunar heights,—the pressure would be aboutone-sixth that at our sea-level. Thus it is seen thateven though the lunarians had as much air per mile ofsurface as we have on the earth, they would have amuch rarer atmosphere. At a height of seven milesfrom the earth, a greater height than has ever yetbeen attained, or than could be attained by man,t the

* Here I take no account of the reduction of the moon’s attractingpower at this height from the surface. The consideration of suchreduction would be important, however, in estimating the heightto which the rarer strata would extend.

f “In the celebrated ascent by Messrs. Glaisher and Coxwell, inwhich the greatest height yet reached by man was attained, Mr. Glaisher became insensible before the balloon had attained a heightof six miles. Mr. Coxwell, after endeavouring to rouse Mr. Glaisher ,found that he was himself losing his strength. Indeed, he wasunable to use his hands, and had he not succeeded in pulling thevalve-string with his teeth, he and his companion must inevitablyhave perished. The height attained before the string was pulledwould seem, from an observation made by Mr. Coxwell, to havebeen about 6£ miles. At this time the temperature was 12° below