56 Mare Vcvporum and the Lunar Clefts. 



composition of which no new chemical element has ever been 

 detected, and from which we should infer a similarity of matter 

 throughout the solar system, strongly contravenes such specu- 

 lations. But the recent discoveries of Huggins, rendering it 

 highly probable that the atmospheres of Jupiter and Saturn 

 contain elements or combinations foreign to our knowledge, 

 again restore the balance, and enable us to call the worthy old 

 Hanoverian into court again. He always deserves at least a 

 hearing. 



Some other peculiarities of these clefts, pointed out by 

 B. and M., in their ' ' Beitr-age," may be mentioned, as the 

 result of their discovery, within six or seven years, of upwards 

 of seventy, in addition to less than twenty previously known. 

 Absolute straightness and singleness characterize the majority, 

 and the average bearing falls between 8h. and llh. of a clock- 

 dial, divided into 24h. There is an optical cause why they 

 should be frequently found in the line of the meridian, but 

 scarcely ever in a 6h. (or E. and W.) direction, namely, the 

 full development in the former, the absence in the latter case, 

 of that internal shadow by which they are most readily dis- 

 tinguished. But no such reason will explain why more than 

 fifty of them should be directed between 8h. and llh., and 

 only some thirty between lh. and 4h. It is remarkable, how- 

 ever, that the prevailing direction of all lunar objects is so 

 much the same that in some regions scarcely any other ten- 

 dency is perceptible ; that in the majority it predominates ; and 

 is absent from none ; so that ridges alike and clefts seem to 

 indicate a similar origin. 



As to that origin, B. and M. consider it to have been due 

 to a modification of the same eruptive force, the "reaction of 

 the interior/' as Humboldt would call it, which has so ex- 

 tensively modified the lunar surface. This would naturally 

 press outwards along the line of least resistance, or, on the 

 supposition of homogeneity of material, perpendicular to the 

 surface; and during its earlier and intenser action would 

 produce regularly circular cavities, or, if it encountered more 

 coherent material, roundish mountains ; as the activity de- 

 creased, and circumstances were changed by the great alter- 

 ation of level, as well as of cohesive power, the direction of 

 the force would be varied; it would take a horizontal course; 

 and while in general it elevated the surface into those long 

 ridges, or banks, of which instances are so abundant, it 

 would occasionally burst it open, so as to form burrows or 

 clefts. This speculation, which had been propounded by 

 Schr. at a much earlier period, does not seem to commend 

 itself by its plausibility. There is a difficulty in conceiving 

 the continuous progress, perhaps for hundreds of miles, of an 



