38 On the Solar Eclipse, 



of the same mountain : the elevation of which, may thus be de- 

 termined to a high degree of accuracy. 



The uniformity of appearance, exhibited by the lunar moun- 

 tains, has been already noticed. This seems to have arisen from 

 the operations of two causes — ^similarity in the grouping, and 

 diversity in the angular position of this " mountain scenery." 

 Generally speaking, it would appear that few detached or soli- 

 tary elevations of any magnitude exist on the moon's surface ; 

 but on the contrary, that the mountains are arranged in exten- 

 sive chains, running in different directions, and separated from 

 each other by large tracts of comparatively low and level ground. 

 On this supposition the appearances already described can easily 

 be explained as optical effects arising from variety of position 

 with regard to the eye of the observer. The appearance of 

 ridges, precipitous at one extremity and sloping gradually 

 towards the other, would be exhibited by those chains which 

 had a direction nearly parallel to the circumference, and which 

 rising immediately from it, atone end, exposed to view the whole, 

 or nearly the whole, elevation of the terminating mountains. By 

 a small inclination from this direction, they v/ould recede towards 

 the interior of the disc either by crossing the periphery, or advanc- 

 ing forwards on the side presented to the spectator ; and in both 

 cases, the elevation would appear gradually to subside, from the 

 spherical surface rising above their summits. In like manner those 

 chains which crossed the circumference nearly at right angles, 

 and placed therefore in the line of vision, would present the ap- 

 pearance of one lofty eminence, towering from a base situate di- 

 rectly on the extreme margin of the disc. This seems to account 

 for the superior altitude of these apparently isolated mountains ; 

 a circumstance which otherwise is difficult to explain. About 

 3" after the central conjunction, that is, about P 51' 40" nearly, 

 an appearance was observed which seems further to confirm 

 this hypothesis. Fig. 4. From the point where the western 

 limbs of the sun and moon appeared to cross, a broad stream 

 of pale reddish light, was seen to dart from the moon's circum- 

 ference, and extending along that part which was not upon the 

 solar disc, illumined with a mild steady lustre, a considerable 



