34 On. the Sol ai' Eclipse, 



therefore, if a review be taken of those which have been given 

 in the course of the last forty years, their results will be found 

 to range from ^ to 5 miles, giving a medium elevation of 

 upwards of 2 miles. The altitudes, however, of the two moun- 

 tains in question, as already stated, fall far short even of the 

 mean, since the higher appears to have extended 1 f , and the 

 other, 1 ^0 miles only in perpendicular elevation. There is 

 this important distinction also, that the two on which these ob- 

 servations were made, appeared to be equal in height to any 

 others visible on the moon's circumference ; hence there is no 

 reason to conclude, that any much higher exist on the planet. 

 But instead of taking the mean as the standard elevation, a 

 comparison is rather to be instituted from those which may 

 justly be considered as the most accurate calculations on this 

 subject. During the above period, few obsei'vers, if any, have 

 given the same attention to the subject, and certainly no one 

 has brought to its examination more of science or practical skill 

 than Sir William Herschel ; who, after a series of observations 

 continued for years, comes to the conclusion, that " when we 

 have excepted a few, the generality of the lunar mountains, does 

 not exceed half a mile in perpendicular elevation." The altitudes 

 of some which were formerly estimated from 8 to 3 miles, in 

 the account of these observations, are stated to extend from f 

 to 1£ miles. The latter is the elevation of mo7is sacer, and 

 is considered by Sir William as mach overrated, owing to cir- 

 cumstances which impeded the observations*. With these 

 measurements, the present results nearly agree ; and it may, 

 perhaps, be regarded as a presumption in favour of their 

 accuracy, that they thus coincide with statements of such high 

 authority, although deduced from principles so totally different. 

 When these calculations, likewise, are compared with the 

 results which analogy furnishes, their agreement is almost 

 equally satisfactory. At the surface of the moon, gravity 

 being diminished nearly one-third, its mountains are probably 

 somewhat more elevated in proportion than those of the earth. 



* Phil. Trans. 



