22 ON THE GENERAL FORM AND 



from the merits of Mr. Playfair, it is more than doubt- 

 ful whether he has succeeded in determining this 

 point. If the form and situation of this mountain 

 were such as to offer great conveniences to the mathe- 

 maticians engaged in this problem, it is, unfortunately, 

 deficient in uniformity and simplicity of structure. 

 Not only is it a matter of extreme difficulty to ascer- 

 tain the true distribution* of the strata throughout the 

 whole mass, but the specific^gravities of the different 

 materials vary in such a manner as to vacillate between 

 2,4 and 3, or even more. All the strata are, at the 

 same time, elevated at high, but unequal angles ; 

 while it is also difficult to discover their relative pro- 

 portions on the surface, and, still more, the positions 

 which the rocks of different specific gravities assume 

 in the interior of the mountain ; a circumstance of 

 considerable importance, on account of the angular 

 differences of the action of the several columns on the 

 plummet. The different strata, it must be remarked, 

 consist of quartz rock, micaceous schist, hornblende 

 schist, and limestone. 



Under these uncertainties, a true mean specific 

 gravity could neither be determined nor applied; that 

 element could only have been perfect, in this case, 

 when the actual specific gravity of each attracting part 

 of the hill, and the quantity of each, were ascertained. 

 A tolerable approximation, it is probable, has never- 

 theless been made. 



It must now however be further observed, that such 

 are the difficulties which attend an accurate solution 

 of this important problem by this method, that the 

 plan pursued by Mr. Cavendish is preferred by ma- 

 thematicians, as are the results which have been ob- 

 tained by means of it. La Place, nearly following 

 this, makes the mean density of the Earth to be 02 



