' UN THK (.KNkKAl. FORM AM' 



increase of density towards the centre does not pre- 

 vent it from being a homogeneous substance, chemi- 

 cally speaking, it is to conjecture of what chemistry 

 is unable to comprehend at present, from not knowing 

 what the consequences of extreme compression would 

 he on any substance. 



The same general results are deducible from those 

 experiments by which the actual specific gravity of the 

 globe of the earth has been determined : it ought ra- 

 ther to be said, by which an approximation has been 

 made to the solution of this problem. It is not here 

 necessary to describe the experiment of Mr. Cavendish ; 

 but a brief sketch of that of Dr. Maskelyne, will not 

 be uninteresting to the geological reader ; as its accu- 

 racy involves certain questions respecting the nature 

 and disposition of the rocks at the surface of the earth. 



In this experiment, a trigonometrical survey of the 

 mountain Schihallien was made, by which its figure 

 and bulk, as far as these were necessary, were ascer- 

 tained ; Meridional stations were then selected on 

 opposite sides, and the distance between these being 

 referred to the known length of the meridian at that 

 parallel, their latitudes were inferred The apparent 

 difference of latitude, deduced from the zenith dis- 

 tances of certain stars observed from the two stations, 

 being then compared with that obtained from the 

 trigonometrical measurement, was found to be 11 '',6 

 greater. Thus the sum of the deviations of the 

 plumb line at the north and south observatories was 

 computed ; the zenith positions having been separa- 

 ted from each other in consequence of the attractions 

 of the plummet towards the vertical, by the mass of 

 the hill. By subsequently comparing the attraction 

 of this mass with that of the whole earth, or to the 

 force of gravity, it was found to be as 1 to 1 7804. 



