CH. xxx. THE SCHEHALLIEN EXPERIMENT. 



279 



FIG. 47. 



exactly how much the lines D F will slope towards each 

 other when no mountain is between them. This measure- 

 ment being known, Maskelyne then made two observations, 

 one on each side of Schehallien, and found that in this case 

 the inclination, instead of being from D to F on each side, 

 was from E to F, because the mountain drew the lead towards 

 itself on either side. So the deflection E F D through which 

 the plumb-line was drawn 

 from the perpendicular showed 

 the difference between the pull 

 of the whole earth and the pull 

 of the mountain. 



Then Dr. Hutton, the cele- 

 brated geologist, set to work 

 to find out the size and weight 

 of Schehallien. This he did 

 by surveying it and measuring 

 it in every direction, and then 

 taking pieces of the different 

 rocks it contained and weigh- 

 ing them carefully. When 

 this was done it was found 

 that the mountain pulled half 

 as strongly in comparison to 

 its size as the earth did for its 

 size. This showed that the materials in the mountain were 

 half as heavy as the average of those in the earth generally, 

 and as they were also about 2\ times as heavy bulk for bulk 

 as water it was proved that the whole globe is about five 

 times heavier than it would be if it was made entirely of that 

 fluid. 



This calculation must be very near the truth, for the 



Schehallien Experiment for estimating 

 the Density of the Earth (Herschel). 



A E, Surface of the earth. D, c, D, Angle 

 formed by the two plumb-lines point- 

 ing to the centre of the earth. 

 E, G, E , Angle formed by the two 

 plumb-lines when drawn aside by the 

 mountain M. 



