GRAVITATION. 81 



Not many years after, a similar experiment was tried in 

 Scotland, upon Mt. Schehallien, with a similar result ; and 

 the influence of the mountain in drawing the weight from 

 a true perpendicular was established beyond a doubt.* 



The particular object of the experiment with Schehal- 

 lien, was not to prove the reality of the attraction exert- 

 ed by the mountain, for this was considered as previously 

 settled, but, to prove from the amount of the attraction 

 accurately ascertained, the iveigkt of the, earth. The 

 size of the mountain was ascertained, and also its at- 

 tracting force, and these were compared with thxxse of 

 the earth, and the result showed that the earth attracted 

 more in proportion to its size than the mountain. The 

 philosophers inferred from this that it was composed of 

 heavier, i. e. denser materials, in the proportion of about 

 two to one. 



5. GRAVITATION OF SMALL BODIES ON THE EARTH'S 

 SURFACE TOWARDS EACH OTHER. 



The preceding facts and statements, going as far as 

 they do towards establishing the fact that every portion 

 of matter attracts and is attracted by a',1 other matter, 

 will very naturally suggest the inquiry whether this 

 power is perceptible between small bodies on the earth's 

 surface. It will be said that if this tendency of matter 

 to approach matter is universal, two balls placed upon a 

 level table would have a tendency to roll together. This 

 tendency might exist, and yet not be easily manifested ; 

 for an attractive power, which, in so large a mass as the 

 earth, might have power to move rocks and avalanches 



* The reader may perhaps have the curiosity to inquire how the 

 deviation of the plumb line from the perpendicular, and particularly 

 its exact amount could be sustained. A telescope was fixed in a 

 perpendicular position by a plumb line, and then moved from 

 its position until it pointed towards a certain fixed star. The dis- 

 tance to which it was moved was noted. The apparatus was then 

 taken to the opposite side of the mountain, and the observation re- 

 peated. It was found that the distance to which the telescope was 

 moved, was different at the two stations. This would not have been 

 the fact, if the plumb lines had been parallel. For the fixed star is 

 at so great a distance that its apparent direction would be in both 

 cases the same. 



