ACCORDANCE OF QUANTITATIVE THEORIES, &c. 209 



possible refinement obtained a slightly higher number, 

 5-660. 



A different method of procedure consisted in ascertaining 

 the effect of a mountain mass in deflecting the plumb-line ; 

 for ? assuming that we can determine the dimensions and 

 mean density of the mountain, the plumb-line enables us 

 to compare its mass with that of the whole earth. The 

 Mountain Schehallien was selected for such an experiment, 

 and the observations and calculations performed by Maske- 

 lyne, Hutton, and Playfair, gave as the most probable 

 result, 4*713. The difference is considerable and the result 

 is valuable, because the instrumental operations are of an 

 entirely different character from those of Cavendish and 

 Baily's experiments. Sir Henry James' similar determin- 

 ation from the attraction of Arthur's Seat gave 5*14. 



A third distinct method consists in determining the 

 force of gravity at points elevated above the surface of 

 the earth on mountain ranges, or sunk below it in mines. 

 Carlini experimented with a pendulum at the hospice of 

 Mont Cenis, 6375 feet above the sea, and by comparing 

 the attractive forces of the earth and the mountains, found 

 the density to be still smaller, namely, 4*39, or as corrected 

 by Giulio, 4*950. Lastly, the Astronomer Royal has on 

 two occasions adopted the opposite method of. observing 

 a pendulum at the bottom of a deep mine, so as to compare 

 the density of the strata penetrated with the density of 

 the whole earth. On the second occasion he carried his 

 method into effect at the Harton Colliery, 1260 feet deep ; 

 all that could be accomplished by skill in measurement 

 and careful consideration of all the causes of error, was 

 accomplished in this elaborate series of observations 6 (see 

 vol. i.p. 340). No doubt Sir George Airy was much sur- 

 prised and perplexed when he found that his new result 



e 'Philosophical Transactions' (1856), vol. cxlvi. p. 342. 

 VOL. II. P 



