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eai-th's surface equal to a degree, was made in Lapland, by Clairaut, 

 who concluded that it was 66^ miles. The first attempt to 

 ascertain the density of the earth was made by Maskelyne, from 

 observations on the attraction of Schehallion. a mountain in Scotland. 

 He inferred that the earth was 41 times heavier than a globe of 

 equal size composed of water. Cavendish, by a different method, 

 arrived at a somewhat different conclusion, and fixed the proportion 

 at 5-48 to 1. Mining operations led to the discovery that the 

 temperature of the earth increases with the descent; and the 

 conclusion thence drawn that a fierce heat exists in the interior, 

 led to the nebular hypothesis of Laplace. This hypothesis is that 

 the whole of the solar system was at one time in a condition of fiery 

 mist or gas, from which the sun and all the planets and satellites, 

 through radiation of heat and condensation, have been evolved by 

 natural processes. 



Playfair. in his experiments, found that there were in-egularities 

 in the movement of the pendulum, owing to the varying density of 

 adjacent rocks, the density being less under a hill than on the plain. 

 There is found to be a bulge on the earth of about a mile in one 

 direction along a line of longitude, and another of about the same 

 amount in another direction almost opposite. The polar diameter 

 is shorter than the equatorial, in the proportion of 292 to 293. 

 Owing to the quantity of water heaped up on the southern hemi- 

 sphere, the centre of gravity of the earth is north of the centre of 

 figure. 



Rocks, as such, probably exist to the depth of twenty miles. 

 Many rocks are seen which have undergone an enormous amount of 

 shrinkage ; the layers of many mountains are found fantastically 

 contorted, and even overturned. The rocks extending through 

 Belgium are so twisted and crumpled, that, if spread out, they 

 would cover a space equal to three times the length of the country. 

 The condition of deeply-seated rocks is of course unknown ; but it 

 is not probable that there is fluidity anywhere, as pressure prevents 

 melting. Sir W. Thomson's investigations lead him to the con- 

 clusion that the earth is nearly as rigid as steel. 



The Lecturer stated that, according to the present state of our 

 knowledge, the earth is a spheroid, nearly rigid ; that its centre of 



