:i9o6.] SEE— THE CAUSE OF EARTHQUAKES. 345 



contraction than other parts. The deflection toward the land at the other 

 six coast-stations can of course easily be understood without at all calling in 

 question the theory. The proximity of the land may easily be conceived 

 sufficient to counteract any effect of the more distant parts of the ocean. It 

 is the fact of even some of the deflections being toward the sea, that bears 

 testimony to the theory, while the others offer no argument to the contrary." 

 " The least, then, that can be gathered from the deflections of these 

 coast-stations is, that they present no obstacle to the theory so remakably 

 suggested by the facts brought to light in India, viz., that mountain-regions 

 and oceans on a large scale have been produced by the contraction of the 

 materials, as the surface of the earth has passed from a fluid state to a con- 

 dition of solidity — the amount of contraction beneath the mountain-region 

 having been less than that beneath the ordinary surface, and still less than 

 that beneath the ocean-bed, by which process the hollows have been produced 

 into which the ocean has flowed. In fact the testimony of these coast-sta- 

 tions is rather in favour of the theory, as they seem to indicate, by excess of 

 attraction towards the sea, that the contraction of the crust beneath the 

 ocean has gone on increasing in some instances still further since the crust 

 became too thick to be influenced by the principles of floatation, and that 

 an additional flow of water into the increasing hollow has increased the 

 amount of attraction upon stations on its shores." ^ 



We have quoted this paragraph to recall how geodesists have 

 heretofore attempted to explain the comparative lightness of the 

 matter beneath the mountains, and the greater density of that 

 beneath the plains and especially beneath the sea. 



Pratt elsewhere says that the hidden cause of the deflection of 

 the plumb line between the mountain masses on the north and the 

 Indian Ocean on the south " may He below, in the variations of the 

 density of the earth's crust." - He then examines various arrange- 

 ments of density, and finally calculates by three hypotheses that 

 the sea level in Great Britain stands at a mean height of 1,567 

 feet higher than it would if the ocean hemisphere with pole in New 

 Zealand became land, other things remaining equal. 



§ 28. Pratt's theo7'em on the eqidlibrmni of the earth hetiveen the 

 land and zvater hemispheres.^ "" 



" There is no doubt that the solid parts of the earth's crust beneath the 

 Pacific Ocean must be denser than in the corresponding parts on the op- 

 posite side, otherwise the ocean would flow away to the other parts of the 

 earth. The following reasoning will explain this. Suppose the earth to be 

 a sphere. Through any point on it suppose a surface drawn separating a 



^ " Figure of the Earth," 3d edition, p. 137. 



^ Ibid., p. 148. 



^ Ibid., pp. 159-160. 



