24 THE BOTTOM OF THE SEA. 



Its entrance in Paris will neither be vertical nor 

 horizontal. It will at once pass at a considerable depth 

 under the English Channel and the ocean, notwith- 

 standing the comparatively great depth of the latter, 

 and will reach the surface at Newfoundland obliquely 

 as it had quitted Paris The same observation applies 

 to all the great seas. The form of the earth being 

 spherical, the bottom of the ocean, so far from being 

 a cavity, is in its general outline convex. 



In order to give the reader an exact idea of the 

 relative thickness of the solid crust of the earth, of 

 its liquid covering, and of its gaseous atmosphere, 

 we cannot do better than draw a section of the 

 equator (fig. 7). In the centre, marked by the 

 diagonal shading, is incandescent fire, of the charac- 

 ter of which we can only form a conception from 

 the productions of volcanic eruptions. A solid crust 

 of comparatively slight thickness envelopes the fluid 

 kernel, and rests upon it like a raft upon the waves. 

 When that internal sea of fire is agitated, its pal- 

 pitations are revealed to us by startling results — in a 

 word, by the breaking-up of that fragile crust upon 

 which repose all our hopes. 



This solid covering is enveloped by a double at- 

 mosphere. The lower (or aqueous) portion is not 

 adapted to our mode of existence ; we can but float 

 upon its surface. It is divided or broken up by the 



