THE EARTH AS IT IS. 81 



centre c would be PePe. The truth in regard to the 

 shape of the earth is represented here, but much exag- 

 gerated how much you shall see. The line PP is on 

 the scale of 2600 miles to the inch, to represent the 8000 

 miles of the earth's diameter. Of course ^th of an inch 

 would be 260 miles, and to make the amount of exagger- 

 ation alluded to above apparent to the eye, an inner cir- 

 cle at this distance from the outer one is drawn. You 

 see, then, that a tenth of the distance between the outer 

 and inner circle (-^nf ) would be 26 miles, and the bulging 

 of the earth at the equator is but half of this amount. 

 To get at the real, unexaggerated fact, then, you must 

 take only the -^jth part of the distance from e to the in- 

 ner circle to represent the bulging of the earth, and this 

 would be adequately represented by merely doubling the 

 line of the figure at e, and letting it gradually diminish to 

 the single line as you go to the poles PP. But small, 

 comparatively, as this equatorial bulging is, it is supposed 

 to be of very great importance in tending to keep the 

 earth always revolving uniformly on one axis the polar 

 axis. With the very rapid revolution of the earth (1000 

 miles every hour), and its more rapid motion in its orbit 

 (68,000 miles every hour), even a slight deviation from 

 regularity in the revolution would be attended with dis- 

 astrous results. There are inferences to be drawn from 

 the shape of the earth in reference to its formation, but 

 these will be spoken of in another chapter. 



158. Crust of the Earth. In the crust of the earth, so 

 often spoken of by geologists, is included all that portion 

 of the globe of which we have any knowledge through 

 their investigations. Of course we know nothing defi- 

 nitely and certainly of the contents of the interior of the 

 earth ; but great depths have been reached in mining, 

 and besides, as you will see in future portions of this 

 book, there have been upheavals of the crust which have 

 opened to view vastly greater depths than the miner has 

 ever reached. The foundation of this crust is every 

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