COMMON THINGS THE EARTH. 



The fixity and absolute repose of the globe of the earth being 

 assumed by the ancients as a physical maxim which did not even 

 admit of being questioned, they perceived the inevitable character 

 of the alternative which the apparent diurnal rotation of the 

 heavens imposed upon them, and accordingly embraced the hypo- 

 thesis, which now appears so monstrous, and which is implied in 

 the term TTNTVERSE, which they have bequeathed to us. 



21. But with the knowledge which has been obtained by the 

 labours of modern astronomers respecting the enormous magnitudes 

 of the principal bodies of the physical universe, magnitudes 

 compared with which that of the globe of the earth dwindles to a 

 mere point, and their distances under the expression of which the 

 very power of number itself almost fails, and recourse is had 

 to colossal units in order to enable it to express even the smallest 

 of them, the hypothesis of the immobility of the earth, and the 

 diurnal rotation of the countless orbs of magnitudes so incon- 

 ceivable filling the immensity of space once every twenty-four 

 hours round this grain of matter composing our globe, becomes 

 so preposterous that it is rejected, not as an improbability, but as 

 an absurdity too gross to be even for a moment seriously enter- 

 tained or discussed. 



22. But if any ground for hesitation in the rejection of this 

 hypothesis existed, all doubt would be removed by the simplicity 

 and intrinsic probability of the only other physical cause which 

 can produce the phenomena. The rotation of the globe of the 

 earth upon an axis passing through its poles, with an uniform 

 motion from west to east once in twenty- four hours, is a suppo- 

 sition against which not a single reason can be adduced based on 

 improbability. Such a motion explains perfectly the apparent 

 diurnal rotation of the celestial sphere. Being uniform and free 

 from irregularities, checks, or jolts, it would not be perceivable by 

 any local derangement of bodies on the surface of the earth, all of 

 which would participate in it. Observers upon the surface of our 

 globe would be no more conscious of it, than are the voyagers shut 

 up in the cabin of a canal boat, or transported above the clouds in 

 the car of a balloon. 



23. It has been shown that a body descending from a great 

 height does not fall in the true vertical line, which it would if the 

 earth were at rest, but eastward of it, which it must, if the earth 

 have a motion of rotation from west to east.. 



24. An ingenious expedient, by which the diurnal rotation of the 

 earth is rendered visible, has been conceived and reduced to 

 experiment by M. Leon Foucault. This contrivance is based upon 

 the principle, that the direction of the plane of vibration of a 

 pendulum is not affected by any motion of translation which may 



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