220 ASTRONOMYr 



a body may be made to turn round, are as many as can be 

 drawn through its centre to opposite points upon its whole 

 surface ; but of these axes none are permanent^ except 

 either its shortest diameter, i. e. that which passes through 

 the heart of the orange from the place where the stalk is 

 inserted into it, and which is but one ; or its longest diame- 

 ters, at right angles with the former, which must all ter- 

 minate in the single circumference which goes round the 

 thickest part of the orange. This shortest diameter is 

 that upon which in fact the earth turns ; and it is, as the 

 reader sees, what it ought to be, a permanent axis ; where- 

 as, had blind chance, had a casual impulse, had a stroke or 

 push at random, set the earth a-spinning, the odds were in- 

 finite, but that they had sent it round upon a wrong axis^ 

 And what would have been the consequence? The difference 

 between a permanent axis and another axis is this. When 

 a spheroid in a state of rotatory motion gets upon a perma- 

 nent axis, it keeps there ; it remains steady and fakhful to 

 its position ; its poles preserve their direction with respect 

 to the plane and to the centre of its orbit ; but, whilst it 

 turns upon an axis which is not permanent, (and the num- 

 ber of those, we have seen, infinitely exceeds the number 

 of the other,) it is always liable to shift and vacillate from 

 one axis to another, with a corresponding change in the 

 inclination of its poles. Therefore, if a planet once set off 

 revolving upon any other than its shortest, or one of its long- 

 est axes, the poles on its surface would keep perpetually 

 changing, and it never would attain a permanent axis of 

 rotation. The effect of this unfixedness and instability 

 would be, that the equatorial parts of the earth might be- 

 come the polar, or the polar the equatorial ; to the utter de- 

 struction of plants and animals, which are not capable of 

 interchanging their situations, but are respectively adapted 

 to their own. As to ourselves, instead of rejoicing in our 

 temperate zone, and annually preparing for the moderate 

 vicissitude, or rather the agreeable succession of seasons, 

 j^hich we experience and expect, we might come to be 

 locked up in the ice and darkness of the arctic circle, with 

 bodies neither inured to its rigours, nor provided with shel- 

 ter or defence against them. Nor would it be much bet- 

 ter, if the trepidation of our pole, taking an opposite course, 

 should place us under the heats of a vertical sun. But, if 

 it would fare so ill with the human inhabitant, who can 

 live under greater varieties of latitude than any other ani- 

 mal, still more noxious would this translation of climate 



