112 THE WORLD. 



now about the 1st of January, but 50,000 years hence, it will be 

 in its perihelion in July, or time of mid-summer in the northern 

 hemisphere, and at that time the* earth's axis will be inclined 

 nearly as at present, unless changed by some great convulsion^- 

 The effect of this change of the direction of the line of apsides 

 will be therefore, to cause the earth to arrive at its perihelion at 

 the time of mid-summer in the northern hemisphere, instead of 

 at mid-winter as at present, thus producing, if the relative distri- 

 bution of land and water remains unchanged, a tropical climate 

 or nearly so, over the whole globe. . 



Such periods of time are however, too remote to be worth much 

 notice from us, except for their interest in a geological point of 

 view, for we believe this to be the true explanation of the greater 

 warmth of the climate of the ancient world, as indicated by fossil 

 flora and fauna ; we shall refer to this again. 



We have given no explanation of the cause of the precession 

 of the equinoxes, or the motion of the apsides. It would be 

 extremely difficult for us to do so in a manner intelligible to the 

 general reader. The facts, however, are unquestionable. The 

 former is caused by the attractions of the sun and moon upon the 

 excess of matter at the equator, for the earth is not truly spherical, 

 but oblate, on account of its diurnal rotation. This equatorial 

 belt, not corresponding with the plane of the ecliptic, is acted upon 

 obliquely, and with varying force by the sun and moon, producing 

 the retrogradation of the nodes. The motion of the apsides is the 

 conjoint effect of the attractions of the planets upon the earth in 

 the various parts of its orbit. 



We here close the first part of our volume, not however, with- 

 out the hope that we have succeeded in making it interesting, 

 and that the reader will feel repaid for the time spent in peru- 

 sing it. 



