378 Cause of Glacial Epochs. 



furthest from the sun (aphelion), the distance is about 

 90 millions of miles, and its smallest distance (peri- 

 helion) is about 89,864,480 miles. The varying amount 

 of ellipticity is owing to the ever-changing positions of 

 the planets in our solar system within and without the 

 orbit of rotation of the earth, and we can imagine a state 

 of combination of the planets, the effect of the attraction 

 of which must be to lengthen the ellipse in the extremest 

 possible degree, so that the earth in aphelion would be 

 98^ millions of miles distant from the sun. This is not 

 a mere guess, for it has been approximately calculated 

 by Leverrier and other astronomers. The eccentricity 

 of the earth's orbit is at present decreasing, and it will 

 reach its minimum in about 24,000 years. 



In connection with degrees of eccentricity, Dr. 

 Croll argues that the distribution of ocean-currents is 

 due to the system of winds, and in the modern world the 

 existing system of winds is due to those astronomical 

 causes that, by help of eccentricity have produced a 

 minor glacial epoch in part of the southern hemisphere 

 at the present day, and a remarkably mild one over 

 Western Europe and great part of the north. This 

 coincidence of winds and great ocean currents is shown 

 by Dr. Croll in a map, the most familiar of which to 

 us, being the westerly and south-westerly winds and 

 currents of the Gulf Stream, the warm winds from 

 which so largely raise the average temperature of 

 the British Islands and the whole of the western part of 

 Europe. There being nothing equivalent to this current 

 running south towards the great Antartic Continent of 

 Victoria Land, this circumstance, taken in connection 

 with the fact that the southern winter occurs in aphelion, 

 has produced in that region a minor glacial epoch, so 

 that in south latitudes, between about 64 and 78, the 



