of the Earth's Orbit. 27 



of climate which have been proved to result from exccntricity. 

 The values have been determined at epochs 50,000 years apart. 

 From the extreme slowness with which the excentricity changes, 

 it was not deemed necessary for our purpose to determine them 

 at shorter intervals. The longitude of the perihelion is given 

 merely to show the great irregularity of the motion of the 

 major axis. 



We have already stated it as our opinion that the glacial epoch 

 of the geologist was the period beginning about 240,000 years 

 ago and extending down till about 80,000 years ago (' Reader/ 

 October 14, December 2 and 9). The time of the greatest cold 

 would be about 200,000 or 210,000 years ago. 



It will be seen from an inspection of the Table that the next 

 glacial epoch prior to this occurred about 750,000 years ago. 

 At that time the excentricity was exactly equal to what it was 

 210,000 years ago. Going back 50,000 years further, we find 

 the excentricity to be only 0*0132. But 50,000 years still fur- 

 ther back, viz. 850,000 years ago, the excentricity almost reached 

 its superior limit. It is quite possible that this, and not 200,000 

 years ago, may have been the period of the boulder-clay. Pro- 

 ceeding backwards the excentricity is again found to diminish, 

 but at the period 950,000 years ago it reached the high value 

 of 0*05 17. Here we have three glacial epochs following each 

 other in close succession — or rather, we should say, one long 

 glacial epoch of about 250,000 years broken up by two mild 

 periods 100,000 years apart. 



It is scarcely necessary to remind the reader that the mild 

 periods to which we allude have no resemblance to what we have 

 designated the warm periods of the glacial epoch resulting from 

 the occurrence of the winter solstice in the perihelion. During 

 those mild periods which occurred 800,000 and 900,000 years 

 ago, when the excentricity was at a low value, the general 

 character of the earth's climate would be similar to what it is at 

 present ; but during the warm, or rather, we should say, equable 

 periods resulting from the position of the solstice-point in rela- 

 tion to the perihelon, the climate would be widely different; 

 for during these periods the winters would be about as warm as 

 the summers. (See ' Reader/ December 9.) 



From the Table it will be seen that a similar condition of 

 things will occur between 800,000 and 1,000,000 years to come. 

 There will occur three glacial epochs in succession — namely, at 

 the periods 800,000, 900,000, and 1,000,000 years to come. 



The calculations have been made from formulae given by 

 M. Leverrier in his " Memoir on the Secular Variations of the 

 Elements of the Orbits of the Planets," published in the "Addi- 

 tions" to the Connaissance des Temps for 1843. 



