and its Influence on Climate. 4-37 



into operation. But the condition of things, we have every rea- 

 son to believe, must have been affected by the greater obliquity 

 of the ecliptic at that period. We have no formula from which 

 we can determine with perfect accuracy the extent of the obli- 

 quity at a period so remote as the one under consideration. If 

 we adopt the formula given by Struve and Peters, we have the 

 obliquity at a maximum about the time that the solstice-point 

 was in aphelion. The formula given by Leverrier places 

 the maximum somewhat later. At all events w r e cannot be far 

 from the truth in assuming that at the time the northern winter 

 solstice was in aphelion the obliquity of the ecliptic was 

 about a maximum, and that since then it has been gradually 

 diminishing. It is evident, then, that the annual amount of 

 heat received by the arctic regions, and especially about the pole, 

 would be considerably greater than at present. And as the 

 heat received on those regions is chiefly employed in melting 

 the ice, it is probable that the extra amount of ice which would 

 then be melted in the arctic regions would prevent that slight 

 increase of ice which would otherwise result in consequence 

 of the winter occurring in aphelion. The winters at that 

 period would be colder than they are at present; but the total 

 quantity of ice on the northern hemisphere would not probably 

 be greater. Let us now turn to the southern hemisphere. As 

 the southern winter would then occur in perihelion, it would 

 tend to produce a slight decrease in the quantity of ice on the 

 southern hemisphere. But on this hemisphere the effects of ex- 

 centricity would not, as on the northern hemisphere, be com- 

 pensated by those of obliquity ; for both causes would here 

 tend to produce the same effect, namely a melting of the ice in 

 the antarctic regions. 



It is probable that at this time the quantity of warm water 

 flowing from the equatorial regions into the Southern Ocean 

 would be much greater than at present. This would tend to 

 raise the temperature of the air of the antarctic regions, and thus 

 assist in melting the ice. These causes, combined with the 

 great increase of heat resulting from the change of obliquity, 

 would tend to diminish to a considerable extent the quantity of 

 ice on the southern hemisphere. I think we may assume 

 that the slight increase of excentricity at that period, the oc- 

 currence of the southern winter in perihelion, and the extra 

 quantity of warm water flowing from the equatorial to the ant- 

 arctic regions would produce an effect on the south polar ice-cap 

 equal to that produced by the increase in the obliquity of the 

 ecliptic. It would therefore follow that for every eighteen 

 pounds of ice melted annually at present at the south pole twenty 

 pounds would then be melted. 



