444 On the Change in the Obliquity of the Ecliptic. 



"Were the obliquity increased by 4°, each square foot of surface 

 at the poles would receive annually 51, 802,000 foot-pounds more 

 heat than at present, assuming that all the extra heat reached 

 the ground. But suppose one half of the rays to be absorbed 

 in passing through the atmosphere, 25,901,000 foot-pounds per 

 square foot would then represent the extra heat received by 

 the poles. This would be sufficient to melt 4*12 cubic feet of 

 ice. The additional heat resulting from the increase of 4° in 

 the obliquity of the ecliptic would consequently melt a sheet of 

 ice one mile in thickness in about 1300 years. A mile of ice 

 removed from off the antarctic continent (and this is not an 

 extravagant quantity, as we hope, to be able to show on a future 

 occasion) would raise the general level of the sea 206 feet. And 

 to this must be added the rise resulting from the displacement of 

 the earth's centre of gravity, which in the latitude of Scotland 

 would amount to about 74 feet. This would give 280 feet as 

 the total rise resulting from the melting of one mile of ice from 

 off the face of the continent. It is quite conceivable that an 

 enormous amount of ice might be melted on the southern hemi- 

 sphere, while the quantity on the northern hemisphere remained 

 undiminished. For if this extreme condition of obliquity were 

 to occur at the time that the excentricity was at a higher 

 value (a very likely event), and the winter solstice in aphe- 

 lion, the effects of excentricity would neutralize those of obli- 

 quity on the northern hemisphere, and consequently the quantity 

 of ice on this hemisphere might not be diminished. But on the 

 southern hemisphere the obliquity and the excentricity would 

 conspire to produce the same effect, viz. a melting of the ice; 

 and hence the effects that we have been considering, which 

 would result from the removal of the ice, would necessarily take 

 place to a greater or less extent. 



The enormous effect that an extreme condition of excen- 

 tricity must have in raising the temperature of the polar regions 

 of the hemisphere which has its winter occurring in perihelion 

 at the time, has been shown on a former occasion *. When 

 such a state of things happens at the time when the obliquity 

 is also at its superior limit, the combined effect of both causes 

 would in all probability completely remove the polar ice-cap, 

 and a submergence of the land on the opposite hemisphere to 

 the extent of hundreds of feet would be the inevitable result. 



It has been a matter of surprise how forest-trees could have 

 flourished near the poles, seeing that they must have been 

 deprived of the sun's rays for several months in the year. But 

 it must be observed that it is not necessary that trees should 

 grow during winter, when deprived of the sun's rays. All that 

 * Phil. Mag. for February 1867. 



