NOMOS. Ill 



failed to produce any perceptible disturbance in the 

 movements of the satellites of Jupiter when (what 

 has happened more than once) they have fallen foul 

 of them. 



But the actual orbit in which the earth moves is 

 an ellipse of slight eccentricity with the 

 sun in one of the foci : and how then are 

 we to account for this ? Does the rate of 

 motion vary in different parts of the orbit 

 in consequence of variation in the reactions of the 

 solar and terrestrial currents ? This is the question 

 which naturally arises under the circumstances, and 

 the only question which can arise ; for it is not pos- 

 sible to conceive of any departure from a circular 

 orbit if the reactions in which the orbital movements 

 originate remain constant. 



Now, on considering the surface of the earth, it is 

 not easy to suppose that these reactions are the same 

 in every part of the orbit. If we do this, we at once 

 perceive the very irregular distribution of land and 

 water, for the land is almost entirely confined to the 

 northern hemisphere. Now we know very well how 

 much the actual temperature of a place is dependent 

 upon the neighbouring quantity of land, and how, 

 for this reason, the centre of a continent is hotter 

 than its shores, and the shores than an island in 

 mid-ocean. We know, for example, that it is owing 

 to the comparative absence of land in the southern 

 hemisphere that the circle of ice extends so much 

 further from the southern than from the northern 

 pole. But heat, according to the premises, is a sign 

 of the operation of that law which rules the move- 



