22 REMAKES ON SIR ROBERT BALLS PAPER. 



and farthest from the sun (Perihelion and Aphelion), these 

 points being reached at the beginning of January and the 

 beginning of July. 



2. That a bisection of the orbit by a line through the sun's 

 centre in any direction but that of coincidence with the 

 major axis of the ellipse will cut the orbit into two unequal 

 divisions, of which that which comprises the perihelion will 

 receive the greater intensity of heat, in accordance with the 

 law of inverse squares of distance. 



3. Nevertheless, as the earth's angular velocity is in the 

 same ratio of inverse squares of distance, the total amount of 

 heat received in the one division of the orbit (and of the 

 year), will exactly equal that received in the other division. 

 Further, the year's supply will be equal in the two hemi- 

 spheres. 



4. That owing to the disturbing attraction of the planets 

 (Venus and Jupiter principally), a slow variation is produced 

 in the length of the minor axis of the earth's orbit, the 

 major axis remaining constant. This amounts to saying 

 that the eccentricity varies. This variation oscillates within 

 certain limits, and occupies an enormously long period. 



5. As a further effect from planetary perturbation, the 

 direction of the major axis undergoes a slow progressive 

 change, making a complete revolution in about 110,000 

 years. 



6. That the moon's attractive force upon the earth's equa- 

 torial protuberance causes a gyration of the polar axis in a 

 circle of 47 degrees in diameter, and the consequent revolu- 

 tion of the line of the equinoxes in the comparatively short 

 period of 25,000 years. 



7. The movement described above (6), known as the "pre^ 

 cession of the equinoxes," and the revolution of the major 

 axis of the orbit (5) being in opposite directions, it follows 

 that they will recur to the same relative positions in the 

 shorter period of 21,000 years. 



8. The elementary fact of the inclination of the polar axis 

 to the plane of the orbit at an angle of 66^ degrees must be 

 takent into account. Upon this, and this only, depends the 

 relative distribution of the total yearly supply of heat 

 between the summer and winter seasons of the year in either 

 hemisphere. This is shown by mathematical formulae to be 

 in the ratio of 63 to 37 nearly, which ratio remains constant 

 under all circumstances. 



There is still one other condition, as laid down by Sir 

 Robert Ball, equally essential, but which I will postpone for 

 the present, and will proceed to discuss the bearing which 

 the foregoing postulates have upon the problem. 



