The eccentricity of the Earth's orbit is periodically change- 

 able. It's mean value rises and falls for a period of about 

 IV2 millions of years, with 16 oscillations. Such a rise and 

 fall I term a cycle, and each cycle is. in the calculated curve, 

 composed of 16 arcs. 



The tidal-wave, which is the most powerful agent in al- 

 tering the sidereal day and in lengthening it, rises and falls, in 

 some measure, with the eccentricity. It so exceeds the other 

 forces that act in altering the length of the day, that the day 

 steadily becomes lengthened, on the average, more quickly in 

 the middle of the cycles, when the mean value of the eccent- 

 ricity is greatest, and more slowly at the limit between them, 

 when the eccentricity is least; and in respect of the respective 

 arcs with increasing speed during rising, and decreasing speed 

 during falling eccentricity. 



The interior of the Globe is plastic owing to the great 

 pressure. The surface or „ crust" opposes the greatest resistance 

 to change of form. But according as the sidereal day becomes 

 lengthened, and the equatorial regions of the Earth increase in 

 weight, a steadily increasing strain acts outwards towards higher 

 latitudes, and that strain increases until the resistance is over- 

 come. We must also bear in mind that forces which are too 

 slight to produce a sudden change in a solid body may still 

 produce a change of form when they act through long periods- 

 Therefore the lengthening of the sidereal day acts not only 

 on the seas, but also on the form of the solid Globe. The Earth 

 approaches, steadily, more and more to the spheriform, but the 

 solid crust is more sluggish in its movement than the seas, which 

 immediately accommodate themselves to the altered time of ro- 

 tation. 



As the motive force of these movements of seas and solid 

 Earth is periodically changeable, according to the eccentricity of 

 the Earth's orbit; these movements take place also, periodi- 

 cally, quicker and slower. And as the seas always accommodate 

 themselves to the forces before the dry land does, it is likely 

 that the beach-lines come to oscillate up and down once, for eacb 



