152 FKOM NEBULA TO NEBULA 



It remains, however, to vindicate my equilibrium 

 solution affirmatively by showing that, under it, the chain 

 of transformations, to and fro, is not only the same (save, 

 of course, as to the fact of necessary reversal), but that 

 all the transitional shapes it presupposes can consistently 

 be figures of equilibrium. All this, I hope the reader 

 will perceive is assured and attained when we conceive 

 that, in being removed outward, the hemispheres imper- 

 ceptibly take on forms more and more gibbous, simu- 

 lating the phases of the moon from first quarter to full, 

 while in the contrary direction the spheres become less 

 and less so, imitating the phases between full and last 

 quarter. Everyone should be able to see for himself that 

 the nearer the minor spheres approach each other, the 

 more does the water seek passage to the rear, as though 

 in fear of being caught "between the bumpers", while 

 in going the other way, things are just vice versa. In 

 Fig. 7 are shown, in juxtaposition, the three sets of trans- 

 formations in the order above described. 



Speaking specifically of the earth, then (though the 

 principle applies universally), her tides are caused by a 

 conflict between two ruling gravitational forces, namely, 

 (1) the integral attraction of the earth upon her own 

 mass, and (2) the extraneous attraction of the sun; the 

 first seeking ever to concentrate her heavier substances 

 at her center and to deploy the lighter on the outside, 

 the latter ever striving to compel her to recognize the 

 sun's rival power and advance her heavier parts toward 

 him. Were the earth solid clear through, as the moon 

 appears to be, she would turn the same face to the sun 

 continuously, but having great mobile oceans, she com- 

 promises by shifting them from in front of the sun, thus 

 giving her center of gravity, as it were, a chance to make 

 obeisance to him. 



