72 FROM NEBULA TO NEBULA 



dividual cases. For the present purposes, it is sufficient 

 to characterize the effect as that of a "back eddy" in this 

 complex gravitational whirlpool of ours. 



Here, too, we have the complete physical explanation 

 of the conservation of the moment of momentum, which, 

 as shown in the preceding chapter, has heretofore been 

 explained teleogically. The Prime Kesultant is, as every- 

 one can readily perceive, a physical force that compasses 

 the entire system, so that all changes of momentum are 

 accelerated throughout in like degree, thus all but con- 

 cealing the fact of change. In other words, the yardstick 

 with which we here measure shrinks and expands syn- 

 chronously and commensurately with what it is employed 

 to measure. The conservation theory is consequently 

 not correct in the abstract sense. Our planetary system 

 is altering its aggregate momentum, in keeping with the 

 acceleration of its cosmic fall. 



Descartes was right in diagnosing the gyrations of 

 our system as vortical in principle, but he failed to 

 establish the fact because he reasoned without universal 

 gravitation. 



THE PRECESSION or THE EQUINOXES 



In explaining the cause of the seasons, the books or- 

 dinarily speak of the earth's axis as remaining constantly 

 parallel to itself, thus tilting the north pole toward the 

 sun in summer and hiding it from him in the winter. 

 This explanation suffices for beginners in the study of the 

 science, but more advanced pupils are taught that the 

 axis does not remain absolutely parallel, but revolves 

 around like the axis of a common top when it is just get- 

 ting ready to fall over. This movement in the earth's 

 case is exceedingly slow, requiring almost two hundred 

 and sixty centuries to complete it ! The way astronomers 

 originally discovered this fact was by noting the times of 

 the recurrences of the vernal equinox. This has since 

 been established to arrive about 20 m. 23 s. earlier each 

 succeeding event, making what is known as our tropical 

 (weather) year that much shorter than the sidereal one. 



