150 FROM NEBULA TO NEBULA 



important as any of these is what is known as the celestial 

 vernal equinox, and it is that sky point where the center 

 of the sun (to the eye of an observer supposed at the 

 center of the earth) crosses the plane of the earth's 

 equator. In my theory this occurs at the precise instant 

 when the center of the earth, being then in advance of the 

 sun, cuts across the line of his orbit. Every year the 

 astronomers spare no pains to locate this point with all 

 nicety possible, in order to keep accurate track of general 

 changes of position. 



It is important to remember that the celestial vernal 

 equinox does not remain fixed with reference to the stars, 

 but progresses westwardly around the zodiac. To under- 

 stand why, you will readily perceive that in traveling 

 around the great circuit and looking back once a year 

 past the sun, just when the centers of both are on the 

 orbit, the latter will be necessarily projected just as many 

 degrees to the west on the celestial circumference as both 

 have advanced in the same time in their common orbit. 

 This annually executed arc has been measured with the 

 most refined nicety and has been found to be 50".2. In 

 other words, the sun covers an arc of his orbit 50". 2 in 

 length each year, and at this rate should complete one lap 

 in 25,810 years. 



THE ORBIT AND VELOCITY OF THE SUN COMPUTED 



Inasmuch as, by hypothesis, the forward motion of the 

 system is due to a definite and single force, to wit, the 

 Prime Eesultant, we might be justified in concluding, 

 without further corroboration, that in one year the earth, 

 from one vernal equinox to the next, advances along the 

 main orbit exactly the diameter of her own a conclusion 

 which, were we to apply the principle of falling bodies, 

 associating with it the principle of the lever, would prove 

 generally true of all the rest of the planets. However, 

 there is another chain of evidence to which I wish now to 

 direct your attention which correlates these several data, 

 namely: the velocity of the earth in her orbit, the length 

 of the arc, the degree of curvature of the arc, the length 



