138 FROM NEBULA TO NEBULA 



Station yourself in fancy vertically over (south of) 

 the Centrum, but far enough away to obtain a bird's-eye 

 view of the whole base of our imaginary cone clear to the 

 circumference. Thus situated you are looking straight 

 down upon the ecliptic and, sighting along the axis of the 

 cone, you see the Vertex, or what is the same thing, its 

 place, projected upon the far distant background of the 

 northern sky. Mark that point and chart it well, for it 

 is what astronomers call the "pole of the ecliptic". 



Leave your position now and with the winged and un- 

 tiring feet of imagination run the circuit of the cone's 

 base, gazing the while constantly down along the funneled 

 sides of the cone, and on through the Vertex as before, 

 watching carefully its new projection on the celestial 

 sphere. This time, of course, the sky point of the Vertex 

 will not remain fixed, but will move with your movement, 

 and since you are running a circuit it will trace a cycle on 

 the sky. More than this, inasmuch as, by description, the 

 apical angle of our cone is 47, the radius of the celestial 

 cycle will be just half, or 23% the same as the inclina- 

 tion of the earth's axis; and its center will, of course, be 

 the so-called pole of the ecliptic. The Vertex, therefore, 

 you see, is, in a very significant sense, at once the pole of 

 the ecliptic and the geographical pole, but it will not do to 

 confuse it with the celestial points recognized by the 

 astronomers. I suggest the name Gravitational pole as 

 both descriptive and consistent with its dual character. 

 Being the gravitational pole, the earth must, of course, 

 perennially turn her center of gravity steadily toward it 

 and, as a companion of the sun in his great orbital jour- 

 ney, keep her axis constantly parallel with the sloping 

 sides of the cone, so that were her axis a hollow tube and 

 your eye peering through it from the south end, you could 

 always keep the place of the Vertex in your field of view 

 and watch its projection upon the celestial sphere in the 

 form of the circle of precession. 



To round out that circle requires, according to latest 

 estimates, and provided the sun's velocity remain uni- 

 form, 25,810 years. Although hitherto attributed to false 

 causes, this circle traced on the heavens by the earth's 



