Page:Popular Science Monthly Volume 80.djvu/457

Rh can never differ greatly from what we know them now. They can neither be materially accentuated nor proportionately reduced.

Though the obliquity of the ecliptic is oscillatory, the motion of the ecliptic pole keeps persistently, though unsteadily, on always in the same sense. Its wanderings trace out an elliptic spiral which never returns into itself. Its vagaries resemble as much as anything an unevenly bent spring carelessly coiled about a mid-position from which it never far departs.

Meanwhile our own pole pursues its relatively sedate march around the other, permitting its position to be calculated at any past epoch not too remote. We can plot its path and thus see near which stars it passed, stars which had the earthly distinction once upon a time of being our cynosure. In this manner we discover that 4,690 years ago, or in 2780 the pole passed within 3' of arc of the star α Draconis. Practically the star was the pole, and it was the last bright star the pole approached before reaching Polaris. In the time of Hipparchus, 140 the pole lay undistinguished in a waste region of the sky. A of the dragon is now a star between the second and third magnitudes, but there is evidence to show that in ancient times it was brighter. It must