On to the upper part of the polar axis is fastened the declination circle, C, 5½ in.
The polar axis of the earth may be defined as the diameter about which the earth rotates.
That the earth revolves round the sun, and rotates on its polar axis, have long been the settled canons of our system.
Certain of these changes have recently been explained by the discovery of a new and hitherto unnoted movement of the polar axis.
A slow motion adjustment independent of the clock is fitted to the polar axis.
The diameter of the earth in latitude 30° is really about 20 miles longer than the polar axis.
If the polar axis is set vertical and the worm wheel unclamped, the instrument is transformed into an alt-azimuth mounting.
Perhaps the globe would deviate from her course; perhaps an alteration in her polar axis would take place.
Mercurial bearings counterbalance the weight of the polar axis in large part.
Thus the wide habitability of the earth is an effect arising from the inclination of its polar axis.