Dante and the early astronomers . of moon and planets areslightly and variously inclined to it. Thus the daily path of a star is aff^ected only by thesimple uniform movement of the entire heaven (inreality the rotation of the Earth) but the daily pathof a planet, or of the sun or moon, results from acombination of this general movement with its ownpeculiar movement, which is generally in the oppositedirection. If it is difficult to conceive a body moving simultane-ously in two different directions, an earthly analogywill make it easy. On a great moving platform, such THE HEAVENLY BODIES. 19 as
Dante and the early astronomers . of moon and planets areslightly and variously inclined to it. Thus the daily path of a star is aff^ected only by thesimple uniform movement of the entire heaven (inreality the rotation of the Earth) but the daily pathof a planet, or of the sun or moon, results from acombination of this general movement with its ownpeculiar movement, which is generally in the oppositedirection. If it is difficult to conceive a body moving simultane-ously in two different directions, an earthly analogywill make it easy. On a great moving platform, such THE HEAVENLY BODIES. 19 as that which encircled the Paris Exhibition in 1900,there are fixed posts etc. which revolve exactly as thewhole platform revolves and do not move aboutamongst themselves. These are like the fixed starson the (apparently) revolving sphere. But humanbeings are free to add their own movements to thatgiven them by the platform on which they man turns his back and walks steadily and very Worth Celestial Pole CelestialEquator. Equator South Celestiai Pole Fig. 4. The star ephere. slowly in the opposite direction, and so he neutralizespart of the platform movement and is not carriedonward quite so quickly as the stationary posts : he isthe sun. A woman walks as he does, but much morequickly, so that she rapidly passes many posts,although all the time she is being carried backwardswith them: she is the moon. Children run backwardsand forwards: they are the planets. Finally, if all 20 APPARENT MOVEMENTS OF these people are also constantly crossing the platfoimslowly from right to left and back again, theirmovements will be oblique to the platform movementand will imitate the north and south movements ofsun, moon, and planets. It is in this fashion that the movements of the skiespresent themselves to careful observers on this seem-ingly stationary earth; and in the youth of the worldthese apparent movements were believed to be ancients thought that the sky was actually
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