Mathematical Geography (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 edition. Excerpt: ...any direction, intersect each other a second time 180 from the first point of crossing, or half way around. The circle of illumination and equator are both great circles and hence bisect each other. If the equator is always bisected by the circle of illumination, half of it must always be in the light and half in the dark. Day's Length at the Poles. The length of day at the north pole is a little more than six months, since it extends from March 21 until September 23, or 186 days. At the north pole night extends from September 23 until March 21, and is thus 179 days in length. It is just opposite at the south pole, 179 days of sunshine and 186 days of twilight and darkness. This is only roughly stated in full days, and makes no allowance for refraction of light or twilight. Longest Days at Different Latitudes. The length of the longest day, that is, from sunrise to sunset, in different latitudes is as follows: The foregoing table makes no allowance for the fact that the vertical ray is north of the equator for a longer time than it is south of the equator, owing to the fact that we are farther from the sun then, and consequently the earth revolves more slowly in its orbit. No allowance is made for refraction, which lifts up the rays of the sun when it is near the horizon, thus lengthening days everywhere. Refraction Of Light The rays of light on entering the atmosphere are bent Fig. -7 out of straight courses. Whenever a ray of light enters obliquely a medium of greater or of less density, the ray is bent out of its course (Fig. 47). Such a change in direction is called refraction. When a ray of light enters obliquely a medium of greater density, as in passing through from the upper rarer atmosphere to the lower denser layers, or from air...