Equator, e-kwa'ter, in geography a great circle, every point of which is 90 degree from the poles, that is to say, midway between them. It divides our earth into a northern and a southern hemisphere. The latitude of places, whether south or north, is reckoned from this circle. The equator is 7926.614 miles in diameter, or 24,912 miles in circumference. Owing to the turning of the earth on its axis, a point on the equator has a rotary motion of 1,000 miles an hour, but as the atmosphere moves with the earth we do not notice the whirling. Twice a year day and night are equal the world over. They are always equal on the equator. At all times half of the equator is in light and half in darkness. A wrong impression prevails that the equator is the line of greatest heat on the globe. Three factors are to be considered. In the first place, the longest day is to be found north of the equator during the northern summer, and south of the equator during the northern winter. This fact in itself causes the line of greatest heat to shift back and forth from north to south, so that, even theoretically, it coincides with the equator only at the fall and spring equinoxes. Furthermore, in crossing the mountains of East Africa, the equator rises into a cool region, and the Andes of Ecuador carry it up into a region of perpetual ice and snow, as cold as any point on the Arctic Circle. The trade winds of the southern hemisphere are the stronger and push back the northern winds, carrying the belt of calm and heat north of the mathematical equator. The equator should be associated with the idea of heat, therefore, in a modified way. In fact, the isotherm of greatest heat crosses the equator twice, but does not coincide with it at any time.