Earth's equator

“ Becoming water and losing its velocity, it would approach the tropics by a similar, but reversed spiral, turning towards the west. Owing to the principle here alluded to, all currents from the equator to the poles should have an eastward tendency, and all from the poles towards the equator a westward. Let us now suppose the solid nucleus of this hypothetical globe to assume the exact form and shape of the bottom of our seas, and in all respects, as to figure and size, to represent the shoals and islands of the sea, as well as the coast lines and continents of the earth. ”

“ If we take the Earth at noonday at the time of the equinox, then a square yard at the equator has the Sun in its zenith, and is fully presented to its light and heat. But, as we move away from the equator, we find that each higher latitude is less fully presented to the Sun, until, when we reach latitude 641⁄2°—in other words just outside the Arctic Circle—7 square yards are presented to the Sun so as to receive only as much of the solar radiation as 3 square yards receive at the equator. We may take, then, latitude 641⁄2° as representing Mars, while the equator represents the Earth. ”

“ Under the equator, owing to the fact that the sun for a considerable belt of land and sea maintains the earth at a high temperature, there is a general updraught which began many million years ago, probably before the origin of life, in the age when our atmosphere assumed its present conditions. Into this region the cooler air from the north and south necessarily flows, in part pressed in by the weight of the cold air which overlies it, but aided in its motion by the fact that the particles which ascend leave place for others to occupy. ”

“ The heat of the sun at the equator expands the air, and thus it rises and flows north and south; having arrived once more at the tropics, owing to the counter current it meets, it descends, as we saw, and flowing along near the earth, receives from it a rotatory motion, which increases as it approaches the pole, where, contracted by the cold, it masses into a dense body, and ultimately is whirled upwards, forming an ascending column, when it once more commences its never-ceasing journey. ”

“ Because the earth is tilted on its axis twenty-three and a half degrees from the perpendicular, the ecliptic runs through the heavens in an oblique circle, crossing the line of the equator at two points called the vernal and autumnal equinoxes. The equator in the heavens is the great circle extending around the celestial sphere half-way between the north and south poles. It is always practically ninety degrees from the north star, and the points at which the ecliptic intersects it are called the equinoxes. ”

“ In addition to the rotation of the earth on its axis once every day, and its revolution about the sun once in a year, there is also a slow, rolling motion of the equator, caused by the attraction of the sun on the excess of matter in equatorial diameters over the polar. ”

“ The primary great circle of a sphere or spheroid, such as the earth, perpendicular to the polar axis, or a line resembling or approximating such a circle. The terrestrial equator is 90° from the earth’s geographical poles, the celestial equator or equinoctial is 90° from the celestial poles. The astronomical equator is a line connecting points having 0° astronomical latitude, the geodetic equator connects points having 0° geodetic latitude. The expression terrestrial equator is sometimes applied to the astronomical equator. The equator shown on charts is the geodetic equator. ”

“ At the equator, or that part of the earth which lies midway between the poles, the sun and stars appear to rise and set perpendicularly to the horizon and at equal times above and below it, it is therefore 12 hours day and 12 hours night; in places not situated on the equator, they do not rise and set perpendicularly to the horizon, but form portions of circles at greater or less altitudes in the heavens, and the nearer the observer is to either of the poles, the smaller the circle, and the more of it is seen ”