equation

[Fr. équation, from Lat. æquatio =an equalizing, an equal distribution; æquo to make level, equal; æquus level, equal.] *I. Ord. Lang.: The act of making equal, the state of being made equal; equality. "Again the golden day resumed its right, And ruled in just equation with the night." Rowe: Lucan, iv. 93, 94. IMG:content-1092.png:[blocks in formation] is an equation; and, since the equality of the members depends on the value a igned to x , it is called an Equation of Condition. The two quantities separated by the sign are called the members of the equation; the quantity to the left of being the first member, and that to the right the second. The quantities separated by the signs + and are called the terms of the equation. Of the quantities some are known and the others unknown. The known quantities are generally represented by numbers. If letters be used, then those employed are gen erally a , b , c , d , & c. i . e., letters at or near the beginning of the alphabet. Unknown quantities are represented re by letters toward the conclusion of the alphabet. If there be one unknown quantity it is generally represented by a ; if two, by z and y ; and if three, by x, y, and z. Sometimes a statement that two expre ions are equal for all numerical values that can be a igned to the letters involved, provided that the same value be given to the same letter in each member, e . g. IMG:content-1093.png:[blocks in formation] tion operating on them is that of the sun, error, though not of considerable magnitude, will be the result. There is a mutual attraction among all the planets; each is capable of producing a perturbation in the orbits of all the rest. An equation is required for every such perturbation before it is po ible to calculate accurately the course of the planet. "We are to find out the extremities on both sides, and from and between them the middle daily motions of the sun along the Ecliptick; and to frame tables of equation of natural days, to be applied to the mean motion by addition or subtraction, as the case shall require." Holder: On Time. 3. Chem .: A chemical equation represents symbolically a chemical reaction, the symbols of the reacting substances being placed on the left hand, and the symbols of the new substances formed by the reaction being placed on the right hand. In a chemical equation the number of atoms of each element must be the same on each side of the equation, thus, 3AgNO3 Na2HPO4=Ag3PO4+ 2NaNO3+HNO3. Three molecules of argentic nitrate and one molecule of di-sodium-hydrogen phosphate equal (that is, form when added together) one molecule of tri argentic phosphate, and two molecules of sodium nitrate, and one molecule of hydrogen nitrate (nitric acid). Chemical equations are imperfect, as they do not show the amount of heat liberated, of absorbed, during the reaction. (1) Annual Equation : Astron.: One of the numerous equations requisite in determining the moon's true longitude. (2) Equation of the Center: Astron.: The equation required to fix the place or orbit of a planet calculated as if it were moving in a circle when it is doing so really in an ellipse. (3) Equation of the Equinoxes : Astron. The equation required to calculate the real position of the equinoxes from its mean one, the disturbing element being the movement called Prece ion of the Equinoxes (q. v.). (4) Equation of Payments. A rule for ascertaining at what time a person should in equity pay the whole of a debt contracted in different portions to be repaid at different times. IMG:content-1094.png:[blocks in formation] (1) A great circle of the celestial vault at right angles to its axis, and dividing it into a northern and a southern hemisphere. It is constituted by the plane of the earth's equator, produced in every direction till it reaches the concave of the celestial sphere. In his progre north and south, and vice vers a, the sun is twice a year in the celestial equator-viz., at the equinoxes (q. v.). The point in the equator which touches the meridian is raised above the true horizon by an arc which is the complement of the latitude. "Thrice had the sun to rule the varying year, Acro the equator rolled his flaming sphere." Falconer: Shipwreck , i. (2) The sun and planets have all equators. They rotate around their several axes, and the plane at right angles in each case is the equator of the heavenly body. pine, pit, sire, sir, marine; gō, pot, equator-sun 2. Geog.: A great circle on the surface of the earth equidistant from its poles, and dividing it into two hemispheres. Its latitude is zero; it is therefore marked on maps as 0. Other parallels of latitude are counted from it, augmenting in their numerical designation as their distance from it north or south increases, the poles being 90°. "It is not enough to know merely the distance of a place upon the earth from the equator." - Malte Brun: Physical Geography , bk. x. 3. Magnetism: A somewhat irregular line, nearly but not quite a great circle of the earth, in which there is no dip of the magnetic needle. It is hence called also the Aclinic Line. It is inclined to the horizon at an angle of 12, and cuts it at two points almost exactly opposite to each other, the one in the Atlantic and the other in the Pacific. It is not far from the geographical equator, but its situation slowly alters year by year, there being a slow oscillation of the magnetic poles, while the geographical equator and poles are fixed. The two points in which the magnetic equator cuts the horizon seem traveling at present from east to west. B. As adjective : (See the compound.) Plane of the Equator : Geog: A plane perpendicular to the earth's axis, and pa ing through its center. (Herschell.) equator-sun, s. The sun viewed as shedding down fierce beams, as he does at the equator. e-qua-tör-e-al, s . [EQUATORIAL.].