In the hyperbola, the squares of the ordinates are as the rectangles of the _abscissa_ by another line, compounded of the _abscissa_ and the transverse axis. But it must be remembered, that the two proportions relating to the ellipsis and hyperbola, the origin of the _abscissas_, or point from whence they began to be reckoned, is supposed to be the vertex of the curve, or, which amounts to the same thing, the point where the axis meets it; for if the origin of the _abscissa_ be taken from the centre, as is often done, the above proportions will not be true. ABSENT, a term used in military returns. It forms a part of regimental reports, to account for the deficiency of any given number of officers or soldiers; and is usually distinguished under two principal heads, viz. ABSENT _with leave_, officers with permission, or non-commissioned officers and soldiers on furlough. ABSENT _without leave_. Men who desert are frequently reported _absent without leave_, for the specific purpose of bringing their crime under regimental cognizance, and to prevent them from being tried capitally, for desertion. ABSOLUTE _Gravity_, in philosophy, is the whole force by which a body, shell, or shot, is impelled towards the centre. See GRAVITY. ABSOLUTE _Number_, in Algebra, is the known quantity which possesses entirely one side of the equation. Thus, in the equation, _xx_ + 10_x_, = 64, the number 64, possessing entirely one side of the equation, is called the _absolute number_, and is equal to the square of the unknown root _x_, added to 10_x_, or to 10 times _x_. ABUTMENT. See BRIDGES. ACADEMY, in antiquity, the name of a villa situated about a mile from the city of Athens, where Plato and his followers assembled for conversing on philosophical subjects; and hence they acquired the name of _Academics_. The term _Academy_ is frequently used among the moderns for a society, of learned persons, instituted for the cultivation and improvement of arts or sciences. Some authors confound _academy_ with university; but, though much the same in Latin, they are very different things in English. An university is, properly, a body composed of graduates in the several faculties; of professors, who teach in the public schools; of regents or tutors, and students who learn under them, and aspire likewise to degrees; whereas an _academy_ was originally not intended for teaching, or to profess any art, but to improve it; it was not for novices to be instructed in, but for those who were more knowing; for persons of distinguished abilities to confer in, and communicate their lights and discoveries to each other, for their mutual benefit and improvement. The first _academy_ we read of, was established by Charlemagne, by the advice of Alcuin: it was composed of the chief wits of the court, the emperor himself being a member.