in Logic, a relative term, expressing an idea which is comprised under some general one called a genus. See Logic, No 68.

in Commerce, the several pieces of gold, silver, copper, &c., which having passed their full Species preparation and coinage, are current in public. See MONEY.

in Algebra, are the letters, symbols, marks, or characters, which represent the quantities in any operation or equation. This short and advantageous way of notation was chiefly introduced by Vie'a, about the year 1590; and by means of it he made many discoveries in algebra, not before taken notice of.

in Optics, the image painted on the retina by the rays of light reflected from the several points of the surface of an object, received by the pupil, and collected in their passage through the crystalline, &c.

It has been a matter of dispute among philosophers, whether the species of objects which give the first an occasion of seeing, be an effusion of the substance of the body; a mere impression which they make on all bodies under certain circumstances; or whether they are not some more subtle body, such as light. The moderns have decided this point by the invention of artificial eyes, in which the species of objects are received on paper, in the same manner as in the natural eye.