Newtonian New*to"ni*an, a. Of or pertaining to Sir Isaac Newton, or his discoveries. Newtonian philosophy, the philosophy of Sir Isaac Newton; -- applied to the doctrine of the universe as expounded in Newton's ``Principia,'' to the modern or experimental philosophy (as opposed to the theories of Descartes and others), and, most frequently, to the mathematical theory of universal gravitation. Newtonian telescope (Astron.), a reflecting telescope, in which rays from the large speculum are received by a plane mirror placed diagonally in the axis, and near the open end of the tube, and thrown at right angles toward one side of the tube, where the image is formed and viewed through the eyeplace. Newtonian theory of light. See Note under Light.