"DEFIN. II. ... Mathematicians uſually conſider the Rays of Light to be Lines reaching from the luminous Body to the Body illuminated, and the refraction of thoſe Rays to be the bending or breaking of thoſe lines in their paſſing out of one Medium into another. And thus may Rays and Refractions be conſidered, if Light be propagated in an inſtant. But by an Argument taken from the Æquations of the times of the Eclipſes of 𝔍upiter's Satellites, it ſeems that Light is propagated in time, ſpending in its paſſage from the Sun to us about ſeven Minutes of time: And therefore I have choſen to define Rays and Refractions in ſuch general terms as may agree to Light in both caſes."