the turning any thing aside from its former course by some adventitious or external cause. The word is often applied to the tendency of a ship from her true course by reason of currents, &c., which turn her out of her right way. It is likewise applied by astronomers to the tendency of the planets from the line of their projection, or the tangent of their orbit.

DEFLECTION of the Rays of Light, a property which Dr Hook observed in 1675, and read an account of before the Royal Society, March 18th the same year. He says he found it different both from reflection and refraction, and that it was made towards the surface of the opaque body, perpendicularly. This is the same property which Sir Isaac Newton calls inflection.