the turning of any thing aside from its course by some adventitious or external cause. The word is often applied to the tendency of a ship to deviate from her true course by means of currents, or the like, which turn her out of her right way. It is likewise applied by astronomers to the tendency of the planets to deviate 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 gave an account of before the Royal Society in March the same year. He says he found it different from both reflection and refraction, and that it was made perpendicularly towards the surface of the opaque body. This is the same property which Sir Isaac Newton calls inflection.