Refraction

·noun The act of refracting, or the state of being refracted.

II. Refraction ·noun The correction which is to be deducted from the apparent altitude of a heavenly body on account of atmospheric refraction, in order to obtain the true altitude.

III. Refraction ·noun The change in the direction of ray of light, heat, or the like, when it enters obliquely a medium of a different density from that through which it has previously moved.

IV. Refraction ·noun The change in the direction of a ray of light, and, consequently, in the apparent position of a heavenly body from which it emanates, arising from its passage through the earth's atmosphere;

— hence distinguished as atmospheric refraction, or astronomical refraction.