the act of refracting, or the state of being refracted.-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.-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.-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.