Optical Lever

and to the long arm of which is attached a mirror or telescope directed to a vertical scale. A spot of light, if reflected from the mirror to a distant scale, will indicate by a considerable displacement any small elongation of the rod. Similarly, a considerable range of the scale will pa over the field of the telescope if the latter be used instead of the mirror. Optic Angle. See OPTIC AXIS. IMG:content-1670.png:[graphic][subsumed][merged small]