contracted f. versed sine VERSED a.
1827. Airy, in Encycl. Metrop. (1845), I. 685. Versin c = 1 – cos c. Ibid. Versin c = versin a – b [etc.].
1859. Parkinson, Optics (1866), 254. The quantity of light received by the disc is 2π2a2B versin α.
