VERNIER

A contrivance for measuring intervals between the divisions of graduated scales or circular instruments. The name is given from that of the inventor, Peter Vernier, who published an account of the contrivance in a work printed at Bru els in 1631. It consists of a small moveable scale, which slides along the graduated scale; the divisions on the one scale being to those on the other in the proportion of two numbers which differ from each other b): unity. The theory of the instrument, and the manner in which it is used, may be explained as follows:— Let A B = a be a distance il M i I! L I I! I ]01 23460:7 8 9 10 on the scale containing n of its divisions. Let v t> be another scale equal in length to » — 1 of the divisions on A B; and let vvbe divided into n equal parts. Since the distance A B = a, and contains n equal parts, each division on the scale = ~ • Hence the length of the vern nier vv — a — "; and, as it is divided into « equal parts, n If a\ a rt J each division on the vernier = ^\" ~;t) "= n~ „" and therefore the difference between a division on the scale and one on the vernier = ~^- Suppose the zero of the vernier to coincide with the division marked A [s. 1303]