V

vernal {spring}

equinox: see equinoxes.

verdigris

The green patination found on weathered brass and copper.

vernier

A small moveable scale for obtaining fractional parts of the subdivisions of a fixed scale. Invented by Pierre Vernier in 1631 (published Brussels, 1638). For circular scales, a Type A vernier has a central zero. After about 1780, sextants commonly had a Type B vernier with the zero on the right of the scale. European instruments often have the very similar nonius.

vertical angle

The angle from the zenith to the horarius circle passing through the sun, measured along the prime vertical (the E-W vertical circle). It is one of the ptolematic co-ordinates.

vertical plane

See principal plane.

volvelle

Tides etc. A ~ has sometimes been included around the rod-gnomon of equiangular dials.