was invented by Peter Nicholson, a British mathematician
, in 1814
. It was used to construct 2-point perspective drawings
where one or both vanishing points
existed outside the drawing board. Draftsmen
could use the instrument in pairs; one for each vanishing point on each side of the station point
Centrolineads were produced in various sizes. Typically a brass fitting clamped the wooden arms together. Fittings were produced in both right and left-handed configuration, and certain adjustable designs could be used on either side.
Two short arms are set to form 90 degree angles against a third, longer drawing edge. Pins
are placed near the edges of the drawing surface and serve as pivots
for the arms. Pin placement is equidistant and symmetric across the horizontal line
. A third centrolinead could be used to construct 3-point perspective
Centrolineads and their use are discussed in W.F. Stanley's book on mathematical instruments.