a Flemish Image of Mathematics in the Sixteenth Century
The use of the shadow square or geometrical quadrant on an astrolabe, simple theodolite or Holland circle.
The shadow square is used to take bearings from either end of a measured baseline MN, and then to transfer these measurements on to a plan drawn to scale (see figure 30).
Gemma Frisius, De astrolabo catholico (Antwerp, 1556)
(catalogue no. 3).
See also figure 30
List of figures
(c) Museum of the History of Science, Broad Street, Oxford, England.