Figure from Stephen Johnston, ‘Making mathematical practice: gentlemen, practitioners and artisans in Elizabethan England’ (Ph.D. Cambridge, 1994). See the contents page for direct access to the chapters and the image gallery for the figures currently available online.

Figure 3.12

Fragments, pp. 26-7 (redrawn).

Baker uses DÃ¼rer’s graphical device for proportional cubes to rescale a plat for a ship one quarter larger than an original ship. For the sake of greater clarity in the figure I have taken the case of a second ship double the size of the first.

AB is a dimension taken from the first ship. As the second ship is to be twice as large, draw AC = 2AB and take it as the radius of semicircle CGD. Join and extend DB and extend AB. Swivel a ruler fixed at C until EG = EF. Then take AE + AB as the diameter of a second semicircle BHE. Erect a perpendicular at A; the line AH is the corresponding dimension of the second ship. AH is then measured against the original scale and its length is the number of divisions with which AB should be marked. Thus divided, AB can be used with the original plat which will now serve for the second ship.