“…In his experimental work, ‘s Gravesande promoted ‘demonstration devices which physically realized Newtonian principles before the eyes of a large audience’ (cf. Schofield, , p. 141; Iliffe, , p. 281) . In Book I, Part III, Chapter XXIII, ‘s Gravesande, for instance, established experimentally that a body which is retained in a curve by a force which tends to a centre describes areas proportional to the time around that centre and vice versa (‘s Gravesande, , I, p. 135) .…”