Watt's Parallel linkage
Author: C J Sangwin
Date: 19 Jan 2006

This construction shows James Watt's linkage for producing a straight line.  You can manipulate the point B with the mouse.  Notice that for small displacements of the point B, the point P moves in a very close approximation to a straight line.

A = (-2.033333333333333, 3.533333333333333)
B_1 = (13.162962962962963, 3.496296296296297)
C_1 = (11.82962962962963, -3.7703703703703693)
D = (21.333333333333332, -3.7666666666666666)
a = Distance(A, B_1)
c = Circle(A, a)
b = Distance(C_1, D)
d = Circle(D, b)
e = Distance(B_1, C_1)
B = Point(c)
f = Distance(B_1, C_1)
g = Circle(B, f)
C = Intersect(d, g, 2)
h = Segment(A, B)
i = Segment(B, C)
j = Segment(C, D)
F = (12.66, -10.14)
E = (12.66, 7.46)
k = Line(E, F)
l = 2.78
p = Circle(B, l)
G = Intersect(p, i, 1)
loc1 = Locus(G, B)