4 Meadowcroft, Treatment of Geodesic Torsion. 



points {Fig. 2). Draw the normal planes to the curve at 

 /, q, r. Each of these planes meets the next in a polar 

 line. Let the two polar lines meet in A. The normals 

 to the surface at/ and q will meet the polar line in a and 



Fig. 2. 



b (say). Let U, V be the centres of curvature at Q and 

 R. Join Up, Uq, Vq, Vr. 



The points A, (J, V, q all lie in the normal plane at q, 

 and are therefore coplanar. They are also concyclic 

 since 



2 

 ,-, UAV-^ UqV. 



