Manchester Memoirs , Vol. lix. (191 5), No. 13. 21 



the plane of the diagram. The method of using the 

 instrument to determine the points E and D {Fig. 1) is 



» Q 



Fig. 13. Trisection Dividers. 



obvious, provided that the radius of the circle be made 

 equal to the distance PQ. 



II. The angle ABC in Fig. 14 may be trisected by 



H 



A 



Fig. 14. Method of Jordanus. 



