22 Gee AND ADAMSON, Trisecting an Angle. 



drawing BH perpendicular to BC and placing a straight 

 line AKE through A so that the intercept KE is equal to 

 the radius of the circle. BG, drawn parallel to AKE is 

 then a trisector. (Compare with Figs. I and 5.) This 

 method is given by a monk, Jordanus Nemorarius. 10 He 

 accomplished the trisection by giving a ruler simul- 

 taneously a rotating and sliding motion, its final position 

 being fixed with the aid of a certain length marked on 

 the ruler. 11 



III. Alsidschzi 12 used the following method: Let ABC 

 be the angle {Fig. 15) to be trisected. With B as centre 



Fig. 15. Method of Alsidschzi. 



and any radius BA describe a circle. Through A place a 



10 "De Triangulis" {circa 1170), printed by Curtze in 1887. 



1 1 See Cantor, " Vorlesungen iiber Geschichte der Mathematik, Vol. II., 

 p. 75, 1892. 



1 - An Arabian mathematician. 



