26 



Gee and Ad 



AlMSON, Trisecting an Angle. 

 Mechanical Methods. 



It is possible to construct a linkwork mechanism so 

 that two of the links shall include a variable angle which 

 is always trisected by two other links. Two such link- 

 works have been devised by one of the authors. 14 



I. The arrangement shown in Fig. 19 is based on the 

 construction given in the last trial method (Fig. 18). AG, 



D 8 A 



Fig. 19. Adamson's Linkwork (No. 1). 



GH, HD and DA form a hinge-jointed parallelogram, 

 HD being slotted. The slotted arm EK is fixed perpen- 

 dicular to AG, AE being equal to half AD. B and L are 

 the middle points of AD and GH respectively. A pin P 

 passes through both slots. B is joined to P and to E by 

 elastic cords or slotted links, and to L by an ordinary link 

 or cord. Then obviously the angle ABP is trisected by 

 BE and BL, the figure being virtually the same as Fig. 18. 

 If the link AD be fixed, P describes a portion of a 



lima co 11 curve, 



> 



14 One of these was exhibited at the Mathematical Congress at 

 Cambridge in 1912 and described at a meeting of the Manchester Literary 

 and Philosophical Society on October 15, 1912. (See Proc, Vol. 57, Part I.) 

 The apparatus is made by Mr. G. Cussons, of the Technical Works, Man- 

 chester, N.W. 



