Manchester Memoivs, Vol. lix. (191 5), No. 13. 27 



2. In the arrangement shown in Figs. 20 and 21 (see 

 footnote 14), two brass strips CD, DF are hinged together 

 at D. BAGH is a hinge-jointed parallelogram the sides 

 of which are all equal. The link GA is constrained so as 

 to move in a slot in the strip DF. The corner B is 

 hinged to a link BE which is also hinged at a fixed point 



C 3 D 



Fig. 21. Adamson's Link work (No. 2). 



E on DF, BE and ED being each equal to the side of 

 the parallelogram BAGH. The hinge B is constrained 

 to lie in CD and may move along in a slot. Another 

 link BG is hinged at B and is slotted so as to pass 

 through the hinge G and form the diagonal of the paral- 

 lelogram. 



It will be obvious from the figure that in any position 

 of the linkwork the angle ABC is trisected by BH and 

 BG. 



In order to facilitate the use of the linkwork as a 

 drawing instrument, the strips BA, BG, BH and BC are 

 shaped so that one edge corresponds to the straight lines 

 in Fig. 21. 



The most convenient way of using the instrument is 

 to place the edge of the strip BA against one line 

 bounding the angle to be trisected, and to hold it in this 

 position by means of a metal plate {Fig. 20) attached 

 to BA for that purpose. The linkwork is then adjusted 



