﻿the Duplex Harmonograpli. 



493 



point d which lies vertically beneath the needle-point when 

 all the pendulums are in their positions of rest. In the 

 figure, pendulum D is shown with its bob displaced positively 

 towards the centre of the square, while the other pendulums 

 are in their positions of rest. The rod from D bears a light 

 skeleton table which carries a standard lantern cover-glass 

 3J in. square, upon which the records are taken. In order 

 to prevent the rotation of the table and consequent distortion 

 of the picture, a line db in the frame of the table forms one 

 side of a parallelogram whose other sides are the rod w 2 , a 

 steel rod Ea, 11 cm. long, fixed in the pendulum shaft, and 

 a light wooden rod W\ borne on a needle-point at a and 

 pivoted with the table at b. 



Fiff. 2. 



: The details of: the construction of the table are shown in 

 fig. 2. This is a perspective sketch of the table as seen 

 from the side BC of the slate slab. The skeleton table (t) 



q 2 and <r 2 refer to the y-diagonal, then the curves drawn will approxi- 

 mate to those having equations derived from 



x = a cos [pt-\- a] -i- c cos [ Vp--\-2p' 2 . t-\-y\ 



y = 6cos[5^-f-/3]-fc?cos [ Vq--\-2(r 2 .£ + £] 



by eliminating- t. The method here sketched is not practical, since the 

 damping is large even when care is taken in designing the couplings. 

 The method also lacks the flexibility in adjustment, which is a valuable 

 feature in the duplex harmonograpli described in the body o( the paper. 



