of Metal Rods with rounded ends. 
269 
Collinearity being thus attained, the rod r 2 (Fig. 2 A), was 
withdrawn by means of the cord, c, to a distance measured, as 
described, by a travelling telescope. This cord is attached to the 
rod by one of the hooks, and passes under a small pulley, P, to a 
hook at the bottom of the dropper, D. The latter is supported by 
the fuse-wire, L, which passes through a hole in the stop, G , and is 
fixed by a binding screw above (Fig. 5). The fuse wire is pulled 
up as high as it will go, so that the top of the dropper is pulled up 
against the stop, G ; the arms, Q, at the same time making contact 
