226 
Fig. 1. 
wire to a binding screw. If the slits are filled with mercury, so that 
the surface bulges out above the plane of the disc, electrical contact can 
be established between various pairs of slits by means of the pins attached 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Each consecutive set 
strip on the under side 
of five slits are connected together by a copper 
of the disc, and each strip is joined by a copper 
