PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 745 
views, fig. 52), were prepared, and the iron squares, put in their proper places, were 
then soldered by their edges to the edges of the connecting piece, and the electrodes 
Fig. 53. 
were soldered to their opposite edges. A view of the whole thus put together, with 
the reference and testing wires described below, is given in fig. 54. A testing con- 
Fig. 54. 
ductor of two yards of No. 18 copper wire was soldered, with its two extremities to 
the copper electrodes, close to the middle points of the edges AL, DM of the iron 
squares ; and a fixed galvanometer electrode was soldered to the middle point, N, of 
the copper connecting piece. 
169. The squares, their electrodes, the connecting piece, and the testing conductor 
