in Alloys of Bismuth and Tin, 563 
made from thin iron and nickel wires were used, one junction 
being fastened at a point on the one bar, the other at a point 
on the second bar, which, under the action of the temperature- 
gradient, assumed as nearly as possible the same temperature 
as the former. 
Fig. 1. 
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The junctions were separated from the rods by thin strips 
of mica, and both rods and baths closely packed with cotton- 
wool. 
Usually four such thermocouples were placed at intervals 
along the rods, so that readings at different temperatures 
could be obtained without disturbing the packing round 
the bars. The free ends of the couples were joined up in 
series with one set of coiis of a sensitive differential Thomson 
galvanometer of low resistance, each couple being joined up to 
the galvanometer in turn by means of mercury cups. 
The galvanometer could be easily arranged to give a 
2 Q 2 
