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gives an electromotive force of 126 to 128 microvolts. An element consisting of pure bismuth wire and an alloy of Sb, Cd, Bi gave 138 to 14o micro~:olts per degree; but the alloy is too brittle for an ordinary thermopile. The most promising thermopile appears to be one having elements of pure bismuth and an alloy of Bi + 6 per cent. tin, joined in series-parallel, as already described.
In conclusion it may be added that in the discussion of theory versus experiment it is not inte~lded to detract from the theoretical contribution to the subject. On the other hand, it is but fair to emphasize the contributions which had to be worked out experimentally. These experiments relate to the most crucial points in thermopile construction, especially the question of heat conduction and emissivity, upon which theory could be of little assistance.
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