The Philosophical magazine; a journal of theoretical, experimental and applied physics . erature on iron at about 15° C. wasone twentieth of a volt, i. e. considerably more than twice asmuch as would be developed in a single element of bismuthand antimony with one junction at 100° C. and the other at0 C. It has long been known that hot iron is negative to coldiron, and this seems to be so at all temperatures, but it hasnot, the author believes, been noticed before* how verysuddenly the negativeness is increased when the temperaturereaches a bright red. If the wire B be heated to a tempera-ture
The Philosophical magazine; a journal of theoretical, experimental and applied physics . erature on iron at about 15° C. wasone twentieth of a volt, i. e. considerably more than twice asmuch as would be developed in a single element of bismuthand antimony with one junction at 100° C. and the other at0 C. It has long been known that hot iron is negative to coldiron, and this seems to be so at all temperatures, but it hasnot, the author believes, been noticed before* how verysuddenly the negativeness is increased when the temperaturereaches a bright red. If the wire B be heated to a tempera-ture between dull red and bright red before being placed onA, there is a current from A to B which can be readilydetected if the condenser be cut out and the galvanometerconnected directly with A and B, but no effect whatever couldbe detected when the condenser was used as in the experiment. Experiment IV. A piece of the same iron wire was connected directly withthe two terminals A, B of a reflecting galvanometer of 7 resistance (fig. 3). A portion C D of the wire was Fig. heated above a bright red by a burner, and as soon as therequired temperature had been reached the burner was • Unless we except Prof. P. G. Taits observations, which will bereferred to presently. of Iron when under Stress or Strain. 51 stiifted suddenly and slightly towards C; almost immediatelyafterwards the light darted off the scale of the galvanometer,indicating a strong current from A to D through C. Theportion C D was again heated above a bright red temperature,and the burner then was shifted suddenly towards D ; thedeflection of the galvanometer needle was now strong in tlieopposite direction, showing a current from B to C through D. Experiment III. furnishes the clue to the ex])lanation ofthe phenomenon described in Experiment IV. The portionC D, when at a bright red, is thermoelectrically negative tothe rest of the iron wire, and is in fact like a different long, however, as t
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