132 Barrett — On some novel Tnermo- Electric Phenomena. 



a copper-steel couple at different temperatures is not the same for a rising as for a 

 falling temperature. This I have found to be the case with couples formed of 

 several other metals, provided one element of the couple is iron or steel or other alloy 

 of iron. When the other metal is platinum, the difference in the tvro curves is 

 well seen, though with a platinum-iron couple, the difference of E. M. F. in heating 

 and cooling is less marked than with a platinum-steel couple. In the latter case, a 

 considerable area is enclosed bj^ the curves (representing the relation between 

 thermo-electric force and temperature) during heating and during cooling. 

 Hence, at a given temperature, say 500° C, of the hot junction, the E. M. F. of a 

 platinum-steel couple is considerably higher during heating than during cooling. 



The reverse is the case with a couple formed of Hadfield's nickel-manganese- 

 steel and cojiper, or a couple formed of the same alloy with platinum ; in both 

 these cases at any given temperature, the E. M. F. is lower during heating than 

 during cooling. With a couple formed of the same alloy and iron, as described in 

 the earlier part of this paper, there is also a slightly lower E. M. F. at corresponding 

 temperatures during heating than during cooling, but the difference only exists at 

 certain parts of the scale, and is so small that it could not be shown on the curve 

 as reduced in the Plate. With the nickel-manganese-steel alloy mentioned on the 

 top of p. 115 (containing 19 instead of 25 per cent, of nickel) coupled with iron, the 

 E. M. F. is slightly higher at corresponding temperatures in heating than in cooling 

 up to the level part of the curve, i.e. about 400° C, where the E. M. F. becomes 

 almost the same in heating as in cooling — very slightly lower, however — and 

 remains so until the curve rises, when the E. M. F. again becomes higher at cor- 

 responding temperatures in heating than in cooling up to the highest temperature 

 reached : in this case, therefore, the curves showing the E. M. F. during heating 

 and cooling cross each other twice, first at about 400° and next about 800° C. 



I hope, in a subsequent paper, to give the results of further investigation which 

 I am pursuing on this interesting phenomenon, together with the curves for the 

 E. M. F. of various couples during heating and cooling — thermo-electric hysteresis 

 curves as they may be called.* It is very probable that the peculiar thermo- 

 electric deportment of iron, and some of the alloys of iron described in this 

 paper, is intimately associated with the phenomenon of recalescence, or rather 

 of the series of recalescent points which exist in iron and steel. 



*As was pointed out by Professor G. F. Fitz Gerald, F.T.C.D., F.E.S., at the meeting of the Society 

 when this paper was read, the thermo-electric hysteresis here referred to is, no doubt, the cause of the 

 thermo-current which is produced in an iron wii'e steadily moved through a flame, a phenomenon first 

 noticed and investigated by Dr. F. T. Trouton, F.E.S. See Proc. Royal BuUin Society, March, 1886. I 

 am also greatly indebted to Professor FitzGerald for other suggestions he has made in reading the proof 

 of this paper. 



