Novel Ther mo-Electric Phenomena. Si 3 



The results are plotted in the second curve shown on the 

 figure. It will be seen that, up to a temperature of 320° C, 

 the E.M.F. of the nickel-steel alloy and iron couple rose 

 rapidly ; it then remained absolutely constant until the 

 temperature rose to 500°, and after this, only a small change 

 occurred up to the highest temperature attainable in the gas 

 furnace employed. The mean E.M.F. between 300° and 

 1000° C. was in round numbers 4000 microvolts, and the 

 extreme variations from the mean E.M.F. throughout this 

 range of 700° C. — that is, from a low black heat to a white 

 heat — were less than 170 microvolts, or about + and — 4 per 

 cent, of the E.M.F. at 300 c C, the cooler junction being kept 

 at 0° 0. It will be noticed that there is a slight and 

 curious oscillation of the E.M.F. about the mean line between 

 300° and 1100° 0., the curve cutting the mean E.M.F. at 

 four points, viz., at 310°, 540°, 810°, and 1030° 0. 



The couple was next exposed to a very low temperature 

 obtained from solid C0 2 , but though a temperature of 

 — 80° C. was reached (the other junction being still kept in 

 melting ice), no other anomalous action occurred, the reverse 

 E.M.F. increasing rapidly as the temperature fell. On again 

 raising the temperature to a white heat, the phenomena 

 previously observed were exactly reproduced, and continued 

 to be so on repeated heating and cooling. 



In place of nearly pure iron, other substances were tried 

 as the second metal in conjunction with this alloy. Ordinary 

 commercial iron wire gave a very similar result, the oscil- 

 lations from the mean E.M.F. being slightly greater. With 

 an ordinary mild steel wire as the second metal, the nickel 

 manganese alloy now gave a different result ; this is shown 

 on the lower, dotted curve in the figure. The E.M.F. is less, 

 remains constant only between 400° and 600° 0., then begins 

 to fall and continues falling slowly to the highest temperature 

 reached, over 1000° 0. 



Platinum, copper, and other metals were also tried in 

 conjunction with this alloy, but in no case was there observed 

 the singular constancy of E.M.F. through a wide range of 

 temperature which occurred when iron was the second metal. 

 With platinum the E.M.F. has an opposite sign (to that 

 occurring when the alloy is coupled with iron) up to a 

 temperature of 210° C. ; inversion takes place at this tem- 

 perature, after which the E.M.F. rapidly rises with increasing 

 temperature in an approximately parabolic curve. 



A small thermo-electric battery was formed of strips of 

 this alloy with strips of iron, the strips being insulated by 

 asbestos, and brazed at their junctions; 25 of these couples 



