130 Barrett — On some novel Thermo- Electric Phenomena. 



the temperature rose to 500^^, and after tliis, only a small change occurred up to 

 the highest temperature attainable in the gas furnace employed. The mean 

 Yi. M. F. between 300° and 1000° C, being 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 wliite heat, being less than 170 

 microvolts, or about + and — 4 per cent, of the E. M. F. at 300° C. , the cooler 

 junction being kept at 0° C. It will be noticed there is a slight and curious oscil- 

 lation of the E. M. F. about the mean line between 300° and 1100° C, the curve 

 cutting the mean E. M. F. at four points, viz., at 310°, 540°, 810°, and 1030° C. 



The couple was next exposed to a very low temperature obtained from solid 

 CO2, 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 jDlace 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 oscillations from the mean E. M. F. being slightly greater. Witli an 

 ordinary mild steel wire as the second metal, the nickel manganese alloy now gave 

 a different result ; this is shown on the lower curve in the Plate. The E. M. F. 

 is less, remains constant only between 400° and 600° C. ; then begins to fall and 

 continues falling slowly to the highest temperature reached, over 1000° C 



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 occui-ring when 

 the alloy is coupled with iron) up to a temperature of 210° C. ; inversion takes 

 place at this temperature, after which the E. M. F. rapidly rises with increasing 

 temperature in an ajiproximately 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 give an E. M. F. of yV of a volt when heated over any flame, the 

 cooler junctions being kept in ice-cold water. A convenient standard of E. M. F. 

 might thus be made if the mean of the readings between 300° and 1000° C. are 

 taken. Whether repeated heating and cooling of the alloy will affect its E. M. F. 

 I cannot say, but I have not yet observed any injury resulting from this cause. 



We know so little of the whole subject of thermo-electricity, that the ex- 

 planation of the remarkable behaviour of this alloy can only be a matter for 

 conjecture. Some light may be thrown on it by the results obtained from the 

 other allo3^s of iron, when their thermo-electric behaviour is examined. So far I 



