Barrerr—On some novel Thermo-EHlectric Phenomena. L330 
have found that reducing the nickel in the alloy from 25 to 19 per cent., the 
other constituents remaining the same, does not destroy the sudden arrest of 
HE. M. F. at about 300° C.; but the range of temperature where the EH. M.F-. is 
nearly constant is less, extending from about 400° to 750° C. 
It has been suggested that the peculiar thermo-electric property of this alloy 
may be connected with the effect observed by Lord Kelvin, the so-called Thomson 
effect, whereby a kind of electric convection of heat occurs. It is very possible 
that it may have some connexion with this, and hence with the neutral point, which 
occurs in the thermo-electric behaviour of certain pairs of metals, such as copper 
and iron. It is well known that at a certain critical difference of temperature 
between the hot and cold junctions of, say, a copper-iron couple, the potential 
difference due to heat disappears; as the temperature rises, inversion of the 
current occurs; and a second inversion may occur at a still higher temperature. In 
the phenomenon described in this paper, the E. M. F., it is true, does not fall to 
zero. If, however, the cooler junction were kept at a temperature of 310° C., this 
would be the case; and we should then have a series of three successive small 
inversions of HE. M.F., occurring at 540°, 810°, and 1030° C. In a copper-iron 
couple the neutral point is 275° C., that is to say, no E. M. F. is produced by heat 
when one of the junctions is as much above 275° as the other is below that 
temperature, the neutral point being the arithmetic mean of the temperatures of 
the hot and cold junctions. If, therefore, the cold junction in a copper-iron couple 
be kept at 0° C., the thermo-electric current falls to zero when the hot junction 
is at 550° C., the current being inverted as the temperature rises beyond this. 
I have noticed that the temperature of the neutral point in a copper-iron, or 
copper-steel couple, is not the same during the heating as during the cooling of the 
couple. Moreover, in a couple formed of copper and mild carbon steel, the 
neutral point becomes lower in successive heatings. Thus, at the jist heating 
the temperature of inversion was approximately 640° C., and in cooling, 500° C; 
in the second heating, 550° C., and in cooling, 465° C.; in the third heating, 
520° C., and in cooling, 465° C. The difference between the temperature of 
inversion in heating and cooling becoming less in each successive heating and 
cooling. The cool junction was here at 16° C. throughout, the neutral points at 
the Ist, 2nd, and 3rd heatings and corresponding coolings of the couple, would 
therefore be approximately as follows: 
Neutral points of copper-steel couple. 
First, Second, Third Heating. 
When heating, . | . 328° 283° 2682 C! 
Wihen\ cooling 2) 258° 241° 241°C. 
It is obvious, therefore, that the curve representing the thermo-electric force of 
