A Neiv Thermoelectric Pheiioinenou. 131 



it oxidises instantly, and heated in clay or glass it combines with 

 the silicon and the resistance becomes infinite almost at once. In 

 the clay tubes, however, I once got a reading of '03, and a single 

 swing indicating -1 volt. I tried it by wrapping ib in asbestos. 

 The general effect was small at first, but there was generally a 

 big swing when the magnesium parted, -3 volt being once 

 indicated. On another occasion, after igniting in the asbestos '03 

 volt was indicated, but as the resistance was very great it was 

 really much more. 



With aluminium I could not get any great effect. When 

 heated in a clay tube there was at once a deflection indicating 

 •0002 volt, but it soon decreased to about two-thirds of this, 

 and after a few seconds to zero, and there was no further 

 effect till the flame was shifted, when the same effect was repeated. 

 Heating in a flame without the tube gave larger and more 

 irregular effects, once up to "0009, and another sudden heating 

 gave a temporary "003. With another specimen the highest 

 effect was -0001 volt. 



In conclusion then, in conti'adiction to the commonly received 

 statement, thermoelectric forces, in many cases of a high order of 

 magnitude, have been observed by heating a homogeneous 

 conductor. This been detected in twelve diflferent metals and 

 four alloys and may fairly be taken as a common property of all 

 metals. The effect cannot be due to chemical change, because it 

 is manifest in some cases at very low temperatures. It is not 

 due to difi'erences of thickness of the metal as mentioned by 

 Clerk Maxwell. It is not due altogether to irregular or 

 unsymmetrical heating, because it was observed several times 

 when symmetrically heated. It is not altogether due to the 

 action of the clay on the metals because it has been observed 

 without the clay, though it must be remembered that the very 

 high efiects were all observed in clay tubes. The abruptness with 

 which the effect occurs or increases at times when the temperature 

 is rising steadily, or, strangest of all, falling, is one of the most 

 extraordinary characteristics of the phenomenon ; this frequently 

 occurs with certain metals, particularly lead, never with others. 

 The phenomenon is independent of the Thomson effect, for it is 

 much more marked in lead in which the Thomson effect is zero, 



