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IV. On the Electromotive Force on the Contact of different Metals. 

 By E. Edlund*. 



IN a previous paper t I have proved that if a voltaic current 

 traverses an electromotor in the same direction as the cur- 

 rent produced by the electromotor itself, an amount of heat is 

 absorbed in the electromotor which is proportional to the electro- 

 motive force multiplied by the intensity of the current. If the 

 current is in the opposite direction, a quantity of heat is pro- 

 duced which is also proportional to the same product. For the 

 same intensity of the current, the quantities of heat absorbed or 

 produced are therefore proportional to the electromotive forces. 

 If a current is allowed to traverse a conducting-wire consisting 

 of two different metals, at the place of contact between them there 

 must be an alteration of temperature, because there exists at that 

 place an electromotive force. If the current goes in the same 

 direction as that caused by the electromotive force, cooling ensues 

 at the place of contact ; but there is an increase of temperature in 

 the opposite case. . Now experiment has long shown that heating 

 or cooling occurs at the place of contact between two metals when 

 a voltaic current traverses it, and that this alteration of heat, as 

 theory requires, is proportional to the intensity of the current. 

 Hence a measurement of the quantities of heat absorbed or pro- 

 duced on the passage of the voltaic current gives a determination 

 of the magnitude of the electromotive force produced by the con- 

 tact of the metals. This method of determining electromotive 

 force has the advantage of keeping the circuit closed during the 

 measurement, so that the force is in full activity. The changes 

 of temperature which are produced at the place of contact of two 

 metals by a current passing through them have been frequently 

 investigated ; but the magnitude of these changes of temperature 

 depends on the specific heat of the metals, on their conductivity 

 for heat, on the cooling during the experiment, &c, and there- 

 fore cannot give a direct measure of the electromotive forces. In 

 the sequel I give the experiments which I have made on this 

 subject in conjunction with Magister Sundell of Helsingfors, 

 and then a comparison of the electromotive and thermoelectric 

 forces of the metals investigated. 



2. In the experiments an air- thermometer was used, the bulb 

 of which was a cylinder of very thin sheet copper 125 millims. 

 in length and 80 millims. in diameter. On the outside of each of 

 the two circular ends a copper tube 45 millims. in length was 

 soldered, in such a manner that the tubes were in the centres of 



* Translated from Poggendorff's Annalen, No. 7, 1870, having been 

 read before the Swedish Royal Academy of Sciences, January 12, 1870. 

 t Pogg. Ann. vol. cxxxvii. p. 474. Phil. Mag. S. 4. vol. xxxviii. p. 263. 



