342 ELEMENTARY LESSONS ON [CHAP. vm. 



CHAPTER VIII. 



THERMO-ELECTRICITY. 



LESSON XXXIV. Thermo-Electric Currents. 



379. In 1822 Seebeck discovered that a current may 

 be produced in a closed circuit by heating a point of 

 contact of two dissimilar metals. Thus, if a piece of 

 bismuth and a piece of antimony be soldered together, 

 and their free ends be connected with a short -coil 

 galvanometer, it is found that if the junction be warmed 

 to a temperature higher than that of the rest of the 

 circuit, a current flows whose direction across the heated 

 point is from bismuth to antimony, the strength of the 

 current being proportional to the excess of temperature. 

 If the junction is cooled below the temperature of the 

 rest of the circuit a current in the opposite direction is 

 generated. The electromotive -force thus set up will 

 maintain a constant current so long as the excess of 

 temperature of the heated point is kept up, heat being 

 all the while absorbed in order to maintain the energy of 

 the current. Such currents are called Thermo-electric 

 currents, and the electromotive -force producing them 

 is known as Thermo-electromotive-force. 



380. Peltier Effect. In 1834 Peltier discovered 

 a phenomenon which is the converse of that discovered 

 by Seebeck. He found that if a current of electricity 

 from a battery be passed through a junction of dissimilar 

 metals the junction is either heated or cooled, according 



