THE PROPERTIES OF METALLIC SUBSTANCES 405 



TABLE CLXII. 



VALUES OF THE THERMOELECTRIC COEFFICIENTS a AND (3 WITH RESPECT 

 TO LEAD IN MICROVOLTS PER DEGREE. 



Metal Si Te a Sb || Fe Li Ag Pb 



a +443 + 163 + 22.6 + 13.4 + 11.6 + 2.3 



(3 X 10 2 . . . . . . . . 3.0 +3.9 -f- 0.76 



Metal Mg Sn Na K Co Ni Bi || 



a 0.12 0.17 4.4 11.620.4 23.3 127.4 



(3 X 10 2 . . 4- 0.20 + 0.20 - 2.1 2.5 - 7.5 0.8 70. 



the opposite ends of the table. Similar inversions are found in the case 

 of other closely related elements, such as iron, cobalt and nickel. 



In alloys, the thermoelectric force is, in general, a function of the 

 composition. The thermoelectric force of heterogeneous alloys varies 

 approximately as a linear function of the composition, while that of 

 homogeneous alloys, in general, exhibits a marked minimum somewhat 

 similar to that of the conductance curve. The thermoelectric power of a 

 compound, in general, differs from that of its component elements. The 

 formation of compounds by a given pair of elements is indicated by dis- 

 continuities in the curves connecting the thermoelectric force with the 

 mean composition of the alloy. As a rule, the thermoelectric force is 

 high for compounds which are relatively poor conductors. For a more 

 detailed discussion of the thermoelectric properties of metals the reader 

 is referred to the various handbooks in which these data have been 

 collected. 



10. Galvanomagnetic and Thermomagnetic Properties. When a cur- 

 rent of electricity flows through a conductor, the distribution of the 

 current in the conductor is altered under the action of an external mag- 

 netic field. The effects observed depend upon the relative direction of 

 the current and of the field. The application of the magnetic field, there- 

 fore, gives rise to potential differences between points in the conductor 

 which normally are at the same potential. With a field acting at right 

 angles to the direction of the current flow, potential differences arise in 

 the conductor transverse to the magnetic field, one at right angles to the 

 direction of the current flow and the other parallel to this direction. 

 With a longitudinal field, that is, a field acting parallel to the direction 

 of the current flow, only a single effect is observable; namely, an electro- 

 motive force parallel to the direction of current flow. Similar effects 

 are observed when a current of heat flows through a conductor in a mag- 



