204 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



coefficient, and the pressure coefficient of tellurium has an abnormally large 

 negative value. The other 19 metals are of different behavior, but in broad 

 outline the behavior of all is alike. 



In his last published investigation * Doctor Bridgman has examined 

 the thermo-electric properties of 22 metals, including thermo- 

 electromotive force, Peltier heat, and Thomson heat: 



The results of this paper, unlike those of the previous paper on resistance, 

 are almost entirely novel ; the nature of the results to be expected was not 

 known, and accordingly these effects, so far as affected by pressure, were not 

 available for any theoretical considerations. Previous measurements on the 

 effect of pressure on thermo-electromotive force are very few in number, and 

 cover a very restricted range. The maximum pressure heretofore reached 

 has been by Wagner, 300 kilograms. 



The range employed in this work covers 20 pure metals and 2 alloys and 

 all pressures up to 12,000 kg./cin. 3 and all temperatures between 0° and 100°. 

 The nature of the results was unexpectedly complicated. The normal state 

 of affairs is apparently a positive effect of pressure on both Peltier and Thom- 

 son heats, but there are numerous examples of negative effects, and almost 

 none of the metals show regular variation of these quantities with pressure 

 and temperature within the range. Three metals, tin, iron, and aluminum, 

 show complicated variations of the thermo-electromotive force. The unex- 

 pected complications found make these results disappointingly meager in their 

 suggestions as to the nature of the thermoelectric mechanism. The results 

 suggest most strongly that the thermoelectric mechanism must be complicated, 

 that it can not be at all of the simplicity imagined by the free electron theory, 

 and that most likely the effects which we measure are the resultant of different 

 effects, which sometimes, at least, work in opposite directions. What these 

 effects may be, we are not in a position at present to speculate. 



It may not be too daring to say that it seems to me that much of my pre- 

 vious work on high-pressure effects at least suggests a direction in which we 

 may look for the explanation of these complications. I have shown in detail 

 that probably the properties of both liquids and solids are to be explained in 

 terms of the same agency, the effect of the characteristic shape of the atoms, 

 or, if one prefers to express it so, the nature of the field of force surrounding 

 the atom. It seems most probable that the electrons in passing from atom to 

 atom, or in playing about between the atoms, may be subjected to forces chang- 

 ing in a complicated way as the atoms are forced into positions of varying 

 degrees of adaptation to each other's irregularities. 



1 Proceedings of the American Academy of Arts and Sciences, Vol. 53, 1918. 



