﻿136 Dr. F. A. Lindemann on the 



positively charged on being placed in contact with, a metal 

 of smaller atomic volume. Similarly, their electrons will go 

 into solution more easily than those of other metals, i.e. they 

 are electropositive. 



Thermoelectric effect. — The internal pressure of the electron 

 space-lattice will obviously depend upon the temperature 

 mainly on account of the thermal expansion of the metal. 

 But it will not necessarily change with the temperature 

 according to the same formula in different metals. Therefore 

 if a ring is formed of two different met. lis and the two 

 junctions kept at different temperatures, the difference of 

 the internal pressures at the one junction will not necessarily 

 be counterbalanced by the difference at the other junction. 

 In all cases in which the pressure differences are not equal 

 and opposite, a current will flow in the ring and continue 

 flowing as long as the temperatures of the two junctions are 

 kept constant. 



In a metal in a state of strain, the relative positions of the 

 atoms and electrons would be slightly different from the 

 positions in the unstrained state. This would lead to changes 

 in the elastic coefficients of the electron space-lattice, and 

 thus probably to thermoelectric effects between parts under 

 different stresses. 



Peltier Effect. — The electron space-lattice in a metal has a 

 certain stability, and may consequently be expected to have 

 a certain latent heat of fusion. The passing of electricity 

 from one metal to another entails the melting of the electron- 

 crystal in the metal connected to the negative pole and the 

 solidifying in the other metal. The difference in the different 

 latent heats of fusion will be absorbed or liberated at the 

 junction according to whether the current flows from the 

 metal whose electron space-lattice has a large latent heat of 

 fusion to the one whose latent heat of fusion is smaller or 

 vice versa. 



Richardson Effect. — Just as any other crystal, a crystal com- 

 posed of electrons must have a certain vapour pressure. As 



in the case of solids, this may be expressed by a formula of the 

 _ E 



form Ae T c , a similar formula to that found already by 

 Richardson. 



Reflexion. — As observed above, the resistance of a metal 

 should be independent of the period of the current if this is 

 greater than v'~ m the period of the atoms. The resistance 

 opposed to the more rapid alternations of the currents 

 induced by reflexion of shorter waves than the " remaining 

 rays" must depend upon the number of electrons involved. 



