﻿138 Dr. F. A. Lindemann on the 



difficulty emphasized by Bragg, that the energy o£ photo- 

 electrons is often greater than the incident energy of the 

 light falling on one electron. A large part of the wave-front 

 can act upon the electron space-lattice. The additional 

 assumption of zero-point energy would of course still further 

 simplify matters. Whether the selective photo-effect is due 

 to peculiarly numerous proper frequencies within a small 

 region, such as Born and Karman found in ordinary crystals, 

 must be decided by experiment. If, as seems more probable, 

 it is due to other intra-atomic electrons, a gas should show a 

 selective effect though it should not have a normal effect. 



Hall Effect. — The Hall effect would be explained exactly as 

 it is done in the ordinary theory. A magnetic field would 

 tend to make the electron space-lattice drift off at right 

 angles as it would do to cathode rays. To explain the 

 inverse Hall effect this theory needs the same hypothesis of 

 atomic magnetic fields as has been introduced to explain the 

 phenomenon on the old lines. 



Thomson Effect. — As the electron space-lattice moves, 

 this being the electric current, the temperature inequalities 

 in it may be expected to move with it. The quantitative 

 relations involve, however, the question of the interchange 

 of energy between the atoms and the electrons, and how 

 elementary our knowledge of this question is, is proved by 

 the quantum theory. 



Nernst-Ettiugsliausen Effect. — Though it is probable that a 

 magnetic field must deform a lonoitudinal elastic wave in an 

 electron space-lattice, thus producing a transverse electro- 

 motive force during heat conduction, the problem cannot be 

 attacked without more detailed knowledge of the interaction 

 of the atoms and electrons. 



Hitherto only crystals have been considered, but in the 

 actual met;ds with which experiments have been made we 

 have to deal with an agglomeration of crystals. Obviously 

 this will not invalidate the conclusions drawn above, for to 

 all intents and purposes all the effects are additive. One 

 could only expect to find a difference if the crystals were of 

 the same order of magnitude as the molecules, for only then 

 would the boundary effects become of the same order as the 

 volume effects. Perhaps the fact that cold drawing increases 

 the resistance of wires, whereas annealing diminishes it, may 

 be an indication that this is true ; for cold drawing obviously 

 breaks up the crystals which tend to join up again through 

 annealing. At first sight one might expect the specific 

 electric resistance of a metal crystal to be different in 



