1. In a recently published paperZeit. für Phys1926 xxxvi 2
2. 1923.Phys. Rev., xxi(2)
3. Vide e.g. Richardson O.W.Electron Theory of Matter306 306
4. Kallmann and Mark .loc. cit.134–134. have independently arrived at this conclusion by a process of reasoning essentially the same as that used here.