646 BELL SYSTEM TECHNICAL JOURNAL 



and the elcclrons.^ The\' may be lonipalihK' with otluT aluni-inodels; 

 it is certainh' incumbent upon the designer of any other to prove that 

 they are compatible with his. Furthermore these deflections indicate 

 that the positi\e charge on the nucleus of the atom is just sufficient to 

 compensate the negative charges of a number TV of electrons, equal 

 to the "atomic number" Z which is the cardinal number defining 

 the position of the element in the Periodic Table of the Elements. 

 This confirmation of the splendid idea of van den Brock and Moseley 

 is so delightful and so precious, that anyone would hesitate long 

 before rejecting the atom-model whereby it is deduced from Ruther- 

 ford's experiments. 



Yet this nuclear atom-model cannot be accepted, without being 

 instantly modified. A system consisting of a positively-charged 

 nucleus and electrons surrounding it, all acting upon one another with 

 inverse-square forces of attraction between nucleus and electrons and 

 repulsion between one electron and another, is not a stable system; 

 it is a suicidal system, doomed to quick and permanent collapse. If 

 the electrons were initially standing still, they would fall into the 

 nucleus; if the electrons were initially swinging in orbits about the 

 nucleus like planets around the sun, they would steadily radiate their 

 energy into space — not in radiation of one single frequency either, 

 but in a mixture of all possible frecjuencies — and would wind their 

 ways spirally into the nucleus. Therefore, the nuclear atom-model 

 must be altered; for instance, by adding a i)roviso, that the electrons 

 shall stand still, and shall not be sucked into the nucleus; or a pro- 

 viso, that the electrons shall revolve in closed orbits planetwise, 

 without radiating any of their energy *, and without gliding by a 

 spiral path into the nucleus. 



-Suppose then that we decide lo make one or llie oilur ol ihcse 

 provisos, in order to save the interpretation of Rutherford's experi- 

 ments. Could we then so shape the proviso, that it would satisfy 

 the four demands which I described as being made upon the atom- 



' -Apart from such deviations in the immediate neighborhood of the nucleus as 

 the most delicate experiments of this sort reveal; which cannot be supposed to 

 extend to the region where the electrons are. 



•To indicate how much this neglect of the radiation from the revolving electron 

 amounts to, I cite the results of a calculation given by W'ien in his lecture Veber 

 Elektrnnen, and doubtless elsewhere. Imagine an electron distant by ten -Xngstrom 

 units from a hydrogen nucleus, and moving with such a velocity that, but for the 

 radiation, it would revolve in a circle about the nucleus. In a single circuit, it 

 should radiate about one ten-millionth part of the kinetic energy it initially possesses. 

 Hence the single circuit will differ very little indeed from a perfect circle; and in this 

 sense, the radiation is truly negligible. Hut the single circuit is described in less 

 than lO""" secomi; hence, in any time-interval long enough to be measured by the 

 most delicate of physical apparatus, the dissipation of energy by radiation is far 

 loo great lo be neglected wilh impunity. 



