XVIII. 3] INTERPRETATION OF THE QUANTUM 249 
What will be the issue of the struggle ? It may happen that 
one of the two theories will occupy step by step the territory of 
the other. Schrodinger in 1922 made some progress in this 
direction when he gave an explanation of Doppler’s principle by 
the theory of quanta. Kramers in 1924 made an attempt to 
account for the law of dispersion of light by employing Bohr’s 
principle of correspondence. On the other hand, it may happen 
that some artificial reunion can be effected between the two 
theories, and several investigators have worked in this direction. 
Probably, in this conflict as in that between other antagonistic 
physical theories, a new and more comprehensive theory will be 
found which will embody the more important principles of the 
two rivals. It seems that already the work of de Broglie and of 
Schrodinger is pointing the way towards such an all-embracing 
theory. 
3. Atomic Models 
Physicists in general take up the pragmatic standpoint 
illustrated by the quotation from Sir Joseph Thomson which 
stands at the head of the present chapter. For them a working 
theory is a theory that works, in the sense that it co-ordinates 
known facts and suggests new lines of investigation. But this 
need not abrogate the quest for a more complete and all-embracing 
synthesis. 
An excellent illustration of the development of theory is 
afforded by the history of the attempts that have been made to 
devise a model of the atom. In the older model of Kelvin and 
J. J. Thomson the electrons were at rest in a sphere of positive 
electricity. Later on J. J. Thomson devised a kinetic model in 
which the electrons revolved in orbits controlled by the positive 
charge. These models served a most useful purpose, especially 
in providing a physical interpretation of the periodic classifica 
tion of the elements. Static models, though somewhat out of 
favour, may still serve a useful purpose, and may even be 
employed for approximate calculations (Chapter IX). The work 
of Ritz, though left uncompleted, emphasized the magnetic 
aspects of the problem of atomic structure, which for a time 
tended to become somewhat obscured. 
The extraordinary success which has attended the theory of 
the nuclear atom developed by Rutherford must not blind us 
to the fact that we have here to do with an atomic model, which 
is probably only a crude representation of the actual facts of 
intra-atomic structure. The law of the inverse square of the 
distance on which the model is based may be interpreted in 
other ways than by the assumption of point charges (Chapter