PROBLEMS OF MODERN SCIENCE 



of earthquake phenomena, and so forth. Perhaps 

 this mere list may serve to shew the very wide 

 range of work which comes within the province 

 of Mathematics, and the arbitrary character which 

 must belong to any selection which can be made 

 for the purposes of a lecture. I must crave indul- 

 gence from my readers for any omission of a sub- 

 ject which would have been found more interesting 

 than those I have selected as types. 



But there is one group of subjects, with which 

 I shall conclude, for which a general title is not 

 readily found. They belong as much to Physics 

 as to Mathematics, being essentially what are called 

 * border-line ' subjects, and include the general 

 laws of dynamics in the microscopic field as 

 distinct from the statistical aggregates of dynamical 

 laws, which are the laws we postulate macro- 

 scopically, that is to say, for matter in bulk the 

 ultimate laws of radiation from the smallest pos- 

 sible system, an atom or an electron, the principles 

 of the Quantum Theory, and the structure of the 

 atom. Perhaps, in view of the nature of the pro- 

 gress now being made rapidly in this domain, 

 we might group all these subjects together as 

 Quantum Theory, for it is the introduction of 

 this theory by Planck which has alone made 

 possible any real advance from the point which 

 the so-called ' older ' electrodynamics had reached 

 several years ago. We may describe this older 

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