CONTEMPORARY ADVANCES IN PHYSICS 295 



can deduce the magnetic moment of the nucleus itself. This has 

 already been done in several cases. Perhaps it will he possible in 

 time to attribute the magnetic properties of solid bodies, even of 

 ferromagnetics, in part to their nuclei; but probal)ly that is looking a 

 long way ahead. 



One more participation of the nucleus in phenomena remains to 

 be recorded. The passage of X-rays and gamma-rays — that is to 

 say, high-frequency light — through strata of matter has been abun- 

 dantly studied. For the most part it is admirably well accounted 

 for by supposing that the corpuscles of these rays possess the power, 

 and only the power, of expelling orbital electrons from atoms through 

 which they pass; any particular corpuscle either makes such an 

 expulsion and vanishes or loses energy in doing so, or else it goes 

 through the substance unafTected. There are two alternative modes of 

 expulsion, but that is a detail into which we need not enter now. 

 The relevant point now is, that with certain kinds of atoms and with 

 particularly high frequencies of light it appears that these processes 

 are not the whole of what is happening. The absorption and the 

 scattering of X-rays are greater than they should be, if the photons 

 interacted only with orbital electrons; and it is supposed that the 

 excess is due to interactions with nuclei. Presumably it would be 

 greater with the rays of immeasurably high frequency which probably 

 form a part of the cosmic radiation. 



Nuclei, then, contain almost the whole of the mass of ponderable 

 matter. They are the seat of radioactivity. They may be disrupted 

 by impacts of other and lighter nuclei, possibly by electrons and 

 photons. They influence spectra through their charges and their 

 masses, and through the closely-connected qualities of magnetic 

 moment and angular momentum. Through their magnetic moments 

 they are responsible in part for the magnetic properties of atoms and 

 of larger pieces of matter. They interact with high-frequency X-rays. 

 Such is the range of phenomena in which the nucleus takes a significant 

 part, and out of which, therefore, the properties of the nucleus are 

 to be derived. 



In the present article I will describe and discuss these phenomena in 

 succession. Some have been treated already in earlier articles in this 

 journal, a fact of which I will avail myself to shorten this one, which 

 nevertheless must extend into following issues. 



The Elementary Particles 



There are now six different kinds of material corpuscles known by 

 direct experiment, of which there is more or less reason to believe that 



