200 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 39 



the end of the first move has coordinates determined by the sum of 

 all the protons and neutrons involved. The second move depends on 

 the element which is formed and the state of disorganization in which 

 it is left. We have observed helium nuclei, protons, and neutrons to 

 be emitted in various instances and also both positive and negative 

 electrons, probably evidencing a proton-neutron or neutron-proton 

 conversion within. In some instances we have observed two successive 

 processes, but in these one or two moves the process completes itself 

 and we are back on one of our permitted squares representing a known 

 stable element. From observations on the energy put in or liberated 

 in its various forms of motion, mass, and radiation we have learned 

 something more than I have been able to tell you of nuclear 

 mechanics. But it is still essentially a great unexplored field which 

 is rich in scientific possibilities. 



We have seen that research in atomic physics has amply justified 

 itself to society by its important applications which have almost 

 remade our technical civilization. We might ask whether the field 

 of nuclear physics has any such potentialities. The answer is un- 

 doubtedly in the affirmative, though it would indeed be a rash prophet 

 who would undertake to state exactly what developments may be ex- 

 pected. It is impossible to tell how soon our knowledge of, and con- 

 trol over, these nuclear processes will have any reaction on our 

 everyday life, but the processes of technical development and dissem- 

 ination are apt to be even more rapid than in the case of atomic 

 physics. We can only consider here one or two of the possibilities 

 that are at present being tentatively explored. In the first place the 

 possibility of obtaining power from the nucleus is not entirely vi- 

 sionary. With our present techniques the process is very inefficient, 

 though great strides have already been made in this direction. Fur- 

 thermore, this power is of a highly specialized kind and will require 

 as yet undeveloped engines for its utilization. In the second place 

 the neutron which is a little-known entity may be either directly or 

 indirectly of biological significance. Its direct effect on tissue and its 

 various constituents will certainly differ from that of X-radiation 

 for instance, but it is too soon to say just what its effects will be and 

 in what instances they will prove beneficial. 



The possibility of making a small fraction of the atoms of almost 

 any substance radioactive is a development with unbounded poten- 

 tialities, and many interesting applications have already been made. 

 The direct therapeutic effects of the radioactive variants of ordinary 

 elements are the same as those of radium, and if there were no other 

 result than the production of large amounts of equivalent radium, it 

 would be one of the most important discoveries ever made. The fact 



