ATOMIC NUCLEI — HARNWELL 191 



within the spans of our own lives, and none of these things would 

 be available had not the curiosity of such pure scientists as Becquerel, 

 Thomson, Roentgen, Hallwachs, and Richardson been aroused to 

 investigate seemingly trivial phenomena in their laboratories. This 

 is the answer to "What good is research in atomic physics?" 



The research of the first quarter of this century may be considered 

 to have laid the groundwork for our investigation of the nucleus 

 or innermost core of the atom. This field is the newest and most 

 fascinating and appears to have the greatest eventual possibilities 

 of future benefit. Wliile something was known of it before the last 

 decade, our first control over these phenomena dates from the work 

 of Rutherford in 1919, Since study implies the possibility of con- 

 trolling conditions, nuclear research was born in 1919 and took its 

 first steps with the discovery of more powerful techniques by Ruther- 

 ford's students at the beginning of the present decade. As research 

 on the atomic nucleus is the result of the knowledge we have gained 

 about the external structure of atoms, the methods of attack are 

 fundamentally the same. These techniques themselves are of con- 

 suming interest for an inquiring mind because of the difiiculty of 

 the problem presented. We are investigating the completely un- 

 known and must free ourselves as far as possible from all prejudices 

 and preconceptions in order to make the most of discoveries as they 

 are made and change our points of view, hypotheses, and methods 

 of investigation to evaluate properly the implications of our data. 

 Atoms themselves are so small that we know we can never see them 

 with our eyes, and their cores or nuclei are as much smaller than 

 atoms as they are themselves smaller than ordinary microscopic 

 objects. None of our senses can ever detect single atoms, but a 

 scientist is not content without the most detailed information about 

 them. And this information must be quantitative and highly precise. 

 When so stated, the problem appears hopeless. That it is not really 

 so is partly due to the ingenuity displayed by the investigators, 

 which represents one of the most remarkable intellectual triumphs 

 imaginable, and partly to the common delusion that all our senses 

 are able to yield us quantitative information and that the more of 

 them we can bring to bear the more complete will be our understand- 

 ing. Actually, our only precise sense is vision, and in the field of 

 atomic physics it can only be applied indirectly. We must realize 

 at the outset that we will never Iniow how an atom looks, feels, 

 or smells and that such properties as precise shape, sharply localized 

 boundaries, smoothness, hardness, color simply have no significance 

 as atomic attributes. 



The question then arises: What can we know and how are we to 

 go about finding it out? One answer is that large-scale visual 

 observations on the motion of microscopic particles which act as 



