226 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



river or cooling tower, owing to the unfortunate inefficiency of the heat 

 engines. 



Heat energy is simply violent agitation of the atoms of which sub- 

 stances are made. These heat motions are random in direction and 

 amount and can only be converted into organized motion, such as the 

 rotation of machinery, i. e., into useful power, by means of heat en- 

 gines. It is an immutable law of nature that the transformation of 

 heat into useful power can be carried out only by processes that waste 

 the larger part of the heat energy. 



The inner parts of atoms are the seat of forces far greater in mag- 

 nitude than those associated with the outer "chemical" part. An atom 

 is similar to a solar system, with a minute sun, or nucleus, at the 

 center, surrounded by satellite electrons. Approximately 100 million 

 atoms placed side by side measure 1 inch, and the nucleus of an atom 

 is so small that 1 million million nuclei placed side by side are needed 

 to measure 1 inch. Yet this minute nucleus contains all the positive 

 electric charge and practically the whole of the mass of the atom. 

 Despite its small size, physical science has gained, by indirect meth- 

 ods, a great deal of information about its properties and structure. 

 The existence of the nucleus was discovered by Lord Rutherford when 

 he held the Chair of Physics in Manchester, and its properties were 

 unraveled by him and his collaborators in Manchester and Cambridge. 

 In fact, nuclear physics, the study of this minute world, is a peculiarly 

 British creation, and remained so until the successful release of nu- 

 clear energy and the colossal expenditure necessary to provide the 

 equipment for research in this field, moved the center of achievement 

 to the United States. Those of us who worked in this fruitful field 

 of human intellectual endeavor harbor nostalgic feelings for the days 

 when it was of purely academic interest and work was stimulated by 

 the knowledge of the structure of matter which it brought, rather 

 than by the desire to make bigger and better atomic bombs or to pro- 

 vide the world with a new source of power. 



We believe the nucleus to be built up from entities to which we give 

 the name "elementary" or "fundamental" particles, because, at the 

 present time, we are unable to demonstrate that they possess any sign 

 of structure. This belief may be as mistaken as the idea of the Vic- 

 torian scientist that atoms themselves were elementary particles that 

 had existed as hard, round billiard balls ever since they were created. 

 The elementary particles in the nucleus are protons, which carry a 

 positive charge of electricity, and neutrons, which have no electric 

 charge. The forces holding these particles together are very large 

 indeed, many orders of magnitude greater than the forces holding to- 

 gether the atoms of ordinary matter. If the atoms in a spider web 

 were held together as strongly as the component parts of the nucleus, 

 a single thread would support a battleship. The number of protons 



