206 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
are low in extranuclear phenomena and high in the case of nuclear 
phenomena. Moreover, physicists for the past several years have been 
studying certain phenomena which represent energy concentrations 
many thousands of times greater than those represented even by 
nuclear phenomena. This range of energies has been called the range 
of ludicrously high energies. So far the only opportunity the physicist 
has had to study phenomena in the range of ludicrously high energies 
is in connection with observations associated with cosmic rays, and we 
shall see in a moment that important knowledge of the elementary 
particles of matter has come from studies of phenomena in the range 
of ludicrously high energies. 
As stated previously, by 1930 two elementary particles of matter 
were known to the physicist, the electron which always occurred with 
a negative electric charge and the proton which always occurred with 
a positive charge. When considered in a manner consistent with the 
theoretical concepts as they had been developed up to that time in 
terms of the quantum mechanics, the negative electron and the positive 
proton served quite successfully as building blocks in terms of which 
to understand the structure of atoms so far as the extranuclear phe- 
nomena were concerned. But when attempts were made to picture the 
structure of the nuclei of the various chemical atoms, or to understand 
nuclear phenomena, the attempts usually ended in failure. 
Then suddenly in 1932 two new elementary particles were dis- 
covered: the neutron and the positive electron, or positron. The known 
elementary particles were therefore doubled in number, increasing from 
two to four, and providing the physicist with more material with which 
to work. 
The discovery of the neutron, which came as a result of experiments 
performed in Germany, in France, and in England, was immediately 
welcomed, for now neutrons together with protons could serve as the 
building stones for the various types of atomic nuclei. One very grave 
and fundamental problem which formerly had been present was now 
removed immediately, for it was no longer necessary to assume the 
existence of electrons inside the nucleus, a concept which always had 
been accompanied by serious theoretical difficulties. 
The discovery of the positive electron, or positron, came during a 
series of experiments being performed for the purpose of measuring 
the energies of the particles produced by cosmic rays. The discovery 
of the positron was an unexpected discovery. This statement is true 
even though, about 2 years before, a British physicist, Dirac, had an- 
nounced a new theory which actually predicted the existence of posi- 
trons. This new feature of physical theory was not welcomed by 
physicists, however; it was on the contrary considered to be an un- 
fortunate defect in the theory, and many attempts, by Dirac himself 
