8 



organizations operating in the field of the nuclear sciences and their applications. 

 This experience had brought about the creation in United States of a few big re- 

 search laboratories such as the Argonne National Laboratory- aud the Brookhaven 

 National Laborator)-. In particular the Brookhaven National Laboratorj- had been 

 created aud run verj- successfully by the Associated Universities, luc. But nothing 

 like it existed in Europe. 



At the same time in many European and American circles, scientists were 

 becoming aware of the continuously increasing gap between the means available in 

 Europe for research in the field of nuclear physics and elemeutarj- particles, and the 

 means available in the United States. It was becoming more and more evident that 

 such a situation could be changed only by a considerable efi"ort made in common 

 by many Euopean nations. 



To these one should add a further important element: immediately after the 

 Second World War cosmic ray research had a ver>- high level in Western Europe 

 and was in part carried out through successful international collaborations. The 

 discover}-, in 1946, by Conversi, Pancini and Piccioni that the cosmic ray mesotron 

 is a weak interacting particle and not a Yukawa particle, the discoveries in 1947 by 

 Lattes, Occhialini and Powell of the jr-meson and of its decay into the muon, and of 

 the first two strange particles by Rochester and Butler, are the most brilliant results 

 of an extensive and rich production obtained in Western Europe. The mountain 

 laboratories m Switzerland, France and Italy and even more the nuclear emulsions 

 laboratories of the Universities of Bristol and Bruxelles, led respectively by Powell 

 and by Occhialini, had become points of encounter of young physicists originating 



