TRANSMUTATION" OF MATTER — RUTHERFORD 207 



conception of the varieties of atomic nuclei which can exist in Nature. 

 Not only has it led to the discovery of about 100 new radioactive 

 elements, but also of several stable isotopes of known elements, like 

 3 H, 3 He, 8 Be, which had previously been unsuspected. It has greatly 

 extended our knowledge of the ways in which nuclei can be built up 

 and broken down, and has brought to our attention the extraordinary 

 violence of some of the nuclear explosions which occur. The great 

 majority of our elements have been transmuted by the bombardment 

 method, and in the case of the light elements which have been most 

 carefully studied, a great variety of modes of transmutation has been 

 established. 



Rapid progress has been made, but much still remains to be done 

 before we can hope to understand the detailed structure and stability 

 of different forms of atomic nuclei and the origin of the elements. I 

 cannot but reflect on the amazing contrast between my first experi- 

 ment on the transmutation of nitrogen in the University of Man- 

 chester in 1919 and the large-scale experiments on transmutation 

 which are now in progress in many parts of the world. In the one 

 case, imagine an observer in a dark room with very simple apparatus 

 painfully counting with a microscope a few faint scintillations origi- 

 nating from the bombardment of nitrogen by a source of a-particles. 

 Contrast this with the large-scale apparatus now in use for experiments 

 on transmutation in Cambridge. A great hall contains massive and 

 elaborate machinery, rising tier on tier, to give a steady potential of 

 about 2 million volts. Nearby is the tall accelerating column with 

 a power station on top, protected by great corona shields — reminding 

 one of a photograph in the film of Wells's, The Shape of Things to 

 Come. The intense stream of accelerated particles falls on the target 

 in the room below, with thick walls to protect the workers from stray 

 radiation. Here is a band of investigators using complicated electrical 

 devices for counting automatically the multitude of fast particles 

 arising from the transformation of the target element, or photograph- 

 ing with an expansion chamber, automatically controlled, the actual 

 tracks of particles from exploding atoms. 



To examine the effect of still faster particles, a cyclotron is installed 

 in another large room. The large electromagnet and accessories are 

 surrounded with great water tanks containing boron in solution to 

 protect the workers from the effect of neutrons released in the appa- 

 ratus. A power station nearby is needed to provide current to excite 

 the electromagnet and the powerful electric oscillators. 



Such a comparison illustrates the remarkable changes in the scale 

 of research that have taken place in certain branches of pure science 

 within the last 20 years. Such a development is inevitable, for, as 

 science progresses, important problems arise which can only be solved 

 by the use of large powers and complicated apparatus, requiring the 



