Presence of Neutrons in a Discharge Tube. 597 



such a particle seems a logical extension of present-day 

 views of nuclear structure. The helium nucleus, for in- 

 stance, is believed to consist of four hydrogen nuclei wilh 

 two binding electrons. It is still an open question whether 

 this synthesis has yet been effected under the condit ons 

 prevailing in the ordinary discharge-tube. But if it occurs 

 it is probable that other intermediate products are also 

 formed, one of the most likely possibilities being the forma- 

 tion of a neutral nucleus containing one hydrogen nucleus 

 and one electron. In the ordinary atom of hydrogen we 

 have a single electron separated from the nucleus by a 

 distance of the order of 10 ~ 8 cm. It is here contemplated 

 that a more intimate union of the two is possible, such as. 

 would be obtained if the electron fell into the nucleus, so 

 that the separation became of nuclear instead of atomic 

 dimensions. Such a particle, to which the name neutron 

 has been given by Prof. Rutherford, would have novel 

 and important properties. It would, for instance, greatly 

 simplify our ideas as to how the nuclei of the heavy 

 elements are built up. This building-up process is appa- 

 rently at work in the evolution of stellar sj r stems from the 

 nebular state. It is, however, difficult to see how an 

 additional positively charged hydrogen or helium nucleus 

 could penetrate into the nucleus of a heavy atom. In the 

 case of Radium C, an u particle is ejected from the nucleus 

 with a speed equivalent to a fall through several million 

 volts, and a speed of this order would be necessary to secure 

 its entrance into the nucleus against the repulsion of the 

 existent positive charge. On the other hand, the entrance 

 of a neutral particle would be much more easily effected, and 

 the subsequent expulsion of the negative electron would 

 achieve the necessary increment of nuclear charge. 



In a search for such particles, the most likely place for 

 their existence seems to be amongst the positive rays in a 

 hydrogen discharge-tube. There is in such a tube a plentiful 

 supply both of free hydrogen nuclei and of electrons. If the 

 hydrogen nucleus in its passage through the residual gas 

 acquired a neutralizing electron in the manner above men- 

 tioned, the neutron would, owing to the much greater 

 momentum of the positive nucleus, continue its course with 

 the positive rays with practically unchanged velocity, just 

 as ordinary neutral hydrogen atoms have been shown to do 

 by Sir J. J. Thomson. 



The detection of such high-speed neutrons would be 

 extremely difficult, and none of the arrangements hitherto 

 adopted in dealing with positive rays seems likely to reveal 

 their presence. Owing to the largo energy of formation it 



