202 PHYSICAL SCIENCE 



result as nitrogen (14): boron (11), fluorine (19), 

 sodium (23), aluminium (27), and phosphorus (31). 

 All these elements, and possibly a few others, 

 give hydrogen scintillations beyond the range of 

 ordinary hydrogen, and are therefore thought to 

 be broken up by the bombardment. 



This interpretation is confirmed by the 

 evidence of the atomic weights. The atomic 

 weights of the elements named are given by 

 the general formulae ^.n + 2 or 4;^ + 3, where 

 71 is a whole number. Other elements such as 

 oxygen (16) or carbon (12), which have atomic 

 weights represented by /[n, are not active. Now 

 when we come to deal with the modern theory 

 of the atom, we shall see that these latter elements 

 may be supposed made up of n helium nuclei each 

 of weight 4, while the active elements have two 

 or three units in addition, which may well be 

 hydrogen nuclei each weighing one unit. Hence 

 all the evidence is in favour of the view that the 

 nuclei of the atoms of the elements boron, nitrogen, 

 fluorine, sodium, aluminium, and phosphorus are 

 built up of helium and hydrogen, and that the 

 nucleus is shattered by a rays, with the ejection 

 of hydrogen particles. 



We shall consider the problem of the structure 

 of the atom in greater detail in the next chapter ; 

 here we are concerned only with the broad result 

 that Sir Ernest Rutherford has not only taught 

 us that radio-activity is due to the spontaneous 

 explosion of atoms, but has now shown us how 

 to produce disintegration in elements usually in- 

 active, by using the concentrated energy of an 

 a ray projectile. 



Thus we approach even nearer to the hope 



