THE CONSTITUTION OF MATTER 13 x 



of its approach to the alpha particle, it can be simply calculated that 

 the centers of the nuclei must have passed within 10 -13 cm. of each 

 other. This is an extraordinarily small distance, even smaller than 

 the diameter of the electron itself. It is thus clear that the nuclei of 

 hydrogen and of helium must be exceedingly minute. It should be 

 borne in mind that such observations only give a maximum limit to 

 the size of the nucleus, and there is no experimental evidence against 

 the view that the nucleus of the hydrogen atom may not actually prove 

 to be minute in volume compared even with the negative electron. If 

 this be the case, it appears probable that the hydrogen nucleus is the 

 'positive electron and that its great mass compared with the negative 

 electron is due to the greater concentration of its charge. According 

 to modern theory, the electrical mass of a charged particle varies in- 

 versely as its radius. The greater mass of the positive than of the 

 negative electron would thus be explained if its radius were only 1/1800 

 of that of the negative electron, viz., about 10~ 16 cm. 



There is no evidence to contradict this point of view, and its sim- 

 plicity has much to commend it. In viewing the essential differences 

 exhibited by positive and negative electricity in connection with matter 

 and the obvious asymmetry of the distribution of the two electricities 

 in the atom, one is driven to the conclusion that there is a fundamental 

 distinction between positive and negative electricity. Since the unit 

 of positive charge is identical in magnitude with the unit of negative 

 charge, the only possible difference is the mass of the two units, and 

 this on modern views is mainly dependent on the dimensions or degree 

 of concentration of the electricity in these fundamental entities. 



If we take the view that the hydrogen nucleus is the positive elec- 

 tron, it is to be anticipated that the nuclei of all atoms are built up of 

 positive and negative electrons, the positive electricity being always in 

 excess, so that the nucleus shows a resultant positive charge. The mass 

 of the atom will depend mainly on the number of the massive positive 

 electrons in the nucleus, although it will be affected to a slight extent 

 by the number of the lighter negative electrons involved in the struc- 

 ture of the whole atom. The" mass of the atom will no doubt be in- 

 fluenced also by the distribution of the positive and negative electrons 

 in the nucleus, for these must be packed so closely together that their 

 field must interact. As Lorentz has shown, the mass of a number of 

 closely packed electrons is not necessarily the same as the sum of indi- 

 vidual masses of the component electrons. Taking such factors into 

 account, we should not necessarily expect the mass of all atoms to 

 be nearly an integral multiple of the mass of the hydrogen atom, 

 although it is known that in a number of cases such a relation appears 

 to hold fairly closely. 



The appearance of a helium atom in such a fundamental process as 

 the transformation of radioactive atoms indicates that helium is one 



