SCIENTIFIC HYPOTHESIS 253 



constitution of the atom from another standpoint but 

 with somewhat similar results. This great physicist 

 had proved that cathode rays are composed not of 

 negatively charged molecules, as had been supposed, 

 but of much smaller particles or corpuscles. Wherever, 

 as in the vacuum tube, these electrons appear, the 

 presence of positively charged particles can also be 

 demonstrated. It is manifest that the atom, instead 

 of being th3 ultimate unit of matter, is a system of 

 positively and negatively charged particles. Ruther- 

 ford in the main concurred in this view, though dif- 

 fering from Sir J. J. Thomson as to the arrangement 

 of corpuscles within the atom. Let it suffice here to 

 state that Rutherford assumes that the greater mass 

 of the atom consists of negatively charged particles 

 rotating about a positive nucleus. The surrounding 

 electrons render the atom electrically neutral. 



This corpuscular theory of matter may throw light 

 on the laws of chemical combination. The so-called 

 chemical affinity between two atoms of such and such 

 valencies, which Davy and others since his time had 

 regarded as essentially an electrical phenomenon, 

 seems now to admit of more definite interpretation. 

 Each atom is negatively or positively charged accord- 

 ing to the addition or subtraction of electrons. Chemi- 

 cal composition takes place between atoms the charges 

 of which are of opposite sign, and valency depends on 

 the number of unit charges of electricity. Moreover, 

 the electrical theory of matter lends support to the hy- 

 pothesis that there is a fundamental unitary element 

 underlying all the so-called elements. The fact that 

 elements fall into groups and that their chemical prop- 

 erties vary with their atomic weights long ago sug- 



