by Locke and investigated so as to reveal its properties. Being like 

 nothing in experience, a modification of the mind or an impression 

 upon it, is like no modification or impression of which we know. 

 Therefore the nature of the idea and the manner of its origin are 

 unintelligible to us. Neither is the manner in which the ideas re- 

 semble or copy objects like any resembling or copying of which we 

 know. Therefore th manner in which ideas copy or resemble 

 things, we cannot comprehend. 



This statement of the theory, its method of procedure, and 

 characteristics will serve as a basis for study and comparison in 

 connection with the other theories here dealt with. 



THE THEORY OF IONS. 



Another type of thinking is represented by the theories presented 

 in Duncan's "The New Knowledge." The theories are as follows. 

 Upon examination, the atomic weights of many of the elements are 

 found to be approximately whole numbers. The elements can be ar- 

 ranged in groups having closely resembling qualities and having con- 

 stant relations between their atomic weights. In short, it is found 

 that, "the properties of an element are a periodic function of its 

 atomic weight." This law has been many times confirmed in differ- 

 ent ways. 



Now the scientist reasons thus: either the elements were created 

 (or are) each unique in substance and structure and the relations be- 

 tween them, expressed by the periodic law, are chance relations; or 

 the atoms of elements are complex, and uniformities in their struc- 

 tures will explain uniformities in their properties. Only if this latter 

 hypothesis is true, can we explain the periodic law. 



But, because the assumption that the atom is complex in struc- 

 ture is the only one upon which the periodic law can be explained, 

 the scientist does not take this assumption to be established theory, but 

 begins to investigate to determine the validity of the assumption. 



He finds that groups of atoms unite together to form bodies with 

 related properties and group relationships, and he finds that groups of 

 atoms unite and act like elements. Thus the scientist reasons, that 

 if combinations of atoms may act like elements and may form, by 

 variation in number and arrangement, compounds related as the ele- 

 ments are related, is it not probable that sub-atoms form elements and 

 by their number and arrangements furnish an explanation of the 

 periodic law? 



But more direct evidence of the complexity of the atom is de- 

 manded and obtained by the scientist. He finds that gases under 

 certain conditions have an increased conductivity. When the gas is 



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