determine the nature of knowledge, and solves the problem by defining 

 knowledge to be the perception of the connection of^and agreement 

 or disagreement of ideas. However, Locke also sought into the 

 origin of knowledge, and set forth the process by which it was 

 produced. This part of his theory falls under the first class of 

 theories in which the problem was that of origin; and solution that 

 of revealing process. We find, that the theory that matter is electrical 

 is also a theory of definition. The problem was to determine what 

 matter essentially is; and the solution consisted in showing that matter 

 is electrical in nature. Thus the theories examined reveal two dis- 

 tinct classes of theories from the point of view of problem and 

 method of solution. 



They also exhibit two well defined classes from the point of view 

 of the method of procedure by which the theories were derived. The 

 method of procedure in one class consists of observation and experi- 

 ment, and inference from facts thus revealed. Some of the theories 

 in this class make use of an occasional assumption. 



I shall first treat of those theories which proceed by observation 

 and experiment and do not make use of assumptions. Darwin's 

 theory is such. He observed the individual variations of plants and 

 animals in nature and under domestication. He also observed how 

 man selects the variations which suit plants and animals to his pur- 

 poses, and how nature selects those variations which fit the organism 

 to live. He experimented to determine more fully how great indi- 

 vidual variations were and how much change could be produced by 

 accumulating them in the off-springs. Thus Darwin determined the 

 existence, nature, and extent of individual variation and natural se- 

 lection, by observation and experiment. Observation also revealed 

 the nature of past organic life, the remains of which had been de- 

 posited in the Earth's crust. The inference of which this theory 

 consists followed directly from these observed and experimental facts, 

 without the assumption of the existence of any others or of their 

 nature. 



The theory of inorganic evolution was derived by the same method 

 of procedure. The transformations of elements under different de- 

 grees of temperature producible by artificial means, and exhibited 

 by solar conditions and in the stars, were observed and carefully 

 investigated. The inference, that diversity of elements had originated 

 by virtue of changes in temperature, was based directly upon these 

 observed and experimental facts. 



There are some theories which make use of the same method of 

 procedure but also contain occasional assumptions. The theory that 

 matter is electrical is such. It is not shown by a direct investiga- 



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