PREHISTORIC SCIENCE 



friction, as illustrated in the rubbing together of two 

 sticks, may produce heat enough to cause afire. The 

 rationale of this last experiment did not receive an 

 explanation until about the beginning of the nineteenth 

 century of our own era. But the experimental fact 

 was so well known to prehistoric man that he employed 

 this method, as various savage tribes employ it to this 

 day, for the altogether practical purpose of making a 

 fire ; just as he employed his practical knowledge of the 

 mutability of solids and liquids in smelting ores, in 

 alloying copper with tin to make bronze, and in casting 

 this alloy in molds to make various implements and 

 weapons. Here, then, were the germs of an elementary 

 science of physics. Meanwhile such observations as 

 that of the solution of salt in water may be considered 

 as giving a first lesson in chemistry, but beyond such 

 altogether rudimentary conceptions chemical knowl- 

 edge could not have gone unless, indeed, the prac- 

 tical observation of the effects of fire be included ; nor 

 can this well be overlooked, since scarcely another 

 single line of practical observation had a more direct 

 influence in promoting the progress of man towards 

 the heights of civilization. 



4. In the field of what we now speak of as biological 

 knowledge, primitive man had obviously the widest 

 opportunity for practical observation. We can hardly 

 doubt that man attained, at an early day, to that con- 

 ception of identity and of difference which Plato places 

 at the head of his metaphysical system. We shall urge 

 presently that it is precisely such general ideas as these 

 that were man's earliest inductions from observation, 

 and hence that came to seem the most universal and 



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