14 PRACTICAL LESSONS IN SCIENCE. 



be more or less in harmony with natural phenomena, and they 

 may more or less fully agree with accepted ideas in science, but 

 they differ from natural laws, in that they attempt to explain 

 how a given order of phenomena might have been produced. 

 They are made by men who are fully acquainted with what is 

 known of the subject and whose gifts are often higher than 

 knowledge. Call it genius, call it intuition, or by whatever name, 

 there is an element which we all recognize in such creative minds 

 that enables them to apprehend truth in a manner and to an 

 extent which ordinary men cannot appreciate or understand. 

 Such theories are inductions and the whole history of science is 

 simply the story of verified inductions. 



Many theories have failed when tested by experiment and ex- 

 perience, others have been verified and are permanent landmarks 

 in the field of science. The theories of Ptolemy and Aristotle 

 dominated the intellectual world for more than a thousand years. 

 Those theories were good working propositions, the best the 

 world then had, and it was hundreds of years before advancing 

 knowledge began to find out their weakness. To us they may 

 seem fanciful and crude, but considering the amount of knowledge 

 possessed by man those theories, for their time, were creditable. 

 If, without telescope, charts, or higher mathematics, one should 

 attempt to formulate some scheme to account for the motions 

 of the sun, moon, planets and stars, his respect for the old 

 Egyptian astronomers would be greatly enhanced. 



At the present time, besides many lesser theories, there are 

 four great systems of science under whose guidance most of the 

 scientific work of to-day is being done. These are the theory of 

 universal gravity, the undulatory theory of light and heat, the 

 molecular theory of matter, and the theory of organic develop- 

 ment. These may or may not stand the test of progressive inves- 

 tigations, but they are good working theories and the best and 

 only ones we have regarding their subject-matter. Their value 

 and bearings will be developed in our treatment of the various 

 branches of science. 



