220 i'ACTS AJSTD THEORIES. 



ago, and in it tells his readers of tlie sad catastrophe that 

 would have occurred, had the sun been made a few times 

 more massive than it is, for that would have so increased 

 its attractive power that the luminous corpuscles shot 

 forth from its surface, would have been drawn back be- 

 fore they reached the planet Mercury, just as the earth 

 draws back a stone before it reaches the clouds. And 

 so, all the planets, our own included, would have re- 

 mained forever in darkness. 



At no time has theory-making gone on more largely 

 than now. At no time have theories influenced more 

 profoundly the currents of thought than to-day. Yet 

 every thinking man knows, partly from the large pro- 

 portion of once fair and flourishing theories that have 

 perished, and partly from the enormous load of 

 hypothesis that many theories carry, that our children 

 will wonder how the present generation could believe 

 many things which now seem indisputable. 



Plain men who make no pretention to be philosophers, 

 but desire to learn all they can from those who they 

 think know so much, may well be perplexed, and ex- 

 claim : " Is there nothing settled in science? Is there 

 nothing real ? Nothing that one can tie to, and be sure 

 that it will always be there ? " 



Yes, there is much that is permanent. All science 

 consists of two very distinct catagories, facts and 

 theories. The latter attract the public eye and are ap- 

 parently much the more important, but the former alone 

 have self-contained value. Facts are true now and al- 

 ways ; all else may change, they never do. Theories 

 may come, and theories may go, but a fact is a fact for- 

 ever. We may, indeed, be mistaken, and regard some- 

 thing as a fact which is not one. But the fault is in 

 ourselves. We have not been careful enough. We have 

 seen incorrectly, or our ears have deceived us, or in 

 some way we have misunderstood. Facts never contra- 



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