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THE POPULAR SCIENCE MONTHLY 



Dr. Taylor tells us that the Coperni- 

 can theory "rests on facts presently 

 occurring before our eyes." So does 

 the Ptolemaic theory ; and not only 

 that, but, if the test is what occurs be- 

 fore our eyes, then the Ptolemaic theo- 

 ry is a thousand times stronger than the 

 Copernican. If the Copernican theory 

 is so obvious, if it " rests on facts pres- 

 ently occurring before our eyes," why 

 did the astronomers of twenty cen- 

 turies fail to discern it? Why could 

 not the divines of Copernicus's time 

 see it when it was pointed out to them? 

 And why could not Lord Bacon admit 

 it a hundred years after Copernicus ? 

 Dr. Taylor says, " It is verified every day 

 by occurrences that happen according 

 to its laws." So was its opposite, the 

 Ptolemaic theory. Our reverend logi- 

 cian says, furthermore: "We know that 

 astronomy is true, because we are veri- 

 fying its conclusions every day of our 

 lives, on land and on sea. We set our 

 clocks according to its conclusions, and 

 navigate our ships in accordance with 

 its predictions." And all this they did 

 with the astronomy that preceded Co- 

 pernicus. Yet the author of this rub- 

 bish airs his logical pretensions, and 

 talks about the "effrontery" of Prof. 

 Huxley. Where is his shame ? 



The Copernican theory is held as 

 demonstrably true, but it is not because 

 everybody can see the demonstration. 

 There was demonstrated truth in the 

 opposite theory, though the proof was 

 not so complete. And in regard to this 

 matter of demonstration, of which so 

 much is said, we have to remember that 

 evidence is a thing of degrees. There 

 may be evidence for a proposition 

 which is so small that we hardly regard 

 its truth as possible we do not believe 

 it. There is a grade of proof that amounts 

 to probability, but leaves us in uncer- 

 tainty. There are higher degrees of 

 proof that confer assured belief, and 

 leave little room for doubt. There is, 

 again, evidence so perfect and decisive 

 as to give certainty of conviction, and 



this we call demonstration. And evi- 

 dence may have a yet higher shade of 

 intensity, as where we cannot even con- 

 ceive the opposite of a proposition to be 

 true, and this may be characterized by 

 the frequent expression, " absolute dem- 

 onstration." The best examples of 

 demonstration are furnished by mathe- 

 matics in consequence of the fewness 

 and simplicity of mathematical ideas, 

 but demonstration by no means neces- 

 sarily involves mathematics. There is 

 plenty of demonstrated truth that is 

 not mathematical. The anatomist de- 

 monstrates his science by observation, 

 and the chemist by experiment*. Fos- 

 sils found in the rocks demonstrate that 

 life existed upon the globe before the 

 rocks were formed; and the vestiges 

 of art found in Western mounds de- 

 monstrate that a race of men superior 

 to the savages formerly lived upon this 

 continent. A theory is said to be de- 

 monstrated when it brings all the known 

 facts into agreement, explains them, 

 excludes all other interpretations, and 

 is consistent with itself and all that is 

 understood of the ways of Nature. 

 Most theories of the operations of Na- 

 ture have about them traces of the 

 imperfection that belongs to all things 

 human, difficulties that are still unre- 

 solved, while yet the evidence for them 

 may be so overwhelming as to be held 

 demonstrative. 



How is it, now, with the proof of 

 the theory of Evolution, which as- 

 sumes that the immense diversity of 

 living forms now scattered over the 

 earth has arisen through a long process 

 of gradual unfolding and derivation, 

 within the order of Nature, and by 

 the operation of natural laws ? It in- 

 volves and is built upon a series of 

 demonstrated truths. It is a fact ac- 

 cordant with all observation, and to 

 which there never has been known a 

 solitary exception, that the succession 

 of generations of living things upon 

 earth is by reproduction and genetio 

 connection in the regular order of Na- 



