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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



is not true is necessarily to be decided by the hu- 

 man judgment, coordinating all the facts which 

 bear upon it. There is no such thing as a revela- 

 tion of scientific truths ; and even if one should 

 claim that there was, the admission or rejection 

 of such a claim would be an act of human judg- 

 ment, which thus becomes the ultimate arbiter in 

 any case. Hence a proposition is to be proved 

 probable or true not by anything in itself, but 

 a more or less long and painful examination of 

 the evidence for and against it. Everything that 

 can be found to militate in favor of it is put into 

 one scale, and everything that can be found to 

 militate against it is put into the other. If the 

 investigator is imbued with the true spirit of sci- 

 ence, bis search is equally vigorous for arguments 

 to go into the two scales. When he says that the 

 proposition is worthy of being received as true, 

 he means not that it bears any recognized seal 

 of truth ; but that the evidence in favor of it en- 

 tirely preponderates over all that can be brought 

 to bear against it. 



You will not understand me as maintaining 

 that every individual man of science constantly 

 maintains this spirit of impartiality, any more 

 than that every Christian constantly lives up to 

 the highest standard of his profession. Hot 

 conflicts have sometimes raged — and there is no 

 reason to suppose that they have entirely ceased 

 even now — in which each combatant could only 

 see one scale. But the spirit I have described is 

 that in which Science exhorts her votaries to ap- 

 proach every question, and in which they will 

 constantly endeavor to approach it, if they are 

 worthy of their profession. 



Let us now approach our main theme, the 

 course of visible Nature. Let me again remind 

 you that of the two universes, the seen and the 

 unseen, I am only going to speak of the former. 

 We find ourselves placed in this world in the 

 midst of a vast theatre of activity. We see an 

 atmosphere agitated by storms ; great masses of 

 water rising in the air to form clouds, and, after 

 falling to the earth, flowing as mighty rivers to 

 the ocean ; countless forms of vegetation rising 

 from the earth, and then returning to it ; a sun 

 vivifying one and perhaps more planets with its 

 heat ; an infinitude of chemical changes going on 

 around us ; countless stars moving through space 

 with velocities which transcend all our concep- 

 tions. To all appearance, these operations have 

 been going on for millions of ages past, and may 

 continue for millions of ages to come. As the 

 thinking man contemplates them, he is led irre- 

 sistibly to the conclusion that they do not go on 



f at random, but that they are joined by connect- 

 ing links, or are in some way the product of 

 knowable causes. From his earliest infancy he 

 sees connections between them which enable him 

 to foresee results. He finds that fire burns, that 

 the sun warms, that food satisfies his hunger, 

 and that heavy bodies fall with a certainty that 

 shows the forces at play to be invariable in their 

 action. To penetrate the mystery in which these 

 forces are enshrouded, he exerted the efforts of 

 his intellect, from its first dawn until the present 

 time. What general conclusions has he reached ? 



From the earliest times at which man began 

 to think, two modes of explaining the operations 

 of Nature have presented themselves to his atten- 

 tion. These modes are sometimes designated as 

 the teleological and the mechanical. 



The teleological explanation of Nature pre- 

 supposes that her operations are akin to human 

 actions, insomuch as they are under the control 

 of and directed by one or more intelligent beings, 

 having certain ends in view ; that the events are 

 so directed as to compass these ends ; and, final- 

 ly, that the relation of the events to the ends 

 admits of being discovered by observation and 

 study. This last condition is a very important 

 one, because without it the teleological explana- 

 tion of the course of Nature would not be a scien- 

 tific one. The doctrine that the author of Nature 

 has certain ends in view, and directs the whole 

 course of events so as to bring them about, will 

 not enable us to explain and predict the events, 

 unless we know what those ends are. But, as I 

 have already said, the test of scientific advance 

 is the power of foresight — of foreseeing what re- 

 sult any combination of circumstances will lead 

 to. If we always had to wait for the result, and 

 could then only say, " I know this is the result 

 which was intended, because it has happened," no 

 actual foresight would be possible ; and, however 

 excellent the doctrine might be as a theological 

 one, it would not admit of being tested by obser- 

 vation and experiment, and the question of its 

 truth would, therefore, not admit of being settled 

 by scientific investigation. You may recall the 

 remark of a satirical philosopher, when he saw 

 the gifts which those who escaped the dangers of 

 a certain treacherous and stormy sea offered up 

 to the goddess who had this sea at her command. 

 " I see no offerings from those who were lost," 

 said he. It was not till the voyager had got 

 safely to shore that he found himself under the 

 protection of the goddess. 



It must be well understood that the teleological 

 theory of Nature, or, as it is now familiarly called, 



