24 



SCIENCE. 



[Vol. XX. No. 492 



than the genius whose machinery and methods have invited 

 public approval. Proposals to do the county sprinkling at 

 so much per acre are invited and offered, and at one time 

 it seemed as if the whole business would be ruined by over- 

 production. 



One of the most interesting phases of this subject was the 

 attitude in reference to it assumed by a large part, possibly 

 the greater part, of the intelligent public. It was one of 

 expectancy and limited confidence. " Why not? " was com- 

 monly asked. "Look at what science has done within the 

 last twenty-five years. Can anything be more astonishing ? 

 and is the artificial production of rainfall more diflBcult and 

 more wonderful than many things which are now common- 

 place ? " To many the logic of the experiments was con- 

 vincing. After many battles rain had fallen, long lists of 

 examples have been prepared, and hence it must be possible 

 to produce rainfall by cannonading. If these views were 

 entertained by a considerable number of intelligent people, 

 and it is believed that they were, the situation is one which 

 ought to be full of interest to men of science, involving, as 

 it does, both a tribute and a warning. 



It would be good for all if the intelligent public was in 

 the habit of looking a little more below the surface of things. 

 It is too much in the way of assuming that the president of 

 the company engaged in exploiting an important invention 

 or device is the genius who first discovered the principle in 

 virtue of which it operates. It loses sight of — no, it does 

 not lose siarht of, because it never knew — the patient toil, 

 the unselfish devotion, and, what is perhaps more impor- 

 tant, the unflinching honesty with which a few men of the 

 highest intellectual capacity have from the earliest times 

 given themselves to the study of the laws of nature. 



It would surprise the public to know how long ago and 

 by whom many of the most recent and most brilliant appli- 

 cations of science were made possible. Would it not be in 

 the interest of all if men of science were more ready and 

 willing to take the intelligent public into their confidence; 

 and would not the public, if familiar with the history of 

 scientific investigation and accustomed to scientific modes of 

 thought and criticism, be less the prey of charlatans and 

 well-meaning but ill-informed enthusiasts ? A better knowl- 

 edge on both sides would lead to a better appreciation of 

 both sides, and the real worker in science would seldom go 

 without that public recognition which has too often been 

 denied to the ablest men. No better illustration of this can 

 be found than in the life of the distinguished first president 

 of this society, to stand in whose place must always be an 

 honor to any man. With his great work as secretary of the 

 Smithsonian Institution the public is fairly well acquainted, 

 and it has not been backward in bestowing honors in recog- 

 nition of that work. Unfortunately, comparatively few know 

 of what must be regarded, I think, as his greater work, the 

 original researches in which he was engaged, and in which 

 he was so singularly successful, before he became identified 

 with the institution to which he gave the greater part of his 

 life. Scant justice has yet been done to this important part 

 of a career which must always be an inspiration to members 

 of this society. 



But I am warned that the brief time during which I can 

 claim your attention to-night is quite insufficient for any- 

 thing like a full exposition of the theme which I have se- 

 lected, and I must, I fear, somewhat abruptly turn about in 

 order that I may leave with you in somewhat more definite 

 language one or two thoughts which I have attempted to 

 develop by illustration and example. 



Recurring to the unfortunate victim of circumstantial evi- 

 dence, whose experience was related in the beginning, it will 

 be admitted that the judge who charged, the jury who con- 

 victed, the witnesses who told the truth, and the approving 

 public were all in error, in that they failed to recognize that 

 there was another way of explaining what had happened. 

 It does not necessarily follow that the explanation which ex- 

 plains is the true one. There are many natural phenomena 

 which are in entire accord with more than one hypothesis. 

 Indeed, there are some things which may be perfectly ac- 

 counted for on an infinite number of suppositions, but it does 

 not follow that all or any one of them must be accepted. There 

 is nothing especially novel in this proposition, but I submit 

 that to a failure to keep it in sight must be attributed a large 

 measure of the uncertainty of the exact sciences, as well as 

 much useless and bitter controversy in science, religion, eth- 

 ics, and politics. 



As a sort of corollary to this proposition I suggest that 

 many reasoning and reasonable people are indifi'erent to, if 

 not ignorant of, the fact that the value of evidence is greatly 

 dependent on the way in which it arranges itself. To many 

 this may be made a little clearer if I borrow a phrase from 

 one of the most exact of modern sciences and speak of evi- 

 dence as presenting itself in series or in parallel. Without 

 pushing the analogy further, the superior strength of the 

 latter arrangement will be evident upon reflection. On an- 

 other occasion, I have referred at some length to the nu- 

 merical representation of the value of testimony, and to some 

 conclusions which are easily reached. As bearing upon the 

 subject in hand, a single example of this method of treat- 

 ment may be useful. 



Let there be two witnesses, A and B. Suppose that A 

 tells the truth 51 times out of 100; that is to say, assume 

 that honesty holds the controlling share in his stock of moral 

 principles. Let B be equally truthful and no more. Then 

 if these two testify independently to the occurrence of a cer- 

 tain phenomenon it is more likely to have occurred than if 

 either one alone bore witness. This is evidence in parallel. 

 If, however, A testifies that B declares that the thing hap- 

 pened, it is less probable than if based on the testimony of 

 either alone. This is evidence in series. Put as boldly as 

 this, no one doubts the higher value of the first arrange- 

 ment; but it is believed that a more careful consideration of 

 this distinction will do much to secure a better judgment, 

 not only where human testimony is involved, for here it has 

 long been an established principle, but where conclusions 

 are based on observation and experiment. 



It is of the utmost importance, therefore, that men of sci- 

 ence, before accepting a theory or a hypothesis as final, 

 should carefully scrutinize the steps by which it has been 

 established to see that they are not only sufficient but neces- 

 sary.- The true philosopher will be slow to claim that the 

 theory which he finds sufficient to explain all of a given 

 class of facts is the necessary and true one; he will be con- 

 stantly on the lookout for a new fact which his theory will 

 not quite explain, and he will have much consideration for 

 his friendly competitor who finds a different hypothesis 

 equally satisfactory and efficient. Above all, he will not 

 pride himself on the steadfastness of his views, and will 

 rarely bind himself to be of the same opinion this year as 

 last. 



If the general public could be made to understand the 

 limitations by which science is circumscribed, the tentative 

 and ever progressive character of scientific investigation, it 

 would be good for the public and good for science. 



