August 31, 1911] 



NATURE 



295 



nd. To take an example from recent scientific anec- 

 dote : I relate the story as I was told it, and, even if 

 incorrect in detail, it will serve its purpose as a parable. 

 The Rontgen rays were discovered originally by their 

 photographic action, but afterwards it was found that they 

 would render a screen of calcium tungstate phosphorescent. 

 I was told that this discovery had been made in this wise : 

 Mr. Edison had a large collection of different chemicals 

 and a number of assistants ; he set his assistants busily to 

 work to try each substance in turn until the right one 

 was found. Now this is not only a genuine scientific 

 process, but it is the fundamental process. Let it be 

 frankly admitted that our instincts are against it. We 

 should much prefer to hear that some hypothesis had 

 pointed the way, even a false hypothesis such as actually 

 led to the discovery of the possibility of achromatism in 

 lenses. Or if memory had played a part : The other day 

 Prof. Fowler identified the spectrum of a comet's tail with 

 one taken in his laboratory, of which he had some recollec- 

 tion, and our human sympathies fasten at once on this 

 idea of recollection as a praiseworthy element in the dis- 

 covery. Nay, even mere accident appeals to us more than 

 brutal industry ; if Mr. Edison had wandered into his 

 laboratory, picked up a bottle at random, and found it 

 answer his purpose, I venture to say that we should have 

 instinctively awarded him more merit ; there would have 

 been just a chance that he was inspired. Let us by all 

 means welcome hypothesis, memory, inspiration, and 

 accident whenever and wherever they will help us ; but 

 they may fail, and then our only resource is to help our- 

 selves by the unfailing method of examining all possibili- 

 ties. The aid of the others is adventitious, and comes, 

 like that of the gods, most readily to those who help 

 themselves. 



The maxim of " leaving no stone unturned " was 

 enunciated from a rather different point of view some 

 dozen years ago by an American geologist, Prof. T. C. 

 Chamberlin, of Chicago, in a short paper for students 

 entitled "The Method of Multiple Working Hypotheses." ' 

 After recalling how much the march of science in earlv 

 days was retarded by the tyranny of a theory formulated 

 too hastily, and how in later times attempts have been 

 made to remedy this evil by holding the theory, provision- 

 ally only, as a working hypothesis, Prof. Chamberlin 

 points out that even the working hypothesis has serious 

 disadvantages : — 



Instinctively there is a special searching-out of pheno- 

 mena that support it, for the mind is led by its desires. 

 . . . From an unduly favoured child it readilv grows to 

 be a master and leads its author whithersoever it will. 

 . . . Unless the theory happens perchance to be the true 

 one. all hope of the best results is gone. To be sure truth 

 may be brought forth by an investigator dominated bv a 

 false ruling idea. His very errors may indeed stimulate 

 investigation on the part of others. But the condition is 

 scarcely the less unfortunate. 



" To avoid this grave danger the method of multiple 

 working hypotheses is urged. It differs from the simple 

 working hypothesis in that it distributes the effort and 

 divides the affections. ... In developing the multiple 

 hypotheses, the effort is to bring up into view every 

 rational explanation of the phenomenon in hand and to 

 develop every tenable hypothesis as to its nature, cause 

 or origin, and to give all of these as impartially as possible 

 a working form and a due place in the investigation. The 

 investigator thus becomes the parent of a family of hypo- 

 theses : and by his parental relations to all is morally for- 

 bidden to fasten his affections unduly upon any one. In 

 the very nature of the case, the chief danger that springs 

 from affection is counteracted." 



For the further elucidation of Prof. Chamberlin 's pro- 

 posals I must refer my audience to his original paper, 

 which is well worthy of careful attention. He does not 

 shirk consideration of the drawbacks — " No good thing is 

 without its drawbacks," he writes. And it may be added 

 that no good thing is entirely new or entirely old. Per- 

 haps it is better to say that it is generally both new and 

 old. The Method of Multiple Hypotheses is new because 

 1 University of Chicago Press, 1897. 



NO. 2182, VOL. 87.] 



it is still necessary to remind scientific workers of all 

 kinds that, so long as they restrict themselves to the 

 examination of one hypothesis only, they can never reach 

 complete logical proof : they can only attain a high 

 measure of probability. What is often called verification ' 

 is not complete proof, but only increase in probability ; for 

 complete proof it is necessary to show that no other hypo- 

 thesis will suit the facts equally well, and thus we 

 are bound to consider other possible hypotheses even in 

 the direct establishment of one. 



But the method is also old in that it has long been 

 adopted in practice, however partially and unconsciously, 

 by scientific workers of all kinds. When, as a boy at 

 school, I began to make physical measurements under Mr. 

 J. G. MacGregor (now Professor of Physics at Edinburgh), 

 I learnt from him one golden rule : " Reverse everything 

 that can be reversed." The crisp form of the rule may 

 be new to many who have long used it in their work : 

 and its use is simply that of " multiple hypotheses." For 

 when the current in a wire is reversed, the hypothesis is 

 tacitly made that the effect observed may be due to the 

 direction of the current : and when a measured spectrum 

 photograph is turned round and remeasured, it is an 

 admission of the hypothesis that the direction of measure- 

 ment may be partly responsible for the observed displace- 

 ments of the spectrum lines. By the various reversals we 

 endeavour, in Prof. Chamberlin's words, " to bring up 

 into view every rational explanation of the phenomenon in 

 hand " which can be brought up into view in this way. 

 But truly " no good thing is without its drawbacks," and 

 one drawback to the recognition of this principle is that, 

 bv a process of mental confusion, it seems sometimes to 

 be regarded as a distinct merit in a piece of apparatus 

 that it can be reversed in a large number of ways. It 

 must be remembered that the hypotheses thus examined 

 and ruled out are chiefly instrumental ones superadded to 

 those of Nature : and the latter are already sufficiently 

 numerous, without our ingenious additions. 



The view which I have endeavoured to put before you 

 of the inevitable course of scientific work is that it will 

 depend more and more on the patient process of " leaving 

 no stone unturned." It may not be an inspiring view, 

 but it should be at least encouraging, for it follows that 

 no good honest work is thrown away. And it is just this 

 encouragement of which the observer, as opposed to the 

 worker in the laboratory and the mathematician, stands 

 sometimes in sore need. The worker in the laboratory 

 can often clear away his hypothesis on the spot : he can 

 reverse his current then and there ; but this is often 

 impossible for the observer, who can and does reverse his 

 spectrum plate for measurement, but to reverse the motion 

 of the earth which affected the lines must wait six months, 

 and to reverse also the motion of the star may have to 

 wait six years, or sixty, or sixty thousand. In many cases 

 he must leave the reversal to others, and thus not only can 

 he not test all his hypotheses, but he may not even be able 

 to formulate them. His aim cannot therefore be to 

 establish within his lifetime some new law, and his work 

 is not therefore to be appreciated or condemned by his 

 success or failure in this respect. There are truer aims 

 and surer methods of judgment. Something is inevitably 

 lost when we endeavour to express these aims in the con- 

 crete ; but, for the sake of illustration, we may say that 

 the true observer is always endeavouring to reach the next 

 decimal place, and is ever on the alert for some new 

 event. Of the pursuit of the next decimal place it is 

 needless to say more : the aim is as familiar in the labora- 



1 To show that ihe facts agree with the consequences of our hypothesis is 

 not to prove it true. To show that is often called verification \ and to 

 mistake verification for proof is to commit the fallacy of the consequent, the 

 fallacy of thinking that, because the hypothesis were true, certain facts would 

 follow, therefore, since those facts are fnund, the hypothesis is true. ... A 

 theory whose consequences conflict with the facts c?nnot he true: but so 

 long as there may be more than one giving the same consequences, the 

 agreement of the facts with one of them furnishesno ground for choosing 

 between it and the others. Nevertheless, in practice, we often have to be 

 content with verification ; or to take our inability to find any other equally 

 satisfactory theory as equivalent to there being none other. In such 

 matters we must consider what is called the weight of the evidence for a 

 theory which is not rigorously proved. But no one has shown how weight of 

 evidence can be mechanically estimated ; the wisest men, and best acquainted 

 with the matter in hand, are oftenest right. — "An Introduction to Logic," 

 by H. W. K. Joseph, Fellow and Tutor of New College, Oxford, Clarendon 

 Press, 1906, p. 486. 



