6io 



NA TURE 



[October 28, 1897 



those who have not the time to make a special study of 

 formal logic. Deduction, or " reasoning from the general 

 to the particular, from a law, principle, or general fact to 

 a particular fact," is as much a part of the scientific or 

 so-called inductive method as induction itself, or " reason- 

 ing from particular to general, from facts to laws or prin- 

 ciples." The scientific method 



" includes all the logical processes, induction, deduction, 

 analogy, verification — every way in which the intellect 

 passes from fact to fact. This is widely different from 

 what Bacon originally meant by inductive method ; but 

 practically no scientific man has ever followed Bacon's 

 method. The inductive method, as illustrated by Dar- 

 win's own work, and as understood by all who think 

 clearly on the subject, consists in the formation of an 

 hypothesis from the facts by induction at the earliest 

 possible moment in an investigation, deductive applica- 

 tion of the hypothesis to known facts, and in the search 

 for others that ought to exist if it is true, until it proves 

 itself imperfect. By the help of the new facts the hypo- 

 thesis is improved (by induction) and again applied, until 

 by successive approximations it reaches the truth. So 

 that in the so-called inductive or scientific method deduc- 

 tion is far more extensively used than induction." 



In fact, as the author states, John Stuart Mill has 

 "described the combination 'hypothesis, deduction, and 

 verification ' as the deductive method." Inasmuch as in- 

 duction and deduction are both absolutely essential to 

 the process above described, neither of them ought to 

 be selected for the purpose of giving it a name ; the pro- 

 cess should always be called "the scientific method." 

 When " induction " is used as a term of commendation, 

 it is employed to mean the whole process, in which 

 deduction, although not more necessary than induction, 

 is "far more extensively used." When "deduction" is 

 used as a term of reproach, it means " reasoning from 

 postulates the truth of which is accepted beyond dispute''^ ; 

 it "starts from principles whose truth is not questioned,'' 

 whereas 



"in the scientific method the object is not merely to 

 deduce consequences from laws or principles, but to 

 establish the truth or falsity of those laws or principles 

 themselves. Hence there is an incessant interplay of 

 induction and deduction." 



In considering " starting-points," it is well shown that 

 Darwin's material lay all round him— the first facts 

 already known, and sometimes the explanation hit upon, 

 but the whole significance as yet unappreciated. This 

 is shown to be the case with the local variation of the 

 Galapagos fauna, the action of earth-worms, the reversion 

 caused by the crossing of pigeons, and the facts upon 

 which the investigation of insectivorous plants was 

 begun. This is not only true, but most encouraging ; 

 such material is still thickly spread around every scientific 

 worker, ready to lead to important researches, and yield 

 the most valuable conclusions when its significance is 

 understood. And the effect of practice and learning 

 from example is well seen in the increasing power which 

 this kind of understanding gains. The beginner who 

 has not yet commenced his first research has much 

 difficulty in finding a subject, and here it is that an 

 inspiring teacher or friend may turn the whole current 

 of his life by a few suggestive words. When he has 

 had experience, the difficulty is to find time to undertake 

 NO. 1461, VOL. 56] 



the innumerable researches which now seem to crowd 

 around him. 



In the chapter on "exhaustiveness " is shown the 

 immense gain which we owe to the patience and thorough- 

 ness with which Darwin conducted his researches, even 

 though 



"he could have secured for himself the priceless gem 

 of '■priority of discovery ' without the tedious years of 

 work." 



" One of the most notable legacies that he left to the 

 ambitious student is his example of great energy and 

 great patience ; his incarnation of the truth that time, as 

 well as reason, is the handmaid of science." 



In giving a brief account of Weismann's theory of 

 heredity (pp. 119- 120), the erroneous impression might 

 be gathered that the theory in question was framed in 

 order to support natural selection and the contention 

 that acquired characters are not transmitted. This is 

 the wrong order ; Weismann's study of the early history 

 of the germ-cells, especially in Hydrozoa, suggested the 

 theory, and this again opened up the question of the 

 transmission of acquired characters and the scope of 

 natural selection. 



The "importance of theory" is well illustrated by the 

 remarks upon Darwin's and Sedgwick's failure to see 

 the traces of glacial action during their careful examin- 

 ation of the rocks at Cwm Idwal. " The secret of their 

 failure is that they were not looking for it. It is usually 

 the things that men look for that they see ; and to look 

 for things as yet unseen requires a theory as a head light " 

 (p. 129). 



Wallace's brilliant suggestion of the warning signi- 

 ficance of the bright colours of caterpillars is described ; 

 but the great development which this and kindred sub- 

 jects have undergone in recent years is undervalued by 

 the writer who only sees " the enormous amount of wild 

 deduction and half-digested observation." In a subject 

 of wide general interest attracting an immense number 

 of observers of all degrees of competence and experience, 

 these strictures are likely enough to have force as regards 

 a large number of the suggestions made ; but, in spite 

 of all errors of interpretation and observation, the whole 

 subject has advanced immensely and greatly gained in 

 extent and solidity since Bates' fruitful suggestion was 

 brought before the Linnean Society in 1861, and 

 Wallace's, before the Entomological Society in 1867. 

 Some of the most important conclusions reached since 

 then have not only been confirmed by an immense body 

 of evidence brought together by their supporters, but 

 have also been verified by the researches of those whose 

 attitude was severely critical. The author's conclusion 

 that " what is most needed is more light on the physio- 

 logical causes at work within the animal, and producing 

 and determining the distribution of colours," is, it is 

 maintained, erroneous. Such researches, some of which 

 have been and are being undertaken, are of the deepest 

 interest and importance, but they are likely to shed but 

 little light upon the significance of colour and pattern in 

 the struggle for existence. 



The very common mistake made by Darwin's critics 

 in supposing that the inability to supply a cause of 

 variation undermines the logical foundation of the theory 

 of natural selection is well exposed (p. 166). In dealing 



