46 THE METHOD OF SCIENCE 



not new in biology. That which, amid such a wealth of patent 

 facts, is very new, is exclusive reliance on obscured facts and a 

 confusing of experimental discovery with experimental testing. 

 " What would the physicist or chemist say if he were told " that 

 he must not use patent facts, for example those of astronomy, 

 when inventing or testing his theories ? An experiment, or any 

 other laboratory inquiry, is a mode of observing, not of thinking. 

 It is sometimes an appeal to reality which results from deductive 

 thinking, but unless correctly thought out, not necessarily a de- 

 cisive appeal. It is valuable as testing our thinking or as making 

 patent a fact previously obscured ; but often we are able to appeal 

 to evidence patent from the first, and an obscured fact, newly 

 discovered, is not necessarily more valuable to us than a patent 

 fact that has long been ignored or insufficiently used. An observer 

 is quite as likely to found illegitimate thinking on the results of 

 experiment as on any other data. Indeed, thinking founded on 

 experiment has often been deplorably reckless and inaccurate. 



76. The function of deduction is not limited to the testing of 

 inductions. " If the hypothesis is true, it will generally be possible 

 to infer deductively from it facts which have not been before ex- 

 plained or which have even been unobserved. ... As Whewell 

 says, * When the hypothesis of itself, and without adjustment for 

 the purpose, gives us the rule and reason of a class of facts not 

 contemplated in its construction, we have a criterion of its reality, 

 which has never yet been produced in favour of falsehood.' l The 

 history of science is full of such extension and prediction. Thus, 

 for example, the discovery of Neptune was predicted by deductive 

 reasoning from the principle of gravitation." 2 Again, the universe 

 is a unity in which every phenomenon is related, however remotely, 

 to every other. A brief yet comprehensive statement, in which 

 the relations of a number of phenomena are summarized, is termed 

 by us a law ; and it is the aim of science not only to express the re- 

 lations of phenomena in laws, but to indicate the relations of these 

 laws to weld them into larger syntheses, more comprehensive 

 interpretations. 3 In this process of welding deduction plays an 



1 Novum Organum Renovatum, p. 90. 



* Welton, Manual of Logic, vol. ii. p. 100. 



3 What is a natural 'law' ? It is commonly described as an "observed 

 uniformity," " the statement of a general truth ; that is, a truth that holds good 

 universally in that science, as contrasted with a particular truth, which holds 

 good in some cases only" (Welton, op. cit., vol. i. p. n). But this definition 

 is too wide (see 586, footnote). The flowers of the common primrose are yellow ; 

 mammals have heads ; birds are bi-pedal. These are observed uniformities, 



