i 7 4 THE POPULAR SCIENCE MONTHLY. 



AIMS AND INSTRUMENTS OF SCIENTIFIC THOUGHT. 



By Professor W. KINGDON CLIFFOED, 



OF UNIVERSITY COLLEGE, LONDON. 

 II. 



I WANT, in the next place, to consider what we mean when we say 

 that the uniformity which we have observed in the course of 

 events is reasonable as well as exact. 



No doubt the first form of this idea was suggested by the marvel- 

 lous adaptation of certain natural structures to special functions. The 

 first impression of those who studied comparative anatomy was, that 

 every part of the animal frame was fitted with extraordinary com- 

 pleteness for the work that it had to do. I say extraordinary, because 

 at the time the most familiar examples of this adaptation were manu- 

 factures produced by human ingenuity ; and the completeness and mi- 

 nuteness of natural adaptations were seen to be far in advance of 

 these. The mechanism of limbs and joints was seen to be adapted, 

 far better than any existing iron-work, to those motions and combina- 

 tions of motion which were most useful to the particular organism. 

 The beautiful and complicated apparatus of sensation caught up indi- 

 cations from the surrounding medium, sorted them, analyzed them, 

 and transmitted the results to the brain in a manner with which, at 

 the time I am speaking of, no artificial contrivance could compete. 

 Hence the belief grew among physiologists that every structure which 

 they found must have its function and subserve some useful purpose ; 

 a belief which was not without its foundation in fact, and which cer- 

 tainly (as Dr. Whewell remarks) has done admirable service in pro- 

 moting the growth of physiology. Like all beliefs, found successful 

 in one subject, it was carried over into another, of which a notable ex- 

 ample is given in the speculations of Count Rumford about the phys- 

 ical properties of water, to which the President has already called 

 your attention. Pure water attains its greatest density at a tempera- 

 ture of about 39^ Fahr. ; it expands and becomes lighter whether it 

 is cooled or heated, so as to alter that temperature. Hence it was 

 concluded that water in this state must be at the bottom of the sea, 

 and that by such means the sea was kept from freezing all through ; 

 as it was supposed must happen if the greatest density had been that 

 of ice. Here, then, was a substance whose properties were eminently 

 adapted to secure an end essential to the maintenance of life upon the 

 earth. In short, men came to the conclusion that the order of Nature 

 was reasonable in the sense that every thing was adapted to some 

 good end. 



Further consideration, however, has led men out of that conclusion 

 in two different ways : First, it was seen that the facts of the case 



