xc INTRODUCTION 



before, but is guided by the general laws and principles 

 of mechanics, will quickly succeed in raising its efficiency. 

 So it is in science : a knowledge of the great general 

 principles confers a judgment and grasp of essentials, which 

 is denied to the mere scientific artisan. 



In the foregoing pages I have endeavoured to draw certain 

 rules of scientific method from an analysis of the causes of 

 the errors into which Lamarck fell. These rules are neither 

 new nor startUng ; yet their importance is so great as to bear 

 almost endless repetition. 



The first principle is one which has never ceased to be 

 preached since the time of Bacon : it emphasises the truth 

 that the methods of science are those of observation and 

 experiment : and that as soon as we travel outside these 

 methods, we become involved in hopeless error and confusion. 

 The second follows from the first : it enjoins upon us the 

 principle, never to seek the explanation of some difficult 

 problem by the manufacture of a new and unknown 

 entity. In every case where Lamarck abandoned this rule 

 he came to grief. I do not mean that we should only believe 

 in the existence of what we can see or feel ; I mean that 

 when we form some hypothesis to explain a process or event, 

 and when that hypothesis involves us in the assumption of 

 some existence not appreciable to our senses, that existence 

 must be invested with similar properties to those possessed 

 by other existences which are appreciable to our senses. 

 That is to say, it must either have the properties of matter, 

 or of material force or energy : and therefore must be 

 capable, theoretically at least, of being some day removed 

 from the sphere of hypothesis to that of observation. To 

 this rule there has never been any exception in the history 

 of science. Wherever any suggested hypothesis has included 

 any factor of a different order from those known to us by 

 observation and experiment, that hypothesis has ultimately 

 decayed or been refuted. The unbroken record of history 

 suffices in itself to establish this general philosophic law, 

 which indeed is thrust upon us with equal force from many 



