5i8 POPULAR SCIENCE MONTHLY. 



priori method of the dogmatists nor the historico-critical method of the 

 humanists is alone adequate for the attainment of definite knowledge 

 of either the internal or the external world, or of their relations to one 

 another. In fact, it has been shown over and over again that man 

 cannot trust his unaided senses even in the investigation of the simplest 

 and most obvious material phenomena. There is an ever-present need 

 of a correction for personal equation. Left to himself, the a priori 

 reasoner weaves from the tangled skein of thought webs so well tied 

 with logical knots that there is no escape for the imprisoned mind except 

 by resort to the weapon applied to cobwebs. And in the serenity of his 

 repose behind the fortress of 'liberal culture,' the reactionary humanist 

 will prepare apologies for errors and patch up compromises between 

 traditional beliefs and sound learning with such consummate literary 

 skill that even 'the good demon of doubt' is almost persuaded that if 

 knowledge did not come to an end long ago it will soon reach its limit. 

 In short, we have learned, or ought to have learned, from ample ex- 

 perience, that in the search for definite, verifiable knowledge we should 

 beware of the investigator whose equipment consists of a bundle of 

 traditions and dogmas along with formal logic and a facile pen; for 

 we may be sure that he will be more deeply concerned with the question 

 of the safety than with the question of the soundness of scientific doc- 

 trines. 



Thirdly, it has been demonstrated equally clearly, and far more 

 cogently, that the sort of knowledge we call scientific, knowledge which 

 has in it the characteristics of immanence and permanence, is founded 

 on observation and experiment. The rise and growth of every science 

 illustrate this fact. Even pure mathematics, commonly held to be 

 the a priori science par excellence, and sometimes called 'the science of 

 necessary conclusions,' is no exception to the rule. Those who would 

 found mathematics on a higher plane have apparently forgotten to con- 

 sider the contents of the mathematician's waste-basket. The slow and 

 painful steps by which astronomy has grown out of astrology and chem- 

 istry out of alchemy; and the faltering, tedious, and generally hotly 

 contested, advances of geology and biology have been made secure only 

 by the remorseless disregard which observational and experimental evi- 

 dence has shown for the foregone conclusions of the dogmatists and the 

 literary opinions of the humanists. Thus it has been proved by the 

 rough logic of facts and events that the rude processes of 'trial and 

 error,' processes which many philosophers and some men of science 

 still affect to despise, are the most effective means yet devised by man 

 for the discovery of truth and for the eradication of error. 



These facts are so well known to most of you, so much a matter of 

 ingrained experience, that the categorical mention of them here may 



