4 o8 POPULAR SCIENCE MONTHLY. 



nominalists during the middle ages could not have been more bitter 

 than this Haeckel controversy threatens to become, and we need have 

 no fear, so far as I can see, that the occupation with intellectual things 

 is blunting the emotional side of the modern thinker's soul. 



It is not my intention to join in the hue and cry against this man 

 who has dared to offer the wdrld a Weltanschauung, nor am I willing 

 to stamp his work as unworthy of notice. It is true, Haeckel has pro- 

 voked a fair share of the abuse that has been heaped upon him by his 

 own intolerant attitude, but after all two wrongs do not make a right. 

 I believe that it will be worth our while to hear patiently what Haeckel 

 has to say, and then to subject his philosophy to the tests by which it 

 will be judged at last when the discordant voices of the present are 

 hushed and the author and his critics are sleeping in their quiet graves. 

 A work that has made such an impression upon an age as the 'World 

 Kiddles' can not be ignored or thrown out of court without a hearing, 

 and the hearing must be impartial and temperate, such a hearing as it 

 is bound to receive at the bar of history. It expresses the views of large 

 numbers of natural scientists to-day, although few would dare to make 

 public confession of their faith, as the fearless Jena biologist has done ; 

 and as an expression of opinion coming from such a quarter, it deserves 

 attention. I shall therefore try in what follows to give an exposition 

 of Haeckel's thought, and to examine its value as a theory of the 

 universe. 



And first let us turn to our philosopher's theory of knowledge.* 

 Our true knowledge, he says, is real in its nature; it consists of ideas 

 (Vorstellungen) which correspond to really existing things. It is true 

 we cannot know the innermost essence of this real world, of the thing in 

 itself, f but we are convinced by impartial and critical observation and 

 comparison that the external world makes the same impressions upon 

 the sense-organs and brain of all normal rational individuals, and that 

 the same ideas are formed by all persons whose organs of thought 

 function normally. All our knowledge depends upon two physiological 

 functions — upon sensation and upon the combination of the impres- 

 sions thus gained, by association. The experiences which we receive 

 from the external world through our sense-organs and sense-centers 

 in the brain are transformed into ideas by other brain-centers, and these 

 are combined into inferences by association. These inferences are both 

 inductive and deductive, processes which have equal value. Other com- 

 plicated brain operations, the formation of chains of reasoning, abstrac- 

 tion and conception, imagination, consciousness, thought and phi- 

 losophy, are all functions of the ganglionic cells of the cerebral cortex. J 



* See particularly ' Die Weltraethsel/ pp. 337ff. 



f See also pp. 437f, op. cit., and ' Monismus/ p. 40. 



X See also ' Weltraethsel/ pp. 19f. 



