Mind and Matter 103 



was and shall ie 9 and whatever does not 

 satisfy this condition must be an accidental 

 or fugitive or essentially temporary con- 

 glomeration or assemblage, and not one of 

 the fundamental entities of the universe. It 

 is interesting to remember that this was one 

 of the opinions strongly held by the late 

 Professor Tait, who considered that per- 

 sistence or conservation was the test or 

 criterion of real existence. 



The question, How many fundamental 

 entities in this sense there are, and what 

 they are, is a difficult one. Many people, 

 including such opposite thinkers as Tait and 

 Haeckel, would say " matter " and " energy " ; 

 though Haeckel chooses, on his own 

 account, to add that these two are one. 

 (Perhaps Professor Ostwald would agree 

 with him there ; though to me the mean- 

 ing is vague.) Physical science, pushed to 

 the last resort, would probably reply that, 

 within its sphere of knowledge at the present 

 stage, the fundamental entities are ether 

 and motion ; and that of other things at 



