292 ON SENSATION AND THE UNITY OF 



o'-the-wisps generated in the marshes of literature 

 and theology, the serious student is sometimes 

 bidden to betake himself to the solid ground of 

 physical science. But the fish of immortal 

 memory, who threw himself out of the frying-pan 

 into the fire, was not more ill advised than the 

 man who seeks sanctuary from philosophical per- 

 secution within the walls of the observatory or of 

 the laboratory. It is said that " metaphysics " owe 

 their name to the fact that, in Aristotle's works, 

 questions of pure philosophy are dealt with im- 

 mediately after those of physics. If so, the acci- 

 dent is happily symbolical of the essential rela- 

 tions of things; for metaphysical speculation fol- 

 lows as closely upon physical theory as black care 

 upon the horseman. 



One need but mention such fundamental, and 

 indeed indispensable, conceptions of the natural 

 philosopher as those of atoms and forces: or that 

 of attraction considered as action at a distance; 

 or that of potential energy; or the antinomies of 

 a vacuum and a plenum; to call to mind the 

 metaphysical background of physics and chemistry; 

 while, in the biological sciences, the case is still 

 worse. What is an individual among the lower 

 plants and animals? Are genera and species 

 realities or abstractions? Is there such a thing 

 as vital force, or does the name denote a mere 

 relic of metaphysical fetichism? Is the doctrine 

 of final causes legitimate or illegitimate? These 



