308 THE EIDDLE OF THE UNIVEKSE. 



another and better grounded theory. But, in spite of 

 this admitted uncertainty, theory is indispensable for 

 all true science ; it elucidates facts by postulating a 

 cause for them. The man who renounces theory alto- 

 gether, and seeks to construct a pure science with 

 certain facts alone (as often happens with wrong-headed 

 representatives of our " exact sciences"), must give up 

 the hope of any knowledge of causes, and, consequently, 

 of the satisfaction of reason's demand for causality. 



The theory of gravitation in astronomy (Newton), 

 the nebular theory in cosmogony (Kant and Laplace), 

 the principle of energy in physics (Meyer and Helrn- 

 holtz), the atomic theory in chemistry (Dalton), the 

 vibratory theory in optics (Huyghens), the cellular 

 theory in histology (Schleiden and Schwann), and the 

 theory of descent in biology (Lamarck and Darwin), 

 are all important theories of the first rank ; they 

 explain a whole world of natural phenomena by the 

 assumption of a common cause for all the several facts 

 of their respective provinces, and by showing that all 

 the phenomena thereof are inter-connected and con- 

 trolled by laws which issue from this common cause. 

 Yet the cause itself may remain obscure in character, 

 or be merely a " provisional hypothesis." The " force 

 of gravity " in the theory of gravitation and in cos- 

 mogony, " energy " itself in its relation to matter, the 

 " ether " of optics and electricity, the " atom " of the 

 chemist, the living " protoplasm" of histology, the 

 "heredity" of the evolutionist — these and similar 

 conceptions of other great theories may be regarded 

 by a sceptical philosophy as " mere hypotheses " and 

 the outcome of scientific " faith," yet they are indis- 

 pensable for us, until they are replaced by better 

 hypotheses. 



