74 THE RELATIVITY OF ALL KNOWLEDGE. 



pose of our argument; since, whether real or fancied, it 

 equally illustrates the mental illumination that results on 

 finding a class of cases within which a particular case may 

 possibly be included. And it may be further noted how, in 

 the instance here named, an additional feeling of compre- 

 hension arises on remembering that the influence conveyed 

 through the nerves to the muscles, is, though not positively 

 electric, yet a form of force nearly allied to the elec- 

 tric. Similarly when you learn that animal heat arises 

 from chemical combination, and bo is evolved as heat is 

 evolved in other chemical combinations — when you learn 

 that the absorption of nutrient fluids through the coats of 

 the intestines, is an instance of osmotic action — when you 

 learn that the changes undergone by food during digestion, 

 are like changes artificially producible in the laboratory; 

 you regard yourself as hnowing something about the natures 

 of these phenomena. 



Observe now what we have been doing. Turning to the 

 general question, let us note where these successive interpre- 

 tations have carried us. ^Ve began with quite special and 

 concrete facts. In explaining each, and afterwards explain- 

 ing the more general facts of which they are instances, we 

 have got down to certain highly general facts: — to a geo- 

 metrical principle or property of space, to a simple law of 

 mechanical action, to a law of fluid equilibrium — to truths 

 in physics, in chemistry, in thermology, in electricity. The 

 particular phenomena with which we set out, have been 

 merged in larger and larger groups of phenomena; and as 

 they have been so merged, we have arrived at solutions that 

 we consider profound in proportion as this process has been 

 carried far. Still deeper explanations are simply further 

 steps in the same direction. TThen, for instance, it is i- 

 why the law of action of the lever is what it is, or why fluid 

 equilibrium and fluid motion exhibit the relations which 

 they do, the answer furnished by mathematicians consists 

 in the disclosure of the principle of virtual velocities — a 



