Will and Guidance 163 



a tacit assumption that they have not been 

 let in. 



There is a similar tacit assumption in 

 treatises on Physics and Chemistry ; viz., 

 that the laws of automatic nature shall be 

 allowed unrestricted and unaided play, that 

 nothing shall intervene in any operation 

 from start to finish save mechanical sequent 

 and antecedent, that it is permissible in 

 fact to exercise abstraction, as usual, to the 

 exclusion of agents not necessarily connected 

 with the problem, and not contemplated by 

 the equations. 



In text-books of Dynamics and in 

 treatises of Natural Philosophy that is a 

 perfectly legitimate precedure ; 1 but when 

 later on we come to philosophise, and to 

 deal with the universe as a whole, we must 

 forgo the ingrained habit of abstraction, 

 and must remember that for a complete treat- 

 ment nothing must permanently be ignored. 



1 It is on a similar basis that there is a science of 

 rigid dynamics, with elasticity and fluidity excluded; 

 and thus also can there be a hydrodynamics in which 

 the consequences of viscosity are ignored. 



