146 HABIT AND INTELLIGENCE. [cHAP. 



the geometrical properties of the parallelogram were known ; 



and it would be impossible to prove, or to state, the law 



that the energy due to a moving body is proportional to 



the second power of its velocity, unless the nature of 



powers and roots were known. Mathematics is thus 



necessary as a foundation for dynamics. 



Dynamics, Among physical laws, the most general are those of 



physical ° force : the laws of force, or, as they are generally called, 



science, the laws of motion, are the only laws which are true of all 



action whatever. Consequently, dynamics is necessarily 



the basis of physical science : or, in other words, the 



theory of force is necessary as a basis for the sciences of 



material things.^ 



Secondary The sciences of sound, radiance, heat, electricity, and 



sciences, magnetism, are merely particular cases of dynamics, being 



applications of the theory of force to special kinds of 



actions. 



The laws of force apply to all the actions of all matter ; 

 but there is a great variety of laws that apply only to those 

 actions, or functions, which are characteristic of particular 

 Chemistry, kinds of matter : I mean the laws of chemistry. The 

 laws of chemistry depend on those of heat and electricity 

 in a very great degree ; so decided indeed is the dependence, 

 that it would be impossible so much as to state many of 

 the most important chemical laws, unless the elementaiy 

 laws of heat and electricity were taken as known. 

 Biology. Finally, the jjroperties of living organisms, and their 

 peculiar actions, in a great degree depend on the general 

 properties of force, and on the special properties of the 

 chemical substances of which the food of the organism, 

 and the organism itself, are composed. Vital properties 

 are certainly more than mere resultants from physical and 



1 It may be said that I contradict myself ia calling mathematics the 

 grmmd of physical science, and dynamics its basis. There is, however, no 

 contradictiou. Dynamics is a part of physical science, but mathematics 

 is not. Physical science is built on mathematics, as a building on the 

 ground ; the other parts of physical science are based on dynamics, as the 

 higher parts of a buUding on its base. 



I attach no importance to these metaphors, but I wish to show that 

 I have not fallen into any inconsistency. 



