440 ACTUAL WORKING IN ORIGINAL RESEARCH. 



electric machine, by mechanical action in a magneto- 

 electric machine, by heat in a thermo-electric pile, or by 

 chemical action in a voltaic battery. But notwithstanding 

 this, as the same cause, acting under the same conditions, 

 always produces the same effect, it is evident that the 

 relation of each guiding condition to each force is of a 

 most fixed and definite character. An exciting or deflect- 

 ing condition often requires little or no expenditure of 

 power ; a mechanical force acting at right angles upon a 

 moving body does but little actual work, although it greatly 

 alters the direction of the final effect. A deflecting con- 

 dition is often a source of a residual effect, and residual 

 phenomena frequently arise from minute statical conditions. 



In every active physical or chemical phenomenon the 

 effect is itself caused by an exertion of power ; but the 

 kind of effect appears to be determined by the species of 

 energy exerted, the kind of substance upon which it acts, 

 and the surrounding conditions ; i.e. the force causes the 

 effect and partly determines its kind, but the substance 

 and its conditions only partly determine the latter. In all 

 cases of the conversion of one physical force into another, 

 there appear to be two chief circumstances, viz., the true 

 cause and a guiding condition : for instance, in thermo- 

 electric action, heat is the true cause, suitable relative mole- 

 cular states of the two substances is the guiding condition, 

 and current electricity is the effect. In magneto-electric 

 action, mechanical power is usually the cause, magnetic 

 state is the guiding condition, and dynamic electricity the 

 effect. 



Guiding conditions are extremely numerous, because 

 effects differ with every different force ; the effect of each 

 force upon substances differs with every different sub- 

 stance, and with the same substance in each of its different 

 molecular states, and at every different temperature ; 



