424 



closed one gives rise to an electroscopic tension. By 

 resistance is signified the obstacle opposed to the passage 

 of the electric current by the bodies through which it has 

 to pass ; it is the inverse of what is usually called their 

 conducting power. 



" When the activity of any portion of the circuit is 

 increased or diminished, either by a change in the electro- 

 motive force, or in the resistance of that portion, the 

 activity of all the other parts of the circuit increases or 

 decreases in a corresponding degree, so that the same 

 quantity of electricity always passes in the same instant 

 of time through every transverse section of the circuit. 



" The force of the current is directly proportional to 

 the sum of the electro-motive forces which are active in 

 the circuit, and inversely proportional to the total resist- 

 ance of all its parts ; or, in other words, the force of the 

 current is equal to the sum of the electro-motive forces 

 divided by the sum of the resistances." 



This may be rendered more familiar by experiment. If 

 we take a plate of amalgamated zinc and a plate of plati- 

 nized silver immersed in diluted sulphuric acid, forming 

 the arrangement invented by Mr. Smee, and known by 

 his name, and connect the plates, decomposition of the 

 water takes place, the zinc being oxidated at the expense 

 of the oxygen of the water, and the corresponding quantity 

 of hydrogen being evolved at the platinized surface. By 

 this the electro-motive force E is developed. I will not 

 now discuss the chemical and contact theories of electricity, 

 but merely state the undisputed fact, that the chemical 

 decomposition and electro-motive force are correllative, not 

 only in being simultaneously developed, but also in quantity. 

 Now the force F, developed in every part of the circuit, 

 may be strictly expressed by E, the electro-motive force 

 of the elements, that is, the water decomposed and the 



