320 TENTH ANNUAL REPORT OF 



trical equilibrium soon ensue. For a continuous excitation of electricity 

 this state of equilibrium must be continuously destroyed ; this is 

 done in frictional electricity, by removing the contact of the closely- 

 touching places of the heterogeneous substances ; in the hydro bat- 

 tery, by the decomposition of the electrolytes ; in the thermo pile, 

 the circulation of electrical equilibrium is produced by the disturbance 

 of thermal equilibrium. 



SECTION SECOND. 

 DETERMINATION OF THE CONSTANT VOLTAIC BATTERY. 



§ 4. Unit of force of current. — Every conductor of electricity, how- 

 ever good, opposes some resistance to its propagation, and many re- 

 searches have been made to determine tlie laws of the transfer through 

 conducting media. The following facts have been established by ex- 

 periment : 



1. Galvanic electricity tends to diffuse itself through the whole 

 capacity of a conductor, and consequently the resistance to conduction 

 will be in proportion inversely to the transverse section of a conductor. 



2. All parts of a closed circuit, including the battery itself, are 

 traversed at the same time by the same quantity of electricity, what- 

 ever be the diversity of their nature. 



It follows irom the second law, that the absolute inten ity of the 

 electricity that passes in a closed circuit depends upon two (ircum- 

 stances : first, on the force which develops the electricity^ and which 

 is called the electro-motive force; and second, on the resistance to 

 conduction presented by the whole circuit taken together. Ohm was 

 the first to give a precise statement of these laws, and to deduce 

 with mathematical precision, from them, consequences which have 

 become of great importance in establishing the theory of the battery 

 as well as in the application of electricity to the arts. 



If we designate by S the value of the current, or its power to pro- 

 duce effects, and by E the electro-motive force of a single element^, 

 whether this be due to contact chemical action, or both, and by R the 

 resistance in the battery, then the relations may be expressed by the 

 equation 



In the foregoing equation we have supposed that the battery con- 

 sists of a single element, and that the metals are joined by so short 

 and thick a conductor that it offers no appreciable resistance. If, 

 however, the battery consist oi n number of elements, joined as before, 

 then the electro-motive power will be n times greater^ and also the 

 resistance will be increased in the same ratio, and therefore we shall 

 have 



n K 



If, now, we introduce an additional resistance in the conductor 



