518 WEBER ON THE MEASUREMENT 



Each of these four members refers exclusively to two of the four 

 electric masses distinguished in the two elements of the current, 

 viz. the first member to the two positive masses « e and «' e\ 



the relative distance of which is r^, velocity -^, and acceleration 



■ g' ; the second to the positive mass a e in the first, and to the 



negative mass — «' e' in the second element, the relative distance 



d 7* d d V 



of which is r^^, velocity -jj, and acceleration , J' , and so on ; 



and in fact all four are members of the masses to which they 

 refer, the distance, velocity and acceleration of which are com- 

 posed in exactly the same manner. 



Hence it is evident that if the entire expression of the electro- 

 dynamic force of two elements of a current be considered as the 

 sum of the forces, which each two of the four electric masses 

 they contain exert upon each other, this sum would be decom- 

 posed into its original constituents, the four above members re- 

 presenting individually the four forces which the four electric 

 masses in the two elements exert in pairs upon each other. 



Hence also the force with which any positive or negative mass 

 E acts upon any other positive or negative mass E', at the 



distance R, with a relative velocity of —j—, and acceleration ^ji^i 



may be expressed by 



_ aa^ EE^ / rfR- _ ^ ddR \ 

 16* RR Kdt"^ df~ /' 



for this fundamental principle is necessary and at the same time 

 sufficient to allow of the deduction of Ampere's electro-dynamic 

 laws, which are confirmed by the above measurements. 



However, this new fundamental principle of electro-dynamics 

 is in its nature move, general than that formerly laid down by Am- 

 pere; for the latter refers merely to the special case, in which four 

 electric magnitudes are given at the same time, subject to the 

 conditions premised for invariable and undisturbed elements of 

 the current, whilst such a limitation to the above conditions 

 does not occur in the former. This fundamental principle, con- 

 sequently, admits of application in those cases where the former 

 is inapplicable ; hence its greater utility. 



If, lastly, the newly-discovered fundamental principle of elec- 



