Measures for Electric and Magnetic Quantities. 387 



our equation (3), while in the static system it gives a different 

 result. If, naniely, we put, first, 



[Qm rf ] = [ML 2 T- 1 ]; 



and divide this equation by (2), there comes 



M = [M*L*], 



which equation agrees with equation (5) above given. But if 

 we put 



[^/^[ML'T- 1 ], 



and divide this by (1), we get 



K] = [M L], (7) 



which is different from our equation (4), at which we arrived 

 by employing equation (3). 



By Maxwell's incorrect formula for the static magnetism- 

 unit the formulse of other units in the static system of mea- 

 sures, dependent on the unit of magnetism, have been ren- 

 dered also incorrect, in a not inexplicable manner. 



§ 4. The Determination of other Units. 



The units of electricity and magnetism in both systems of 

 measures having been determined, the units for the other 

 quantities also which occur in electric and magnetic investi- 

 gations can now be easily deduced. Of these the most impor- 

 tant only may here be mentioned. 



The unit of the intensity of a current results very simply 

 from understanding by current-intensity the quantity of 

 electricity -flowing in unit time through a cross section. 

 Hence we only need here to divide the unit of electricity by 

 the unit of time; and we thereby obtain, if i denotes intensity, 

 the following equations relating to the two systems : — 



W=-[f]=[M*L^T- 2 ], (8) 



M = [f] = [M*L*T- 1 ] (9) 



The unit of electromotive force is most simply determined 

 from the condition (which holds universally) that the product 

 from the units of electromotive force, current-intensity, and 

 time, or (what is the same) the product from the units of elec- 

 tromotive force and quantity of electricity, must be equal to 

 the unit of mechanical work. From this, namely, we obtain, 



