oe 
( 257 ) 
It is easily seen that 
(A ak O_O 
Oe Ov’ pek Ot Ot 
Hence, if we take the mean values of every term in the equations 
(D—{(V) and (4), as we shall soon do, we may replace d and b by 
d and 6, Divy by Div 3 ete. 
§ 4. Before proceeding further, it is necessary to enter into some 
details concerning the charged particles we must suppose to exist in 
ponderable bodies. 
Each of these particles calls forth in the surrounding aether a field, 
determined by the amount, the distribution and the motion of its 
charges, and it may be shown that, if x, y, 2 are the coordinates 
relatively to an origin © taken somewhere within the particle, and 
if the integrations are extended to the space occupied by it, the field, 
at distances that are large as compared with the dimensions of the 
particle, is determined by the values of the expressions 
fear. etl ere ct ee Ee Cae are ees (3) 
fox fever fener, NDE eN 
. 
ford, ford forser we Serr. ee eto 
a = 
fervar | 
a 
Now, we might conceive particles of such a nature that for each 
of them all these quantities had to be taken into consideration. For 
Ovcy dt, forende, cte., Ronse (5) 
the sake of clearness, it will however be preferable to distinguish 
between different kinds of particles, the action of each of these kinds 
depending only on some of the integrals (3)—(6). 
a. If the charge of a particle has the same algebraic sign in all 
its points, the actions corresponding to the integrals (8) and (5) will 
far surpass those that are due to (4) and (6); we may then leave 
out of consideration these latter integrals. Such particles, whose field 
is determined by their charge and their motion as a whole, may be 
called conduction-electrons. We shall imagine them to be crowded 
together at the surface of a charged conductor and to constitute by 
their motion the currents that may be generated in metallic wires. 
