Electric Residue in the Ley den Jar. 419 



fluence, whereas undei' the magnetic moment of a magnet the 

 idea of stability is associated, or at any rate the idea that within 

 pretty large limits the magnetic moment is essentially indepen- 

 dent of external influences. Nevertheless, for the condition and 

 mode of action of a body in whose interior the electi'ic fluids are 

 unequally distributed, and are only capable of extremely slow 

 motion or of none at all, we have no better term, inasmuch as the 

 condition itself is hypothetical, and hence it may not be deemed 

 inappropriate to introduce the expression " electric moment." 



Let us conceive the possibility of the neutral electricity within 

 an insulator being by some cause or other so separated, that 



a. under the surface on the one side a stratum of positive, 

 and on the opposite side a stratum of negative electricity formed 

 itself; or that 



b. a series of such alternate pai-allel strata were arranged be- 

 hind each other ; or that 



c. in every ultimate particle the separation took place in the 

 same direction, but that the electricity could not pass from one 

 particle to another ; and if we now further assume that such a 

 state can exist after the cause which produced this separation of 

 the electricities has ceased to act, then such an insulator could 

 exercise an action, i. e. an electromotive force, on an external 

 point. 



d. A fourth condition is also conceivable ; for instance, in 

 every particle of the glass the electricities may be naturally sepa- 

 rated, but in general without external action (for exactly the same 

 reason as the molecular currents in soft iron are so, that is, be- 

 cause their own condition of equilibrium does not permit it) ; but, 

 through some influence or other, the several particles, together 

 with the fixed electricities clinging to them, may be so turned 

 more or less in the same direction, that in this case also the sum 

 of the distances of all positive particles from any plane may be 

 difi"ercnt from the sum of the distances of all negative particles 

 from the same. In reference to some one plane, the difl^erence 

 of these sums may, under certain circumstances, be greatest; 

 and in reference to this plane, or to a normal erected on it, the 

 electric moment of the body will be a maximum, and the normal 

 may be called an electric axis. 



By way of example, let us suppose a glass plate with its prin- 

 cipal faces (J and h symmetrically placed between two parallel 

 surfaces, <?. g. metallic plates, which we will call G and II, and 

 which we will suppose to be charged with opposite electricities, 

 then one of the four states a, b, c, or d may be conceived gra- 

 dually to take place in the glass. Through the electromotive 

 force of these metallic plates on the interior of the glass, the 

 natural electricities might there be separated, so that, if G be 

 2 F2 



