M. E. Edlund on the Nature of Galvanic Resistance. 203 



2. We will first endeavour to ascertain what we are to under- 

 stand by the expression " galvanic resistance." 



We picture to ourselves a tube, the cross section of one half 

 of which is I, and that of the other half n\, filled with a fluid 

 which is in translatory motion in consequence of forces acting 

 upon it at one end of the tube. If, now, at one place in the 

 tube we wish to lessen the motion or its velocity by a counter- 

 pressure (e. g. a piston or the like), we must apply n times as 

 much pressure in the wider half as in the narrower, in order to 

 produce the same effect. The diminution of the velocity or the 

 strength of the current does not depend on the absolute quan- 

 tity of this counterpressure, but on its quantity on the unit of 

 surface of the cross section. If the pressure on the unit of sur- 

 face is equally great in the wider and in the narrower tube, the 

 lessening of the strength of the current is the same in both 

 cases. This will be the relation, whatever may be the nature 

 and constitution of the resistance ; only the particles of the fluid 

 must be sufficiently mobile to propagate the pressure in all di- 

 rections. What has just been said is directly applicable to a 

 galvanic current. Whatever view one may entertain on the 

 nature of electricity, all are perhaps agreed in this — that it is a 

 fluid the particles of which are readily movable, and that it must 

 therefore possess the property of communicating pressure in all 

 directions. Galvanic resistance obstructs electric motion. It 

 thus produces a counterpressure ; and this is equally distributed 

 over all points of the cross section of the conductor. When, for 

 example, two wires of different metals and of unequal thickness 

 produce an equal diminution of a given current-intensity, these 

 resistances are said to be equal; and we have then, in accordance 

 with the foregoing, to assume that, on the unit of surface of the 

 cross section, the counterpressure which each of them opposes 

 to the propagation of the current is also equal. Consequently 

 it is only the counterpressure on the unit of the cross section 

 that can come into question in the determination of resistances. 

 This is a consequence of hydrodynamical laws, and cannot be 

 conceived in any other way, inasmuch as electricity is a fluid. 



That galvanic resistance depends on the physical and chemical 

 constitution of the conductor is readily understood; but the 

 possibility can also be foreseen that it may be dependent on 

 other conditions also. The resistance might be regarded as ari- 

 sing from the friction experienced by the aether molecules in 

 pressing through between the material molecules of the con- 

 ductor. We have already remarked that the density of the free 

 aether in all bodies is equal. Therefore in equal volumes there 

 are equal quantities of free aether. If, then, a current comes 

 from a wire with the cross section I, and passes into another 



