298 ROUGH WAYS MADE SMOOTH. 



any substance connecting those poles which possesses the 

 property of being what is called a good conductor of elec- 

 tricity. But the reader is not to assume that there is such 

 a current, or that it is known to flow either from the positive 

 to the negative pole, or from negative to positive pole ; or, 

 again, that, as some have suggested, there are two currents 

 which flow simultaneously in opposite directions. We speak 

 conventionally of the current, and for convenience we speak 

 as though some fluid really made its way (when the circuit 

 is complete) from the positive to the negative pole of the 

 compound battery. But the existence of such a current, or 

 of any current at all, is purely hypothetical. I should be 

 disposed, for my own part, to believe that the motion is of 

 the nature of wave- motion, with no actual transference of 

 matter, at least when the circuit is complete. According to 

 this view, where resistance takes place we might conceive 

 that the waves are converted into rollers or breakers, ac- 

 cording to the nature of the resistance - actual transference 

 of matter taking place through the action of these changed 

 waves, just as waves which have traversed the free surface 

 of ocean without carrying onward whatever matter may be 

 floating on the surface, cast such matter ashore when, by 

 the resistance of the shoaling bottom or of rocks, they 

 become converted either into rollers or into breakers. 



I may also notice, with regard to good conductors and 

 bnd conductors of electricity, that they may be compared to 

 substances respectively transparent and opaque for light- 

 waves, or again, to substances which allow heat to pass freely 

 or the reverse. Just as light-waves fail to illuminate a trans- 

 parent body, and heat-waves fail to warm a body which 

 allows them free passage, so electricity-waves (if electricity 

 really is undulatory, as I imagine) fail to affect any sub- 

 stance along which they travel freely. But as light-waves 

 illuminate an opaque substance, and heat-waves raise the 

 temperature of a substance which impedes their progress, so 

 waves of electricity, when their course is impeded, produce 



