of Electric Induction and Conduction. 365 



supports, by reason of the slipping of their rings on a and b. 

 This represents that no opposition electromotive force is gene- 

 rated in the electrolyte itself, but that it offers a little ordinary 

 resistance to the passage of the current; also that the current 

 is conveyed by a bodily transfer of material — that it is, in fact, 

 a convection-current. "Further, since the buttons do not slip 

 on the cord, the length of cord between any two of them re- 

 mains constant ; i. e. there is no internal charge developed in 

 the electrolyte. This natural length of cord between two adja- 

 cent buttons may be called the " molecular charge ;" it appears 

 to be the same (up to a simple factor) for all substances, and 

 is what Maxwell calls one molecule of electricity. 



Now let button No. 9 reach the electrode Z ; it travels on, 

 compressing the elastic supports and calling out an opposition 

 force which may be sufficient to check the descent of W, or it 

 may not. Suppose that it is not ; then the button still moves 

 on, its pressure against the knife-edge increases, until the button 

 is cut in half and released from the cord. The tension being 

 thus suddenly relieved, the cord makes a bound forward, the 

 " molecular charge " of No. 9 passes over the pulleys, and 

 No. 8 comes into contact with the electrode, to be opposed, cut, 

 and released in like manner. When a button has been cut, it 

 merely hangs by its rings to the rods a and b, offering a little 

 passive obstruction because it has to be pushed forward by the 

 others ; but it presently gets pushed off the ends of the rods, 

 and it then falls away. The cord thus progresses in a rapid 

 succession of jerks; but as in any actual circuit the number 

 of cords parallel to one another is very great, the average 

 motion is continuous and not jerky. 



The procession of buttons towards Z represents the proces- 

 sion of the atoms of the cathion (say hydrogen) toward the 

 cathode ; when they reach it, they at first develop an opposi- 

 tion electromotive force at its surface ; but presently getting 

 released, they deliver up their molecular charges to it, rise 

 through the liquid, slightly increasing its resistance, and escape 

 as gas. 



In order to diminish the polarization of the electrode, the 

 knife-edge may be sharpened, which corresponds to making 

 the electrode of gold or platinum instead of copper or iron ; or 

 the buttons may be softened and rendered easier to cut, which 

 represents either a cathion less electro-positive than hydrogen, 

 or else the addition of a solvent like nitric acid. Strengthen- 

 ing or weakening the springs which support Z does not 

 affect the electromotive force called out; but it does alter 

 the time during which the reverse current lasts. Platinum 

 (when not covered with " black," as in Smee's cell) must be 



