1884.] Electric Conduction- Resistance at Cathodes. 35 



"because such portion is shown by this research to be in the electro- 

 positive position during certain conditions of a tidal stream. 



It should be pointed out that similar conditions of galvanic action 

 obtain in all our iron structures in tidal estuaries or rivers, the action 

 of the salt and fresh water in course of diffusion constituting a source 

 of galvanic disintegration independent of any difference in composi- 

 tion of the metals. It should also be observed that in circumstances 

 where the electromotive force arising from causes here pointed out 

 acts in concert with any E.M.F. from differences of composition of the 

 metals employed in structures, a very considerable total electrolytic 

 disintegration is likely to ensue. From data kindly furnished to the 

 author by Dr. H. Clifton Sorby, F.R.S., an indication is afforded of 

 the nature of the changing composition of the waters of tidal 

 estuaries at various places and depths. The Table B of electromotive 

 force, &c., together with the diffusion resistance curve (fig. No. 1), 

 afford some index of the changing E.M.F. arising from such tidal 

 difference of potential. 



In approaching the subject in the manner stated in this memoir, 

 the author trusts he has been able to afford some indication of the 

 extent of the electromotive force from the action of tidal streams on 

 the various metals experimented upon. 



III. " On Unequal Electric Conduction-Resistance at Cathodes." 

 By G. GORE, F.R.S., LL.D. Received April 30, 1884. 



During some experiments which I have been making on the 

 unequal resistance to the deposition of a metal upon cathodes of 

 different metals in the same solution by the same current (see 

 " Some New Phenomena of Electrolysis "), I have been led to 

 investigate the resistance of cathodes of different metals to the 

 passage of the current into them. 



I have found that by taking a good conducting electrolyte, 

 immersing in it a positive sheet of zinc, and a smaller negative one of 

 another metal, connecting the plates with a galvanometer of low 

 resistance, reducing all the other resistances in the circuit to the 

 minimum except that of the negative plate ; then making a series of 

 measurements of strengths of current of different couples formed by 

 the zinc and about twelve other metals, during removal of polarisation 

 by stirring the liquid ; also making another series of measurements of 

 the electromotive forces of the same couples during stirring ; calcu- 

 lating from these data the total resistance in each case, then 

 deducting the portion of resistance due to the galvanometer, also that 

 due to the liquid itself, and to opposing contact-potential, and 



D2 



