Electromotive Force in Tidal Streams. 



[May 8, 



Twelve accurate curves of the electromotive force (each the result 

 of ninety-one observations) were obtained, showing the effect of this 

 tidal action on the various groups of metals under observation. The 

 general contour and character of these affords interesting information 

 respecting such action on the different metals employed. For 

 brevity, however, the results are abridged and summarised in one 

 Table, B. 



The highest E.M.F. was rapidly reached, and generally from this 

 point to the end of a tidal period of six hours, a regular reduction of 

 E.M.F. ensued. In every instance the greatest electromotive force 

 \vas observed from the tidal action on the " hard " steels. 



The " soft " steels affording on the averages less E.M.F. than the 

 rolled wrought iron, but this group of steels generally gave a higher 

 E.M.F. near the commencement of each experiment. 



The rolled wrought iron gave more E.M.F. than the hammered 

 wrought iron, which latter, together with cast metal No. 2, gave the 

 least E.M.F. in these observations. 



The preceding results give a quantitative measurement of the 

 electromotive force under the conditions stated, and hence afford an 

 indication of the extent of similar action on structural ironwork in 

 tidal rivers during diffusion between the surface and lower waters, the 

 electromotive force observed being not only appreciable, but in many 

 instances very considerable, reaching not unfrequently the one-tenth 

 to the one-seventh of a volt. 



FIG. 1. 



This destructive action would appear to be exerted most extensively 

 on the lower portion of iron or steel vessels, metallic structures, Ac., 



