1884.] Difference of Potential in Tidal Streams. 



29 



unfrequently be observed arising from the previous unequal action of 

 the solutions on the metal. 



The series of groups of metals employed in this investigation, viz., 

 wrought irons, various steels, and cast metals, &c., were especially 

 selected in order to render the research of more practical value. 



The two dissimilar solutions used were sea water (from Filey Bay) 

 and distilled water. 



The author devised the arrangement described below for carrying 

 out this research. 



The experiments were made on large round bars of each of the 

 following metals, of known chemical composition and specific gravity, 

 every bar was 2f^- inches diameter, carefully turned and polished 

 quite bright, the metals being each especially prepared throughout 

 for these observations. 



A careful selection was made with reference to the percentage of 

 combined carbon, specimens containing the highest and lowest being 

 taken, in order that extreme results in each case might be arrived at. 

 The descriptive terms " soft " and " hard " have reference solely to 

 percentages of combined carbon. 



This large size and round form of bar were employed to ensure in 

 the manipulation of the metals as uniform a molecular structure as 

 practicable. 



The steel and iron bars in each case were prepared from the same 

 ingot or bloom and sawn into equal lengths when finished, so that 

 the bars of the same metal (turned and finished) were identically of 

 one composition, &c. The same exact care was exercised in the 

 preparation of the cast metal bars. 



The chemical composition and specific gravities of the metals are 

 shown in Table A. 



Table ~A. Analyses of the Wrought Iron, various Steels, and Cast 



Metals employed. 



* Combined carbon in these samples was determined by combustion, and in the 

 other samples by the colour test. 



