184 Dr. C. E. A. Wright and Mr. C. Thompson. [May 3, 



that the production of currents by atmospheric oxidation might he 

 practically effected on the large scale. 



We found it difficult to obtain sharp and concordant valuations of 

 the E.M.F. actually set up in cells containing oxidisable fluids, the 

 more so, as the numbers appeared to vary, not only with the nature of 

 the aeration plate and the fluid in contact therewith, but also with the 

 character of the incorrodible plate immersed in the oxidisable fluid, and 

 with the nature and strength of that fluid also. With cells containing 

 oxidisable metals, however, and electrolytic fluids in which the oxides 

 formed were soluble, we found no difficulty in obtaining far more 

 concordant and approximately constant values than would at first sight 

 have appeared likely, or even possible with combinations in which one 

 ingredient was so unstable an element as a film of gaseous matter 

 attracted to the surface of a condensing solid, and simultaneously 

 in contact with a fluid capable of dissolving the gas. Obviously, 

 mechanical disturbances, rapid alterations of temperature, and such 

 like causes would be likely to cause large variations from time to 

 time in the readings of any one particular cell ; whilst unavoidable 

 differences in the conditions of surface of otherwise duplicate plates 

 (such as variations in degree of polish, &c.) would render it likely 

 that the average readings of any two duplicate cells would occasion- 

 ally exhibit considerable divergence; we succeeded, however, in 

 reducing these sources of fluctuations to comparatively small limits, by 

 setting up the cells in an apartment where the temperature varied but 

 little, and only slowly, the readings being mostly taken in the morn- 

 ings after standing at rest all night ; whilst alteration of the fluid by 

 evaporation, attraction of moisture, carbonic acid, &c, from the air, 

 falling in of dust, and so on, was avoided as much as possible by 

 covering over the vessel containing the aeration plate with a bell- jar 



