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II. Fourth Letter on Voltaic Comhinations, with reference to the Mutual Relations of 

 the Generating and Conducting Surfaces. Addressed to Michael Faraday, Esq. 

 D.C.L. F.R.S., Fulleria?i Prof. Chem. Royal Institution, 8^c. Sgc. 8^c. By 

 J. Frederic Daniell, F.R.S., Prof Chem. in King's College, London. 



Received January 18, — Read January 25, 1838. 



My dear Faraday, 



In my second* letter to you upon Voltaic Combinations, I sug-gested that, in a theo- 

 retical point of view, the most simple and perfect combination would probably consist 

 of a solid sphere (or rather active point) of a generating- metal, surrounded by a hol- 

 low sphere of an inactive conducting metal, with an intervening liquid electrolyte ; 

 the circuit being completed by a conducting wire properly disposed for connecting 

 the two metals. Further reflection led me to believe that a series of experiments 

 commencing as nearly as possible with these most simple conditions of the problem, 

 might throw some light upon the relative dimensions, positions and actions of the 

 generating and conducting plates of voltaic combinations in general; which appeared 

 to me not to liave received all the elucidation of which they might be susceptible. 

 The subject, it is true, has not escaped the attention of experimenters ; but most of 

 the results with which I am acquainted are so involved in the errors arising from the 

 variable condition of the source of the current itself, which I have already pointed 

 out, as to leave it in a very unsatisfactory state. I moreover proposed to myself, in 

 the investigation which I consequently undertook, to trace the self-distribution of 

 the force from its origin, by the indications of reduced copper, in the manner described 

 in my first letter-}-. I have thus been led to some results which I trust you will con- 

 sider of sufficient importance to justify my troubling you with another communica- 

 tion upon the subject. 



My first apparatus, which it is necessary to describe, consists of two hollow hemi- 

 spheres of brass, fitting together water-tight by means of exterior flanges half an inch 

 wide, and a collar of leather, and thus forming a sphere, the interior diameter of which 

 is 9J inches ; consequently exposing a surface of about 268*8 square inches. The 

 lower hemisphere is fitted into a frame carrying buttons, by which the upper can be 

 securely wedged down upon it ; and underneath there is a small cock, by which any 

 liquid in the interior may be drawn ofl". The upper part of the upper hemisphere 

 terminates in a tube of about one inch in length, forming an opening through which 

 a membranous bag may be introduced, and from which it may be suspended. The 



* Philosophical Transactions, 1836, p. 128. t Ibid. p. 113. 



MDCCCXXXVIII. G 



