372 Prof. Oliver Lodge on the Seat of the 



of an important determination made by Sir William Thomson*, 

 the preceding figures give a superior limit of the attraction 

 of the coatings, which is as large as one ninth of the optically 

 equivalent compressing weight. As to a definite solution of 

 the question, I hope to attempt that, or something equivalent, 

 very soon, in a set of experiments which I have had in view 

 for some time. 



Glasgow, 26th August, 1885. 



XLV. Sequel to Paper on the Seat of the Electromotive Forces 

 in a Voltaic Cell. Theories of Wiedemann and o/Helmholtz. 

 By Professor Olivee LoDGEf . 



IN a recent Beiblatter%, Prof. Gr. Wiedemann points out that 

 in my summary of views and work in connection with 

 the seat of E.M.F. in the pile I have ignored his theory. I 

 had in fact been mainly concerned with possible explanations 

 of the Volta-effect ; while Prof. Wiedemann starts with this as 

 a datum, and on ihe strength of it explains the action of the 

 pile. Moreover, since most of the theoretical opinions held on 

 this subject are summarized at the end of the second volume of 

 his Elektricitat, while his own theory is given in the first volume, 

 along with the account of Volta- force experiments, I had over- 

 looked it. To make amends for this oversight, for which I 

 beg to express my regret, and because I find it difficult to 

 summarize his opinions briefly, I trust I may be permitted 

 to give a rough semi-literal translation of his most conspicuous 

 passages as a help to other students of the subject. 



Theory o/Ot. Wiedemann, 1870. (Wied. JElek. i. p. 251 et seq.) 



" We have now to investigate in what way the electrical 

 forces in a closed circuit of two metals and a liquid {e.g. Zn, Cu, 

 dilute HC1) are excited. We know that the constituents of 

 the binary compound contained in the liquid separate by the 

 passage of the current in such a way that the one (H) is set free 

 at the copper and an equivalent quantity of the other (CI) at 

 the zinc, and that the latter combines with an equivalent 

 quantity of zinc to form ZnCl. This process shows that the 

 deportment of the binary body between the metals consists no 

 longer only in a simple overbalancing attraction of its whole 

 mass for one or the other electricity, as in metals, but also in 



* Reprint of Papers on Electrostatics (§ 340). 



+ Communicated by the Author, in continuation of paper in Phil. Mag. 

 for March, April, May, and June of the current year. 



J Beiblatter zu den Annalen der Physik und Chemie, 1885 No. 7, 

 Band ix. p. 533. 



