This article, published in the Philosophical Magazine Series 6, presents a contribution to the theory of electrocapillarity by David Leonard Chapman. The paper discusses the electrocapillarity phenomenon, focusing on the distribution of potential and electric density within a solution, and the capacity of the double layer formed by the double layer theory. The author derives equations that relate the potential difference between the solution and the metal to the charge on the double-layer condenser. The paper also includes a detailed calculation of the surface energy of mercury in contact with an electrolyte, using a reversible cycle of operations to determine the surface tension. The results show that the surface tension changes with the potential difference, and that the assumption of a constant capacity of the condenser is not valid. The author concludes that the observed changes in surface tension can be largely explained by the electric charges in the double layer. The paper also mentions the importance of further research on electrocapillary curves in the region of maximum capillarity, particularly with solutions that do not produce electromotive force in contact with mercury. The article is accompanied by plates VI and VII. The author also acknowledges the contributions of Professor H. Stroud and Mr. H. Morris-Airey. The paper is part of a series of articles on electrocapillarity and electrification associated with dust-clouds.This article, published in the Philosophical Magazine Series 6, presents a contribution to the theory of electrocapillarity by David Leonard Chapman. The paper discusses the electrocapillarity phenomenon, focusing on the distribution of potential and electric density within a solution, and the capacity of the double layer formed by the double layer theory. The author derives equations that relate the potential difference between the solution and the metal to the charge on the double-layer condenser. The paper also includes a detailed calculation of the surface energy of mercury in contact with an electrolyte, using a reversible cycle of operations to determine the surface tension. The results show that the surface tension changes with the potential difference, and that the assumption of a constant capacity of the condenser is not valid. The author concludes that the observed changes in surface tension can be largely explained by the electric charges in the double layer. The paper also mentions the importance of further research on electrocapillary curves in the region of maximum capillarity, particularly with solutions that do not produce electromotive force in contact with mercury. The article is accompanied by plates VI and VII. The author also acknowledges the contributions of Professor H. Stroud and Mr. H. Morris-Airey. The paper is part of a series of articles on electrocapillarity and electrification associated with dust-clouds.