1881.] 



On the Refraction of Electricity. 



435 



From this we may draw the conclusion, that either the materials of 

 the earth have about the strength of granite at 1,000 miles from the 

 surface, or they have a much greater strength nearer to the surface. 



This investigation must be regarded as confirmatory of Sir William 

 Thomson's view, that the earth is solid nearly throughout its whole 

 mass. According to this view, the lava which issues from volcanoes 

 arises from the melting of solid rock, existing at a very high tempera- 

 ture, at points where there is a diminution of pressure, or else from 

 comparatively small vesicles of rock in a molten condition. 



XIX. " On the Refraction of Electricity." By Alfred Tribe, 

 F.I.C., Lecturer on Chemistry in Dulwich College. Com- 

 municated by Dr. Gladstone, F.R.S. Received June 7, 

 1881. 



On December 15, 1880, I had the honour of communicating to the 

 Royal Society the latest results of my work on electric distribution. 

 In that paper there is included a description of results which form the 

 basis of a graphic and electro-chemical method of investigating the 

 field of electrolytic action. These results may be classed under three 

 heads : — 1st. Distribution of electricity on metallic conductors in elec- 

 trolytic media. 2nd. Physical differences in corresponding parts of 

 non-homogeneous electrolytic fields. 3rd. Direction in which the 

 energy is transmitted. 



As the detailed account of these experiments has not yet been 

 published, it is necessary for the appreciation of the evidence to be 

 adduced to give in this place the groundwork of that part of the 

 method relating to the direction in which the energy is transmitted. 

 It will be convenient to do this under three heads. Let it be remem- 

 bered that a rectangular electrolytic cell was used, that the electrolyte 

 was a solution of copper sulphate, and the electrical relations of the 

 liquid were ascertained by immersing in it a rectangular silver plate 

 (called an analysing plate or analyser), on which the ions were depo- 

 sited. In all cases the positive ion separates and is distributed on that 

 part of the plate which may be supposed to receive — electrification, or 

 by which the + energy enters the analyser, while the — ion separates 

 on that part of the same plate which receives + electrification, or 

 from which the energy emerges. 



a. When the course of the energy* is parallel with any two edges of 

 an analyser, and therefore with the sides, the boundary lines of the 

 ions on both sides of the plate are parallel with the plane of the elec- 



* I assume that the energy in a homogeneous field runs in straight parallel lines 

 from one electrode to another, and that this course is not appreciably disturbed by 

 an analyser. 



