FIXING ELECTRICAL FIGURES. 4 3 



nomena ; and believing, as I have for many years, that electri- 

 city is nothing else but motion or change in matter, or a force 

 and not a fluid, I have recently made some experiments to 

 ascertain whether similar effects took place in cases where 

 electrical light is visible upon insulated surfaces only, a great 

 number of experiments having already shown that the par- 

 ticles of metals or conducting bodies are projected when the 

 electrical spark proceeds from them. 



M. Du Moncel has shown that when two plates of glass, 

 coated respectively on their exteriors with metallic plates, are 

 kept separate and electrised, a brilliant electrical light is seen 

 between the plates.* I thought I might render evident the 

 molecular change which I believed to be taking place on the 

 opposed surfaces of glass in such cases, and the following 

 experiments, selected from many others, will, I think, prove 

 that this is the fact : 



1. Two plates of window-glass, 3 by 3^ inches, were im- 

 mersed in nitric acid, then washed, and dried by a clean silk- 

 handkerchief until their surfaces gave a uniform flush when 

 breathed on. Between these plates was then placed a piece 

 of hand-bill printed on one side only ; pieces of tinfoil rather 

 smaller than the glasses were placed on the outside of each, 

 and these coatings were connected with the secondary termi- 

 nals of a Ruhmkorff coil After a few minutes' electrisation 

 the coatings were carefully removed, and the interior surface 

 of the glass, when breathed on, showed with great beauty the 

 printed words which had been opposite it, these appearing 

 as though etched on the glass, or having a frosted ap- 

 pearance; even the fibres of the paper were beautifully 

 brought out by the breath, but nothing beyond the margin 

 of the tinfoil. 



2. It now occurred to me that I might render these im- 

 pressions permanent by the use of hydrofluoric acid, and a 

 similar experiment was made, the naked plate of glass after 

 electrisation being exposed over a leaden dish containing 

 powdered fluor spar and sulphuric acid, and slightly warmed ; 

 the letters came out rather imperfectly, but some creases in 

 the paper were beautifully reproduced. 



* Notices sur Vappareil de Ruhmkorff^ p. 46. 

 DD2 



