NATURAL PHILOSOPHY. 147 



ON SOME NE\Y METHODS OF PRODUCING AND FIXING ELECTRICAL 



FIGURES. 



From certain experiments recently made by Mr. "W. R. Grove, published 

 in the Philosophical Magazine, the way appears to be opening for new ap- 

 plications of electricity, and for investigations rich in promise alike to 

 science and art. It was known vears ago to some of the German savans, 



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that a coin or medal placed on a smooth vitreons or metallic surface and 

 electrized, would leave impressions on that surface which became visible 

 when breathed on. From the latter peculiarity they were called " roric 

 figures ; " and attempts were made to fix them by exposure to vapor of mer- 

 cury or iodine, but without success. AVhere the Germans failed, Mr. Grove 

 has succeeded : " Believing as I have for many years," he says, " that elec- 

 tricity is nothing else than motion or change in matter, a force and not a 

 fluid, I have made experiments to ascertain whether similar effects take 

 place in cases where electrical light is visible upon insulated surfaces only." 



We give a brief sketch of the experiments, adopting Mr. Grove's descrip- 

 tion where it suits our purpose. Two plates of window-glass, about three 

 inches square, were dipped in nitric acid, then washed, and dried with a 

 clean silk handkerchief, and coated on the outside with pieces of tinfoil a 

 little smaller than the glass. A piece of printed hand-bill was laid between 

 the plates thus prepared; the tinfoil coatings were connected with the 

 secondary terminals of Ruhmkorff's coil, and removed after a few minutes' 

 electrization. Now, "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 appear- 

 ance ; even the fibres of the paper were beautifully brought out by the 

 breath, but nothing beyond the margin of the tinfoil." These impressions 

 were fixed by holding them over hydrofluoric acid, powdered fluor spar 

 and sulphuric acid slightly warmed in a leaden dish. 



" I now cut out of thin white letter-paper," proceeds Mr. Grove, " the 

 word Volta, and placed it between the plates of glass. They were submit- 

 ted to electrization as before, and the interior surface of one of them, without 

 the paper letters, was subsequently exposed in the hydrofluoric acid vapor ; 

 the previously invisible figures came out perfectly, and formed a permanent 

 and perfectly accurate etching of the word Volta, as complete as if it had 

 been done in the usual mode by an etching ground. This, of course, could 

 be washed and rubbed to any extent without alteration ; and the results 

 obtained give every promise for those who may pursue this as an art, of pro- 

 ducing very beautiful effects, enabling even fine engravings to be copied on 

 glass, etc." 



A plate on which the invisible image was impressed, was immersed in a 

 bath of nitrate of silver, in the usual manner as for a photograph. " It was 

 then held opposite a window for a few second:-, and taken back into the 

 darkened room ; and on pouring over it a solution of pyrogallic acid, the 

 word Volta, and the border of the glass. beyond the limits of the tinfoil, were 

 darkened, and came out with perfect distinctness, the other parts of the glass 



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