NATURAL PHILOSOPHY. 113 



about two square metres, on metal plates, by means of metallic points 

 directed perpendicularly to their surface. 



Nobili, in 1827, afterwards produced colored rings on platinum, 

 gold, silver, and brass plates, by putting them in communication with 

 one of the two poles of a voltaic pile, plunging them into metallic and 

 non-metallic solutions, and then by directing perpendicularly to their 

 surface a platinum point connected with the other pole. With posi- 

 tive silver, for instance, and solution of sea-salt, he obtained a series 

 of concentric circles surrounded with varied irises, the tints being 

 slightly dimmed by contact with the air. On heating the plates all 

 the rings took a red tint. 



M. Becquerel stated, that he began to study the electro-chemical 

 coloration of metals in 1843 ; his chief object being, not to produce 

 colored rings, but to deposit on plates of gold, platinum, copper and 

 silver, thin and uniform layers of peroxide of lead, presenting suc- 

 cessfully, according to the duration of the operation, which was gen- 

 erally very short, the rich colors of the spectrum. The operation 

 consists in plunging into an alkaline solution of protoxide of lead 

 the piece to be colored, put in connection with the positive pole of 

 a voltaic pile charged with nitric acid and composed of many layers 

 of plates, and closing the circle with a platinum wire in communica- 

 tion with the negative pole, and of which but the point, which alone 

 touches the alkaline solution, is continually in motion. In contact 

 with the object to be colored, the protoxide of lead, which forms the 

 positive electrode, super-oxidizes, becomes insoluble in the alkali, 

 and deposits itself on the surface in slight adherent layers, producing 

 the color of the thin plates. Air and light gradually fade these 

 colors a disadvantage which may in great measure be avoided by 

 covering the colored surface with alcohol varnish, which acts but very 

 slightly on the peroxide. With a little practice all the tints desired 

 may be given to a large object with hollows and projections, and 

 each part painted with the appropriate color. M. Becquerel then 

 described in detail a process discovered by himself by which these colors 

 may be rendered permanent. 



SINGULAR PROPERTIES OF TVAY's ELECTRIC LIGHT. 



The following facts respecting Way's electric light (for description 

 of which see Annual Sci. Dis., 1861, page 108) are derived from the 

 columns of the London Photographic News. The light which is ob- 

 tained from the fluid mercury poles in Professor Way's arrangement 

 is of a very peculiar character, unlike the ordinary electric light, 

 which, as our readers are aware, is produced between two carbon 

 poles, and contains at least as many different colored rays as sunlight 

 itself. The mercurial light consists of only six definite homogeneous 

 colors, each occupying a particular space in the solar spectrum, and 

 having wide black intervals between them. The carbon electric 

 light will thus illuminate any object with the exact color which it is 

 best able to reflect ; but with the mercury light it is Hobson's choice, 

 the object must either reflect one of the six colors evolved by the 

 light, or it must remain in darkness. The colors are as follows : 

 First, at the lowest end of the spectrum comes a brick-red tint, next 

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