M. Nobili on New Electro-Chemical Phenomena. 315 



deep, surrounded with a slight iris, and, lastly, another circle 

 almost black. On platina positive there is no appearance, but 

 on the same metal negative there are two small circles bor- 

 dering on black round a white circle. 



Nitrates of Copper and Silver mixed together. — On 

 Silver Positive there is in the centre a brilliant circle of silver,, 

 then a dark circle, then a second circle of silver, and, lastly, 

 another darkish circle. 



Phosphoric Acid. — On Silver Positive there is in the cen- 

 tre a small yellow circle, then a reddish circle, then a silvery 

 white circle ; and lastly, a wide area of different colours, be- 

 ginning with yellow and ending with violet. 



Oxalic Acid. — On Silver Positive there are three distinct 

 circles, the first yellow, the second reddish, and the third like 

 the first, but larger. 



Subcarbonate of Potash. — Upon Silver Positive there 

 is an elegant arrangement of concentric circles, which dilate 

 before the eye, and finish by exhibiting a fine degradation of 

 tints. I covered the piece of silver with a piece of muslin, to 

 see if the phenomenon would be altered by it, but it suffered 

 no change. There was no appearance upon gold or tin posi- 

 tive. 



Common Salt. — Upon Silver Positive there was a series 

 of concentric circles surrounded with various irises. The phe- 

 nomenon is here more vague than in the preceding cases, and 

 it retains its lustre only during a short time. The contact 

 of air weakens and confounds a little the tints which are 

 in perfect harmony. When the silver disc is suddenly heated, 

 all the rings assume a fine red colour, whose intensity varies 

 in the different circles ; after which the tints acquire a certain 

 permanence. By the action of heat, some of the exterior 

 zones disappear, and also part of the central zones. This ac- 

 cident does not appear difficult to explain. The arrangement 

 in thin plates, of the electro-magnetic substances, begins at the 

 centre of the disc of silver, and goes on diminishing to its cir- 

 cumference. The exterior strata are of great tenuity, * and 



* Ihis we do' not understand. If the colours are those of thin plates, 

 as the author believes, the thickness of the plates must increase from the 

 centre to the circumference. — En. 



