produced by Electro-cJiejnical Agency and hy Heat. 53 



this in such a manner that the distance between the point and 

 the plate may be about half a line. A solution of acetate of 

 lead is next poured into the vessel, so as not only to cover the 

 plate, but to rise two or three lines higher than the point. 

 The plate and the point are now brought into communica- 

 tion, the former with the positive and the latter with the ne- 

 gative pole of an electric pile. At the moment when the 

 voltaic circuit is closed, a series of rings similar to those 

 formed at the centre of the Newtonian lenses is to be seen on 

 the surface of the plate precisely under the point." The same 

 process has been adopted to produce the films, the investiga- 

 tion of which will be detailed in an after part of this paper. 

 The voltaic powers consisted of two small batteries, con- 

 structed on the principles of Professor Daniell's, and the ef- 

 fects were produced in small platina dishes or capsules for the 

 convenience of investigation. We must now pass on to an- 

 other part of Professor Nobili's memoir, in order to collect the 

 facts and their explanation. At p. 106, we find, " The ap- 

 pearances which constitute the chromatic scale are due to the 

 electro-negative elements of the solution (oxygen and acid), 

 which being transferred by the current to the positive pole, 

 are then spread out into thin transparent films, from which 

 all the colours of the scale arise. The electro-positive ele- 

 ments (such as hydrogen and the metallic bases) are, on the 

 contrary, transferred to the negative pole, and then deposited 

 in layers which never produce the colours of thin plates." 

 Again, at page 109, Professor Nobili adds, " I will not under- 

 take to say by what species of affinity or force it is that these 

 elements" (oxygen and acid) " are attracted to each other 

 and spread out into thin films on the platina. It is certain 

 however, that they attach themselves to the platina without 

 oxidizing it in the slightest degree. We must not suppose 

 that this happens because platina is a metal difficult to be 

 oxidized. Iron and steel belong to the class of metals most 

 easily oxidized, and yet it is well known that they will bear 

 to be covered with electro-negative layers without becoming 

 rusted. My electro-chemical experiments, multiplied and 

 varied in a thousand ways, leave no room for reasonable 

 doubt on this point: they show that oxygen and certain acids 

 may adhere to the surface of metals without producing the 

 slightest chemical change in them. This is a novel state 

 for oxygen and the acids, and is distinguished from their 

 ordinary combination by the three following peculiarities : 

 1st, the metal retains, beneath the deposited layer, its natural 

 brilliancy; 2ndly, this layer produces the phsenomenon of the 



