'produced hy Electro-chemical 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 phaenomenon of the 
