536 Prof. Faraday on the Experimental Relations 
that even at the distant parts of the deposit. It was most 
striking to contrast the thinnest and faintest portion of such a 
film with the neighbouring parts of the glass from which it had 
been wiped off. It must be remembered that such a preparation is 
a layer of separate particles; that these particles are not like those 
of starch or of crystals, for they have no action whilst m a plane 
perpendicular to the polarized ray ; nor have they a better action 
for being in a thick layer, as in the central parts of the deposit. 
The particles seem to form the equivalent of a continuous plate 
of transparent substance; and as im such a plate it is the two 
surfaces which act, so there appears to be the equivalent of these 
two surfaces here ; which would seem to imply that the particles 
are so small and so near, that two or more can act at once upon 
the individual atoms of the vibrating ether. Their association 
is such as to present as it were an optical continuity. 
The gold films by phosphorus were then submitted to experi- 
ment, and gave exactly the same result. All of them depolarized, 
and required direct rotation of the analyser to arrive at a mini- 
mum, or to pass from the red to the blue tints. Graduated films, 
of which I should judge from the depth of tint that one place 
was at least twenty times as thick as another, gave the effect as 
well in the thinnest as the thicker or any intermediate part ; 
indicating that thickness of the plate, and therefore any quality 
equivalent to crystalline force of the particles, had nothing to do 
with the matter. A glass beaker, which had been employed to 
contain ruby fluid, had a film of gold deposited on its inner sur- 
face so thin, as to be scarcely perceptible either by reflexion or 
otherwise, except by a ruby tint which appeared upon it in cer- 
tain positions; but bemg examined by a polarized ray, it gave 
an effect as strong and as perfect as gold-leaf, showing how thin 
a film of gold was sufficient for the purpose. This thin film 
appeared to be almost perfect in its continuity, for when the red 
image was brought in, direct rotation of the analyser reduced it 
to a minimum which was quite dark ; after which, further rota- 
tion brought in a good blueimage. The least touch of the finger 
removed the film of gold and all these effects with it. These 
films, though they are certainly porous to gas, and to water in 
some form, for it can evaporate from beneath them through its 
body, have evidently optical continuity. 
In order to submit the gold fiuids to experiments, cells were 
made of two glass plates, separated by the thickness of a card, 
and fastened at the edges by varnish internally and gum exter- 
nally. These being filled with dense ruby or blue fluid, gave no 
indication of action on the ray, showing that the diffused particles 
were inoperative. The same fluids, dried on plates of glass so 
as,to leave films, did act just as the gold deflagrations had done ; 
