5388 On the Experimental Relations of Gold to Light. 
the analyser reduced at a little distance to a minimum and then 
converted to blue. A film of mercury produced by sublimation, 
a film of arsenic produced in like manner, and a film of smoke 
from a candle, though all of them sufficiently pervious to light, 
did not produce any result of depolarization. Films of the 
smoke of burning zinc, of antimony, or of oxide of iron produced 
no effect. 
I placed some metallic solutions in a weak atmosphere of 
sulphuretted hydrogen. Gold and platinum gave no films; 
silver so poor a film as to be of no use; and lead one so brittle 
as to be unserviceable. That obtained with palladium I believe 
to be the metal itself. The films of sulphuret of mercury, sul- 
phuret of antimony which was orange, and sulphuret of copper 
which was pale brown, all acted on the light and depolarized it. 
The sulphuret of copper presented a difference from the metals 
generally, worth recording: it depolarized the light, producing 
an image which, if not blue at once, was rendered blue by a 
little direct rotation of the analyser ; after which the same motion 
brought in a minimum and then produced an orange or red 
tint, 7.e. with the sulphuret of copper the warm and cold tints 
appear on opposite sides of the minimum to those where they. 
occur when films of the metals are employed, though the mini- 
mum in both cases is in the same direction. 
Many of the results obtained in the sulphide of carbon were 
produced also in camphine, the analyser being in each case ad- 
justed to the minimum of light before the metallic plate or film 
was introduced. I pass, however, to a very brief account of 
some polarizations effected by the metals themselves in the sul- 
phide of carbon, in which case the polarizing Nicol prism was 
dispensed with. The results show that all the dry forms of gold 
accord in giving the same nianifestation of action on light, what- 
ever the state of their division, provided they be disposed in a 
thin regular layer, equivalent to a continuous film. It was first 
ascertained that a plate of crown-glass in an inclined position in 
sulphide of carbon gave no signs of polarity to a ray of light 
passing through it. When fine gold-leaf was on the glass and 
inclined to the ray, it polarized the light, and exactly in the 
same manner and direction as a bundle of glass plates in the 
same position in the air. More light passed than when the gold- 
leaf was in air, but it could not be so completely polarized; the 
mininium light was of a pale bluish colour. A thinned gold- 
leaf produced the same effect, but let more common light through. 
I think the difference between gold-leaf and sulphide of carbon 
is sensibly less than that between the metal and air.. The depo- 
sitions of deflagrated gold, the films of gold obtained by phos- 
phorus, and even the heated deflagrated gold, produced polar- 
