176 
DE. FAEADAT ON THE EXPEEDIENTAE EELATIONS 
In some of these jellies the ruby particles are so determinate as to give the brown 
reflexion by common observation ; in others they are so fine as to look like ruby solu- 
tions, unless a strong sunlight and a lens be employed ; and the impression again arises, 
that gold may exist in particles so minute as to have httle or no power of reflecting 
light. Ruby particles of extreme fineness, when present in small amount in water, 
appear to remain equally diffused for any length of time ; if in larger amount, that which 
settles to the bottom will remain for weeks and months as a dense raby fluid, but with- 
out coming together : both chcumstances seem to imply an association of the particles 
of gold with envelopes of water. Many circumstances about the ruby jeUies imply a like 
association with that animal substance, and many of the stains of gold upon organic sub- 
stances probably include an affinity of the metal of the like kind. 
Melations of Gold {and other metals) to jpolarized Light. 
It has been akeady stated, that when a ray of common hght passes through a piece of 
gold-leaf inclined to the ray, the hght is polarized. MTien the angle between the leaf 
and the ray is small, about 15°, nearly all the light that passes is polarized; but as the 
leaf is really very irregular in thickness, and Hi-stretched as a film, parts mchned at 
different angles are always present at once. The light transmitted is polarized in the 
same direction as that transmitted by a bundle of thm plates of glass, inclined in the 
same direction. The proportion of light transmitted is small, as might be expected from 
the high reflective power of the metal. The polarization does not seem due to any con- 
strained condition of the beaten gold, for it is produced, as uIU be shortly seen, by the 
annealed colourless leaf-gold, and also by deposits of gold particles ; but is common to it 
with other uncrystallized transparent substances. It would seem that a very small pro- 
portion of the gold-leaf can be occupied by apertures, since the hght which passes is 
nearly all polarized. On subjecting thin gold-leaf, or heated gold-leaf, or films of gold, 
or any preparations which required the support of glass, results of polarization were 
obtained, but the observations were imperfect because of the interfering effect of the 
glass. 
Proceeding to employ a polarized ray of light, it was found that a leaf of gold pro- 
duced generally the same depolarizing effect as other transparent bodies. Thus, if a plate 
of glass be held perpendicular to the ray, or inclined to it either in the plane of polari- 
zation or at right angles to it, there is no depolarization ; but if inclined in the inter- 
mediate positions, the ray is more or less depolarized. So it is with gold-leaf ; the same 
effects are produced by it. Further, the depolarization is accompanied by a rotation of 
the ray, and in this respect the quadrants alternate, the rotation being to the right-hand 
in two opposite quadrants, and to the left in the intervening quadrants. So it is nith 
gold-leaf; the same effects are produced by it, and the rotation is in the same direction 
with that produced by glass, when inclined in the same quadrant. 
As further observation in this direction was stopped by the necessity of employing 
glass supports for the leaves, films, &c., I sought for a medium so near glass in its cha- 
