of Gold and other Metals to Light. 409 
there during the beating. At first I thought the gold was abso- 
lutely red in these parts, but am inclined to believe that in the 
greatest number of cases the tint is subjective, being the result 
of the contrast between the white light transmitted through 
bruised parts, and the green light of the neighbouring continuous 
parts. Nevertheless, some of these places, when seen in the mi- 
croscope, appeared to have a red colour of their own, that is, to 
transmit a true red light. As I believe that gold in a certain 
state of division can transmit a ruby light, I am not prepared to 
say that gold-leaf may not, in some cases, where the effect of 
pressure in a particular direction has been removed, do the same. 
Many of the prepared films of gold were so thin as to have 
their reflective power considerably reduced, and that in parts 
which, under the microscope and in other ways, appeared to be 
quite continuous: this agrees with the transmission of all the 
rays already mentioned, but it seems to imply that a certain 
thickness is necessary for full reflexion; therefore, that more 
than one particle in depth is concerned in the act, and that 
the division of gold into separate particles by processes to be 
described, may bring them within or under the degree necessary 
for ordinary reflexion. 
As particles of pure gold will be found hereafter to adhere 
by contact, so the process of beating may be considered as one 
which tends to weld gold together in all directions, and espe- 
~ cially in that transverse to the blow,—a point favourable to con- 
tinuity in that direction, both as it tends to preserve and even 
reproduce it. 
If a polarized ray be received on an analyser so that no light 
passes, and a plate of annealed glass, either thick or thin, be in- 
terposed vertically across the ray, no difference is observed on 
looking through the analyser,—the image of the source of light 
does not appear; but if the plate be inclined until it makes an 
angle of from 30° to 45°, or thereabouts, with the ray, the light 
appears, provided the inclination of the glass is not in the plane 
of polarization or at right angles to it, the effect beg a maxi- 
mum if the inclination be in a plane making an angle of 45° 
with that of polarization. This effect, which is common to all 
unerystallized transparent bodies, is also produced by leaf-gold, 
and is one of the best proofs of the true transparency of this 
metal according to the ordinary meaning of the term. . In like 
manner, if a leaf of gold be held obliquely across an ordinary ray 
of light, it partly polarizes it, as Mr. De la Rue first pointed out 
to me. Here again the condition of true transparency is esta- 
blished, for it acts like a plate of glass or water or air. But the 
relations of gold and the metals in different conditions to polar- 
ized light shall be given altogether at the close of this paper. 
