412 Prof. Faraday on the Experimental Relations 
have employed sovereigns laid on glass for the terminals), a de- 
posit of metallic gold in fine particles is produced. The densest 
parts have a dark slate-violet colour passing into violet and ruby- 
violet in the outer thinner portions; a ruby tint is presented 
occasionally where the heat of the discharge has acted on the 
deposit. The deposited gold was easily removed by wiping, 
except actually at the spot where the discharge had passed. 
When these deposits were heated to dull redness they changed 
and acquired a ruby tint, which was very fine at the outer and— 
thinner parts. The portions nearer the place of discharge pre- 
sented ruby-violet and then violet tints, suggesting that accu- 
mulation of that which presented a fine ruby tint would, by 
stopping more and more light, transmit a ruby-violet or violet 
ray only. Pressure with the agate surface had a like effect as 
before, both with the heated and the unheated portions, 7. e. with 
the violet and the ruby particles; but the effect was not alto- 
gether so good, and the tint of the transmitted ray was rather a 
ereen-violet than a pure green. Still the difference produced by 
the pressure was very remarkable. The unheated particles at 
the surface, away from the glass, presented by reflexion almost 
a black; being heated, they became much more golden and 
metallic in appearance. 
I prepared an apparatus by which many of the common metals 
could be deflagrated in hydrogen by the Leyden battery, and 
bemg caught upon glass plates could be examined as to re- 
flexion, transmission, colour, &c. whilst in the hydrogen and in 
the metallic, yet divided state. The following are briefly the 
results; which should be considered in connexion with those 
obtained by employing polarized hght. Copper: a fine deposit 
presenting by reflexion a purplish-red metallic lustre, and by 
transmission a green colour, dark in the thicker parts, but always 
green; agate pressure increased the reflexion where it was not 
bright, and a little diminished the transmission, rendering the 
green deeper, but not changing its character as in the case of 
gold. Tin gaye a beautiful bright white reflexion, and-by trans- 
mission various shades of light and dark brown; agate pressure 
diminished the transmission and increased the reflexion in places 
before dull or dead; the effect appeared to be due simply to the 
lateral expansion of the separate particles filing up the space. 
Tron presented a fine steel-gray, or slate metallic reflexion and a 
dark brown transmission ; agate pressure gave the same effect 
as with tin, but no change of colour. Lead: a bright white re- 
flexion, the transmission a dark smoky brown; agate pressure 
appeared to change this brown towards blue. Zinc: the reflexion 
bright white and metallic; the transmission a dark smoky colour 
with portions of blue-gray, brown-gray and pale brown; agate 
