404 On the Experimental Relations [1857. 



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 presented ruby-violet and then violet tints, suggesting 

 that accumulation 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, 

 i. e. with the violet and the ruby particles ; but the effect was 

 not altogether so good, and the tint of the transmitted ray was 

 rather a green 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 re- 

 flexion 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 

 being caught upon glass plates couldbe examined as to reflexion, 

 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 light. 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, render- 

 ing the green deeper, but not changing its character as in the 

 case of gold. Tin gave a beautiful bright white reflexion, and 

 by transmission 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 filling 

 up the space. Iron presented a fine steel grey, 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 reflexion, the transmission a dark smoky brown , 



