1857.] of Gold (and other Metals) to Light. 403 



change to a ruby, still preserving their metallic reflecting power, 

 and this ruby is in character quite like that which is presented 

 in the arts by glass tinged by gold. This change is often far 

 better shown in the more distant and thinner parts of the 

 deposit, than in those nearest to the line of discharge ; for near 

 the latter place, where the deposit is most abundant, the metal 

 appears to run up into globules, as with gold-leaf, and so 

 disappears as a film. I believe that the ruby character of the 

 deposit in the line of discharge, is caused by the same action of 

 heat produced at the moment by the electricity passing there. 

 In the distant parts, the deposit, rubified by after-heat, is not 

 imbedded or fused into the glass, rock-crystal, topaz, &c., but 

 is easily removed by a touch of the finger, though in parts of 

 the glass plate which are made very hot, it will adhere. 



If the agate pressure before spoken of, in respect of gold-leaf, 

 be applied to ruby parts not too dense, places will easily be 

 found where this pressure increases the reflective power con- 

 siderably, and where at the same time it converts the transmitted 

 ray from ruby to green ; making the gold, as I believe, then 

 accord in condition with beaten gold-leaf. On the other hand, 

 if parts of the unheated electric deposit, where they are purple- 

 grey, and so thin as to be scarcely visible without care, be in 

 like manner pressed, they will acquire the reflective power, 

 and then transmit the green ray ; and I think I am justified by 

 my experiments in stating, that fine gold particles, so loosely 

 deposited that they will wipe off by a light touch of the finger, 

 and possessing one conjoint structure, can in one state transmit 

 light of a blue-grey colour, or can by heat be made to transmit 

 light of a ruby colour, or can by pressure from either of the 

 former states be made to transmit light of a green colour ; all 

 these changes being due to modifications of the gold, as gold, 

 and independent of the presence of the bodies upon which for 

 the time the gold is supported ; for I ought to have said, if I 

 have not said so, that these changes happen with all the deposits 

 upon glass, mica, rock-crystal, and topaz, and whatever the 

 atmosphere in which they were formed. 



When gold is deflagrated by the voltaic battery near glass 

 (I have employed sovereigns laid on glass for the terminals), a 

 deposit of metallic gold in fine particles is produced. The 

 densest parts have a dark slate-violet colour passing into violet 



