148 Dr. J. H, Gladstone, [May 20, 



In illustration of the effect of intensity in causing lights actually 

 coloured to produce very nearly the sensation of white, the electric 

 light, from charcoal points, was exhibited under red and blue glasses, 

 when it appeared dazzling and almost white ; though no white light 

 was really transmitted, and such objects as common paper, when 

 illuminated by it, reflected the coloured radiance. This will explain 

 the phenomenon so frequently observed by M. Coulvier Gravier, of a 

 white meteor becoming bluish or reddish as it approached the horizon ; 

 and also the paradox of an " intensely radiant cloud " white in itself, 

 but throwing a blue light on the walls of houses. In these cases it 

 seems highly probable that the incandescent meteors were really emit- 

 ting coloured light, but that this colour did not become apparent till 

 the light was reduced either by distance, or by reflection from other* 

 objects. In a similar manner, the fact of a yellowish meteor becoming 

 more or less green as it passes away from the spectator, so frequently 

 noticed in the French observations, may be explained by the well- 

 known changes in the chromatic impressions produced by yellow rays 

 according to their intensity. 



In reference to the effect of contrast it was remarked, that every 

 lady is aware of the alteration that may be produced in the apparent 

 tint of any article of dress by the juxtaposition of some other bright 

 colour; and indeed it may be laid down as a general law that the 

 apparent colour of every object is affected to a greater or less degree 

 by the colours of all other objects seen at the same time. This remark 

 holds good equally of self-luminous bodies, as, for instance, the flame 

 of a gas-lamp, which assumes a rather bluish tint when the intensely 

 yellow soda flame is brought beside it. This also must be a source of 

 error in the observations of meteors. 



After making due allowance for these points of difficulty and 

 probable fallacy, we may approach the question — How far are these 

 chromatic phenomena in accordance with the cosmical theory ? Were 

 pieces of iron to be shot through our atmosphere at the rate of twenty 

 miles per second, there is good ground for believing that the friction 

 would make them red-hot, if not incandescent. An iron wire, heated in 

 tiie galvanic circuit, was observed by the speaker to emit at first princi- 

 pally orange and green rays, but as the heat increases the true red rays 

 are emitted in an increasing degree, till " bright redness " is attained ; 

 and when combustion begins blue rays are also given forth, the general 

 impression being then that of a reddish whiteness. The combustion 

 and scintillation both of ordinary and of meteoric iron were shown in 

 several ways. The metallic masses which fall through the air are never 

 composed solely of iron, and it is difficult to say which metal or which 

 other constituent would be the first ignited. Nickel in combustion 

 displays a larger amount of green rays ; sulphur, as is well known, 

 burns with a blue, and phosphorus with a white flame. Two 

 pieces of iron pyrites, attached to the wires of a powerful galvanic 

 battery, when brought momentarily into contact, were ignited with a 

 very luminous flame, whicli exhibited the characters of both burning 

 iron and sulphur ; and on one occasion, when the experiment was tried, 



