162 THE INFLUENCE OF MATTER UPON LIGHT. 



ganic bodies we have peculiar molecular constitution, by 

 which an absorption of light appears to take place. 



The subject is one of the greatest difficulty; the 

 torch of science is too dim to enable us to see the causes 

 at work in producing these marvellous effects. The 

 investigation leads, to a certain extent, to the elucida- 

 tion of many of the secrets of luminous action ; and the 

 determination of the question, whether light is an 

 emanation from the sun, or only a subtile principle 

 diffused through all matter, which is excited by solar 

 influence, is intimately connected with the inquiry. 



It has been stated that matter is necessary to the 

 development of light ; that no luminous effect would be 

 produced if it were not for the presence of matter. Of 

 this we not only have no proof, but such evidence as we 

 have is against the position. There is no loss of light in 

 the most perfect vacuum we can produce by any artificial 

 means, which should be the case if matter was concerned 

 in the phenomena of light, as a cause. 



Colour is certainly a property regulated by material 

 bodies ; or rather, the presence of matter is necessary to 

 the production of colour. Chlorine gas is a pale yellow, 

 and nitrous vapour a yellowish red. These and one or 

 two other vapours, which are near the point of con- 

 densation into fluids, are the only coloured gaseous or 

 vaporiform bodies. The sky is blue, because the 

 material particles of the atmosphere reflect back the 

 blue rays. But we have more practical illustrations 

 than this. The flame of hydrogen burning with oxygen 

 gives scarcely any light ; allow it to impinge on lime, a 

 portion of which is carried off by the heat of the flame, 

 and the most intense artificial light with which we are 

 acquainted is produced. Hydrogen gas alone gives a 

 flame in which nearly all but the blue rays are wanting : 

 place a brush of steel or asbestos in it, and many of the 

 other rays are at once produced. An argand lamp, and 

 more particularly the lamp in which camphine a 



