ACTION OF ABSORBENT MEDIA AND IDEAL COLOURATION. 99 



CHAPTER X. 



EXPERIMENTS ON THE CHEMICAL ACTION OF SOLAR LIGHT. 



(From the Journal of the Franklin Institute for June, July, August, and September, 1837.) 



CONTENTS : Action of Absorbent Media. Ideal Colouration of the Chemical Rays. 

 Specific Absorption. Colorific Absorption. Calorific Absorption. Specific Absorp- 

 tion of the Chemical Rays. Effect of Yellow Solutions. 



Decomposition of Carbonic Acid by Leaves. Penetration of Dimensions in Gases. 

 Decomposition of Carbonic Acid under various coloured Media. Gas from Leaves 

 contains Nitrogen. Chemical Rays of different Colours. Identity of Volume in the 

 absorbed and evolved Gas. Cause of the Decomposition. 



Hitter's Experiments of the Non-oxygenation of Phosphorus. 



Decomposition of the Salts of Silver. Prismatic Spectrum on Bromide of Silver. In- 

 terference of Chemical Rays. Salts decomposed by Light. Moonlight and Artificial 

 Flames are Inactive. 



Of Perihelion Motions. Dew of Water and Mercury. Iodine. Chloride of Gold. 

 Non-deposition on a Glass Plate. Current Action. Action of Flame. Action of 

 Metal Screens. Protecting Action of a Metal Ring. Is there Electricity in the 

 Solar Ray? 



Cause of the Green Colour of Leaves. Plants grow in Lights of various Colours. 

 Seeds also germinate in Red, Yellow, and Blue Light. Chemical Rays of different 

 Colours. 



383. THE effect of absorbent media upon the colorific rays of light has been, as was 

 predicted by an eminent writer on optics, of singular service in developing new views 

 of this subtle agent, and giving us a more precise knowledge of the complex constitu- 

 tion of the solar beam. Hitherto, the action of these media upon the calorific and 

 chemical rays has not been thoroughly investigated, nor are there, so far as I know, 

 any experiments on record exhibiting this matter in its full importance. 



384. We have been accustomed to regard the chemical properties of the solar spec- 

 trum as due to the violet ray. A similar opinion was formerly maintained respecting 

 the calorific constitution of the red ray. The position to which we are brought by 

 advanced investigation has long ago established the separate existence of heat-making 

 rays, and the experiments here communicated give much weight to the doctrine that 

 the chemical rays have also a separate existence. It is true it cannot yet be proved, 

 though analogy and probability are favourable to the idea that there are subdivisions 

 both of the chemical and calorific rays, similar to those of which our senses give evi- 

 dence in the colorific ray, each of which is endued with distinct powers of its own. 



385. How complex is, then, the constitution of the solar beam ! a ray of heat, com- 

 posed, perhaps, of three or more rays of different refrangibility; a ray of light, composed 



