7 g THEORY OF ABSORPTION. 



CHAPTER IX. 



THEORY OF THE ABSORPTION OF THE TITHONIC RAYS AND LIGHT. 



CONTENTS : Estimate of the Extent and Power of the Solar Radiations. Influence still 

 exists in the Moonbeams. Absorptive Action of Chlorine and Hydrogen. Detitho- 

 nization of the Ray and Tithonization of the Gaseous Mixture. Curve and Law. 

 Deductions as to Latent Light and Definite Action. Functions discharged by the 

 Chlorine and Hydrogen respectively. 



281. IN pursuing our discussion of the phenomenon which we have under consider- 

 ation-r-the digestion of plants we have successively traced the source of action to the 

 yellow region of the spectrum, and to the ray of LIGHT. 



282. In what manner, then, does this light act ? How does it come to pass that it 

 can exert so great a force as to effect the reduction of carbonic acid in the cold ? We 

 have briefly seen what are the results it impresses on the forming vegetation, that the 

 leaf turns green and oxygen is given off. What are the corresponding and contem- 

 poraneous changes which happen to the light 1 Action and reaction are always equal, 

 and if a given beam can produce a result which demands the most energetic chemical 

 force, it is reasonable to suppose that in doing so it undergoes itself a change. 



283. These considerations show us that the question in what manner yellow light 

 acts in controlling the function of digestion in plants, is not only exceedingly interest- 

 ing in a physiological point of view, but also that it involves the whole theory of the 

 action of radiant matter, whether it be of light, heat, or tithonicity, in producing chemi- 

 cal change. 



284. There are few authors who have written on the action of light or the tithonic 

 rays in producing chemical changes, who have not directly ascribed all those changes 

 to absorption of the imponderable principle. The connexion between absorption and 

 the production of these phenomena is clearly apparent. Still, however, in looking over 

 what has been written, we find little precision in those views ; instead of a distinct con- 

 ception of a plain fact, we find only loose and imperfect ideas. 



285. In animals, voluntary and involuntary motions are under the government of the 

 nervous system. Each movement which is executed is attended with a corresponding 

 consumption of organized matter, either in the muscular or nervous tissues, or both. 

 The motions which my fingers are executing in writing these lines do not spring forth 

 from nothing, but are the offspring of the destruction, in a regulated manner, of organ- 

 ized matter originally derived from food. How perfect, then, is the animal machine, 

 which, fed from day to day by a small portion of carbonaceous matter, executes motions 

 with an inconceivably small expenditure of material ! How great, also, are the results 

 which may arise from the return of those organized atoms to their pristine inorganic 



