and of Indigo Light on Plants. 11 



extent has never been suspected. In the irritability of the 

 iris physiologists have always seen the influence of nervous 

 matter, but in plants no such agent exists to complicate the 

 phaenomenon, and therefore the action is due to light only. 



In this newly-discovered property light is also more closely 

 assimilated to the other imponderables, for both heat and elec- 

 tricity are capable of producing motion. 



Part III. Some applications of the preceding facts, Sfc. 



35. Numerous applications to vegetable physiology will 

 suggest themselves to the reader, but it is my purpose to treat 

 only of the following. 



The intimate relation which exists between the rays which 

 produce chlorophyll the decomposition of carbonic acid, and the 

 luminous spectrum. — The maximum for the formation of green 

 matter has been shown to reside in the yellow ray. Dr. 

 Draper (in this Magazine, September 1843) discovered the 

 maximum action for the decomposition of carbonic acid to be 

 between the green and yellow, or more correctly in the yellow. 

 Sir W. Herschel and Fraunhofer placed the maximum for 

 light in the same space. 



36. The relation goes further, for if the quantities obtained 

 by Dr. Draper for decomposing action, as measured by libe- 

 rated gas; Fraunhofer for illuminating power determined by 

 the eye ; and my estimate, obtained in time and by the eye, 

 be rendered commensurable and tabulated, they will give 

 quantities nearly allied. To produce such a table I assume 

 ail the maxima equal to unity. My results being given in 

 time and theirs in effect, the inverse proportion is taken for 

 each value given in article 14-. 



Table showing the. force of the solar rays in producing the green 

 colour of plants, the decomposition (f carbonic acid, and illu- 

 mination. 



