-1859] WRITINGS OF JOSEPH HENRY. 123 



minute quantity of foreign substance is added, and sprink- 

 ling with distilled water. In this case the plant will yield 

 the usual amount of carbon or charcoal, although there was 

 none in the soil in which it grew. 



In the decomposition of the carbonic acid by the chemical 

 ray a definite amount of power is expended, and this re- 

 mains (as it were) locked up in the plant so long as it con- 

 tinues to grow; but when it has reached its term of months 

 or years, and some condition has been introduced which 

 interferes with the balance of forces, then a reverse process 

 commences, the plant begins to decay, the complex organic 

 molecules begin to run down into simpler groups, and then 

 again into carbonic acid and water. The materials of the 

 plant fall back into the same combinations from which they 

 were originally drawn, and the solid carbon is returned in 

 the form of a gas to the atmosphere whence it was taken. 

 Now the power which is given out in the whole descent is, 

 according to the dynamic theory, just equivalent to the 

 power expended by the impulse from the sun in elevating 

 the atoms to the unstable condition of the organic molecules. 

 If this power is given out in the form of vibrations of the 

 setherial medium constituting heat it will not be appreciable 

 in the ordinary decay — say of a tree, extending as it may 

 through several years ; but if the process be rapid, as in the 

 case of combustion of wood, then the same amount of power 

 will be given out in the energetic form of heat of high in- 

 tensity. This heat will again radiate from the earth, and 

 in this case, as in that we have previously considered, the 

 impulse from the sun merely lingers for a while upon the 

 earth, and is then given back to celestial space changed in 

 form, but undiminished in quantity. It may continue its 

 radiating course tlirough stellar space until it meets planets 

 of other systems; but to attempt to trace it further would be 

 to transcend the limits of inductive reason, and to enter 

 those of unbridled fancy. 



In the process we have described, the carbon, hydrogen, 

 and other substances which are absorbed from the atmos- 

 phere are returned to this great reservoir to be used again, 



