HOW PLANTS ABSORB CARBONIC ACID. 47 



In tracing the operations of nature, I have always laid it down 



a rule, to endeavor to discover the intentions of the Supreme 

 Find, in the qualities and in the appliances of the objects of in- 

 estigaiion. In tracing the operations of carbonic acid, we find it 

 j) possess great weight, a weight much greater than any other gas ; 

 ) great that it may be poured from one vessel into another, with- 

 it mixing with the surrounding atmosphere. If this gas were in- 

 nded to feed vegetation through the leaves, then would its pon- 

 ^rosity be adverse to such appliance. If, on the contrary, the 

 is were intended to feed plants through tho roots, then would this 

 niderosity cause it to descend to the ground, and there supplying 



e necessary food by means of the roots. 



The atmosphere is found by analysis to be always and in every 

 juation the same, to afford in the diseased cell, in valleys, and on 

 ills, the same results ; yet we know that various gases are conti- 

 ] ally pouring into it ; but is is evident they do not chemically 

 <mbine with the atmosphere. Most of the gases are much 

 ll;hter than the atmosphere ; these ascend beyond our reach, and 

 (iscend again in rain and snow storms. Carbonic gas, the princi- 

 jil food of plants, being much heavier than the atmosphere, must 

 I'cessarily fall to the ground, where it would afford nourishment 

 tj vegetation. Carbonic gas is called by the miners choke-damp • 

 a'd when in moderate quantities, is always near the ground. If a 

 dg, or other animal that holds down its head, pass into it, it is im- 

 E'diately killed by inhaling the noxious fluid, whereas the work- 

 D'n, whose heads are above the gas, sustain no injury from it.* 



Were the gases suspended in the atmosphere within the reach 

 animals, it would soon become totally unfit for sustaining ani- 

 nl life. This would be peculiarly the case with carbonic gas, 

 vich instantly destroys life. How wise, then, is the arrange- 



,Our correspondent seems here to forg'et the fact, of which he is certainly aware, 

 til in all i)arls of 'he atmosphere the carbonic acitl is equally distributed. The ex- 

 aination of portions brought from the greatest height to which man has ascended 

 hi given the same quantity as is found near the surface. This arises from two 

 CJjes— first, the constant motion of the air by winds, which would mix the different 

 gi;s — and secondly, the tendency which all gases have to comingle even when at 

 re, Thus, if a vessel containing hydrogen — the lightest of all gases — be inverted 

 Uji a vessel containing carbonic acid — the heaviest gas — and kept in a state of per- 

 fe rest for a few hours they will be fouml mutually difl'used through each other, and 

 th although the communication be only th' jgh a very fine tube. We say this only 

 to )rrect a matter of fact, and not as bearing upon the point which our correspondent 

 «8 scussing.— Eds. 



