430 



Miscellaneous. 



But I must assume, for the present, on the supposition that these 

 bodies were original constituents of the atmosphere, that they both 

 existed in the air, during the primary periods, or, at all events, antece- 

 dent to the secondary, in much larger quantity than they do now : and 

 the proofs are obvious. Consider the immense deposits of vegetable 

 matter in the carboniferous strata. All the carbon and nitrogen of 

 which this is composed must have been originally present in the air as 

 carbonic acid and ammonia. The greatest part of this vegetable matter 

 is carbon; and hence it follows, that, as the carbon of the carbonic 

 acid was retained, and its oxygen liberated, the air of the present day 

 must be much poorer in carbonic acid, but much richer in oxygen, 

 than that of former ages. Dr. Daubeny denies the possibility of am- 

 monia ever having been present in the air in much larger quantity 

 than at present ; and, in proof of his view, he cites the experiments of 

 Christison and Turner, that ^ of ammoniacal gas in air acts as a 

 poison to the vegetable kingdom. To this it may be replied, that am- 

 moniacal gas is never present in the atmosphere. It is always in 

 union with carbonic acid as carbonate of ammonia ; and it is well 

 known that water impregnated with this salt in the proportion of 

 30 : 1, is very beneficial to vegetation. One pound of rain water con- 

 tains rather less than \ grain of carbonate of ammonia. Now, even 

 supposing that the rain of former ages contained 800 times this quanti- 

 ty, it would not be prejudicial to plants, but administer to the luxuri- 

 ance of vegetation. Again, it has been found that plants flourish with 

 great luxuriance in an atmosphere containing as much as ~ its bulk 

 of carbonic acid. But the air of the present day contains only one 

 volume of this gas in 2,000 volumes of air. Hence it follows, that the 

 air of former ages may have contained more than 150 times this amount, 

 without injury to vegetation. These facts are sufficient to prove that 

 the air formerly may have been much richer in the food of plants. 

 Brogniart believed this to be the case many years since, and founded 

 upon this view some ingenious speculations. Doubtless an atmos- 

 phere with quantities such as we have mentioned, would prove fatal 

 to animal life, but we will shortly shew that the express duty of former 

 plants was to prepare the world for the reception of animals, and final- 

 ly, for that of an intellectual being. One question, then, only remains : 

 from whence did the atmosphere receive this carbonic acid ? Dr. Dau- 

 beny conceives by a gradual evolution from the interior of the earth. 

 He supposes that this carbonic acid was furnished to plants during 

 their life — not that a certain amount was originally emitted into the 

 great magazine of food— the atmosphere. But it is difficult to conceive 



