Dr Seller on the Nutrition of Plants. 61 



does it clearly appear that the sources of its extrication from 

 the bowels of the earth are in uninteiTupted operation. 



It has been Avell remarked by Professor Johnson, that the 

 ammonia which rises into the air can hardly escape frequent 

 resolution into its elements, since electric shocks decompose 

 it with ease in the laboratory. In this way it would, accor- 

 ding to Liebig, be irrecoverably lost to organic nature. 



To this source of waste, I would add, that the ammonia 

 which rises from the decomposition of animal substances at 

 the earth's surface, must, by the law of the diffusion of 

 gases, especially during the long absence of rains, extend it- 

 self upwards beyond the limits of aqueous vapour, and will, 

 therefore, set at nought the power of rain to bring it back to 

 the earth's surface. In short, unless the electricity of the 

 higher atmosphere can decompose ammonia, it must go on, 

 slowly accumulating above the point to which aqueous vapour 

 reaches, descending only when the supply from the earth to 

 the lower atmosphere is less copious ; and if ammonia be 

 decomposed in the higher atmosphere, we obtain one soui'ce 

 of inflammable gas, namely, hydrogen, to feed luminous me- 

 teors in that region, the same electric power being capa- 

 ble of causing its union with oxygen into water.* It is to be 

 remarked, however, that, if this decomposition went on for 

 ages evolving nitrogen, there would be an increase in the pro- 

 portion of atmospheric nitrogen, unless it were again con- 

 verted into ammonia at the surface. 



It would be easy to point out other sources of the waste 

 of ammonia. For example, nitre is formed chiefly (accor- 

 ding to Liebig exclusively, as I should infer) at the expense 

 of the nitrogen of animal matter, and it does not appear that 



* Under the ordinary atmospheric pressure at the earth's surface, am- 

 moniacalgas requires, for its liquefaction, a cold equal to — 61° of Fah- 

 renheit. This is inferior to the calculated temperature of the planetary 

 spaces, which, according to Fourier, cannot be below — 57° F. But, as 

 the cold required for the liquefaction of a gas must increase with its rare- 

 faction, there is no room for the belief that ammonia can separate from 

 the higher atmosphere by passing into the liquid state, and thereby de- 

 scending into the region of watery vapour. 



