THEORY OF AGRICULTURE. 419 



tatmg the nutritious part of the vegetable, from ammonia, which 

 is itself a compound of nitrogen and hydrogen, and supplied 

 partially by rain, by the decay or putrefaction of animal matter, 

 and in the excrements of animals. In the escape of ammonia 

 from our dung heaps, it is supposed a great portion of their most 

 valuable material passes off; and attempts have been made to fix 

 this volatile substance, so as to secure it for the service of the 

 plants, to be taken up by them as required. For this purpose, 

 gypsum has been strongly recommended to be sprinkled in 

 stables, and to be spread upon manure heaps. It is quite doubtful 

 whether its effect has met the sanguine expectations which were 

 formed of it. In the report given by Professor Henslow, which 

 he has been kind enough to send me, of fifteen attempts to fix 

 ammonia by the application of gypsum to dung, the result seems 

 to leave the question wholly undetermined. His conclusions 

 from these experiments are given in this result : &quot; It will be 

 seen that, with turnips, the effect has been uniformly in favor of 

 gypsumed dung. With the straw of wheat, the result is twice 

 in favor of the gypsumed dung, once against it, and in one case 

 there is no difference. In respect to the wheat itself, it is six 

 times in favor of the gypsumed dung, and six times against it. 

 The practical inference to be deduced from this part of the 

 inquiry favors the idea of using gypsumed dung for a turnip 

 crop, but shows that it produces no better effect than ungyp- 

 sumed dung upon a wheat crop.&quot; Such results certainly lead 

 to no very strong conclusions. But the beneficial effects of 

 covering manure heaps with mould, in order, in the first place, to 

 prevent the escape of the volatile parts of the manure, and, in 

 the next place, to absorb the gases, so that the soil used for a 

 covering becomes itself a valuable manure, are points long ago 

 determined by the practice of many enlightened farmers. 



Whatever may be the success or the ill success of dealing 

 with the mineral qualities of the soil, or with those subtile gases 

 of which vegetables are composed, there are processes of a prac 

 tical nature to be applied, the propriety and utility of which are 

 established. The practice of agriculture is still very much in 

 advance of the theory of agriculture. I do not undervalue 

 scientific agriculture. Science may do as much for agriculture 

 as for any other department of business, or art, or health, or 

 comfort, or enjoyment. In no department is success more 



