THEORETICAL KNOWLEDGE STILL VERY DEFECTIVE. ** .9 



land — on the kind of crop to be raised — on the general climate of the 

 district — on the maxima and minima of temperature — or on the quanti- 

 ty of rain which falls? 



So with gypsum. Why are its effects lauded in one district, doubted 

 in another, and decried in a third! Are no rules or principles to be 

 discovered, by which these diversified effects are to be explained, and 

 the true purpose and fit use of these and other mineral substances clear- 

 ly pointed out? Such principles are yet 1o be sought for; but if 

 sought by the way of well devised and accurately conducted experi- 

 ment, they are sure to be discovered. 



The land is exhausted by frequent cropping. "What language more 

 familiar, what statement more true than this? Yet how few under- 

 stand what exhaustion implies; how few can explain either how it 

 takes place, by what means it can be remedied, or how, if left to her- 

 self, nature at length does apply a remedy ! 



Have you any doubt in regard to the prevailing ignorance on this 

 subject ? To be satisfied, you have only to look with an experienced 

 eye on the agricultural practice of the county of Durham. Are there 

 not thousands of acres in the centre of this county which exhibit a de- 

 gree of unproductiveness not natural to the soil ; — which have been 

 overcropped, and worn out, and impoverished? A soil comparative- 

 ly fertile by nature has been rendered unfertile by art. That which 

 was naturally good has been rendered as unproductive and unprofitable 

 as that which was naturally bad. Has this state of things arisen from 

 ignorance, from design, or from necessity ? By whichever of these it 

 ha:s been immediately caused, it is clear that the requisite degree of 

 knowledge on the part of the owners of the soil would have retarded if 

 not wholly prevented it. 



The same knowledge will enable them to reclaim these lands again, 

 and gradually restore them to a more fertile condition ; for the changes 

 which the soil undergoes in such circumstances are all chemical 

 changes, — either in the relative quantities of the substances it contains, 

 or in the state of combination in which they exist. 



The art of culture indeed is almost entirely a chemical art, since 

 nearly all its processes are to be explained only on chemical principles. 

 If you add lime or gypsum to your land, you introduce new chemical 

 agents. If you irrigate your meadows, you must demand a reason 

 from the chemist for the abundant growth of grass which follows. Do 

 you find animal manure powerful in its action, is the effect of some 

 permanent, while that of others is speedily exhausted ? — does a mixture 

 of animal and vegetable manure prepare the land best for certain, kinds 

 of grain? — do you employ common salt, or gypsum, or saltpetre, or ni- 

 trate of soda, with advantage ? — in all these cases you observe chemical 

 results which you would be able to control and modify did you possess 

 the requisite chemical knowledge. 



It is not wonderful that even theoretical agriculturists should be far 

 behind in the knowledge of those principles on which their most impor- 

 tant operations depend. The greatest light has been thrown upon the 

 art of culture by the researches of organic chemistry, a branch which 

 may be said to have started, if not into existence, at least into a new 

 life, within the last ten j sars. Every day too is adding to the number 



