144 ON THE PRINCIPLES OF 



tility of exhausted fields by means of the excrements of man 

 and animals dej^ends upon their proportions of these matters; 

 if the effect of the manures accelerating- the veg-etation de- 

 pends upon their proportions of ammonia, it is clear that we 

 can only dispense with the latter when we provide all effi- 

 cacious elements exactly in those proportions and in that 

 form most pro})er for assimilation by the veg'etable org-anism 

 in which they are found in the most fertile soil or in the 

 most efficacious manure. 



According- to our present knowledg-e of the effect of the 

 constituent i)arts of manure, I feel convinced that it is indif- 

 ferent to the ]ilants from which source they are derived. The 

 dissolved apatite (phosphate of lime) from Spain, the potash 

 derived from the felspar, the ammonia from the g-as-works, 

 must exercise the same effects on vegetable life as the bone 

 earth, the potash, or the ammonia, which we provide in 

 nature. 



We live in a time when this conclusion is to be subjected 

 to a comprehensive and accurate trial ; and if the result 

 corresponds with the expectations which Ave are entitled to 

 make, if the animal excrements can be replaced by their 

 efficacious elements, a new era of ng-riculture must beg-in. 



I invite the enlightened farmers of England to imite with 

 me for that purpose, and to lend me their aid. Whatever 

 may be the result of these experiments, it is necessary for 

 the future prosperit}^ of ag-ricultm-e that they be made. They 

 will enrich us with a number of valuable facts ; we shall as- 

 certain where we have wasted efficacious matters in the 

 common course of farming- ; we shall acquire an exact know- 

 ledg-e of those substances which are necessary, and of those 

 which are dispensable. 



For a number of years, m3'Self and many young- talented 

 chemists have been occupied with the analj'sis of those 

 mineral substances which are constituent elements of our 

 plants of culture, and with the examination of the excre- 

 ments of man and animals, as well as of a g-reat number of 

 soils acknowledged as fertile. These labours have been laid 

 before the scientific world long- since, but only a very con- 

 fined application has been made of them in agriculture. 



The farmer is, by his position, not in the condition to 

 procure and to command the efficacious elements necessary 

 for the restoration and increase of the fertility of his fields in 

 a right proportion and suitable form. For this purpose, 

 science and industry must combine their aid. 



