MINERAL OR SALINE MANURES. 25 



experimental farming, in which not only distinct and definite, but 

 comparative results are especially wanted, the means of answer- 

 ing them is indispensable. I shall have occasion hereafter to 

 show that many of the experiments hitherto made in practical 

 agriculture, and published as strictly comparative, and therefore 

 safe guides for reasoning, are deprived of all trustworthiness 

 and comparative value because of the entrance into them of the 

 indeterminate element of farm-yard manure a variable, inde- 

 finite, and constantly changing admixture of vegetable and 

 animal substances. 



Mineral or saline manures are combinations, or mixtures of 

 different combinations, of one or more of those mineral sub- 

 stances which exist and are found in living plants. These saline 

 substances are fixed and definite in their composition, and are 

 admirably adapted for rigorous experimenting. But to use 

 them right to apply them in the proper place, at the proper 

 time, and in the proper quantity to understand their action, 

 how they ought to be mixed, and why their effects vary in dif- 

 ferent circumstances and localities all this requires that they 

 should be thoroughly known, and their mode of action, as single 

 substances and as mixtures, understood. 



It will be seen, also, that no one of the several departments 

 of knowledge we have adverted to, can guide us correctly of 

 itself: they must be taken together. The composition of the 

 plant and that of the soil must be taken in connexion with that 

 of the manure and with the changes of which it is susceptible, 

 if the mind of the experimenter is to be enabled to judge cor- 

 rectly of the effect of his applications to the land he cultivates 

 faithfully to register what he does and observes, and correctly 

 to interpret his observations and results. 



3. General principles of husbandry Knowledge of local and 

 individual practice. 



It is supposed that the suggester is acquainted with the 

 general principles of practical husbandry, and with the ordinary 

 farm routine. But he ought also to know the most important 

 specialties connected with the district or farm in or for which 

 his experimental trials are specially recommended. 



