384 On Pnhlk Institutions for the 



superadded. Again, the state of the weather, in itself a very 

 compheated problem, often materially affects the result, and the 

 accounts given of its condition, by those who think it worth noticing 

 at all, are seldom so precise or so comprehensive as to embrace 

 all the elements on which its influence depends. 



Thus, after all, the information we obtain by the empirical 

 method may fail even in its narrowest application, namely, that of 

 enabling us to discriminate the kind of land, or the descrijdion of 

 crop, which a particular manure appears to favour, and still less 

 able is it to afford us a clue to the discovery of fit substitutes for 

 itj when the material itself is unattainable. 



How superior to this, even in point of practical utility, is the 

 scientific mode of proceeding, which sets out with investigating 

 the precise manner in which a particular manure acts upon the 

 soil and crop! If, indeed, it appear at first sight more difficult 

 to attain in this way the end proposed, we are rewarded at least 

 in the long run, by acquiring a knowledge applicable — not merely 

 to the individual case for which it is sought — that is, to a given 

 crop, on a given soil, belonging to a given country, and under 

 circumstances of climate in all respects analogous — but likewise 

 to all future times, and to every other kind of soil of which the 

 chemical constitution has been duly ascertained. 



Let us, by way of illustration, take the case of nitrate of 

 soda, respecting the utility of which the empirical method of re- 

 search has as yet presented us only with the most conflicting evi- 

 dence. Let us suppose it to have been placed beyond the reach 

 of doubt, by a series of carefully conducted experiments, that this 

 salt operates beneficially, not by communicating a direct stimulus 

 to vegetation, but by supplying nitrogen and soda, ingredients 

 which many crops require for their food. Let us also suppose it 

 to have been ascertained, by another series of experiments, that 

 the nitric acid of the salt supplies nitrogen only by becoming 

 previously the instrument of generating ammonia, and that for 

 this to take place the influence of a certain intensity of solar light 

 is indispensable. Irrelevant as such speculative truths as the 

 above may appear to the every-day operations of farming, it will 

 not be difficult to show, that they are calculated to fulfil more 

 important practical ends, than experiments designed to ascertain 

 by direct means the increase of produce arising from the applica- 

 tion of the said manure to a particular field. 



Once furnished with these particulars, we may infer, for ex- 

 ample, that the salt in question is only appropriate for soils in 

 which nitrogen is deficient, or, in other words, where ammonia is 

 neither supplied sufficiently from the materials of the land itself, 

 nor from the animal matters superadded. So also a knowledge 

 of the atmospheric conditions necessary to bring about its de- 



