188 Bibliography. 



them. Would he know what varieties of domestic animals may be 

 most advantageously raised for any particular purpose, or how certain 

 qualities may be obtained by cross-breeding ; zoological knowledge 

 will afford him important assistance. If it be desirable to ascertain 

 whether a certain crop, or kind of fruit, may be expected to succeed in 

 a given district ; meteorology provides the data for resolving the en- 

 quiry, by giving the mean temperature of the year, recording the 

 greatest heat of summer and cold of winter for a series of years, the 

 liability to sudden and great changes of temperature at particular sea- 

 sons, the average quantity of rain which falls during each year, or 

 month. These data, compared with the atmospheric condition of a 

 country where the crop in question is successfully cultivated, afford the 

 requisite information. The nature of the soil no less demands the 

 farmer's attention ; the character of the subsoil, and the results that 

 may be expecfed from bringing it to the surface ; the cause of the di- 

 versities which different portions even of the same field exhibit, where 

 the land is to ordinary observation similar ; these and similar points 

 geology offers to explain. 



Moreover, if a soil be naturally barren, or be rendered so by a long- 

 continued system of wretched tillage, like that which has impoverished 

 extensive portions of our Southern States, it is very important to know 

 whether it may be improved or reclaimed so as to repay the outlay, 

 and how this may best be effected. Barrenness may be owing to the 

 presence of some injurious substance, or it may arise from the absence 

 of an element that is essential to the production of a given crop. How 

 is the cultivator to distinguish between these two cases, and apply to 

 each the proper remedy ? When a field is exhausted by over-cropping, 

 how are we to ascertain what is exhausted, and consequently what must 

 be restored to the soil before it can recover its former fertility } To 

 these and to a thousand such questions, " chemistry alone can and will 

 give a satisfactory answer." It is true that many useful results have 

 been attained by mere accident, and pursued apart from all considera- 

 tions of the wliy and loherefore ; but it is no less true that we know not 

 half the value of any such discovery, until we understand the princi- 

 ples upon which it rests, and can apply them intelligently to analogous 

 cases. Gypsum, for instance, is found wonderfully to fertilize certain 

 soils, while upon others it produces no good effect whatever. It is ob- 

 vious that the farmer cannot derive the fullest advantages from this 

 agent, nor be acquainted with all its useful applications, until he under- 

 stands how its fertilizing effects are produced, and under v/hat circum- 

 stances it is useless or even injurious. And so likewise with respect to 

 the use of marl, lime, and various manures ; the mode of whose ope- 

 ration can only be learned from chemistry and vegetable physiology. 



