XX INTRODUCTION. 



facts to a sound theory, by determining with care the 

 effects of all those bodies which can exert any influence 

 upon vegetation, and the modes of their action, we shall 

 be able to deduce principles, the application of which 

 will greatly accelerate the progress of the most impor- 

 tant of our arts. 



J. All the sciences have a natural course from which 

 they never deviate : they begin by collecting and prov- 

 ing facts ; and when these facts are well established, they 

 compare them with each other, and deduce from them 

 principles of general application. 



The facts in agriculture are already numerous; but 

 have the modifications wrought by the nature of the 

 soil, the action of manures, the state of the atmosphere, 

 the influence of climate, and the varieties of exposure, 

 been "sufficiently attended to? Will a fact observed in 

 one place be constantly reproduced in another ? Since 

 such is not the case, we must necessarily come to the 

 conclusion, that solitary facts are not sufficient to estab- 

 lish principles in agriculture. It is necessary that they 

 should have been observed and verified, under the in- 

 fluence of all the agents of which I have spoken ; and 

 that we should know J:he modifications which each one 

 produces, in order to be able to draw from them general 

 and practical consequences. If the agents of vege- 

 tation were constantly tlie same, if their effects were 



^ everywhere the same, one fact alone would be sufficient 

 to establish a principle, applicable to all localities ; but 

 the difference of their action under different circum- 

 stances necessarily produces important changes in their 

 results : and this it is, that causes the kind of agriculture 

 which prospers in one country, to be unsuccessful in an- 



