294 Dr Davy's Agricultural Discourse. 



d.nd, in consequence, the solvent power of the mensirutmi 

 ii diminished, and depositions of silica, and carbonate of 

 lime, and other ingredients, take place. This view, it ap- 

 pears to me, is not only recommended by its simplicity, but 

 also by a certain beauty and exactness of adjustment, and 

 economy of means. Is it not very admirable that a gaseous 

 acid, which, with water, is to yield to the plant, by decompo- 

 sition, its organic elements, should be the solvent and vehicle 

 of its inorganic parts 1 



Limited as I am in the delivery of this discourse by time, 

 my main object has been to give general views, precise in 

 themselves, and I believe correct, and involving principles 

 capable of being carried out into practice, — the test and con- 

 firmation of scientific truths. 



On the practical part of the subject of Manures, it is not 

 my intention to enter at any length. I have neither time for 

 it, nor the experience to do it justice, or to treat of it in the 

 manner I could wish. In the farther observations which I 

 propose to make, I shall restrict myself to such remarks as I 

 hope may be suggestive, — may excite curiosity and inquiry, 

 and so have a chance of being useful ; intelligent inquiry 

 being, as I think, the one thing perhaps the most needful, — 

 without which agriculture can never speedily advance, and 

 under which it cannot fail to advance, and from an art, 

 which it is at present, and obscure in many of its parts, be- 

 come a science, as certain as to results as is compatible with 

 the uncertainty of the weather, and of other cii»cumstances 

 not under the controlling power of man. 



What are the principal sources of manures, or of fertiliz- 

 ing means \ 1 shall briefly speak of them under a few heads. 

 1*^, Atmospheric, chiefly in the form of rain ; 2dli/, Of ani- 

 mal matter ; Zdli/, Of vegetable matter ; and, lasili/, Of mi- 

 neral. 



1^^, Of the fertilizing means derived from the atmosphere. 

 The atmosphere, as you are aware, is a mixture of two gases, 

 azote and oxygen, in certain, almost constant proportions ; 

 and of carbonic acid and aqueous vapour, — the former in 

 small quantity, little variable,— the latter in a variable quan- 

 tity, and extremely variable according to circumstances of 



