PRECONCEIVED NOTIONS. 293 



chiefly have been sought in tliose nutritive substances 

 whicli are of themselves immovable, and not in those 

 which possess the power of circulation ; especially wlien 

 it was ascertained that part at least' of the latter sponta- 

 neously came back to the field every year. But at eveiy 

 stage in the developement of a science, preconceived 

 ideas will for a time assert their sway ; and such is the 

 case with those notions which ascribe to nitrogen a pre- 

 eminent importance in the cultivation of land. 



In the consideration of a natural phenomenon, and in 

 the investigation of its causes, we cannot tell at first 

 whether it be simple or compomid ; whether it be due to 

 one or to several causes ; hence we are led to attribute 

 the results to those alone which are Jirst discovered in ope- 

 ration. Xo long time ago, people beheved that all the con- 

 ditions of growth lay in the seed alone ; then they found 

 that water, and next that the ai}\ had a very decided 

 influence; bye-and-bye they ascribed to certain organic 

 remains in the ground, a most important part in the 

 fertihty of the soil. When at length they discovered 

 that, among all the substances used for manure, the 

 excrements of animals and the parts and constituents of 

 animals, suri:)assed all the rest in operative power ; when, 

 too, chemical analysis had shown that nitrogen was the 

 chief element in these substances, it is not surprising 

 that nitrogen was then esteemed the sole, and afterwards 

 the principal, agent in manure. 



This process of reasoning is in accordance with nature, 

 and cannot be found fault with. At that time, it was not 

 known that the ash constituents of plants, potash, lime, 

 and phosphoric acid, play as important a part as nitrogen 

 in the vital processes of plants ; nay, not even an idea 

 had been formed of the manner in which the nitrogen of 

 nitrogenous compounds operates. Men simply held by 



