278 AMMONIA AND NITEIC ACID. 



such decrease would first and chiefly have been sought 

 in those nutritive substances which are of themselves 

 immovable, and not in those which possess the power 

 of circulation ; especially when it was ascertained that 

 part at least of the latter spontaneously came back to 

 the field every year. But at every stage in the devel- 

 opement of a science, preconceived ideas will for a time 

 assert their sway ; and such is the case with those no- 

 tions which ascribe to nitrogen a preeminent impor- 

 tance 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 compound ; whether it be due 

 to one or to several causes ; hence we are led to attrib- 

 ute the results to those alone which vxe first discovered 

 in operation. No long time ago, people believed that 

 all the conditions of growth lay in the seed alone ; then 

 they found that water, and next that the air, had a 

 very decided influence ; bye-and-bye they ascribed to 

 certain organic remains in the ground, a most impor- 

 tant part in the fertility 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, surpassed all the rest in opera- 

 tive 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 na- 

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

 was not known that the ash-constituents of plants, pot- 

 ash, 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 the fact that horn, claws, blood, 

 bones, urine, the solid excrements of animals and men, 

 exerted a favourable influence ; while woody sub- 

 stances, sawdust and similar materials, had no effect, 

 or as good as none. If in the one case the presence of 



