26 THE SCIENTIFIC PRINCIPLES 



especially as to the source of the combined carbon, 

 and the combined nitrogen, accumulated in the total 

 existing vegetable and animal life and remains. He 

 traced these to carbonic acid, and ammonia, evolved 

 by volcanic action. It may be observed that one 

 source of combined nitrogen is undoubtedly electrical 

 action, especially in equatorial regions, but it will 

 be seen further on, that so far as quantitative evi- 

 dence is at command on the point, the amounts of 

 combined nitrogen available from atmospheric sources 

 over a given area, within a given time, are, at any 

 rate in temperate latitudes, quite inadequate to ac- 

 count for the amounts recovered in crops over the 

 same area, and in the same time. It will be seen 

 too, that the question of the sources of the nitrogen 

 of our crops, is one upon which very conflicting views 

 are still entertained. 



For a period of more than twenty-five years, 

 Dr. Daubeny continued to give lectures from time to 

 time on various branches of Eural Economy, generally 

 with some reference to the discussions of the day. 



But independently of discourses of this expository 

 or critical kind, he, in 1845, described the results of 

 some experiments he had made to elucidate the prin- 

 ciples involved in the rotation of crops. To this 

 end he had set apart a number of plots in the 

 Botanic Garden, each 10 feet square. On some of 

 these he grew the same description of plant year 

 after year for several years in succession, whilst on 

 others he alternated the different crops. The soil 

 was admittedly not very favourable, being made 

 ground, and the plots were very small. Still the 

 results clearly showed that more produce was ob- 

 tained from a given area when the different plants 

 were grown in alternation, than when . the same 



