S07 



LECTURE VIII. 



On the Improvement of Lands by Burning; chemical 

 Principles of this Operation. On Irrigation and its 

 effects. On Fallowing; its Disadvantages and 

 Uses. On the convertibl Husbandry founded on 

 regular Rotations of different Crops. On Pasture; 

 Views connected with its Application. On various 

 Agricultural Objects connected with Chemistry. 

 Conclusion. 



The improvement of sterile lands by burning 

 was known to the Romans. It is mentioned by Vir- 

 gil in the first book of the Georgics: " Saepe etiam 

 steriles incendere profuit agros." It is a practice still 

 much in use in many parts of these Islands; the theory 

 of its operation has occasioned much discussion; both 

 amongst scientific men and farmers. It rests entirely 

 upon chemical doctrines; and I trust I shall be able to 

 offer you satisfactory elucidations on the subject. 



The basis of all common soils, as I stated in the 

 Fourth Lecture, are mixtures of the primitive earths 

 and oxide of iron; and these earths have a certain de- 

 gree of attraction for each other. To regard this at- 

 traction in its proper point of view, it is only necessary 

 to consider the composition of any common siliceous 



