C is ] 



between 1665 and 1680, stated that a small part of it 

 only was consumed in the respiration of animals, and 

 in the combustion of inflammable bodies ; but the 

 true statical analysis of the atmosphere is comparative- 

 ly a recent labour, achieved towards the end of the 

 last century by Scheele, Priestley, and Lavoisier. 

 These celebrated men shewed that its principal 

 elements are two gases, oxygene and azote, of which 

 the first is essential to flame, and to the life of animals, 

 and that it likewise contains small quantities of 

 aqueous vapour, and of carbonic acid gas ; and La- 

 voisier proved that this last body is itself a compound 

 elastic fluid, consisting of charcoal dissolved in oxy- 

 gene. 



Jethro Tull, in his treatise on Horse-hoeing, pub- 

 lished in 1 733, advanced the opinion that minute 

 earthy particles supplied the whole nourishment of the 

 vegetable world ; that air and water were chiefly useful 

 in producing these particles from the land ; and that 

 manures acted in no other way than in ameliorating the 

 texture of the soil, in short, that their agency was 

 mechanical. This ingenious author of the new system 

 of agriculture having observed the excellent effects 

 produced in farming by a minute division of the soil, 

 and the pulverisation of it by exposure to dew and air, 

 was misled by carrying his principles too far. Duh- 

 amel, in a work printed in 1 754, adopted the opinion 

 of Tull, and stated that by finely dividing the soil, any 

 number of crops might be raised in succession from 

 the same land. He attempted also to prove, by di- 

 rect experiments, that vegetables of every kind were 



