8 
rately afford all the principles concerned in ve- 
getation ; and it is only by examining the che- 
mical nature of these principles, that we are 
capable of discovering what is the food of plants, 
and the manner in which this food is sup- 
plied and prepared for their nourishment The 
principles of the constitution of bodies, conse- 
quently, will form the first subject for our con- 
sideration. 
By methods of analysis dependent upon che- 
mical and electrical instruments discovered in late 
times, it has been ascertained that all the varieties 
of material substances may be resolved into a com- 
paratively small number of bodies, which, as they 
are not capable of being decompounded, are con- 
sidered in the present state of chemical knowledge 
as elements. The bodies incapable of decom- 
position at present known are fifty-two. Of these 
forty are metals; eight are inflammable bodies; 
and five are substances which unite with metals 
and inflammable bodies, and form with them 
acids, alkalies, earths, or other analogous com- 
pounds. The chemical elements acted upon by 
attractive powers combine in different aggregates. 
In their simpler combinations, they produce 
various crystalline substances, distinguished by 
the regularity of their forms. In more compli- 
cated arrangements, they constitute the varieties of 
vegetable and animal substances, bear the higher 
character of organization, and are rendered sub- 
servient to the purposes of life. And by the in- 
fluence of heat, light and electrical powers, there 
is a constant series of changes; matter assumes 
