S3 
ferent degrees of force : thus sulphuric acid and 
magnesia unite with more readiness than distilled 
vinegar and magnesia ; and if sulphuric acid be 
poured into a mixture of vinegar and magnesia, 
in which the acid properties of the vinegar have 
been destroyed by the magnesia, the vinegar will 
be set free, and the sulphuric acid will take its 
place. This chemical attraction is likewise called 
chemical affinity. It is active in most of the 
phenomena of vegetation. The sap consists of a 
number of ingredients, dissolved in water by che- 
mical attraction ; and it appears to be in con- 
sequence of the operation of this power, that cer* 
tain principles derived from the sap are united to 
the vegetable organs. By the laws of chemical 
attraction, different products of vegetation are 
changed, and assume new forms : the food of 
plants is prepared in the soil ; vegetable and ani- 
mal remains are changed by the action of air and 
water, and made fluid or aeriform ; rocks are 
broken down and converted into soils \ and soils 
are more finely divided and fitted as receptacles 
for the roots of plants. 
The different powers of attraction tend to pre- 
serve the arrangements of matter, or to unite them 
in new forms. If there were no opposing powers, 
there would soon be a state of perfect quiescence 
in nature, a kind of eternal sleep in the physical 
world. Gravitation is continually counteracted by 
mechanical powers, by projectile motion, or the 
centrifugal force ; and their joint agencies occa- 
sion the motion of the heavenly bodies. Cohesion 
and chemical attraction are opposed by the re- 
D 
