8 FINAL CAUSES. 



law, and are necessarily restrained within certain 

 limits, which they never can exceed, and by 

 which the permanence of the system is effectu- 

 ally secured. All the terrestrial changes de- 

 pendent on these motions partake of the same 

 constancy. The same periodic order governs 

 the succession of day and night, the rise and 

 fall of the tides, and the return of the seasons : 

 which order, as far as we can perceive, is inca- 

 pable of being disturbed by any existing cause. 



Equally definite are the operations of the 

 forces of cohesion, of elasticity, or of whatever 

 other mechanical powers of attraction or repulsion 

 there may be, which actuate, at insensible dis- 

 tances, the particles of matter. We see liquids, 

 in obedience to these forces, collecting in spheroi- 

 dal masses, or assuming, at their contact with 

 solids, certain curvilinear forms, which are sus- 

 ceptible of precise mathematical determination. 

 In different circumstances, again, we behold 

 these particles suddenly changing their places, 

 marshalling themselves in symmetric order, and 

 constructing by their union solid crystals of de- 

 terminate figure, having all their angles and 

 facets shaped with mathematical exactness. 



The forces by which dissimilar particles are 

 united into a chemical compound have been 

 termed Chemical Affinities ; and the operation of 

 these peculiar forces is as definite and determi- 

 nable as the former. They are now known to be 



