THEIR CAUSE. 227 



tating it briskly, solid crystals of cream of tartar 

 are immediately deposited. A solution of a salt of 

 magnesia also, which is not rendered turbid by 

 the addition of phosphate of ammonia, deposits the 

 phosphate of magnesia and ammonia on those parts 

 of the vessel touched with the rod employed in 

 stirring. 



In the processes of combination and decomposition 

 under consideration, motion, by overcoming the vis 

 inertia, gives rise immediately to another arrange- 

 ment of the atoms of a body, that is, to the produc- 

 tion of a compound which did not before exist in 

 it. Of course these atoms must previously possess 

 the power of arranging themselves in a certain 

 order, otherwise both friction and motion would be 

 without the smallest influence. 



The simple permanence in position of the atoms 

 of a body, is the reason that so many compounds 

 appear to present themselves, in conditions, and 

 with properties, different from those which they 

 possess, when they obey the natural attractions of 

 their atoms. Thus sugar and glass, when melted 

 and cooled rapidly, are transparent, of a conchoidal 

 fracture, and elastic and flexible to a certain degree. 

 But the former becomes dull and opaque on keep- 

 ing, and exhibits crystalline faces by cleavage, 

 which belong to crystallised sugar. Glass assumes 

 also the same condition, when kept soft by heat for 

 a long period ; it becomes white, opaque, and so 

 hard as to strike fire with steel. Now, in both 



Q2 



