108 CLEAVAGE. SECT. XIV. 



forms of carbonate of lime split into six-sided figures, 

 called rhombohedrons (N. 166), whose alternate angles 

 measure 105*55 and 75-05, however far the division 

 may be carried ; therefore the ultimate particle of car- 

 bonate of lime is presumed to have that form. However 

 this may be, it is certain that all the various crystals of 

 that mineral may be formed by building up six-sided 

 solids of the form described, in the same manner as chil- 

 dren build houses with miniature bricks. It may be 

 imagined that a wide difference may exist between the 

 particles of an unformed mass,, and a crystal of the same 

 substance between the common shapeless limestone 

 and the pure and limpid crystal of Iceland spar, yet 

 chemical analysis detects none ; their ultimate atoms 

 are identical, and crystalization shows that the difference 

 arises only from the mode of aggregation. Besides, all 

 substances either crystalize naturally, or may be made to 

 do so by art. Liquids crystalize in freezing, vapors by 

 sublimation (N. 167) ; and hard bodies, when fused, crys- 

 talize in cooling. Hence it may be inferred that all sub- 

 stances are composed of atoms, on whose magnitude, 

 density, and form their nature and qualities depend ; 

 and as these qualities are unchangeable, the ultimate 

 particles of matter must be incapable of wear the same 

 now as when created. 



The oscillations of the atmosphere and the changes 

 in its temperature, are measured by variations in the 

 heights of the barometer and thermometer. But the 

 actual length pf the liquid columns depends not only upon 

 the force of gravitation, but upon the cohesive force, or 

 reciprocal attraction between the molecules of the liquid 

 and those of the tube containing it. This peculiar action 

 of the cohesive force is called capillary attraction or ca- 

 pillarity. If a glass tube of extremely fine bore, such as 

 a small thermometer tube, be plunged into a cup of wa- 

 ter or spirit of wine, the liquid will immediately rise in 

 the tube above the level of that in the cup ; and the sur- 

 face of the little column thus suspended will be a hollow 

 hemisphere, whose diameter is the interior diameter of 

 the tube. If the same tube be plunged into a cupful of 

 mercury the liquid will also rise in the tube, but it will 

 never attain the level of that in the cup, and its surfnce 



