100 CONSTITUTION OF BODIES. S CT. XIV. 



their form, perfect mobility will exist among them re- 

 sulting from the similarity of their attractions, and they 

 will offer great resistance when compressed ; properties 

 which characterize liquids in which the repulsive prin- 

 ciple is greater than in the gases. When the distance 

 between the particles is still less, solids are formed. 

 But the nature of their structure will vary, because at 

 such small distances the power of the mutual attraction 

 of the particles will depend upon their form, and will 

 be modified by the sides they present to one another 

 during their aggregation. Besides these three condi- 

 tions of matter, there are an infinite variety of others 

 corresponding to the various limits at which the two 

 contending forces are balanced, which may be observed 

 in the fusion of metals, and other substances passing 

 from hardness to toughness, viscidity, and through all 

 the other stages to perfect fluidity and even to vapor. 



The effort required to break a substance is a measure 

 of the intensity of the cohesive force exerted by its 

 particles, which is as variable as the intensity of the 

 repulsive principle. In stone, iron, steel, and all brittle 

 and hard bodies, the cohesion of the particles is powerful 

 but of small extent. In elastic substances, on the con- 

 trary, its action is weak but more extensive. Since all 

 bodies expand by heat, the cohesive force is weakened 

 by an increase of temperature. 



Every particle of matter, whether it forms a con- 

 stituent part of a solid, liquid, or aeriform fluid, is 

 subject to the law of gravitation. The weight of the 

 atmosphere, of gases and vapor, shows that they consist 

 of gravitating particles. In liquids the cohesive force 

 is not sufficiently powerful to resist the action of gravi- 

 tation. Therefore although their component particles 

 -still maintain their connection, the liquid is scattered by 

 their weight, unless when it is confined in a vessel or 

 has already descended to the lowest point possible, and 

 assumed a level surface from the mobility of its particles 

 and the influence of the gravitating force, as in the 

 ocean, or a lake. Solids would also fall to pieces by 

 the weight of their particles, if the force of cohesion 

 were not powerful enough to resist the efforts of gravi- 

 tation. 



