[From the Encydopetdia Britannica.] 



I A X X V 1 1 1. Constitution of Bodies. 



IIIK question whether the smallest parts of which bodies are composed are 

 finite in number, or whether, on the other hand, bodies are infinitely divisible, 

 rvl.iUw to the ultimate constitution of bodies, and is treated of in the article 

 ATOM. 



The mode in which elementary substances combine to form compound sub- 

 stance* is called the chemical constitution of bodies, and is treated of in 



'lIKMISTBY. 



The mode in which sensible quantities of matter, whether elementary or 

 compound, are aggregated together so as to form a mass having certain observed 

 properties, is called the physical constitution of bodies. 



Bodies may be classed in relation to their physical constitution by con- 

 sidering the effects of internal stress in changing their dimensions. When a 

 body can exist in equilibrium under the action of a stress which is not uniform 

 in all directions it is said to be solid. 



When a body is such that it cannot be in equilibrium unless the stress 

 t every point is uniform in all directions, it is said to be fluid. 



There are certain fluids, any portion of which, however small, is capable 

 f expanding indefinitely, so as to fill any vessel, however large. These are 

 called gases. There are other fluids, a small portion of which, when placed in 

 a large vessel, does not at once expand so as to fill the vessel uniformly, but 

 remains in a collected mass at the bottom, even when the pressure is removed. 

 These fluids are called liquids. 



When a liquid is placed in a vessel so large that it only occupies a 

 part of it, part of the liquid begins to evaporate, or in other words it passes 

 int.. the state of a gas, and this process goes on either till the whole of the 

 liquid is evaporated, or till the density of the gaseous part of the substance 



