INTERNAL, OR MOLECULAR FORCES. 23 



Do all bodies "^^ bodies possess the property of elasticity, but in very 

 possess elas- different degrees. Tliere are some in wliicii tlae atoms, after 

 " ^ bending, or displacement, almost perfectly resume their former 



position. Such bodies are especially termed elastic, as tempered steel, India- 

 rubber, ivory, etc. Other bodies, like iron, lead, etc., are elastic in a limited 

 degree, not being able to bear any great displacement of their atoms without 

 breaking, or permanent disarrangement. Putty, moist clay, and similar bodies, 

 possess a very slight degree of elasticity. 



31. If we compress a certain quantity of gas, as common 

 ^n71o *of r^- ^^^' ^^^ i^^QT^ aUow it to dilate, by removing all restraint, it 

 pulsion acting will expand without limit, and fill every really empty space 

 bie^diatance!'" ^bich is open to it. This takes place through the agency of 



an internal forco which tends to drive the particles from one 

 another. There are many reasons which lead us to suppose that the repuls- 

 ive force which tends to keep the particles of matter asunder is the agent 

 known as heat. Gases may be considered as perfectly elastic. 



32. Accordino; as the attractive or repulsive 



In what three *-' , ,. .,, 



forms or con- forcBS prevail, all bodies will assume one of 



ditions does to i ■ • i 



all matter ei- three lorms or conditions — the solid, the 

 ist? ... ' 



LIQUID, or the aeriform,-" or gaseous con- 

 dition. 

 What is a 33. A SOLID body is one in which the par- 



^"^^^ tides of matter are attracted so strongly to- 



gether, that the body maintains its form, or figure, under 

 all ordinary circumstances. 

 What is a 34. A LIQUID body is one in which the par- 



Liquid? tides of matter are so feebly attracted together, 



that they move upon each another with the greatest 

 facility. 



Hence a liquid can never be made to assume any particular form, except 

 that of the vessel in wliieh it is inclosed. 



.^^^j. . ^ 35. An aeriform, or gaseous body is one 



Gaseous in which the particles of matter are not held 



together by any force of attraction, but have a 

 tendency to separate and move off from one another. 



A gaseous body is generally invisible, and, like the air sur- 



properties of a rounding US, affords to the sense of touch no evidence of its 



Gaseous existence when in a state of complete repose. Gaseous bodies 



may be confined in vessels, from whence they exclude liquid.'^ 



• Aeriform, having the form, or resemblance, of air. 



