INTERNAL, OR MOLECULAR FORCES. 25 



are, Cohesion, Adhesion, Capillary Attraction, and 



Affinity, 



„ 39. Cohesion, or Cohesive Attraction, is 



What is Co- i • i i • i a i 



hesiveAttrac- that force wliich binds together atoms of the 

 same kind to form one uniform mass. 



The force which holds together the atoms of a mass of iron, wood, or stone, 

 is cohesion, and the atoms are said to cohere to each other. 



What is Ad- 40. Adhesion is that form of attraction 

 hesion? -^hich cxists between unlike atoms, or particles 

 of matter, when in contact with each other. 



Dust floating in the air sticks to the wall or ceiling, through the force of 

 axihesion. When we \vrite on a wall with a piece of chalk, or charcoal, the 

 particles, worn oiF from the material, stick to the wall and leave a mark, 

 tlirough the force of adhesion. Two pieces of wood may be fastened together 

 by means cif glue, in consequence of the adhesive attraction between the par- 

 ticles of th(j wood and the particles of glue. 



41. Capillary Attraction is that form of 



WTiat is Ca- 



piiiaryAttrac- attraction which, exists between a liquid and 

 the interior of a solid, which is tubular, or 

 porous. 



When one end of a sponge, or a lump of sugar is brought into contact with 

 water, the li()uid, by capillary attraction, will rise, or soak up above its level, 

 into the interior of the sponge, or sugar, until all its pores are filled.* 



What is Af- 42. Affinity is that form of attraction which 

 *°*'^' unites atoms of unlike substances into com- 

 pounds possessing new and distinct properties. 



Oxygen, for example, unites with iron, and forms iron-rust, a substance 

 different from either oxygen oi' iron. The consideration of the attraction of 

 Affinity belongs wholly to Chemistry. 



How does the 43. Thc forcc, or strength of Cohesive At- 

 Bi'vrAttTac-^' traction varies greatly in different substances, 

 tionvary? accordlng as the nature, form, and arrange- 

 ment of the atoms of which they are composed vary. 



44. These modifications of the force of At- 



What proper- . . . ., , - . - 



Kes of bodies tractiou, actmg at insensible distances between 

 variation of thc atoms of different substances, give rise to 



Attraction? . . . . , , . , ■ , 



certain important properties m bodies, which 

 are designated under the names of Malleability, Duc- 



• Capillary Attraction is treated of more fully under the department of Hydrostatics 

 and Hydraulics. 



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