206 LECTURES. 



smooth and flat glasses attracted at one distance, repelled at another, 

 &c. Experiment very delicate ; care required to exclude electrical 

 and other extraneous actions. 



(79.) The molecular forces are confined to exceedingly small ranges 

 of distances. The alternations above mentioned take place within the 

 5000th part of an inch. The two plates of glass are brought into the 

 sphere of cohesion by sliding them together, and when strongly pressed 

 for sometime become incorporated as one. 



Probable explanation of this. 



(80.) Coarsely powdered substances which do not cohere, when 

 finely powdered and submitted to great pressure become solid. 



Cannon ball fired into the mouth of a large cannon filled with sand 

 produces sandstone. 



Explanation of this. 



(81.) Although the molecular action is confined to insensible dis- 

 tances, yet the forces are of the same nature as those of gravitation 

 and magnetism, tending to produce motion in the molecules as the 

 others do in the masses. Proof of this. 



Molecular constitution of matter. 



(82.) The phenomena of the transmission of sound, of light and 

 heat — of dilatability and compressibility — of porosity, &c., all lead 

 us to adopt the hypothesis that matter under its apparent volume does 

 not consist of a plenum, but that its molecules are widely separated in 

 reference to their size by void spaces ; or by spaces occupied only by 

 the imponderable agents or agent of light, heat, and electricity. 



The molecules, however, must be supposed to be so small and so 

 near that many myriads of them exist in the length of an inch, and 

 on this account produce on our senses the effect of perfect solidity. 



The primary molecules may be supposed to be formed of the union 

 of others of an inferior order separated in the same way and so on as 

 far as the actual phenomena may indicate. 



Each molecule must be submitted to the action of attraction and re- 

 pulsion, and these forces predominate at different distances. 



(83.) According to the molecular hypothesis, frequently adopted, 

 the attraction belongs to the molecules of the matter, but the repul- 

 sion is due to the atmospheres of the imponderable agent of heat, which 

 is supposed to surround them ; or in otlier words, between the mole- 

 cules of matter there is attraction, between the atoms of heat, repulsion, 

 and between heat and matter, attraction. 



The electrical hypothesis of the constitution of bodies. 



(84.) The different states of bodies depend on the condition of the 

 molecular forces. In gases the cohesion is nothing and the particles 

 tend to separate but probably not continually, at a certain distance 

 gravitation would predominate. In liquids the attraction and repul- 

 sion are balanced and the molecules have perfect mobility among them- 

 selves; but in solids besides cohesion there is another force, polarity/ 

 which prevents lateral motion while the molecules are free to oscillate. '' 



