LECTURES. 207, 



Atomic theory of Boscovich. 



(85.) This is similar to the foregoing and may be expressed in the 

 following postulates : 



1st. Matter consists of indefinitely small indivisible and inert 

 atoms. 



2d. These are endowed with attracting and repelling forces, which 

 vary both in intensity and direction by a change of distance, so that 

 at one distance two atoms atttract and at another repel. 



3d. The law of variation is the same in all atoms, and the action 

 mutual. 



4tli. At all sensible distances the force is attraction, and known by 

 the name of gravitation. 



5th. Within the insensible distance in Avhioh physical contact is 

 observed, there are several alternations of attraction and repulsion. 



6th. The last force which is exerted between two atoms as their 

 distance diminishes is an insuperable repulsion, no force however great 

 can press two atoms into mathematical contact. 



The property of inertia was not assigned to the atoms of Boscovich, 

 but it is necessary to explain the phenomena. 



(86.) Use of such a theory — an expression of a limited generaliza- 

 tion including many facts — may be continually improved and modified 

 as new facts are discovered. Importance of general views of this kind 

 as aids to discovery. 



The theory ex;pressed mathematically — Distances, attraction, and 

 repulsion represented by the abscissas and ordinates of a curve which 

 cuts the axis several times — parts above the line attractions — below 

 repulsions. The primary branch forming an asymptote expresses a 

 continued increasing repulsion. The final branch gradually assimi- 

 lates itself to the law of gravitation. 



Illustration of the theory. 



(87.) Stable and instable points. For small distances the curve 

 may be considered a straight line ; the force is therefore inversely as 

 the^ distance — atoms in stable points are inactive — when pushed nearer 

 they repel — when drawn apart attract. 



Formation of a polarized molecule of an assemblage of such atoms — 

 construction of a solid. 



Diagram and models to illustrate hypothetical constitution of 

 matter. 



Crystalline forms produced by grouping of atoms — development ot 

 polarity — attempt to explain the liquid and solid states. Shrinking 

 of ice in melting, &c. 



The internal structure of inorganic bodies may be studied, 1st, by 

 cleavage : 2d by the action of polarized light ; 3d, by vibrations. 



Daniell's method of developing thecrystallinestructure of amorphous 

 solids. Alum in water . Metals in mercury. 



Derangement of the molecules in a rod of glass by bending, shown 

 by' polarized light. The extreme mobility of the particles of the most 



