150 



ATTRACTION. 



is to be called primitive, especially as neither of 

 them can fill space without leaving vacuities, 

 nor can they produce any arrangement suffi- 

 ciently stable to form the basis of a permanent 

 crystal." 



" To obviate this incongruity, Dr. Wollaston 

 (Phil. Trans. 1813,) has very ingeniously pro- 

 posed to consider the primitive particles as 

 spheres, which, by mutual attraction, have as- 

 sumed that arrangement which brings them as 

 near as possible to each other. When a num- 

 ber of similar balls are pressed together, in the same plain, they form 

 equilateral triangles, with each other ; and 

 if balls so placed were cemented together, 

 and afterwards broken asunder, the straight 

 lines in which they would be disposed to 

 separate, would form angles of 60 with 

 each other. A single ball placed any where on this stratum, would 

 touch three of the lower balls, and die planes touching their surfaces 

 would then include a regular tetrahedron. A square of 

 four balls, with a single ball resting upon the centre of 

 each surface, would form an octohedron ; and upon ap- 

 plying two other balls at opposite sides of this octohe- 

 dron, the group will represent the acute rhomboid. 

 Thus the difficulty of the primitive form of fluor, above alluded to, is 

 done away, by assuming a sphere as the ultimate molecula. By ob- 

 late and oblong spheroids, other forms may be obtained."* 



Dr. Wollaston has demonstrated, geometrically, that by assorting 

 spheres and spheroids in particular groups and modes, all the solids 

 of crystals may be constructed. The cannon balls in an arsenal, are 

 often arranged in such a manner as to illustrate this subject. One 

 group forms a square and another a triangle, and by piling them 



* Brande, quoted by Hare. 



