54 I^^' WoLLASTON on the tltmentary Particles 



corresponded with his ; and I shall hope that, by the assistance 

 of such authority, they may meet with a more favourable 

 reception. 



The theory to which I here allude is this, that, with respect 

 to fluor spar and such other substances as assume the octohe- 

 dral and tetrahedral forms, all difficulty is removed by suppos- 

 ing the elementary particles to be perfect spheres, which by 

 mutual attraction have assumed that arrangement which brings 

 them as near to each other as possible. 



The relative position of any number of equal balls in the 

 same plane, when gently pressed together, forming equilateral 

 triangles with each ether (as represented perspectively in 

 fig. 4.) is familiar to every one; and it is evident that, if balls 

 so placed were cemented together, and the stratum thus formed 

 were afterwards broken, the straight lines in which they would 

 be disposed to separate would form angles of Gd* with each 

 other. 



If a single ball were placed any where at rest upon the pre- 

 ceding stratum, it is evident that it would be in contact with 

 three of the lower balls (as in fig. 5.), and that the lines join- 

 ing the centres of four balls so in contact, or the planes touch- 

 ing their surfaces, would include a regular tetrahedron, having 

 all its sides equilateral triangles. 



The construction of an octohedron, by means of spheres 

 alone, is as simple as that of the tetrahedron. For if four balls 

 be placed in contact on the same plane in form of a square, 

 then a single ball resting upon them in the centre, being in 

 contact with each pair of balls, will present a triangular face 

 rising from each side of the square, and the whole together 

 will represent the superior apex of an octohedron ; so that a 



