ATTRACTION. 



143 



Dr. Hare, Fig. 1 to 14. 



>~J f "As each of the sides of 



an hexagonal prism of calca- 

 reous spar, is bounded by 

 two edges, one at each end of 

 the prism ; there are six edges 

 at each end, and in all, twelve 

 edges. If to every one of 

 the twelve edges a knife be 

 forcibly applied, in the direc- 

 tion indicated in figure 1 , one 

 of the edges, a b c, a b c, 

 bounding each side, will yield 

 so as to expose a smooth nat- 

 ural facet, making an angle of 

 45 with the adjoining side. The alternate edges will not split off 

 so as to present surfaces corresponding either in smoothness, or obli- 

 quity, with those above described, so that the six facets will be equal- 

 ly divided between the two ends of the prism, each having three facets 

 alternating with three remaining edges." 



" If the dissection be continued, by applying the knife in directions 

 parallel to the facets, finally a rhomboid R will be developed, which 

 exists not only in the hexagonal prism, but in many other crystalline 

 forms of calcareous spar." 



"All these other forms are called secondary. The rhomboid, 

 which is their common nucleus, or primitive form, is beautifully ex- 

 emplified in the Iceland spar." 



FIG. 2. 



L 



" The same author teaches us that a cu- 

 ^ bic crystal of fluor spar, can be split only 

 in directions parallel to the faces of an oc- 

 tohedral nucleus, whose situation, relatively 

 1 to the containing cube, is represented by 

 figure 2." 



" By various dissections, analogous to 

 those which have been adduced, it is ren- 

 X " J dered highly probable that every crystalli- 



zable substance has an appropriate form, which it assumes in the first 

 instance, and which is the basis of all its other forms." 



" The nuclei may sometimes be obtained by percussion, sometimes 

 by heat ; in other cases by heat followed by refrigeration." 



" Although a nucleus cannot be extracted in every instance from 

 crystals, the existence in them of primitive forms, is usually inferred 



