On tin Infiiiiufi- $f mi-tun- of Crystals. 



duced by a combination of the forms 001, 110, 010. The angle /:? was 

 found to measure 71" 16', and thus only differs from the angle of a 

 tetrahedron (which is 70 30') by 46 minutes. The angle of the prism 

 110 was found to be 122 24', or 2 24' greater than that of a regular 

 hexagon. 



The packing of the atoms in graphite is the most open we have yet 

 encountered ; in diamond, not only the closest, but the closest possible. 

 Yet graphite is the commoner form of carbon, and the more easily pro- 

 duced by artificial means. Nature therefore does not seem to especially 

 favour closest possible packing, rather leaning on the contrary to the 

 more open arrangements. The relative hardness of the two forms of 

 carbon would seem to be connected with their structure, graphite 

 one of the softest of minerals, and diamond without exception the 

 hardest. As Professor Miers siiggests, the sectility of graphite may 

 perhaps be connected with its open structure, but on other differences 

 in the physical characters of the two substances the structure seems 

 to throw no li^ht. 



