VII] OF RIFTS AND CRACKLES 523 



and 180°. Hence the rift, dipping down at the angle TT\ will 

 never dip at a greater angle than 45°, and generally much less. 

 Now a spherical bowl whose hp is at 45° to the horizontal has a 



depth of times its lip diameter, or approximately one-fifth. 



And one-fifth of the diameter of the column is, approximately, the 

 depth of the deepest bowl. 



The hexagonal pattern and the three-way corners on which it 

 is based are characteristic (as we have already explained) of a 

 condition of symmetry or uniformity .under which a partition is 

 as hkely to arise in any one direction as in any other, and no 

 series of partitions has precedence over the rest. We have seen, 



Fig. 2U2. Crackles on a porcelain bowl. From H. Hukusima. 



in the dragon-fly's wing and in cambium-tissue, how different is 

 the result when primary partitions are first established and con- 

 solidated, to be followed by a secondary and a weaker set. The 

 "crackles" on a porcelain bowl look somewhat like a cellular 

 epithelium; but the porcelain has been under strain in more ways 

 than one. The plastic clay was first shaped upon a wheel, and 

 potential stress-energy so acquired is stored up even in the finished 

 ware ; again, as the ware cools and shrinks after it is drawn from the 

 kiln the glaze is apt to cool quicker and shrink more than the paste 

 below, and tension -energy is stored up till the glaze ruptures and 

 the cracks appear.' Various rates of cooling and of contraction, the 

 nature of paste and glaze, the shape of the ware, and even the way 

 in which the potter worked the clay, may all influence the pattern 

 of the crackle. The primary crack will be perpendicular to the 



