178 



tal so as to split the boule to favor the correct cutting, but the crack 

 tends to turn around to the other side of the boule. I suspect that this 

 is due to the follo^ving fact : As was said above, the flattened face of 

 the boule is almost always parallel to the longer axis of the oval cross- 

 section of the boule. Now natural ruby tends to cleave parallel to the 

 basal planes, but only feebly so. The boules are under internal strain, 

 somewhat as Prince Rupert's drops are, and when the surface of the 

 boule is abraded oven slightly, crnokliig follows and the strain is relieved. 



FiQureHB. j^uku 

 A/ieujedon toc^r 



l\y cracking ainiig tlic li iigtii of the boule at right angles to tlie i)lane of 

 the flattened surfaeo a smaller cros.s-section i.s ina<l(' than wdiild he made 

 rtere the boule to split parallel to the basal planes. The natural cleavage 

 is so feeble that I sus])ect the split follows the other direction as a line 

 of least resistance. At any rate the boules sjtlit conli-ary to the natural 

 cleavage and disadvantageously as regards cutting to produce the best 

 color. By slitting with the diamond saw after the break has occurred 



