188 MR. J. B. DANCER ON 



long time in this direction ; but the results of his experi- 

 ments, and also those of many others, have not been very 

 satisfactory. 



The examination of a number of precious stones by the 

 aid of the microscope has suggested that this instrument 

 would be a valuable assistant in detecting spurious from 

 real gems ; of course I mean in those sufficiently trans- 

 parent for microscopical examination. 



I imagine there are but few stones used in jewellery 

 which are so perfect that the microscope will not reveal 

 some flaws, although possibly very minute ones. On com- 

 paring these imperfections with those so abundant gene- 

 rally in artificial stones, it is easy, with a little experience, 

 to decide, by this method alone, whether the stone is spuri- 

 ous or genuine. This applies to all gems mounted in open 

 settings. 



With respect to the formation of those crystals con- 

 taining fluid-cavities, Sir David. Brewster states, in a paper 

 read before the Royal Society of Edinburgh, March 1862, 

 that ^^ In my paper of 1826 I was driven to the conclu- 

 sion that cavities containing the two new fluids were formed 

 by highly elastic substances, when the minerals them- 

 selves were either in a state of fusion, or rendered soft by 

 heat. At this time I was acquainted only with the two new 

 fluids, and some of their chemical and physical properties ; 

 but when I had studied their arrangement in strata, this 

 opinion acquired additional weight. Had these cavities 

 been arranged in planes parallel to the primitive or the se- 

 condary face of the crystal, some argument might have been 

 urged in favour of their aqueous formation ; but when it 

 was found that the strata of cavities traversed the crystal 

 in all possible directions, that they were bent also into 

 curves of contrary flexure, and that even individual cavities 

 had a curvilinear shape, it was impossible to resist the 

 conclusion that the cavities were formed and thus capri- 



