384 LETTERS ON NATURAL MAGIC. 



spheres, all of which are moveable within the cavity. In 

 some cavities the two new fluids occur in an indurated 

 state, and others I have found to be lined with a powdery 

 matter. This last class of cavities occurred in topaz, and 

 they were distinguished from all others by the extraordi- 

 nary beauty and symmetry of their form. One of these 

 cavities represented a finely-ornamented sceptre, and, 

 what is still more singular, the different parts of which it 

 is composed lay in different planes. 



When the gem which contains the highly-expansive 

 fluid is strong, and the cavity not near the surface, heat 

 may be applied to it without danger ; but in the course of 

 my experiments on this subject, the mineral has often 

 burst with a tremendous explosion, and in one case 

 wounded me on the brow. An accident of the same kind 

 occurred to a gentleman, who put a crystal into his mouth 

 for the purpose of expanding the fluid. The specimen 

 burst with great force and cut his mouth, and the fluid 

 which was discharged from the cavity had a very disagree- 

 able taste. 



In the gems which are peculiarly appropriated for 

 female ornaments, cavities containing the expansible fluid 

 frequently occur, and if these cavities should happen to be 

 very near the surface or the edge of the stonej the fever f 

 heat of the body might be sufficient to burst them with an 

 alarming and even dangerous explosion. I have never 

 heard of any such accident having occurred ; but if it has, 

 or if it ever shall occur, and if its naturally marvellous 

 character shall be heightened by any calamitous results, the 

 phenomena described in the preceding pages will strip it 

 of its wonder. 



There are no facts in chemistry more interesting than 

 those which relate to the changes of colour which are 

 produced by the mixture of fluids, and to the creation of 

 brilliant colours by the combination of bodies in which no 



