332 LETTERS ON NATUBAL MAGIC. 



Having fallen upon a method of opening the cavities, 

 and looking at the fluids, I was able to examine their 

 properties with more attention. When the expansible 

 fluid first rises from the cavity upon the surface of the 

 topaz, it neither remains still like the fixed oils, nor 

 disappears like evaporable fluids. Under the influence, 

 no doubt, of heat and moisture it is in a state of constant 

 motion, now spreading itself on a thin plate over a large 

 surface, and now contracting itself into a deeper and 

 much less extended drop. These contractions and exten- 

 sions are marked by very beautiful optical phenomena. 

 When the fluid has stretched itself out into a thin plate, it 

 ceases to reflect light like the thinnest part of the soap- 

 bubble, and when it is again accumulated into a thicker 

 drop, it is covered with the coloured rings of thin 

 plates. 



After performing these motions, which sometimes last 

 for ten minutes, the fluid suddenly disappears, and leaves 

 behind it a sort of granular residue. When examining 

 this with a single microscope, it again started into a fluid 

 state, and extended and contracted itself as before. This 

 was owing to the humidity of the hand which held the 

 microscope, and I have been able to restore by moisture 

 the fluidity of these grains twenty days after they were 

 formed from the fluid. This portion was shown to the 

 Reverend Dr. Fleming, who remarked that, had he 

 observed it accidentally, he would have ascribed its 

 apparent vitality to the movements of some of the animals 

 of the genus Planaria. 



After the cavity has remained open for a day or two, the 

 dense fluid comes out and quickly hardens into a trans- 

 parent and yellowish resinous-looking substance, which 

 absorbs moisture, though with less avidity than the other. 

 It is not volatilized by heat, and is insoluble in water 

 and alcohol. It readily dissolves, however, with efferves- 



