376 LETTERS ON NATURAL MAGIC. 



causes. Fluids and vapours of a similar character exist 

 in the very gems and precious stones which science has 

 contributed to luxury and to the arts. 



In examining with the microscope the structure of 

 mineral bodies, I discovered in the interior of many of the 

 gems thousands of cavities of various forms and sizes. 

 Some had the shape of hollow and regularly-formed 

 crystals : others possessed the most irregular outline, and 

 consisted of many cavities and branches united without 

 order, but all communicating with each other. These 

 cavities sometimes occurred singly, but most frequently in 

 groups forming strata of cavities, at one time perfectly flat 

 and at another time curved. Several such strata were 

 often found in the same specimen, sometimes parallel to 

 each other, at other times inclined, and forming all 

 varieties of angles with the faces of the original crystal. 



These cavities, which occurred in sapphire, chrysoberyl, 

 topaz, beryl, quartz, amethyst, peridot, and other substances, 

 were sometimes sufficiently large to be distinctly seen by 

 the naked eye, but most frequently they were so small as 

 to require a high magnifying power to be well seen, and 

 often they were so exceedingly minute that the highest 

 magnifying powers were unable to exhibit their outline. 



The greater number of these cavities, whether large or 

 small, contain two new fluids different from any hitherto 

 known, and possessing remarkable physical properties. 

 These two fluids are in general perfectly transparent and 

 colourless, and they exist in the same cavity in actual 

 contact, without mixing together in the slightest degree. 

 One of them expands thirty times more than water ; and at 

 a temperature of about 80 of Fahrenheit it expands so as 

 to fill up the vacuity in the cavity. This will be under- 

 stood from the annexed figure, where A B D is the 

 cavity, m n p o the highly-expansible fluid in which at low 

 temperatures there is always a vacuity V, like an air-bubblo 



