410 
HYDROPHANE. 
pletely transparent after they had been for some 
time in the acid. If is said he made the most of 
his discovery, and to augment the price of his stones 
gave them the pompous title of eye of the world ; 
and they are still very generally known both in Ger- 
many and other countries, by the name of oculus 
mundi or lapis mutcibilis. 
Mere infusion in any aqueous fluid is enough to 
render this stone transparent, and therefore water is 
commonly used as the most convenient for the pur- 
pose. As soon as the hydrophane is put into water 
it exhales a musty smell, several bubbles of air 
arise, and it gradually becomes transparent. Some of 
these stones are colourless when transparent, while 
others assume different tints, such as yellow or red ; 
and some acquire a beautiful mother of pearl co- 
lour. Engerstrom notices the hydrophanes which 
are preserved in the British Museum, the largest of 
which is about the size of a cherry-stone, though of 
an oval shape. It is opaque, and its colour like 
that of a common yellow pea. When this stone 
has lain in water some hours it becomes transparent, 
and of a yellow amber colour. This change begins 
soon after the emersion, and at one end in the form 
of a little spot, which increases by slow degrees 
until the whole of the stone has become uniformly 
clear throughout : when taken out of the water it 
loses its transparency, first at one end, and then 
gradually over the remainder, until the whole stone 
has recovered its former opacity; and this change is 
effected in less time than the other. 
