Marvels of the Universe 759 
in the atmosphere is deter- 
mined by its particular 
shape, that is to say, all 
prism-shaped crystals will 
occupy the same position, 
while all other shaped crys- 
tals will occupy different 
planes, and will therefore 
be negligible quantities in 
the effect produced. Again, 
the light must vibrate a 
definite number of times 
before it is in a fit condi- 
tion to be absorbed and 
reflected by the ice-prisms, 
and that means that only 
those crystals which are 
distant twenty-three de- 
grees from the luminary’s 
dise are available for 
“mediums” in the trans- 
mission of light. To sum 
up, it is the presence of 
innumerable prism-shaped 
STIBNITE CRYSTALS. 
Crystals most dissimilar in outward appearance may be found to have the adjacent 
ice-crystals in the atmo- 
sphere, situated aye al given sides forming equal angles, and are therefore considered to belong to the same family. 
Stibnite is a member of the hexagonal group. 
distance from the sun or 
moon’s disc and held in suspension at a particular angle, and so refracting the light directly to the 
observer, that produces the solar or the lunar halo. 
CRYSRAIES 
BY RICHARD KERR, F.R.A.S., F.G.S. 
CRYSTALS, owing to their peculiarly matchless beauty and durability, are the objects of costly 
ambition to the rich as well as the admiration of all classes of people. 
We are indebted to Pliny the Second for putting together in a work an almost complete and 
compendious account of all the stores of information regarding the mineral kingdom extant in the 
first century A.D. From this justly-celebrated work, the Historia Naturalis, a true idea may be 
formed of the high estimation in which ornamental stones were held by the Greeks and Romaps. 
It is noteworthy that all the stones that are most highly valued are either transparent or 
translucent. 
Great heat on a scale beyond the powers that man can employ, together with a pressure equally 
unattainable by man, must have been two, at least, of the great agents employed in Nature in order 
to reduce the elements of which precious stones are constituted to a condition of vapours or liquids. 
The substances destined, if we may so put it, to become the composition of precious stones or 
crystals and to render them homogeneous throughout, could not have been mixed together 
mechanically by the grinding together of solid materials. Nature is an extensive laboratory with 
ample means for effecting marvellous changes. In conjunction with the two agents already named, 
electricity and magnetism may have been employed. 
