melted before the oxyhydrogen blowpipe. The simple silicates, ternary bodies, are fusible at a much lower temperature; and the multiple silicates offer no serious resistance.
temperature of fusion of precious stones, since it is allied in a
remarkable manner with their hardness, serves as a good characteristic
for distinguishing them.
a luminous ray passes through a homogeneous medium, its course is in a
straight line, as shown in Fig. 16, a phenomenon with which everyone is
familiar. But when it passes from one medium into another, the case is
generally different, and the ray suffers a remarkable modification. It
is then more or less diverted from its primitive direction, and has the
appearance of being broken, whence the phenomenon has been termed refraction. A stick plunged into water will exemplify this effect.
extent to which the luminous rays are diverted in traversing
transparent bodies varies greatly. This variation is generally
connected with differences in the nature and composition of the
refracting bodies; but it is likewise intimately connected, as
experiments prove, with the molecular