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GLOSSARY.
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295
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Lithospheee.—The region of land, as distinguished from air
and water. Magma.—The rock-bulk. Crystals separating from the Magma
are those that crystallise out while the bulk of the rock is
in a fluid or semi-fluid condition. Mammilated.—Having the rounded form of the mamma or
breast. Meniscus.—A solid contained between two surfaces of different
curvatures, or between two such surfaces and the surface
of a cylinder; the former is thicker in the centre than at
the edges, while the reverse is the case in the latter form. Milling Cutter.—A wheel «,rmed with cutting edges arranged
like the teeth of a circular saw and so mounted that it can
be made to move in a required direction while rotating. Mineral.—A homogeneous substance formed without the
agency of organic life ; it is of definite composition and
usually of definite form. Mineral Veins.—Fault fissures which have been filled with
mineral matter, usually that deposited from uprising heated
water. Molecule.—The smallest amount of a chemical substance
that can exist by itself. Monochromatic.—Of one colour. Newton's Eings.—Rings of coloured light seen when a thin
film of air, or other matter, is left between two surfaces
separated by a very small distance from one another. Normal.—At right angles. Thus, a plane normal to an axis of
a crystal is so placed that any line in the plane is at right
angles to that axis. Optically Denser Medium.—A substance through which
light waves travel with less rapidity than they do through
the standard substance. Optically Barer Medium.—A substance through which light
waves travel with greater rapidity. Osmosis.—A force which impels a solvent through a semipermeable medium, from a less concentrated solution to a
more concentrated.
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