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APPLTANCES USED IN EXAMINATION. 175

The QualUy of the Mirror.—These appliances should constantly be
in good condition to insure clear definition in the image. The best
kind of glasses are those in which the surface is covered by a deposit of
jTj^, YW pure silver. This furnishes a better reflect-
ing surface and is more durable than is the
so-called " silverinsr " with tin and
146.
mercury.
Magnifying lenses of about
four diameters are useful to de-
tect minute defects either in the
teeth or in the condition of pre-
vious operations upon the teeth.
They are used either directly to
magnify the parts, or else to mag-
nify the image shown on the face
of the plane mirror when direct
rays of light cannot be caught.
The latter method gives a clearer
definition than the magnified image
of the concave mirror.
The magnifying glass may be
the ordinary Avatchmaker's glass
held before the eye by the muscles
of the brow and cheek
Fig. 145.
or the lens mounted
b ^
as shown in Fig. 144.
Such glasses are indis-
pensable to the careful
practitioner, since witli
their aid defects of the
teeth and of operations
may be detected which
would escape obser-
vation by other means.
Explorers are, es-
sentially, prolongations
of the fingers ; they
convey impressions by
Magnifying lens. Explorer.
^^iQlV vibratious
their vibrations to thetO the
Self-contained
socket.
tactile nerves, and are principally intended to be
applied to parts where direct rays of light cannot reach. The forms
required are simple and few. Their points should be delicate, to enable
the smaller apertures and spaces to be entered, and are best when made