3B SCIENTIFIC PHYSICS U30000 Instrucciones De Uso página 3

3B SCIENTIFIC® PHYSICS
Operating instructions
1/03 ALF
Originating from the Chinese Han dynasty (206 BC - 24 AD),
the magic mirror combines optical and mechanical
principles with highly advanced metallurgy. Knowledge
of how it was made was lost during the Song dynasty
(960 – 1127) and remained a mystery until 1975. It is
only then that Chinese craftsmen and scientists were
able to rediscover the secret behind this mirror.
If sunlight or a nearly parallel light beam impinges on
this mirror and the light is reflected on to a white sur-
face, decorative patterns on the rear of the mirror be-
come visible in the image.
Description, technical data
The special features of this bronze mirror are attribut-
able to the casting and grinding techniques used to
manufacture it. The reflective body consists of a very
thin central section (60 mm Ø) embossed on the rear
and possessing a thick edge (see Figure 1a). When the
cast mirror cools, its relatively thick edge loses heat
energy more slowly than its thinner center, thus exert-
ing a moment on the center (see Figure 1b). As a re-
U30000 Magic mirror
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sult, the mirror is subjected to internal stress, which
increases during the grinding and polishing processes.
The thinnest parts of the mirror are only about 1 mm
in thickness. The thick edge presses the thinner, re-
flective material together, thus lending the mirror its
convex shape. Grinding and polishing have a more pro-
nounced effect on the mirror's thinner parts than its
thicker ones (see Figure 1c). These minimal differences
in curvature influence the quantity of light reflected
by all the various parts of the mirror on to a white
surface. As shown in Figure 2, light from the more con-
vex parts of the mirror are scattered more widely com-
pared with the less convex (thinner) parts, therefore
creating darker patches in the reflected image. This is
how the patterns on the rear of the mirror become
visible.
The mirror is stowed in a robust, wooden box with a
fabric and velvet lining.
Diameter: 75 mm
Thickness: 10 mm
Storage box: 110 mm x 110 mm x 25 mm
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