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The circle is an ellipse with coinciding focuses.
In the ellipse, the focuses become further apart
as the ellipse gets longer until it becomes a parabola with only one focus
(the other one has, so to speak, become infinite).
The infinite rays that come from this focus are parallel lines.
Reflecting on the parabola, they gather in the actual focus.
Therefore, if we want to gather parallel lines (or
practically parallel, like sun-rays),
in a given point, we'll need to use a glass the shape of a parabola.
By doing so, it is possible to construct a burning mirror,
capable of lighting a piece of paper or wood put in its focus.
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The legend according to which Archimedes (III sec. B.C.) burnt Roman ships with a
burning mirror
gave rise to a considerable amount of reseach
up until the late 17th century.
In our exhibit, the heat generated by a bulb put in the focus of a mirror,
manages to light a match in the focus of another mirror.
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