| Rainbow
colors
refracting through the glass. Lower image shows lighthouse bulb
through
the fresnel lens.
Lens was invented in 1790s to concentrate light
from oil torches. an electric bulb is now there.
As lens turns, beams flash past one's eye every so often. Tour guide says lens must keep turning, or
curtain must
be drawn, on sunny days. Light from the sun can be concentrated
enough
to start grass fires in the field below; like starting a fire with a
magnifying
glass. * I have
a link on this page to another site about fresnel lenses. The
owner of that site is sending me a desktop size lens in exchange. |
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