G
o
o
g
l
e
×
Please click
here
if you are not redirected within a few seconds.
All
Images
Videos
Books
Maps
News
Shopping
Search tools
Any time
Any time
Past hour
Past 24 hours
Past week
Past month
Past year
All results
All results
Verbatim
Heliograph
View all
A heliograph is a solar telegraph system that signals by flashes of sunlight reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter.
Wikipedia