Then Bill
sighted through the unsilvered spot in the mirror and shifted the rod up
and down until the tip end came squarely in line with the door of our
straw hut, where Jack was seated, notebook in hand, to take down our
message. Reddy stood by him with his wigwag flag to answer back. When the
instrument was properly sighted the shutter was set up directly in front
of it and the sighting disk turned up to cover the point of the sighting
rod. Then came the rather troublesome task of focusing the mirror. The
mirror reflected a square panel of light, in the center of which there was
a small shadow spot made by the unsilvered peep hole. The object was to
get this shadow to fall on the center of the sighting disk. We knew that
then the mirror would reflect the sunlight squarely on the straw hut. We
found it quite easy to direct this shadow spot to the disk by holding a
sheet of paper in front of the mirror six or eight inches away, and
following up the spot on the paper until it reached the disk.
Heliograph Signaling.
[Illustration: Fig. 160. Top View, showing position of Mirror and Shutter.]
When at last we succeeded in properly focusing the mirror Bill pressed the
key down three times, sending three quick flashes to Jack as a signal that
he was ready to begin.
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