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.  Reddy wigwagged back O. K., and then the first heliographic message was sent from the ledge to the island.  It was a rather mixed-up message, and kept Jim and Reddy wigwagging back and forth very strenuously to straighten matters out.  It was my duty to keep the mirror focused.  As the sun moved across the sky the shadow spot would move off the disk, and I had to keep shifting the mirror to bring the spot back where it belonged.  We used the International Telegraph Code, which we had been studying every evening for a week, but it was many weeks before we learned how to use it correctly, even slowly.  The International Telegraph Code is as follows: 

A . — B — . . .  C — . — .  D — . .  E — F . . — .  G — — .  H . . . .  I . .  J . — — — K — . — L . — . .  M — — N — .  O — — — P. — — .  Q — — . — R . — .  S . . .  T — U . . — V . . . — W . — — X — . . — Y — . — — Z — — . . 1 . — — — 2 . . — — — 3 . . . — — 4 . . . . — 5 . . . . . 6 - . . . . 7 - . . . 8 - - - . 9 - - - - . 0 — — — — —

The three short flashes Bill sent represented the letter S, which stood for the word “signal.”  A was formed by a short flash followed by a long flash; B by a long flash followed by three short ones, and so on.  The key was held down three times as long for the long flash as for the short one.  We found the best way of learning to send the signals properly was to count 1 for each short flash, and for each pause between parts of the letter, and 3 for each dash and for each pause between letters.  Between words we counted 6.  Thus, for the letter A the key would be down when we counted 1, up when we counted 2, down while we counted 3, 4, 5, and up while we counted 6, 7, 8, for the pause after each letter.  It was rather a confusing code, I admit, but in time we mastered it, all but Reddy and Fred, who never would learn, but instead used the wigwag code, letting a short flash stand for 1, a long flash for 2 and a double long flash for 3.

The Double Mirror Instrument.

[Illustration:  Fig. 161.  The Double Mirror Instrument.]

Our heliographing instrument did excellent service sending flashes from the cliff to the island, but we couldn’t make it work very well sending messages from the island to the cliff, because we had to face almost due north, and then the sun was nearly always at our backs and couldn’t shine squarely on the mirror.  This led to our building a double mirrored heliograph the following summer.  To begin with, we built an instrument which was the exact duplicate of our first heliograph; then, in addition,