human
Look there, Harry! he said.
gpt
Do you see the sun flashing on something on the roof of that house over there? What do you suppose that is?
human
Whew! Harry whistled.
gpt
You ought to know that, Dick! A heliograph--field telegraph. Morse code--or some code--made by flashes. The sun catches a mirror or some sort of reflector, and it's just like a telegraph instrument, with dots and dashes, except that you work by sight instead of by sound. That _is_ queer! Try to mark just where the house is, and so will I.