"So you are really going to shoot?" said the Professor.
"If you so urge it, yes."
"Then let me suggest what to do. All savages have a keen sense of direction. It is one of their chief accomplishments. You and Harry go back, up the river, a quarter of a mile, or so, and take with you one of our coverings. Then shoot behind the blanket, so the flash will not be seen, and I will remain here and watch the effect."
There was no delay in their preparations. Within fifteen minutes the shot rang out, and almost immediately thereafter every light had disappeared. The boys were also keen enough to note the extinguished lights, and returned to the Professor in a hurry.
"The disappearance of the lights is not conclusive evidence that human beings were there. It might have been a mere coincidence."
"Coincidence! What do you mean by that?"
"Did it not occur to you that the lights might be natural phenomena?"
"Of what?"
"Of phosphorescence."
"Do you mean 'will-o'-the-wisp'?"