"What is his game?" asked Charlie.
"I presume he wants to use the flash lamp to give a signal at night to some German submarine," said Blake quietly—very quietly, under the circumstances, it might seem.
"And you let him take a light for that?" cried Joe.
"Wait a bit!" advised Blake, and he smiled at his chum. "Do you know anything about these flashlights, Joe?"
"A little—yes. I know a powerful one, like that you gave Labenstein, can be seen a long way on a dark night."
"Well, then maybe you know something else about them, or you may have forgotten it. Like the proverb which says 'blessings brighten as they vanish,' so the light of these lamps sometimes glows very strong just before the battery goes on the blink and douses the glim."
Joe looked at his chum for a moment, uncomprehendingly, and then a smile came over his face.
"Do you mean you gave him a light with a battery in it that was almost played out?" he asked.
"Exactly," answered Blake, with another smile. "This is a light I have had for some time. I noticed, only last night, that it was brighter than usual. Just as a fountain pen—at least, the old-fashioned kind—used to flow more freely when there were only a few drops of ink left, so this battery seems to be strongest just before it gives out altogether.
"I suspected this was going to happen, but I tested the battery with a galvanometer to-day and I found out it has about ten flashes left. After that the light will be dead."