“What is it?” he asked, after looking in the direction for a few moments. “I can see nothing.”
“Wait! Watch!” Galabin returned in an excited whisper. “There! Look! Above the wall,” he continued as Von Tressen made no response. “There! again!”
“It was nothing but a bird flying over——”
“Yes, a bird. You saw it plainly?”
“Quite.”
“For how long?”
“For a second.”
“Why no longer?” Galabin asked, with the triumphant satisfaction bred of a discovery.
“The bird was lost in the darkness.”
“And yet it flew nearer to us. Ah, there is the same thing again! How did we see it at all, my friend? I’ll tell you. The bird was attracted by and flew over a light. A vertical shaft of light this time; not strong enough to be apparent of itself from here, and only to be detected by the evidence of an object passing through it. Now, watch again.”