“What I can’t understand,” he said, “is the ease with which we’ve got away with it. Now if I’d been Kar—”
“But you’re not. Get to the point, man. What did we discover?”
“Ah me, these excitable, highly-strung Nordic races!” sighed Duval. “What we did was to make a type of low-powered radar set. Besides radio waves of very high frequency, it used far infrared — all waves, in fact, which we were sure no creature could possibly see, however weird an eye it had.”
“How could you be sure of that?” asked Stormgren, becoming intrigued by the technical problem in spite of himself.
“Well — we couldn’t be quite sure,” admitted Duval reluctantly. “But Karellen views you under normal lighting, doesn’t he? So his eyes must be approximately similar to ours in spectral range. Anyway, it worked. We’ve proved that there is a large room behind that screen of yours. The screen is about three centimetres thick, and the space behind it is at least ten metres across. We couldn’t detect any echo from the far wall, but we hardly expected to with the low power which was all we dared use. However, we did get this.”
He pushed across a piece of photographic paper on which was a single wavy line. In one spot was a kink like the autograph of a mild earthquake.
“See that little kink?”
“Yes; what is it?”
“Only Karellen.”
“Good Lord! Are you sure?”