We came to the entrance of a tunnel. It was the cross passage leading to the cellar corridors of the palace five hundred feet away. It seemed deserted, and was very dimly illumined by hidden lights. I followed the great metal figure of Migul, which stalked with stiff-legged steps in advance of me. The arch of the tunnel-roof barely cleared the top of Migul's square-capped head.
My hand was in the side pocket of my jacket, my fingers gripping the ray cylinder for instant action. But it was a singularly ineffectual weapon for me under the circumstances, in spite of the sense of security it gave me. I could only use the cylinder against a human—and, save Tugh, it was the Robots, not the humans who were my enemies!
We had gone no more than a hundred feet or so when Migul slowed our pace, and began to walk stooped over, with one of its abnormally long arms held close to the ground. The fingers were stiffly outstretched and barely skimmed the floor surface of the tunnel. As we passed through a spot of light I saw that Migul had extended from each of the fingertips an inch-long filament of wire, like finger nails.
The Robot murmured abruptly, "Tugh's vibrations are here. I can feel them. He has passed this way recently."
ugh's trail! I knew then that Tugh's body, touching this ground, had altered to some infinitesimal degree the floor-substance's inherent vibration characteristics. Vibrations of every sort are communicable from one substance to another. Tugh's trail was here—his vibration-scent—and like a hound with his nose to the ground, Migul's fingers with the extended filaments were feeling it. What strange sensitivity! What an amazing development of science was manifested in every move and act and word of this Robot! Yet, in my own Time-world of 1935, it was all crudely presaged: this now before me was merely the culmination.
"He recently passed," said Migul. We stopped, I close beside the stooping metal figure. The Robot's voice was a furtive sepulchral whisper that filled me with awe.
"How long ago?" I asked.
"He passed here an hour or two ago, perhaps. The vibrations are fading out. But it was Tugh. Well do I know him. Put your hand down. Feel the vibrations?"