The Robot murmured abruptly, "Tugh's vibrations are here. I can feel them. He has passed this way recently."

Tugh'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?"

"I cannot. My fingers are not that sensitive, Migul."