The groom proved to be a rather dull-witted fellow, and left us pretty much to our own devices.
"Ya-as—sparks—I saw 'em," he drawled in answer to Kennedy's question. "So did Mr. Gaskell. Naw—I don't know nawthin' about 'em."
He had lumbered out into another part of the stable when I heard a low exclamation from Craig, of "Look, Walter!"
I did look in amazement. There were indeed little sparks, in fact a small burst of them in all directions, where there were metal surfaces in close proximity to one another.
Kennedy had brought along with him a strange instrument and he was now looking attentively at it.
"What is that?" I asked.
"The bolometer," he replied, "invented by Professor Langley."
"And what does it do?"
"Detects waves," he replied, "rays that are invisible to the eye. For instance, just now it tells me that shooting through the darkness are invisible waves, perhaps infra-red rays."
He paused, and I looked at him inquiringly.