It was a weird journey.  The swaying lantern shot its beams abroad into the darkness of the great, dim galleries, casting instantaneous flashes on the objects in the cases, so that they leaped into being and vanished in the twinkling of an eye.  Hideous idols with round, staring eyes started forth from the darkness, glared at us for an instant and were gone.  Grotesque masks, suddenly revealed by the shimmering light, took on the semblance of demon faces that seemed to mow and gibber at us as we passed.  As for the life-sized models—­realistic enough by daylight—­their aspect was positively alarming; for the moving light and shadow endowed them with life and movement, so that they seemed to watch us furtively, to lie in wait and to hold themselves in readiness to steal out and follow us.  The illusion evidently affected Ruth as well as me, for she drew nearer to me and whispered: 

“These figures are quite startling.  Did you see that Polynesian?  I really felt as if he were going to spring out on us.”

“They are rather uncanny,” I admitted, “but the danger is over now.  We are passing out of their sphere of influence.”

We came out on a landing as I spoke and then turned sharply to the left along the North Gallery, from the centre of which we entered the Fourth Egyptian Room.

Almost immediately, a door in the opposite wall opened; a peculiar, high-pitched humming sound became audible, and Jervis came out on tiptoe with his hand raised.

“Tread as lightly as you can,” he said.  “We are just making an exposure.”

The attendant turned back with his lantern, and we followed Jervis into the room from whence he had come.  It was a large room, and little lighter than the galleries, for the single glow-lamp that burned at the end where we entered left the rest of the apartment in almost complete obscurity.  We seated ourselves at once on the chairs that had been placed for us, and, when the mutual salutations had been exchanged, I looked about me.  There were three people in the room besides Jervis:  Thorndyke, who sat with his watch in his hand, a grey-headed gentleman whom I took to be Dr. Norbury, and a smaller person at the dim farther end—­undistinguishable, but probably Polton.  At our end of the room were the two large trays that I had seen in the workshop, now mounted on trestles and each fitted with a rubber drain-tube leading down to a bucket.  At the farther end of the room the sinister shape of the gallows reared itself aloft in the gloom; only now I could see that it was not a gallows at all.  For affixed to the top cross-bar was a large, bottomless glass basin, inside which was a glass bulb that glowed with a strange green light; and in the heart of the bulb a bright spot of red.

It was all clear enough so far.  The peculiar sound that filled the air was the hum of the interrupter; the bulb was, of course, a Crookes tube, and the red spot inside it, the glowing red-hot disc of the anti-cathode.  Clearly an X-ray photograph was being made; but of what?  I strained my eyes, peering into the gloom at the foot of the gallows, but though I could make out an elongated object lying on the floor directly under the bulb, I could not resolve the dimly seen shape into anything recognisable.  Presently, however, Dr. Norbury supplied the clue.