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.