“Look at it,” he added, handing it to her.

Long Sin took a bladder of water from a table nearby and concealed it under his coat.  “Now, you stab me,” he directed.

Mary hesitated.  But he repeated the command and she plunged the knife gingerly at him.  It telescoped.  He made her try it over and she stabbed more resolutely.  The water from the bladder poured out.

“Good!” cried Long Sin, much pleased.  “Now,” he added, seating himself beside her, “I want you to lure Elaine here.”

Mary looked at him inquiringly as he returned the knife to its scabbard on the wall.  “Remember where it is,” he continued.  “Now, if you will come into the other room I will show you how to get her.”

I had been amusing myself by rigging up a contrivance by which I could make it possible to see through or rather over, a door.  The idea had been suggested to me by the cystoscope which physicians use in order to look down one’s throat, and I had calculated that by using three mirrors placed at proper angles, I could easily reflect rays down to the level of my eye.

Kennedy, who had been busy in the other end of the laboratory, happened to look over in my direction.  “What’s the big idea, Walter?” he asked.

It was, I admit, a rather cumbersome and clumsy affair.

“Well, you see, Craig,” I explained, “you put the top mirror through the transom of a door and—­”

Kennedy interrupted with a hearty burst of laughter.  “But suppose the door has no transom?” he asked, pointing to our own door.

I scratched my head, thoughtfully.  I had assumed that the door would have a transom.  A moment later, Craig went to the cabinet and drew out a tube about as big around as a putty blower and as long.

“Now, here’s what I call my detectascope,” he remarked.  “None of your mirrors for me.”

“I know,” I said somewhat nettled, “but what can you see through that putty blower?  A key hole is just as good.”

“Do you realize how little you can really see through a key hole?” he replied confidently.  “Try it over there.”

I did and to tell the truth I could see merely a little part of the hall.  Then Kennedy inserted the detectascope.

“Look through that,” he directed.

I put my eye to the eye-piece and gazed through the bulging lens of the other end.  I could see almost the whole hall.

“That,” he explained, “is what is known as a fish-eye lens—­a lens that looks through an angle of some 180 degrees, almost twice that of the widest angle lens I know of.”

I said nothing, but tossed my own crude invention into the corner, while Craig went back to work.

Elaine was playing with “Rusty” when Jennings brought in a card on which was engraved the name, “Miss Mary Carson,” and underneath, in pencil, was written “Belgian Relief Committee.”

“How interesting,” commented Elaine, rising and accompanying Jennings back into the drawing room.  “I wonder what she wants.  Very pleased to meet you, Miss Carson,” she greeted her visitor.