permit you to go unmolested as soon as you have made some explanation to
me."

"If you do not unlock the door immediately I shall take this machine and
fling it through the front window out on the street. The crashing glass
on the pavement will soon bring someone to my rescue, Professor, and, as
I have a voice of my own and small hesitation about shouting, I shall
have little difficulty in directing the strangers where to come."

As Jennie spoke she moved swiftly towards the table on which stood the
strange aggregation of reflectors and bent glass tubing.

"No, no, no!" screamed the Professor, springing between her and the
table. "Touch anything but that--anything but that. Do not disturb it an
inch--there is danger--death not only to you and me, but perhaps to the
whole city. Keep away from it!"

"Very well, then," said Jennie, stepping back in spite of her endeavour
to maintain her self-control; "open the door. Open both doors and
leave them so. After that, if you remain seated in your chair, I
shall not touch the machine, nor shall I leave until I make the
explanations you require, and you have answered some questions that
I shall ask. But I must have a clear way to the stair, in case you
should become excited again."

"I'll unlock the doors; I'll unlock both doors," replied the old man
tremulously, fumbling about in his pockets for his keys. "But keep away
from that machine, unless you want to bring swift destruction on us
all."

With an eagerness that retarded his speed, the Professor, constantly
looking over his shoulder at his visitor, unlocked the first door, then
hastily he flung open the second, and tottered back to his chair, where
he collapsed on the tiger skin, trembling and exhausted.

"We may be overheard," he whined. "One can never tell who may sneak
quietly up the stair. I am surrounded by spies trying to find out what I
am doing."

"Wait a moment," said Jennie.

She went quickly to the outer door, found that it closed with a spring
latch, opened and shut it two or three times until she was perfectly
familiar with its workings, then she closed it, drew the inner door
nearly shut, and sat down.

"There," she said, "we are quite safe from interruption, Professor
Seigfried; but I must request you not to move from your chair."

"I have no intention of doing so," murmured the old man. "Who sent you?
You said you would tell me. I think you owe me an explanation."

"I think you owe me one," re