t would
have thrown the case into one of the unsolved mysteries. Electricity is
a dangerous tool in the hands of clever crooks."

"It leaves no trace!" said Delaney, rising and standing by his chief.
"It isn't made out of anything except little shakes in the wire or
something like that."

Drew smiled good-naturedly. "It's a mystery to most people," he said,
turning toward the windows and listening. "It's a bigger mystery to a
woman than to a man," he added. "It's a good agent if properly used and
kept within bounds. It brings back life as well as takes it. It creates
and also destroys. No one knows what it is. All that we do know about
it is its action on material substances--the power to transform
mechanical energy into vibrations and then back again into mechanical
energy."

"Like a voice on a wire?" asked Loris.

"Yes, Miss Stockbridge. The mechanical vibration of a diaphragm in a
telephone transmitter is changed to electrical vibrations, passes along
a wire and changes back to the same thing we had at the beginning.
Cuthbert took advantage of this fact. All that was sent into the
library was Morphy's voice on the wire. The wire left no trace. The
voice actuated the diaphragm and at the same time the fine heating coil
at the cap on the cartridge. The energy of the voice was sufficient to
raise the temperature of the coil. This raise in temperature flashed
some compound set in the wire. The flash started the fulminate of
mercury in the cap. The cap exploded the smokeless powder. It was a
series of steps each a little higher than the one below it."

"Was there any other way of doing the same thing?" Nichols inquired, as
he rose lankily and stood over Loris.

"Yes!" declared Drew. "I can look back over what I found in the
technical books about electricity and telephony and see several other
ways for Cuthbert to accomplish the same result. The electrical pistol
did not necessarily have to be actuated by the human voice."

"How terrible!" Loris whispered, with her brow puckering. "Perhaps
others will use the same idea to slay their enemies."

"We'll keep it a close secret," the detective said. "It rests with us
four, now. Outside of us, there is only Morphy who knows."

"How else could the pistol be discharged?"

"Two other ways that I see, Miss Stockbridge. It would be rather easy
to arrange a little magnetic trigger in the receiver. This trigger
could be actuated by an excess of current--say the connecting o