going on in Creighton's laboratory.

"Of course I can't very well get into the safety vault under the bank,"
he mused. "I wish I could."

He walked past Creighton's without seeing anything happen. The next
building was a similar two-story brick affair. A sign on it read,
"Studios and Offices For Rent."

An idea seemed to be suggested to him by the sign. He wheeled and
entered the place. Inquiry brought out a caretaker who showed us several
rooms unoccupied, among them one vacant on the first floor.

Kennedy looked it over carefully, as though considering whether it was
just the place he wanted, but ended, as I knew he intended, in hiring
it.

"I can't move my stuff in for a couple of days," he told the caretaker.
"Meanwhile, I may have the key, I suppose?"

He had paid a good deposit and the key was readily forthcoming.

The hiring of the ground floor room accomplished without exciting
suspicion, Kennedy and I made a hasty trip up to his own laboratory,
where he took a small box from a cabinet and hurried back to the taxicab
which had brought us uptown.

Back again in the bare room which he had acquired, Craig set to work
immediately installing a peculiar instrument which he took from the
package.

It seemed to consist of two rods much like electric light carbons, fixed
horizontally in a wooden support with a spindle-shaped bit of carbon
between the two ends of the rods. Wires were connected with binding
screws at the free ends of the carbon rods.

First Craig made a connection with an electric light socket from which
he removed the bulb, cutting in a rheostat. Then he attached the free
wires from the carbons to a sort of telephone headgear and switched on
the current.

"What is it?" I asked curiously.

"A geophone," he replied simply.

"And what is a geophone?" I inquired.

"Literally an earth-phone," he explained. "It is really the simplest
form of telephone, applied to the earth. You saw what it was. Any high
school student of physics can make one, even with two or three dry
batteries in circuit."

"But what does it do?" I asked.

"It is really designed to detect earth vibrations. All that is necessary
is to set the carbon stick arrangement, which is the transmitter of this
telephone, on the floor, place myself at the other end and listen. A
trained ear can readily detect rumblings. Really it is doing in a
different and often better way what the seismograph does. This
instrument is so sensitive