in the pendulums, to prevent them from continuing to vibrate
after the first shock. Thus they are ready in an instant to
record another tremor. Other seismographs continue to vibrate for
a long time as a result of one tremor only. Besides, they give
little indication of the direction from which the tremors come.

"I think you must all appreciate that your tiptoeing up the hall
must cause a far greater disturbance in this delicate seismograph
than even a very severe earthquake thousands of miles away, which
it was built to record."

He paused and examined the papers sharply.

"This is the record made by the 'ghost's' walk the other night,"
he said, holding up two of them in his left hand. "Here on the
table, on two other longer sheets, I have records of the
vibrations set up by those in this room walking to-night.

"Here is Mr. Jameson's--his is not a bit like the ghost's. Nor is
Mr. Vandam's. Least of all are Dr. Hanson's and Inspector
O'Connor's, for they are heavy men.

"Now here is Mr. Farrington's"--he bent down closely, "he is a
light man, and the ghost was light."

Craig was playing with his victim like a cat with a mouse.

Suddenly I felt something brush by me, and with a swish of air
and of garments I saw Mrs. Popper fling herself wildly at the
table that bore the incriminating records. In another instant