The frank, "Yes," of the young fellow was convincing enough.

"What I want," pursued Kennedy, "is to have some one inside this
house who can tell me as much as he can see of the visitors, the
messengers that come here this morning. It will be an act of
loyalty to your employer, so that you need have no fear about
that."

Edward bowed, and left us. While I had been seeking him, Kennedy
had telephoned hastily to his laboratory and had found one of his
students there. He had ordered him to bring down an apparatus
which he described, and some other material.

While we waited Kennedy sent word to Pitts that he wanted to see
him alone for a few minutes.

The instrument appeared to be a rubber bulb and cuff with a rubber
bag attached to the inside. From it ran a tube which ended in
another graduated glass tube with a thin line of mercury in it
like a thermometer.

Craig adjusted the thing over the brachial artery of Pitts, just
above the elbow.

"It may be a little uncomfortable, Mr. Pitts," he apologised, "but
it will be for only a few minutes."

Pressure through the rubber bulb shut off the artery so that
Kennedy could no longer feel the pulse at the wrist. As he worked,
I began to see what he was after. The reading on the graded scale