"Take the wheel, Walter," he muttered. "I'll tell you what turns
to make. We must get to the State line of New York without being
stopped. We can beat almost any car. But that is not enough. A
telephone message ahead may stop us, unless we can keep from being
seen."

I took the wheel, and did not stop the car as Kennedy climbed over
the seat. In the back of the car, where Mrs. Cranston was sitting,
he hastily adjusted the peculiar apparatus.

"Sounds at night are very hard to locate," he explained. "Up this
side road, Walter; there is some one coming ahead of us."

I turned and shot up the detour, stopping in the shadow of some
trees, where we switched off every light and shut down the engine.
Kennedy continued to watch the instrument before him.

"What is it?" I whispered.

"A phonometer," he replied. "It was invented to measure the
intensity of sound. But it is much more valuable as an instrument
that tells with precision from what direction a sound comes. It
needs only a small dry battery and can be carried around easily.
The sound enters the two horns of the phonometer, is focused at
the neck, and strikes on a delicate diaphragm, behind which is a
needle. The diaphragm vibrates and the needle moves. The louder
the sound the greater the movement of this needle.

"At this end, where it looks as though I were sighting like a
surveyor, I am gazing into a lens, with a tiny electric bulb close