At breakfast time, Thursday morning, just at the change of shift, the geophone expert reported voices.
There was a tense five minutes as the geophone expert listened.
Nothing at all of any value was being recorded by the geophone when Kennedy glanced quickly at his watch.
The geophone expert was at his bedside, waiting impatiently.
"The vibrodyne machine isn't running," he remarked finally after repeated adjustments of the geophone.
The first geophone used by the western powers in the war was invented by the French.
We entered our bare little room and Kennedy set to work as though to detach the geophone, while I explained it to our client.
If the enemy were burrowing in the ground anywhere within a distance of 75 yards the geophone would tell about it.
"That's what the geophone man heard," Owens commented to the reporter.
An electronic receiver designed to pick up seismic vibrations on or below the Earth's surface and to convert them into electric impulses that are proportional to the displacement, velocity, and acceleration of ground movement. Geophones detect motion in only one direction and are usually used in groups of at least three, oriented at different angles, so that a three-dimensional record of ground movement can be obtained.