Front:
SEISMOGRAPH
This instrument records severe earthquakes
in every part of the world.
THE SEISMOGRAPH AT SELFRIDGES
This instrument is capable of recording an earthquake happening in every
part of the world. When an earthquake occurs, waves of different types
are set up which penetrate the whole mass of the earth. They travel
completely through the earth in 20 mins. 18 sec. This horizontal pendulum
can 'feel' those very minute tremors, which after travelling a few thousand
miles become far too feeble to be felt by the human senses. The movements
of the pendulum are magnified and written down. The inscription is called
a Seismogram. The various types of waves travel at different speeds. The
difference in the time of recording the various waves gives the information
required for estimating the distance of the shock. The first wave to
arrive comes in a direct line from the place of occurrence. A Seismograph
is very susceptible to the SLOW waves of an earthquake, but it is
comparatively irresponsive to the RAPID tremors caused by the street traffic.
This is installed in Selfridge's Information Bureau-Third Floor.
Back:
THE SEISMOGRAPH AT SELFRIDGE'S
400 Oxford St., London, W.1.
2- 2506
