The new seismometer is developed from the original Willmore instrument, using the same principle of a suspended magnet and five spoke suspension to yield a compact portable instrument capable of either horizontal or vertical operation. In the new version the flux linkage has been more than doubled to give an e.m.f. exceeding 200 volts/m/sec. from a 500 ohm coil. A device has been introduced which enables the period to be adjusted between 0.6 and 3.0 seconds, and the use of new elastic material for the springs enables the instrument to operate without readjustment over a temperature range of ±50°C. Multi-tap coils are provided to give any desired degree of damping for a low impedance load up to critical at 0.6 second periods and up to five times critical at 3 seconds. The case has been modified to improve the water-proofing, whilst allowing access to the period and mass-position adjustments from outside.

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