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and Power Co. Ltd., by a rotary converter. For rectifying alternating current the converter has proved more economical than Nodon Valves, which were used only for charging the high tension battery of the radio receiving set, for which purpose the converter is unsuitable. Becoming gradually less efficient the valves were finally discarded in July in favour of a Tungar rectifier, which has worked satisfactorily.
IX.-MISCELLANEOUS.
Seismograph. The Milne-Shaw seismograph received in December, 1922, was set up on the west side of the seismograph pier in the newly completed Underground Room on May 3. It is orientated to record movements in an East-West direction. The instrument received in September 1921 remained on a temporary mounting until August 8, in order that its records might be compared with those of the new instrument on the underground pier. It was then set up parallel to the new instrument on the same pier.
An examination of the records showed that during an earthquake, the movements of the two pendulums side by side, though generally similar, were not identical.
The older pendulum was mounted in its final position at right angles to the other pendulum on September 3, thus completing the outfit for obtaining the north and east components of earth movements.
The result of comparisons of the records of the instrument on the temporary and permanent mountings is given below :--
Phenomenon. Temporary mounting. Underground Pier. Diurnal Tilt. Very marked; magnitude depending on daily range of temperature. So small as to be usually unmeasurable. Effect of typhoons. Very marked; large irregular movements superposed on tremor storms. Only slight tremor storms. Tremor Storms. Very marked; fairly frequent and occasionally lasting for several days at a time. Very slight; only occasional. Irregular microseisms. Very marked; fairly frequent and occasionally lasting for several days at a time. Very slight; only occasional.