Watheroo Magnetic Observatory April to June, 1933

April 30‐May 2 1933—This magnetic storm of moderate intensity began at 16h 27m 50s on April 30 with a sudden commencement which was very definitely recorded in all three elements. During the half‐hour preceding the commencement there appeared on all the traces rapid fluctuations of small amplitude; the la Cour rapid trace showed the period of these oscillations to be about 90 seconds and their average amplitude (semi‐range) about 2γ. In the sudden commencement a decrease in H of about 2γ was followed immediately by an increase of 33γ within 5 minutes. In Z the initial impulse represented a slight increase of the force followed by a decrease of 12γ in six minutes. The declination increased westerly at the time of commencement and immediately showed an easterly swing of about one minute of arc in three minutes of time. Irregular movements of only moderate intensity follow in all three elements and continued until 0h 30m on May 1; then followed a quiet period of 12 hours after which what was presumably the same disturbance again became manifest by large irregular movements in all elements, continuing until 2h on May 2 when the traces resumed their normal appearance. It is during this last period of the disturbance that the maximum ranges occurred. The ranges were: Declination 24″; horizontal intensity, 125γ; vertical intensity, 144γ. Time of commencement was taken from the la Cour horizontal‐intensity trace; the Mitchell inductometer showed time of commencement also as 16h 27m 50s. All times are Greenwich mean time.