DEPARTMENT OF TERRESTRIAL MAGNETISM. 357 



The magnetic storm of May 13-17, 1921, at the Watheroo Observatorj^, Austraha. W. C. 

 Parkinson. Terr. Mag., vol. 26, 26-28 (March- June 1921). 



This paper describes in detail some of the features of the unusual magnetic 

 storm of May 13-17, 1921, as recorded on the magnetograms at the Watheroo 

 Magnetic Observatory. Much of the magnetic record was lost on account 

 of the severity of the disturbance which carried the trace off the recording 

 sheet. The commencement in all three elements was very sudden at 21^ 09™ 

 (120th east meridian standard time) on May 13, with an almost immediate 

 increase in horizontal intensity, H, of about 7O7 and decrease in vertical 

 intensity, Z, of about 277. The rapid and violent movements in all elements 

 during the 4 days are described. At about 10'' on May 15 the H magnet 

 was found hard against the stops and, after being deflected back by a small 

 magnet, returned at once to the stops. The registering spot could onty be 

 made to stay on the sheet by turning the torsion head. The torsion head was 

 restored to the original reading at 19^" 24°^ on the same day, but at 16*^ on 

 May 16 the magnet was again found against the stops and was again brought 

 back by the torsion head. Following this for the next 8 hours the short- 

 period fluctuations were absent, but on May 17 after midnight until 1^^ the 

 movements were of moderately short period and Hmited range until normal 

 conditions returned. 



On the evening of May 16 there was what might have been a fine display 

 of aurora australis but for a bright moon and some clouds. Various striking 

 features were noted, some being visible as much as 15° above the horizon. 

 The appearances were, in general, of short duration. 



According to a letter of the Deputy Postmaster-General of Western Aus- 

 traha, there were on May 14, 15, and 16, earth-currents showing on the gov- 

 ernment telegraph lines of Western Australia and of South Australia. 



