KOTES ON THE ^MAGNETIC STORM OF SEPTEMBER 25TH, 



1909. 



Bv G. W. HoPKiNSON. A.M.I.E.E. 



On Saturda}/, September 25th, at about 2 p.m., it was noticed 

 in the Central Telegraph Office (Bloemfontein) that all the telegraph 

 lines were affected in a peculiar manner. At first it appeared as 

 though the lines were all in contact, but on further investigation 

 it was found that what we generall}^ term " Earth Currents " were 

 present on all the lines, or, to use another expression, a " Magnetic 

 Storm. " was in progress. On communicating with Cape Town, 

 Johannesburg. Kimberley and Port Elizabeth they all mentioned 

 that they were affected. 



I took measurements of the currents and found as follows : — On 

 a line to Brandfort. a distance of 35 miles, the current varied 

 from 5.5 milhamperes positive to the same negative, and remained 

 fairly steady for about 20 seconds at 2 milhamperes. On a line 

 to Kroonstad, a distance of 120 miles, the current varied from 3 

 milhamperes positive to the same negative, and, as in the former 

 case, remained fairly steady at 2 milhamperes for periods of about 

 20 seconds. On a line to Harrismith, about 200 miles in length, 

 practically the same readings were given on the miliammeter, and 

 on a line to Port Elizabeth, 450 miles in length, the milliammeter 

 registered up to 4 milhamperes. The difference in length of the 

 lines did not appear to make much difference in the strength of the 

 current — in fact, when changing the meter quickly from one line 

 to another the same reading continued. 



I particularly noticed that the currents were both positive and 

 negative, and I had continually to reverse my meter to take the 

 different readings. 



I compared my notes with a colleague, who had also taken read- 

 ings, at Kimberley, and his notes gave the strength of the current 

 on a line from Kimberley to Warrenton, 45 miles in length, as 

 10 milhamperes at one time during his test ; the reversing of the 

 current was also noted by him. 



The disturbances ceased late in the evening, and on Sunday 

 morning the lines were quite clear. 



To give an idea of the strength of these currents I might mention 

 that the usual current for telegraph purposes is from 17 to 20 

 milhamperes, and that in an ordinary incandescent lamp is about 

 500 milhamperes or half an ampere, the ampere being one-tenth 

 of the absolute unit of current strength. 



THE AURORA AUSTRALIS IN LOW LATITUDES.— 



The Aurora Australis which occurred on the evening following the 

 magnetic storm of September 25th, 1909, was seen at Bloemfontein by 

 Mr. Arthur Stead, B.Sc. Bloemfontein is in latitude 29° 7' S. and is 

 about 250 miles from the sea. It is believed that this is the first 

 recorded occasion of an aurora being seen in such a low latitude. 

 In a letter published in Nature of October 21st, 1909, Mr. W. 



