MAGNETIC STORM

Nelson Evening Mail, Volume LXXI, 4 May 1937, Page 9

MAGNETIC STORM

DISTURBS TELEGRAPH WORKING i EXPERIENCES IN THE SOUTH ISLAND An electrical phenomenon not observed by the generality of people, but nevertheless of sufficient importance to disturb the smooth-working of parts of the Dominion’s telegraph system, occurred early last week when the Christchurch Telegraph Office reported to the General Post Office that heavy earth currents were being experienced on all circuits from that city to the West Coast. This continued on the following day and then began to diminish. Fortunately these earth currents do not maintain high intensity for great lengths of time but they are sufficiently strong to interfere with telegraph operating by introducing into the circuit unexpected currents making a signal quite unlike that which the operator has sent through the medium of the morse key. Telephoning is done on a complete metallic circuit and cannot be interrupted by earth currents, but telegraph signals, it should be explained, are sent along a single wire and the return is through the earth. When there are electrical impulses in both sides of the circuit (controlled signals on the wire and uncontrolled ones in the earth) reliable communication is interrupted. In such an emergency the Post Office utilizes complete metallic circuits for its telegraph signals though these are not normaly needed. So business goes on and the electrical disturbances in the earth do not interfere with the messages. A long experience of the effect of earth currents on telegraph working in New Zealand suggests that they are most in evidence when there are bright displays of Aurora Australis, although this is not invariably the case. It is, however, a well proved fact that their influence is stronger on telegraphic circuits running east and west. In the recent occurrence the telegraphic circuits, Christchurch-Greymouth-Westport were subjected to the greatest interruption, although on the second day it was found that earth currents were fairly general throughout New Zealand and most marked so far as the North Island is concerned in working the morse from Wellington to Hawera. Some years ago earth currents between Christchurch and the West Coast

of the South Island became so strong that telegraph signals could not be reliably exchanged between these points. j The experiment was then tried of j switching out the battery current from | the telegraph wire between Christ- j church and Greymouth and putting a j morse key into what would normally ii; be a dead circuit. The strong earth currents then prevailing entered the wire so that by making and breaking the circuit between earth and wire a Morse instrument transmitted readable | signals to the West Coast. These mag- j netic disturbances usually make an j occasional appearance for two years, | after which there is an interval of i about five years before their re-appear- | ance. j The emergency method of maintain- | ing communication when earth currents j interrupt the normal telegraph circuit j has been mentioned, but the Post Office j has in hand a comprehensive pro- j gramme for utilising the multiple voice-frequency system on its principal telegraph circuits. The term “voice frequency” is used because it is a channel of ordinary speech split into a [ number of narrow tracks, each provid- ij ing a means of telegraphic comnumi- j cation over a complete metallic circuit. [j Magnetic storms may send their dis- | turbing influences through the earth, II but the voice-frequency circuit being j carried completely along wires, runs no j risk of receiving these variable currents so perplexing to morse operators j! using earth-return circuits. j