MAGNETIC STORM.

Horowhenua Chronicle, 4 May 1937, Page 8

MAGNETIC STORM.

DISTURBS TELEGRAPH EXPERIENCES IN SOUTH ISLAND. An electrical phenomenon not observed by the generality of people, but nevertheless of sufficient importance todisturb the smooth-working of parts of the Dominion’s telegraphic 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 continue! on the. following day and then began 1o diminish. Fortunately these earth currents do not maintain high intensity for great, lengths of time, but they are sufficiently strong to interfere with teleghaph. operating by introducing into the circuit unexpected (ferreuts mhking a. 'signal quite unlike that which theoperator has sent through the medium, of the Morse key. Telephoning is done on a completemetallic circuit and cannot be: interrupted by earth currents, but telegraphic 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 theearth) reliable communication, is interrupted. In such an emergency the post, office utilises complete metallic cir-: cults for its telegraph signals, though, these are not normally heeded. Sobusiness 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 tele--graph working in New Zealand suggests that they are most in evidehee when there are bright displays ,of theAurora Australis, although tnis is not invariably the case. It is, however, a, well proved fact that their influence is stronger on telegraphic circuits,, Christchurch-Greymouth- W estport were subjected to the greatest interruption,, although on the second day it waa; found that earth currents were fairly general throughout New Zealand and. most marked §o 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. The experiment 'Whs then tried , of switching out the battery "current from, the telegraph wire between Christchurch: and Greymouth and putting a Morse key into what would normally 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 tothe West Coast. These magnetic disturbances usually make an occasional appearance for two years, after which there is an interval of about five years, before their re-appearance. The emergency method of maintaining communication when earth currents interrupt the normal telegraph circuit, has been mentioned, but the post office has in hand a comprehensive programme for utilising the multiple voice-fre-quency 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 providing a means of telegraphic communication over a. complete metallic circuit. Magnetic storms may send their disturbing influences through the earth, but the voice-frequency circuit being carried completely along wires, runs no risk of receiving- these variable currents So perplexing .to Morse operators using., earth-return circuits.