ELECTRICITY IN THE AIR

Otago Daily Times, Issue 22293, 20 June 1934, Page 9

ELECTRICITY IN THE AIR

A STUDY OF THUNDERSTORMS SOME LITTLE-KNOWN FACTS. The address which was given at the meeting o£ the Astronomical Institute last night was of unusually wide interest, the lecturer (Dr W. A. Macky) choosing as big subject “ Thunderstorms and the Electricity of the Atmosphere.” Dr Macky, who is lecturer on physics at the University of Otago, was, until recently engaged in research on the subject at Cambridge University under Professor Wilson, the world’s greatest authority on the questions with which the address dealt. It was. about 300 years, said Dr Macky, since the first record on lightning had been taken by an Englishman named Gray, who had suggested that it was merely a large-scale effect of sparks such as one saw issuing from an electrical machine, and in 1752 Franklin, an American, had shown that electricity Could be drawn from the clouds by means of kites. During the next 40 years many observations bad beeu made with crude instruments, but little had then been done until 3860,' when Lord Kelvin had revived the whole subject and had invented an instrument called the “water dropper,” which measured the eleertieity in the air, and actually was largely in use to this day. The first self-recording instrument of this type had been installed at Kew in 1801, and had been in action ever 1 since; giving the longest series of unbroken measurements in the world.

There was a current of electricity continually flowing from the air into the earth, said Dr Macky, and its value was found to be close to 1000 amperes over the whole earth. The great problem was where this came from, and it might not be solved for some time. The gradient varied throughout the day, but it had been shown that the variation was such that the maximum occurred at the same time all over the earth—about 6 o’clock in the morning in New Zealand. Proceeding to deal with thunderstorms, the lecturer stated that it had been shown that when they occurred there were up-currents of air. This was shown by the fact that airships became out of control and were earned upwards. Incidentally, some thunderstorms were the source of all the atmospherics that one heard on the wireless, and this fact had been used to detect from what point storms were coming. It was hoped that it would be possible to give warning of storms in the Tasman Sea. It had been proved by means of experiments that the discharge.,of electricity jn a flash of lighting amounted to 1,000,000,000 volts, the current reaching the earth varying from 20,000 to 100,000 amperes. If one bad to pay for the current the cost would be £SO. ,

Dr Macky went on to refer to the examinations of the progress of lightning flashes that had been made by means of rotating cameras. Schonland had been able to show, by means of experiments in South Africa, that those people who had talked of thunderbolts and.fireballs had been nearer* the truth than they had imagined. Schonland bad discovered that in many cases the first discharge of lightning consisted of a “leader stroke,’* which travelled to the earth at 5000 miles an hour. It blazed a trail through which the stroke returned at the increased rate of 30,000 miles an hour. Turning to the frequency with which thunderstorms occurred in various parts of the world, Dr ■ Mack}' stated that in Sumatra and Java, as well as in Panama, there were 250 days in the year on which thunderstorms occurred, whereas in Dunedin there were less than five. Ip New Zealand the number of days on which there were thunderstorms varied from five to 20, the furthest north aud_to the west coast of the South Island having the greatest number. In New Zealand very little damage was caused, parly because here were fewer people to be hit than in some other parts of the earth. Seven people had been killed by lightning in }sew Zealand ip the first 25 years of this century, with an average death rate of .26 per 1.000,000 persons a year. In the United States, however, five out of every 1,000,000 persons were killed by lightning every year. In reply to a question Dr Macky stated that he believed thunder to be due either to the expansion of air in a cloud due to the heat of the lightning, or to_ the contraction of the cloud when the lightning had left it. Wildfire was, no doubt, distant flashes of lightning. On the motion of Mr J. C. Bcgg the lecturer was accorded a vote of thanks.