THUNDERSTORMS

Evening Star, Issue 21751, 20 June 1934, Page 5

THUNDERSTORMS

ADDRESS BY DR MAGKY A lecture of wide interest, ‘ Thunderstorms and the Electricity of the Atmosphere,’ was given by Dr W. A. Macky at the meeting of the Astronomical Institute last evening. Dr Mackay is lecturer on physics at the University, and was recently engaged in research on the subject at Cambridge University under Professor Wilson, the world’s greatest authority on the question with which the address dealt. It was about 200 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 forty years many observations had been made with crude instruments, but little had then been done until 1860, when Lord Kelvin had revived the whole subject and had invented an instrument called the “ water dropper,” which, measured the electricity in the air and actually was largely in use tothis day. The first self-recording instrument of this type had been installed at Kew in 1861, and had been in action ever, 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 1,000 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 Dealing 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 carried 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 in a. flash of lightning amounted to 1,000,000,000 volts, the current’ reaching,the earth varying from 20,000 to 100,000 amperes. If one had to pav for the current the cost would be £SO. Dr Macky then referred 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 had discovered that in many cases the first discharge of lightning consisted of a “ leader stroke,” which travelled to the earth at 5,000 miles an hour. It blazed a trail through which the stroke returned at the increased rate, of 30,000 miles an hour. In connection with the frequency with which thunderstorms occurred in various parts of the world, Dr Macky 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. In New Zealand the number of days on which there were thunderstorms varied from five to twenty, the furthest north and to the west coast of the South Island having the greatest number. In New Zealand, very little damage was caused, partly because here were fewer people to lie hit than in some other parts of the. earth. Seven people had been killed by lightning in New Zealand in the first twenty-five years of this century, with an average death rate of .28 per 1.000. persons a year. In the United States, however, five out of every 1.000. persons were killed by lightning every year. Replying 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. The lecturer was accorded a vote" of thanks on the motion of Mr J. C. Begg.