NEW LIGHT ON LIGHTNING.

Wanganui Chronicle, Volume LX, Issue 17111, 12 October 1917, Page 7

NEW LIGHT ON LIGHTNING.

HOW THUNDERSTORMS ARE

CAUSED.

The extraoridnary fact about thunderstorms is that while the forces it work in them are so terrific they do such exceedingly small damage. It s only quite recently that an attempt has been made to measure the power expended in a single HgVt'iing flash. There is danger in such experiments, for two or three of those engaged in earlier days in scientifically observing lightning were killed in their laboratories. The measurements made by Mr. C. E. Wilson at Cambridge show that the energy expended in .a discharge of lightning is 600,000 ton-metres—a force sufficient, that is to say, to lift 1,000 tons 2,000 ft. in the air. By way of comparison it may be said that the broadside of the Queen Elizabeth's eight loin, guns would, according to German figures, exert a po*wer at the muzzle of 210,000 ton-metres. The average lightning flash, therefore, exerts the power of three broadsides from .. ' 'lecn ilUizabeth.

Sir Joseph Thomson, to whose brilliant lectures at the Rcjyal Institution we are inde l ',ed for the main facts as to\reecnt discoveries about thunder and lightning, states that thunder is due to a w,ive of high pressure which is produced along the course of the flash. Those who have seen a wireless "sending" instrument will remember the very passable imitation of lightning and thunder which it gave-4 —first the brilliant fla^li and then the rattling noise like the discharge of a gun, so that in the old days before appliances for reducing the noise were introduced the rattle and crash coull be henrd over the whole ship. There, too, the spark is iollawed by a rush of ail' and a detonation like that of an enormous popgun. The size of the Ightning; flash may be very considerable. Some at least of the flashes measured by' Mi\ Wilson were six miles long. There are apparently flashes which are accompanied by no report, like the light obtained, in a vacuum tube, where no noise attends tlie rush of electricity.

The nature of thunderstorms has recantly been illustrated by the discovery that whenever a drop of water.splits up while it is suspended in air the water of the drop is positively electrified and the air around it negatively electrified. .When big drops of water are broken up in the air into small drops, then an electrical effect is produced, and this has been noticed with sprays of water aha1 at waterfalls. What happens in a thunderstorm :s that, first, a current of maisture-ladeh air is carried up from near the ground into a cooler stratum. As\it rises :t cools and the moisture condenses into drops and then begins to fall, when it breaks up into smaller drop:;. As >t breaks up the air about the drops is negatively charged and the drops are positively charged. Finally there is a condition in a thundercloud in which the upper stratum is composed of tiny drops of water negatively charged and the lower, of larger drops positively charged. Discharges begin in the cloud, or if there is a wind which separates the two parts of the cloud* negatively and positively charged, between the cloud and the earth.

The electrical effect may be increased by drops jostling each other. Incidentally, the theory that gunfire may affect electrical tension in the air is demolished by the stupendous character of the poiwer locked up in the constituents of the universe. Sir J. J. Thomson calculates that all the energy of a lightning flash (i.e., the equivalent of twen-ty-four rounds from the 15in. gun) oquld be obtained from the electrical charge of the hydrogen molecules in a quarter of a cubic inch of that gas, could We only extract and utilise the forca..