CAUSE OF LIGHTNING

Hawera Star, Volume LIV, 2 March 1935, Page 6

CAUSE OF LIGHTNING

Scientific Explanation , of Wafer arid Electricity

AIR RESISTANCE EFFECT OBSERVATIONS SINCE 1752

A .scientific explanation of lightning and some comments on its effects, from the viewpoint of an electrical en,meer, were given by Mr. I*: B. Hutton, at Auckland, m the course of an' address to the conference of civil engineer's. He disbussed methods of averting the effects of lightning, and described an interesting .system of lightning observation and recording that was begun in Southland four years ago. w “Apart from being regarded as a necessary evil,’’ said Mr. Hutton, little was known about lightning till 1752, when Bennjmin Franklin demonstrated that electricity could be drawn from the clouds. Research into the subject then stood still for 100 years, until in 1800 Lord Kelvin became interested and carried out measurements of the amount of electricity in the air. It is worth noting that an instrument invented by him was installed at Kew in 1861, and has been in service ever since.

“We have had to wait until comparatively recent times for. an explanation of. how lightning flashes are actually formed. In 1592, Lenard showed that when pure water splashes against a solid obstacle electrification results, the water becoming- charged with positive electricity, while the negative remains suspended in the air. In 1908 Simpson extended this experiment to show that a similar separation of electricity takes place when a drop of water is broken up in the air without striking an obstacle.

WATER ANT) ELECTRICITY. “When a drop of water falls from a cloud, it meets more and more resistance from the air as it gains speech With this increase in resistance, there cornea a change in the shape of the drop, which' commenced its fall as a sphere. It becomes flatter and flatter, until when its width is about, one-half centimetre, the resistance tends to break it up into smaller drops. Each small drop takes the positive charge, while the negative is imparted to the surrounding air. “If there is an ascending current of air, as is often the case, the pressure from this current is added to the resistance normally met by the falling drop The ascending current also carries with it the small drops or spray formed as the result of the dismtegra r tion of the larger ones. As they rise, they tend to coalesce again, forming larger drops, until they are heavy enough to fall again, when the process of disintegration is repeated. The air thus becomes more and more negatively charged, as opposed to the positive charge in the drops. If this goes on long enough, there will be a passage of electricity or lightning flash. “This discharge might take place between cloud and .earth or between cloud and cloud. The chief point of origin will- be the point of separation of the electrical charges, for here is to be found the greatest concentration of positive charge.

° LIGHTNING AND' RADIUM, Tests had proved, Mr. Hutton said, the ionisation of the atmosphere to some extent must take place before a lightning stroke can pass. Recent investigators suggested that the chief factor in ionisation near the earth’s surface was radio-active emanation, and it had been shown in Russia that regions susceptible to lightning corresponded tq points of high, radioactive intensity. ■ After describing the effects of direct strokes and lightning ora transmission lines and adjacent equipment, he said that as the cose of an arrester at each transformer would be too great, a way must be found to ensure that the occasional arrester mounted on the primary distribution line would serve the same purpose. He then described in detail the system of observation in Southland, which had enabled the incidence of lightning in various localities to be recorded and accurately mapped out, so that its occurrence might be anticipated and provided against.