HOW LIGHTNING STRIKES

Press, Volume LXXIV, Issue 22355, 19 March 1938, Page 21

HOW LIGHTNING STRIKES

Photographs of lightning strokes which travel at the speed of 10,000 miles a second have revealed the existence of ‘'lightning guides” which leap up from the earth and guide the bolt from the clouds to its earthly landing. This discovery was reported by Mr Karl B. McEachron, maker of artificial lightning in the United States General Electric Company’s high voltage laboratories. Many lightning strokes which appear to crash from the clouds to the ground actually are met part way by Irmll flash, or streamer, onginatrom the earth, which' guides therf, to their destination, Mr McEacflron reported. 'Three years of close observation of natural lightning striking the Empire State Building in New York City, during which hundreds of pictures were taken with a special highspeed camera, not only revealed the “lightning guide,” he said, but further showed its manner of action. The photographs, revealed that the leader stroke of a lightning flash often started from the tower of the building and shot upward to the cloud, to be followed immediately by successive flashes over the exact path from the cloud. Another strange phenomenon observed was that the leader stroke, which immediately preceded all lightning flashes, moved toward the ground in a series of hesitating steps of about 200 feet in length. “These streamers progress for this short distance, substantially die out, and then, after a wait of a few millionths of a second, proceed in a second step, and so on until they reach the earth. Often as many as 30 or more steps are taken in a single flash,” he stated. Mr McEachron reported thart a lightning discharge often travelled a considerable distance over the surtface of the ground, after having struck a tall tree, for example. If one could be present to observe the situation, no doubt the ground all around the tree would be covered With sparks, streamers reaching out from the base of the tree. “This illustrates the great necessity, where lightning rod systems or other arrangements are made on the surface of the earth for conducting lightning to the ground harmlessly, of so arranging these conductors that they will have a low ground resistance, so that the' charges in the earth are free to move Up into the cloud channel without causing damage to structures on the garth’s surface.”

Prehistoric Oxen From time to time the River Thames yields relics of the past, the latest being a fine of the horns of an aurochs which were dredged from the river in Berkshire. The span of the latest find is just over three feet, and a portion of the skull is attached. The aurochs in

Britain dates back probably about 5000 years,. but the last known specimen in Europe was slain in Poland, in 1627. Judging from the bones dug up from time to time in the Thames valley the animal must have been a gigantic specimen of the ox tribe, probably black, and standing about six feet, high at the shoulder.