LUNAR PULL

Evening Post, Volume CXIX, Issue 111, 13 May 1935, Page 4

LUNAR PULL

TIDAL SWAY OF AIR

The tides of the sea; may control the movements of ships and bathers, and even on occasion provide London with flood alarms. But Professor Sydney Chapman, of the Royal College of Science, South Kensington, prefers another kind .of tides—those raised by the moon in the atmosphere, of which most people have hot even heard, says the London "Morning Post." , For nearly twenty years ;he has been making calculations of the pull of the moon on. the "air; Aided by a formidr able array of calculatmg machines, he has worked out the time and extent of air,.tides at more than twenty,stations, from Honolulu to. Buenos-Aires.' '.. •Now heihas found that his records can be used to throw new light on the radib-refiecting layers' of the upper atmosphere. But Ijhe main reason why he prefers aerial tides is that.they are relatively regular the world over. The ocean of the air i^ unconfined. ' , -.; At'the Equator: the eir tides correspond: with a' total - barometric change of only one-sixteenth of a millimetre, less;than the width of the ink trace' in a barograph. : ', y "' ■- : i ••■ At the Equator,; alsbj h.e finds that the air. is pulled;back :and forth to the extent of about 150 yards each::way during a lunar day.- ■ : 1- ; :\ It is because-"the changes are sb 'small"thai;'many.months' wprkr < are heeded to sort out j the iuhar-Vtides from random pressure movements, as well as from the daily, change due to the'sun's heat. •. -- ■ -• " The connection\with radio-reflectmg atmospheric strata.is due to the fact1 ■that toe tidal' movement of .the air. produces, electrical changes high ' in iffiie ..earth's atmosphere. For the same reason the passage, of the moon across .the.sky afifects. the strength -. of the .eatth's magnetism;.; . -.' . , \ .'.'A' former" Astronomer Royal, Sir; George Airy, made the first attempt to work out the. air tides at Greenwich more than fifty years ago. He failed. Professor Chapman succeeded as a result of throwing away two-thirds of the available records—those in which normal barometric changes were at all big.' ■'" ". ■'-■ - - . ■ ■:•• ; Encouraged "by the advent of calculating machines similar to those used inncounting .the "Morning Post", test vote,- he.has steadily expanded His activities. Heiisoibw tackling.the Mel-' bourne 'records;. He states that: there is much more to be learned about the earth's atmosphere. " *■■■ "" :