FORTELLING THE WEATHER.

Temuka Leader, Issue 2150, 15 January 1891, Page 4

FORTELLING THE WEATHER.

Mr Clement Wragge, E.E.G.S., E.R. Met. Society, the Government Meteorologist of Brisbane, who has been forecasting the weather of Aus: tralasia with such surprising has been explaining to the representar tive of the Sydney Daily .Telegraph “ how it’s done.” He has given an exceedingly clear and . intelligible account of what to most;-people is a very mysterious business, and ouif readers may be glad if we reproduce' in brief the substance of bis remarks; JN early all the : atmospheric disturbances which affect the southern half of Australia, and especially the southwestern district of Western Australia, with the whole of New South Wales, the southern part of South Australia and Tictoria, it appears, travel east-: wards from the Indian Ocean. So far ss can be seen at present it is highly probable that 'some at least of these disturbances circumnavigate, as itj were, the Southern Hemisphere,; Such disturbances, we are told, must; not be confused with the tropical! disturbances which during the hurricane season effect the Queensland! coast. Such come down from the; equatorial regions, travel southwest-! wards to the east coast of Australia,; and then usually meet the high pres-i sure system which at such seasons ofr the year frequently obtains over the! south east quarter of Australia, and! then deflect towards New Zealand.; These, it must be remembered then, are two totally distinct influences.: The latter more particularly affects: Queensland, and the former New : South Wales. Very nearly the whole of those influences which affect the latter colony come from the extreme southern portion of the Indian Ocean,

We cow know the quarter from which most of our “ weather ” comes.; We have still to learn bow the skilled meteorologist knows when it will probably arrive and what it will be like when it does come. What Mr Wragge does at bis office in Brisbane is] this : Having received barometric observations by telegraph from all parts of the colonies, he notes them: on a blank chart of Australia. Having done this, he joins by equal lines those places having equal pressures. He can then see distinctly those areas: of land and ocean over which the; barometer is high and over which it is low. High pressure systems are; known by the name of anti-cyclones.i The anti-cyclone, as Mr Wragge graphically puts it, is a great mound or mountain of atmosphere, at the centre or summit of which the barometer reads higher than at the stations around it, The cyclone on the other hand, is a valley or depression of atmosphere, in the centre of which the barometer reads lower than at stations around it. Around highpressure systems in the Southern Hemisphere the wind circulates in the opposite direction to the hands of a clock. Hence it will be readily understood that on the northern side of an anti-cyclone the wind will be easterly, on the southern side of such it will be westerly, on the eastern side it will be southerly, and on the west| ern side ic will be northerly, Tim is the meteorologist’s grand secret whi'e enables him to evolve something like system and certainty out of conditions apparently so fickle and unstable as those wuich rule the weather. By dividing such a system of high pressure—which is always more or less circular, though hardly ever a precise circle—into quarters, it is at once clear that different winds, different temperatures, different centres of humidity, and different atmospheric conditions altogether will obtain on each quadrant, so that by noting the first advance of such high-pressure system from the Indian Ocean over the western half of Australia it becomes possible, having carefully estimated its course and rate of travel, to forecast the conditions that will obtain on each quadrant during its progress across the Australian continent and the adjacent waters. The low pressure or storms systems which traverse the Southern Ocean are dealt with in the same way, only in this case the winds circle in the same direction as the hands of the clock—that is the reverse of the high pressure system. The calculations are

farther complicated from the fact that; most of the low pressure systems which traverse the Southern Oceanj instead of being circular in shape, havcj frequently outlines bearing the fond 1 of an inverted V.” The rate ai which these systems -travel is pretty accurately .known,, so- that the meteor* oligist can calculate when they raacU a particular spot and when the change in the wind is likely to take placet Should great ; barometric differences obtain they indicate ' special atmoi spheric gradients, and hence, the of wind—whether, lor instance, -it is likely to obtain the proportions-of serious gale—can by careful, icalcnlaf tipu and judgment be accurately , fprejcast, to the great advantage -of all interested in shipping. >