The Star. MONDAY, FEBRUARY 6, 1883.

Star (Christchurch), Issue 4610, 5 February 1883, Page 2

The Star. MONDAY, FEBRUARY 6, 1883.

Thb mhtbobologioai*. wobk of Atjstb_l_BlA. has hut recently assumed a definite form; and the results placed before the publio must for the present be regarded as in the experimental stage. With this proviso, it may be olaimed that although the task of the collector of the daily observations ia beset with difficulties that can be appreciated only by the initiated, the praotioal outcome is of great value. All telegraph stations being in the hands of the Government, it beoomes a comparatively simple matter to get eyatematio readings of the barometer at a given time ; and these readings are taken every morning at 9 o'clook. From certain prinoipal stations, the observed results are tele* graphed to the Meteorological Depart" ment at Wellington. A message is also received daily from Australia, giving a series j of barometric readings over the southern I area of that continent ; and in this system Tasmania is inoluded. From the information so obtained it is possible to construct a weather ohart showing the whereabouts of areas of low pressure, or storm centres, and the direction in whioh they are travelling. Such charts are now being published in the leading morning journals of this Oolony. In order to have a clear conception of a weather map, or of the verbal indications whioh may be published, it is neoessary that the prinoiple whioh governs barometrical fluctuations should be clearly understood. "No soientifio theory oan be considered complete," says the good old rule, " unless it oan be easily ex* i plained to the first man whom you meet." In the first plaoe, then, it must be borne in mind that the atmosphere at sea level exercises a pressure of 15 pounds per square inoh, and that this pressure is capable of counterbalancing a column of mercury 30 inohes high. This is the prinoiple upon whioh all barometers work, no matter what may be their constructive details. The atmospheric pressure, however, is constantly varying: as it becomes dense and heavy, the barometer rises: as it beoomes rarified, the barometer falls. For " weather " purposes, we have to note the differences in pressure— at the same moment of time— in various localities, as well the changes that are taking plaoe at a given point (say, at Christohuroh). Other things have also to be noted : the wind, for instance, for " Every wind has its weather," and the appearances of the upper strata of clouds. Here, our " weather $ can often be foretold by these higher clouds. In the south-west, a few filmy streaks will be seen, — faint streamers rising from a point behind the Port hills ; and perhaps the first puff of the indicated sou-- wester will not be felt until the following day. A similar appearance is at times the faint, but unerring indication of a hot blow from the nor'-weit. If we examine a series of weather charts, it will be observed that they consist of concentric curves, all of a more or less oireular form. The curved lineß are called isobars ; or lines of equal pressure. This means that if a series of barometers were placed along any one curve, they would p.ive identioal results. There are two kinds of these ourve-groups, the one representing areas of high barometrio pressure, and termed anti-cyclones. Within these areas fine wf ather prevails. The other kind represents areas of low barometrio pressure, of rain, and of storm. We need only concern ourselves with the last-men-tioned. The first great law is this :— '• All great rtorms and tempests exhibit a wind blowing around a calm nuoleui. This nuoleus has the lowest barometer ; and the barometrio pressure increases all around to the very limit of the storm." The next law is, that (in this hemisphere) the rain and storm winds always blow in the direotion of the hands of aclook ; whilst fine weather winds blow always in the opposite direction. Further, whatever may be the direction of the wind, its highest pressure (in this hemisphere) is on the left of its course. These storm areas, with their circling winds, move along at varying rates, and usually in an easterly direotion ; so that if we know tbe kind of weathers that are being experienced in Australia and Tasmania at a given time, we may form a fairly safe estimate of what >New Zealand's subsequent weather is likely fto be. The storm areas of course vary in I j extent ; and they also vary in their rate of | progress and in their degree of violence. I Hence another law, whioh is this : — " What- j | ever may be the height of the moronry, a euodec and rapid fall is a sure sign of foul weather, and the quicker and more sudden, the sooner will the ohaDge be over." Some other points of interest; muat be reserved for a final meteorological article.