Page:Hunt - The climate and weather of Australia - 1913.djvu/134

Rh The degree of accuracy of all forecasts issued averages 88 per cent., and it may be said that material improvement cannot be looked for until the laws which govern the apparent vagaries of movements of cyclones and anticyclones both as to rate and course, and also the, at present, disconcerting fluctuations in pressure which occasionally occur, are determined. The majority of failures in the forecasts may be attributed to want of knowledge on these two points.

Various methods have been adopted to anticipate the divergences from the usual direction of movement of anticyclones and depressions of temperate latitudes, but none have as yet proved satisfactory. It might reasonably be thought that the areas of maximum pressure change would indicate the probable path of advancing centres, or that areas of decided rise and fall in temperature might also give a clue, but the results of extended experiment have proved disappointing.

M. Gabriel Guilbert submitted a method (to the Société Météorologique de France in 1891) of anticipating the approach and progress of depressions by applying the relation of surface winds to the barometric gradient. His theories are strongly supported on parts of the Continent, and appear to have a local application, but they do not seem to apply as satisfactorily in other parts of the world where they have been tested.

Mr. Edward H. Bowie, of the Washington Bureau, has attained a high degree of accuracy in forecasting by a somewhat similar method of his own, but in his case much depends upon the personal equation of the interpreter of the system.

With regard to fluctuations in pressure, we know that such occur by actual translation of the "highs" and "lows," but it is also possible for a super-wave movement to be operating over a relatively stationary lower atmosphere without materially affecting the weather at the surface, and again a dynamical upward and downward action may be a possible explanation.

These suggestions are but tentatively submitted as a desperate attempt to account for certain marked variations of pressure from day to day without a commensurate wind or weather demonstration.