TABLE 7.-Some Harmonic Constants in the Diurnal Curves of Barometric Pressure and Temperature Variability at Treandrum.

TABLE 8.-Some Harmonic Constants in the Diurnal Curves of Barometric Pressure and Temperature Variability at Greenwich.

TABLE 9.-Some Harmonic Constants in the Diurnal Curves of Barometric Pressure and Temperature Variability at Kimberley.

TABLE 10. Some Harmonic Constants in the Diurnal Curves of the Variability of Relative Humidity at Kimberley.

AFRICAN WEATHER.

BY COLONEL H. E. RAWSON, C.B., F. R. MET. Soc., F. PH. Soc., ETC.

To anyone holding the clue to South African weather, the study of meteorological problems, not only on this continent but generally over the whole globe, becomes a most fascinating one. South African weather does not present those samples which are so well known in the British Isles, and which are so bewildering by the rapid and inexplicable way they follow one another. Nor are the records which we possess here a mere conglomeration of dry bones, requiring almost a magician's wand to give them life and make them of value. Few as the first-order meteorological stations are in South Africa, they have given us observations of exceptional value and importance, owing to the comparative ease with which they can be interpreted, and an intelligible idea be formed from them of what is going on. We owe a real debt of gratitude to the comparatively large band of volunteers, who supplement our records with local observations, and who help to increase the value of the more precise and accurate data issued by the observatories.

The object of this paper is to submit this clue to you for your consideration, and to lay before you some of the reasons why it is worthy of your attention.

PERMANENT ANTICYCLONIC SYSTEMS.

They

Before our weather can be intelligently studied, a preliminary knowledge of the seasonal movements of the so-called permanent anticyclones in our neighbourhood is indispensable. For a long time it was held that such systems formed persistent girdles, or belts, of high pressure round the world on both sides of the equator, at about Lats. 25° to 30°. At certain seasons of the year they were said to decrease in intensity and dissipate, to appear once more when the season returned. Thus in winter in the northern hemisphere two well-defined high-pressure systems were found to prevail for quite two months or more at a time over Eastern Siberia and over North America. gradually diminished as summer approached, and eventually broke up and gave way to cyclones. On the other hand, during summer high pressure prevailed over certain parts of the Atlantic, and especially in the neighbourhood of the Azores, which completely disappeared in winter and was replaced by low pressure, with its destructive storms. The gradual changes from high to low pressure and back again to high pressure were described as "reversals," and were looked upon as continuous processes caused by the seasonal increase and decrease of the sun's heat over the areas where these systems were found to prevail. In 1898 I ventured to combat this view, and I put forward the theory * that the permanent anti-cyclonic systems did not dissipate, or disperse, when they disappeared; but that they gradually moved off to localities where the conditions were more congenial.

*Quarterly Journal of the Royal Meteorological Society, Vol. XXIV., No. 170, July, 1898. Anticyclonic Systems and their Movements.