JUNfi I, 19051] 



NATURE 



ISLANDS FOIi 



WEATHER 

 PURPOSES. 



FORECASTING 



'X'HE aim of meteorology from a practical point of view 

 is the forecasting of the amount of rainfall and the 

 approach 6f sforms. 



The former ■ will tell us whether we may expect high 



sili^lsg:^ 



I.— The wind system duri 

 hemisphere. The black dots 

 pressure or anticyclonic areas. 



epresent islands, and the lett< 



river flows producing floods and much damage, an average 

 amount of water for successful crop production, or a 

 deficiency of rain which might result in a disastrous 

 drought and possibly a famine. In the case of storms, 

 a means will be afforded of saving many lives and ships, 

 and also, probably, much property ashore. 



The study of the weather, there- 

 fore, should be fostered to its fullest 

 extent, and every advantage should 

 be taken of means which will bring 

 us nearer the goal of satisfactory fore- 

 casting. 



Investigations carried out during 

 the last decade have indicated the 

 importance of each weather bureau 

 extending its area of inquiry beyond 

 the region for which it is making its 

 forecasts. Needless to say, many of 

 these institutions have for some years 

 been in telegraphic communication 

 with outlying stations. Thus, for 

 instance, the Indian Meteorological 

 Service receives information from a 

 station so far distant as Mauritius, 

 while the U.S. Weather Bureau 

 utilises valuable observations by tele- 

 graph from stations in the West 

 Indies, Azores, Europe, &c. 



It is important to bear in mind 

 that rain-bearing winds are those 

 that have passed over large stretches 

 of water, and that the rainfall of a 

 country is deficient or well supplied 

 with this commodity according to its 

 geographical position in relation to 

 the oceans or inland seas, mountain 

 ranges, and the prevailing winds. It 



is for these reasons that the nearer the coast is approached 

 from the centre of any continent, the greater becomes the 

 rainfall. Thus, for instance, the interior of Australia, the 

 Sahara, the Arabian Desert, Tibet, &c., are all very dry 

 areas. 



For forecasting purposes, therefore, attention should be, 



NO. 1857, VOL. 72] 



and in rnany regions is, paid to the region from which the 

 prevailing winds come, due consideration being given to 

 the particular barometric system of which the wind forms 

 part. 



From the above the important functions of islands con- 

 veniently situated become obvious. It is not, however, 

 every country bordering on the ocean that is blessed with 

 such an island in the direction of the 

 pievailing wind, and the British Isles, 

 in consequence, suffer very much from 

 this very defect. In Great Britain 

 the main rain-bearing wind is that 

 from the south-west. In summer this 

 forms part of a large anticyclonic 

 system situated in mid-Atlantic to- 

 wards the south-west (see Fig. i), 

 while in winter it is a portion of a 

 cyclonic system the centre of which 

 is near Greenland (see Fig. 2). With 

 no islands in the track, the only 

 meteorological information that is at 

 once useful is that which can be 

 gathered from messages sent by the 

 Marconi system of wireless tele- 

 graphy from steamers en voyage. 

 Hritish weather forecasters are thus 

 undoubtedly heavily handicapped by 

 the lack of some permanent outlying 

 source of information in this region. 



Mention has already been made of 

 the use of islands by the United 

 States and India. The latter is par- 

 ticularly fortunate, for Mauritius, 

 Seychelles, Chago.s (marked with dots 

 in the figures), and other islands are 

 all conveniently situated to render in- 

 formation if necessary. 



Another region which very probably 

 would gain considerably by utilising observations made at 

 island stations is South Africa. 



In a previous number of this Journal (vol. l.xxi. p. 342, 

 February) Mr. E. Hutchins, Conservator of Forests, Cape 

 Town, gave an excellent account of the general weather 

 conditions in this region. He pointed out that South Africa 



of high 



t± 





IG. 2.— The wind sy 

 hemisphere, 

 cyclonic are; 



the northern heinisphe 



the centre of a low pressure 



lies on the border of the south-east trade area. In 

 summer, from Cape Town to the Zambesi, the country 

 comes entirely under the influence of the south-east trade 

 winds. In winter, on the other hand, the southern portion 

 of Cape Colony is subject to " another type of weather, 

 due to the passage of storms from the South Atlantic, the 



