rKFSIDKXTlAr. ADDRKSS— SlATIOX A. 21 



and weather, he has to take into account the seasons of the v.'ar. 

 the geographical position of the pressure systems, as well as the 

 position of the Kx^alities for which his forecasts arc made, in 

 regard to probable tracks of the pressure systems. 



A few examples will show how he may apply his knowledge. 

 The pressure chart shows, for instance, to the' American fore- 

 caster, a depression over Texas with very close isobars in the 

 western half, and a high area over British Columbia. There 

 will, therefore, be a strong movement of air from the front of 

 the anticyclone, where winds are from the north-west, to the 

 rear of the cyclone, where winds are north-westerly also. If 

 this occurs in the winter season, he can with confidence predict 

 a cold wave from the north-west over the Central States, and. 

 as the probable track of the Texan cyclone, as well as its probable 

 rate of displacement, are fairly well known in North America, 

 he can for two or three days beforehand predict a cold wave over 

 the Eastern States. If positions are reversed, in summer for 

 instance, and an anticyclone has persisted for some time over 

 the south-east, Florida, Cuba, etc., he can, if he sees a depression 

 forming in the north-west with a steep gradient, predict for 

 similar rea'^ons a hot wave over the Central States, which will 

 move from east to west, and give notice of it one or two days 

 beforehand. The Calif ornian fruit-grower who has a consignment 

 of fruit on the road to the East can telegraph suitable instruc- 

 tions to his agents along the line for the preservation of his 

 cargo. In the same way a forecaster in Central Europe can 

 foresee floods in the spring when he sees a cyclone coming from 

 the west towards the Alps with close isobars in the front. There 

 will be a strong movement of air from the Alpine region towards 

 the advancing depression. The air, although coming from the 

 cold regions of the Alpine ridge, will, in its descent to the lower 

 levels of the valleys and central plains, become warmer and 

 usuallv melt, in one day, more snow in the valleys than would be 

 melted in a fortnight under ordinary circumstances. A higli 

 barometer over the vSahara and a low barometer over the 

 ^Mediterranean will, for similar reasons, allow him to forecast 

 the dry hot sirocco over the northern part of Africa. For 

 .South Africa Mr. Wood, who is in charge of the Transvaal fore- 

 casting service, gives the following typical cases : — There is a low 

 barometer inland, and a high barometer is forming in the west. 

 If this high barometer is ofif the West Coast, it will, in the course 

 of a day or two, invade the Southern tableland, and form an 

 anticyclone over Bechuanaland, Southern Rhodesia, and the 

 Transvaal, bringing with it the usual anticyclone weather, which 

 for us here means south-east wind, with a period of unpleasant 

 cold weather, followed by some days of fine, dry weather. In 

 summer this invariably breaks up a period of rainy weather in 

 Southern Rhodesia. If the high pressure appears in the south- 

 west of the Cape, it usually skirts around the inland depression, 

 and forms a system of steep gradients from the sea to the land. 



