IX 



Climates of the World 153 



siderable distances apart, that can throw light on the state 

 of the atmosphere and the associated weather. About 

 thirty years ago the first synoptic charts showing the 

 isobars of a country were introduced as an aid to the study 

 of weather, and such weather-charts enable storms to be 

 foreseen in many cases. In nearly every country there is 

 now a number of meteorological stations where observa- 

 tions of barometer, thermometer, wind, etc., are made at 

 the same hour morning and evening, and telegraphed to a 

 Central Meteorological Office maintained by Government. 

 Here charts are prepared showing at one glance the state 

 of the atmosphere both as regards pressure and tempera- 

 ture (corrected to their value at sea-level) over the whole 

 country and surrounding districts. If the student will take 

 the trouble of tracing in red ink on thin paper the figures 

 of a cyclone and anticyclone given above (Figs. 29 and 

 30), and will then lay this tracing over the map of the 

 British Islands (Plate IX.), he will see exactly how the 

 weather varies in different parts of the country according 

 to the distribution of these types of atmospheric pressure. 



212. Weather Forecasts. Several arrangements of 

 isobars besides those into cyclones and anticyclones may 

 occur. Isobars drawn from actual observations may be 

 straight, showing that they form part of neither cyclone nor 

 anticyclone ; sometimes they are sharply curved, forming 

 V-shaped areas of low pressure or wedge-like areas of high 

 pressure lying between adjacent anticyclones or cyclones ; 

 and they very often form loops, showing the existence of a 

 small secondary cyclone inside a larger. Each type of pres- 

 sure-distribution corresponds to a special 'kind of weather, 

 and the relation between isobars and weather has been 

 carefully studied and is well known to practical meteoro- 

 logists. The commonest weather in the British Islands is 

 that produced by the passage of cyclones eastward from 

 the Atlantic, and this may be taken as a characteristic 

 example to illustrate weather forecasts. If the student 

 places a tracing of Fig. 30 on Plate X. so that the large 

 arrow points north-east and its head is on the south-west of 

 Ireland, and then moves the tracing gradually north-east- 



