Teacher's Leaflet. 1149 



A low area is called a cyclone and a high area an anti-cyclone. The destructive 

 winds popularly called cyclones, which occur in certain regions, should be called 

 tornadoes instead, although, in fact, they are simply small and violent cyclones. 

 But a cyclone, when used in the meteorological sense, extends over thousands of 

 square miles and is not violent, while a tornado may be only a few rods in 

 diameter and be very destructive. The little whirlwinds, which lift the dust in 

 the roads, are rotary winds also, but merely the eddies of a gentle wind. 



In a cyclone or " low " and also in a tornado the air blows in all directions 

 tozvard the center where there is a column of ascending air. 



In an anti-cyclone or " high " the air blows outward in every direction from a 

 central column of descending air. 



The weather conditions during the passage of a cyclone are briefly as follows: 

 Small, changing wisps of cirrus clouds appear about 24 hours before rain ; these 

 gradually become larger and cover the whole sky, making a nimbus cloud. 



The wind changes from northeast to east or southeast to south. 



The barometer falls; the thermometer rises, that is, air pressure is less to the 

 square inch and the temperature of the atmosphere is warmer. 



Rain begins and falls for a time, varying from an hour to a day or more. 



After the rain there appears breaks in the great nimbus clouds and finally the 

 blue sky conquers until there are only a few or no clouds. 



The wind changes to southwest and west; the barometer rises, the temperature 

 falls. 



The rain ceases, the sun shines out brightly. 



The low has passed and a high is approaching to last about 3 days. 



Lesson XVIII. 



HOW TO KEEP A DAILY WEATHER MAP. 



The pupils of a school should keep a daily weather record for at least 

 six months. The observations should be made twice each day and always 

 at the same hours. While it would be better if these records could be 

 made at 8 o'clock in the morning and again at 8 o'clock in the evening, 

 this is hardly practicable and they should, therefore, be made at 9 o'clock 

 and at 4. The accompanying chart may be drawn enlarged. Sheets of 

 Manilla paper are often used so that one chart may cover the observations 

 for a month. 



A few schools are able to have a working barometer, but observations 

 of temperature and sky should be made in every school. Almost any 

 boy can make a weather vane, which should be placed on a high 

 building or tree where the wind will not be deflected from its true direc- 

 tion when striking it. A thermometer should be placed on the north 

 side of a post and on a level with the eyes ; it should not be hung to a 

 building, as the temperature of the building might affect it. 



