52 The Ottawa Naturalist. [May 



speak, about Iceland behave, and it is tliis secondary or gyratory 

 motion especially that gives us storms. It appears that the 



valley of the St. Lawrence has the largest number of the storms 

 of any section of the globe, i.e. areas of high and low barometer 

 passing over it. The greater number of American storms 

 originate in the Saskatchewan country or on the south-eastern 

 slope of the Rocky Mountains. A minor number are developed 

 in the Caribbean Sea and the Gulf of Mexico. Our worst storms 

 in summer are traceable to Texas, whereas the winter ones come 

 mostly from the North-west. The Rocky Mountains are such a 

 barrier that it is seldom that a storm of the Pacific crosses them 

 and reaches us. The ultimate course of low area storms is 

 somewhat north of east. The number of well defined low area 

 storms which cross the United States and Canada average eight 

 in each month from May to August inclusive ; nine from Sep- 

 tember to November and in April ; eleven in February, March 

 and December, and twelve in January. The average velocity of 

 low area storms fluctuates for the different months between 25 

 and 38 miles per hour, the maximum being in January. To 

 summarize, low area'storms have a wind circulation inward and 

 upward, arc elliptical m form, are characterized in their eastern 

 quadrants by cloudy weather, southerly and easterly winds, 

 precipitation, temperature oppressive in summer, and abnormally 

 high in winter, falling barometer, increasing humidity ; and are 

 followed by clearing weather, rising barometer, decreasing 



humidity, and falling temperature in the western quadrants. 



Areas of high barometer, or anti-cyclones, in which the 

 barometric pressures are defined by isobars successively higher 

 toward the centre, are about forty per cent, less frequent than 

 low area storms. In winter the advance of these high areas, 

 though always attended by a decided fall in temperature, is for 

 the most part characterized by clear skies, by calms near the 

 •centre and light or fresh winds on the outskirts of the area. This 

 -condition of affairs permits rapid nocturnal radiation and tends 

 to lower the temperature of the air at the centre of an anti-cyclone^ 



( To be co7jtinued. ) 



