32 liLAIR— EXPLORATION OF THE UPPER AIR [March s, 



During these five days an area of high pressure which was central 

 over Vermont on the fifteenth moved south westward over the 

 observatory. The highest pressure in this area was 775.2 mm. on 

 the morning of the fifteenth; this decreased to 765.0 mm. on the 

 morning of the nineteenth. Under the influence of this area of 

 high pressure, the surface wind was northeast on the fourteenth, 

 southeast on the fifteenth and northwest during the remainder of 

 the period. On the fourteenth anrl fifteenth the change in wind 

 direction with altitude was counter-clockwise, while during the 

 remainder of the period it was clockwise. The upper current in 

 which the inversion occurred varied from north-northeast on the 

 fifteenth to north-northwest on the nineteenth. These warmer 

 northerly winrls aloft are apparently due to an area of low pressure 

 which was central about 300 kilometers east of the southern ex- 

 tremity of Florida at 8 a.m. on the fourteenth and moved north- 

 northeast along the coast, reaching the Gulf of St. Lawrence at 8 

 a.m. on the nineteenth. This area of low pressure seems to have 

 overhung the weak area of high pressure. 



Fig. 10 shows the horizontal projection of the path of a sound- 

 ing balloon. It illustrates not only the variability of the winds 

 both as to direction and velocity with altitufle, but the method of 

 determining these elements when sounding balloons are used. What- 

 ever the wind direction at the surface, the kites do not often go 

 more than 3,000 meters high without coming into a wind with a 

 strong westerly component. These changes in the wind, together 

 with the temperature gradient, enable us to get the depth of a great 

 many of the storms as they pass us. 



Fig. II shows the map for February 26, 1908. The wind direc- 

 tions shown by the flight of this day were as follows: 



Surface XW. 



1,000 meters WXW. 



2,000 meters W. 



3,000 meters WSW. 



4,000 meters SW. 



The peculiar arrangement of the two low pressure areas in the 

 northeast is the interesting feature. The wind flirections observed 

 on this day during the kite flight show that the small or secondary 

 low pressure area was only 2,000 meters deep. At this altitude the 



