Xocal TOnae. 107 



through the whole bulk of air at normal 

 pressure, was sufficient to cause ignition. A 

 cubic yard of air on the surface of the earth 

 would occupy a much larger space if carried a 

 mile above it. From this it is easy to see that 

 ff a volume of air at that height had a temper- 

 ature of TO or 80 degrees it would be very hot 

 when condensed into a very much smaller 

 volume, as it would be if it were forced down 

 to the surface of the earth. These winds are 

 the result of some superior force that is active 

 in the upper regions of the atmosphere, be- 

 cause it is natural for heated air to rise, and 

 this is what happens when the power that 

 forced it down to the earth is no longer active 

 to hold it there. 



Reference has been made in a former chap- 

 ter to tornado winds; they are rather excep- 

 tional phenomena and not thoroughly under- 

 stood. The winds seem to blow in from all 

 directions toward an area of very low pressure 

 at a single point. The spiral motion that is 

 common to all cyclones, in a tornado seems to 

 be gathered up into a condensed form, like a 

 funnel. The direction of movement is the 

 same as that of the cyclone that is, in the re- 

 verse direction to that of the hands of a watch. 

 The upward motion of the air inside of the 

 funnel is at a rate of over 170 miles an hour. 

 The onward movement of the whole system is 

 about thirty miles per hour. 



