THE ENGINE OF THE AIR 161 



rant and almost ceases at any station with the arrival of the 

 minimum pressure. . . . The source of moisture-supply (that 

 furnishes the energy of the cyclone) is through the winds in 

 the rear right-hand quadrant, and the precipitation is due to 

 the forced ascension produced by the convergence of these 

 winds with those of the front right-hand quadrant. The pri- 

 mary cause of tropical cyclones is the convergence of air 

 currents. The cyclone itself persists by continuous redevelop- 

 ment over the area of the greatest precipitation, and the core 

 of the cyclone is inclined from the area of the lowest surface 

 pressure (or center) forward into the cloud region over the 

 area of maximum precipitation. (The center moves forward 

 to the right in a tilted cone. ) As the cyclone travels, the area 

 of low pressure moves towards that of precipitation." The 

 storm tides (which can rise up to twenty feet above normal) 

 that are built up in advance of the cyclone are found only 

 directly in front of the approaching storm or in front of its 

 forward right-hand quadrant. 



The hurricane, the cyclonic storm at its greatest intensity, 

 in basic nature varies little from the milder storms we are used 

 to in the so-called temperate zone of the northern hemisphere. 

 Therefore, before we consider how changing climatic condi- 

 tions in the past have influenced the oceanic heating system 

 and even the destructive rise and fall of ocean levels, it may 

 be a good idea to look at the kind of force a hurricane can 

 exert. The wind strength that defines hurricane weather 

 ranges from above 60 miles an hour to 1 50 miles an hour — or 

 until the measuring instrument lets go and disappears. This 

 kind of wind strength, customarily associated only with trop- 

 ical hurricanes, often exists in the high airs of northern areas. 

 Winds as high as 200 miles an hour have been recorded by 

 the Government bureau on top of Mt. Washington in New 

 Hampshire at 6,288 feet. When winds of this strength occur 

 they lift sea and solid alike and change the immediate face 

 of things. 



