TEE METEOROLOGY OF THE FUTURE 33 



trend inward toward the center to such an extent that the hurricane 

 can not be considered as a system of circular rotations, hut of spiral 

 inflowing ascending and overflowing currents of air, or the ideal cyclonic 

 vortex movement. The same conclusion was soon formed with regard 

 to the waterspout and tornado, the only differences being as to the 

 question what are the angles of inflow, ascent and overflow? Since 

 1871 a still more careful analysis of the United States daily weather 

 maps has shown that it is necessary to consider the fact that the winds 

 on the west side are colder and drier than those on the east side of the 

 storm center. Thus it follows that in the northern hemisphere we have 

 cold dry northwest winds swirling around the central low pressure and 

 running under the more moist southerly winds, sometimes even going 

 so fast as to overflow these for short distances while pushing them aside. 

 In this respect a hurricane storm lies intermediate as to its mechanism 

 between the thunder-storm and the waterspout. In the waterspout we 

 have a relatively small mass of air, no great differences of temperature, 

 a rapid ascension with a rapid horizontal rotation. In the thunder- 

 storm we have a simple horizontal overturning; cooler or drier air 

 descends from overhead and warmer or moister air ascends from below. 

 In every style of storm and in every form of atmospheric circulation 

 there is and must be overturning with overflow and underflow. 



The problems of simple overturning have been studied by Margules 

 from the thermo-dynamic point of view. Perhaps I can illustrate these 

 problems by means of this glass box with vertical divisions. I will 

 place this dividing blanket in the middle. On the left-hand side we 

 have a mass of air cooled by this adjacent ice; on the other side is an 

 equal volume of air at the temperature of the room. If I quickly 

 remove the blanket the cold air settles down, flowing beneath the warm 

 moist air and covering the bottom, while the warm air is raised to the 

 top. The differences of density have caused an interchange of energy 

 due to the action of the force of gravity quite independent of radiation 

 or conduction of heat. The descending cold air has expended some of 

 the potential energy of its position in elevating the warm air. If the 

 warm air was anywhere near the point of saturation, then its small loss 

 of temperature due to its rising and expanding may have produced a 

 haze in our little experiment, but in nature it often produces a great 

 thunder cloud, and every gradation of cloud from that form down to 

 the thinnest stratum. 



These overturnings are perpetually going on in every room of our 

 buildings and of course in the atmosphere. If a cloudy mass descends 

 it is warmed by compression as it descends; evaporates all its cloudy 

 particles, and in its further descent eventually has its own temperature 

 raised. In general we have very low temperatures at great altitudes 

 in the atmosphere, but if such air were brought down rapidly to the 



vol. lxxviii. — 3 



