THE NEW SCIENCE OF METEOROLOGY 



hands of a watch held with its face upward. The 

 velocity of the cyclonic currents will depend largely 

 upon the difference in barometric pressure between the 

 storm-centre and the confines of the cyclone system. 

 And the velocity of the currents will determine to some 

 extent the degree of deflection, and hence the exact 

 path of the descending spiral in which the wind ap- 

 proaches the centre. But in every case and in every 

 part of the cyclone system it is true, as Buys Ballot's 

 famous rule first pointed out, that a person standing 

 with his back to the wind has the storm-centre at his 

 left. 



The primary cause of the low barometic pressure 

 which marks the storm-centre and establishes the cy- 

 clone is expansion of the air through excess of tem- 

 perature. The heated air, rising into cold upper re- 

 gions, has a portion of its vapor condensed into clouds, 

 and now a new dynamic factor is added, for each par- 

 ticle of vapor, in condensing, gives up its modicum of 

 latent heat. Each pound of vapor thus liberates, ac- 

 cording to Professor Tyndall's estimate, enough heat 

 to melt five pounds of cast iron; so the amount given 

 out where large masses of cloud are forming must enor- 

 mously add to the convection currents of the air, and 

 hence to the storm-developing power of the forming 

 cyclone. Indeed, one school of meteorologists, of 

 whom Professor Espy was the leader, has held that, 

 without such added increment of energy constantly 

 augmenting the dynamic effects, no storm could long 

 continue in violent action. And it is doubted whether 

 any storm could ever attain, much less continue, the 

 terrific force of that most dreaded of winds of temperate 



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