System of Winds on the Earth. 505 



4. Down-currents of equal magnitude correspond to the 

 up-currents, and in these the velocity of the air is retarded in 

 the same proportion as that of the upflow is accelerated. 



5. If the heating of the lower strata of air takes place 

 within a limited area, a local upflow occurs reaching to the 

 uppermost regions of the air, and presenting the appearance 

 of whirling columns with ascending spiral currents of air 

 inside and similarly directed descending currents outside. 

 The result of these whirling currents is a diffusion of the 

 surplus heat of the lower strata through which the adiabatic 

 equilibrium is disturbed, to the whole column of air which 

 took part in the whirling motion. 



6. When the sphere of disturbance of the indifferent (or adia- 

 batic) equilibrium is very extended, comprising for instance 

 the whole torrid zone, the equalization of temperature can no 

 longer be effected by local ascending whirling currents, but 

 these mnst comprise the whole atmosphere. The conditions 

 are the same as with local currents, viz. an accelerated ascent 

 and retarded descent of the air, so that the velocity of the air 

 due to the action of the heat is at the different latitudes 

 approximately inversely proportional to the air-pressure pre- 

 vailing there. 



7. As the air of every latitude rotates with approximately 

 the same absolute velocity in consequence of the constant 

 meridional currents which the heat produces and maintains, 

 the meridional combine with the terrestrial currents to form 

 the great system of currents of air surrounding the whole 

 earth, whose function it is to give a share of the surplus heat 

 of the torrid zone to the whole atmosphere by transferring 

 equatorial heat and moisture to the middle and higher lati- 

 tudes and by originating local air-currents in them. 



8. These latter are due to the local production of alternate 

 increase and decrease of pressure through the disturbance of 

 the indifferent equilibrium in the upper strata of the atmo- 

 sphere. 



9. The maximum and minimum air-pressures are effects of 

 the temperature and velocity of currents of air in the higher 

 strata of the atmosphere. 



From what precedes, the investigation of the causes and 

 effects of the disturbance of the indifferent equilibrium of the 

 atmosphere may be considered as one of the most essential 

 problems of meteorology, and the investigation of the geo- 

 graphical origin of the air-currents passing over us on their 

 way to the poles as the most important problem in the pro- 

 gnostication of the weather. 



Phil. Mag. S. 5. Vol. 30. No. 187. Dec. 1890, 2 N 



