System of Winds on the Earth. 503 



atmosphere on the earth's surface. Frequently, however, 

 light clouds indicate an alteration already set in in the higher 

 strata ; and so in my paper, " On the Conservation of Energy 

 in the Earth's Atmosphere," I placed the origin of the maxima 

 and minima in the upper strata of the atmosphere, in the tem- 

 perature and velocity of which constant alterations take place, 

 depending upon the place of ascent of the air, i. e. on its tem- 

 perature and hygroscopic state before it ascends. If no change 

 in the seasons took place, there would probably be great regu- 

 larity in the currents in the upper strata of the atmosphere, which 

 would bring about a certain sequence in the changes of weather 

 not hitherto attained. We are not yet able to find out where 

 the air comes from which flows at any moment over any 

 portion of the earth's surface in a polar direction along the 

 higher strata of the atmosphere, and upon the place and the 

 season of the ascent will depend the temperature and velocity 

 of this air. As the expenditure of heat during the ascent of 

 the air, i. e. during its working expansion, depends upon the 

 degree of its attenuation, and therefore on its elevation, 

 nearly the same diminution of heat takes place with hot as 

 with cold air. At all heights of the atmosphere differences 

 of temperature must make their appearance equal in degree 

 to those existing on the earth's surface, for any surplus of 

 heat which the air possesses before its ascent must be retained 

 by it after it has been rarefied and cooled through the ascent. 

 On this account the general condition of the atmosphere will 

 not be that of unstable equilibrium but so-called stable equili- 

 brium, for the higher strata of the atmosphere, on account of 

 their equatorial origin, will be warmer and lighter throughout 

 than they should be according to the adiabatic scale of tem- 

 perature of the place over which they are. The velocity of 

 ascent of the air will increase with the quantity of heat 

 and moisture which it contains before its ascent ; and 

 therefore in the higher strata of the atmosphere of the 

 mean and higher latitudes, relatively warm and light cur- 

 rents of air of greater velocity must intermingle with colder 

 and slower currents. Such a current of relatively light 

 and warm air, completely or partially occupying the upper 

 atmosphere, disturbs on its side the indifferent equilibrium 

 of the lower strata of the atmosphere. The lower atmo- 

 sphere, relatively at rest on the boundaries of the strata, 

 must be under too great a pressure, and must therefore ex- 

 pand and be carried along with the quick-flowing lighter air 

 above it. As von Helmholtz has shown, this carrying away 

 must go on with great energy, producing waves, and in con- 

 sequence there must be an expansion and flowing up of the 



