SCIENTIFIC WRITINGS. 415 



ing motion of air, according as the invading higher 

 currents of air are too warm or too cold, thus also 

 too light or too heavy for the indifferent equilibrium. 

 This ascending or descending aerial motion must last 

 until the indifferent equilibrium of the column of air 

 is again restored, and the consequence then is, that 

 the pressure of the atmosphere at the surface of the 

 earth becomes as great as it would be, if the tempe- 

 rature of the whole column of air had changed as 

 much as the equatorial current, causing the disturbance, 

 deviates from the adiabatic temperature corresponding 

 to its place and its height. As the consumption of 

 heat during the active expansion of a quantity of air 

 is independent of its commencing temperature, the air 

 ascending at different places in the torrid zone must 

 retain the differences of temperature, which it possessed 

 before the rise. Hence it follows , that relatively 

 warm and cold currents of air flow polewards with 

 different velocity in the higher and highest strata of 

 air, and thereby disturb the indifferent equilibrium of 

 the atmosphere in its whole course. Slowly flowing, 

 too cold currents will give off their surplus pressure 

 to the lower aerial strata on which they are resting, 

 without ; causing important disturbances, by compressing 

 them, and thereby causing a rising barometric pressure 

 in a calm atmosphere. Air -currents, which are rela- 

 tively light, hot, and therefore strongly accelerated 

 during their ascent, will on the other hand cause to 

 undulate and carry with them the surface, insufficiently 

 weighted by them, of the aerial strata over which 



