i6 SCIENCE PROGRESS 



broad rules hold : In high-pressure areas the lower strata 

 are warm, the fall of temperature with height continues to 

 about 12 km., and the strata above 12 km. are cold. In 

 cyclonic areas the lower strata are cold, the vertical tempera- 

 ture gradient ceases at a lower level than usual, and above 10 

 km. the strata are warm. The temperature of the air depends 

 closely upon the pressure and upon the time of year, but except 

 quite close to the earth it does not depend upon the direction 

 of the wind. 



Since there are strong reasons against supposing that the 

 coldness of the lower layers of a cyclone are due to loss of 

 heat by radiation, we are driven to ascribe it to dynamical 

 cooling. Calculation shows that air at a height of 6 km. in 

 an anticyclone would have to rise 2*4 km. on entering a cyclone 

 in order to cool dynamically to the temperature of the cyclone. 

 On the other hand, air between 12 km. and 14 km. in the 

 anticyclone would, on entering the cyclone, have to descend 

 I "3 km. in order to warm dynamically to the higher tempera- 

 ture of the latter. That a general rise of air does actually 

 occur in the .lower parts of a cyclone is proved by the in- 

 draught of the surface winds across the isobars. The diffi- 

 culty consists in seeing exactly how this upward current is 

 induced, how, in fact, cold and heavy air which one would 

 expect to be sinking is forced to rise. The solution of this 

 problem would constitute a big advance in meteorological theory. 

 Atmospheric Stirring measured by Precipitation (L. F. 

 Richardson, Roy. Soc. Proc, 96, Aug. 191 9). — Since the aver- 

 age water-content of the atmosphere is not increasing, the 

 water which descends as precipitation must have been stirred 

 up into the atmosphere. Consequently, from a knowledge 

 of the mean precipitation at any height taken over the whole 

 earth, the mean amount of stirring can be deduced by suitable 

 mathematical processes. The heights dealt with are o'5 metre, 

 500 metres, and 8,500 metres. Over this range the density 

 of the air and the coefficient of stirring cannot be taken as 

 being independent of the height, as was done by G. I. Taylor 

 Phil. Trans., A, vol. 215, 191 5) in his pioneer work on this sub- 

 ject, consequently a more general treatment has been followed. 

 In order to measure the stirring, a quantity ^ was used to 

 replace the eddy-diffusivity k, of Taylor's equations, | being 

 defined by the equation 



?^ _i. ( pbi\ 

 hh ~ hp \^ hp) 



where p = pressure 

 h — height 

 X = mass of water per unit mass of atmosphere. 



