RECENT ADVANCES IN SCIENCE 



17 



It is assumed that in the free air the rainfall at 500 metres does 

 not differ materially from that at 0-5 metre, both heights 

 being almost always below the level of the rain clouds, so that 

 ordinary rainfall statistics can be employed for these heights. 

 For the level of 8,500 metres consideration of the mean cloudi- 

 ness at that height, together with the size of the ice particles, 

 furnishes a rough estimate of the precipitation. From these 

 data the following mean values were found for ^ : 



Height 



8,500 metres 3 to 180 cm."^ grm.^ sec."^ 

 500 ,, 140,000 

 0-5 ,, 1,000 or even less. 



The stirring is therefore very much greater at 500 metres than 

 at the other levels ; and it is interesting to observe that the 

 value found for this height when transformed into its equiva- 

 lent value of K, agrees very closely with the mean deduced by 

 G. I. Taylor from an analysis of the temperature records at the 

 Eiffel Tower. 



Wind Velocity in the Stratosphere (M. J. Rouch, Comptes 

 Rendus, June 23, 1919). — ^The notion that the velocity of the 

 wind must diminish with increasing altitude on passing from 

 the troposphere to the stratosphere, i.e. at a height of about 

 1 1 km., is an attractive one from the theoretical point of view, 

 and were it found to be true one would be able to determine 

 the height of the stratosphere by observations of wind alone. 

 During the war a number of pilot-balloon ascents were made at 

 coast stations in France, and those which attained to an alti- 

 tude of 1 1 km. or more have been tabulated to see whether 

 they throw any light upon this question. Taking the velocity 

 at 10 km. as a standard of reference, departures from this 

 have been calculated to the nearest metre per second, and 

 their frequency of occurrence is shown in the following table : 



These figures do not accord with the theory of a falling off of 

 the wind, as they tend to show that the wind continues to 

 increase with increasing altitude above the base of the strato- 

 sphere. It must be borne in mind, however, that such alti- 

 tudes are only attained on days specially favourable owing to 



