METEOROLOGY 8g 



very few regions recording stations are unnecessarily close together, 

 but in most they are still too far apart, and international co-operation 

 is difficult to organize when, as in some of the British territories, 

 the collection of data is the duty in one of the agricultural depart- 

 ment, in another of the survey department, in others of admin- 

 istrative or medical departments. 



For the development of airways climatological observations 

 require to be supplemented by observations of visibility, height and 

 amount of low cloud, direction and velocity of upper winds obtained 

 by pilot balloons, and, if possible, temperature in the free air as 

 recorded by aeroplanes and registering balloons. 



The devfilopment of engineering works raises another aspect of 

 the application of meteorology. In certain areas regions of ex- 

 tremely high rainfall are not very far removed from arid regions 

 where water is required for the supply of towns or for irrigation. 

 The time may come when the value of the products of intensive culti- 

 vation might justify the expense of collecting mountain rainfall in 

 reservoirs for transference in canals or pipes to arid regions nearby. 



For agricultural purposes the form in which rainfall data are 

 presented is of im.portance. In comparing different parts of Africa 

 it is usual to deal with the annual rainfall, or sometimes the 

 monthly rainfall, but experience is showing that even the monthly 

 unit is too large, and that ten days is the longest unit of real agri- 

 cultural value for research. Since the year cannot be divided into 

 ten-day periods, the pentad (five days) might prove a more 

 satisfactory unit. In a year divided in this way, February 29th 

 would be included with the appropriate pentad to make a six-day 

 period once in four years. Whatever the unit selected, a uniform 

 method of presentation over the widest possible area is desirable, 

 this might be based on the five-day unit, and give figures for each 

 unit's total rainfall and for the number of days of rain in each unit. 

 In making such a suggestion it is presumed that the daily readings 

 would be permanently available for research purposes in the several 

 meteorological offices. The wet and dry seasons of those regions 

 in which the year falls into two periods of contrasted rainfall 

 should also be studied as units, though of varying duration. In 

 many places the study of evaporation from water and land surfaces 

 is also important. 



