ing, or in extreme cases impossible, but it has not been possible hitherto to test 

 the truth of this supposition. Through the courtesy of Mr D. A. Davies, Director of 

 the East African Meteorological Department, climatological data for his area, and a 

 statement of the hours of office work in certain parts of Africa, have been supplied 

 to me. 



The statement concerning hours of office work is as follows: 



A Uganda and Tanganyika (including Lake Area) - Normal office hours with lYi hr 



lunch break. 



B Kenya Highlands and East of Rift — Normal office hours. 



C Rest of Kenya - Normal office hours with 2hr lunch break, except that sometimes 



in Northern Province Area there is no afternoon work. 



D Zanzibar and Pemba — No work in the afternoon. 



The following stations were selected as characteristic of each of the four areas: 



A Kitgun 



B Nairobi, Nakuru 



C Mombasa 



D Chukwani 



The data were represented in a diagram as in Fig. 2, the monthly mean of the 

 daily maximum temperature being plotted against the monthly mean of the daily mini- 

 mum relative humidity, which will be approximately synchronous, except that for 

 Chukwani the 15h mean values are plotted. It was thought that observations from 

 Area A (Kitgun) should be about marginal between conditions possible and impos- 

 sible for afternoon work, and that in Fig. 2 points representing area B should fall to 

 the left of those for Kitgun, and those representing areas C and D should fall mainly 

 to the right of those for Kitgun. Fig. 2 only shows observations for Kitgun, Nairobi 

 and Chukwani, the other stations selected for insertion being left out for the sake of 

 clarity. A number of places in area B (e.g. Nakuru) were represented in Fig. 2 by 

 points to the left of the strip covered by the Nairobi observations and so were not 

 retained in the final form of the diagram. 



Area D, where no work is done in the afternoon, is represented by Chukwani in 

 Fig. 2. The points representing monthly values for Mombasa, where there is a 2hr 

 lunch break, fall so closely within the same area as those for Chukwani, that they 

 were omitted. The line CC which has been drawn in Fig. 2 is the line CC of Fig. 1, 

 and it appears to give as good a fit as can be expected for the marginal conditions 

 represented by the observations. 



The view that CC is a boundary having some practical value is put forward in 

 the hope that either further confirmation will be available, or other observations are 

 available which show that this boundary requires revision. There must be some such 

 boundary for work of any specified degree of activity and it is an important matter 

 to obtain as close a specification as possible. 



I will assume for the rest of this paper that I am correct in using CC as a boun- 

 dary such that conditions represented in the area to the right of CC will make it im- 



214 



