- 50OC 



DEPTH IN CMS. 

 I I I I I 1 — I I I I I I I I I I I I — r—i — I I I I — I I I I 



X 5 cms 10 15 20 25 cms 



40 



o 



: . ^-^Z ^J^V]^ : 



SAND TEMPERATURES 

 AUGUST 1922 



oO^C 



40*^ 



DEPTH IN CMS, 



Figure 5. 

 Temperature in Sand — Observed and Calculated Values 



Microclimatic conditions were also investigated in two caves in the sides of the 

 wady, the first cave in August and March, the second in March and December, with a 

 few extra observations at other times of the year. The values for temperature and humi- 

 dity are shown in Table 11, and diagramatically in Fig. 6. 



Fig. 6 also illustrates an interesting point with regard to relative humidity. It was 

 found that the vapour pressure inside the cave tends to come into equilibrium with that 

 outside. Vapour pressure is generally lower in winter than in summer, but the differ- 

 ence in temperature results that relative humidity is higher in winter than in summer. 

 Since at a depth of about 20 metres into one of these caves the annual temperature is 

 almost constant it follows that the relative humidity inside the cave tends to be higher 

 in summer than in winter, just the opposite to what is happening outside. It must be 

 remembered, of course, that these caves are surrounded by completely dry rock. Under 

 normal European conditions cave air tends to be quite saturated with moisture. 



24 



