528 DR. J. W. GREGORY OX THE [Nov. I 894, 



isobaric surfaces would rise and air rush in from below. There 

 would thus be a high-level radial outflow, and a low-level inflow. 



The air would not, however, be free to move radially from the 

 mountain equally in all directions, for along the Equator there is a 

 prevailing westerly wind. This is due to two factors: as the heated 

 air rises, if its proper easterly motion were to remain the same, its 

 radius vector would increase; its velocity has therefore, by Newton's 

 second law, to diminish, and it lags behind as a westerly wind. 

 Then the air that rushes in to the Equator from north and south 

 has a lower eastward velocity than points on the lower latitude ; it 

 therefore also drags to the west. Therefore any low-pressure area 

 on the Equator is simply in the position of a stationary eddy on a 

 westward-flowing stream, and is supplied mainly from the east. 

 Thus Uganda, as it is in the neighbourhood of the low-pressure 

 area of the Nyanza, has its prevalent winds from the east. But 

 east winds in this part of Africa are dry ones, because they arise on 

 the dry barren steppes or ' Nyika ' between the mountains and the 

 sea ; for the monsoons blow parallel to the coast, and thus cut off 

 any large wind-supply from the Indian Ocean. The wet winds are 

 those from the great forest-regions of the west ; thus it is that the 

 snow-line is so much lower on the western sides of Kilima Njaro and 

 Kenya than on the eastern ; in the former, the glaciers reach the level 

 of 13,800 feet on the western side and only 18,700 on the eastern. 

 The different amounts of snow on the two sides of the main southern 

 arete of Kenya show that the same condition holds there. 

 The points to which these observations have led up are : — 

 lstly. The meteorological conditions of Kenya and doubtless also of 

 Kilima Njaro 1 are very different from those on the surrounding plains, 

 for there is a daiiy reversal of the wind-direction, so that westerly 

 winds can come in at all times of the year and not only during the 

 chauging of the monsoons. There is therefore no such sharp 

 differentiation on these mountains into wet and dry seasons. 



2udly. If the whole region were raised 5400 feet, an enormous 

 tract of country would be placed under these conditions, and not 

 only a few isolated peaks. 



Let us next consider what influence would result therefrom on the 

 conditions of atmospheric circulation, and thus on the rains and 

 plant-distribution. 



At the present time this region of Africa appears to be one of low 

 pressure. If we take Dr. Buchan's isobaric charts for each month 

 and calculate from these the mean for 5 points — viz. the north end 

 of Lake Nyassa, Zanzibar, the first point at which the Congo crosses 

 the Equator, the Nyanza, and Khartum — we get indications that the 

 low-pressure area of Arabia and the Sahara has a branch up the 

 Nile Valley to the south. This is shown in fig. 5. In the time of 



1 Hans Meyer has discussed ('Across East African Glaciers,' pp. 307-310) the 

 winds of Kilima Njaro, which are not now under the same conditions as those 

 of Kenya, for it is over 200 miles south of the Equator, and therefore is within 

 the region of the trade winds, and not of the Equatorial westerly drift. It is, 

 moreover, nearer the southern line of maximum pressure. 



