IN PRODUCINa ASCENDING ATMOSPHERIC CURRENTS. 213 



of the northern tropic, as the Himalayas do, there being no 

 other mountains near; and then endeavour to consider how 

 the atmosphere within the tropics would be affected by such 

 a state of things. From the evidence already adduced, it is 

 reasonable to infer that evaporation would take place from 

 the tropical seas, as at present, and the air over them would 

 be pretty fully saturated with vapour. But as there would 

 be no elevated land near those seas excepting the imagined 

 mountains to the north, the slight disturbances which are 

 always occuring in the atmosphere would force some of this 

 vapour up the imagined mountains, and produce such ascend- 

 ing currents as would draw all the air and vapour from the 

 tropical seas towards themselves. Winds would then blow 

 from the tropical seas towards the north, leaving the imagined 

 low belt of tropical land in Africa and America a dry desert. 

 The temperature of the air over this land might possibly reach 

 120° or lAi)"^, but there is no reason to believe Jthat such air 

 would rise and flow over in the upper regions towards either 

 pole, seeing that there would be no condensation going on 

 in it. But while the temperature of the air over the sea 

 near to the mountains would probably rise only to about 80'^, 

 and even that temperature be limited to the part near the 

 surface, a temperature very high for the elevation would be 

 carried up the mountains, where the expansion of the air 

 would nevertheless condense an abundance of vapour and 

 produce copious rains and strong winds. 



Now we have facts similar to these in the existing state of 

 things near the tropics, with the exceptions of the particular 

 localities of the m.ountains and deserts. The imagined deserts 

 would be only such as now exist in Arabia and Africa, and 

 the mountains would be similar to the present Himalaya 

 range. It would not be more surprising that vapour should 

 then pass from the tropical Atlantic Ocean to be condensed 

 against mountains to the north, than it is that it now passe* 



