ATMOSPHERIC MOTION. 83 



local causes ; but on the tropical seas there is a wind 

 constantly blowing between east and north-east on the 

 north, and east and south-east on the south, of the 

 parallel of greatest heat, while in the upper regions of 

 the air there is a wind in the opposite directions. The 

 cause of the first is the immediate action of the sun, 

 and, therefore, it is most powerful within the tropics ; 

 the cause of the latter is in the high latitudes from 

 which the air is drawn by the former, and, therefore, 

 it is felt the most in the temperate regions. These 

 winds are most felt in the southern hemisphere in our 

 winter, and in the northern in our summer. They are 

 sufficient to make the south-west wind the most prevail- 

 ing one in Britain at all times, and it is probable that, at 

 a certain height in the atmosphere, the south-west wind 

 is constant with us. While the wind was at east and 

 dry, and continued so for some days before and after, 

 we have found a south-west wind with showers on the 

 top of Ben Nevis. Indeed we never met with any but 

 a south-west wind on the top of our very high moun- 

 tains. We do not mean to say that it is constant 

 there, but it is so much more so than in the vallies or 

 on the plains, as to leave not the least doubt that there 

 is an elevation at which it is constant, and quite unin- 

 fluenced by the varying winds, the storms and the calms, 

 that arise from the action of the varied surfaces below ; 

 as from the action of causes in the atmosphere itself 

 which, for the sake of having a verbal explanation, 

 where the real one had not been found, it has been cus- 

 tomary to refer to electricity, as if electricity at least 

 the sensal appearance of it (and beyond sensal ap- 

 pearances we know nothing, except our own mental 



