1865.] of the Atmosphere of the Atlantic. 347 



fleecy clouds travelling from the N.E. None but those who have expe- 

 rienced these calms can imagine how anxiously wind is looked for : to the 

 N.E. of us there was an arch of clouds in the sky extending from the S.E. 

 to the N.W. points of the horizon, with a calm and low barometer on the 

 south side of it where we were, and (as we found afterwards) the N.E. 

 trade and a higher barometer on its north side; therefore the arch of 

 clouds was probably formed by the condensation of moisture as the air 

 rose, while we lay becalmed at the foot of the inclined plane of still air, up 

 which the N.E. trade was just commencing its ascent. 



Travelling south across the equator, it will be noticed how uniformly 

 the barometer rises until we arrive at the southern limit of the S.E. trades ; 

 but on referring to the homeward curves in February, it will be noticed 

 how much lower the barometer ranged then than in August. The home- 

 ward route through the Atlantic differing much from the outward, does 

 this difference of barometer arise from difference of seasons or difference of 

 longitude? By comparing the routes near the equator, where they come 

 very close to each other, and where the difference of height in the quick- 

 silver is as great as in any other part, I am led to think that it depends 

 upon the different seasons. 



Whilst speaking of the homeward route, it is interesting to remark how 

 on leaving the Cape of Good Hope we invariably had a valley, as it were, 

 in the atmosphere, which quickly rose as we sailed to the N.W., even 

 though we may have started in a south-easter, which is the high-barometer 

 wind in these latitudes. I had noticed that after rounding Cape Agulhas 

 with a south-easter and high barometer, the column fell suddenly after 

 rounding the Cape of Good Hope, though the S.E. wind continued ; and I 

 suppose that the fall is caused by the air's ascending as it comes in contact 

 with the high land : the curves seem to support this opinion. 



It will be noticed that at both seasons of the year there is a heaping-up 

 of the air at the polar end of each trade, in the place where Maury tells us 

 that two upper currents come to the surface of the earth ; the one we 

 have already alluded to, which comes from the equator towards the pole, 

 moving above the trades, clouds proving its existence ; the other, Maury 

 tells us, rises at the pole, and travels as an upper current, above the strong 

 westerly winds which prevail in high latitudes, towards the equator ; it can 

 hardly be expected to have many clouds, he says, as its moisture must 

 have been condensed by cold before rising at the pole, so that it becomes 

 cold dry air. 



We may ask what evidence the sailor can give for this theory as 

 deduced from observation. 



First, then, from these heaps of air he finds two surface winds blowing 

 in opposite directions: the one moving towards the equator is cool, dry, and 

 heavy, the other moving towards the pole is warm, damp, and light. 

 He may well say, If two surface winds blow in opposite directions from 

 this heap of air, there must be air brought to it by an upper current or 



VOL. xiv. 2 c 



