ggQ WINDSOFTHEGLOBE. 



atmosphere, in a direction contrary to the trade-winds, towards the polar limits of 

 the latter, or to about 30° N. lat. and descended there. 



Then the same principle was extended to dry, hot continental areas, where a 

 powerful ascending current must exist on account of the heating by the sun, and 

 this was proved by the great decrease of pressure in summer time. 



Buchan extended the idea af ascending and descending currents further, sup- 

 posing there was an ascending current over every area of low barometer, not only 

 near the equator and on warm continental areas, but also in high latitudes, as on 

 the North Atlantic, the North Pacific, etc. This air, he supposed, descended over 

 areas of high pressure, as for example those existing in winter in Northern Asia 

 and North America. Thus the supposition is, that the air flowing out of areas of 

 high barometers, to a certain extent, comes from above, and again where the baro- 

 meter is low, air ascends and flows in the higher strata, towards areas of high 

 pressure. 



I must repeat here, that this is a supposition, though a very plausible one, and 

 that the actual facts which would prove the existence of such upper currents, 

 with the exception of the so-called counter-trades in the region of the trade-winds, 

 are very scarce. To these principles I would refer the direction of the wind at 

 Dodabetta in the Neilghiris, in Southern India (above 8000 feet), which is nearly 

 opposite to that observed in the lower strata in Central India, being from the N. W. 

 in summer, that is, from the heated regions of the Punjab, where pressure is very low. 

 In the lower regions, the winds on the contrary are S. E. and S., that is, the air 

 is flowing towards Punjab. Another remarkable fact is the strong, constant, and 

 warm "W. wind observed in winter on some mountains near Lake Baikal. At that 

 time of the year, the air is generally calm in lower regions, the cold intense, and 

 pressure high. This west wind of the higher regions would thus seem to be a 

 compensating current, flowing perhaps from Iceland towards the region of highest 

 pressure of Eastern Siberia. 



The observations on two of the highest peaks of the Rocky Mountains, above 

 14,000 feet, have failed to show an upper current of air blowing in a direction 

 different from the lower one. As Ave have said before, our information as to upper 

 currents is very scanty, and thus great caution seems yet necessary in drawing 

 conclusions. 



On the other hand, the influence of pressure on the winds near the surface of 

 the earth is so well authenticated and reliable that we need not hesitate to base 

 further conclusions on it. 



The greater part of the earth being covered with water, we can first consider 

 what would be the case if there were no intervening continents. What in this 

 case would be the normal arrangement of pressure on the oceans ? A belt of low 

 pressure near the equator, a belt of high pressure at about 30° north and south, 

 and a belt of low pressure about from 60' to 65°, after which the pressure would 

 rise again towards the pole. This gives us three systems of winds at the surface 

 of the earth, easterly (polar) in the lowest latitudes, westerly (equatorial) in the 

 middle latitudes, and again polar in the highest latitudes, in each hemisphere. A 



