ROTCII. — THE ATMOSPHERE IN THE TROPICS. 2G5 



Teneriffe (Canaries), and St. Vincent (Cape Verdes). Since these bal- 

 loons were only intended to show the atmospheric drift, they did not 

 carry self-recording instruments, and their direction and velocity at 

 increasing heights were determined from angular measurements at the 

 ends of a base-line laid off on the lee shore of the islands mentioned. 

 One balloon, carrying a self-recording barometer and thermometer, was 

 launched from the yacht off' the island of Palma (Canaries), but, 

 though its drift was observed, the balloon could not be recovered. It 

 was found possible sometimes to follow the balloons in the telescope 

 until they reached a height of 11,000 or 12,000 meters. 



The observations obtained with the kites at 500 and 1000 meters, 

 and the simultaneous observations at sea-level, are given in Table I, 

 which is divided into two parts, the first containing the observations 

 made in an east-southeast direction across the Atlantic, and the second 

 part those made in a southerly direction within the northeast trade 

 and on its borders. West of the Azores, on the westerly slope of the 

 permanent area of high barometric pressure, the observations between 

 longitudes 69° and 39° show a slow decrease of temperature with in- 

 crease of height, amounting to 4.5° per 1000 meters. In the lower 

 500 meters the decrease is only 0.24° per 100 meters, owing to inver- 

 sions of temperature within the first few hundred meters in half the 

 flights. In the next 500 meters there is the more rapid decrease of 

 0.66° per 100 meters. Upon the easterly and southeasterly slopes 

 of the high pressure, between longitudes 25° and 19°, latitudes 38° and 

 33° north, the temperature falls at the adiabatic rate of one degree 

 per 100 meters in the lower 500 meters, and then declines more slowly, 

 namely, 0.20° per 100 meters, up to 1000 meters. The adiabatic rate 

 appears to prevail over the ocean at night as well as in the day- 

 time, and the bases of the cumulus clouds generally are not higher 

 than 500 meters. The relative humidity decreases with height on 

 the west of the high pressure, and increases to above 500 meters on 

 the southeast side. In the former region southwest winds prevail, 

 and in the latter locality northeast winds, the southwest winds turn- 

 ing to the left when facing them up to 500 meters, with increasing ve- 

 locity up to 1000 meters, and the northeast winds turning to the 

 right and increasing slightly in velocity up to 500 meters, but diminish- 

 ing above that level. The mean directions and velocities in this table 

 are resultants derived geometrically. In the column for wind-direction, 

 a plus sign before the figures representing the diff'erences per hundred 

 meters indicates a turning towards the right hand, and a minus sign a 

 turning towards the left. 



The observations on the northern edge of the northeast trade, that is, 



