200 PHYSICS. 
shape of the surrounding bodies of land; only in its southern portions 
between New Holland and Madagascar, between 12° and 28° 8.L., a 
south-east trade wind prevails the whole year. In its northern part south- 
west and north-east winds (monsoons) alternate ; of these the former blow 
from April to October, the latter in the remaining half of the year. The 
cause of this phenomenon is to be found in the unequal heating of the 
neighboring regions inclosing this sea, and possessing opposite seasons at 
the same time. In the summer half year, when the sun is north of the 
celestial equator, the north or, north-east countries, Arabia, Persia, and 
India, are the warmer, and the wind therefore blows over the sea to the 
land from the south-west; in the other half of the year, the sun standing 
south of the equator, the country to the south-west (Africa) becomes 
warmer, thereby producing north-east winds. 
The upper current from the equator to the poles has, in the northern 
hemisphere, a south-westerly. in the southern, a north-westerly direction. 
The altitude at which this current commences has not yet been determined ; 
on Teneriffe it prevails at an elevation of 9000 feet, while Humboldt found 
the easterly trade wind on South America at an altitude of 8000 feet. In 
all cases, the equatorial current becoming cooler, sinks deeper and deeper, 
finally reaching the surface of the earth. Thus in the higher latitudes the 
two opposite currents meet, and mutually interfere without any regular 
alternation taking place between them. On the great seas the west winds 
are tolerably regular between 30° and 40°, more so in the southern than 
in the northern hemisphere, and are used in the voyage to the Cape of Good 
Hope. In northern and western Europe the south-west winds decidedly 
predominate. The same is the case on the Atlantic, between Europe and 
North America, for which reason the voyage from Europe to America 
generally lasts longer than that from America to Europe. According to 
the recent calculations of Mahlmann at the mean latitude of the temperate 
zone, in both continents, a west-south-west wind is to be considered as the 
prevailing one See the chart of the winds (pl. 47. fig. 1) illustrating what 
has just been said. 
The following table gives the number of times, that is, the number of days 
in the 1000, during which, on an average, each one of the eight principal 
winds blows in the countries mentioned in the table : 
Countries. N. New Ee Be S. E. s. Ss. W Ww. N. W 
England... 82 111 99 81 111 295 171 120 
France... . 126 140 84 76 117 192 155 110 
Germany ..| 84 98 | 119 87 97 | 185 | 198 | 131 
Denmark . . 65 98 100 129 92 | 198 161 156 
Sweden ..- | 102 104 80 110 128 | 210 159 106 
Russia. “ue 99 | 191 8] 130 98 143 166 192 
|'N. America| 96 | 116 | 49 | 108 | 123 | 197 | 101 | 210 
The season of the year has a great influence upon the direction of the 
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