ABOUT THE WEATHER. 121 



into the region of constant weather, and the region of the 

 changeable. So far as the influence of the trade-winds 

 extends on each side of the tropical region, the weather 

 may be prophecied, almost to the day and hour, many 

 years beforehand. The median zone (from 2 4 N. L.), 

 is that in which nocturnal showers and storms alternate 

 with excessive heat and calms, without interruption, 

 throughout the whole year. On either side, towards 

 north and south, follows a zone (from 4 10 N. L.), 

 wherein such phenomena only occur in the summer ; 

 in the winter the trade-wind causes a rainless sky. 

 Next comes a zone (from 10 20 N. L.) in which 

 the incessant trade-winds allow no bedimming of the 

 eternal blue of heaven, and often years pass, without one 

 short, rapidly passing shower moistening the parched 

 earth. Finally, one more zone extends north and south 

 from 20 30 N. L.), the boundaries of the constant 

 weather, in which the trade-winds cause a rainless summer, 

 while the winter brings a warm but not quite constant 

 rain. The approximative statement of the latitude relates 

 only to the northern hemisphere and the Atlantic Ocean, 

 the only place whereof we possess sufficiently accurate 

 observations. To these follow a zone about 24 broad, in 

 which a constant struggle between the Polar currents 

 with the returning Equatorial currents, produces a most 

 changeable climate, which appears to us so capricious and 

 accidental, because the circumstances determining the 

 prevalence of the one or other current in a particular 

 locality, are so complicated, that we have not yet been 

 able to deduce the law of the changes from the various 

 observations. Looking somewhat closely into the matter 

 we find the following facts. According to the statements 

 already made, there are but two wind-currents upon the 



