82 DISTURBING INFLUENCES. 



Of course, the effect of these changes is to produce 

 north winds in one latitude and south winds in 

 another, according to the particular wind (equatorial 

 or polar) that happens to be in contact with the 

 earth. At the points where these two currents 

 cross, in changing places, we necessarily have calms, 

 or conflicting and variable winds. 



Here, then, we have the first of the constant dis- 

 turbing causes, and of apparent irregularities, in the 

 winds. The Earth, as every one knows, whirls 

 rapidly on its axis from west to east. At the 

 equator the whirl is so rapid that the atmosphere 

 does not at once follow the Earth's motion. It 

 lags behind, and thus induces an easterly tendency 

 to the winds, so that a north wind becomes a north- 

 east, and a south wind a south-east. Here we have 

 another constant cause of variation from the nor- 

 therly and southerly flow. We tnus account for an 

 easterly tendency to the winds, but whence their 

 westerly flow 1 It is simply explained thus : 



The motion of the Earth is greatest at the equator. 

 It diminishes gradually towards the poles, where 

 there is no motion at all. The atmosphere partakes 

 of the Earth's 'motion when in contact with it ; and 

 when thrown upwards by heat, as at the equator, it 

 keeps up the motion for some time, as it meets with 

 no resistance there. Bearing this in mind, let us 

 now follow a gush of warm atmosphere from the 

 equator. It rushes up, and, turning north and 

 south, seeks the poles. We follow the northern 



