218 WINDS 



west, or in other words, when its course does not 

 vary from the parallel of latitude from which it 

 starts ; because this is the only case in which any 

 point of the surface, at which the current arrives, 

 has exactly the same rate of motion round the 

 earth as any which it has left. 



But, if the wind blows from the pole towards 

 the equator, it will be always passing from 

 places moving with less, to places moving with 

 greater speed. Tor instance, the speed of revolu- 

 tion of any point on the earth's surface under the 

 thirtieth degree of latitude, is twelve hundred and 

 twenty-nine feet in a second ; under the twenty- 

 ninth degree it amounts to thirteen feet more ; 

 and under the twenty-eighth, to twenty-nine feet 

 more in a second. Air, therefore, which moves 

 from the thirtieth to the twenty-ninth parallel, 

 keeps its original rate of revolution — that due to 

 the thirtieth degree — and, therefore, when it reaches 

 the twenty-ninth degree, is still turning, it is true, 

 in the same direction as the earth ; that is, from 

 west to east, but is moving round eastwards more 

 slowly than the earth below it, by thirteen feet in 

 each second, — and, when it reaches the twenty- 

 eighth degree, twenty-five feet in each second, more 

 slowly than the ground. It must seem, therefore, 

 to an observer, who feels this lagging behind of 

 the wind as an actual resistance — and its effect 

 upon all bodies which share the movement of the 



