44 



normal or abnormal order. Some might think, from the 

 constant changes that take place in the direction of the wind — 

 the vane continually shifting backwards and forwards, occa- 

 sionally even veering quite round the compass, and then 

 retracing its steps within a very short time — that the winds 

 could hardly be said to observe any order at all. Yet such 

 is the case notwithstanding. Though fickle even to a proverb, 

 long observation shows that they still conform with more or 

 less regularity to a given law — the law first enunciated by 

 Dove under the name of " the law of g}'ration " — all deviations 

 from which are sure to be set right in the end. The law may 

 be thus explained. In consequence of the rotation of the 

 earth on its axis, combined with the circumstance of the 

 several parallels of latitude moving with increased velocity as 

 they approach the equator, any body of air flowing from north 

 to south is, at every point of its progress, passing from places 

 moving with less, to places moving with greater speed. The 

 effect of this is to cause it to become more and more a north- 

 easterly wind, while in the case of a current from south to 

 north, or from the equator to the pole, the effect is in the 

 opposite direction, and from a southerly it becomes more and 

 more a south-westerly wind. 



From this circumstance the wind has at all times a pre- 

 ponderating tendency to veer round the compass in the 

 direction of the sun's motion, i.e., to pass from north, through 

 north-east, east, south-east, to south ; and in like manner 

 through south-west, west, and north-west, to north. It may 

 remain stationary for a time in any one of these points, or it 

 may retrograde even to the extent of a whole revolution, but 

 after a time it always recovers itself, the normal direction 

 being reassumed. At the end of a year, if the vane be found 

 to have made a certain number of revolutions in the wrong 

 direction, it will be found to have made a much larger number 

 in the right. " The vane of Osier's Anemometer at Green- 



