NO. 17.] 



WIND. 



303 



In every month and season the range is much greater with the stronger 

 winds than with the weaker. PI. II (1 cm. ^ 1 m. p. s.). 



With the weaker winds, we have in the winter and in the dark season 

 the minimum about noon, and the maximum at 2 a. m. This is the reverse of 

 the general rule. The range is rather small. In the other seasons we have 

 the minimum about 4 a. m., and the maximum about noon, with a relatively 

 small range. 



With the stronger winds, the period has the ordinary run, with a 

 minimum about 2 a. m. and a maximum about noon. We have in winter 

 and in the dark season a range nearly as great as in the other parts of 

 the year, and in winter even greater than in summer. The spring and the 

 equinoctial months show the greatest range. 



This seems to indicate that the diurnal period of the velocity of the wind 

 is vastly more influenced by the average velocity of the wind during the day 

 than by the change of the radiation in the course of the 24 hours. 



We have seen that a smaller amount of cloud and a lower average 

 velocity of the wind during 24 hours generally give a smaller range of the 

 diurnal period of the velocity of the wind, and that a larger amount of cloud 

 and a higher velocity of the wind give a greater range of the diurnal period 

 of the velocity of the wind. We have intimated (p. 294) that the first-named 

 conditions point to an anticyclonic, the last-named to a cyclonic state of the 

 atmosphere. In order to verify this relation, I have calculated the mean 

 values of the pressure of the air corresponding to the velocities of the wind 



