210 MR. J. BAXENDELL ON THE 



forth until the proper energy of discharge of propulsive 

 gases has been acquired. As soon as this is the case, the 

 rocket frees itself and then rushes forth impressed with and 

 possessing every condition of a true rifle projectile, com- 

 bined with all those important properties which rockets 

 possess as implements of warfare. 



XV. On a Diurnal Inequility in the Direction and Velo- 

 city of the Wind, apparently Connected with the Daily 

 Changes of Magnetic Declination. By Joseph Baxen- 



DELL, F.R.A.S. 



Read before the Physical and Mathematical Section, January 5 th, 1869. 



While engaged lately in a discussion of the observations 

 of rainfall made at the stations belonging to the Manchester 

 Corporation Water- works, a question arose which rendered 

 it desirable to ascertain, if possible, whether any law of 

 periodicity existed in the daily changes of direction and 

 force of the wind. It has long been known that the force 

 or velocity of the wind is generally greater during the day 

 than during the night ; but I am not aware that this diurnal 

 variation of force has been discussed in connexion with the 

 direction of the wind, or with other meteorological pheno- 

 mena. On proceeding to collect materials for such a dis- 

 cussion, I found that the only published results of observa- 

 tions of the wind that were available for this purpose were 

 those given in the annual volumes of the Radcliffe Obser- 

 vatory, Oxford, which are derived from bi-hourly observa- 

 tions with a self-registering anemograph. This instrument 

 was first mounted in July 1856, at a height of 22 feet from 



