XIV 



INTRODUCTION. 



must of course be entirely supplied by the air within the annulus, 

 and that which descends in the annulus itself. When upmoving 

 currents are formed by superior heat, clouds will more frequently 

 begin to form in the morning, increase in number as the heat in- 

 creases, and cease altogether in the evening, when the surface of 

 the earth becomes cold by radiation. 



The commencement of up-moving columns in the morning, 

 will be attended with an increase of wind, and its force will in- 

 crease with the increasing columns ; both keeping pace with the 

 increasing temperature. This increase of wind is produced partly 

 by the rush of air on all sides at the surface of the earth towards 

 the centre of the ascending columns, producing fitful breezes ; 

 and partly by the depression of air all round the ascending col- 

 umns, bringing down with it the motion which it has above, which 

 is known to be greater than that which the air has in contact with 

 the asperities of the earth's surface. 1 The rapid disturbance of 

 equilibrium, which is produced by one ascending column, will 

 tend to form others in its neighborhood ; 2 for, the air being pressed 

 outwards from the annulus, or at least retarded on the windward 

 side, will form other ascending columns, and these will form other 

 annuli, and so the process will be continued. These ascending 

 columns will have a tendency to approach, and finally unite ; for 

 the air between them, as between 2 and 3, (p. xii.) must descend, and 

 in descending, the temperature of the whole column will increase, 



1 On the comparative force of the wind during the twenty -four hours, by 

 Mr. Osier. 



Mr. Follett Osier, brought before the British Association, a paper, in which 

 he gave the results of his investigations respecting the direction and force of 

 the wind, deduced from the mean of 26,000 hourly observations, taken by the 

 anemometer, at the Philosophical Institution, at Birmingham, during the years 

 1837-8, and 1839, We extract one of Mr. Osier's tables. 



Table, showing the Relative Force of the Wind for each hour of the day, distin- 

 guishing the Seasons ; from a mean of the years 1837-8, and 1839. 



la.m.2 34567 



9 10 11 12 lp.m.2 



4 5 



78 9 10 11 12 



Winter. 

 Spring 1 ,. 

 Summer, 

 lutu . n. 



Totals, 



49| 47 | 47 | 48 | 48| 51 



120 115 112 120 117 116 134 



73| 82| 

 82 

 47 



85 | 70 | 75 



53 44 

 53 44 



217 247 274 295 286 280 247 224 



65) 63 | 63 | 63 | 59) 61 | 57 



193 169 156 153 136 136 12G 



As direction is not regarded in this table, a total of more than one thousand 

 observations is given for each hour of the day. In tabulating these, the curve 

 obtained, is found to be almost identical with that of the thermometer not 

 only for the whole year, but for each season. The increase in the tempera- 

 ture, however, precedes the rise of the wind by a short interval, until it has 

 attained its maximum force ; but as evening approaches, the wind declines 

 more rapidly than the temperature. 



* The annexed figure, is a copy of three water-spouts, seen by Lieut. Og- 

 deu, at one time, on the edge of the Gulf stream, which is described at page 



