MR RANKINE'S OBSERVATIONS MADE WITH WHEWELL'S ANEMOMETER. 35'1 



whose sides will necessarily represent the portion referrible to the two adjacent 

 cardinal points. Thus for reducing the intercardinal NE, SE, SW, NW, to the 



cardinal points, the fraction j^ is used as the multiplier ; for reducing in a similar 



12 4 

 manner the subordinate winds NNE, ENE, SSE, &c. jg and ^^ are used ; for the 



no R R 



oblique winds N^?, S^, E^, &;c. jr and — ; and for NEw, SEs, SWs, kc. ^ and 



83 



-- are used as multipliers.* In this reduction the days are resolved into periods 



during which a certain group of neighbouring winds were prevalent. 



The mode of registration employed renders it impossible to present in a gra- 

 phical form every successive change in the direction of the wind. At each 

 reading the amount was put down in the column corresponding to the direction 

 in which such a quantity of wind had passed over the anemometer, leaving out 

 of account altogether the order of succession : for instance, within the space of 

 twelve hours the wind may have blown from two or three points of the compass, 

 but we are unable to find, by a mere reference to the register, what direction was 

 first in the oi^der of time. It must be recollected, however, that this is not an 

 imperfection in the instrument, but merely in this particular mode of registering 

 its indications. 



But though fit'om the register employed the minute changes cannot be pre- 

 sented in a graphical form, yet we may take the mean direction and magnitude 

 of certain groups of neighbouring winds, as found in the Second Table, and com- 

 pounding them, give in a continuous line the average dnection and magnitude 

 that belongs to the whole time of observation. This accordingly has been done, 

 and shews very remarkably the general features of the wind during last winter. 

 (See Plate XIX.) It will be remembered that the month of December was very 

 mild, with south and west winds, and though frost set in about the beginning 

 of January, SW winds still continued to prevail till the 8th ; a change then took 

 place and east winds prevailed, accompanied by severe frost, with little intermis- 

 sion, up to the 6th of March. All these changes are very distinctly shewn in the 

 line drawn in the way just stated ; in fact, the general character of the atmo- 

 spheric currents, and the severity or mildness of the season, is much more remark- 

 ably shewn than if every minute change in the direction had been traced out. 



It would be interesting to compare the foregoing results with those of similar 

 instruments at other stations, but, so far as I am aware, the observations made 

 at Plymouth and Cambridge during the last winter have not been published. 



* The notation Ne, Se, &c. denotes what is commonly represented by NbE, SbE, &c. ; and 

 NEw, SEs, &c. what is commonly represented by NEbN, SEbS, &c. 



