38 RESULTS OF METEOROLOGICAL OBSERVATIONS 



From an inspection of the zigzag lines we can infer that no such exceptions to 

 the regularity of the annual fluctuation occur (at Brunswick, Me.) as has been sup- 

 posed. The temperature on May 30, 31, and June 1 is indeed somewhat depressed; 

 but not suflaciently so, when compared with its probable error, to make sure of the 

 existence of an exceptional cold period. The October curve is quite regular in its 

 descent. 



DIRECTION OF THE WIND. 



The three observations taken each day, at morning, noon, and evening, though 

 not at equal intervals, are yet sufficient to give, by their combination, a tolerably 

 reliable daily mean. There are but a few omissions in the record between Novem- 

 ber, 1807, and December, 1859, in consequence of which the monthly number of 

 observations does not come fully up to the true sum. Occasional blanks, in some " 

 cases, undoubtedly refer to calms, of which, hoAvever, there is no special men- 

 tion. The direction of the wind is supposed to be given with reference to the true 

 meridian -^ and the horizon is supposed to be divided in eight principal directions, 

 the nearest of which, to that of the wind, is recorded. The force of the wind is 

 not stated ; the resulting directions will therefore be given under the hypothesis 

 of equal velocity. 



The general formulae for the reduction of observations of direction and force of 

 the wind, are the following : — 



Let 01 02 03 .... be the angles which the direction of the wind makes with 

 the meridian reckoned round the horizon, from the south westwards to 360°, a 

 direction corresponding to that of the rotation of the winds in the northern hemi- 

 sphere, and Vi v^ Vg . . . the respective velocities which may be supposed 

 expressed in (st.) miles per hour. The observations are supposed to be made at 

 equal intervals. Adding up all velocity numbers referring to the same wind during 

 a given period (say one month), and representing these quantities by Sj Sj Sg . . . ., 

 the number of miles of air transferred bodily over the place of observation by winds 

 from the southward is expressed by the formula 



R^ = Sj cos Oi + Sg cos 02 + S3 cos 08 -|- . . . . 

 and for winds fi-om the westward 



Ry, T= Sj sin 01 -|- §2 sin 6^ + Sj sin 03 + • • • • 

 The resulting quantity R and the angle 4' it forms with the meridian, are found by 



, R^ 



R = ^R; + RJ tan^=^ 



These general formulae in the case of eight principal winds assume the following 

 convenient form : — 



R, =:{S—N) + {SW—NE)k/1 — {NW—SE)VI 

 R^ = {W—E) 4- {S W—NE) >/i + {NW—SE) v/| 



' The magnetic decliaation of the needle is nearly 1 1^° W. for the middle period of the series of 

 observations. 



