MADE WITH A NEW ANEiMOMETER. 308 



examining the motions of the vane, for it often swings into a new 

 position or stands still awhile before it swings back again. 



In consequence of this circumstance the direction of the wind cannot 

 be ascertained with very great precision. By carefully taking the middle 

 of the broad path, the direction may be read off to a single point of 

 the compass; but in the observations at the Society, we contented 

 ourselves, for the most part, with reading off to the double points (one 

 sixteenth of the circumference). 



The vertical scale is divided into tenths of inches, and read off by 

 means of two indexes, which slide on the same vertical rod which 

 guides the pencil. Tiie detail of the process of observation Avill be 

 best understood by attending to the following directions. It may be 

 observed that the cylinder is of brass japanned white, on which common 

 pencil marks can be rubbed out in the way described below. 



Directions for observing uith WhewelVs Anemometer. 



1. Place the instrument in a situation well exposed on all sides, 

 and fix it so that when the wind is South, the pencil is oti the line S 

 on the ban-el. 



This may be done by clamping the weathercock part of the instru- 

 ment with the pencil on the line S, then turning the box till the vane 

 points due north, and then fixing it in that position. 



2. Read off the instrument every day at a constant iiour. 



The pencil in descending will make a broad path, in consequence 

 of the wavering of the wind. The darkest part of this path must be 

 taken ; and from this, the direction of the wind determined, by reference 

 to the points of the compass marked at the bottom of the cylinder: 

 and, as the wind changes, the directions of the successive strips of wind 

 must be noted. 



