98 DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



are nearly equal and oppositely directed. The direction of the resultant is read off 

 on the divided circle C. In order to read off the intensity of the resultant on the 

 same scale as that used for the components, we follow the circles from the point at the 

 end of the resultant to one of the central lines of the one divided sheet. 



The discontinuous use of the instrument will be understood at once. If the 

 directions of the given vectors are represented by vector-lines, the two divided 

 sheets are adjusted so as to be tangential to one line of each set. If the directions 

 are given by isogons, the adjustment of the sheets is made by use of the divided 

 circle C. In this case it will not be necessary to place the instrument on the chart. 

 Two workers can cooperate. One manages the instrument, while the other reads 

 off from the chart the given data and introduces the results on it. 



Continuous use of the instrument will also be possible. We can then go 

 along an isogonal curve, having the one disk fixed in the angle represented by the 

 isogon, while the other is turned according to the value of the angle represented 

 by the other set of isogons. The intensities of the two vectors are observed, and 

 thus by short steps we can follow the variations of the angle and the intensity of the 

 resultant and mark the points where integer values occur. But this work will 

 require keen attention. 



