158 



DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



intensity-curves. In the first case the points situated on the same curve will be 

 displaced in the same direction, in the second along the same length. This will at 

 the same time make the construction easy and the figure conspicuous. A complicated 

 picture will, however, appear in places where one series of points is displaced beyond 

 the initial places of another series. 



This difficulty may be completely avoided if we choose the points according 

 to another principle, namely, so that the final situation of one point shall be the 

 initial situation of another. In this manner we get chains of points (fig. in) 

 which have a certain similarity with the lines of flow and would coincide with them 

 if we drew the displacements for infinitely short intervals of time. 



Fig. hi. Displacements in 3 hours. U. S. A., 1905, Nov. 28, 8 to 11 a. rn. 



It will be understood at once that from the corresponding charts of vertical 

 velocity we can derive the correlated vertical displacements, but it will be of no 

 use to enter into details before we come to the more general problem of dynamic 

 prognosis. It will be sufficient that we have indicated here the general principle 

 of kinematic prognosis . 



192. Different Forms of the Equation of Continuity. Before we leave the 

 question of kinematic prognosis we have to examine the prognostic value of the 

 equation of continuity. We have already alluded to the prognostic nature of 

 this equation, but we have used it hitherto exclusively for diagnostic purposes. 

 For the more general purpose we have first to give the complete mathematical formu- 

 lation of the equation of continuity. The two theorems, section 114 (A) and (B), 



