METEOROLOGY. 323 



tically disappeared. All technical difficulties in obtaining such obser- 

 vations have been overcome by modern aerology. Thus, if in a country 

 of the extent of the United States 50 meteorological stations were 

 equipped for the ascents of kites and for the observation of au'-motion 

 by use of pilot balloons, it should probably be possible, not only to 

 precalculate wind for short intervals of time with satisfactory accu- 

 racy, but also to produce general weather forecasts of practical value. 



The attempt at precalculating the wind directly, while failing in 

 its direct purpose, has led indu'ectlj^ to another result which may be 

 of practical importance. Isallobaric charts have been used hitherto 

 only for extrapolating future charts of pressure. Taking the dy- 

 namic point of view, the rational use of the isallobaric charts will be, 

 however, to extrapolate the future chart of wind, and the method of 

 performing this extrapolation is very simple.^ 



The problems of weather forecasting based upon rational dynamic 

 principles have been taken up also along other lines. Instead of apply- 

 ing directly' the dynamic equations to a number of selected points, we 

 may try to bring into appUcation general theorems deduced from these 

 equations. Thus a kinematic analysis of the charts of wind has shown 

 that in the immediate environs of the lines of convergence and of 

 divergence there exists a very characteristic distribution of vortices. 

 This makes it possible to bring the theorems of the formation of vor- 

 tices into application for finding the laws of the propagation of these 

 lines. The result is the following simple rule: 



For one looking along the line in the direction of the wind a line of con- 

 vtrgence will move to the right and a line of divergence to the left in the 

 northern hemisphere. 



This theoretical conclusion has been confirmed very satisfactorily by 

 an examination of charts of wind from Europe. As these lines have 

 very characteristic meteorological properties (thus every cold wave and 

 every line-squall is preceded by a strong line of convergence) , this rule 

 may be of importance for weather forecasting. 



'Ueber die Beziehiing zwischen Beschleiinigungen und Gradientenandeningen und ihr« 

 prognostisch* Verwendung. 



