15 



DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



senting the breadth dn (fig. 104), only with other intervals. Finally we perform the 

 graphical division by v. The field resulting is given by the chart of fig. 106, represent 

 ing in terms of pressure the topography relatively to the ground of a surface of flow 

 formed by those lines of flow which at the initial curve C have a height above the 

 ground defined by unit decrease of pressure. The contour-lines dp l = const, of 

 this chart have the same course as the curves T 1 = const, of fig. 105, only with 

 changed intervals. The curves 1, 2, 3, 4, 5, . . . show the points where pressure 

 is 1, 2, 3, 4, 5, . . . units smaller than at the ground. According as we use 

 m-bar, c-bar or d-bar as unit of pressure, these curves will represent the approximate 



Fig. 106. Topography of a surface of flow relatively to the earth. U. S. A., 1905, Nov. 28, 8 a. m. 



h eights of 7.5, 15, 22.5, 30, 37.5, ... of 75, 150, 225, 300, 375, . . or of 75, 

 1500, 2250, 3000, 3750, . . . meters above the ground. Whether it be legitimate 

 to go to greater heights will depend upon whether the given chart gives a true 

 picture of the average horizontal motion between the ground and these heights. 

 We have drawn no curve inside the curve 5, which, according to the different 

 interpretations, represents an approximate height of 37.5, of 375, or of 3750 meters. 

 But the formal construction, in losing its physical significance, would give an infinity 

 of contour-lines inside this curve, indicating an infinite increase of height of the 

 surface of flow as we approach the point or the lines of convergence. The lowest 

 part of the surface is represented by the curves 0.9, 0.8, 0.7 .. . which are found 

 partly outside the curve C, and partly inside it, especially a little south of the point 

 of convergence and between two of the lines of convergence. 



