172 DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



plate XL. We can interpret the chart as giving vertical velocity in millimeters per 

 second at the height of ioo meters above the ground, or in centimeters per second 

 at the height of iooo meters above the ground. If we venture to extrapolate to 

 the latter height we get free vertical velocities of the same order of magnitude as 

 the forced vertical velocity derived by the surface-condition. This free vertical 

 velocity is seen to have a very irregular distribution. A certain tendency to be 

 opposite to the forced one is manifest in different places. But as to its general 

 features free vertical motion is seen to be governed by pressure. Generally speaking 

 the area of depression is an area of ascending motion, except in the details, inasmuch 

 as smaller areas of descending motion exist even in the immediate neighborhood 

 of the cyclonic center. 



We can in this case make the simple experiment of compounding free and forced 

 vertical velocity for the height of iooo meters above the ground. The result is given 

 on plate XLI. When this chart is compared with the simultaneous data regarding 

 the distribution of precipitation, of cloudiness, and of blue sky, a considerable accord- 

 ance will be seen to exist in spite of the great extrapolation involved in the estimation 

 of vertical velocities at so great heights from observations taken only at the 

 ground. 



202. Practical Applications of the Charts of Motion. It will involve no diffi- 

 culty to introduce the drawing of charts like that of plate XXXVIII, representing 

 the horizontal motion by lines of flow and curves of equal intensity, into the daily 

 meteorological service for the forecast of the weather. When the chart is to be 

 drawn only for qualitative purposes, it will not be required to use the more circum- 

 stantial method to draw first the isogonal curves. The main course of the lines of 

 flow can be sketched directly. When the drawing of the lines of flow and of the 

 curves of equal intensity is distributed between two workers, and these have acquired 

 some experience, it will cause them no difficulty to have the chart of motion ready 

 in a space of time comparable to that required for drawing the common charts 

 representing pressure, temperature, and other data. 



These charts of motion possess many characteristic features in the form of 

 singularities which are in an obvious relation to the conditions of the weather. 

 Therefore we have reason to believe that experience will gradually lead to practical 

 rules for weather-forecasts based upon the examination of the charts of motion in 

 themselves or in connection with the other charts. 



When the draftsman has acquired sufficient experience, a rapid examination 

 of the chart of horizontal motion will show him the places for the strongest forced 

 vertical motion and for the strongest free one. By making a few measurements in 

 these places he will be able rapidly to sketch charts of the vertical motion, and there 

 is hardly any reason to doubt that these charts would prove useful for the forecast 

 of precipitation. 



The charts of motion may also be useful for aerial navigation. For instance, a 

 glance at the chart of plate XXXVIII will show at once that an air-ship which moves, 

 e. g., 15 meters per second will not be able to go in a straight line say from Bismarck 



