92 DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



way we can draw a topographic chart for every standard isobaric surface reached by 

 the ascents. A set of such charts gives a perspicuous representation of the distribu- 

 tion of pressure in the investigated part of the atmosphere. Examples are given 

 in figs. 13 and 19. 



To find the correlative representation of the distribution o mass, we have to 

 remember that the figures representing the mutual distances from one standard 

 surface to the next at the same time represent the average specific volume of the air 

 in the sheets between the surfaces. A chart of mutual topography of two successive 

 standard isobaric surfaces will therefore also represent the field of average specific 

 volume in the sheet between the two surfaces. We may draw these charts directly 

 from the figures representing the thickness of the sheets (example 1, column 7, 

 table J, p. 70 example 2, column 8, table K, p. 74) or indirectly from the charts of 

 absolute topography, using the method of graphic subtraction, the latter method 

 being, however, less accurate. Charts of this description are given in figs. 14 and 20. 



Of course we might also have represented the distribution of mass by topographic 

 charts of the isosteric surfaces. But, however interesting these might be, the 

 above representation, obtained in immediate connection with the distribution of 

 pressure, will generally be found the more useful, apart from the greater facility 

 with which it is found. 



In order better to conceive the topography represented by the charts it will be 

 usetul to draw profile curves of the isobaric surfaces. A set of such verticals as 

 the second of fig. 4 are drawn at horizontal distances corresponding to the distances 

 between the stations. Joining the points belonging to the same isobaric surface, we 

 get the profile curves. Taking the other set of divisions on the same verticals, we 

 may also get the profile curves of the isosteric surfaces. If both sets of profile curves 

 be drawn on the same diagram, as in figs. 17 and 21, they intersect each other, show- 

 ing the deviation from the hydrostatic principle of the coincidence of the surfaces. 

 These vertical sections are not of the same practical interest as the charts of abso- 

 lute and relative topograph}-, but have still interesting theoretical properties, and 

 enable us to get a more complete conception of the content of the charts. An im- 

 portant geometrical relation between the section containing the profile curves and 

 the charts of relative topography will be given presently (section 73). 



65. Charts of Absolute Pressure and of Mutual Pressure Differences in 

 Level Surfaces. On the chart containing the stations we can then note the num- 

 bers representing the pressure found at a certain level, and guided by these numbers 

 draw an isobaric chart for this level, in the same manner as such charts are drawn 

 for sea-level in the daily weather service. A set of such charts, drawn for a set of 

 standard levels, will give as complete a representation of the distribution of pressure 

 as the preceding one by topographic charts of isobaric surfaces. Examples of such 

 isobaric charts at different levels are given in figs. 15 and 22. As too many charts 

 would be acquired if drawn for every standard level, i. e., for every dynamic meter 

 of height, we have only drawn them for intervals a thousand times greater, i. e., for 

 level differences of 1,000 dynamic meters. The pressures represented by the 

 isobaric curves are added in m-bars. 



