62 CONSTRUCTION OF ISOBARIC CHARTS 



the number of isobaric surfaces included between two level surfaces of gravity, as well 

 as the number of the level surfaces included between any pair of isobaric surfaces, 

 can not be everywhere the same, as is the case under static conditions, but on the 

 contrary all the isobaric surfaces are in a state of continuous movement and deforma- 

 tion relative to the level surfaces of gravity, as is well known from the study of daily 

 synoptic weather maps. 



Therefore, in order to find the relative positions of the isobaric surfaces and the 

 level surfaces of gravity under dynamic conditions, the quantities ITj^-, py, E^-, and T,, 

 must be calculated along every vertical in the atmosphere and for every instant. 

 The practical carrying out of this problem would require the sending up simultaneously 

 from a number of stations, kites or balloons carrying self- registers, by means of whose 

 records the four above-mentioned quantities for the verticals at the stations can be 

 calculated. The values thus obtained for these quantities can then be entered on 

 synoptic charts and graphically interpolated, just as is now done, daily, for the 

 barometric readings observed at the meteorological stations and reduced to sealevel. 



The kite- and balloon-ascensions heretofore executed may be classed under four 

 types, viz.: ascents reaching great altitudes by means of sounding balloons, as at 

 Trappes, near Paris ; ascents in manned balloons, such as are made in Germany ; 

 ascents to great heights by means of kites, as at Blue Hill, Mass., and Trappes ; 

 and finally the kite-ascents carried out by the Weather Bureau from a large 

 number of specially equipped kite-stations, e. g., the 17 kite-stations of 1898. In 

 cooperation with the manned balloon ascents in Germany, frequent simultaneous 

 ascents of manned and unmanned balloons are carried out at many other European 

 stations {i. e., the international balloon-ascensions). These international balloon- 

 ascensions in Europe and the kite-ascensions made by the U. S. Weather Bureau in 

 America, are especially adapted to synoptic presentation of the four quantities E^;, 

 n{';, Py and Vp in the atmosphere, because the pressure may be calculated from them 

 along a number of verticals in the atmosphere for the same moment of time. In the 

 present paper I shall work up only the observations with kites executed by the U. S. 

 Weather Bureau. 



For the purpose of synoptical study of the Weather Bureau kite-observations it 

 is very desirable that they be carried out at those hours for which the daily weather 

 maps are made, viz., at 8 A. M. and at 8 P. M., 75th meridian time. Since, how- 

 ever, the wind-conditions often made it impracticable to send up the kite at so early 

 or so late an hour, therefore the observations made at any time during the day must 

 be extrapolated to 8 A. M. or to 8 P. M. The rules for this extrapolation can be 

 deduced only after the proper study of all the kite-observations heretofore made. 



