74 



CONSTRUCTION OF ISOBARIC CHARTS 



At the central office of the Weather Bureau by means of these numbers charts 

 can be drawn presenting synoptically the values of 11"'""', 1140 goo, Pioooo, Psoooo, El;:^, V.,-;.-o 

 and ^23.0- The first step is to separate the figures of the telegrams and to supply the 

 missing figures, with the following result : 



23 Sept., 1898. 8 A. M. 



The second step is to enter these values at the appropriate stations on a series of 

 skeleton maps. The sketch map forming Fig. 4 on page 67 gives a synoptic map of 

 the quantity n^"*"'. Fig. 5, page 67, shows a similar map for the quantity n^oolllJ. 

 The ma})S, Figs. 4 and 5 and curves have been drawn just as the isobars for sealevel 

 are drawn on the usual isobaric maps. The three maps following, viz., Figs. 6, 7, 8, 

 pages 67, 69, show the quantities p^, iJ^om, fsoooo, respectively. The map for^o, Fig. 6, 

 is copied directly from the Weather Bureau map of barometric pressure reduced to 

 sealevel. The ^40000 map, Fig. 7, which is a map of the isobars at the level surface 

 F" = 40 000, is constructed graphically by superposition of the p^ chart, Fig. 6, and 

 the n^*'*'" chart, Fig. 4, making use of the relation 



/'40000 — Fo — ■'■'■0 



The j»8oooo niap. Fig. 8, page 69, is constructed in an analogous way by superposing 

 Figs. 5 and 7, using the relation 



■prSOOOO 



PSOOOO — l* 40 000 ■''40 000- 



The synoptic map of the values Tlf^mo forming Fig. 9, of page 69, will be discussed later. 

 Fig. 10, on page 71, shows the synoptic distribution of the quantity F27.5, i. c, the 

 number of level surfaces of gravity between sealevel and the isobaric surface for 

 p — 27.5 inches ; it is constructed from the telegraphed values of F27 g superposed 

 on the map of isobars for sealevel. The last map on page 69, Fig. 11, shows the 

 distribution of the values of F25.0, ?". e., the number of level surfaces between sealevel 

 and the isobaric surface ;3 = 25.0. It is constructed by superposing Fig. 10 for F^g 

 and Fig. 12 for EtjJ using the relation 



' !5.0 — ' 27.5 "T ■'^27.5- 



The first map on page 71, viz.. Fig. 12, presents a synoptic view of the values 



