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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 51 



adiabatic curves corresponding to the transition out of the rain 

 stage into the snow stage. 



As we have already in the construction of the pressure and tem- 

 perature diagram as previously explained, constructed lines of 

 equal altitude from the adiabats, so now the lines of equal pressure 

 are drawn in order to be able to read off the pressure changes from 

 this diagram, taking as the basis the initial altitude o meter and pres- 

 sure 76o mm . The isobars run in straight lines, inclined downward 

 toward the lower temperatures and separated farther and farther 

 from each other as the altitudes increase. 



But in this diagram there is a special system of pressure lines 

 for the dry adiabats and another for the condensation adiabats. 

 The departure of one from the other is first noticeable at consider- 

 able altitudes and remains always very slight, amounting to only 

 6 mm even at 6000 meters of altitude. In this diagram the pressure 

 lines for the condensation stage are drawn as given by the tempera- 

 tures corresponding to the adiabats that have been constructed. 

 The value for any other given pressure is easily interpolated from 

 table 7; see, for example table L. 



Table L 



If we desire exact values of the pressure for the dry adiabats at 

 great altitudes we can obtain them from equation (1). 



In order not to overburden the diagram, the pressure lines are 

 only drawn through for each difference of ioo mm of pressure and the 

 remaining lines at intervals of io mm are indicated as to their begin- 

 ning and ending on the two sides of the diagram by short dashes. 

 By means of these dashes, laying a straight edge across the diagram 

 or, perhaps, by ruling the lines in another color, such as blue, these 

 dashes may be utilized. 



For the determination of the point of transition from the dry 

 stage into the condensation stage and to determine the quantity 

 of moisture at any point of the diagram, the curves of constan 



