6\ DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



isobaric surface to all other isobaric surfaces situated below the next higher and 

 above the next lower standard surface. The distance is counted positive upward 

 and negative downward. It gives the first approximation value U of the height 

 H n p from the standard isobaric surface to a point of the pressure p. 



(C) Table iim. Distances in dynamic meters from the earth'' s surface to the 

 nearest standard isobaric surfaces, the average virtual temperature of the sheet 

 being o C. This table differs from the preceding one only in the arrangement. 

 As argument appears the pressure observed at the earth's surface. The tabulated 

 quantities are the distances to the two nearest standard surtaces above and to the 

 nearest standard surface below the point where the pressure is observed. The dis- 

 tance upward from the earth is counted positive and the distance downward nega- 

 tive. Of course the standard surface below the earth has no real existence. It 

 may, however, for obvious reasons, be useful to bring it under consideration. The 

 table gives the first approximation H to the height H v n from the earth's surface, 

 where the pressure is p, to the standard surface of pressure ;/. 



(D) Table I2m. Corrections to tables iom and 1 1 m for temperature. This 

 table is calculated according to formula (b") with the two arguments, the average 

 virtual temperature t iP between the two surlaces n and p and the height JT found 

 from table iom or iim. This correction for temperature may be either positive 

 or negative according to the sign of the temperature t iP . But as it has equal 

 numerical values for equal numerical values of r, it will not be necessary to intro- 

 duce signs in the table. The first part of the table, extending to the value noo 

 dynamic meters for height H and to values 34 C. tor temperature, will be suf- 

 ficient for most cases practically occurring. The continuation gives the extension 

 to the limiting height of 10,000 dynamic meters and to the values ioo C. of 

 temperature. 



52. Calculation of the Height Corresponding to a Given Pressure. If the 



virtual-temperature diagram be given as a curve connecting virtual temperature 

 and pressure, tables 9M to 12 m will at once enable us to calculate the height corre- 

 sponding to any pressure. From the diagram (fig. 5), we take the average virtual 

 temperature, first between the earth's surface, where the pressure is ft a , and the 

 lowest standard surface, then between the successive standard surfaces, and finally 

 between the highest of these and the isobaric surface of the given pressure p b . By 

 tables 11 m and 12 m we then find the height of the lowest standard surface above the 

 earth, by table 9M the thickness of the successive standard sheets, and by tables iom 

 and 12 m the height of the given isobaric surface above the highest standard surlace. 

 Adding these heights we get the height of the isobaric surface p b above the ground, 

 and adding the height of the ground above sea-level we get the height above sea- 

 level of the given isobaric surface. As all the other heights, that of the ground is 

 to be expressed in dynamic meters. The first of the problems defined in section 

 49 will then be solved. 



Suppose now the virtual-temperature diagram to be given with the heights in 

 dynamic meters as ordinates (fig. 6). The pressure observed at the station at the 



