66 DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



and therefore also in inverse proportion to the average virtual temperature of this 

 sheet, reckoned from absolute zero. Thus the two heights H' H n and H H n 

 must be in the proportion 



H' -H = (H- H) 273 



v " ; 273+t 



Subtracting H H n , we find the following value for the required correction: 



AH "= H> - H = - (H - H) 7 



K "' 273 + T 



This may finally be written in the form 



the auxiliary quantity r' having the value 



273T 

 (b) 



273 +T 



Formula () has the same form as formula ("), section 51, tabulated in table 12 m. 

 But, to use table 12M for the determination of the height correction A// in the case 

 now treated, we have to use the artificial temperature t' instead of the real tem- 

 perature r. This artificial temperature is tabulated according to formula (&) in 

 table 13 m of our Meteorological Tables. Using this table in connection with 

 tables 9M to 12M, we can calculate the pressure at any given height. 



The practical procedure will turn out somewhat differently according as the 

 virtual temperature is known at a given height or for a given pressure. In both 

 cases we first determine the height of the standard isobaric surface as described in 

 the preceding article. Then, if the virtual temperature be known for a given 

 height, we immediately find from the diagram the average virtual temperature t for 

 the sheet between the heights H and H n . On the other hand, if the virtual tem- 

 perature be known for a given pressure, we use table iom to find an approximate 

 value p' of the pressure at the height H. Taking from the diagram the average 

 virtual temperature between the pressures n and p' we get a temperature r, which 

 with sufficient approximation can be identified with the average virtual temperature 

 of the sheet between the heights H n and H. 



This temperature t being found, we take the corresponding artificial temper- 

 ature t' from table 13 m. Using this and the height H H n in table 12M, we find 

 the required correction AH. This correction added to the height H H n gives the 

 height H' H n , which used in table iom gives the required pressure ft at the 

 height H. 



The third and fourth of the problems defined in section 49 are thus solved. 



54. Examples of a Complete Interpretation of the Results of a Meteorological 

 Ascent. On pages 68-75 are given the schemes for the complete hydrostatic appli- 

 cation of the observations obtained, under different suppositions, from an ascent 



