124 DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



Where 



(g) A 5 ,0,p = I a 35,0, p dp 



W As,0,D= I P35,0,Dd-D 



and 



(/) A/= f et/Z* 



Here (^") represents the normal depth corresponding to a given pressure, *. e., 

 the depth tabulated in table 7 h; (//) the normal pressure at a given depth, i. e., the 

 pressure registered in table 15 h. We have therefore henceiorth to occupy our- 

 selves only with equations (3s") and (_/), the first of which gives the anomaly of depth 

 tor a given pressure, while the second gives the anomaly of pressure at a given 

 depth. 



76. Fundamental Approximation Rules. The anomalies of depth or of pres- 

 sure should be determined in accordance with the observed values of salinity and 

 temperature. Generally the values of these quantities are obtained ior known 

 values of depth, measured in meters by means of the sounding-line. In other 

 cases a manometer is used, giving the pressure at the places from whence the 

 samples of water are taken, the temperature and salinity of which are determined. 



Between the depths of a certain number of common and the same number of 

 dynamic meters there is a difference of about 2 per cent. Between the depths 

 represented by a sea-pressure of a certain number of decibars and that represented 

 by the same number of dynamic meters there is a variable difference not exceeding 

 3 per cent in the upper layers and 5 per cent in the greatest depths of the sea, as 

 seen from table 7 h. Between the depth represented by a sea-pressure of a certain 

 number of decibars and that represented by the same number of common meters 

 there will finally be a variable difference not exceeding 1 per cent in the smaller 

 and 3 per cent in the greatest depths of the sea. To these differences (from 1 to 5. 

 per cent) of the total depth there will correspond only very small differences of 

 temperature and salinity. For in the upper sheets, where relatively great differ- 

 ences of temperature and salinity may occur, this difference of depth will be very 

 small, and lower down the variations of temperature and salinity will be exceed- 

 ingly gradual. Thus, these small differences of temperature and salinity will have 

 no appreciable influence upon the small corrections AD and Ap. Suppose, there- 

 tore, a sample of water to be taken up from a depth of a certain number of common 

 meters. If it be convenient for the calculation we can, without restricting the 

 accuracy of the final result, consider it as taken from the depth of the same number 

 of dynamic meters, or from the isobaric surface of the same number of decibars. 

 Or, suppose the sample to be taken from a place where the manometer has shown 



