30 DYNAMIC METEOROLOGY AND HYDROGRAPHY. 



(*> p = tIt 



Two variables # r and ft appearing on the right side of each of these equations, and 

 each of the variables having a wide range of variation, the complete tabulation of 

 a and p would be very laborious and lead to very bulky tables. We shall there- 

 fore use the equations (a) or (b) for eliminating a or p of our equations. After- 

 wards we shall give an indirect way to obtain the geometric representation of the 

 fields of specific volume or of density in the atmosphere. As an aid for this, table 

 14 M of Meteorological Tables, giving the value of the specific volume for the 

 standard pressures, will be found useful. 



26. Investigations of the Physical Properties of Sea-Water. The physical 

 properties of sea-water have been subject to elaborate investigations in connection 

 with the international exploration of the northern European waters.* 



The specific volume of sea-water and its reciprocal value, the density, depend 

 upon three variables pressure, temperature, and salinity. Generally the salinity 

 is not determined directly, but deduced from the content of chlorine found by titra- 

 tion, s denoting the salinity and CI the quantity of chlorine, both expressed in per 

 milles (/oo) of weight, s and CI are, according to Martin Knudsen, connected by 

 the equation 

 () 5 = 0.030+1.805001 



By this equation, which is tabulated in Martin Knudsen's tables, we can pass from 

 the independent variable CI used by Martin Knudsen to the independent variable 

 s, which we shall use consistently. 



To express the results obtained for the specific volume or the density of sea- 

 water, we shall introduce the following notations: a srp means the specific volume 

 and p STp the density of sea-water of salinity 5 / 00 , temperature t C, and sea- 

 pressure of ft decibars. By sea-pressure we then mean the total pressure dimin- 

 ished by the pressure exerted by the atmosphere against the surface of the sea. 

 The decibar is employed as a practical unit instead of the unit centibar belonging 

 to the m.t.s. system, because the pressure increases approximately by 1 decibar for 

 every meter increase of depth. 



Instead of writing the whole number representing a value of the density p, say 

 the number 1.02674, practical hydrographers usually write the four last figures 26.74. 

 This quantity being denoted by a, we have thus 



"r P = Ow - 1) 1000 



Martin Knudsen: Berichte iiber die Konstantenbestimmungen zur Aufstellung der hydrographischen 

 Tabellen von Carl Forch, Martin Knudsen, und S. P. L. Sorensen. Memoires de l'Academie Royale des Sciences 

 de Danemark. Copenhague, 1902. 



Martin Knudsen: Berechnung der hydrographischen Tabellen und Diskussion der Ergebnisse. Wissen- 

 schaftliche Meeresuntersuchungen herausgegeben von der Komission zur Untersuchung der deutschen Meere in 

 Kiel, Band 2, 1903. 



Martin Knudsen : Hydrographical Tables according to the measurings of Carl Forch, J. P. Jacobsen, Martin 

 Knudsen, and S. P. L. Sorensen. Copenhagen and London, 1901. 



V. Walfrid Ekman : Die Zusammendriickbarkeit des Meerwassers, etc. Conseil permanent International 

 pour L'Exploration de la Mer. Publication de Circonstance N 43. Copenhague, 1908. 



