16 



ployed as arguments. Helland-Hansen and wSandstrom in ''Report 

 on the Norwegian Fishery Investigations, Volume II, No. 4, Bergen, 

 1903," first provided a way to avoid such a ponderous, unwieldly 

 work by calculating, as an initial step, the values of specific volume 

 at frequent depths, and covering the normal range of change in com- 

 pressibility in an ocean of 0° C, and a salinity of 35 per mille. A 

 correction called the anomaly of specific volume is then added to this 

 first figure, representing the specific volume of any charactered water, 

 but under a similar pressure. According to these arrangements all 

 corrections are embodied in a total of four small handy tables. The 

 details of this ingenious method of tabulation are also described in 

 Bjerknes', ''Dynamic Meteorology and Hydrography," Carnegie 

 Institution Publications, 1910-11. Later table groupings have been 

 made and published by Hesselberg and Sverdrup, "Beitrag zur 

 Berechnung der Druckund Massenverteilung im Meere," Bergens 

 Museums Aarbok, 1914-15. 



GIVEN TEMPERATURE AND SALINITY— A GRAPHIC METHOD TO 



FIND DENSITY 



The specific volume in situ, as determined by the foregoing tables, 

 is based upon an initial given density, usually found by means of 

 Knudsen's Hydrographical Tables with addendum. There is con- 

 siderable labor attached to interpolating when there are perhaps 

 several hundred observational records of temperature and salinity 

 which require conversion into density form. The Geo-Physical 

 Institute, Bergen, where the writer spent some time, finds it con- 

 venient to facilitate such work by the construction of a graph based 

 upon the three arguments of temperature, salinity, and density, within 

 the range which prevails for the first two in the temperate zones. 

 The method possesses such great advantages over the use of the 

 tables that it is set forth here for the benefit of future investigators 

 who may have to deal with a large number of field observations. 



The construction of the graph is based upon the three formulae of 

 Knudsen : 



(1) 5 = 0.30+1.805 CI. 



(2) 5-0= -0.069+ 1.4708 CI -0.001570 CZ2 + 0.0000398 Cl\ 



(3)5t = St+(5o + 0.1324)[l-A + 5t (do-0.1324)]. 



(For do, dt, 2t, At, and Bt see Martin Knudsen's, "Hydrographical Ta- 

 bles," Copenhagen, 1901.) Density values are plotted as abcissse, 

 salinity values as ordinates, and isotherm curves, determined in ac- 

 cordance with the fixed relation existing between the tlu-ee variables, 

 run diagonally across the graph. In order to determine the latter 

 with a sufficient degree of accuracy, it is necessary to fix definitely a 



