FIELDS OF FORCE AND OF MASS IN THE SEA. 141 



But, then, instead of drawing profile curves of true specific volume, we may draw 

 profile curves for constant values of the anomaly of the specific volume. In order 

 to draw sections of this kind we have to place at proper mutual distances verticals 

 like the second of figs. 25 and 26 and join points of the same value of pressure and 

 points of the same value of the anomaly of the specific volume. In the same way, 

 by taking verticals like the third of figs. 25 and 26, we might draw curves through 

 points of the same potential values and through points of the same value of the 

 density anomaly. 



These curves for equal values of the anomaly show on an exaggerated scale the 

 deviation of the isosteric or of the isopycnic curves from the horizontal course. 



85. Example : Northern European Waters, May, 1904. Since November, 

 1901, hydrographic expeditions have been sent out iour times a year from most 

 northern European states for the exploration of the northern European waters. 

 The chart (fig. 29) shows the places where soundings were made by the expedi- 

 tions in May-June, 1904.* The soundings are very far from being simultaneous. 

 But having no data from true simultaneous soundings, and our object here being 

 mainly to exemplify our methods, and not as yet to discuss the actual states of the 

 sea, we have treated the soundings as if they were simultaneous. How great errors 

 consequently may be introduced it is not possible to find out before more is known 

 of oceanic motion. 



The charts of fig. 27 show the topography of surfaces of equal sea-pressure 

 relatively to the physical sea-level, or, according to the other interpretation, the 

 topography of the true isobaric surfaces relatively to the ideal initial surface of the 

 pressure of 10 decibars. The curves are drawn ior every dynamic centimeter of 

 depth. The most direct method of obtaining them is to note on the chart the depths 

 calculated from the different soundings and to draw the curves by means of these 

 numbers. But it facilitates the work to note not the absolute depths (column 

 15 of tables U and W, pp. 126, 128), but the anomalies of depth (column 14 of same 

 tables). For the course and the mutual distance between the curves is determined 

 by the anomalies, while the addition of the constant normal depth of the surface 

 is required only to determine the situation of one of the curves representing an in- 

 teger value of the total depth. The heavy curves show the intersection of the iso- 

 baric surfaces with the bottom of the sea. As the isobaric surtaces are practically 

 level, these limiting curves are obtained at once from a bathymetric chart. 



The first six charts of fig. 27 show the topography of six isobaric surfaces with 

 the interval of pressure of 10 decibars, the next six that of six others with the interval 

 of pressure of 100 decibars. A general view of the charts shows that they contain 

 a greater number of lines the more we proceed downward. This does not mean, 

 of course, that the deeper surfaces are necessarily less level than the higher ones. 

 On the contrary, at a certain depth, differing according to circumstances, the iso- 

 baric surfaces will show a minimum of deviation from the absolute level surfaces. 

 The greater depths of the isobaric surfaces below the physical sea-level along the 



* Bulletin des Resultats Acquis pendent les Courses Periodiques, Annde 1903-1904. No. 4. Mai, 1904, pp. 

 74-98. Copenhague, 1904. 



