PHYSICAL OCEANOGRAPHY 213 



purposes in horizontal plans and vertical sections. It is To show 

 necessary, in order to be able to see anything in the sections, ^oSfo^g i,^ 

 to exaggerate the scale of depth in comparison with the scale of diagrammatic 

 horizontal distance. This is shown in Fig. 152, which represents necessary' to 

 the floor of the Atlantic Ocean along the parallel of 40" N. exaggerate 

 The upper line (A) shows the section drawn to the same scale scaie.^'^''^^ 

 for depths and horizontal distances ; the variations in the depth 

 are represented by a thin uneven line, indicating how relatively 

 small is the depth of the Atlantic Ocean compared with hori- 

 zontal distances on the earth's surface ; the lower diagram (B) 

 shows the section with the depths exaggerated 500 times. 

 Drawing the depth on a larger scale brings out the details of Section across 

 the relief of the ocean-bed : thus off Portugal there is seen a Atk^dc* 

 narrow continental shelf, and then a rapid falling-off towards 

 the deep water (the continental slope) ; farther west (about the 

 middle of the figure) there is a corresponding slope, on the 

 summit of which the Azores appear ; then another fall towards 

 the western basin of the North Atlantic, followed by the 

 continental slope on the American side, where again a narrow 

 continental shelf borders the coast. The continental shelf is 

 seen to be wider on the American side than on the European 

 side of the section. This exaggeration of the vertical scale 

 allows of the representation of a number of details, but, of course, 

 the lines look very much steeper than they really are. One 

 must not imagine that the continental slopes are so marked as 

 they appear in the figure, for the angle is usually not so much 

 as two degrees, the slope being similar to that of our common 

 roads and railways ; real submarine precipices do occur, but 

 mostly as rare exceptions. 



At a comparatively early date it was known that the The temp^^ 

 temperature^ of _ike_-jseazsuiiace_w^ by ti-,e tureo t esea^ 



c urre nts. In the beginning of the seventeenth century, for 

 instance, it was noticed that there was a sudden change of 

 temperature on passing from the cold Labrador current south 

 of the Newfoundland Banks to the adjacent warmer waters of 

 the Gulf Stream. Benjamin Franklin, who made a careful Benjamin 

 study of the Gulf Stream (see Fig. 153), advised ships' officers Ji^'cuif ""'"^ 

 to use the thermometer in order to find out when they entered Stream. 

 the Gulf Stream, so that they might take advantage of the 

 current when voyaging eastward, and steer clear of it when 

 sailing westward. 



The American naval officer M. F. Maury (i 806-1 873), Maury. 



