the Scripps Institution of Oceanography; it is this: Imagine, if you 

 will, that we shrink the Pacific Ocean down to a lake 10 miles 

 across. On this scale, the maximum depth corresponds to 60 feet. 

 Further, let us place a toothpick on this lake. This toothpick 

 represents the oceanographic vessels which we use. You have 

 heard, of course, that the oceanographer uses cables to lower his 

 instruments and to sample the bottom. On this same scale, it 

 would take a filament finer than the finest spider thread to plumb 

 this 60-foot depth. You can understand the apparent futility of 

 trying to accomplish useful work with this extremely fine filament. 

 This model illustrates the oceanographer 's problem. 



Many of you may be under the impression that the ocean is 

 essentially a huge mass of homogeneous fluid. If this were the 

 case, the ocean as we know it would not exist; it would be dead and 

 without life. The inhomogeneities within the oceaji make it tick, 

 and in many cases make it possible for life to exist. These in- 

 homogeneities are often small, but, due to the tremendous thermal 

 capacity of the ocean, these small differences represent relatively 

 large amounts of energy. Hence, the oceanographer often finds it 

 necessary to nnake measurements with a precision which surprises 

 his land-based colleagues. For instance, a temperatvire difference 

 of one one -hundredth of a degree is often highly significant. Very 

 small differences of electric conductivity are likewise important. 

 Sometimes it is possible to take advantage of the geometry of a 

 given system and measure a gradient directly. This is preferable 

 to the common case where it is necessary to take differences 

 between relatively large numbers. 



Now I would like to turn back the clock about 200 years. 

 Benjamin Franklin published a chart of the Gulf Stream in about 

 1782 (fig. 6.1). For its time it was a creditable task and well done. 

 He discussed the work leading to it in correspondence as early as 

 1776. How he came to make this discovery is hypothetical -- pro- 

 bably by discussing and learning of variations in ship speeds or by 

 talking with ship captains. He was an instrvunental genius and 

 proceeded to make measurements. He used two very simple de- 

 vices, a bucket, probably a wooden bucket, with which he sampled 

 water, and a thermometer, with which he made measurements of 

 the water temperature. He was so impressed with his results that 

 he developed what he called "thermometrical navigation, " wrote 

 considerably on the subject, and recommended it to many of his 

 friends. 



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