The Survey of the Coast. 6Y 



clearly as to render the descriptions in the deed intelligible. 

 This is but a single instance of the practical application of the 

 knowledge gained ; and if its general usefulness may be judged 

 by the numerous inquiries made of the Bureau, it is not unreason- 

 able to assume that time will bear increasing testimony of its great 

 economic value from those who traverse the land, as well as those 

 who sail on the waters. 



The study of the recurrence of the tides along our extensive 

 Coast lines, and determination of laws that would satisfy the 

 great variance in the different periods, was a problem of no little 

 magnitude but the greatest possible importance to our commerce. 

 Much of the traffic along the coasts literally moves with the 

 tides, and the cost of transportation is enhanced or diminished 

 as the tide retards or advances it. Hundi'eds of dollars of ex- 

 pense may be incurred on a single cargo that must enter on the 

 high water, but through imperfect knowledge of the master of 

 the ship, is forced after sighting his port, to wait for the next tide, 

 perhaps over night, and is driven to sea by a sudden storm and 

 the voyage made several days longer. Such mishaps are not 

 infrequent, and even at the great port of New York certain 

 classes of vessels must "wait for the tide." The investigation of 

 this complex subject has resulted in the acquirement of a knowl- 

 edge that enables the prediction of the time of high and low 

 water, and the height of the tidal wave, years in advance ; and the 

 mariner may now carry veith him the tables published on the sub- 

 ject wherever he goes, and be independant of the doubtful com- 

 munications he may otherwise receive from the shore. How many 

 lives, how many dollars, have been saved by the knowledge 

 gained ? 



But the investigation of the Tidal phenomena is of great sci- 

 entific importance also ; and a practical assistance in the great 

 problems involved in the preservation and improvement of our 

 harbors, but in this connection it probably falls more properly 

 under the head of that greater study of the currents and their 

 effects in the erosion, and building of the shores ; the movement 

 of the sands and formation of shoals and channels; termed " Physi- 

 cal Hydrography." Our commerce depends largely on this study 

 for its pex'petuation, for without harbors commerce must cease ; 

 and without harbors that will admit vessels of the largest class it 

 must deteriorate. If commerce ■ finds increased profits in large 

 vessels it demands increased facilities, and the bars to the har- 

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