INTRODUCTION. f>9 



As the observation of them is tlie hourly occu- 

 pation of the navigator, it is unnecessary to call it 

 to mind ; yet it would not be beside the purpose 

 to pay attention to the direction of the winds in a 

 vertical sense, in order to learn whether, as some 

 persons pretend to have observed, certain winds 

 blow more from below, and others more from 

 above. The strength of the wind, too, should be 

 more frequently measured, which may be done by 

 means of a wind-gage, on the plan of Bouguer or 

 Woltmann. 



The proper theatre, however, of the physical 

 labours of the navigator, is the element itself which 

 he navigates. Notwithstanding the thousands of 

 ships that have traversed the ocean in all direc- 

 tions, far and near, we still know so little of the 

 numerous interesting phenomena of this immense 

 mass of water, which covers two-thirds of the sur- 

 face of our globe, that this is precisely a main object 

 of every voyage undertaken for the improvement 

 of science. It is, therefore, worth the while to 

 recite in order, the single remarkable properties 

 of it, and to recommend them to the attention of 

 the navigator. 



We begin with those phenomena which are of 

 the highest importance, not only to geology, but 

 to navigation — the great mechanical phenomena 

 of the tides and the currents. 



The ebb and flood cannot, indeed, be observed 

 on board the ship, for even in a ship lying at 



r 3 



