Hydrography^ and the Art of Navigation, 9t^ 



cises in such matters, we may state, that navigators equally de-> 

 serving of confidence, have assigned as the greatest height of 

 waves, in some instances Jive metres, and in others thirty-three. 

 What science now requires is not rude estimates, but actual 

 measurements, of what it is possible to appreciate the exact nu- 

 merical value. 



These measurements, we are aware, are attended with great 

 difficulties ; these, however, are not insurmountable, and, at all 

 events, the question is of too great interest to justify any hesi- 

 tation about the degree of exertion necessary to solve it. We 

 have no doubt that our young fellow-countrymen will them- 

 selves, upon reflection, devise some means for performing the 

 operation which we require of their zeal ; but a few brief con- 

 siderations may assist in guiding them. 



Let us suppose, for a moment, that the waves of the ocean 

 are petrified and immovable ; what, in that case, would be neces- 

 sary to be done in a vessel likewise stationary, and placed in the 

 trough of one of the waves, in order to measure the real height, 

 — to determine the vertical distance of the crest of the wave 

 and the trough ? An observer would gradually ascend the 

 mast, and stop at the point where the visual horizontal line, 

 parting from his eye, seemed to touch the crest in question ; the 

 vertical height of the eye above the surface on which the vessel 

 was floating, would be the height required. This operation, 

 then, it would be necessary to attempt in the midst of all the 

 commotions and disorders of a tempest. 



In a vessel at rest, as long as the observer does not change his 

 place, the elevation of his eye above the sea remains uniform, 

 and can be very easily determined. In a vessel tossed by the 

 waves, the rolling and pitching incline the masts sometimes to 

 one side, sometimes to another. The height of the points of 

 the top-masts varies incessantly, and the officer who has taken 

 his station on the mast cannot ascertain the value of his vertical 

 line, unless by the assistance of a second person placed on tlie 

 deck, whose object it ought to be to follow the movements of 

 the mast. If one Hmit their pretensions to ascertain this line 

 within a third of a metre, for example, the problem appears to- 

 us completely solved, particularly if the moments choseff for 



