i 



Sect. III.] 



HYDROGRAPHY. 



96 a 



fPm 



rt^ ! 



\ 



■.fMt 



c r 



V 



U^. 



f 



• fl 



measure 



water line, which we may presume will be double the 

 height of the wave above the mean water level. It will 

 necessarily require several observations to be made before 

 any satisfactory conclusion can be arrived at. The dis- 

 tance of the waves apart may possibly be tested by actual 

 measurement, by means of the lead-line and a float 

 veered out to such a distance that the float shall be on 

 the crest of one wave when the ship is on the top of the 

 other. And the rate may be determined by the time 

 occupied by the wave in passing from the float to the ship : 



the rate of the ship through the water and the angle her 

 course makes with the route of the wave being known. 



There are other methods of determining this hiterestin 

 problem which will no doubt occur to the intelligent 

 observer, and they are sufficiently numerous to afford 

 ample exercise of his ingenuity, but all are attended with 

 difficulty owing to the circumstanc 



under which the 



made 



U H 



> 



gii' 



e4 



