NAVIGATION. 133 



discerned at a distance exceeding 150 miles. Now 

 it requires an elevation of 28,000 feet to render an 

 object visible at the distance of 200 geographical 

 miles. 



The high rock of Cape Dudley Digges was ob- 

 served to rise from 2 to 5 within an hour, and in 

 the next half hour it descended in appearance nearly 

 to the level of the water. 



In estimating the depression of the horizon of the 

 sea, corresponding to the different heights of the ob- 

 server's eye, the horizon is supposed to be raised by 

 terrestrial refraction one fourteenth part of the de- 

 pression due to the spherical figure of the earth, and 

 the corrections for different heights, rigorously com- 

 puted, are reduced accordingly in that proportion in 

 the best tables. 



British and Foreign Ships entered in 1825.* 



British. Foreign. 



At London . . 758,565 tons . 302,122 tons. 

 Liverpool . 315,115 . . 222,187 

 Hull . . . 328,204 . . 100,733 

 Leith .... 57,230 . . 55,276 

 Greenock . 51,249 . . 6,229 

 Of the above amount of foreign tonnage, the fol- 

 lowing amount belonging to particular states arrived 

 in England, viz. 



To Prussia 151, 790 tons. 



France 49,067 



United States of America . 178,949 ' 

 Norway 140,334 



* This statement refers only to five of the principal seaports, 

 but furnishes a comparative estimate of the whole. 



