SURVEY OF THE COAST OP THE UNITED STATES. 233 



the coast ; and some of the Uglit liouses, jilaced on the princi- 

 pal capes or at the entrance of the principal harbours, ap- 

 pear to be the most ehgil)le places for that purpose, as being 

 objects particularly interesting to navigators, visil)le at a 

 great distance, and generally erected on spots on whicli simi- 

 lar buildings will be continued so long as navigation exists. 



8. A trigonometrical survey of the coast between those 

 points of which the position shall have been astronomically 

 ascertained ; in the execution of which survey, the position 

 of every distinguisliable permanent object should be care- 

 fully designated, and temporary beacons be erected at pro- 

 per distances on those parts of the coast on which such ob- 

 jects are rarely found. 



3. A nautical survey of tiie shoals and soundings of the 

 coast, of which the trigonometrical survey of the coast itself, 

 and the ascertained position of the light houses and other dis- 

 tinguishable objects would be the bases ; and wliich would 

 therefore depend but little on any astronomical observations 

 made on board the vessels employed on that part of the 

 work. 



Biit this is submitted to your consideration not for tlie 

 purpose of pointing out any plan in preference to another, 

 but only in order to shew the view which we have taken of 

 the subject, and the degree of accuracy which we arc desi- 

 rous of obtaining. 



I will only add, tliat the greatest practical difficulties which 

 have heretofore occurred, relate to what I call the nautical 

 survey ; and on that j)art of the subject the following itKjui- 

 ries have arisen : — Can a correct survey be taken with one 

 vessel alone ? Can angles be taken with sufficient correct- 

 ness from on board a vessel, so as to ascertain its position in 

 relation to three visible olyects on shore? Or is it neces- 

 sary that the vessel's position, at the time of taking any par- 

 ticular sounding, should be ascertained by observers on 

 shore? And many others which an examination of the sub- 

 ject will naturally suggest to you. 



