NAVITECTURE. 451 



shoals, rocks, mud, trees, and snags, from the channel: and these im- 

 provements are effected by various means ; as by washing, that is, 

 causing a sudden flood to carry away the obstructions ; or by dred- 

 ging, removing the earthy matter with a dredging machine ; or by 

 blasting, for the removal of rocks ; or by cutting and dragging, for 

 the removal 6"f driftwood, snags, and sawyers. These latter, stand 

 erect in the water ; but the snags are fixed ; while the sawyers have 

 a vibratory motion. Where the current is deadened, producing a 

 shoal, the remedy is a wing dam, diminishing the width, and increas- 

 ing the velocity. Where the current is too strong, producing rapids, 

 the remedy is a short canal, with locks, and a dam if necessary at its 

 upper end ; for passing around the rapids or falls. 



Harbors are improved, by removing obstructions, as above ex- 

 plained ; and by building wharves, docks, and marine railways, for 

 lading or repairing vessels ; with light-houses, and beacons, to guide 

 ships in entering ; and piers, moles, jetties, or breakwaters, to 

 shelter the harbor; or sea walls, and revetments, to protect the shores 

 from abrasion. Dry docks, are so constructed, with strong gates 

 bracing outward, that the water may be exhausted, after the ship has 

 entered to be repaired. Wet docks, are made to be kept always full, 

 and entered by ships only at high tide; in harbors where, without this 

 aid, the falling tide would leave them aground. Jetties, are walls 

 designed to turn the current, and wear the channel deepest in certain 

 parts of the harbor. Breakwaters, are usually formed of a great 

 mass of stone thrown into the sea, till it forms a wall rising above 

 the surface, to shelter an important and exposed position from the 

 waves. This subject is an extensive one ; but we have no room 

 here to pursue it. 



CHAPTER V. 



NAVITECTURE. 



THE branch of Navitecture, or Ship Building, relates to the con- 

 struction of all vessels ; whether ships or steamboats. We here ex- 

 tend the term to include a description of the rigging of ships ; to- 

 gether with the construction of small boats, technically called boat 

 building. The name Navitecture, is derived from the Greek i>ai>j, a 

 ship, and fsxtw, a builder; and the appellation of navitect, would 

 be applicable to persons engaged in this branch of art. The word 

 ship, is from the Saxon scip, or the German schiff; and it is often 

 used in a general sense, as synonymous with vessel ; though it has 

 also a specific meaning. Ship building is an art of great antiquity 

 and importance; requiring a knowledge of the higher principles of 

 Mechanics, and of Hylurgy, and Architecture, for its successful 

 prosecution. 



The first vessels, built in the primitive ages, were small boats, or 

 rafts ; sometimes covered with skins, and used for crossing rivers, 

 or coasting within sight of the shore. The invention of sails has 



