Harbours and Docks - Their Physical Features, History, Construction, Equipment and Maintenance with Statistics as to their Commercial Development (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1885 Excerpt: ... be landed on the island. Distance from the mainland, and difficulties in landing are the main obstacles in such cases, and were the causes of the preference for iron being given in the construction of the Roches-Douvres lighthouse. Bock Lighthouses. The really serious difficulties in lighthouse construction arise when a lighthouse has to be built on an isolated rock in the sea, at a distance from the mainland, where no shelter for the workmen can be provided, where the materials have to be landed on the rock as they are required, and more especially when the rock is covered by the tide, and the approach is difficult, uncertain, and even dangerous at times. The important considerations for these lighthouses are the level of the rock in relation to the sea level, the extent of the rock and its hardness, the exposure of the site, and its distance from the nearest suitable port for the conveyance of materials. In many cases the rock forming the foundation for the lighthouse is below high water, of which all the illustrations given are instances. (Plate 9, Figs. 1 to 9.) In some places the rock rises very little above low-water level, and is restricted in area, as at Bell Rock, Minot's Ledge, Des Barges, 364 Difficulties-in erecting Rock Lighthouses. pt. 1. and Ar-men; whilst at Spectacle Reef in Lake Huron, where there is no rise of tide, the rock is several feet below the surface of the water. Unless the rock is hard, compact, and without f1ssures, it is inexpedient to erect a lighthouse upon it, as the tower increases the surf on the rock, and by its weight on a small base, and the shocks which it transmits to its foundations, would soon impair any unsound portions of the rock. The strokes of the sea against Smeaton's Eddystone lighthouse caused the shaking ...