In former ages the efforts of man to provide a refuge to the mariner from the fury of the raging gale were feeble and insignificant. Content with the harbours that nature had provided, it was then thought quite sufficient to line a river-bank with quays or to enclose a natural pond by walls. The idea of raising colossal breakwaters by casting whole quarries into the deep, or of extending artificial promontories far into the bosom of the ocean, is of modern date, and would have appeared chimerical not only to the ancients but to our fathers not a century ago. The first great work of this description is the famous breakwater planned by De Cessart in 1783, and terminated in 1853, which has converted the open roadstead of Cherbourg into a land-locked harbour. Rising from a depth of 40 feet at low spring tides, on a coast where the floods attain a height of 19 feet, it opposes a front of 12,700 feet to the fury of the storm, and carries 250 pieces of the heaviest cannon on its formidable brow. It far surpasses in extent and boldness of construction the breakwater at Plymouth, nor will it be eclipsed by the moles now forming at Portland, Holyhead, and Alderney; but although it is a more impressive spectacle to see man struggling with the ocean and producing calmness and shelter in the midst of the raging storm, than to contemplate his operations where he has no such adversaries to subdue, still such buildings as those just described are neither the largest nor the most expensive works required for the accommodation of shipping. Witness the Cyclopean grandeur of the Liverpool docks or of the Great Float at Birkenhead, which alone covers an area of water of 121 acres, and whose portals, with a clear opening of 100 feet, will admit the largest screw-steamer or sailing ship the wildest imagination has yet conceived. Six millions of money is the cost of this one work alone--more than would be required to raise a pyramid like that of Cheops--and even this sum is a trifle when compared with what has been spent on the harbours of Liverpool, London, and other great commercial cities. Not satisfied with erecting his lighthouses on wave-worn rocks or defying the waves with his colossal breakwaters, man spans bridges over arms of the sea and excavates mines under the abysses of the deep. The locomotive now rolls full speed 100 feet above high water over the strait which separates Anglesea from the mainland; and in Botallack and several other Cornish mines the workman, while resting from his subterranean labours, hears the awful voice of the ocean rolling over his head.