"Iron buoys are hollow, with air-tight compartments, and are made of three shapes, called nun, can, and ice-buoys. The nun-buoys are almost conical in form; the can-buoy is in shape the frustum of a cone, nearly approaching a cylinder, and the ice-buoy is found much like a spar-buoy, of great length, slight thickness, and of the largest diameter near its middle. Each shape is classified by size, and diversified by color and number. They were once made of wooden staves, like barrels, but their rapid destruction by submarine worms caused the substitution of boiler-iron. "The cost of these buoys varies with the price of iron, and they have been sold to the Government for $41.81 in the case of third-class buoys, up to $150 for those of the first-class. "Buoys are exposed to many dangers, not the least of which is that of being run down and ripped open by passing steamers. As the iron buoys are made with compartments, they are rarely sunk, but their line of floatation is often lowered, and their usefulness accordingly decreased. "Spar-buoys frequently lose a portion of their length, which is cut off by strokes of colliding propeller-blades. Despite state and national statutes forbidding it, vessels will sometimes make fast to buoys, thus gradually dragging them off their bearings. A buoy has sometimes been set adrift that a reward might be obtained for its recovery; but this is not a profitable operation, as the reward paid is varied with the circumstances of each case. "The buoy's worst enemy, however, is ice, when moving in mass, and with a tide or current. A well-made, well-moored buoy at the mouth of a narrow river can create an ice-gorge; but usually, when the ice moves in force, the buoys met have their mooring-loops torn out, their mooring-chains broken, or their mooring-anchors weighed; and in each case the buoys are carried out to sea, when the buoy tenders give chase, and, if successful in their capture, return them to position. [Illustration: CAPE ELIZABETH.] "The sea-going qualities of the large buoys are shown by their volunteer voyages. One is now anchored off the coast of Ireland, where it was picked up, about six weeks after it had been wrenched from its place in New York harbor, and turned over to the Irish light-house establishment, by which it was reported to the United States Light-House Board, when it was presented to the Irish Board, who simply added to its former marks their own, and moored it near the point where it came ashore, in commemoration of its peculiar voyage.