ROLLERS

The name given by seamen to unusually heavy waves, which set in upon a coast or island without wind. They are frequent at Ascension. ROLLING, in Mechanics, is when all the parts of the surface of one body come into succe ive contact with those of another, and under such conditions as that, at every instant, the portion of the two surfaces which have been in contact are exactly equal. When this condition is not fulfilled, the one surface is said to slide upon the other. The friction of bodies in rolling is much le than in that of sliding; and hence the advantage of wheels to all kinds of carriages. See Friction. Rolling. In Naval language, the lateral oscillation of a ve el. This motion, which is often very great when the ve el is running before the sen, endangers the masts, strains the sides, and loosens the decks at the waterways; it is also liable to cause the guns to break adrift. When the centre of gravity is too low, the oscillations begin and end violently. The changes in the stowage nece ary to modify the nature or extent of the roll are made by seamen from experimental knowledge. [s. 1083]