‹‹‹ Vitr. 10.3.5 | Table of Contents | Vitr. 10.3.7 ›››
6For as, if the fulcrum be placed under the middle of a lever, it is but with difficulty that the weight is moved, and that only when the power is applied at the extremity of the lever, so when the sails are no higher than the middle of the mast, they have less effect on the motion of the vessel: when, however, raised to the top of the mast, the impulse they receive from an equal wind higher up, causes a quicker motion in the ship. For the same reason the oars, which are made fast with rope to the thowls, when plunged into the water and drawn back by the hand, impel the vessel with great force, and cause the prow thereof to cleave the waves, if their blades are at a considerable distance from the centre, which is the thowl.
6As a lever thrust under a weight is harder to manage, and does not put forth its strength, if the pressure is exerted at the centre, but easily raises the weight when the extreme end of it is pushed down, so sails that are only halfway up have less effect, but when they get farther away from the centre, and are hoisted to the very top of the mast, the pressure at the top forces the ship to make greater progress, though the wind is no stronger but just the same. Again, take the case of oars, which are fastened to the tholes by loops,—when they are pushed forward and drawn back by the hand, if the ends of the blades are at some distance from the centre, the oars foam with the waves of the sea and drive the ship forward in a straight line with a mighty impulse, while her prow cuts through the rare water.