As the fall of the barometer gives warning of the approach of a hurricane, so the laws of the storm’s motion afford the seaman knowledge to guide him in avoiding it. In the northern temperate zone, if the gale begins from the S.E. and veers by S. to W., the ship should steer to the S.E.; but, if the gale begins from the N.E., and changes through N. to N.W., the vessel should go to the N.W. In the northern part of the torrid zone, if the storm begin from the N.E., and veer through E. to S.E., the ship should steer to the N.E.; but, if it begin from the N.W., and veer by W. to S.W., the ship should steer to the S.W., because she is in the south-western side of the storm. Since the laws of storms are reversed in the southern hemisphere, the rules for steering vessels are necessarily reversed also. A heavy swell is peculiarly characteristic of these storms. In the open sea the swell often extends many leagues beyond the range of the gale which produced it. Waterspouts are occasioned by small whirlwinds, which always have their origin at a great distance from that part of the sea from which the spout begins to rise, where it is generally calm. The whirl is produced by two currents of air, which, running in opposite directions, compress one another by their impetus, so that they rise in spiral eddies to the clouds. They move slowly along the surface of the sea, sometimes in vertical, and sometimes in twisted spirals, putting the sea into violent agitation as they pass, and carrying the water aloft by the force of gyration. Occasionally the eddies begin in the clouds and dip down to the sea. SECTION XVI. Sound—Propagation of Sound illustrated by a Field of Standing Corn—Nature of Waves—Propagation of Sound through the Atmosphere—Intensity—Noises—A Musical Sound—Quality—Pitch—Extent of Human Hearing—Velocity of Sound in Air, Water, and Solids—Causes of the Obstruction of Sound—Law of its Intensity—Reflection of Sound—Echoes—Thunder—Refraction of Sound—Interference of Sounds.