The Gulf Stream is the best known of all the great ocean currents. The northeast and southeast trade-winds, constantly blowing, drive a great mass of water from the Atlantic Ocean into the Caribbean Sea, and westward through the passages between the Windward Islands, which is contracted by the converging shores of the Yucatan Peninsula and the Island of Cuba, so that it pours between them into the Gulf of Mexico, raising its surface considerably above the level of the Atlantic. These currents then move towards the Florida Peninsula, and pass around the Florida Reef and out into the Atlantic. It is estimated by the Coast Survey that the hourly flow of the Gulf Stream past the reef is nearly ninety thousand million tons of water, the speed at the surface of the axis of the stream being over three and one-half miles an hour. To conceive what the immensity of this flow means, it is stated that if a single hour's flow of water were evaporated, the salt thus produced would require to carry it one hundred times the number of ocean-going vessels now afloat. The Gulf Stream water is of high temperature, great clearness and a deep blue color; and when it meets the greener waters of the Atlantic to the northward, the line of distinction is often very well defined. At the exit to the Atlantic below Jupiter Inlet the stream is forty-eight miles wide to Little Bahama Bank, and its depth over four hundred fathoms. There are numerous harbors of refuge among the Florida Keys, and that at Key West is the best. This is a coral island seven miles long and one to two miles broad, but nowhere elevated more than eleven feet above the sea. Its name, by a free translation, comes from the original Spanish name of _Cayo Hueso_, or the Bone Island, given because the early mariners found human bones upon it. Here are twenty thousand people, mostly Cubans and settlers from the Bahamas, the chief industry being cigar-making, while catching fish and turtles and gathering sponges also give much employment. There are no springs on the island, and the inhabitants are dependent on rain or distillation for water. The air is pure and the climate healthy, the trees and shrubbery, with the residences embowered in perennial flowers, giving the city a picturesque appearance. Key West has a good harbor, and as it commands the gateway to and from the Gulf near the western extremity of the Florida coral reef, it is strongly defended, the prominent work being Fort Taylor, constructed on an artificial island within the main harbor entrance. The little Sand Key, seven miles to the southwest, is the southernmost point of the United States. Forty miles to the westward is the group of ten small, low and barren islands known as the Dry Tortugas, from the Spanish _tortuga_, a tortoise. Upon the farthest one, Loggerhead Key, stands the great guiding light for the Florida Reef, of which this is the western extremity, the tower rising one hundred and fifty feet. Fort Jefferson