"Ten years afterwards, or in 1523, Fernando Cortez had conquered Mexico, and proposed a waterway through the Isthmus of Tehuantepec. He employed Gonzalo Sandoval to make a very careful survey of the route, and continued to urge his proposition after the Emperor Charles V. had removed the government of Mexico from his control. But the emperor was not favorably impressed with the scheme, which contemplated the expenditure of a vast amount of money, and, besides, he was more interested in obtaining a revenue from Mexico than in doing exactly the reverse. The proposal of Cortez was rejected as emphatically as was that of Balboa, but it is a remarkable circumstance that these two routes are the northern and southern extremes of the lines proposed for inter-oceanic canals. "By reference to a book by a celebrated Portuguese navigator of the sixteenth century, Antonio Galvao, it appears that, up to the year 1550, four routes had been discovered and examined, though none of them had been surveyed with care. Galvao states in his book that a maritime canal can be cut in four different places: First, between the Gulf of Uraba and the Gulf of San Juan; second, through the Isthmus of Panama; third, along the San Juan River, and through Lake Nicaragua; and, fourth, through the Mexican Isthmus. Several explorers were sent to examine these routes, but they encountered many difficulties, and none of them brought back any exact information. So, you perceive, the principal routes for an inter-oceanic canal were known to the geographical world three hundred years ago." [Illustration: Map.] There was a pause to enable Frank and Fred to examine the map which was spread before them, showing the routes which Mr. Colné had mentioned. When the examination was completed their entertainer continued: "Very little attention was given to the subject for about two hundred years from the time I have mentioned. In the latter part of the eighteenth century the idea was revived again; England thought it would be of great value to her if she could obtain control of a passage from ocean to ocean, and in 1778 she sent an expedition against Nicaragua in order to obtain possession of the country. The enterprise was unsuccessful, and the commander, Lord Nelson, narrowly escaped with his life. "In 1780 and '81 surveys were made of the Panama and Nicaragua routes, the former by order of King Charles III. of Spain, and the latter by Antonio de Bucareli, Viceroy of Mexico. These were the first technical surveys of the routes, all previous examinations having been made without the aid of engineering instruments, and unaccompanied by calculations as to the amount of earth to be removed, and the probable cost of the work.