This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
By MANUEL EISSLER, M.E., of San Francisco, Cal.
When Cortez, in the year 1530, made the observation that the two great oceans could be seen from the peaks of mountains, he, in those remote days, preoccupied himself with the question to cut through the Cordilleras.
Therefore, the idea of an interoceanic canal is by no means a modern one, as travelers and navigators observed that there was a great depression among the hills of the Isthmus of Panama. As Professor T.E. Nurse, of the U.S.N., says in his memoirs:
"This problem of interoceanic communication has been justly said to possess not only practical value, but historical grandeur. It clearly links itself back to the era of the conquest of Cortez, three and a half centuries."  It is a problem which has been left for our modern era to solve, but nevertheless its history is thereby rendered still more interesting, having needed so many centuries to bring it to an issue.
[Footnote 1: From Prof. Nurse's historical essay. See Survey of Nicaragua Canal, by Com. Lull.]
Spain, which acquired through her Columbus a new empire, lying near, as it was supposed, to the riches of Asia, could not be indifferent, from the moment of her discoveries, to the means of crossing these lands to yet richer ones beyond.
India, from the days of Alexander and of the geographers, Mela, Strabo, and Ptolemy, was the land of promise, the home of the spices, the inexhaustible fountain of wealth. The old routes of commerce thither had been closed one by one to the Christians; the overland trade had fallen into the hands of the Arabs; and at the fall of Constantinople, 1453, the commerce of the Black Sea and of the Bosphorus, the last of the old routes to the East, finally failed the Christian world. Yet even beyond the fame of the East, which tradition had brought down from Greek and Roman, much more had the crusaders kindled for Asia (Cathay) and its riches an ardor not easily suppressed in men's minds.
The error of the Spanish Admiral in supposing that the eastern shores of Asia extended 240 degrees east of Spain, or to the meridian of the modern San Diego, in California--this error, insisted on in his dispatches and adopted and continued by his followers, still further animated the earlier Spanish sovereigns and the men whom they sent into the New World to reach Asia by a short and easy route.
Nobody in Europe dreamt that Columbus had discovered a new continent, and when Balbao, in 1513, discovered the South Sea, then it was known that Asia lay beyond, and navigators directed their course there. On his deathbed, in 1506, Columbus still held to his delusion that he had reached Zipanga, Japan. In 1501 he was exploring the coast of Veragua, in Central America, still looking for the Ganges, and announcing his being informed on this coast of a sea which would bear ships to the mouth of that river, while about the same time the Cabots, under Henry VII., were taking possession of Newfoundland, believing it to be part of the island coast of China.
Although these were grave blunders in geography and in navigation, the discoveries really made in the rich tropical zones, the acquirement of a new world, and the rich products continually reaching Europe from it, for a time aroused Spain from her lethargy. The world opened east and west. The new routes poured their spices, silks, and drugs through new channels into all the Teutonic countries. The strong purposes of having near access to the East were deepened and perpetuated doubly strong, by the certainties before men's eyes of what had been attained.
Balbao, in 1513, gained from a height on the Isthmus of Panama the first proof of its separation from Asia; and Magellan enters the South Sea at the southern extremity of the country, now first proven to be thus separate and a continent. Men in those days began to think that creation was doubled, and that such discovered lands must be separate from India, China, and Japan. And the very successes of the Portuguese under Vasco da Gama, bringing from their eastern course the expectancy of Asia's wealth, intensely excited the Spaniards to renew their western search.
The Portuguese, led around the Cape of Good Hope, had brought home vast treasures from the East, while the Spanish discoverers, as yet, had not reached the countries either of Montezuma or of the Inca. Their success "troubled the sleep of the Spaniards."
Everything, then, of personal ambition and national pride, the thirst for gold, the zeal of religious proselytism, and the cold calculations of state policy, now concurred in the disposition to sacrifice what Spain already had of most value on the American shores in order to seize upon a greater good, the Indies, still supposed to be near at hand. And since it was now certain that the new lands were not themselves Asia, the next aim was to find the secret of the narrow passage across them which must lead thither. The very configuration of the isthmus strengthened the belief in the existence of such a passage by the number of its openings, which seemed to invite entrance in the expectancy that some one of them must extend across the narrow breadth of land.
For this the Spanish government, in 1514, gave secret orders to D'Avilla, Governor of Castila del Oro, and to Juan de Solis, the navigator, to determine whether Castila del Oro were an island, and to send to Cuba a chart of the coast, if any strait were possible. For this, De Solis visited Nicaragua and Honduras; and later, led far to the south, perished in the La Plata. For this, Magellan entered the straits, which, strangely enough, he affirmed before setting out, that he "would enter," since he "had seen them marked out on the geographer Martin Behaim's globe." For this, Cortez sent out his expeditions on both coasts, exposing his own life and treasure, and sending home to the emperor, in his second relation, a map of the entire Gulf of Mexico (Dispatch from Cortez to Charles V., October 15, 1524). For this great purpose, and in full expectancy of success in it, the whole coast of the New World on each side, from Newfoundland on the northeast, curving westward on the south, around the whole sweep of the Gulf of Mexico, thence to Magellan's Straits, and thence through them up the Pacific to the Straits of Behring, was searched and researched with diligence. "Men could not get accustomed," says Humboldt, "to the idea that the continent extended uninterruptedly both so far north and south." Hence all these large, numerous, and persevering expeditions by the European powers.