At the Isthmus of Darien _altitudes of from one to two thousand feet_ are found. Cullen’s pass of 150 feet proved to be estimated at one-ninth of its true height. The least elevation of the divide is that given by M. Bourdial. This engineer did not cross the Isthmus, and his statement is so vague, the reader is left in doubt whether he actually reached the summit. Notwithstanding this uncertainty, there still exists a faint hope that “it is to the Isthmus of Darien we must first look for a solution of the question of an interoceanic canal.”
From another statement in this very valuable report, we feel reluctantly compelled to dissent. By imposing unnecessary conditions in the statement of the problem, its solution may be indefinitely postponed.
“The interoceanic canal,” it is affirmed, “in width, depth, in supply of water, in good anchorage and secure harbors at both ends, and in absolute freedom from obstruction by lifting-locks, or otherwise, must possess, as nearly as possible, the character of a strait.”
To insist that the canal must possess the character of a strait, may give rise to the necessity for a thorough-cut of such extreme depth, or a tunnel of so great length, as to render the work practically impossible. A line suitable for a thorough-cut may possibly be found, but so important a project should not be endangered by limiting its practicability to a communication of that nature.
If, by the employment of “lift-locks,” the cost of the canal can be materially reduced, the question to be considered is, to what extent such structures would obstruct navigation? This question depends upon the amount of trade drawn to the Isthmus by the canal.
The relative cost of the two methods for piercing the Isthmus can be best determined by a comparison of the cost of a canal in an open country with one by means of tunnels. These considerations, since they afford criteria for judging of the merits of different routes, may be considered more minutely. Let us assume the trade passing over the Isthmus—were the canal now completed—to increase one hundred per cent. in ten years; there would then be 2,066 tons in transitu daily, requiring seven ships of about 300 tons burthen each.[5] The progressive increase in the size of ships will raise this average to between 500 to 1,000 tons; reducing the number of ships arriving at the Isthmus daily, to five and three respectively. But, assuming the smaller average, giving the larger number of seven ships daily passing through the canal; an increase of four hundred per cent. in the trade would be equivalent to fourteen ships, or to seven ships leaving opposite extremities of the canal, and passing each other daily upon homeward and outward voyages.