From a purely engineering standpoint the most serious objection to this route is the liability to interruption for lack of water in seasons of extreme drought which are not at all uncommon in that region. Upon first thought it seems that a lake 3,000 square miles in extent cannot be other than an ideal source of supply, but such is not the case. By the proposed dam on the lower San Juan river the channel of the stream would become an arm of the lake through which all shipping would have to pass, the depth of water being, of course, dependent upon the lake level. This level has a natural variation of 13 feet. Under the projected conditions the whole outflow would pass over the dam about 50 miles away from the lake proper. The present high water mark cannot be exceeded without flooding valuable lands, nor, on the other hand, can the channel depth be made as great as desirable because the river bed is crossed by many rock ledges, and the cost of excavation fixes a limit to the depth economically practicable. The Isthmian Canal Commission of 1899–’01 concluded that the variation would have to be reduced to 7 feet. This means that the level would be held between 104 and 111 feet above tide water and the river bed excavated enough to give a minimum sailing depth of 40 feet. Records show no regular succession of high and low lake years; and as it is plainly impossible to keep a reserve sufficient to control such an enormous expanse of water, the regulation of this most important matter would be left to the judgment of the operator controlling the overflow at the dam. Carelessness or bad judgment on his part might therefore easily stop traffic for an indefinite period. There is a similar question in regard to Gatun Lake of the Panama line although the majority of authorities anticipate no trouble from that source. A more complete discussion of this danger will be given later. Concerning the actual difficulties of construction at Nicaragua, little need be said inasmuch as no work is now contemplated there. The San Juan dam of the Nicaragua and the Gatun dam of the Panama route both present conditions which have never been met before. Also the deep cuts of the Culebra find their counterpart in portions of the longer route. The time-saving element is of more apparent than real importance because the time lost on the longer sea-voyage for the Panama route would be practically balanced by the gain of time in actual passage through the canal, the Nicaragua route being about four times as long as the Panama route. Henry L. Abbot, in his “Problems of the Panama Canal”, estimates that 34 hours more time would be required for passage by way of the Nicaragua than by way of the Panama route. An excellent reason for the adoption of the Panama rather than the Nicaragua route was the existence of a good railroad and the fact that the French had actually completed about two fifths of the work required. SUMMARY OF COMPARISON