The project of an Atlantic telegraph involved two problems: Could a cable be stretched across the ocean? and if it were, would it be good for anything to convey messages? The first was a question of mechanical difficulties, requiring a careful survey of the ocean itself, fathoming its depth, finding out the character of its bottom, whether level, or rough and volcanic; and all the obstacles that might be found in the winds that agitate the surface above, or the mighty currents that sweep through the waters below. The second problem was purely scientific, involving questions as to the laws of electricity, not then fully understood, and on which the boldest might feel that he was venturing on uncertain ground. Such were the two elements or forces of nature to be encountered--the ocean and the electric current. Could they be controlled by any power of man? The very proposal was enough to stagger the faith even of an enthusiast. Who could lay a bridle on the neck of the sea? The attempt seemed as idle as that of Xerxes to bind it with chains. Was it possible to combat the fierceness of the winds and waves, and to stretch one long line from continent to continent? And then, after the work was achieved, would the lightning run along the ocean-bed from shore to shore? Such were the questions which had puzzled many an anxious brain, and which now troubled the one who was to undertake the work. To get some light in his perplexity, Mr. Field, the very next morning after his interview with Gisborne, wrote two letters, one to Lieutenant Maury, then at the head of the National Observatory at Washington, on the nautical difficulties of the undertaking, asking if the sea were itself a barrier too great to be overcome; and the other to Professor Morse, inquiring if it would be possible to telegraph over a distance so great as that from Europe to America? The mail soon brought an answer from Lieutenant Maury, which began: "Singularly enough, just as I received your letter, I was closing one to the Secretary of the Navy on the same subject." A copy of this he inclosed to Mr. Field, and it is given here. It shows the conclusions at which, even at that early day, scientific men were beginning to arrive: "National Observatory, Washington, February 22, 1854.