In the middle of the nineteenth century, for the second time, it was the need of improved communication between the east and west of the American Continent which provided a sufficient inducement to improve the Isthmian route. At this time the Government of the United States were much occupied with projects of trans-Isthmian communication, particularly by canal, not with a view to Transpacific commerce, but with the object of improved communication between the east and west of their own territory. In 1846 a treaty was made with the State of New Grenada (afterwards Colombia) with a view to providing facilities for transport in the war between the United States and Mexico. In its most important provision it is similar to the present treaty between the United States and the new Republic of Panama, viz., the United States guarantee the sovereignty of the State in question over the Isthmian territory. Hence the Isthmus was thus early constituted a Protectorate of the United States. But at this time it was generally thought that Lake Nicaragua provided the best route for a trans-Isthmian canal. The Pacific seaboard having recently acquired importance to the United States, the Government desired to further the canal project on that account. The only practicable Atlantic terminal of a Nicaraguan canal lay within territory over which Great Britain had long exercised control. Further, the Pacific Coast of Canada had recently acquired importance to the eastern provinces and to the home country, and access thereto was extremely difficult. The outcome of these circumstances was the conclusion in 1850 of the celebrated Clayton-Bulwer treaty between the United States and Great Britain, which was duly ratified by Congress. By this instrument it was agreed that neither Government should ever obtain or maintain for itself any exclusive control of any canal connecting the Atlantic and Pacific Oceans, nor erect fortifications commanding the same. This treaty remained in force until 1901, and I shall have to refer to it again. Meanwhile the great rush of gold-seekers to California had supplied the needful stimulus to a scheme, already mooted, of an Isthmian railway terminating at Panama. In spite of the enormous difficulties entailed by the pestilential climate, the undertaking was completed in 1855. This achievement, originating in New York, was the work of W.H. Aspinwall, Henry Chauncey, and John L. Stephens. [Illustration: RE-LOCATION OF RAILWAY ABOVE GATUN.] [Illustration: MOTOR TROLLEY FOR INSPECTION OF WORKS.]