The culmination of the political agitation for the dissolution of the Federal Union, and the commencement of actual hostilities between the government and the seceding states, found WILLIAM F. SMITH, only a captain by law, after fourteen years of continuous service, a few months over thirty-seven years of age, and in the full maturity of his faculties. As before stated, his health was never afterwards altogether stable, but it was sufficiently re-established to enable him to throw himself heartily into the struggle and to perform such duties as fell to his lot with a fair degree of endurance. Although a Democrat, as far as he had any party connection, his sympathies were all with the Union and National Government, and impelled him to lose no time, but make haste, on his return from Key West and Havana, to obtain such employment as might be open to him. The first duty that was offered him was in New York, where he was engaged for several weeks in mustering the volunteers into the United States service. During this period, on the 24th of April, 1861, he was married to Miss Sarah Lyon, a young lady of New York, who was famous for the loveliness of her person and character, whom he had first met two years before. It was on a short wedding trip to his native state that he offered his services to the Governor. The latter had already raised and organized two regiments of infantry but without hesitation he promised Captain Smith the next, as soon as it should be called for. Meanwhile he was still subject to duty as an engineer officer, and as such, strangely enough was ordered to report to Major General Benjamin F. Butler, fresh from the life of a successful lawyer, then in command at Fortress Monroe, where he arrived on the 1st of June, 1861. While there he conducted several important reconnaissances in the direction of Yorktown and Big Bethel, and thus became acquainted with a region in which he was afterwards to play a most important part. His services lasted something less than two months, and became still more notable from the fact that they made him thoroughly acquainted with General Butler. They were brought suddenly to an end by the reappearance of his old trouble, which in time made it necessary for him to take a sick-leave. The surgeon who had him in charge directed him to again seek the tonic climate of Brattleborough in his native State. According to promise, his good friend, the Governor, took the earliest opportunity to send him his commission as Colonel of the Third Regiment of Vermont Volunteer Infantry, to date from July 16th. But owing to the scarcity of regular officers, he had previously been ordered to duty on the staff of General McDowell, then commanding the army in front of Washington, though, his health did not permit him to join in time to take part in the forward movement which ended in the disastrous battle of Bull Run.