In the course of the following year the organization of the Baltimore and Ohio Railroad, a part of which had already been constructed under the immediate personal supervision of Lieutenant Whistler, assumed a more permanent form, and allowed the military engineers to be transferred to other undertakings of a similar character. Accordingly, in June, 1830, Captain McNeill and Lieutenant Whistler were sent to the Baltimore and Susquehanna Railroad, for which they made the preliminary surveys and a definite location, and upon which they remained until about twenty miles were completed, when a lack of funds caused a temporary suspension of the work. In the latter part of 1831 Whistler went to New Jersey to aid in the construction of the Paterson and Hudson River Railroad (now a part of the Erie Railway). Upon this work he remained until 1833, at which time he moved to Connecticut to take charge of the location of the railroad from Providence to Stonington, a line which had been proposed as an extension of that already in process of construction from Boston to Providence. In this year, December 31, 1833, Lieut. Whistler resigned his commission in the army, and this not so much from choice as from a sense of duty. Hitherto his work as an engineer appears to have been more an employment than a vocation. He carried on his undertakings diligently, as it was his nature to do, but without much anxiety or enthusiasm; and he was satisfied in meeting difficulties as they came up, with a sufficient solution. Henceforward he handled his profession from a love of it. He labored that his resources against the difficulties of matter and space should be overabundant, and if he had before been content with the sure-footed facts of observation, he now added the luminous aid of study. How luminous and how sure these combined became, his later works show best.