 Severing his connection with the Long Island Railroad in 1897, Cattell opened an office as Consulting Engineer in New York City and until 1905 was engaged in the general practice of his profession, serving during that time as Consulting Engineer for the Brooklyn Park Department for bridge construction; the Ohio Southern Railroad for bridges and general improvement; and the Manhattan Beach Company for the installation of electric light, power, and refrigerating plant, electric railroad, marine bulkheads, and shore protection.During this time he was associated with prominent New York engineers in the valuation of many manufacturing plants, and made reports covering important existing and projected railways as well as terminals.He also reported on extensive irrigation projects since constructed by the United States Reclamation Service, and on a number of water supply and power projects in various parts of the United States.