a day. During the winter months when most construction activities ceased, Jervis, ever mindful of economy, reduced the size of the staff in each division. The organization of the Engineering Department that was used on the Croton Aqueduct served as a model and was carried over into many later projects by the engineers who furthered their pro- fessional training on this great weiter system. Sources American Railroad Magazine and Mechanics Magazine. April 15, 1839. Douglass, David Bates, MSB. Hobart and William Smith College, Geneva, New York. Jervis, John B. MSB. Jen/is Public Library, Rome, New York. King, Charles. A Memoir of the Construction, Cost, and Capacity of the Croton Aqueduct. New York: Charles King, 1843. Lart^in, F. Daniel. John B. Jervis, An American Engineering Pioneer. Ames, Iowa; Iowa State University Press, 1990. figure 19: Possibly by John B. Jervis. Elevation of Regulating Gates at Croton Dam, c.1841, watercolor and ink on paper Courtesy Jervis Public Library, drawing #189 (different version m exhibition) Photo: G. R. Farley Kemp Introduction Having resolved on the work, they carried it forward with a degree of constancy and energy alike remarkable, so that in the space of five years, an aqueduct was completed, which, for the natural difficulties overcome, the substantial character of its structures, the very remark- able verification, in the results, of the previous calculations of the engi- neers as to the flow of the waters, and the quantity that could be delivered, for the extent of its course, and the abundance of its supply, may be ranked among the foremost of like undertakings throughout the world. Yet, with all this energy and perseverance, there was no rashness. The calculations of the cost, were carefully made, and it is a circum- stance unparalleled probably in the history of like undertakings, and one which reflects great credit on the exactness of the knowledge of the chief engineer, Mr. Jervis, and on his professional skill and fidelity, that the very first estimate he gave, after he had made himself master of the details of the proposed work, and had the experience of some 26 few contracts, has turned out to be within, and not much differing from, the actual cost.^ This statement appeared in Charles King's A Memoir of the Construction ...of the Croton Aqueduct published around the time of its opening. Not only does King present details on the con- struction, cost, and operation of the new Aqueduct, but he places this great engineering worl< in the same category as the Roman aqueducts and compares it favorably with more modem European water supply schemes of his day. In many ways King's evaluation was correct. Excepting trans- portation works such as the Erie canal, the Croton Aqueduct was the greatest public work in antebellum America. It is little wonder that much has been written about this work from the time of its completion until our own day.^ But there has been little in the wealth of published material to explain how the Aqueduct was designed and how it functioned. The engineering design of this extraordinary achievement can be considered in two parts, namely, the hydraulic design, and the structures necessary in order to ensure that the hydraulic design would supply the required amount of water to New York City. Before describing the salient engineering features of the Aqueduct from the Croton River to Manhattan Island, however, it is well to discuss the design methods employed for the Aqueduct. Hydraulic design Engineering design is a creative activity more nearly akin to art than to science, although in modem times, engineering has depended Increasingly upon scientific knowledge to produce the most accept- able designs. As there is no unique solution in engineering design, the success of a particular engineering work can be measured as much on its form in relation to its function and the materials applied, as in questions of aesthetics, economics, scale, and utility. On these criteria the Croton Aqueduct provides an outstanding case study of the factors inherent in the design of any successful, large scale engineering work. The first step was to determine the quantity of water to be deliv- ered at the Croton Distributing Reservoir at 5th Avenue and 42nd Street in Manhattan. The system was designed for a population of 450,000 people using 20 gallons per day, which would give the requirement of 9 million gallons to be delivered by the Aqueduct. It is interesting to note that this appeared to be perfectly adequate in the minds of the designers who had no idea that the New York met- ropolitan area would exceed 10 million In population in our day and use perhaps five times as much water per capita. After the engineers Canvass White and Major Douglass studied a number of potential water sources in the New York City area,