Legislature of New-Jersey as well as that of New- York, and it was also questionable whether such obstructions could be placed in navigable rivers without in- terfering with the powers of Congress to regulate the com- merce of the nation. It was feared that in locking vessels 72 through, the salt water would become mingled with the fresh above the dam where a supply would be taken for the city, to such a degree, that it would render it unfit for domestic use. The quantity of land that would be overflowed by the water set back by the dam, presented another objection. The space of time that the tide would be sufficiently low to allow the wheels to work in pumping water into the reser- voir, would be entirely too short to insure a supply. This objection was offered by Frederick Graff, Esq., the superin- tendent of the Philadelphia Water Works, who stated that although the dam on the Schuylkill River is raised 6 feet 6 inches above the highest tides, the delay in pumping, occa- sioned by the tides, averages seven hours out of the twenty- four ; and in full moon tides, from eight to nine hours. The projector of this plan set forth many advantages which he thought would arise from the construction of the dam, but the obstruction to the navigation of the river, the destruction of the shad fishery, and various objections be- sides those already mentioned, induced the Water Commis- sioners to reject the idea of building a dam across the Hudson. We have now gone over most of the preliminary steps which were taken before deciding upon the source for a supply of water. — Having fixed upon the Croton River as a stream possessing the requisite advantages for a supply, questions naturally arose as to the manner in which it should be conveyed to the city. The distance being about forty miles, over a country extremely broken and uneven, and following a direction, for a portion of this distance, parallel with the Hudson River, encountering the streams which 73 empty into it and form deep valleys in their courses. It will be interesting to notice the different plans which were suggested for forming a channel-way to conduct the water. The following modes were presented : — a plain channel formed of earth, like the ordinary construction of a canal feeder : — an open channel, protected against the action of the current by masonry : — an arched culvert or conduit, com- posed essentially of masonry ; and iron pipes. In deci- ding which of these modes should be adopted, it was neces- sary to make a comparison among them as to their effi- ciency for conducting the water in purity, and in the quan- tity required, their permanency as structures, and their cost. The disadvantages attendant upon an open canal were, that by filtration through the banks there would be a heavy loss of water ; — the difficulty of preserving the water from receiving the wash of the country, and preventing injurious matter from being thrown into it and rendering it impure, and the impurities which might be contracted by passing through different earths. Evaporation would also occasion a serious loss of water. The banks would be liable to failure in seasons of long-continued rains, and the city depending upon this for a supply, would be cut off, except there should be sufficient in the reservoirs to furnish a supply during the period of repairs. The canal could never be subjected to a thorough repair, because of the necessity of keeping it in a condition for furnishing water constantly during the whole year, so that all repairs would be done under great disad- vantages, and the channel would be yearly growing worse until its failure might become a public calamity. In regard to the open channel having the sides protected by masonry, the 19 74 objections were found to be such as would apply equally to every species of open channel ; namely, that it would be exposed in many situations to receive the wash of the coun- try ; that it would be unprotected from the frost, and liable to be interrupted thereby, and lastly, that there would be a loss by evaporation. It was supposed that these objections might be obviated by certain precautions ; for example, the wash could be avoided by making sufficient side drains ; and the interruption liable to occur from frost and snow, and the evaporation, to a certain extent, could be prevented by closing the channel entirely with a roof over the top. The close channel or culvert, composed essentially of masonry seemed to possess all the requisite advantages for conduct- ing the water in a pure state and keeping it beyond