masonry on the aqueduct, with- in the tunnels, 2476 feet, being an increase, during the last six months, of 1964 feet in length. 4th. Foundation and Protection Wall — The foundation wall now laid, amounts CROTON AQ.UEDUCT. 175 to 115,210 cubic yards, and the protection wall to 114,384, making a total of 229,594 cubic yards of dry wall, which shows an increase, during the last six months, of 63,344 cubic yards of wall. 5th. Ventilators and Waste Weirs, — There are 24 of these necessary structures now finished complete. A large portion of them are intended as ventilators to discharge the superabundant air collected in the aqueduct, and a few of them are fitted for waste weirs, for discharging the water from the aqueduct, if at any time repairs should be required, or any other cause make it necessary. There were six complete on the first of July last, making an increase of eighteen in this description of the work. Besides the foregoing, there has been a great deal of work performed, which cannot be described with the neces- sary degree of accuracy and plainness to make it understood, such as earth and rock ex- cavation, which has been performed before the grade of the aqueduct could be reached ; embankment and backfilling, performed after the aqueduct is in form, &c. There is still about six and a half miles of aqueduct to complete, in the county of Westchester, and about seven and a half miles of aqueduct and pipe work, on the island of New York, making the length of the unfinished work, about fourteen miles. This was a very trying year for financial arrangements ; nevertheless, the city conti- nued to face all its engagements with punctuality, and to meet the great expenditure on account of the aqueduct ; and the Commissioners, although not charged with any agency in raising the money needed for the work, nevertheless express their clear conviction that it would be better to pay higher interest, if necessary, for the amount required for the next year, than to incur the loss of interest, the claims of damages from contractors, and the unavoidable injury to the unfinished works, that would result from a suspension. The Commissioners at the same time estimate the wants of the year 1840, at $2,100,000. The high bridge was contracted for in August, 1839, at $737,755, conditioned that it should be completed in August, 1843. Meantime, it will have been perceived in the report of Mr. Jervis, that he suggested as a temporary expedient, the laying down pipes along the coffer dam in the river, through which the Croton water might be conducted to the New York shore. The Commissioners repeat this suggestion without expressing an opinion concerning it, but in referring to the rapid execution of the general work they say " there is hardly a doubt that the whole line from the Croton to the Harlem, will be finished, some years, before the expensive and difficult work over the latter river can be." Much, however, and of very difficult and expensive construction, remained to be done on the island of New York. Independently of the stupendous works at the Harlem river, scarcely yet commenced, there were the expensive crossings at Manhattanville, and at the Clendening valley, besides the two reservoirs, on all of which, as yet, but little progress had been made. Indeed, so heavy and so costly was the work on the island, that it alone, 176 MEMOIROFTHE extending through only seven miles, was estimated to cost more than three millions of dollars, about two thirds of the original estimates by Major Douglas and Mr. Martineau, for the whole work. These two engineers, without consultation or co-operation, made separate estimates in 1835. That of Major Douglas, was for $4,786,637 00, that of Mr. Martineau, for $4,225,814 00. The difference arose from the mode of passing the Harlem, which, by Mr. Douglas's plan was on a high bridge, and Mr. Martineau's by inverted syphons, on a low bridge. With such apparent agreement, the Commissioners were well foun ded in assuming that Jive millions would certainly accomplish the work, yet the result has proved the es- timates in question, to be entirely delusive. This may be explained, without impeaching the sagacity or accuracy of those engineer, by the facts, that they had no actual experi- ence derived from the price at which contracts would be taken — that the difference in the cost of land from that which it bore in 1835, and that afterwards placed on it by speculators and interested persons, was beyond calculation — and that the prices of work and materials were largely enhanced between 1835 and 1837. "The whole project, in fact," say the Com- missioners, " was entirely new, and perhaps without precedent as