spring — and nei- ther outside nor inside had anything occurred to interfere with the regular action, which the various structures were designed to accommodate and promote. Among the enumerated causes of injury to the Roman aqueducts, it may be remem- bered, was the formation on the bottom and sides of the channel way, of a stony concretion, produced by matter deposited by the water. It is therefore satisfactory to know, what in- deed might a priori have been anticipated from the purity of the sources whence the Croton is fed, and the granitic region through which it passes, that no such deposit is made by its waters. " A fine sediment," says Mr. Jervis, in a letter to the author of 22d April, " has been deposited on the bottom and sides of the aqueduct, but as yet its depth or thickness is too small to be measured with much accuracy. As near as I can estimate, it might reach one inch in thickness in thirty or forty years, if left so long undisturbed. It is, however, so easily removed, that in a few days the whole conduit could be washed clean, and the sediment be discharged by floating it out at the waste weirs. It appears to be a fine allu- vial matter, which is readily washed from the masonry, and I do not anticipate that it can ever be a serious inconvenience to the usefulness of the aqueduct." The temperature of the water in the conduit has been found to vary but few degrees between winter and summer. After the water had been in the aqueduct about two months, it was ascertained, by sending down the current a self-registering thermometer on a float, that its temperature, as compared with that of the water at its head, had fallen some four or five degrees. This was in warm weather ; the opposite result would occur in cold weather, The utmost range of the thermometer, between summer and winter, in the conduit, before the water was let in, was from 45° to 55° of Fahrenheit. That range would be changed by the temperature of the water at different seasons, and brought nearer to its own variations. As yet, however, no sufficient experiments have been made on this point. Enough is known, nevertheless, to prove that the conduits are beyond the influence of frost — and, constructed as they are, with fidelity and of the best materials, a duration may be anticipated for the Croton aqueduct equal to that of the Aqua Alsie- tina of Rome, of which it is related that, one thousand years after the Goths had cut off its supply, Cardinal Orsini, in the year 1693, re-introduced water into it, and that it flowed on for 20 miles to Rome, without loss or interruption, and as freely as in its ancient day. CROTON AQ.UEDUCT. 217 The average flow of water since its introduction into the Croton aqueduct, has been about fourteen million gallons daily, which gives a height in the conduits of two feet four inches. Its capacity for delivery is more than quadruple this quantity, and the sup- ply is equal to the utmost capacity. And now, having concluded the narrative and descriptive parts of the Memoir, it will not be deemed an unreasonable indulgence of patriotism civic or pride, to present a brief and flattering comparison between this New York Aqueduct, and the most magnificent of those constructed in ancient or in modern times, the relative population and wealth of the respective countries or communities by which such undertakings have been accom- plished, the cost so far as it is ascertainable, and the sort of labor employed. Rome claims the first place, both of ancient and modern days, for the abun- dance of her supplies of water through aqueducts. The grandest of her gigan- tic works was executed by an imperial master and servile hands ; but even under her consuls, the people had no share either in the labor or the burden, of the two grandest aqueducts ever constructed. The Anio Vetus, in the year of Rome 480, was paid for from the spoils taken from Pyrrhus, overthrown by the Consul, M. Curius Dentatus, in the preceding year — and the Aqua Marcia, a yet more magnificent work, was commenced in the year of Rome, 608, the same year in which the great rival of Rome, Carthage, surrrendered, and in which the Consul Mummius destroyed Corinth, carrying off a prodigious plunder. From means thus acquired, was this aqueduct probably provided for. These were the two great works of republican Rome, but they were cemented by the blood of slavery, and defrayed by the spoils robbed from the conquered and the oppressed. Imperial Rome constructed the Claudian, and the Anio Novus, each a river of