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 thickness is too deposited on the bottom and sides of the aqueduct, but as yet its depth or 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 alluvial 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 Alsietina 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