points in connection with them.  In order to allow of the deposit of suspended matters, piscinae, or settling reservoirs, were constructed in a very ingenious manner.  Each had four compartments, two upper and two lower; the water was conducted into one of the upper compartments, and from this passed, probably by what we should call a standing waste or overflow pipe, into the one below; from this it passed (probably through a grating) into the third compartment at the same level, and thence rose through a hole in the roof of this compartment into the fourth, which was above it, and in which the water, of course, attained the same level as in the first compartment, thence passing on along the aqueduct, having deposited a good deal of its suspended matter in the two lower compartments of the piscinae.  Arrangements were made by which these two lower compartments should be cleaned out from time to time.  The specus or channel itself was, of course, constructed of masonry, generally of blocks of stone cemented together, and it was frequently, though not, it would appear always, lined with cement inside.  It was roofed over, and ventilating shafts were constructed at intervals; in order to encourage the aeration of the water, irregularities were occasionally introduced in the bed of the channel.  The water supplied by the different aqueducts was of various qualities; thus, for instance, that of the Alsietine, which was taken from a lake about 18 miles from Rome, was of an inferior quality, and was chiefly used to supply a large naumachia, or reservoir, in which imitation sea fights were performed; while, on the other hand, the water of the Marcian was very clear and good, and was therefore used for domestic purposes.  Frontinus gives the most accurate details as to the measurements of the amount of water supplied by the various aqueducts, and the quantities used for different purposes.  From these details Mr. Parker computes the sectional area of the water at about 120 square feet, and says:  “We can form some opinion of the vast quantity if we picture to ourselves a stream 20 ft. wide by 6 ft. deep constantly pouring into Rome at a fall six times as rapid as that of the river Thames.”  He considers that the amount was equivalent to about 332 million gallons a day, or 332 gallons per head per day, assuming the population of the city to be a million.  When we consider that we in London have only 30 gallons a head daily, and that many other towns have less, we get some idea of the profusion with which water was supplied to ancient Rome.  But the remains of Roman aqueducts are not only to be found near Rome.  Almost every Roman city, whether in Italy or in the south of France, or along the north coast of Africa, can show the remains of its aqueduct, and almost the only things that are to be seen on the site of Carthage are the remains of the Roman water tanks and the ruins of the aqueduct which supplied them.  The most beautiful aqueduct bridge in the world, on the course