Fig. 111.-PONT DU GARD, NISMES. About 180 feet high, sixteen centuries old. Three rows of arches, the upper row 873 feet long. land, about 5 miles south of Keswick. The aqueduct thence to Manchester comprises 141 miles of tunnels, cut-and-cover, 36 miles; and cast-iron piping 45 miles, weighing about 55,000 tons. The tunnels and cut-and-cover have a capacity equal to the full supply of 50,000,000 gallons per day, but five lines of pipes are necessary to convey this quantity, a single line affording a 10,000,000 gallon supply. The inclination in the tunnels and cut-and-cover is 20 inches to the mile, and in the pipes generally 24 inches to the mile. The tunnels are 8 feet 6 inches wide where valleys, where the pressure is equal to as much as 400, and 425 feet head. Fig. 113, Plate VIII., illustrates the laying of the last line of pipes. in Scardale Valley. At all places where the channel changes from one kind to another, as tunnel, or cut-andcover to piping, and back again, a well is sunk containing valves for the automatic prevention of the forward flow of the water if a fracture should occur in the syphon on the lower or discharging side of the well. These automatic valves are very remarkable structures. They occur at the heads of each line of syphon, that Fig. 112.-Tunnels, and Cut-and-Cover on the Manchester-Thirlmere Aqueduct. there is no necessity for side walls and arching, and 7 feet 1 inch where lined with concrete or brickwork. The cut-and-cover is formed of concrete, and has the same internal section as the lined portion of the tunnels. The floors in all cases are concreted, either from necessity, or to give the water an easy flow. Fig. 112 shows typical sections of tunnels and cut-and-cover. is where the pipe lines go down from, or come up to the tops of the valleys in which they are laid. The pipe line is formed mostly of 48-inch pipes, 12 feet long, united with socket and spigot joints, run with lead, without yarn, and caulked. The thicknesses differ according to the pressure in different localities, being from 1 in. to 13 inches. The latter occur in the deep But besides these, there are other selfacting valves placed in the descending and ascending portions. Those on the latter are of reflux type, to prevent, in case of a cessation of the flow of water, the return of that which has passed the valve. Numerous stop valves, operated by hand, are also fitted and enclosed in valve houses. Air valves are fitted at intervals in the pipe line, on the highest summits, and these are enclosed in inspection boxes. Overflow chambers are also fitted. In the Manchester-Thirlmere supply no less than twenty-three bridges carry the aqueduct over rivers and railways. There are also ten subways that carry the pipes under railways. Bridges span the Ribble, the Lune, the Mint, the Sprint, the Brock, the Yarrow, the Darwen, the Calder, and others. The aqueduct is carried over the Ribble on an arch bridge of three spans of 70 feet each, built of cast-iron segmental arches. That over the Lune is similar, but it is a skew bridge. In both cases the segmental ribs are tied together transversely by six girders, each alternate one of which is of cast iron, the others of wrought iron. The Birmingham - Welsh aqueduct, opened in 1904, is second only in length to the Manchester-Thirlmere one, being 733 miles long. Of this the various tunnels extend to 13 miles, the cut-and-cover to 23 miles, and the pipes to 37 miles. The longest tunnel is the Dolan, of 44 miles, which was driven from four headings, two from the ends, and two from shafts. The Knighton tunnel, 2 miles. long, was driven from the ends only. Over Deepwood Dingle the aqueduct is carried in brick on a masonry bridge 500 feet long, with an area large enough to convey the full ultimate supply of 75,000,000 gallons per day. The pipes are 42 inches diameter, some being of steel where the pressure is greatest (240 lb. to the square inch), others of cast iron. Each line of pipes will convey 12 million gallons per day. These pipes are carried over a steel arched bridge 3 miles from Bewdley, having a span of 150 feet. Among modern works one of the largest aqueducts carries the Lower Ganges Canal over One of the most remarkable features of this great work was that three-fourths of the expenditure was swallowed up in works below ground. Of well-sinking alone for brick foundations there was 15,019 lineal feet, or nearly 3 miles. Arbor. The term arbor is often used in a very loose manner to signify various spindles used in connection with machine tools, some of which designations are not generally accepted, but are due to the fancy of workmen, or writers. Thus nearly all classes of driving spindles have been in turn called arbors, though they should for clearness be termed spindles, or sometimes, as in the case of lathes, mandrels. Mandrels which are driven from the main spindle and carry work, such as lathe mandrels and gear wheel mandrels, are also frequently designated arbors. But the more correct meaning and the one generally employed is that which denotes |