SUBTRACTION. 653 SUBWAYS. to be found is called the difference or the re- mainihr. SUBUR'RA. A district of ancient Rome in the valley between the Esquiline, Quirinal, and Viminal Hills. It was thickly populated and bore an evil reputation as the resort of jjeddlera, footpads, and prostitutes. SUBWAYS ( FOR Pipes and Wires ) . Under- ground galleries which contain and render ac- cessible at any point the multitudinous pipes and wires beneath city pavements ; or else ducts for inclosing underground wires only, in such a way as to make them accessible at intervals. Subterranean passages for the accommodation of street traffic are either nothing more than streets or footpaths placed in tunnels, which need no description, or they are underground rail- ways, which are described in the article on Tu'x.N-EL. The chief advantages of subways for pipes and tingham, England. Subsequently a number of subways were added to the first ones built in London and Nottingham. The London subways range in size from 14 feet wide and 7 feet high to 8X7 feet. The walls are of brick, laid in cement. The roofs arc formed by semicircular brick arches, with ventilators extending to the streets at intervals of 100 feet. Tlie London subways contain gas, water, electric light, hy- draulic power supply, telephone, and telegraph mains. The placing of wires and a great variety of pipes in the sewers of Paris is one of the no- table features of that city. In the United States the nearest approach to subways like those of Europe is at Saint Paul, where a number of miles of sewers have been constructed in the form of tunnels in the soft sand-rock which underlies the city, and water mains have also been placed, separately, in simi- lar tunnels. Brancli tiuiiiels connect with the ■wires are : ( 1 ) They increase the life and general houses, in the same general way as branches Subway for 'i ] Beiirical Mains^i <^' H ah Level Drcrin j|v Iron Ppe "■ 6a^ Service Hjh Level Wafer Main 1 ^ter Service mnf Floor ■ j^sacreway cfnd , 6allery for Becfncal Wires Subway for Electrical Mains Cbobs-Section of Chicago Street, Showing Proposed Arrangement of SrswAve. serviceability of pavements and prevent the in- terruption to traffic caused by street excava- tions to gain access to pipes when simply buried in the ground. (2) They facilitate both the in- spection and repair of all classes of underground furniture, and thus lessen the number of trouble- some and dangerous leaks from water and gas mains ; they also aid in the prevention of elec- trolysis, or the electrical decomposition of iron and lead conduits through stray electrical cur- rents from overhead trolley s}'stems. (3) Ven- tilated and relatively dry subways may greatly lengthen the life of pipes and wires through better protection against corrosion than is pos- sible when such furniture is laid directly in the earth. One of the earliest attempts to avoid the dis- turbance of pavements was carried out in Liver- pool, where a gallery 21,4 feet wide was built under the sidewalk and in it were placed an oval pipe sewer 27X18 inches, a 10-incli water main, and a 10-inch gas main. The bottom of the trench was 13 feet below the surface of the sidewalk. Little or no provision for repairs was made. The London subways date from 1801 or 1862, when one was built in a new street from Covent Garden Market to Saint Martin's Lane. A few months later a subway was buiit at Not- lead to the buildings along the line of the Euro- pean subways. Besides the sewers and water mains at Saint Paul some private companies have placed telephone lines in like tunnels. Tun- nels for telephone cables have been constructed in Chicago. Electrical Subw.ws. Although there are no instances of subways for both pipes and wires in the L^nited States, the practice of putting wires underground is rapidly growing. It is getting to be a comparatively common practice, even in small towns, for telephone companies to bury tlieir wires; and though the work is often done cheaply and rather crudely, the wires are never- theless removed from overhead and at the same time are so arranged that little subsequent dis- turbance of the street is necessary. In a grow- ing number of the larger cities electrical wires for light and power, together with the ordinary and the police and fire alarm telegraph lines, are also placed underground. Electrical subways con- sist of a single pipe or tube, or a group of such, designed to protect imderground wires from in- jury due to settlement of the earth or the picks and shovels of workmen. At the same time these subways afford access to the wires through man- holes placed at intervals, for repairs, connec- tions, or the drawing in of new wires. Some
