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Page:Popular Science Monthly Volume 70.djvu/526

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522
POPULAR SCIENCE MONTHLY
square, eight feet high above the eaves, and about eighteen inches more at the ridge-pole. . . . It is better to have the cupola open into the operating room when the room is in the top story of a building, and cleats are fastened round the inside, bored with a number of holes, corresponding to the number of wires required. . . . The wires, after entering are led to the lightning arrester, then run through the holes in the cleats, which run round the base of the cupola, to the ceiling of the operating room, along which they are carried, PSM V70 D526 Telephone wiring through the window.pngFig. 37. on other hard wood cleats, to the switchboard. . . . Where the main lines are not sufficiently numerous to render a cupola necessary, they may be brought through a window in the central office. . . . (Fig. 37.) The line wires are strung on (pony) glass insulators, which are fitted to wooden pins, driven into crossarms. These crossarms are supported on poles or house-top fixtures, which should be run in trunk-routes through the city or town, branch lines being run to any desired point. It is advantageous to use poles wherever practicable, for the following reasons: Pole lines are not liable to interference from householders, being entirely out of their control; they are much more accessible at all times, and when they are out of order at all the trouble is more easily located and removed; the cost is generally about the same, where the number of wires to be carried does not exceed forty or fifty. Poles should be not less than twenty-five feet long, with a diameter of six inches at the top; and should be set five feet in the ground. Before being set up, poles should be carefully stripped of the bark, and, when used in cities, should be painted. It is the usual practise to place all the crossarms on one side of the pole, fastening them with bolts and nuts. It is sometimes, however, absolutely necessary to run house-top lines. Trunk routes should then be selected, and along these routes structures must be erected at an average distance of about three hundred feet apart. Fig. 38 represents a roof fixture, with four cross-bars, each bar having glass insulators on its upper side, and 'hook' insulators on its under side, thus doubling its capacity for carrying wires. Hooks being expensive, porcelain knobs may be substituted for them as an economical measure. (A foot note reads: It is much better to avoid adding hook or other fixtures to the lower edge of cross-bars. It is apt to bring the wires too near together, and cause trouble from 'induction.' It should be done only when new fixtures cannot possibly be erected.) A correct idea of a 'double wall fixture' may be obtained from Fig. 39. It is in many cases desirable to use this style of fixture in preference to a roof fixture, as removing all danger of causing leaks in roofs; or in cases where flat roofs are not attainable, or where the point of support is necessarily a high party wall or the side wall of a building. . . . Bad construction, necessitating frequent clambering over roofs, while it may do no real harm to the premises, annoys owners and tenants, whose condemnations and complaints soon reach the ears of others, and this is apt to put stumbling-blocks in the way of securing permission for entering upon new