In large buildings, pairs of wires, called _risers_, branch out from the service wires and carry the current up through the building. These have still other branches--_floor mains_, _etc._, that pass through halls, etc., smaller branches finally reaching the lamps. The sizes of all of these wires depend upon how much current has to pass through them. The mains in large cities are usually placed underground. In some places they are carried on poles. [Illustration: Fig. 161.] =140. Electric Conduits= are underground passages for electric wires, cables, etc. There are several ways of insulating the conductors. Sometimes they are placed in earthenware or iron tubes, or in wood that has been treated to make it water-proof. At short distances are placed man-holes, where the different lengths are joined, and where branches are attached. [Illustration: Fig. 162.] Fig. 154 shows creosoted wooden pipes; Fig. 155 shows another form of wooden pipe. Fig. 156 shows a coupling-box used to join Edison tubes. The three wires, used in the three-wire system, are insulated from each other, the whole being surrounded by an iron pipe of convenient length for handling. Fig. 157 shows sections of man-holes and various devices used in conduit work. [Illustration: Fig. 163.] =141. Miscellaneous Appliances.= When the current enters a house for incandescent lighting purposes, for example, quite a number of things are necessary. To measure the current a meter is usually placed in the cellar. In new houses the insulated conductors are usually run through some sort of tube which acts as a double protection, all being hidden from view. Fig. 158 shows a short length of iron tube with a lining of insulating material. Wires are often run through tubes made of rubber and various other insulating materials. Where the current is to be put into houses after the plastering has been done, the wires are usually run through _mouldings_ or supported by _cleats_. Fig. 159 shows a cross-section of moulding. The insulated wires are placed in the slots, which are then covered. [Illustration: Fig. 164.] [Illustration: Fig. 165.] [Illustration: Fig. 166.] [Illustration: Fig. 167.] Fig. 160 shows a form of porcelain cleat. These are fastened to ceilings or walls, and firmly hold the insulated wires in place. Fig. 161 shows a wood cleat. Fig. 162 shows small porcelain _insulators_. These may be screwed to walls, etc., the wire being then fastened to them. Fig. 163 shows how telegraph wires are supported and insulated. Fig. 164 shows how wires may be carried by tree and insulated from them. [Illustration: Fig. 168.] [Illustration: Fig. 169.] [Illustration: Fig. 170.]