d cover of the cable, sets up a chemical action, resulting in the
destruction of the lead. Wood offers but little protection for the
cable, as it is too easily damaged and broken through in the frequent
street openings made by companies operating lines of pipe in the
streets, and as one of the main purposes of a subway is that of a
protection to cables, wooden ducts have little to recommend them except
their cheapness.

Iron pipes are either laid in trenches filled in with earth or are laid
in cement. Iron pipe will of course rust out in time, and if absolute
permanence in construction is desired, should be laid in cement, for
after the pipe rusts out, the duct of cement is still left. However, if
we are going to the expense of laying in cement, it would be much
preferable to use cement lined pipe, which is not only cheaper than iron
pipe, but makes the most perfect cable conduit, as it affords a
perfectly smooth surface to draw the cable over and give a good duct
edge.

It is not necessary, however, in small installations of cable,
especially where additional connections will not be of frequent
occurrence, to go to the expense of subways, for cable may be safely
laid in the ground in trenches filled in with earth, or can be inclosed
in a plain wooden box or a wooden box filled with pitch.

There are, of course, many localities where, if the cable is laid in
contact with the earth, a chemical action would take place which might
result in the destruction of the cable.

Underground cables are of the following classes: 1. Rubber insulated
cables, insulated with rubber or other homogeneous material. 2. Fibrous
cables, so called from the conductors being covered with some fibrous
material, as cotton or paper, which is saturated with the insulating
material, paraffine, resin oil, or some special compound. Under this
latter head is also included the dry core paper cables.

The first thing to do is to get the cable drawn into the ducts, and on
the proper accomplishment of this depends to a great extent the success
or failure of the whole installation. Probably the ducts have been wired
when the subway was constructed, but if not a wire must be run through
as a means of pulling in the draw rope. There are several kinds of
apparatus for getting a wire through a duct--rods, flexible tapes,
mechanical "creepers," etc.; but probably the best is the sectional rod.
This simply consists of three or four foot lengths of hard wood r