the conduit far in excess of the extra cost of a duct of better design and construction.

In the interest of good conduits it is a satisfaction to note a growing demand for ducts so designed that they can be easily placed and maintained in correct position in relation to each other.

A monolithic conduit has lately been designed and has been installed and operated to some extent. This system provides a continuous concrete conduit from manhole to manhole, the ducts being simply holes in the concrete.

The method of constructing this conduit is to prepare a trench and place in the trench at a manhole a hollow box of the size and shape of the conduit; this box is then drawn like a sled from one manhole to another and, as it proceeds, a sufficient quantity of concrete to form the conduit is poured into the box; as the box moves on, the concrete is left behind in the shape of a conduit. The holes for the ducts are formed by short steel tubes in the box and are maintained by long rubber or paper tubes inflated by water under pressure, When the concrete has hardened, the water is removed and the deflated tube drawn out of the ducts. A simple device has been designed for coating the interior of the ducts with waterproof compound.

This system, which is understood to be covered by patents, is certainly of interest and has many good points, but as the writer understands that the system is not now sufficiently perfected to be proposed for constructing large conduits, it would seem premature to discuss it at this time.

It is understood, however, that an adaptation of the system has been perfected for laying a conduit composed of thin fiber tubes enclosed in asphaltum concrete, to contain bare wires carrying current of low voltage.

Underground conduits may be used for the wires of electric railways, telegraph companies, telephone companies, or electric light and power companies, and while the same general style of conduit is adapted to the use of either, the requirements in details of distribution are quite different, and the nature of the service required must be considered in locating the conduit and determining the number, location, and size of manholes.

The layout of a distributing system for the feed wires of an electrie railway is such as will provide a direct and convenient route for cables from the power station to certain fixed feed points on the line of the railway; no provision need be made for intermediate

distribution and the manholes are required only to be built of such a size and placed at such intervals as to provide for the convenient and proper handling of the cables.

A distributing system for telegraph wires is required principally to provide for trunk lines in and out of the cities, but the occasional lines run to private offices and the wires for messenger calls make it necessary to provide for reaching all important buildings, and for this purpose the conduit should be so located as to be accessible at practically all points in the business district, and the man

holes should be so located as to conveniently connect from them to the required building.

The underground distributing system for the wires of a telephone company must provide for trunk lines in various directions, and also for connecting to individual buildings in all parts of the district; the problem in this case is considerably simplified by the fact that because the service required is all of the same character and the amount of current used is so very small, many wires for all the service in a locality may be bunched together in a small space and carried through or along the sides of buildings without danger to persons or property or detriment to the service.

In designing a conduit system to properly accommodate the

wires used to distribute the current from an electric light and power station, the conditions to be considered are much more complicated than those mentioned above. The conduits should be such as will properly contain and protect cables carrying heavy currents, and the manholes so equipped as to provide means of protecting the cables of various voltages from each other, and of such size and shape as to allow for the safe and proper handling of the cables and space for installing such junction boxes, transformers, etc., as may be required.

The local distribution of electric light and power wires is a matter on which engineers, electricians, and municipal and insurance officials have many opinions; it is a subject which should certainly be handled with care and intelligence.

In some cases the customers in the vicinity of the stations have been supplied by laying a solid system of tubes for low tension currents from the stations through the main streets and connecting directly with the buildings to be served.

In other cases, a combination of drawing-in system and solid system has been employed by sending low-tension current through cables in conduits from the station to certain determined points throughout the district, and there connecting to solid tube lines which carry the current to individual buildings.

Another method is to send high-tension current from the station through cables in conduits to points in the immediate vicinity of the customers to be served, and there transform to a voltage suitable for the work, and distribute the weaker current into the buildings. The transformers may be placed in manholes or vaults or on poles or buildings.

The current is also sent out from the station at from 500 to 3,000 volts or more, and used without transforming for power or lighting.

It is of great advantage to determine which of the above methods or what combination of them is to be used before laying out the conduit system, which can then be designed to suit the plan of distribution decided upon.

When an underground system is to be laid out, it is generally designed to take the place of an overhead distributing system, and in that case the plan is often to place only the main lines underground at first, to connect at convenient points to pole lines or house tops and continue the local overhead distribution. This is somewhat of a saving at first, but in practice the combination has generally been only temporarily continued and eventually the

thoroughly underground system with individual building connections has been adopted as tending to true economy and good service. Having in mind the varied conditions as noted above that may arise, it is evident that in making the original design for a system of underground conduits for an electric light and power plant, due consideration should be given to the probability that there will be an ultimate demand for an entirely underground distributing system. This will often be a factor in choosing locations for conduits and manholes, and a reasonable extra expense is in some cases

warranted in the original work in order to provide for probable future requirements.

A scheme which is often proposed and sometimes finds favor with managers and engineers who desire to do thorough work, is to construct either one or two conduits in each street, separate from the main line, to be used only for local distribution; on these smaller conduits sub-manholes for taking off connections are located at regular intervals and connections are at once made to all buildings where service is, or may at any future time be, required.

This would seem to provide well for future business and preclude the necessity of any further excavation in the street-two important features in its favor and which make it in a few special cases an ideal system.

For use in the average city, however, this system is more ideal than practicable; the discrepancy between the possibilities which must be provided for in such a system and the use that is actually made of the facilities provided is so great that the cost figures out of all proportion to the probable benefit to be derived.

A satisfactory and ultimately economical method of handling local distribution is to thoroughly investigate the buildings in a district to determine the definite locations for connections required for present business before the conduit is built; the manholes and sub-manholes are then laid out so as to connect economically and satisfactorily with the points of entrance determined upon and also to provide in a general way for reaching in the future all other buildings and vacant lots in the district.

With the manholes and connections thus thoroughly planned. it is generally practicable to lay portions of many connections in the same trench with the conduit and also to place considerable lengths of two or three connections in one trench apart from the conduit.

This method of utilizing the trenches is an economy in construction and also caters to the public sentiment in favor of doing all work in a street at practically the same time.

It is at times considered very desirable to construct a common conduit system for the wires of two or more companies, in the interest of economy and to avoid the inconvenience of constructing parallel lines in the same street. If the work is laid out and constructed without proper consideration and care, there is great chance for trouble from such a combination, but if the use each company is to make of the system is intelligently considered in designing the conduit and locating the manholes, and the proper extra care taken in construction because of the peculiar nature of the work, it is perfectly feasible to construct an underground conduit system which shall be satisfactory for the use of two or three companies.

The number, location, and size of manholes to be built is governed by the requirements of the system and local conditions; it is possible to properly operate a conduit with stretches of 700 to 800 feet between manholes, but it is considered best to limit the distance to about 400 feet where practicable, and manholes may be placed as often as is necessary to meet the local conditions.

Manholes should be located at the low points in the grade, if