Still another convenience of the incandescent lamp is that of being able to locate a magnet in the base of it, by which means the lamp is retained in any desired position by simply placing it against any iron or steel surface. This is a matter of great convenience when working in dark corners or making repairs under machines, where the usual fixed lights are of little use and where ordinary incandescent lamps must be held in the hand; and also in awkward positions such as are frequently found during the work of erecting heavy machinery or repairing it.

These convenient characteristics of the incandescent lamp render it valuable for practical use in the machine shop. It may be readily placed in confined situations where an arc light could not, and it may be used much nearer the eyes of the workman without injury.

It would therefore seem wise, in devising a system of artificial lighting, to avail ourselves of the advantages offered by both the arc and the incandescent lamps, each in the places where their special merits can be made use of. Both types of lamps may be operated by the current from one dynamo, by the use of proper transformers, but it will usually be found more practical to put in a dynamo specially designed for each system.

More recently a light has been produced by the action of an electric current upon mercury confined in a glass tube two feet or more in length. A peculiarity of this light is to render yellow tints more pronounced and giving a peculiar green tint to many objects.

Ample space has been provided in the engine room for dynamos for this purpose, as well as for furnishing the necessary current for operating the traveling crane in the machine shop and the power required in the foundry.

In the machine shop the clear space needed for the traveling crane precludes the suspending of arc lamps through this central portion, but they may be placed between and a little inside of the line of the columns. They should be about 50 feet apart, which would require 14 lamps on the main floor. In addition to these a sufficient number of incandescent lamps should be provided to accommodate the individual needs of the men operating machines, wherever such additional illumination is necessary from the location of the machines and the character of the work.

They should also be provided at the small tool-distributing room and in the foremen's offices, and a number should also be hung upon the columns, having sufficient length of conductor cord attached to them so that they may be used in erecting machines in the central space.

From the character of the machines employed and the work done in the galleries the incandescent lamp will be the most suitable. There should be at least one to each machine and in the case of long lathes one to every ten or twelve feet of bed. A lamp should also be hung at the head of each stairway.

The large open space of the foundry may well be provided with arc lamps, four of which will be sufficient, supplemented by a few incandescent lamps with long cords hung on the columns, for use in deep molds and similar places left in darkness by the arc-light shadows.

The chipping and pickling room will require one arc lamp and several incandescent lamps, all provided with wire nettings for protecting them from flying chips. The core room, wash room, foreman's office, water-closets, the space under the cupola platform, etc., will require incandescent lamps.

The forge shop will be best served by two arc lights in the main part, and by incandescent lamps in the foreman's office, wash rooms, water-closets and perhaps in the bar stock storage space.

One arc lamp in the storehouse and one in the carpenter shop, with « perhaps two or three incandescent lamps in the latter, will be sufficient.

The boiler room will require an arc lamp hung over the tram track so as to fully illuminate the boiler fronts, and two or three incandescent lamps convenient to the space in the rear of the boilers and in similar places. The same number and kind of lamps will answer for the engine room. The adjoining wash rooms and water-closets should be provided with incandescent lamps, say four in each of the former and three in each of the latter.

An arc lamp erected on a pole 20 feet high should be located in the yard between the foundry and the power house and about 35 feet from the machine shop. A similar one should be placed in the center of the space between the storage sheds, carpenter shop, power house, and the forge shop. These will greatly facilitate yard work near the close of the short winter days.

The entire front building, including the offices, tool rooms, pattern shop, pattern storage loft, drawing room, etc., should be lighted by incandescent lamps, those in each room being arranged to suit the peculiar conditions in each case, as to the kind of shades and reflectors employed.

To equip the entire plant as described above will require say 27 arc lamps and 267 incandescent lamps, the latter number being somewhat lessened or considerably increased according to the character of the machinery to be manufactured, as whatever change in this respect is made would most likely affect the incandescent lamps and possibly the arc lamps as well.

In providing for the amount of current necessary to supply this system of lighting we should make allowance for any possible increase that may be called for by unforeseeen circumstancs, or by a change in the products of the concern, and it would usually be safe to add for this purpose at least 10 per cent.

The power necessary to run the dynamos with the added 10 per cent will be about 30 horse-power for the arc lamps and 20 horse-power for the incandescent lamps, or a total of say 50 horse-power to be provided for, in calculating the capacity of the proposed engines.

By referring to the general plan drawing given in Chapter II (General Plans), the arrangement of the lamps as herein described may be readily understood.