This will include "lighting-up time" divided among the different months as follows: January, 102 hours; February, 60 hours; March, 32 hours; May, 8 hours; June and July, none; August, 8 hours; September, 20 hours; October, 50 hours; November, 78 hours; and December, 102 hours.

To properly provide for sufficient lighting during these periods we must select some one of the many systems in use, and the one which seems best adapted to the conditions of the case. Whatever may be the future development, either as to perfecting and simplifying its application, extending its sphere of usefulness, or reducing its cost, electricity at present stands at the head, when the question of a perfect light, or at least the most available one, is considered, for the illumination of nearly all classes of large buildings, particularly such as are used for manufacturing purposes.

Fig. 74. Vertical Cross Section.

Still there seem to be indications that there may be yet other systems of artificial lighting which by development may become dangerous rivals of the popular systems of electric lighting - acetylene gas, for instance. This method is still in the infancy of its development and use, and there seem very few of the usual difficulties to be overcome excepting the danger of its explosion in the hands of inexperienced persons. This difficulty will probably be overcome in time and the use of it be as safe, both to generate and to manage, as electricity.

It is also true that the system of electric lighting has many fatal accidents charged against it. These may all have been due to improperly constructed apparatus, the careless management of it, or the imperfect knowledge of its properties and action. The same may be said of acetylene gas.

That we have yet attained to the perfect artificial light no one will have the courage to assert, since improvements are continually in progress in this direction, but at present we must be satisfied with electricity, with gas as a supplementary light when the electric current is not available.

To provide an ample, proper, safe, and thorough system of illumination for buildings in which a large number of persons are obliged to labor for so many hours each year by its aid, would seem to be a matter that need not be argued or advocated. Yet there are many shops at the present time so constructed that some kind of an artificial light is needed all through the day, and in some at nearly all seasons of the year, and this condition prevails over a considerable part of the working space.

The result must necessarily be that both the quantity and the quality of the work done is below the standard, while the health and the eyesight of the employees are both unnecessarily impaired, since sunlight and fresh air are two very important elements necessary to the health, activity, and usefulness of the human family. Ofttimes the evil results from a lack of consideration or appreciation of these necessities, and sometimes perhaps from a false idea of economy on the part of those having charge of such matters, which has led them to provide very indifferent substitutes for sunlight, or, in its absence, a proper artificial light.

For it is true, "and pity 'tis, 'tis true," that in some shops, even in this enlightened age, many hours' work is done by the smoky glimmer of dirty oil lamps, these relics of a bygone age, since they are not many steps in advance of the vessels of oil with their fibrous wicks resting against one side, used in the days of Abraham, 1920 B.C.

Although the common use of petroleum oils in various degrees of refining have revolutionized the old-time lamp, and the simplifying of the processes for generating and purifying illuminating gas have produced two very useful illuminants within the reach of nearly every one, they will probably never regain the position which they lost when the practical utility of electric lighting became a recognized fact.

The one great drawback to all artificial means of illumination is that to produce light we must generate heat; and hence, however we produce light, whether by the combustion of oil or gas, or by the generation of an electric current, to form a brilliant arc, or a glowing incandescence, we must necessarily waste a large percentage of energy in producing heat which we do not want and which is often a very serious objection.

We shall therefore not have the perfect light until we have been able to produce the illumination we desire without generating heat. Whether we shall ever realize that much-sought condition is a question for future development and invention to demonstrate.

In the application of the electric light in manufacturing operations we have the choice of the arc lamp and the incandescent lamp. Both have their objections as well as their merits. The arc lamp, being much more powerful and projecting its rays a much greater distance than the incandescent lamp, is well adapted to illuminating large areas, where there are comparatively few obstructions. In confined situations, or where there are many obstructions, it produces disagreeable shadows, and its glaring brilliancy is hurtful to the eyesight of the workmen.

Translucent globes or shades may be used, of course, but these devices necessarily reduce the illuminating power of the lamp. Again, the arc lamp is not readily moved from place to place, even short distances, so that the workmen must often stand literally "in his own light".

The incandescent lamp gives a much softer and more agreeable light to the eyes of the workmen, who may work many hours by its aid with less discomfort than by almost any other light. It is also much more portable than the arc lamp, since it may be provided with flexible conducting cords of any convenient length, and hung up or held in the hand in the most desirable positions.