burners or the lighting apparatus must be of such a nature that the lowest possible radiating effect is obtained. As the best source of light, other conditions being the same, must be considered that in which the heat-radiation per candle-power of light is the lowest. The heat

radiation of an ideal source of light should be extremely small. From this standpoint the color of the light is not without significance, since a light which possesses many red rays indicates, in general, a high, and a light with principally green and blue, on the other hand, a low heat-radiation.

"5. Sources of light that possess a high reflecting power, in which a large amount of light falls upon a unit of surface, must be shaded from the eyes or weakened in

some way.

"6. Flickering of the source of light and decrease in the intensity of the light are to be prevented in the illumination of rooms. A uniform, steady light is everywhere to be desired, and is absolutely necessary where work is carried on in which the eyes are used for a long time, or to a large extent (school-rooms, certain factories, etc.).

"7. The dangers-poisoning, explosion, fire, electric shock-to which the consumers or the public is exposed in general through installation or conduction of illuminating-arrangements, shall be as small as possi

ble.

The

"8. Of not less importance, and for certain rooms (school) of more importance than the supplying of as large a quantity of light as possible, are the uniform distribution of the light and the reduction of shadow-production. This requirement can be fulfilled in direct illumination only under especial circumstances. end is most simply and surely attained by the use of indirect (electric) light. For school-rooms this is the only mode of illumination which meets all the hygienic requirements. It can also yield very good results in factories. The discomfort from heat-radiation is entirely

removed, because the source of light is raised high above the heads of the occupants.

"A combination of direct light with indirect, by means of white-glass reflectors, is not to be recommended where there is shadow-formation (as in writing), and metal reflectors are to be preferred."

CHAPTER XII.

SCHOOL HYGIENE.

SUCH a large proportion of the ill health of a community is found in children of school age, and since such a large percentage of this ill health can be prevented, it is necessary to treat briefly the subject of school hygiene.

Site, or Location, with Reference to Drainage Capacity of the Soil.-In school architecture a question of primary importance, the consideration of which is frequently neglected, is that of location with regard to the nature of the soil and its drainage capacity. Satisfactory sanitary arrangements can rarely be secured in any building unless the site of the building is carefully selected with regard to the drainage capacity of the soil. The soil structure as regards the preponderance of definite-sized grains, coarse or fine, influences the drainage capacity, and consequently the healthfulness of the site. The amount of slope and the proximity of streams, either surface or underground, also influence the character of the soil. For these reasons it is of primary importance that the site selected for a school-building shall be of such a nature as to afford the very best facilities for drainage, not only for refuse and excreta collected in the building, but for surface- and rain-water flowing over the soil. Whenever the soil of the site is not perfectly dry, it should first be underdrained.

Parkes states that the conditions which insure healthy habitations are:

I. A site that is dry and not malarious, and an aspect which gives light and cheerfulness.

2. A pure supply and proper removal of water, by

means of which perfect cleanliness of all parts of the house can be secured.

3. A system of immediate and perfect sewage removal, which renders it impossible that the air or water shall be contaminated from excreta.

4. A system of ventilation which carries off all respiratory impurities.

5. A condition of house construction which insures perfect dryness of the foundation, walls, and roof.

Structure of Walls.-Having selected a proper site for the building, the nature of the building is of considerable importance. The building itself should be detached, so as to obtain an abundant supply of fresh air and the greatest amount of light. The character of the materials composing the walls and the thickness of the walls, the number of layers composing them, all have an important influence on the character of the building. The walls should be rendered impervious to moisture, and it is preferable, therefore, to have double walls with an air space between the inner and outer surface. The materials employed in constructing the walls will be governed by circumstances, and their nature is not of great importance if they are properly used. Stone walls are usually somewhat damp, but can be rendered perfectly dry by allowing an air space between the inner and outer layers.

Cubic Space and Floor Space.-Cubic Space. From calculations made by Prof. Parkes and Dr. de Chaumont, the amount of air required for each adult per hour, in order to maintain a certain degree of purity in the atmosphere, is 85 cubic meters. The respiratory impurity added to the air will, of course, be less with children than adults, consequently the amount of air required to maintain the standard of purity will be less. Though children evolve less carbon dioxid in a given time than adults, yet relatively for their body-weight they expire more. fixing a standard for schools, the age of the children. ought also to be considered; the average amount of air re

In

quired being about 55 cubic meters per hour. Parkes says that it is highly desirable that some general agreement should be arrived at as to the amount of air necessary, even if it be admitted that the desired amount cannot always be obtained. If we adopt the following amounts of carbon dioxid as being evolved during an hour in repose, we shall not be far from the probable truth:

Adult males. (say 70 kilograms weight), 0.72 cubic foot

=20

liters.

The amount of fresh air that must be supplied in order to prevent the impurity due to products of respiration exceeding a particular limit, is measured by the quantity of carbon dioxid present in excess over that in external air, according to either of the standards in use, and may be calculated from the formula d, where e

r =

r

=

amount

of carbon dioxid expired in liters per head per hour; = admissible limit of carbon dioxid due to respiratory impurity, stated per liter; d = delivery of fresh air per head in cubic meters.

Under these conditions the amount of fresh air to be supplied in health during repose ought to be:

The law of Massachusetts requires that each occupant of a school-room receive a quota of 850 liters of air per minute. If this is taken as the basis for the minimum amount of air required by each child, and we require further that the air be changed but three times each hour, then the minimum amount of cubic space allowable for each child is 17 cubic meters. This is slightly lower than the theoretical amount, as shown by the calculations of Parkes,