of neighboring buildings, an increased illumination may be obtained by the use of ribbed glass which causes a larger portion of the light to be refracted into the building. (Fig. 5.) Windows should always be kept clean, as the amount of light entering the room may be reduced 40 per cent by dirt upon the glass.

Artificial illumination is that which must be provided at night or when daylight illumination is insufficient. The source of the light may be from the burning of hard fats as in candles, mineral oils as in lamps, illuminating gas, or electricity. A spermaceti candle

FIG. 5.-Typical relation of loft buildings in the Women's Garment Industries, New York City, to the sky and adjacent structures. The two lower sections show the action of prismatic glass in refracting the rays of light into the room.

burning two grains a minute is used as the standard for measuring artificial illumination; a foot candle is the lighting effect produced upon an object by a standard candle at a distance of 1 foot; at 2 feet, the effect would be not one-half foot candle, but one-fourth foot candle, etc. A lamp which would give off 16 candlepower uniformly in all directions would produce a uniform illumination of 1 foot candle at a distance of 4 feet in any direction. Lamps should be kept scrupulously clean, should be filled and have their wicks carefully trimmed each day, as otherwise they will emit a disagreeable odor.

Illuminating gas may be either coal gas, water gas, or natural gas. Coal gas is produced by heating coal in closed chambers and the gases thus obtained, after being freed from certain impurities, are stored and distributed as needed through pipes to buildings for lighting and cooking purposes. Water gas is made from coke or anthracite coal, steam, and petroleum. The poisonous properties of both coal gas and water gas are due to carbon monoxide, a gas known to miners as "white damp." Water gas contains 35 per cent carbon monoxide, coal gas from 6 to 7 per cent, and natural gas only 0.21 per cent. Illuminating gas (except natural gas) as now used in cities is a mixture of coal gas and water gas, most municipalities limiting by ordinance the amount of water gas in the mixture to 10 per cent.

The symptoms caused by poisoning from illuminating gas may be either acute or chronic. In acute poisoning they are violent headache, vertigo, shortness of breath, weakness of the legs, convulsions, and unconsciousness. The carbon monoxide unites with the coloring matter of the blood and prevents it from taking oxygen to the tissues. The danger of breathing this gas in small quantities is that a condition develops in which the patient is dull and listless, can not sleep at night, his gait is slow, and his memory bad. Some of the symptoms of acute poisoning may also be present.

As 0.4 per cent of carbon monoxide in the air will produce fatal results, the necessity for exercising care in the use of illuminating gas is evident. Gas pipes and street mains should be tight so that none of the gas can leak into rooms and produce poisoning. Gas jets should not be left burning where a gust of air may blow them out and let the gas escape into the room.

The treatment in acute cases of carbon monoxide poisoning consists of loosening the clothing about the neck and chest, performing artificial respiration (p. 276), and oxygen should be given by inhalation. If the patient is conscious and able to swallow, hot coffee or tea should be administered. Dr. W. G. Fralick, of 33 East Sixtieth Street, New York City, has had great success in the department of charities hospitals and other hospitals in New York treating these cases by an intravenous isotonic solution of sodium hypochlorite used in strength of to 1 per cent, in quantities of 500 to 1,000 c.c., repeated, if necessary, in four hours. The hypochlorite solution destroys the carbon monoxide hemoglobin by oxidation and sets the hemoglobin free so that it can again take oxygen to the tissues.

Electricity is used to supply light by the direct method, where the light is refracted directly downward; the semi-indirect, where a part of the light passes through a frosted bowl and the rest is thrown upon the ceiling and reflected therefrom over the room; and the indirect method, in which the bulbs are contained in an opaque bowl and all the light received in the room is reflected from

the ceiling. The amount of light which should be supplied for general illumination naturally varies with conditions. The following table, taken from the transactions of the Illuminating Engineering Society gives the minimum permissible and the desirable intensities which should be maintained:

Foot candles at the work.

Ordinary Minimum. practice.

(a) Roadways and yard thoroughfares..

(b) Storage spaces..

(c) Stairways, passageways, aisles..

(d) Rough manufacturing such as rough machining, rough assembling, rough bench work..

Rough manufacturing, involving closer discrimination of detail.

Fine manufacturing, such as fine lathe work, pattern and tool making, light, colored textiles.

(g) Special cases of fine work, such as watchmaking, engraving, drafting, darkcolored textiles.

(h) Office work such as accounting, typewriting, etc..

With modern illuminating units and suitable reflectors, a current consumption of about 1 watt to each square foot of surface should yield an intensity of about 4 foot candles. Every effort should be made to prevent glare, which is present when some object in the field of vision is brighter than the object toward which the eye is directed. Glare makes seeing difficult and is injurious to the eyes. Walls should be finished with a yellow or light-green matte surface. Brown or deep green absorb light and make the room dark. White walls and polished surfaces cause glare. Welsbach lights and electric bulbs should be frosted or they should be provided with deepbowl or cone reflectors extending below the light so that the eyes will be protected from the direct rays. Fish-tail gas burners and other open lights should be discarded on account of the flickering of the flame and the glare caused by the exposed light.

Ventilation.

Ventilation is the process by which air in inclosed spaces is frequently changed. By this means the bad effects of unfavorable air conditions are to a great extent overcome. These effects depend to a large extent upon the temperature and humidity of the air. The humidity is usually expressed as relative humidity, which is the ratio of the amount of moisture in the air at a given temperature compared with the amount it is possible for the air to contain at that temperature. It is determined by means of an instrument known as the Sling psychrometer (fig. 8), which consists of a pair of thermometers provided with a handle which permits them to be whirled rapidly. The bulb of the lower of the two thermometers is covered