Systems of Lighting
Direct lighting is secured by fixtures which throw the light downward into the room from which the eyes are protected by properly adjusted shades. Indirect lighting is from bowl-like fixtures in which electric lights are placed and the light rays are reflected upward toward the ceiling with no light penetrating the bowl. Semi-indirect is accomplished by using a bowl which will permit some of the light rays to penetrate.
The best results are obtained by a combination of the direct and indirect methods of lighting and in some cases by a semi-indirect way. It has been observed that the direct rays of light should not fall squarely into the eyes. It is also quite essential that in some cases there should be direct rays on the work or object under observation. To accomplish this and at the same time to keep the light out of the eyes there must be a judicial use of shades and other means of softening the light.
There are some objections to the indirect method in that all the light is thrown on the ceiling. This gives a very soft light in the room, but is not sufficiently bright and faces lose their expression; there is insufficient modeling of objects, and the interior will be almost devoid of character. This form of lighting, therefore, is undesirable for home and offices, but is not objectionable for places of amusement.
There are also objections to the direct system since the strong direct light makes too harsh shadows and a light glare which is very objectionable. By properly diffusing this direct light and adding sufficient upward light we get a much more effective and pleasing illumination.
By using the two systems, or better still, by combining the two systems into the semi-indirect, a method is obtained which will furnish an abundance of light and at the same time give one that is so perfectly diffused there will be no objectionable shadows and no harmful glare.
Insufficient light may be quite as injurious to the eyes as too much light. As a matter of fact it is not so much a question of too great an intensity as it is of the proper light direction; it is hardly possible to get a light of greater intensity than that of the sun, but we are very careful that the sun’s direct rays do not enter the unprotected eye; neither is it good to permit the reflection of the rays into the eyes, as from a printed page.
(For schoolroom lighting see chapter on School Hygiene.)
CHAPTER VII
WATER
WATER
GENERAL CONSIDERATIONS
Necessity for Proper Supply
History of Public Supply
Composition of Water
CHEMICAL ELEMENTS
FOREIGN INGREDIENTS
States of Aggregation
Universal Solvent
Necessity for Water in Body
Chemically Pure Water
HOW OBTAINED
TASTE OF WATER
Hard and Soft Water
PERMANENT
TEMPORARY
Elimination of Water from Body
Amount of Water Needed for All Purposes
FOR THE BODY
FOR DOMESTIC PURPOSES
FOR CITY USE
Water Waste
CAUSES FOR
USES OF METERS
SOURCES OF WATER SUPPLY
Rain Water
SUPPLY NOT RELIABLE
EASILY POLLUTED
FILTERING NECESSARY
DESIRABLE FOR LAUNDRY PURPOSES
Surface Water
STREAMS
LAKES
IMPOUNDING RESERVOIRS
SOURCES OF IMPURITIES IN SURFACE SUPPLY
Ground or Subsoil Water
WELL WATER
SPRING WATER
TEMPERATURE IN WELLS
SHALLOW AND DEEP WELLS
CONSTRUCTION OF WELLS
SOIL AS A FILTER
METHODS OF PURIFICATION
Natural Methods of Water Purification
BY FREEZING
SELF-PURIFICATION
WATER VEGETATION
DILUTION
STORAGE AND SEDIMENTATION
SUNLIGHT
Artificial Methods of Water Purification
DISTILLATION
BOILING
FILTRATION
CHEMICAL PURIFICATION
Swimming Pools
SANITATION OF
SWIMMERS INSTRUCTED IN POOL SANITATION
SEWAGE AND REFUSE DISPOSAL
Methods of Sewage Disposal
DRY
WET
Sewage Purification
SCREENED
SEPTIC METHOD
Refuse Disposal
INCINERATION
CITY COLLECTORS
CHAPTER VII
WATER