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