Man's physical universe

xanabras

282 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME

trol of the accuracy of fine machining operations and provides protection

from dust and dirt as well as increased comfort and efificiency for

the workmen.

Air Conditioning Is Changing Building Construction.

The cooling load may be decreased as much as 50 per cent in

older types of buildings by use of awnings, circulation of air through

the attic, insulation of walls and ceiling, and installing weather stripping.

The Hershey Chocolate Corporation of Hershey, Pennsylvania, has

completed a large, three-story general office building without a single

window. All external noises are shut out. Lighting is constant and

ideal.

Long ago, large stores found that windows represented a loss of wall

space.

It is possible that, in the future, homes will be built either without

windows or with a few immovable double plate-glass windows that

will permit the enjoyment of desirable views. The glass bricks which

are coming into use for building purposes will permit the home to be

lighted during the day without windows.

Insulation, So Important in Air Conditioning, Depends upon a Knowledge

of the Three Ways in Which Heat Is Transferred.

Heat is transferred from one place to another or from one body to

another by conduction, convection, and radiation.

1. Conduction. It is a common observation that some materials

conduct heat better than others.

the

Cloth pot-lifters and wooden handles

are used to handle hot metal utensils because cloth and wood are poor

conductors {i.e., good insulators) of heat.

All metals are good conductors of heat, although they differ considerably

among themselves. Nonmetals are poor conductors of heat.

The conductivities of some common substances,

standard, are listed in the following table.

Relative Heat Conductivities

Silver 1.096

Copper 1.000

Aluminum 0.50

Iron 0.167

Mercury 0.0201

Glass 0.002

Water 0.0014

Hard wood 0.0005

Paraffin 0.0005

Alcohol 0.00043

Hair felt 0.00009

Air 0.000057

taking copper as a

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