Man's physical universe

xanabras

UNIT I

SECTION 4

OBSERVATIONS MUST BE CONTROLLED AND CHECKED

TO INSURE THEIR RELIABILITY

Introduction.

Man is excelled in each of his senses by some other animals, but he is

distinguished from these animals by his intelligence, which enables him

not only to plan and control his observations but also to devise instruments

to aid or supplement his senses. The habit of getting along

without the use of the senses, in so far as possible, leads not only to less

interesting living but also to less intelligent living because observations

are necessary for the testing of generalizations.

It is the purpose of this section to show how observations in the realm

of physical science are aided, controlled, and checked to insure their

reliability.

At Best, Man's Senses Are Very Limited.

A brief survey of some of man's best known senses will be sufficient

to show how limited is the range of his sensory faculties.

1. Vision. There are many kinds of motions that are too quick or

too slow for the unaided eye to detect them. The eyes cannot shift

from one image to another more often than ten times a second, so that

projection of sixteen separate pictures per second leads to the illusion

of the continuous, smooth, steady motion of the movies.

The range of vision is also greatly limited as to the size of particles

that are visible and as to the distance at which they are visible.

The normal human eye cannot see separately the components of any

color but receives all of the wave lengths of the visible spectrum as one

sensation. Thus white light is seen to be white rather than a mixture

of all

the colors of the rainbow.

2. Hearing. The human ear is sensitive to sound waves having

frequencies between 30 and 30,000 per second. Vibrations below and

above these frequencies are very difficult to detect. The ear can recognize

only a limited number of simultaneous sounds.

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