Man's physical universe



interests in making observations. How can these errors due to the

human equation be eliminated?

3. Instruments Must Be Calibrated. Calibration consists of comparing

instruments with standards and adjusting the instruments so

that they will give the same results as other similarly calibrated instruments.

Cheap thermometers, for example, may give temperature

determinations which vary several degrees among themselves, but

every thermometer which has been carefully calibrated will give the

same temperature reading under similar conditions.

It is

never safe to assume that an instrument will yield reliable re-

Perhaps the person who last used a calibrated weight touched it


with an oily hand, thus changing its weight. The careful observer

frequently checks and rechecks his instruments to be sure that they are

yielding reliable data.

It is quite possible that every instrument of a given type will yield

inaccurate data because of errors or limitations which are inherent in

the instruments themselves.

How may such errors be eliminated?

4. Checking Is the Most Successful Method of Eliminating Errors

in Observation. Repetition of observations by any one observer enables

him to detect errors which may have entered into one observation

but not another.

Repetition of observations using different instruments of a given

type serves to eliminate errors due to faulty calibration.

Repetition of observations using instruments of entirely different

types serves to eliminate errors inherent in any given type of instrument.

Repetition of observations by different observers serves to eliminate

errors due to the prejudices or to the differences in the sensitivity or

alertness of the observers.

Mistakes are avoided in scientific laboratories, banks, stores, hospitals,

or at home by checking and rechecking. No information should

be accepted as being reliable until it has been checked.

Gullibility is

inaccuracy, and even costly mistakes are the common

results of the failure to check observations in all of the phases of daily


Experimentation Is Observation under Controlled Conditions.

Many phenomena are so complex that they can be studied only by

observing the changes resulting from altering one factor at a time while

other factors are kept constant.

Perhaps the most significant feature of controlled observation is that

it enables many different observers to study exactly the same situations

and to check, correct, or supplement each other's results.

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