lead to
the discovery of some mistake in observation or some error in reasoning.

Evidence of unreliability shown by a writer may generally be
discovered, if care is exercised. His temperament, age, environment,
training, religion and other facts will contribute. One who is
dogmatic or abusive in stating what are obviously mere opinions which
cannot be demonstrated, or who is intolerant of those who reach
different conclusions, is obviously by temperament untrustworthy. A
writer who in a single instance can be shown to have intentionally
distorted facts should, of course, be at once and forever rejected;[2]
one who has distorted facts unintentionally may perhaps be forgiven
once. So a writer who, in a matter not capable of mathematical
demonstration, and to some extent a matter of opinion, sets out to
prove a preconceived idea, shows himself in general not possessed of
the qualities which should inspire confidence.

By these and other tests the student should constantly be on the watch
to form his opinion of the credibility and reliability of a writer or
experimenter whose work he is studying. He {18} may thus guide himself
as to the books which he should pursue carefully, remembering the
dictum of Bacon that "Some books are to be tasted, others to be
swallowed, and some few to be chewed and digested," except that very
few, if any, are to be literally swallowed without digestion. By
careful observance of the injunction to study constantly the
credibility of a writer one may become what may be termed a
discriminating student.

(_f_) ANOTHER ESSENTIAL ELEMENT OF A PROPER ATTITUDE OF MIND IS
CAUTION.--Always realize the possibility of error both in another and
in yourself. Be on your guard against intentional or unintentional
deception. As Bacon said, "Read not to contradict and to confute, nor
to believe and take for granted, nor to find talk and discourse, but to
_weigh and consider_."[3] The author you are reading may have made a
mistake, or may be trying to mislead you. "When we think of the
difficulty of finding the way, when we are most desirous to go right,
how easy to mislead those whom we wish to go wrong!" Be, therefore,
always suspicious of {19} your author, and subject all his statements
to the test of your own intelligence.[4]

(_g_) STUDY WITH AN OPEN MIND, AND WITH NO PRECONCEIVED
IDEAS.--Cultivate the scientific attitude of mind, which means, first
to formulate clearly a problem, then t